Applied Surface Science (v.391, #PB)

Energy and environmental photocatalytic materials by Jiaguo Yu; Mietek Jaroniec (71).
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A review on g-C3N4-based photocatalysts by Jiuqing Wen; Jun Xie; Xiaobo Chen; Xin Li (72-123).
The photocatalytic fundamentals, versatile properties, design strategies and potential applications of g-C3N4-based photocatalysts were systematically summarized and addressed.Display OmittedAs one of the most appealing and attractive technologies, heterogeneous photocatalysis has been utilized to directly harvest, convert and store renewable solar energy for producing sustainable and green solar fuels and a broad range of environmental applications. Due to their unique physicochemical, optical and electrical properties, a wide variety of g-C3N4-based photocatalysts have been designed to drive various reduction and oxidation reactions under light irradiation with suitable wavelengths. In this review, we have systematically summarized the photocatalytic fundamentals of g-C3N4 -based photocatalysts, including fundamental mechanism of heterogeneous photocatalysis, advantages, challenges and the design considerations of g-C3N4-based photocatalysts. The versatile properties of g-C3N4-based photocatalysts are highlighted, including their crystal structural, surface phisicochemical, stability, optical, adsorption, electrochemical, photoelectrochemical and electronic properties. Various design strategies are also thoroughly reviewed, including band-gap engineering, defect control, dimensionality tuning, pore texture tailoring, surface sensitization, heterojunction construction, co-catalyst and nanocarbon loading. Many important applications are also addressed, such as photocatalytic water splitting (H2 evolution and overall water splitting), degradation of pollutants, carbon dioxide reduction, selective organic transformations and disinfection. Through reviewing the important state-of-the-art advances on this topic, it may provide new opportunities for designing and constructing highly effective g-C3N4-based photocatalysts for various applications in photocatalysis and other related fields, such as solar cell, photoelectrocatalysis, electrocatalysis, lithium battery, supercapacitor, fuel cell and separation and purification.
Keywords: Carbon nitride (g-C3N4); Composite photocatalysts; Co-catalysts; Artificial photosynthesis; Z-scheme heterojunction; Nanocarbons;

Semiconductor metal oxides: Modifications, charge carrier dynamics and photocatalysis.Display OmittedMetal oxide semiconductors (TiO2, WO3 and ZnO) finds unparalleled opportunity in wastewater purification under UV/visible light, largely encouraged by their divergent admirable features like stability, non-toxicity, ease of preparation, suitable band edge positions and facile generation of active oxygen species in the aqueous medium. However, the perennial failings of these photocatalysts emanates from the stumbling blocks like rapid charge carrier recombination and meager visible light response. In this review, tailoring the surface-bulk electronic structure through the calibrated and veritable approaches such as impurity doping, deposition with noble metals, sensitizing with other compounds (dyes, polymers, inorganic complexes and simple chelating ligands), hydrogenation process (annealing under hydrogen atmosphere), electronic integration with other semiconductors, modifying with carbon nanostructures, designing with exposed facets and tailoring with hierarchical morphologies to overcome their critical drawbacks are summarized. Taking into account the materials intrinsic properties, the pros and cons together with similarities and striking differences for each strategy in specific to TiO2, WO3 & ZnO are highlighted. These subtlety enunciates the primacy for improving the structure-electronic properties of metal oxides and credence to its fore in the practical applications. Future research must focus on comparing the performances of ZnO, TiO2 and WO3 in parallel to get insight into their photocatalytic behaviors. Such comparisons not only reveal the changed surface-electronic structure upon various modifications, but also shed light on charge carrier dynamics, free radical generation, structural stability and compatibility for photocatalytic reactions. It is envisioned that these cardinal tactics have profound implications and can be replicated to other semiconductor photocatalysts like CeO2, In2O3, Bi2O3, Fe2O3, BiVO4, AgX, BiOX (X = Cl, Br & I), Bi2WO6, Bi2MoO6, etc., to improve their competence for various environmental applications.
Keywords: TiO2; WO3; ZnO; Modifications; Structure-electronic properties; Defect chemistry; Photocatalysis; Performance comparison;

Alternative photocatalysts to TiO2 for the photocatalytic reduction of CO2 by Aspasia Nikokavoura; Christos Trapalis (149-174).
Display OmittedThe increased concentration of CO2 in the atmosphere, originating from the burning of fossil fuels in stationary and mobile sources, is referred as the “Anthropogenic Greenhouse Effect” and constitutes a major environmental concern. The scientific community is highly concerned about the resulting enhancement of the mean atmospheric temperature, so a vast diversity of methods has been applied. Thermochemical, electrochemical, photocatalytic, photoelectrochemical processes, as well as combination of solar electricity generation and water splitting processes have been performed in order to lower the CO2 atmospheric levels. Photocatalytic methods are environmental friendly and succeed in reducing the atmospheric CO2 concentration and producing fuels or/and useful organic compounds at the same time. The most common photocatalysts for the CO2 reduction are the inorganic, the carbon based semiconductors and the hybrids based on semiconductors, which combine stability, low cost and appropriate structure in order to accomplish redox reactions. In this review, inorganic semiconductors such as single-metal oxide, mixed-metal oxides, metal oxide composites, layered double hydroxides (LDHs), salt composites, carbon based semiconductors such as graphene based composites, CNT composites, g-C3N4 composites and hybrid organic-inorganic materials (ZIFs) were studied. TiO2 and Ti based photocatalysts are extensively studied and therefore in this review they are not mentioned.
Keywords: Photocatalytic reduction; CO2; Photocatalysts; Semiconductors; Solar fuels; Artificial photosynthesis;

Fabrication and photocatalytic activity enhanced mechanism of direct Z-scheme g-C3N4/Ag2WO4 photocatalyst by Bicheng Zhu; Pengfei Xia; Yao Li; Wingkei Ho; Jiaguo Yu (175-183).
Display OmittedHerein, a direct Z-scheme graphitic carbon nitride (g-C3N4)/silver tungstate (Ag2WO4) photocatalyst was prepared by a facile in situ precipitation method using g-C3N4 as a support and silver nitrate as a precursor. X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and elemental mapping demonstrated that β-Ag2WO4 nanoparticles were evenly distributed on the surface of g-C3N4 nanosheets, which acted as a support for the nucleation and growth of β-Ag2WO4 and inhibited the phase transformation of metastable β-Ag2WO4 to stable α-Ag2WO4. Photocatalytic experiments indicated that the g-C3N4/Ag2WO4 nanocomposite photocatalyst displayed a better photocatalytic activity than pure g-C3N4 and Ag2WO4 toward the degradation of methyl orange. The enhanced photocatalytic performance of g-C3N4/Ag2WO4 could be well explained by a direct Z-scheme photocatalytic mechanism. This mechanism was related to the efficient space separation of photogenerated electron–hole pairs and the great oxidation and reduction capabilities of the g-C3N4/Ag2WO4 system. This work provided new insights into the design and fabrication of g-C3N4-based direct Z-scheme photocatalysts.
Keywords: Direct Z-scheme; g-C3N4; β-Ag2WO4; Methyl orange; Degradation;

Enhanced visible light activity on direct contact Z-scheme g-C3N4-TiO2 photocatalyst by Juan Li; Min Zhang; Qiuye Li; Jianjun Yang (184-193).
Display OmittedDirect contact Z-scheme g-C3N4-TiO2 nanocomposites without an electron mediator are prepared via simple annealing the mixture of bulk g-C3N4 and nanotube titanic acid (NTA) in air at 600 °C for 2 h. In the process of annealing, the bulk g-C3N4 transformed to ultra-thin g-C3N4 nanosheets, and NTA converted to a novel anatase TiO2, then the two components formed a close interaction. The XPS result reveals that some amount of nitrogen is doped into this novel-TiO2, and g-C3N4 nanosheets exist in the composites. The results of XRD, TEM and TG indicate that the thickness of g-C3N4 nanosheets is very thin. The ESR spectrum shows the existence of Ti3+ and single-electron-trapped oxygen vacancy in the 30%g-C3N4-TiO2 composites. In photocatalytic activity test, the 30%g-C3N4-TiO2 nanocomposites showed an excellent photo-oxidation activity of propylene under visible light irradiation (λ≥ 420 nm), and the removal efficiency of propylene reached as high as 56.6%, and the activity kept nearly 82% after four consecutive recycles. Photoluminescence (PL) result using terephthalic acid (TA) as a probe molecule indicated that the g-C3N4-TiO2 nanocomposites displayed a Z-sheme photocatalytic reaction system and this should be the main reason for the high photocatalytic activity. A possible photocatalytic mechanism was proposed on the basis of PL result and transient photocurrent-time curves.
Keywords: g-C3N4 nanosheets; Z-scheme; Nanotube titanic acid (NTA); Photo-oxidation of propylene;

A plate-on-plate sandwiched Z-scheme heterojunction photocatalyst: BiOBr-Bi2MoO6 with enhanced photocatalytic performance by Shengyao Wang; Xianglong Yang; Xuehao Zhang; Xing Ding; Zixin Yang; Ke Dai; Hao Chen (194-201).
Display OmittedIn this study, a direct Z-scheme heterojunction BiOBr-Bi2MoO6 with greatly enhanced visible light photocatalytic performance was fabricated via a two-step coprecipitation method. It was indicated that a plate-on-plate heterojunctions be present between BiOBr and Bi2MoO6 through different characterization techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoelectrochemical measurements. The crystal structure and morphology analysis revealed that the heterointerface in BiOBr-Bi2MoO6 occurred mainly on the (001) facets of BiOBr and (001) facets of Bi2MoO6. The photocatalytic activity of the BiOBr-Bi2MoO6 was investigated by degradation of RhB and about 66.7% total organic carbon (TOC) could be removed. Ciprofloxacin (CIP) was employed to rule out the photosensitization. It was implied that the higher activity of BiOBr-Bi2MoO6 could be attribute to the strong redox ability in the Z-scheme system, which was subsequently confirmed by photoluminescence spectroscopy (PL) and active spices trapping experiments. This study provides a promising platform for Z-scheme heterojunction constructing and also sheds light on highly efficient visible-light-driven photocatalysts designing.
Keywords: BiOBr; Bi2MoO6; Z-scheme heterojunction; Photocatalysis mechanism;

Facile preparation of Z-scheme WO3/g-C3N4 composite photocatalyst with enhanced photocatalytic performance under visible light by Lifeng Cui; Xiang Ding; Yangang Wang; Huancong Shi; Lihua Huang; Yuanhui Zuo; Shifei Kang (202-210).
Display OmittedVisible-light-driven WO3/g-C3N4 composites photocatalysts were synthesized via a facile one-step simultaneously heating procedure with urea as the main precursor. These prepared catalyst samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), transmission electron microscopy (TEM), N2 adsorption, ultraviolet-visible diffuse reflection spectroscopy (UV–vis), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The photocatalytic activity of the WO3/g-C3N4 composites was evaluated by the photo-degradation of Rhodamine B (RhB) under visible light irradiation. The results indicated that the composites with 25 wt.% WO3 content exhibited highest photocatalytic activity compared to pure WO3, bare g-C3N4 and other WO3/g-C3N4 composites. The favorable photocatalytic activity of WO3/g-C3N4 composites was mainly attributed to the excellent surface properties, enhanced visible-light absorption and the desirable band positions. A possible Z-scheme photocatalytic mechanism was proposed based on structure and electrochemical characterizations results, which can well explain the enhanced migration rate of photogenerated electrons and holes in WO3/g-C3N4 heterojunctions.
Keywords: WO3/g-C3N4; Mixing and annealing; Heterojunctions; Z-scheme charge carrier transfer; Visible light photocatalysis;

One-dimensional Z-scheme TiO2/WO3/Pt heterostructures for enhanced hydrogen generation by Hongqing Gao; Peng Zhang; Junhua Hu; Jimin Pan; Jiajie Fan; Guosheng Shao (211-217).
We reported one-dimensional solid-state Z-scheme photosynthetic heterojunction system with Pt nanoparticle as an electron collector and WO3 as a hole collector, leading to effective charge separation.Display OmittedOne-dimensional Z-scheme TiO2/WO3/Pt heterostructures were fabricated by integrating a facile electrospinning technique and subsequent annealing in air. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopy, were used to characterize the as-fabricated samples. The results showed that the H2-generation of the as-fabricated one-dimensional Z-scheme TiO2/WO3/Pt heterostructures (S2) was greatly enhanced compared with pure TiO2 nanofibers (S0) and TiO2/WO3 nanofibers (S1). The enhanced photocatalyst activities were mainly attributed to the solid-state Z-scheme photosynthetic heterojunction system with Pt nanoparticle as an electron collector and WO3 as a hole collector, leading to effective charge separation on these semiconductors, which were evidenced by electrochemical impedance spectroscopy (EIS) and photocurrent analysis.
Keywords: Electrospinning; Composite nanofibers; Photocatalyst; Water splitting;

Fabrication of TiO2 nanorod assembly grafted rGO (rGO@TiO2-NR) hybridized flake-like photocatalyst by Kangle Lv; Shun Fang; Lingling Si; Yang Xia; Wingkei Ho; Mei Li (218-227).
To efficiently separate the photo-generated electron–hole pairs of TiO2 hybrid, anatase TiO2 nanorod assembly grafted reduced graphene oxides (rGO@TiO2-NR) hybrid was successfully fabricated using potassium titanium oxalate (PTO) and graphene oxides (GO) as starting materials and diethylene glycol (DEG) as reductant. The effect of GO content on the structure and photocatalytic activity of rGO@TiO2-NR composite was systematically studied. Results show that, in the absence of GO, only TiO2 microsphere assembly is obtained from TiO2 nanorods. The presence of GO results in the formation of a flake-like TiO2-nanorod-assembled grafted rGO hybrid. The photocatalytic activity of rGO@TiO2-NR composite increases first and then decreases with increase in the amount of GO from 0 wt.% to 10 wt.%. The hybridized S4 sample prepared with 4 wt.% GO possesses the highest photocatalytic activity with a constant rate of 0.039 min−1 in the photocataytic degradation of Brilliant X-3B dye (X3B); this sample was enhanced more than three times when compared with pure TiO2 sample (0.012 min−1). The enhanced photocatalytic activity of the rGO@TiO2-NR hybrid was attributed to the strong interaction between TiO2 nanorods and rGO. The unique hierarchical structure of 1D nanorod assembly TiO2–rGO flakes facilitates the injection and transfer of photo-generated electrons from TiO2 to graphene, thus retarding the recombination of electron–hole pairs and enhancing the photocatalytic activity. The enlarged BET surface areas, not only increasing the number of active sites, but also facilitating the adsorption of the dye, and improved light-harvesting ability also contribute to the enhanced photoreactivity of rGO@TiO2-NR hybrid.
Keywords: TiO2; Graphene oxide; Photocatalytic degradation; Hybrid;

Facile synthesis of bird’s nest-like TiO2 microstructure with exposed (001) facets for photocatalytic degradation of methylene blue by Guozhong Zhang; Shuqu Zhang; Longlu Wang; Ran Liu; Yunxiong Zeng; Xinnian Xia; Yutang Liu; Shenglian Luo (228-235).
Display OmittedThe scrupulous design of hierarchical structure and highly active crystal facets exposure is essential for the creation of photocatalytic system. However, it is still a big challenge for scrupulous design of TiO2 architectures. In this paper, bird’s nest-like anatase TiO2 microstructure with exposed highly active (001) surface has been successfully synthesized by a facile one-step solvothermal method. Methylene blue (MB) is chosen as a model pollutant to evaluate photocatalytic activity of as-obtained TiO2 samples. The results show that the photocatalytic activity of the bird’s nest-like sample is more excellent than P25 in the degradation of MB due to high specific surface area and highly active (001) crystal facets exposure when tested under simulated solar light. Besides, it can be readily separated from the photocatalytic system by sedimentation after photocatalytic reaction, which is a significant advantage against conventional powder photocatalyst. The bird’s nest-like microspheres with novel structure may have potential application in photocatalysis and other fields.
Keywords: TiO2; Solvothermal method; Bird’s nest-like structure; Surface; Photocatalysis;

Photocatalytic enhancement of floating photocatalyst: Layer-by-layer hybrid carbonized chitosan and Fe-N- codoped TiO2 on fly ash cenospheres by Jingke Song; Xuejiang Wang; Yunjie Bu; Xin Wang; Jing Zhang; Jiayu Huang; RongRong Ma; Jianfu Zhao (236-250).
Display OmittedDue to the advantage of floating on water surface, floating photocatalysts show higher rates of radical formation and collection efficiencies. And they were expected to be used for solar remediation of non-stirred and non-oxygenated reservoirs. In this research, floating fly ash cenospheres (FAC) supported layer-by- layer hybrid carbonized chitosan and Fe-N-codoped TiO2 was prepared by a simple sol-gel method. The catalysts were characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy(DRS), nitrogen adsorption analyses for Brunauer-Emmett-Teller (BET) specific surface area. It is indicated that Fe-N codoped narrowed the material’s band gap, and the layer of carbonized chitosan (Cts) increased the catalyst’s adsorption capacity and the absorption ability of visible light. Comparing with Fe-N-TiO2/FAC and N-TiO2/FAC, the composite photocatalyst show excellent performance on the degradation of RhB. Photodegradation rate of RhB by Fe-N-TiO2/FAC-Cts was 0.01018 min−1, which is about 1.5 and 2.09 times higher than Fe-N-TiO2/FAC and N-TiO2/FAC under visible light irradiation in 240 min, respectively. The dye photosentization, capture of holes and electrons by Fe3+ ion, and synergistic effect of adsorption and photodegradation were attributed to the results for the improvement of photocatalytic performance. The floating photocatalyst can be reused for at least three consecutive times without any significant decrease on the degradation of Rhodamin B after each reuse.
Keywords: TiO2; Fly ash cenospheres; Chitosan; Fe-N-codoped; Photocatalysis; Adsorption studies;

Hydrogen evolution from aqueous-phase photocatalytic reforming of ethylene glycol over Pt/TiO2 catalysts: Role of Pt and product distribution by Fuying Li; Quan Gu; Yu Niu; Renzhang Wang; Yuecong Tong; Shuying Zhu; Hualei Zhang; Zizhong Zhang; Xuxu Wang (251-258).
Display OmittedPt nanoparticles were loaded on anatase TiO2 by the photodeposition method to investigate their photocatalytic activity for H2 evolution in an aqueous solution containing a certain amount of ethylene glycol (EG) as the sacrificial agent. The surface properties and chemical states of the Pt/TiO2 sample were characterized by X-ray powder diffraction analysis, Brunauer–Emmett–Teller surface area analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and electrochemical resistance. The aqueous-phase photocatalytic EG reforming using Pt/TiO2 and anatase TiO2 generated not only H2 and CO2, but also CO, CH4, C2H6, and C2H4. Moreover, the amount of formate and acetate complexes in the solution increased gradually. The EG adsorption and gas-phase intermediates during photocatalytic reaction processes were investigated by the in situ FTIR spectrum. Finally, the photocatalytic EG reforming reaction mechanism was elucidated. This helped to better understand the role of a sacrificial agent in a photocatalytic hydrogen production.
Keywords: Ethylene glycol; Chemisorption; Photocatalytic reforming; Sacrificial agent; Water splitting;

Display OmittedHighly efficient TiO2 photocatalysts co-modified by amorphous-Ti(IV) hole cocatalyst and Ni(OH)2 electron cocatalyst (referred to as Ni(OH)2-Ti(IV)/TiO2) were prepared by facile two-step process which was the initial formation of amorphous Ti(IV) on the TiO2 surface via hydrolysis method and the following formation of Ni(OH)2 via precipitation reaction. It was found that the Ni(OH)2-Ti(IV)/TiO2 showed obviously high hydrogen-production performance. When the amount of Ni(OH)2 and Ti(IV) was 1 wt% and 0.1 wt%, respectively, the hydrogen-production rate of the resultant Ni(OH)2-Ti(IV)/TiO2 reached 7280.04 μmol h−1  g−1, which was significantly higher than that of TiO2, Ti(IV)/TiO2 and Ni(OH)2/TiO2 by a factor of 215, 63 and 1.8, respectively. Moreover, it was found that Ni(OH)2-Ti(IV)/TiO2 photocatalyst preserved a steady and highly efficient H2-production performance during repeated tests and also exhibited a high transient photocurrent density. The enhanced hydrogen-production performance of Ni(OH)2-Ti(IV)/TiO2 can be attributed to the synergistic effect of Ti(IV) hole cocatalyst and Ni(OH)2 electron cocatalyst to simultaneously accelerate the interfacial transfer of photogenerated holes and electrons. The present surface modification of dual cocatalysts can be regarded as one of the ideal strategies for the preparation of highly efficient hydrogen-production materials in view of their abundance, low cost and facile method.
Keywords: TiO2; Cocatalysts; Amorphous Ti(IV); Ni(OH)2; Synergistic effects; Hydrogen evolution; Photocurrent response;

Iron(III) meso-tetra(4-carboxyphenyl) porphyrin (FeTCPP) loaded on the surface of TiO2 nanotubes (TNTs) has been successfully prepared through improved hydrothermal and heating reflux process. The new photocatalyst has been characterized and analyzed by TEM/EDS, BET, XRD, FT-IR, DRS, PL, XPS and EPR. The photocatalytic activity of FeTCPP/TNT nanocomposite was evaluated by the photodegradation of MB under visible light irradiation. The degradation results showed a purification of more than 90% MB in simulating wastewater, and confirmed that the prepared FeTCPP/TNT nanocomposite has acquired superior photocatalytic activitiy. The 6 times cycled results suggested the great stability of the photocatalyst. These results confirmed the FeTCPP played an important role in capturing photons and expanding the absorption wavelength to the visible light region, and the FeTCPP/TNT photocatalyst is also beneficial for the electron transfer and long-distance transmission, and could efficiently increase the separation of the electron-hole pairs, and accelerate the decomposition of organic pollutants. In addition, nano-sized structures can increase adsorption capability.
Keywords: Metalloporphyrin; TiO2 nanotube; Visible-light driven photocatalyst; Nanocomposite; Electron transfer;

C, N co-doped TiO2/TiC0.7N0.3 composite coatings prepared from TiC0.7N0.3 powder using ball milling followed by oxidation by Liang Hao; Zhenwei Wang; Yaoqing Zheng; Qianqian Li; Sujun Guan; Qian Zhao; Lijun Cheng; Yun Lu; Jizi Liu (275-281).
Display OmittedBall milling followed by heat oxidation was used to prepared C, N co-doped TiO2 coatings on the surfaces of Al2O3 balls from TiC0.7N0.3 powder. The as-prepared coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectrophotometer (UV–vis). The results show that continuous TiC0.7N0.3 coatings were formed after ball milling. C, N co-doped TiO2/TiC0.7N0.3 composite coatings were prepared after the direct oxidization of TiC0.7N0.3 coatings in the atmosphere. However, TiO2 was hardly formed in the surface layer of TiC0.7N0.3 coatings within a depth less than 10 nm during the heat oxidation of TiC0.7N0.3 coatings in carbon powder. Meanwhile, the photocatalytic activity evaluation of these coatings was conducted under the irradiation of UV and visible light. All the coatings showed photocatalytic activity in the degradation of MB no matter under the irradiation of UV or visible light. The C, N co-doped TiO2/TiC0.7N0.3 composite coatings showed the most excellent performance. The enhancement under visible light irradiation should attribute to the co-doping of carbon and nitrogen, which enhances the absorption of visible light. The improvement of photocatalytic activity under UV irradiation should attribute to the synergistic effect of C, N co-doping, the formation of rutile-anatase mixed phases and the TiO2/TiC0.7N0.3 composite microstructure.
Keywords: TiC0.7N0.3 powder; C, N co-doping; Composite coatings; Ball milling & oxidation; Photocatalysis;

TiO2 Processed by pressurized hot solvents as a novel photocatalyst for photocatalytic reduction of carbon dioxide by Martin Reli; Marcin Kobielusz; Lenka -->Matějová; Stanislav Daniš; Wojciech Macyk; Lucie Obalová; Piotr Kuśtrowski; Anna Rokicińska; Kamila Kočí (282-287).
Display OmittedAnatase-brookite TiO2 photocatalysts were prepared by the sol-gel process controlled within reverse micelles and processing by pressurized hot solvents–water/methanol/water (TiO2(M)) and water/ethanol/water (TiO2(E)), as an unconventional alternative to common calcination. The main goal of this work was to prepare anatase-brookite mixtures by processing by two different alcohols (methanol and ethanol) and evaluate the influence of the alcohol on the photocatalytic activity. Prepared photocatalysts were characterized by organic elemental analysis, nitrogen physisorption, XRD, UV–vis, photoelectrochemical and spectroelectrochemical measurements and XPS. The prepared photocatalysts efficiency was tested on the photocatalytic reduction of carbon dioxide and compared with commercial TiO2 Evonik P25. Both prepared nanocomposites were more efficient towards methane production but Evonik P25 was the most efficient towards hydrogen generated through water splitting. The higher performance of anatase-brookite mixture towards methane production can be explained by (i) a higher photocatalytic activity of brookite than rutile; (ii) a large surface area of anatase-brookite composites enabling better carbon dioxide adsorption; (iii) the photoinduced electron transfer from the brookite conduction band to the anatase conduction band. On the other hand, a higher production of hydrogen in the presence of Evonik P25 is caused by a better charge separation in anatase-rutile than anatase-brookite phase compositions. TiO2(M) appeared more active than TiO2(E) in the photocatalytic reduction of carbon dioxide due to a lower density of defects created in the crystal lattice.
Keywords: Anatase/brookite nanocomposite; Nanoparticle; Sol-gel preparation; Pressurized hot solvents; Photocatalysis; CO2 reduction;

Phosphate modified N/Si co-doped rutile TiO2 nanorods for photoelectrochemical water oxidation by Xiaofan Zhang; Bingyan Zhang; Yanping Luo; Xiaowei Lv; Yan Shen (288-294).
We report on phosphate modified N/Si co-doped TiO2 nanorods film for photo-electrochemical water oxidation, exhibiting a photocurrent density of 1.44 mA cm−2 under light illumination.Display OmittedSurface modification of TiO2 film provides possibilities to improve photoelectrochemical (PEC) activity. In this study, we report on phosphate modified N/Si co-doped TiO2 nanorods films (Pi-N/Si-TiO2 NRs) for PEC water oxidation. Compared to the pristine TiO2 NRs, the Pi-N/Si-TiO2 NRs photoanode shows a 4.65-fold enhanced photocurrent density (1.44 mA cm−2) under light illumination. This significant improvement can be attributed to the synergistic effect of phosphate modification and the N and Si co-dopants. In addition to the improvement of ultraviolet and visible light response by N and Si co-dopants, phosphate modification is mainly responsible for charge transfer at the interface of the photoanode/electrolyte.
Keywords: Phosphate; Doping; TiO2; Photoelectrochemistry; Water oxidation;

Pouous TiO2 nanofibers decorated CdS nanoparticles by SILAR method for enhanced visible-light-driven photocatalytic activity by Fengyu Tian; Dongfang Hou; Fuchao Hu; Kui Xie; Xiuqing Qiao; Dongsheng Li (295-302).
A heterojunction photocatalyst with CdS Nanoparticles self-assembled via SILAR Method at surfaces of electrospun TiO2 nanofibers shows enhanced visible-light photocatalytic activities.Display Omitted1D porous CdS nanoparticles/TiO2 nanofibers heterostructure has been fabricated via simple electrospinning and a successive ionic layer adsorption and reaction (SILAR) process. The morphology, composition, and optical properties of the resulting CdS/TiO2 heterostructures can be rationally tailored through changing the SILAR cycles. The photocatalytic hydrogen evolution and decomposition of rhodamine B (RhB) of the as-synthesized heterostructured photocatalysts were investigated under visible light irradiation. Compared to TiO2 nanofibers,the as-obtained CdS/TiO2 heterostructures exhibit enhanced photocatalytic activity for hydrogen production and decomposition of RhB under visible-light irradiation. The heterojunction system performs best with H2 generation rates of 678.61 μmol h−1  g−1 under visible light irradiation which benefits from the two effects: (a) the 1D porous nanofibrous morphology contributes to not only more active sites but also more efficient transfer of the photogenerated charges (b) the synergetic effect of heterojunction and photosensitization reducing the recombination of photogenerated electrons and holes.
Keywords: Pouous TiO2 nanofiber; CdS nanoparticle; Heterostructure; Photocatalytic activity;

Self-assembled Bi2MoO6/TiO2 nanofiber heterojunction film with enhanced photocatalytic activities by Hua Li; Tianxi Zhang; Chao Pan; Chenchen Pu; Yang Hu; Xiaoyun Hu; Enzhou Liu; Jun Fan (303-310).
Display OmittedTiO2 nanofiber film (TiO2 NFF) was successfully fabricated by an ethylene glycol-assisted hydrothermal method, and then self-assembled flake-like Bi2MoO6 was grown on the surface of TiO2 nanofiber under alcohol thermal condition. The investigations indicate that the nanofiber structure of TiO2 films exhibits excellent visible light scattering property, the scattering light overlaps with the absorption band of Bi2MoO6, which can enhance the utility of incident light. The prepared Bi2MoO6/TiO2 composites show obviously enhanced photocatalytic activity for methylene blue (MB) degradation compared with pure TiO2 nanofiber under visible light irradiation (λ > 420 nm). The enhanced photocatalytic activity is primarily attributed to the synergistic effect of visible light absorption and effective electron-hole separation at the interfaces of the two semiconductors, which is confirmed by photoluminescence (PL) and electrochemical tests.
Keywords: Bi2MoO6/TiO2; Heterojunction; Light scattering; Self-assembled;

Display OmittedAnatase TiO2 nanocrystals exposed with {001} facets were fabricated by solvothermal strategy in HF-C4H9OH mixed solution, using titanic acid nanobelts (TAN) as a precursor. The shape of TAN is a long flat plane with a high aspect ratio, and F is easily adsorbed on the surface of the nanobelts, inducing a higher exposure of {001} facet of TiO2 nanoparticles during the structure reorganization. The exposed percentage of {001} facets could vary from 40 to 77% by adjusting the amount of HF. The as-prepared samples were characterized by transmission electron microscopy, N2 adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscope. The photocatalytic measurement showed that TiO2 nanocrystals with 77% {001} facets exhibited much superior photocatalytic activity for photodegradation of methyl orange, methylene blue, and rhodamine B. And what’s more, the mineralization rate of methyl orange was as high as 96% within 60 min. The photocatalytic enhancement is due to a large amount of the high energetic {001} facets exposing, the special truncated octahedral morphology and a stronger ability for dyes adsorption.
Keywords: TiO2; {001} facet; Titanic acid nanobelts; Photocatalytic activity;

Carbon wrapped and doped TiO2 mesoporous nanostructure with efficient visible-light photocatalysis for NO removal by Di He; Yongli Li; inshu Wang; Junshu Wu; Yilong Yang; Qier An (318-325).
Display OmittedCarbon wrapped and doped mesoporous anatase TiO2 nanocrystals were prepared by a hydrothermal approach in acetic acid aqueous containing chitosan. A designed post-thermal treatment was employed to enhance the incorporation between carbon and TiO2. After hydrothermal process, mesoporous anatase TiO2 formed with wrapped by a few layers of carbon shell. Here chitosan was used as not only the template for the formation of mesopores, but also the carbon source toward the carbon layers coating. Furthermore, chitosan provided doping element into TiO2 lattice and induced to form Ti―C bond which caused Ti(III) with oxygen vacancies. The Ti(III)-oxygen vacancy are partly responsible for visible-light response and high photocatalytic activity, which can accelerate electron transfer thus inhibit photogenerated charge recombination. The photocatalytic activity was evaluated using photo-oxidation of gaseous NO under visible light irradiation as the probe reaction. In the optimum result, 71% of NO with starting concentration at ppb level was photo-degraded. Our results also showed that the photogenerated electrons played a key role in photodegradation of NO, as a result, the environmental humidity level had a negligible effect on the photocatalysis.
Keywords: Carbon wrapped and doped TiO2 (CWDTO); Mesoporous nanostructure; Photocatalysis; NO removal;

Effect of band gap engineering in anionic-doped TiO2 photocatalyst by Emy Marlina Samsudin; Sharifah Bee Abd Hamid (326-336).
Display OmittedA simple yet promising strategy to modify TiO2 band gap was achieved via dopants incorporation which influences the photo-responsiveness of the photocatalyst. The mesoporous TiO2 was successfully mono-doped and co-doped with nitrogen and fluorine dopants. The results indicate that band gap engineering does not necessarily requires oxygen substitution with nitrogen or/and fluorine, but from the formation of additional mid band and Ti3+ impurities states. The formation of oxygen vacancies as a result of modified color centres and Ti3+ ions facilitates solar light absorption and influences the transfer, migration and trapping of the photo-excited charge carriers. The synergy of dopants in co-doped TiO2 shows better optical properties relative to single N and F doped TiO2 with c.a 0.95 eV band gap reduction. Evidenced from XPS, the synergy between N and F in the co-doped TiO2 uplifts the valence band towards the conduction band. However, the photoluminescence data reveals poorer electrons and holes separation as compared to F-doped TiO2. This observation suggests that efficient solar light harvesting was achievable via N and F co-doping, but excessive defects could act as charge carriers trapping sites.
Keywords: TiO2; Dopant; Anionic; Band gap; Photocatalysis;

Chemical bath deposited rutile TiO2 compact layer toward efficient planar heterojunction perovskite solar cells by Chao Liang; Zhenhua Wu; Pengwei Li; Jiajie Fan; Yiqiang Zhang; Guosheng Shao (337-344).
Display OmittedTiO2 is a best choice of electron transport layers in perovskite solar cells, due to its high electron mobility and stability. However, traditional TiO2 processing method requires rather high annealing temperature (>500 °C), preventing it from application to flexible devices. Here, we show that TiO2 thin films can be synthesized via chemical bath deposition below 100 °C. Typically, a compact layer of rutile TiO2 is deposited onto fluorine-doped tin oxide (FTO) coated substrates, in an aqueous TiCl4 solution at 70 °C. Through the optimization of precursor concentration and ultraviolet-ozone surface modification, over 12% power conversion efficiency can be achieved for CH3NH3PbI3 based perovskite solar cells. These findings offer a potential low-temperature technical solution in using TiO2 thin film as an effective transport layer for flexible perovskite solar cells.
Keywords: Chemical bath deposition; Rutile TiO2; Perovskite solar cells; Ultraviolet-ozone treatment;

A facile strategy to fabricate Au/TiO2 nanotubes photoelectrode with excellent photoelectrocatalytic properties by Guowei Zhang; Hui Miao; Xiaoyun Hu; Jianglong Mu; Xixi Liu; Tongxin Han; Jun Fan; Enzhou Liu; Yunchao Yin; Jun Wan (345-352).
Display OmittedHighly ordered titanium dioxide nanotubes (TiO2 NTs) were prepared by a low-temperature hydrothermal process with Ti sheet as precursor in NaOH solutions. Gold nanoparticles (Au NPs) were then deposited on the surface of TiO2 NTs by a microwave-assisted chemical reduction route. The investigation reveal that the Au NPs are well dispersed on the surface of TiO2 NTs in metallic state, and Au NPs can effectively promote the separation of photogenerated electron-hole pairs. Besides, Au NPs also can enhance the visible light absorption of TiO2 NTs due to their localized surface plasmon resonance (LSPR) effect. The experimental results indicate that 0.5 Au/TiO2 NTs film with an photocurrent of 19.0 μA/cm2 exhibits the highest photoelectrocatalytic (PEC) activity, when under a low bias of 0.5 V, in the degradation of methylene blue (MB). Additionally, the mechanism for the enhanced PEC performance of Au/TiO2 NTs is preliminarily discussed. The Au NPs decorated TiO2 NTs displayed a more effective separation of photogenerated electron-hole pairs. The enhanced visible light absorption was owning to the Au NPs localized surface plasmon resonance (LSPR) effect. Finally, the mechanism for the enhanced PEC performance of Au/TiO2 NTs was also proposed.
Keywords: TiO2 nanotubes electrode; Gold nanoparticles; Surface sensitization; Photoelectrocatalytic activity;

Display OmittedA novel Cu2O/TNS composite structure of single crystal TiO2 nanosheet (TNS) arrays decorated with flake-like Cu2O were synthesized by a facile hydrothermal reaction followed by the electrodeposition process. The effects of deposition potential on the microstructure, morphology, and optical property of the thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis spectrophotometer. When the deposition potential is higher than −0.4 V, peaks corresponding to Cu appear, meanwhile, flake-like Cu2O become agglomerating, and transform into dense Cu2O particles. Additionally, photoelectrochemical experiments indicate that the films deposited at −0.4 V show the lowest resistivity and highest exciton separation efficiency. This enhanced photoelectrochemical properties can be explained by synergistic effect of p-type flake-like Cu2O and n-type TiO2 heterojunctions combined with two-dimensional TiO2 nanosheet with exposed highly reactive {001} facets.
Keywords: TiO2 nanosheet arrays; Flake-like Cu2O; Photoelectrochemical properties; {001} facets;

Display OmittedConstructing special nanostructures with large surface areas and tuning the band gap by element doping are efficient strategies to enhance the photocatalytic activity of semiconductor materials. Here we combined both strategies in one material to form sulfur-doped graphitic carbon nitride porous rods (S-pg-C3N4) in one pot by simply pyrolysis of the melamine-trithiocyanuric acid complex with different temperatures. The samples were characterized by XRD, FT-IR, and elemental analysis; nitrogen adsorption isotherms, SEM and TEM images; and UV–vis DRS and photoluminescence spectra. Characterizations showed that S-pg-C3N4 possessed porous rod structure with a larger surface area (20–52 m2/g) than that of bulk g-C3N4, and the surface area of the S-pg-C3N4 samples increased with the increase of heating temperature. Meanwhile, the trace sulfur remained in the framework of g-C3N4 formed sulfur doped g-C3N4, and the visible light absorption edge of the S-pg-C3N4 was extended, corresponding to a narrowed band gap. As a result, the S-pg-C3N4 samples exhibited an enhanced physical adsorption and photocatalytic activity in the degradation of Rhodamine B dye under visible light.
Keywords: Graphitic carbon nitride; Porous materials; Supramolecular; Photodegradation; Visible light;

Graphitic carbon nitride nanosheet for photocatalytic hydrogen production: The impact of morphology and element composition by Zhao Zhang; Yijie Zhang; Luhua Lu; Yanjie Si; Si Zhang; Ying Chen; Kai Dai; Ping Duan; Limei Duan; Jinghai Liu (369-375).
The intrinsic morphology and basal plane defects on g-C3N4 nanosheet have important influences on its electronic structures and photocatalytic activity. In this work, we report extending thermal treatment time of g-C3N4 at 550 °C not only change the morphology of g-C3N4 but also element composition of g-C3N4. The morphology variation results in largely increased SSA from 40.22 to 117.27 m2  g−1, obviously reduced pore size from 3.99 to 2.77 nm for g-C3N4 and formation of in-plane holes. Moreover, composition variation of g-C3N4 has also been found to have changed as the pyrolysis time extended. These changes have significant impact on the optical properties and photoelectrical characters of g-C3N4, which were investigated by UV-DSR, PL and Photocurrent measurement. The photocatalytic activity of g-C3N4 obtained via 9 h thermal treatment at 550 °C has shown highest photocatalytic activity, which is 1.77 times than that of g-C3N4 obtained via 3 h thermal treatment under visible irradiation and 1.99 times under UV irradiation respectively.
Keywords: Graphitic carbon nitride; Photocatalytic hydrogen evolution; Specific surface area; Morphology; Element composition;

Enhanced visible light photocatalytic degradation of Rhodamine B over phosphorus doped graphitic carbon nitride by Bo Chai; Juntao Yan; Chunlei Wang; Zhandong Ren; Yuchan Zhu (376-383).
Display OmittedPhosphorus doped graphitic carbon nitride (g-C3N4) was easily synthesized using ammonium hexafluorophosphate (NH4PF6) as phosphorus source, and ammonium thiocyanate (NH4SCN) as g-C3N4 precursor, through a direct thermal co-polycondensation procedure. The obtained phosphorus doped g-C3N4 was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), UV–vis diffuse reflectance absorption spectra (UV-DRS), photoelectrochemical measurement and photoluminescence spectra (PL). The photocatalytic activities of phosphorus doped g-C3N4 samples were evaluated by degradation of Rhodamine B (RhB) solution under visible light irradiation. The results showed that the phosphorus doped g-C3N4 had a superior photocatalytic activity than that of pristine g-C3N4, attributing to the phosphorus atoms substituting carbon atoms of g-C3N4 frameworks to result in light harvesting enhancement and delocalized π-conjugated system of this copolymer, beneficial for the increase of photocatalytic performance. The photoelectrochemical measurements also verified that the charge carrier separation efficiency was promoted by phosphorus doping g-C3N4. Moreover, the tests of radical scavengers demonstrated that the holes (h+) and superoxide radicals (•O2 ) were the main active species for the degradation of RhB.
Keywords: Phosphorus doped g-C3N4; Photocatalytic activity; Degradation; Charge carrier separation;

Display OmittedA commercial calcium carbonate particle as hard template is employed to synthesize mesoporous carbon nitride (mpg-C3N4) by a thermal polycondensation process using dicyandiamide as a precursor, then it can be easily removed using diluted hydrochloric acid. Compare with the other hard templates, such as SiO2 and porous anodic aluminium oxides (Al2O3), the industrially available calcium carbonate particles are not only low-cost, but also environment friendly. A certain amount of carbon dopants were generated in the resulting mpg-C3N4 matrix, and the concentration of carbon dopants can be controlled by the amount of calcium carbonate particle. The synthesized mpg-C3N4 not only possesses high specific surface area, but also has the enhanced visible light absorption range from 460 nm to 800 nm. The photocatalytic activity increases as the mass ratio of template to dicyandiamide increases, when the mass ratio is 1.0, the photocatalytic performance is up to the maximum, which is 12.3 times higher than that of bulk g-C3N4. The enhancement of the photocatalytic performance of mpg-C3N4 is contributed to its improved specific surface areas and the enhancement of the visible light absorptions from 450 nm to 800 nm.
Keywords: Mpg-C3N4; Commercial calcium carbonate; Template; Photocatalysis;

Construction of stable Ta3N5/g-C3N4 metal/non-metal nitride hybrids with enhanced visible-light photocatalysis by Yinhua Jiang; Peipei Liu; YeCheng Chen; Zhengzhong Zhou; Haijian Yang; Yuanzhi Hong; Fan Li; Liang Ni; Yongsheng Yan; Duncan H Gregory (392-403).
Display OmittedIn this paper, a novel Ta3N5/g-C3N4 metal/non-metal nitride hybrid was successfully synthesized by a facile impregnation method. The photocatalytic activity of Ta3N5/g-C3N4 hybrid nitrides was evaluated by the degradation of organic dye rhodamine B (RhB) under visible light irradiation, and the result indicated that all Ta3N5/g-C3N4 samples exhibited distinctly enhanced photocatalytic activities for the degradation of RhB than pure g-C3N4. The optimal Ta3N5/g-C3N4 composite sample, with Ta3N5 mass ratio of 2%, demonstrated the highest photocatalytic activity, and its degradation rate constant was 2.71 times as high as that of pure g-C3N4. The enhanced photocatalytic activity of this Ta3N5/g-C3N4 metal/metal-free nitride was predominantly attributed to the synergistic effect which increased visible-light absorption and facilitated the efficient separation of photoinduced electrons and holes. The Ta3N5/g-C3N4 hybrid nitride exhibited excellent photostability and reusability. The possible mechanism for improved photocatalytic performance was proposed. Overall, this work may provide a facile way to synthesize the highly efficient metal/metal-free hybrid nitride photocatalysts with promising applications in environmental purification and energy conversion.
Keywords: Ta3N5; g-C3N4; Metal/non-metal nitride hybrids; Visible-light photocatalytic activity; Synergistic effect; Photostability;

Display OmittedCu-Cu2O nanoparticles (NPs) decorated porous graphitic carbon nitride (g-C3N4) (Cu-Cu2O/g-C3N4) photocatalysts were prepared. When investment of copper source materials in the experiment increased to 7 wt%, the highest H2 evolution rate (400 μmol g−1  h−1) was obtained under visible light irradiation in triethanolamine solution. This is about triple of pure g-C3N4 (140 μmol g−1  h−1). Moreover, various amount of Erythrosin B dye was added into Cu-Cu2O/g-C3N4 photoreaction solution and a significant enhancement of H2 production rate was achieved. The highest H2 production rate was 5000 μmol g−1  h−1 with 5 mg Erythrosin B in photoreaction system. Erythrosin B dye sensitized Cu-Cu2O/g-C3N4 presented stable photocatalytic H2 evolution ability and no noticeable degradation or change of photocatalyst were detected after six recycles. A possible photocatalytic mechanism of Erythrosin B dye sensitized Cu-Cu2O/g-C3N4 for the enhancement of photocatalytic H2 evolution is proposed.
Keywords: Cu-Cu2O/g-C3N4; Hydrogen evolution; Photocatalytic; Sensitization;

Display OmittedThis work reported a novel AgFeO2/g-C3N4 composite with enhanced photocatalytic activity, which was fabricated by a simple precipitation method. The g-C3N4 sheets with thickness of 2•4 nm were successfully loaded on the surface of the AgFeO2 particles. As compared to pure AgFeO2 and pure g-C3N4, the as-prepared AgFeO2/g-C3N4 photocatalysts exhibited superior absorption in the visible-light region and displayed promising visible-light photocatalytic performance in the degradation of organic contaminations both in water and in air. About 94% of Acid red G (ARG) can be degraded by the optimized AgFeO2/g-C3N4 sample, which is ∱/47.5 and ∱/410.7 times higher than that by pure AgFeO2 and pure g-C3N4, respectively. Meanwhile, it can also effectively degrade ∱/487% of gaseous formaldehyde to CO2 within 9 h. The enhanced photocatalytic property and stability of the AgFeO2/g-C3N4 composite can be attributed to its specific nanostructure, effective electron-hole separation and the formation of Z-scheme heterostructure between AgFeO2 and g-C3N4. This work could provide new and helpful insights into the photocatalytic application of Ag-based delafossite materials.
Keywords: Delafossite; Z-scheme; AgFeO2/g-C3N4; Core-shell; Photocatalyst;

Enhancement of photocatalytic and photoelectrocatalytic activity of Ag modified Mpg-C3N4 composites by Qiuchen He; Feng Zhou; Su Zhan; Yifan Yang; Yujun Liu; Yu Tian; Naibao Huang (423-431).
Display OmittedIn this study, mpg-C3N4/Ag composites of surface plasmon resonance structures were fabricated to improve the photocatalytic and photoelectrocatalytic activities of g-C3N4 via photo-assisted reduction method, which were characterized by XRD, EDS, XPS, FT-IR, FE-SEM, TEM, DRS and BET. The photocatalytic and photoelectrocatalytic activities were evaluated by the degradation of methylene blue (MB) and the oxygen reduction experiment under visible light. The results showed the photocatalytic and photoelectrocatalytic activities were dependent on the weight ratio of Ag and the optimum photocatalytic activity of mpg-C3N4/Ag at a weight ratio of 3% is almost 3 times as high as that of mpg-C3N4. Additionally, mpg-C3N4/Ag exhibited a significantly enhanced oxygen reduction performance under visible light. The limit current density was increased about 2 times by the modification of Ag nanoparticles, compared with that of pristine mpg-C3N4. Finally, based on the first principle, the enhancement mechanism of the photocatalytic and photoelectrocatalytic activities was discussed by the calculation on the band structure and density of states in the mpg-C3N4/Ag composites. The appropriate amount of Ag modification would cause the surface plasmon resonance effect, which improved the photocatalytic, photoelectrocatalytic, and oxygen reduction activities of mpg-C3N4.
Keywords: Photocatalysts; Mesoporous g-C3N4; Ag nanoparticles; Oxygen reductive reaction; Surface plasmon resonance;

Display OmittedLow-temperature solid-state method were gradually demonstrated as a high efficiency, energy saving and environmental protection strategy to fabricate composite semiconductor materials. CdS-based multiple composite photocatalytic materials have attracted increasing concern owning to the heterostructure constituents with tunable band gaps. In this study, the ternary CdS/g-C3N4/CuS composite photocatalysts were prepared by a facile and novel low-temperature solid-state strategy. The optimal ternary CdS/g-C3N4/CuS composite exhibits a high visible-light photocatalytic H2-production rate of 57.56 μmol h−1 with the corresponding apparent quantum efficiency reaches 16.5% at 420 nm with Na2S/Na2SO3 mixed aqueous solution as sacrificial agent. The ternary CdS/g-C3N4/CuS composites show the enhanced visible-light photocatalytic H2-evolution activity comparing with the binary CdS-based composites or simplex CdS. The enhanced photocatalytic activity is ascribed to the heterojunctions and the synergistic effect of CuS and g-C3N4 in promotion of the charge separation and charge mobility. This work shows that the low-temperature solid-state method is efficient and environmentally benign for the preparation of CdS-based multiple composite photocatalytic materials with enhanced visible-light photocatalytic H2-production activity.
Keywords: Low-temperature solid-state; CdS; Synergistic effect; Photocatalytic H2 evolution activity;

Display OmittedNovel and highly efficient visible-light-driven g-C3N4/Ag2CO3/AgBr multi-heterostructured photocatalysts are achieved from the surface modification of g-C3N4/Ag2CO3 with AgBr nanoparticles by a facile and efficient ion-exchange method. The as-prepared g-C3N4/Ag2CO3/AgBr photocatalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), scaning electron microscopy (SEM) and UV–vis diffuse reflectance spectrometry (DRS). Compared with g-C3N4/Ag2CO3, g-C3N4/Ag2CO3/AgBr hybrids exhibit enhanced the degradation activity for typical RhB, MB, and MO dyes under visible light excitation (>420 nm). Photoluminescence (PL), photo-induced current and electrochemical impedance spectroscopy (EIS) results demonstrate the g-C3N4/Ag2CO3/AgBr heterojunctions can effectively suppress the recombination of the generated electron–hole pairs. The higher photocatalytical performance of g-C3N4/Ag2CO3/AgBr can be ascribed to the efficient separation of photogenerated electron–hole pairs due to the formation of multi-heterojunctions, in which the Ag nanoparticles acted as the charge transmission bridge. In addition, the possible transferred and separated behavior of electron–hole pairs and photocatalytic mechanisms based on the experimental results are also proposed in detail.
Keywords: Ag2CO3; g-C3N4; AgBr; Multi-heterojunction; Photocatalysis;

Display Omittedg-C3N4 has been attracting much attention for application in visible light photocatalytic water splitting due to its suitable band structure, and high thermal and chemical stability. However, the rapid recombination of photogenerated carriers has inhibited its wide use. For this reason, novel g-C3N4/SiC composites were prepared via in situ synthesis of g-C3N4 on the surface of SiC, with which g-C3N4 shows tight interaction (chemical bonding). The g-C3N4/SiC composites exhibit high stability in H2 production under irradiation with visible light (λ ≥ 420 nm), demonstrating a maximum of 182 μmol g−1  h−1, being 3.4 times higher than that of pure g-C3N4. The enhanced photocatalytic H2 production ability for g-C3N4/SiC photocatalysts is primarily ascribed to the combined effects of enhanced separation of photogenerated carriers through efficient migration of electron and enlarged surface areas, in addition to the possible contributions of increased hydrophilicity of SiC and polymerization degree of g-C3N4. This study may provide new insights into the development of g-C3N4-based composites as stable and efficient photocatalysts for H2 production from water splitting.
Keywords: Photocatalysis; Water splitting; Carbon nitride; Silicon carbide; Heterojunction;

Growth of ZnO nanowires on polypropylene membrane surface—Characterization and reactivity by Marta Bojarska; Bartosz Nowak; Jarosław Skowroński; Wojciech Piątkiewicz; Leon Gradoń (457-467).
Display OmittedNeed for a new membrane is clearly visible in recent studies, mostly due to the fouling phenomenon. Authors, focused on problem of biofouling caused by microorganisms that are present in water environment. An attempt to form a new membrane with zinc oxide (ZnO) nanowires was made; where plasma treatment was used as a first step of modification followed by chemical bath deposition. Such membrane will exhibit additional reactive properties. ZnO, because of its antibacterial and photocatalytic properties, is more and more often used in commercial applications. The authors used SEM imaging, measurement of the contact angle, XRD and the FT–IR analysis for membrane characterization. Amount of ZnO deposited on membrane surface was also investigated by dithizone method. Photocatalytic properties of such membranes were examined through methylene blue and humic acid degradation in laboratory scale modules with LEDs as either: wide range white or UV light source. Antibacterial and antifouling properties of polypropylene membranes modified with ZnO nanowires were examined through a series of tests involving microorganisms: model gram-positive and −negative bacteria. The obtained results showed that it is possible to modify the membrane surface in such a way, that additional reactive properties will be given. Thus, not only did the membrane become a physical barrier, but also turned out to be a reactive one.
Keywords: Membrane preparation; Plasma treatment; Zinc oxide nanowires; Photocatalytic properties; Antibacterial properties;

Down-conversion phosphors as noble-metal-free co-catalyst in ZnO for efficient visible light photocatalysis by Haipeng Chu; Xinjuan Liu; Jiaqing Liu; Wenyan Lei; Jinliang Li; Tianyang Wu; Ping Li; Huili Li; Likun Pan (468-475).
ZnO-Lu3(Al,Si)5(O,N)12:Ce3+ hybrid photocatalysts were synthesized via a fast microwave-assisted approach for visible light photocatalytic degradation of organic pollutions with a high degradation rate of 91%.Display OmittedExploring novel visible light responsive photocatalysts is one of greatly significant issues from the viewpoint of using solar energy. Here we report the yellow-orange emitting α-Si3N4-doped Lu3Al5O12:Ce3+ (Lu3Al5-xSixO12-xNx:Ce3+) phosphors as a noble-metal-free co-catalyst for enhanced visible light photocatalytic activity of ZnO. The results show that ZnO-Lu3Al5-xSixO12-xNx:Ce3+ hybrid photocatalysts using a fast microwave-assisted approach exhibits a 91% methylene blue (MB) degradation under visible light irradiation at 240 min, which evidence the synergistic effect of ZnO and Lu3Al5-xSixO12-xNx:Ce3+ that suppress the rate of charge recombination and increase the self-sensitized degradation of MB. ZnO-down conversion phosphors can be envisaged as potential candidate in environmental engineering and solar energy applications.
Keywords: Down conversion phosphors; ZnO; Photocatalysts; Microwave-assisted approach;

Effects of Ag loading on structural and photocatalytic properties of flower-like ZnO microspheres by Xiaodong Zhang; Yuxin Wang; Fulin Hou; Hongxin Li; Yang Yang; Xinxin Zhang; Yiqiong Yang; Yin Wang (476-483).
Display OmittedFlower-like Ag/ZnO samples were successfully fabricated via a simple and cost efficient method without surfactants. The morphologies, structural and optical properties of Ag/ZnO samples with various Ag content were investigated. The samples were systematically characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 adsorption-desorption isotherm, diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). It was found that ZnO was wurtzite phase and metallic Ag particles were wrapped by ZnO nanosheets. Compared with pure metallic Ag, the binding energy of Ag 3d for the Ag/ZnO samples distinctly shifted to the lower binding energy, which was attributed to the interaction between ZnO and Ag. With the increase of Ag content, surface plasmon absorption band of Ag/ZnO samples was obviously widened; meanwhile, PL intensity was decreased. The photocatalytic performance of Ag/ZnO samples were carried out by the degradation of methylene blue (MB) solution under visible light irradiation. The deposition of a certain amount of Ag was beneficial to the improvement of photocatalytic activity. The degradation rate of the Ag/ZnO sample with Ag/Zn ratio 1/20 was greater than fourfold times faster than that of ZnO. It was suggested that photoexcited electrons transferred from Ag to ZnO due to surface plasmon resonance (SPR), which could effectively reduce the recombination of electron–hole pairs and prolong lifetime of the electron–holes pairs, promoting the degradation efficiency. The deposition of a large amount of Ag was unfavorable for the formation of flower-like Ag/ZnO samples, and caused the decrease of specific surface area and the aggregation of Ag nanoparticles, leading to the reduction of photocatalytic performance.
Keywords: Ag/ZnO; Flower-like morphology; Hydrothermal method; Surface plasmon resonance; Photocatalysis; Free oxygen radicals; Visible light;

Display OmittedGraphene quantum dots co-doped with sulfur and nitrogen (S,N:GQDs) are successfully combined with leaf-templated ZnO nanoparticles (L-ZnO) to obtain hierarchical L-ZnO/S,N:GQD composites exhibiting highly surface area. The morphology, structure, and the visible-light-driven photocatalytic activity are investigated. Compared with non-templated ZnO/S,N:GQDs, L-ZnO/S,N:GQD composites exhibit higher photocatalytic activity for the degradation of rhodamine B under visible light irradiation. Such elevated photocatalytic activity results from two main effects: one is the highly effective charge separation in L-ZnO/S,N:GQD composites; the other is the high surface area, allowing for efficient capture of the visible light.
Keywords: ZnO; Graphene quantum dots; Nanocomposites; Visible light; Photocatalytic activity;

Bi metal deposited on Bi2WO6 composite photocatalysts have been successfully synthesized via a simple in-situ reduction method at room temperature with using Bi2WO6 as self-sacrificing template and NaBH4 as reducing agent. The reduction extent can be easily modulated by controlling the concentration of NaBH4 solution. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectra, N2 adsorption-desorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), diffuse reflection spectroscopy (DRS) and photoelectrochemical measurements were carried out to analyze the phase, morphology, optical property and photoelectrochemical property of the as-prepared samples. The photocatalytic activity is surveyed by degradation of phenol under visible light (λ > 420 nm), which showed that the BWO-0.2 photocatalyst exhibited the highest efficiency, which was over 3 times as high as pure Bi2WO6. The enhanced photocatalytic activity should be attributed to strengthened photoabsorption and charge separation efficiency derived from the surface plasmon resonance (SPR) of Bi metal.
Keywords: Bi2WO6; In-situ reduction; Metallic Bi; Visible-light irradiation; Photocatalytic activity;

Synthesis and photocatalytic property for H2 production of H1.78Sr0.78Bi0.22Nb2O7 nanosheets by Bing Zhang; Yingxuan Li; Jianmin Luo; He Zhao; Jie Zhao; Guohui Dong; Yunqing Zhu; Chuanyi Wang (499-506).
Display OmittedThe SrBi2Nb2O9 platelets with a thickness of about 600 nm were synthesized by molten salt synthesis method. The treatment of the SrBi2Nb2O9 platelets with hydrochloric acid resulted in the formation of the protonated H1.78Sr0.78Bi0.22Nb2O7 platelets. Through a top–down approach in ethylamine solution, the H1.78Sr0.78Bi0.22Nb2O7 platelets were exfoliated into H1.78Sr0.78Bi0.22Nb2O7 nanosheets with a thickness of about 2.6 nm. The evolution of the structure, composition, morphology, optical, and photocatalytic properties of SrBi2Nb2O9 platelets was studied as it is converted into H1.78Sr0.78Bi0.22Nb2O7 platelets and subsequently exfoliated into H1.78Sr0.78Bi0.22Nb2O7 nanosheets. The absorption edge shifts to a lower wavelength accompanied by the protonation and exfoliation. The photocatalytic H2 evolution of the three samples were evaluated under the irradiation of a 300 W Xenon lamp from CH3OH/H2O solution, indicating that H1.78Sr0.78Bi0.22Nb2O7 nanosheets Exhibit 5.5 and 26.2 times higher activity than that of the H1.78Sr0.78Bi0.22Nb2O7 and SrBi2Nb2O9 platelets, respectively. The enhanced activity for the H1.78Sr0.78Bi0.22Nb2O7 nanosheets is mainly attributed to the higher separation efficiency of the photogenerated carriers and the larger specific surface area caused by the significant reduction in thickness.
Keywords: H1.78Sr0.78Bi0.22Nb2O7 nanosheet; Molten salt synthesis method; Photocatalysis; Hydrogen evolution;

In situ controllable synthesis of novel surface plasmon resonance-enhanced Ag2WO4/Ag/Bi2MoO6 composite for enhanced and stable visible light photocatalyst by Jiali Lv; Kai Dai; Jinfeng Zhang; Luhua Lu; Changhao Liang; Lei Geng; Zhongliao Wang; Guangyu Yuan; Guangping Zhu (507-515).
Display OmittedA novel hierarchical Ag2WO4/Ag/Bi2MoO6 ternary visible-light-driven photocatalyst was successfully synthesized by in situ doping Ag2WO4 with Bi2MoO6 nanosheets through a facile hydrothermal and photochemical process. The morphology, structure, optical performance and crystallinity of the products were measured by field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS), UV–vis diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The results showed that Ag2WO4/Ag was uniformly dispersed on the surface of Bi2MoO6 nanosheets. The photocatalytic performance of Ag2WO4/Ag/Bi2MoO6 heterostructures was evaluated by the degradation of methylene blue (MB) under 410 nm LED arrays. The ternary Ag2WO4/Ag/Bi2MoO6 nanocomposite exhibits higher photocatalytic activity than Bi2MoO6 and Ag2WO4. The synergistic effect of Ag2WO4 and Bi2MoO6 could generated more heterojunctions which promoted photoelectrons transfer from Ag2WO4 to Bi2MoO6, leading to the improvement of photocatalytic performance by photoelectrons-holes recombination suppression. At the same time, the surface plasmon resonance of Ag2WO4/Ag/Bi2MoO6 is another crucial reason for the high photocatalytic performance of organic pollutants degradation. And the 20 wt% Ag2WO4-loaded Bi2MoO6 shows the optimal photocatalytic performance in the degradation of MB. In addition, the ternary composites can be easily reclaimed by precipitation and exhibits high stability of photocatalytic degradation after five recycles.
Keywords: Bi2MoO6; Ag2WO4; Photocatalysis; Visible-light-response; Charge transfer;

Influence of photoinduced Bi-related self-doping on the photocatalytic activity of BiOBr nanosheets by Dan Wu; Songtao Yue; Wei Wang; Tiacheng An; Guiying Li; Liqun Ye; Ho Yin Yip; Po Keung Wong (516-524).
Display OmittedUnder UV irradiation, self-doped Bi5+ is evidenced to be generated on the surface of BiOBr nanosheets, but with well-preserved crystal structure and morphology compared with pure counterpart. Bi5+ self-doping BiOBr (BiOBr-4) exhibits distinct photocatalytic mode for dyes degradation, as compared with pure BiOBr nanosheets. These photodegradation distinctions are mainly due to the simultaneous occurrence of two photoinduced hole (h+) mediated oxidation processes on the BiOBr surfaces: (1) a portion of photoexcited h+ participates in the photocatalytic oxidation of dyes, and (2) partial h+ involves the oxidation of Bi3+ to Bi5+. Notably, BiOBr-4 nanosheets comparatively show superior photocatalytic activity for the phenol decomposition as well as the bacterial inactivation. Besides Bi5+ induced narrowed bandgap and enhanced light adsorption capacity, significantly, the oxidative Bi5+ acts as electron traps to promote the photoexcited electron-hole separation and accelerate h+ migration, resulting in the considerable photocatalytic enhancement of BiOBr-4 nanosheets. These novel findings will not only give new insights into the photocatalytic mechanism but also explore new route to enhance photocatalytic performance of Bi-based materials.
Keywords: BiOBr nanosheet; Self-doping; Hole oxidation; Photocatalysis; Bacterial inactivation;

Display OmittedIn this paper, in order to enhance photo-induced electron-hole pairs separation of BiOBr, flowers-like BiPO4/BiOBr p-n heterojunction composites was fabricated by a mixing in solvent method. The as-prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), UV–vis absorption spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption. Meanwhile, their photocatalytic properties were investigated by the degradation of gaseous o-dichlorobenzene under visible light irradiation. Due to its strong adsorption capacity and the formation of p-n heterojunction, compared with BiPO4 and BiOBr, the BiPO4/BiOBr composites showed higher photocatalytic activity in the degradation of gaseous o-DCB under visible light. Among them, 2% BiPO4/BiOBr showed the maximum value of the activity, whose degradation rate was about 2.6 times as great as the pure BiOBr. Furthermore, the OH• was confirmed the main active species during the photocatalytic process by the trapping experiments. The outstanding performance indicated that the photocatalysts could be applied to air purification for chlorinated volatile organic compound.
Keywords: BiPO4/BiOBr; p-n heterojunction; Photocatalytic oxidation; Gaseous o-dichlorobenzene;

Photocatalytic hydrogen production over solid solutions between BiFeO3 and SrTiO3 by Lingwei Lu; Meilin Lv; Gang Liu; Xiaoxiang Xu (535-541).
We have successfully prepared a series of SrTiO3-BiFeO3 solid solutions. These materials own strong visible light absorption and demonstrate appealing photocatalytic activity under both full range and visible light irradiation.Display OmittedConstituting solid solutions has been an appealing means to gain control over various physicochemical properties. In this work, we synthesized a series of SrTiO3-BiFeO3 solid solutions and systematically explored their structural, optical and photocatalytic properties. Our results show that all solid solutions crystallize in a primitive cubic structure and their band gap values can be easily tuned by adjusting molar ratios between SrTiO3 and BiFeO3. Photocatalytic hydrogen production under both full range and visible light irradiation is greatly improved after forming solid solutions. The highest hydrogen production rate obtained is ∼180 μmol/h under full range irradiation (λ ≥ 250 nm) and ∼4.2 μmol/h under visible light irradiation (λ ≥ 400 nm), corresponding to apparent quantum efficiency ∼2.28% and ∼0.10%, respectively. The activity is found to be strongly influenced by surface area and light absorption. Theoretical calculation suggests that Fe contributes to the formation of spin-polarized bands in the middle of original band gap and is responsible for the band gap reduction and visible light photocatalytic activity.
Keywords: BiFeO3; SrTiO3; Photocatalyst; Water splitting; Hydrogen production;

Photocatalytic perfermance of sandwich-like BiVO4 sheets by microwave assisted synthesis by Suqin Liu; Huiling Tang; Huan Zhou; Gaopeng Dai; Wanqiang Wang (542-547).
Sandwich-like BiVO4 sheets were successfully synthesized via a facile microwave-assisted method. The as-prepared samples exhibit a high activity for the degradation of methyl orange under visible light irradiation.Display OmittedSandwich-like BiVO4 sheets were successfully synthesized in an aqueous solution containing bismuth nitrate, ammonium metavanadate and polyethylene glycol with a molecular weight of 10,000 (PEG-10000) using a facile microwave-assisted method. The as-prepared samples were characterized by scanning electron microscopy, N2 adsorption-desorption, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy. The results show that the presence of PEG-10000 plays a critical role in the formation of BiVO4 sheets, and Ostwald ripening is the primary driving force for the formation of sandwich-like structures. The sandwich-like BiVO4 sheets exhibit a high activity for the degradation of methyl orange under visible light irradiation (λ ≥ 420 nm). The enhancement of photocatalytic activity of sandwich-like BiVO4 sheets can be attributed to its large surface area over the irregular BiVO4 particles.
Keywords: Microwave-assisted; BiVO4; Sandwich-like; Photocatalytic;

Effect of reaction parameters on photoluminescence and photocatalytic activity of zinc sulfide nanosphere synthesized by hydrothermal route by T. Inakhunbi Chanu; Dhrubajyoti Samanta; Archana Tiwari; Somenath Chatterjee (548-556).
Display OmittedZinc Sulfide (ZnS) nanospheres have been synthesized using amino acid, l-Histidine as a capping agent by hydrothermal method. The as prepared ZnS have been characterised using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HRTEM), Photoluminescence (PL), Fourier Transform Infra-Red spectroscopy (FTIR), UV–vis absorption spectroscopy and X-ray Photo Electron Spectroscopy (XPS). Effect of reaction parameters on particle size has been investigated. The morphology and size of the ZnS can be tuned based on the reaction parameters. ZnS nanosphere with a particle size of 5 nm is obtained when the reaction parameters are kept at 120 °C for 3 h. The PL of ZnS shows multiple defect emissions arising from interstitials/vacancies. Particle size of ZnS nanoparticles plays an important role in determining the photo catalytic activity. A chronological study on synthesis of ZnS nanosphere and its photo catalytic activity under the sunlight are discussed here, which reveals the photo degradation of Rhodamine B (RhB) upto 87% as observed with ZnS nanosphere having a particle size of 5 nm.
Keywords: Hydrothermal synthesis; ZnS nanosphere; Photoluminescence; Degradation mechanism of RhB; Photocatalysis;

Synthesis of Mn-doped ZnS microspheres with enhanced visible light photocatalytic activity by Lu Wang; Peng Wang; Baibiao Huang; Xiaojuan Ma; Gang Wang; Ying Dai; Xiaoyang Zhang; Xiaoyan Qin (557-564).
Display OmittedZnS microspheres with a series of Mn-doping concentration were synthesized via a facile solvothermal route. The phase structures, morphologies, and chemical states were characterized by X-ray powder diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The phase structure of the synthesized Mn-ZnS microspheres is hexagonal from the XRD patterns. UV–vis diffuse reflectance spectra were employed to analyze the absorption properties of the samples. The Mn-doped ZnS exhibited stronger visible light absorption with the increasing of Mn content. Their photocatalytic activities were evaluated by H2 production from water and reducing Cr6+ under visible light irradiation. The as-prepared Mn-doped ZnS exhibited better photocatalytic performance than that of pure ZnS and the optimal doping concentration was 7%. The enhancement in photocatalytic activity can be attributed to the expansion of light absorption and the increase in life time of photogenerated carriers.
Keywords: Hexagonal ZnS; Mn2+ doping; Microsphere; Photocatalysis; Visible light; First principle calculations;

Facile synthesis of CNTs/CaIn2S4 composites with enhanced visible-light photocatalytic performance by Yang Xia; Qin Li; Xiaofeng Wu; Kangle Lv; Dingguo Tang; Mei Li (565-571).
Display OmittedIn response to the continuous concerns to environmental contamination and energy crisis, visible-light-driven photocatalysis has attracted broad attention for its potential applications in environment remediation and energy conversion. In this study, visible-light-responsive CNTs/CaIn2S4 (CIS) composite photocatalyst was designed and synthesized by a facile one-step microwave hydrothermal method. The effects of CNTs content on the crystallinity, structure, light absorption, specific surface area and photocatalytic performance of CIS semiconductor were systematically studied. The results demonstrated that the prepared composite with a suitable amount of CNTs exhibited an apparently enhanced photocatalytic activity than bare CIS for both X-3B dye degradation and H2 production under visible-light irradiation. The optimal content of CNTs was found to be 1 wt%. The corresponding apparent rate constants of photocatalytic degradation and H2-production rate are about two times as that of bare CaIn2S4 semiconductor. Comprehensive analysis demonstrated that such enhancement was mainly attributed to the strong coupling interface between CNTs and CIS, which largely improved the separation efficiency of photogenerated charge carriers in space. However, excessive CNTs resulted in a decreased photocatalytic activity due to the shield of active sites and absorbed photons on the surface of CIS photocatalyst. This work could shed new light on the design and synthesis of carbon material/chalcogenide composite with enhanced photocatalytic performance.
Keywords: Carbon nanotubes; CaIn2S4; Photocatalysis; Interfacial charge transfer;

Enhanced selective photocatalytic CO2 reduction into CO over Ag/CdS nanocomposites under visible light by Zezhou Zhu; Jiani Qin; Min Jiang; Zhengxin Ding; Yidong Hou (572-579).
Display OmittedPhotocatalytic reduction of carbon dioxide can convert chemically inert carbon dioxide into useful chemical fuel in a mild manner. Herein, Ag-CdS nanocomposites were prepared by photodeposition method and examined for photocatalytic CO2 reduction under visible light. Meanwhile, the nanocomposites were characterized by XRD, SEM, TEM, XPS, DRS and PL in detail. The results show that, the deposition of Ag improves the photocatalytic performance of CdS, especially in the selectivity of CO2-to-CO. The highest photocatalytic activity is achieved over 1.0 wt.% Ag/CdS, with an increase by 3 times in comparison to CdS. In this reaction system, Ag can serve as electron trap as well as active site for CO2 reduction, which is probably responsible for the enhanced activity and selectivity of CO2 to CO over Ag/CdS. The possible mechanism of CO2 photoreduction over Ag/CdS was proposed in view of the abovementioned analysis.
Keywords: Ag; Cocatalyst; CO2 reduction; CdS; Artificial photosynthesis;

Constructing 2D layered hybrid CdS nanosheets/MoS2 heterojunctions for enhanced visible-light photocatalytic H2 generation by Song Ma; Jun Xie; Jiuqing Wen; Kelin He; Xin Li; Wei Liu; Xiangchao Zhang (580-591).
Enhanced visible-light photocatalytic H2 production could be achieved over the 2D layered hybrid CdS nanosheets/MoS2 heterojunctions.Display OmittedIn this work, a 2D hybrid CdS nanosheets(NSs)/MoS2 layered heterojunctions were successfully synthesized by a two-step hydrothermal method and subsequent ultrasonic treatment. The results showed that the loading ultrathin MoS2 NSs as co-catalysts could significantly boost the photocatalytic H2-evolution activity of CdS NSs. It is demonstrated that the optimized 2D CdS NSs/MoS2 (1.0 wt%) layered heterojunctions could achieve the highest photocatalytic H2-evolution activity of 1.75 mmol g−1  h−1 from an aqueous solution containing sulfide and sulfite under visible light, which is 2.03 times as high as that of the pristine CdS NSs. It is believed that the deposition of ultrathin MoS2 NSs and intimate 2D–2D coupling interfaces are mainly responsible for the excellent H2-evolution performance of 2D CdS NSs/MoS2 layered heterojunctions, owing to the effectively promoted separation and transportation of charge carriers and the enhanced following surface H2-evolution kinetics. Interestingly, the lactic acid and formic acid have also been demonstrated to be better sacrificial reagents than the Na2S/Na2SO3, for the photocatalytic H2 evolution over the 2D CdS NSs/MoS2 layered heterojunctions. It is hoped that the strategy of 2D–2D interfacical coupling based on CdS NSs can become a general strategy to improve the H2-evolution activity over various kinds of conventional semiconductor NSs.
Keywords: Visible-light photocatalysis; Hydrogen evolution; 2D layered heterojunctions; MoS2; CdS nanosheets;

Effect of thermal annealing on the microstructures and photocatalytic performance of silver orthophosphate: The synergistic mechanism of Ag vacancies and metallic Ag by Tingjiang Yan; Wenfei Guan; Ying Xiao; Jun Tian; Zheng Qiao; Huishan Zhai; Wenjuan Li; Jinmao You (592-600).
Display OmittedIn this work, a simple thermal annealing route has been developed to improve the photocatalytic performance of silver orthophosphate (Ag3PO4) photocatalyst toward organic pollutants degradation under visible light irradiation. The experimental results indicated that thermal treatment of Ag3PO4 led to an obvious lattice shift towards right and significantly narrowed band gap energies due to the formation of Ag vacancies and metallic Ag during Ag3PO4 decomposition. These structural variations notably affected the photocatalytic performance of Ag3PO4 photocatalysts. The activity of the annealed samples was found to be significantly enhanced toward the degradation of MO dye. The highest activity was observed over the sample annealed at 400 °C, which exceeded that of pristine Ag3PO4 by a factor of about 21 times. By means of photoluminescence spectroscopy and photoelectrochemical measurements, we propose that the enormous enhancement in activity was mainly attributed to the efficient separation of photogenerated electrons and holes driven by the synergistic effect of Ag vacancies and metallic Ag. The strong interaction between annealed particles also inhibited the dissolution of Ag+ from Ag3PO4 into aqueous solution, contributing to an improved photocatalytic stability. The strategy presented here provides an ideal platform for the design of other highly efficient and stable Ag-based photocatalysts for broad applications in the field of photocatalysis.
Keywords: Silver orthophosphate; Thermal annealing; Metallic Ag; Ag vacancies; Photocatalysis;

Self-propagating solar light reduction of graphite oxide in water by N. Todorova; T. Giannakopoulou; N. Boukos; E. Vermisoglou; C. Lekakou; C. Trapalis (601-608).
Display OmittedGraphite Oxide (GtO) is commonly used as an intermediate material for preparation of graphene in the form of reduced graphene oxide (rGO). Being a semiconductor with tunable band gap rGO is often coupled with various photocatalysts to enhance their visible light activity. The behavior of such rGO-based composites could be affected after prolonged exposure to solar light. In the present work, the alteration of the GtO properties under solar light irradiation is investigated. Water dispersions of GtO manufactured by oxidation of natural graphite via Hummers method were irradiated into solar light simulator for different periods of time without addition of catalysts or reductive agent. The FT-IR analysis of the treated dispersions revealed gradual reduction of the GtO with the increase of the irradiation time. The XRD, FT-IR and XPS analyses of the obtained solid materials confirmed the transition of GtO to rGO under solar light irradiation. The reduction of the GtO was also manifested by the CV measurements that revealed stepwise increase of the specific capacitance connected with the restoration of the sp2 domains. Photothermal self-propagating reduction of graphene oxide in aqueous media under solar light irradiation is suggested as a possible mechanism. The self-photoreduction of GtO utilizing solar light provides a green, sustainable route towards preparation of reduced graphene oxide. However, the instability of the GtO and partially reduced GO under irradiation should be considered when choosing the field of its application.
Keywords: Reduced graphene oxide; Solar light; Photoreduction; Capacitance;

Synthesis of ZnWO4 Electrode with tailored facets: Deactivating the Microorganisms through Photoelectrocatalytic methods by Su Zhan; Feng Zhou; Naibao Huang; Yujun Liu; Qiuchen He; Yu Tian; Yifan Yang; Fei Ye (609-616).
Display OmittedThe exotic invasive species from the ballast water in the ship will bring about serious damages to ecosystem. Photocatalyst films have been widely studied for sterilization. In this study, ZnWO4 with different exposed facets was synthesized by hydrothermal method, and ZnWO4 film electrodes have been applied in ballast water treatment through the electro-assisted photocatalytic system. Then the samples were investigated by X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS), Field emission on scanning electron microcopy (FE-SEM), Transmission electron microscopy (TEM), UV–vis diffuse reflectance spectroscopy (DRS), BET specific surface area analysis, Fourier transform infrared (FT-IR) and Electrochemical impedance spectra (EIS). ZnWO4 with an appropriate exposure of (0 1 1) facets ratio exhibited the best photocatalytic and photoelectrocatalytic activities. The microorganisms deactivated completely in 10 min by ZnWO4 films with 3 V bias. The mechanisms of (0 1 1) facets enhanced the photocatalytic and photoelectrocatalytic activities which were deduced based on the calculated result from the first principles. Simultaneously, appropriate exposed facets and applied bias could reduce the recombination of the photogenerated electron-hole pairs, and improve the photocatalytic activities of ZnWO4.
Keywords: Photoelectrocatalysis; ZnWO4 films; Ballast water; Microorganism; First principle calculation; Exposed (0 1 1) facets;

Display OmittedThe direct α-alkylation of ketones with primary alcohols to obtain the corresponding saturated coupled ketones was achieved with bimetallic gold(Au)-palladium(Pd) nanoparticles(NPs) supported on a transition metal oxide (such as CeO2). This system demonstrated a higher catalytic property than Au/CeO2 and Pd/CeO2 under visible light irradiation at 40 ± 3 °C in an Ar atmosphere. Such phenomenon was caused by the synergistic effect between Au and Pd. Isopropyl alcohol was used as the solvent and CH3ONa as the base. The effect of the bimetallic Au-Pd mass ratio and the two different transition metal oxide supports (such as CeO2 or ZrO2) during the reaction process was studied. The highest catalytic activity of those examined happened with the 1.5 wt% Au-1.5 wt% Pd (Au and Pd mass ratio 1:1)/CeO2 photo-catalyst. The intensity and wavelength of the visible light had a strong influence on the system. The catalyst can be reused for four times. A reaction mechanism was proposed for the α-alkylation of ketones with primary alcohols.
Keywords: α-Alkylation; Ketones; Primary alcohols; Visible light; Bimetallic photo-catalysts;

Influence of interface combination of RGO-photosensitized SnO2@RGO core-shell structures on their photocatalytic performance by Hao Shen; Xiaoru Zhao; Libing Duan; Ruidi Liu; Hongjing Wu; Tian Hou; Xianwu Jiang; Haodi Gao (627-634).
Display OmittedSnO2@reduced graphene oxide (RGO) core-shell structures were successfully synthesized by two different strategies (electrostatic interaction method and direct chemical bonding reaction method). The investigation of morphologies and microstructures showed that RGO was wrapped tightly on the surface of SnO2 microspheres with different interface combinations, i.e., electrostatic interaction and chemical bonding. Raman spectroscopy and photoluminescence (PL) spectra demonstrated that graphene as a photosensitizer could transfer photogenerated electrons to the conduction band (CB) of SnO2 and receive holes from the valence band (VB) of SnO2, resulting in the separation of photogenerated electron-hole pairs. The photocatalytic activity of the synthesized composites was evaluated by the photodegradation of methyl orange (MO) under ultraviolet (UV) light irradiation. It was found that SnO2@RGO with chemical bonding interface combination exhibited higher photodegradation rate (k = 0.038 min−1) than those with electrostatic interaction interface combination (k = 0.021 min−1) and pure SnO2 (k = 0.010 min−1). The enhanced photocatalytic activity could be attributed to the photosensitization of RGO and the intimate interface combination between SnO2 and RGO.
Keywords: SnO2; Graphene; Interface combination; Photocatalytic performance;

Well-crystallized ZnCo2O4 nanosheets as a new-style support of Au catalyst for high efficient CO preferential oxidation in H2 stream under visible light irradiation by Kai Yang; Yujuan Zhang; Chao Meng; FangFang Cao; Xun Chen; Xianzhi Fu; Wenxin Dai; Changlin Yu (635-644).
Display OmittedA kind of high dispersed gold catalyst supported on the spinel ZnCo2O4 nanosheets was readily fabricated by a facile template-free wet chemical method for CO oxidation in H2-rich streams at room temperature under visible light irradiation or not, which was found to be a high performance catalyst. As verified by X-ray powder diffractometry (XRD), Raman spectra, N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscope (XPS), photoelectrochemical measurement and photoluminescence (PL) spectra results, the contribution of high crystallinity, the enhanced mass and charge transport, the longer lifetime of surface electrons as well as the optical absorbance properties on Au/ZnCo2O4 enabled the superior CO preferential oxidation. Notably, electron paramagnetic resonance (EPR) and CO chemisorption (TPD-MS) results indicate that visible light could promote the adsorption and activation of both CO and O2 at Au/ZnCo2O4 due to both the photo-response of Au nanoparticles and the photo-excitation of ZnCo2O4 band gap under visible light irradiation. This study indicates that Au/ZnCo2O4 may be highly desirable for a promising photo-assisted Au catalyst.
Keywords: Au/ZnCo2O4; Spinel structure; Nanosheets; Visible-light; CO preferential oxidation;

Visible-light activity of N-LiInO2: Band structure modifications through interstitial nitrogen doping by Kaiqiang Xu; Difa Xu; Xiangchao Zhang; Zhuo Luo; Yutang Wang; Shiying Zhang (645-653).
Display OmittedElement doping is a promising strategy to improve the photo-response and photocatalytic activity of semiconductor photocatalyst with a wide band gap. To reduce the band gap of LiInO2 that is considered as a novel photocatalyst, nitrogen-doped LiInO2 (N-LiInO2) is successfully fabricated by treating LiInO2 and urea at 200 °C. It is found that interstitial instead of substitutional configurations are formed in the crystal structure of N-LiInO2 due to the low-treating temperature and rich-oxygen conditions. The interstitial N-doping forms a doping state with 0.6 eV above the valence band maximum and a defect state with 0.1 eV below the conduction band minimum, reducing the band gap of LiInO2 from 3.5 to 2.8 eV. N-LiInO2 exhibits higher photocatalytic activity towards methylene blue (MB) degradation under 380 nm light irradiation, which is 1.4 times that of pure LiInO2. The enhanced photocatalytic activity of N-LiInO2 is attributed to the extended light absorption and the improved charge carrier separation, which result in more reactive species participating in the photcatalytic process. This work provides a further understanding on tuning the band structure of semiconductor photocatalyst by N-doping strategies.
Keywords: LiInO2; Interstitial nitrogen doping; Band structure modification; Superoxide radicals; Dye sensitization;

Surface oxygen vacancies on WO3 contributed to enhanced photothermo-synergistic effect by Yingying Li; Changhua Wang; Han Zheng; Fangxu Wan; Fei Yu; Xintong Zhang; Yichun Liu (654-661).
WO3−x acts as efficient and stable photothermocatalyst for detoxification of gaseous acetaldehyde.Display OmittedPhotothermooxidation has demonstrated a high efficiency in the removal of volatile organic compounds in air. Among photothermocatalysts, attention is presently focused on composites of noble metal/metal oxide or metal oxide/metal oxide. Instead, in this work, we present a case of single oxide WO3 subjected to hydrogen treatment as photothermocatalyst. With the increase of hydrogen treatment temperature, the color of WO3 changes from yellow to blue to dark blue and a phase transition from WO3 to WO2.72 to WO2 is accompanied, suggesting an increase of concentration of oxygen vacancy. Photothermocatalytic test against degradation of gaseous acetaldehyde at 60 °C under UV light shows that WO3−x sample with low concentration of oxygen vacancy displays the most significant synergetic effect between photocatalysis and thermocatalysis. Its photothermocatalytic activity in terms of CO2 evolution rate is 5.2 times higher than that of photocatalytic activity. However, WO3–WO2.72 and WO2 with high degree of oxygen deficiency show insignificant synergetic effect between photocatalysis and thermocatalysis. The reason for the different synergistic effect over above samples is believed to lie in balance between decreased activation energy of lattice oxygen and recombination of photogenerated electrons and holes induced by oxygen deficiency.
Keywords: Phase transition in WO3; Photothermocatalytic; Visible-NIR response; Oxygen vacancy; WO3;

VUV photo-oxidation of gaseous benzene combined with ozone-assisted catalytic oxidation: Effect on transition metal catalyst by Haibao Huang; Haoxian Lu; Yujie Zhan; Gaoyuan Liu; Qiuyu Feng; Huiling Huang; Muyan Wu; Xinguo Ye (662-667).
Mn nanoparticles are highly dispersed on ZSM-5 and most efficient in benzene degradation in the VUV-OZCO process.Display OmittedVolatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O3, the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O3 catalytic decomposition and utilization. Benzene and O3 removal efficiency reached as high as 97% and 100% after 360 min, respectively. O3 was catalytically decomposed, generating highly reactive oxidants such as •OH and •O for benzene oxidation.
Keywords: VUV photo-oxidation; Ozone-assisted catalytic oxidation; ZSM-5; Transition metal doping; Benzene degradation;

A facile fabrication of nitrogen-doped electrospun In2O3 nanofibers with improved visible-light photocatalytic activity by Na Lu; Changlu Shao; Xinghua Li; Fujun Miao; Kexin Wang; Yichun Liu (668-676).
Display OmittedSemiconductor photocatalysis demonstrates to be an effective approach for eliminating most types of environment contaminants and for producing hydrogen. Herein, a facile synthesis route combining electrospinning technique and thermal treatment method under NH3 atmosphere has been presented as a straightforward protocol for the fabrication of nitrogen-doped In2O3 (N-In2O3) nanofibers, the nitrogen content of which can be well controlled by adjusting the annealing temperature. Photocatalytic tests show that the N-In2O3 nanofibers demonstrate an improved degradation rate of Rhodamine B (RB) compared with pure In2O3 nanofibers under visible-light irradiation. This can be attributed to the nitrogen atom introducing at interstitial sites as well as the generation of oxygen vacancy on the surface of In2O3 nanofibers, resulting in the enhanced utilization of visible light for the N-In2O3 nanofibers. Furthermore, the obtained N-In2O3 nanofibers with the advantage of ultra-long one-dimensional nanostructures can be recycled several times by facile sedimentation and hence present almost no decrease in photocatalytic activity indicative of a well regeneration capability. Therefore, the as-fabricated nitrogen-doped In2O3 nanofibers as a promising photocatalyst present good photocatalytic degradation of organic pollutant in waste water for practical application.
Keywords: In2O3 nanofibers; Electrospinning; Gaseous ammonia treatment; Interstitial nitrogen doping; Visible light photocatalysis;

Low-temperature processed SnO2 compact layer for efficient mesostructure perovskite solar cells by Jinxia Duan; Qiu Xiong; Bingjie Feng; Yang Xu; Jun Zhang; Hao Wang (677-683).
SnO2 nanoparticle film has been synthesized via low- temperature (∼180 °C) solution-processing and proposed as compact layer in mesostructure perovskite-type solar cell (PSC). Low-temperature processed SnO2 compact layer (cl-SnO2) brings perfect crystal-lattice and band-gap matching between electron selective layer and FTO substrate and close interface-contact between cl-SnO2 and mesoporous TiO2 layer (mp-TiO2), which contributes to suppressing carrier recombination and optimizing device performance. In varied thickness cells, 70 nm cl-SnO2 device exhibits maximum power conversion efficiency (PCE). In order to further restrain photoelectron recombination and improve the photovoltaic performance, the surface modification of cl-SnO2 by SnCl4 aqueous solution has been carried out. The recombination behavior in the cell interior is greatly retarded via SnCl4 treatment and champion PSC after SnCl4 treatment has acquire PCE of 15.07%, which is higher than PCE of cl-TiO2 based PSC fabricated with same mp-TiO2 and perovskite procedures (13.3%). The stability of cl-SnO2 PSC via SnCl4 treatment has also been measured and its PCE reduces to 13.0% after 2 weeks in air.
Keywords: SnO2 compact layer; Perovskite solar cell; Low-temperature processed;