Applied Surface Science (v.319, #C)

TiO2 microspheres have been employed as a promisingly new photocatalyst for water and wastewater treatment. P25 TiO2 is commonly employed and its properties are well established as photocatalyst. In this study, photocatalytic activities of the two TiO2 samples are compared by degrading sulfosalicylic acid (SSA), phenol, and 2,4-Dichlorophenoxyacetic acid (2,4-D) under 365 nm UV illumination in a suspension system at neutral pH and associated optimized TiO2 dosages. The results showed that the three organic compounds unexceptionally degraded more rapidly on P25 than on TiO2 microspheres in terms of the concentration–time curves and total organic carbon removals at 120 min. This might me attributed the presence of oxygen vacancies and Ti(III) defects already present on P25 as determined by electron paramagnetic resonance, implying that the defects played an important role for the enhancement of the charge transfer step as rate-determining step. The degradations of three organic compounds on P25 and TiO2 microspheres could be well described by the first-order rate equation, while the degradation kinetics of SSA on TiO2 microspheres was quite different. The difference was ascribed to the medium adsorption ability of SSA on the TiO2 surface.
Keywords: Photocatalysis; TiO2 microspheres; P25; Organic degradation; Defects;

The nanocomposites of reduced graphene oxide based nitrogen doped TiO2 (N–TiO2–RGO) and reduced graphene oxide based nitrogen and vanadium co-doped TiO2 (N, V–TiO2–RGO) were prepared via a facile hydrothermal reaction of graphene oxide and TiO2 in a water solvent. In this hydrothermal treatment, the reduction of graphene oxide and the intimate contact between nitrogen doped TiO2 (N–TiO2) or nitrogen and vanadium co-doped TiO2 (N,V–TiO2) and the RGO sheet is achieved simultaneously. Both N–TiO2–RGO and N,V–TiO2–RGO nanocomposites exhibit much higher visible light photocatalytic activity than N–TiO2 and N,V–TiO2, and the order of visible light photocatalytic activity is N,V–TiO2–RGO > N–TiO2–RGO > N,V–TiO2  > N–TiO2  > TiO2. According to the characterization, the enhanced photocatalytic activity of the nanocomposites is attributed to reasons, such as enhancement of adsorption of pollutants, light absorption intensity, minimizing the recombination of photoinduced electrons and holes and more excited states of these nanocomposites under visible light irradiation. Overall, this work provides a more marked contrast of graphene based semiconductor nanocomposites and a more comprehensive explanation of the mechanism.
Keywords: Graphene; N–TiO2–RGO; N,V-TiO2-RGO; Hydrothermal; Photocatalytic activity;

Reprint of “Photocatalytic reduction of CO2 on MgO/TiO2 nanotube films” by Qiuye Li; Lanlan Zong; Chen Li; Jianjun Yang (16-20).
A facile development of highly efficient MgO/TiO2 nanotubes network (MgO/TNTs) films is described. These MgO/TNTs films have a unique one-dimensional (1D) network nanotubular structure, and the different contents of MgO existed as amorphous thin layers located on the surfaces of TiO2 nanotubes. They exhibited excellent photoreduction efficiency of CO2 to methane compared with the bare TiO2 film. MgO plays a critical role in CO2 methanation, because it has the strong adsorption ability of CO2 and initiates the reaction by binding a CO2 molecule, forming a magnesium carbonate species on the surface. For further improve the photocatalytic activity, Pt nanoparticles were loaded on MgO/TNTs films by the photo-reduction method. It was found that the loading of Pt notably improved the transformation efficiency of CO2 to methane, and the highest evolution rate of methane reached 100.22 ppm/h cm2. The fast electron-transfer rate in MgO/TNTs film and the efficient electron–hole separation by the Pt nanoparticals were the main reasons for the enhancement of the photoreduction activity. The synergy effect of Pt nanoparticles and MgO in the nanocomposites played an important role in CO2 photoreduction.
Keywords: CO2 photoreduction; TiO2 nanotube; MgO; Titanate nanotubes; Methane;

Heterostructured TiO2/SnO2 nanofibers deposited with ultrafine Pt nanocrystals (Pt-TiO2/SnO2) were prepared by combining electrospinning and polyol reduced method. The samples have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence spectra (PL) and nitrogen adsorption-desorption isotherm analysis. The results indicated that heterojunctions formed between TiO2 fibers and SnO2 fibers in the side-by-side structure with Pt nanocrystals in a crystallite size of 4.5 nm uniformly deposited on them. The Pt-TiO2/SnO2 nanofibers photocatalysts possessed large surface-exposure area, broadened spectral response range, stable recyclability, and efficient charge-separation properties. Furthermore, the photocatalytic activity of Pt-TiO2/SnO2 for the degradation of methylene blue was much higher than that of bare TiO2 and SnO2 nanofibers, which could be ascribed to the formation of heterojunctions in the TiO2/SnO2 nanofibers and the rapid transportation of electrons to the surface assisted by Pt nanocrystals. The results presented herein provide new insights into heterostructured materials as high-performance photocatalysts and their potential use in environmental protection.
Keywords: Electrospinning; Heterostructured; Titania nanofibers; Photocatalysts; Platinum;

TiO2 functionalization for efficient NO x removal in photoactive cement by S. Karapati; T. Giannakopoulou; N. Todorova; N. Boukos; S. Antiohos; D. Papageorgiou; E. Chaniotakis; D. Dimotikali; C. Trapalis (29-36).
Commercial titania nanoparticles (P25 Evonic-Degussa) were modified with organic compounds oleic acid (OA), oleylamine (OM) and equimolar concentrations of both modifiers (OAOM) through a biphase toluene/water emulsion processing in order to be endowed with hydrophobic properties. Specific molar ratio 3 between modifier and titania powder was used. The modified and the initial P25 photocatalysts were embedded in cement matrix in low percentage loading (2.5, 1, 0.5%). The grafting of the modifier to the titania nanoparticles was verified by thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FT-IR). Light absorption measurements revealed that the energy band gap of the photocatalysts was lowered after the modification. The average size (nm) and polydisperse index of the initial and modified P25 were determined via dynamic light scattering (DLS). The photocatalytic activity of the photocatalysts alone and the composite cement specimens was evaluated via ISO standard NO x oxidation procedure. The photocatalytic cements containing modified P25 exhibited 2–5 times better NO x removal than those with non-modified P25 even for the lowest photocatalyst loading. The results were attributed to the hydrophobic properties of the modified titania and its behavior during the incorporation in the cement matrix. This conclusion was confirmed by the SEM/EDX analysis which demonstrated a gradual increase of hydrophobic photocatalyst from the bottom to the surface of the cement specimens.
Keywords: Photocatalysis; Modified TiO2; Cement; Visible light; NO x ;

Titanium dioxide (TiO2) doped with visible-light-responsive metal oxides has been widely reported for improving the visible light absorption performance of TiO2 and its photocatalytic activity. The metal oxides could function as ‘charge-carrier traps’ that transport electrons from TiO2 through the heterojunction of the TiO2-metal oxides. In this work, the common transition metal oxides, i.e. FeO x , CuO x , NiO, CoO x and ZnO, were doped onto MWCNT@TiO2 core–shell nanocomposites. The effects of the metal oxide dopants on the photoactivity of the core–shell nanocomposites on CO2 reduction were studied. Characterization with diffuse-reflectance UV–vis showed significant improvement on visible light absorption after doping MWCNT@TiO2 with CuO x , FeO x and CoO x with the adsorption band-edge position red-shifted into the wavelength range of 480–630 nm. CuO-MWCNT@TiO2 appeared to be the most active one among all the studied photocatalysts, achieving a total methane formation of 0.93 μmol/g-catalyst.
Keywords: Transition metal oxides; Metal dopants; Visible light; CO2 photoreduction; Methane formation;

Photocatalytic and photoelectrochemical oxidation mechanisms of methanol on TiO2 in aqueous solution by Amira Y. Ahmed; Tarek A. Kandiel; Irina Ivanova; Detlef Bahnemann (44-49).
Methanol is an available, small, and colorless molecule, which can be used for the photocatalytic activity evaluation without the sensitization problem associated with most dye molecules. Thus, TiO2 suspended in aqueous methanol solutions is commonly employed as a model test for the photocatalytic degradation of organic pollutants in aerobic system or for photocatalytic hydrogen production in absence of molecular oxygen. It is, hence, important to explore the mechanism of its photocatalytic and photoelectrochemical oxidation on TiO2 in aqueous solution. In this mini-review, the possible mechanisms for water and methanol oxidation on TiO2 will therefore be presented and discussed.
Keywords: Photocatalysis; Titanium dioxide; Methanol photooxidation; Water photooxidation;

Although there are many publications about S-doped TiO2, the related mechanism is still not well elucidated. In order to investigate the origin and trend of S substituting for O in TiO2 crystal lattice with proper dopant concentration, a combination of DFT calculation and experiment was used. Bader charge and electronic location function analysis indicate that the largely ionic character between Ti and S bonding in titanium dioxide decreases and there is free electron gas like behavior around S and neighbor Ti for the S-doped anatase TiO2. From DFT calculation, ST2.78 model is found to stabilize the structure of S substitution for lattice O with lower formation energy and its absorbance in visible light increases. Experiment results demonstrate that the sulfur doping results in the shift of the absorption edge for TiO2 to lower energy region, which leads to the nanoparticles active within the wavelength range of 650 nm.
Keywords: S-doped; TiO2; Visible light; DFT; Bader analysis; ELF;

The TiO2 fiber was prepared by using cotton fiber as a template, and then Ag3PO4/TiO2 fibers were synthesized via in situ Ag3PO4 particles onto the surface of TiO2 fiber. Their structure and physical properties were characterized by means of scanning electron microscopy (SEM), specific surface analyzer, X-ray diffraction (XRD), UV–vis absorption spectra and photoluminescence spectra (PL). SEM analysis indicated that the well-defined surface morphology of natural cotton fiber was mostly preserved in TiO2 and Ag3PO4/TiO2 fibers. Compared with TiO2 fiber, the absorbance wavelengths of Ag3PO4/TiO2 fibers were apparently red shifted and the PL intensities revealed a significant decrease. By using the photocatalytic degradation of black liquor as a model reaction, the visible light and ultraviolet light catalytic efficiencies of TiO2, Ag3PO4 and Ag3PO4/TiO2 fibers were evaluated. The reaction results showed that Ag3PO4/TiO2 fibers had stronger photocatalytic activity and excellent chemical stability in repeated and long-term applications. Therefore, the prepared Ag3PO4/TiO2 fibers could act as an efficient catalyst for the photocatalytic degradation of black liquor, which suggested their promising applications. It was proposed that the •OH radicals played the leading role in the photocatalytic degradation of the black liquor by Ag3PO4/TiO2 fibers system.
Keywords: Ag3PO4; TiO2 fiber; Black liquor; Photocatalyst; Cotton fiber;

and constructing heterojunction structures based on (0 0 1) facets dominated anatase TiO2 has attracted much attention for acquiring higher photocatalytic activity. Here, SrTiO3/TiO2 heterostructure nanosheets with different SrTiO3 contents were fabricated by in situ hydrothermal reaction, in which anatase TiO2 nanosheets with dominant exposed (0 0 1) facets were used as templates and initial reactants. Compared with pure TiO2 nanosheets, SrTiO3/TiO2 nanosheets exhibit better photocatalytic activity in degradation of rhodamine B (RhB) owing to the formation of nano–nano heterojunction. More importantly, the SrTiO3/TiO2 composites exhibit excellent photocatalytic stability and outstanding catalytic activity with the increase of utilizing cycles. Particle size and morphology of SrTiO3 nanostructures were found to dominate the photocatalytic activity of SrTiO3/TiO2 composites through regulating the adhesion and aggregation of TiO2 nanosheets as well as the number of reaction active sites. It is the first time to fabricate SrTiO3/TiO2 heterojunction structure on limited two-dimensional nanosheets in situ, which is beneficial for understanding the growth of SrTiO3 from TiO2 in initial period. These results may further promote the applications of SrTiO3/TiO2 composites in environment cleanup, solar cells, sensors and photonic and optoelectronic devices.
Keywords: Heterostructure; Photocatalysis; Degradation of dye; TiO2 nanosheets; SrTiO3/TiO2;

Dye-sensitized solar cells based on TiO2 nanoparticles/nanobelts double-layered film with improved photovoltaic performance by Jiajie Fan; Zhenzhen Li; Wenyuan Zhou; Yucong Miao; Yaojia Zhang; Junhua Hu; Guosheng Shao (75-82).
The combination of TiO2 nanoparticle underlayer with a high specific surface area and TiO2 (B) nanobelts overlayer with close packing density via linear and planar contacts within one photoanode is promising in enhancing the performance of dye-sensitized solar cells.Dye-sensitized solar cells (DSSCs) were fabricated using double layers of nano-structured TiO2 films as photoanodes. Different anode architectures of double-layered TiO2 films were fabricated in order to study the structural effect of photoanodes on the solar cell efficiency. The performances of DSSCs based on composite photoanodes in the forms of TiO2 nanoparticles/nanobelts (TiO2 P–B), TiO2 nanoparticles/nanoparticles (TiO2 P–P), TiO2 nanobelts/nanobelts (TiO2 B–B) double-layered electrodes with the same film thicknesses were studied in detail, and their corresponding efficiencies were 4.81%, 3.55% and 0.36%. The work shows that significant improvement of efficiency can be achieved through combined enhancement in optical scattering using the TiO2 nanobelts and high dye absorbing capacity of the TiO2 nanoparticles.
Keywords: TiO2 nanoparticle/nanobelt; Double-layered photoanode; Optical scattering film; Dye-sensitized solar cells (DSSCs);

Facile synthesis, structure and visible light photocatalytic activity of recyclable ZnFe2O4/TiO2 by Xiaodi Zhu; Fan Zhang; Mengjiao Wang; Jianjun Ding; Song Sun; Jun Bao; Chen Gao (83-89).
A kind of sponge-like ZnFe2O4/TiO2 composite was facilely synthesized by a solution combustion method. The physicochemical properties, including the crystalline phase, surface morphology, spectral response, photogenerated charge carriers’ separation and transfer efficiency, were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption isotherms, X-ray photoelectron spectroscopy, UV–vis absorption spectroscopy and photoluminescence spectroscopy techniques and analyzed to interpret the relationship between the structure and photocatalytic activity. The sponge-like morphology promotes the adsorption of reaction species as well as functions as a good light harvesting structure for the enhancement of spectral utilization. The heterojunction effectively inhibited the recombination of photogenerated charge carriers. With these synergistic effects, the degradation rate of methylene blue on ZnFe2O4/TiO2 was up to 93.2% under visible light irradiation and remained stable even after five consecutive reaction runs. Moreover, owing to the magnetic property, ZnFe2O4/TiO2 can be recycled easily. Additionally, a photocatalytic mechanism of ZnFe2O4/TiO2 was proposed.
Keywords: Photocatalysis; Solution combustion; ZnFe2O4; TiO2;

A method for immobilizing TiO2–PANI composite using ENR and PVC as adhesives was successfully developed. The immobilized system known as TiO2/PANI/ENR/PVC plate was characterized by FTIR, Raman, diffuse reflectance UV–vis, photo luminescence spectroscopy and HRTEM. The optimum weight ratio for the TiO2:PANI composite was 1:0.0035. The band gap energy of the optimum immobilized composite TiO2/PANI/ENR/PVC (1:0035) was 2.86 eV where polyaniline (PANI) formed a core–shell coating of about 0.9 nm with a strong TiO2–PANI interaction. Photo-etching of the immobilized TiO2/PANI/ENR/PVC (1:0.0035) composite for 7 h increased its surface area and improved its photocatalytic activity. TiO2/PANI/ENR/PVC (1:0.0035)-7 h was visible light sensitive where 85% of 30 mg L−1 reactive red 4 (RR4) dye was decolorized after 60 min of irradiation. The immobilized TiO2/PANI/ENR/PVC (1:0.0035)-7 h was reusable and its photocatalytic activity was sustainable with an average pseudo first order rate constant value of 0.103 ± 0.002 min−1. Adding PANI to the immobilized P25 TiO2 has enhanced its photocatalytic activity throughout the entire ten recycled applications due to the increased BET surface area and lower ecb and h+ recombination.
Keywords: Polyaniline; TiO2; Immobilized; Reactive red 4; Photocatalytic degradation;

P-doped TiO2 with superior visible-light activity prepared by rapid microwave hydrothermal method by Jinfen Niu; Pan Lu; Mei Kang; Kunfa Deng; Binghua Yao; Xiaojiao Yu; Qian Zhang (99-106).
Photocatalytic degradation of MB (a) and Tc (b) over different photocatalysts.Phosphorous-doped anatase TiO2 powders (P-TiO2) were prepared by rapid microwave hydrothermal method. The resulting materials were characterized by XRD, SEM, XPS, DRS and N2 adsorption. P-doping decreased the band gap and enlarged the surface area of P-doped samples than that of undoped TiO2 samples. Therefore, the photocatalytic degradation of methyl blue (MB) and tetracycline hydrochloride (Tc) experiments showed that the P-TiO2 catalysts, especially the two-steps-controlling products P-TiO2-2, exhibited higher degradation efficiency than the undoped TiO2 and commercial P25 under visible-light irradiation. Hydroxyl radicals (•OH) have been confirmed to be the active species during the photocatalytic oxidation reaction. The microwave hydrothermal method confirms to be very suitable for the synthesis of superior visible-light activity P-doped samples.
Keywords: TiO2; Phosphorous doping; Microwave hydrothermal; Photocatalytic; MB; Tc;

Enhanced visible light photocatalytic degradation of methylene blue by F-doped TiO2 by Wei Yu; Xinjuan Liu; Likun Pan; Jinliang Li; Junying Liu; Jing Zhang; Ping Li; Chen Chen; Zhuo Sun (107-112).
F-doped TiO2 is synthesized using a modified sol–gel method for visible photocatalytic degradation of MB with a high degradation rate of 91%.F-doped TiO2 (F-TiO2) were successfully synthesized using a modified sol–gel method. The morphologies, structures, and photocatalytic performance in the degradation of methylene blue (MB) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–vis absorption spectroscopy, and electrochemical impedance spectra, respectively. The results show that F-TiO2 exhibits an enhanced photocatalytic performance in the degradation of MB with a maximum degradation rate of 91% under visible light irradiation as compared with pure TiO2 (32%). The excellent photocatalytic activity is due to the contribution from the increased visible light absorption, promoted separation of photo-generated electrons and holes as well as enhanced photocatalytic oxidizing species with the doping of F in TiO2.
Keywords: F-doped TiO2 (F-TiO2); Sol–gel method; Photocatalytic; Methylene blue (MB);

Composite TiO2/clays materials for photocatalytic NOx oxidation by N. Todorova; T. Giannakopoulou; S. Karapati; D. Petridis; T. Vaimakis; C. Trapalis (113-120).
TiO2 photocatalyst received much attention for air purification applications especially for removal of air pollutants like NOx, VOCs etc. It has been established that the activity of the photocatalyst can be significantly enhanced by its immobilization onto suitable substrates like inorganic minerals, porous silica, hydroxyapatite, adsorbent materials like activated carbon, various co-catalysts such as semiconductors, graphene, reduced graphite oxide, etc.In the present work, photocatalytic composite materials consisted of mineral substrate and TiO2 in weight ratio 1:1 were manufactured and examined for oxidation and removal of nitric oxides NOx (NO and NO2). Commercial titania P25 (Evonik-Degussa) and urea-modified P25 were used as photocatalytically active components. Inorganic minerals, namely kunipia, talk and hydrotalcite were selected as supporting materials due to their layered structure and expected high NOx adsorption capability. Al3+ and Ca2+ intercalation was applied in order to improve the dispersion of TiO2 and its loading into the supporting matrix.The X-ray diffraction analysis and Scanning Electron Microscopy revealed the binary structure of the composites and homogeneous dispersion of the photocatalyst into the substrates. The photocatalytic behavior of the materials in NOx oxidation and removal was investigated under UV and visible light irradiation. The composite materials exhibited superior photocatalytic activity than the bare titania under both types of irradiation. Significant visible light activity was recorded for the composites containing urea-modified titania that was accredited to the N-doping of the semiconductor. Among the different substrates, the hydrotalcite caused highest increase in the NOx removal, while among the intercalation ions the Ca2+ was more efficient. The results were related to the improved dispersion of the TiO2 and the synergetic activity of the substrates as NOx adsorbers.
Keywords: Photocatalysis; Visible light; TiO2; Clays; Composite photocatalysts; NOx;

We studied changes in structural, optical and photocatalytic properties of TiO2 thin films due to doping process with chromium. Powders of undoped TiO2 and chromium-doped TiO2 (Cr:TiO2) were synthesized by sol–gel method and, thin films were deposited by doctor blade method. The properties of the thin films were studied by X-ray diffraction (XRD), infrared spectroscopy (IR) and diffuse reflectance. The XRD patterns indicated that doping process changed the crystalline phases radio of TiO2 thin films, furthermore, the optical analysis showed that band gap value of Cr:TiO2 thin films was 31% fewer than undoped TiO2 thin films. Along, Langmuir–Hinshelwood model was used to obtain kinetic information of the photo-mineralization process; results indicated that photocatalytic activity of Cr:TiO2 thin films were four times better than undoped TiO2 thin films; finally the synergic effect was tested by addition of the H2O2, photocatalytic yield was improved from 26% to 61% when methylene blue photo-mineralization was assisted with slightly amount of H2O2.
Keywords: Doping; Thin film; Band gap; Photocatalysis;

Surface deposition of silver nanoparticles (Ag NPs) onto the 100% anatase titania (Ag/TiO2) for evolution of surface plasmon resonance (SPR) was achieved sustainably with the assistance of solar energy. The preparation resulted in Ag/TiO2 photocatalyst with varied Ag depositions (0.5 wt%, 1.0 wt%, 3.0 wt% and 5.0 wt%). All obtained photocatalysts were characterized for the evolution of SPR via crystalline phase analysis, morphology, lattice fringes, surface area and pore size characteristics, chemical composition with chemical and electronic state, Raman scattering, optical and photoluminescence properties. The deposition of synthesized Ag NPs exhibited high uniformity and homogeneity and laid pathway for effective utilization of the visible region of electromagnetic spectrum through SPR. The depositions also lead for suppressing recombination rates of electron–hole. The photocatalytic evaluation was carried out by adopting two different class of endocrine disturbing compound (EDC) i.e., amoxicillin (pharmaceutical) and 2,4-dichlorophenol (pesticide) excited with artificial visible light source. Ag/TiO2 with Ag > 0.5 wt% exhibited significant degradation efficiency for both amoxicillin and 2,4-dichlorophenol. Thus synthesized Ag/TiO2 revealed the implication of plasmonics on TiO2 for the enhanced visible light photocatalytic activity.
Keywords: Surface deposition; Sunlight; Plasmonic photocatalyst; Surface plasmon resonance; Amoxicillin; 2,4-Dichlorophenol;

Flexible N–doped TiO2/C ultrafine fiber mat and its photocatalytic activity under simulated sunlight by Nan Wu; Yingde Wang; Yongpeng Lei; Bing Wang; Cheng Han (136-142).
Flexible N-doped TiO2/C ultrafine fiber (NTCf) mat has been produced via electrospinning and subsequent heat treatment, analyzed by a combination of characterizations. The nitrogen content can be modulated by the addition of urea. The composite fiber with mean diameter of around 500 nm exhibits outstanding mechanical flexibility. The TiO2 in the fiber obtained at 700 °C is anatase with a mass ratio of 23 wt%. In the photodegradation experiment under simulated sunlight, the as-prepared flexible mat demonstrates remarkable efficiency in the degradation of methylene blue (MB) due to the well-proportioned distribution of TiO2 nanoparticles and the improvement of charge transfer process. The nitrogen species in TiO2 lattice and the nitrogen functional groups on the surface of the fiber play crucial impacts on the photocatalytic activity.
Keywords: TiO2; Carbon fiber; Photocatalyst; Electrospinning;

A novel route for the production of TiO2 photocatalysts with low energy gap, via Triton-X and oleic acid surfactants by A. Athanasiou; A. Mitsionis; T. Vaimakis; P. Pomonis; D. Petrakis; L. Loukatzikou; N. Todorova; C. Trapalis; S. Ladas (143-150).
Mesoporous anatase TiO2 photocatalysts with high specific surface area between 70 and 110 m2/g were prepared via a novel sol–gel technique using surfactants oleic acid and Triton-X in the presence or absence of diethanolamine. Titania materials showed increased photocatalytic performance in UV light. The production of active species seem to be high enough to perform the degradation of methylene blue dye solution in low catalyst concentration; and a relatively high efficiency in NO oxidation in gaseous phase. All materials prepared showed high photocatalytic activity and degradation efficiency similar or higher compared to commercial Degussa P25 material.
Keywords: Photocatalysis; Mesoporous TiO2; Diethanolamine; Terephthalic acid; NO x ; Methylene blue;

Singular effect of crystallite size on the charge carrier generation and photocatalytic activity of nano-TiO2 by Mathias Strauss; Murilo Pastorello; Fernando A. Sigoli; Juliana M. de Souza e Silva; Italo O. Mazali (151-157).
Photocatalytic processes on nanometric titanium oxide have been extensively studied from the standpoint of solar energy utilization and remediation of water and gas streams polluted with organic molecules. It is accepted that TiO2 crystallite size and crystalline phase are among the parameters involved in the control of the photocatalytic activity. However, while changing the catalyst nanoparticle size, other attributes important to assess photocatalytic activity may be modified, making thus difficult to define to which extension the photoactivity changes are related only to size differences. Therefore, aiming at studying exclusively the size effect and the parameters directly related to size on the photocatalytic activity of nanometric TiO2, in this work it was explored a method to synthesize TiO2 nanoparticles with controlled size, highly similar morphology and comparable phase and degree of crystallinity. A set composed of four samples of nano-TiO2 loaded porous Vycor glass, each sample having a specific TiO2 nanoparticle size, was tested on the photoactivated process of depollution of solutions of salicylic acid and methylene blue. The photocatalytic activity observed for the organic compounds tested was inversely proportional to the TiO2 nanoparticle size. An opposite tendency was observed for the generation of OH radicals during photocatalyst illumination, as more radicals are formed on the material containing the larger TiO2 nanoparticles. Results of this study suggest that photocatalytic activity of nano-TiO2 is less favored by the enhanced light absorption response and the higher generation of oxidative species observed for the larger nanoparticles. Better catalysts were obtained when nano-TiO2 exhibited high surface-to-volume ratio and had small recombination volumes, which respectively favors pollutant adsorption-desorption on catalyst surface and reduce the number of recombined charge carriers.
Keywords: TiO2; Nanoparticles; Photodegradation; Photocatalysis; Size effect; Crystallinity;

A new method for immobilizing nano-scaled TiO2 on the surface of montmorillonite (Mt) clay has been developed. First, cationic surfactants were introduced into the Mt galleries through ion exchange and physical adsorption processes. Next a titanium precursor with negative charges was allowed to hydrolyze and condense around the nature clay to form meso-phase assemblies on the external and internal surface of the Mt. After the removal of the surfactant, a highly porous TiO2 pillared clay with mesopores was formed. The cationic surfactant has a templating role, which not only tailored the formation of TiO2 but also controlled the TiO2 content in the composite. The photocatalytic performances of these new porous materials were evaluated by using methylene blue degradation. The photocatalytic activity of these TiO2 composite is higher than that of P25 although TiO2 only accounts for about one-third of the sample's mass in the composite samples.
Keywords: Montmorillonite; Surfactant; Titanium dioxide; Pillared clay;

Vectorial doping-promoting charge transfer in anatase TiO2 {0 0 1} surface by Peng Zhou; Jionghua Wu; Weilai Yu; Guanghui Zhao; Guojia Fang; Shaowen Cao (167-172).
The exhibited vectorial doping of C and F atoms in TiO2 {0 0 1} surface makes a great contribution to the enhanced photocatalytic activity of TiO2.Doping-induced visible-light adsorption is often considered as the main reason for the enhanced photocatalytic activity of TiO2. However, this work provides a new understanding on the effect of doping on the photocatalytic activity of TiO2. The investigation on the C–F codoped anatase TiO2 {0 0 1} surface reveals that the impurity C and F atoms prefer to substitute for the outmost O atoms in the TiO2 {0 0 1} surface rather than those in the bulk TiO2. The exhibited vectorial doping of C and F atoms in TiO2 {0 0 1} surface produces a conducting layer with low electric resistance, which can promote the charge transfer in the photocatalytic reaction. This effectively inhibits the undesirable bulk recombination of photogenerated electron and hole. Hence, the optimized charge transfer in the C–F codoped TiO2 {0 0 1} surface makes a great contribution to the enhanced photocatalytic activity of TiO2. Further, the surface doping treatment is a potential method to improve the performance of photocatalyst.
Keywords: Vectorial doping; TiO2 {0 0 1} surface; Metallic property; Charge transfer; Photocatalytic reaction;

Photocatalytic activity of titanium dioxide modified by Fe2O3 nanoparticles by Dawid Wodka; Robert P. Socha; Elżbieta Bielańska; Magdalena Elżbieciak-Wodka; Paweł Nowak; Piotr Warszyński (173-180).
Photocatalytic activity of Fe2O3/TiO2 composites obtained by precipitation was investigated. The composite material containing 1.0 wt% of iron(III) oxide nanoparticles was obtained by depositing Fe2O3 on the Evonic-Degussa P25 titania surface. SEM, XPS, DRS, CV and EIS techniques were applied to examine synthetized pale orange photocatalyst. The XPS measurements revealed that iron is present mainly in the +3 oxidation state but iron in the +2 oxidation state can be also detected. Electrochemical analysis indicated that surface modification of Degussa P25 by Fe2O3 causes the appearance of surface states in such a material. Nevertheless, based on the DRS measurement it was shown that iron(III) oxide nanoparticles modified the P25 spectral properties but they did not change the band gap width. The photocatalytic activity of Fe2O3/TiO2 composite was compared to photocatalytic activity of pristine P25 in photooxidation reaction of model compounds: oxalic acid (OxA) and formic acid (FA). Photodecomposition reaction was investigated in a batch reactor containing aqueous suspension of a photocatalyst illuminated by either UV or artificial sunlight (halogen lamp). The tests proved that nanoparticles deposited on titania surface triggers the increase in photocatalytic activity, this increase depends however on the decomposed substance.
Keywords: Titanium dioxide; Photocatalysis; Iron oxide nanoparticles; Water purification; Surface states; Photo Fenton;

Effect of the composition of Ti alloy on the photocatalytic activities of Ti-based oxide nanotube arrays prepared by anodic oxidation by Dingding Tang; Yixin Wang; Yuwei Zhao; Yijia Yang; Lieyu Zhang; Xuhui Mao (181-188).
Three types of Ti-based oxide nanotube arrays are prepared by anodic oxidation of pure Ti and Ti alloys (Ti–0.2Pd and Ti–6Al–4V) in the glycol–2 wt% H2O–0.3 wt% NH4F solution. The nanotube arrays are characterized by a series of techniques, including SEM, TEM, EIS, XRD, EDS, ICP, XPS and UV–vis DRS, to elucidate the effect of alloying elements on the properties of titania nanotube arrays. The results suggest that aluminium and vanadium elements greatly slow down the growth rate and therefore decrease the yield of nanotube arrays. Al and V deteriorate the photoreactivity of the resultant nanotube arrays. The palladium inside the Ti–0.2Pd alloy-derived nanotube arrays cannot be detected by EDS or XPS, but is quantitatively determined by ICP analysis. Incorporation of Pd significantly improves the photocatalytic activity of the resultant titania nanotube arrays powder. The presence of Pd element not only enhances the light absorption, but also facilitates the separation of photogenerated charge carriers. The uniform doping of Pd into the microstructure endows nanotube arrays with resistance to sulphur poison and preferable stability for organic degradation. This study suggests that anodization of Ti alloys, rather than pure Ti metal, allows to produce micron-sized high-performance photocatalysts for environmental and energy applications.
Keywords: Oxide nanotube arrays; Anodic oxidation; Ti alloys; Photocatalytic degradation; Doped titania;

Mesoporous titania spheres were prepared by modified sol–gel method using chitosan/poly(vinyl alcohol) hydrogel beads as a template. Effects of calcination temperature on physical parameters were investigated by X-ray diffraction (XRD), N2 adsorption–desorption, Fourier transform infrared (FT-IR) spectra, thermogravimetry and differential thermal analyses (TG-DTA), high-resolution transmission electron microscope (HRTEM) and scanning electron microscopy (SEM). The photocatalytic activity of mesoporous titania spheres prepared was also evaluated by photocatalytic degradation of phenol as a model molecule under UV irradiation. With increasing calcination temperature, average crystallite size and pore size increased. In contrast, Brunauer–Emmett–Teller (BET) specific surface areas, porosity and pore volumes steadily decreased. Results of characterization proved that prepared titania spheres with highly organized pores were mesoporous structure. The photocatalytic activity of mesoporous titania spheres calcined at 500 °C was more effective than those calcined at other temperatures, which were attributed to the porous structure, large BET surface area, crystalline, and smaller crystallite size. This work may provide new insights into the preparation of novel mesoporous titania spheres and further practical applications in the treatment of wastewater.
Keywords: Mesoporous titania; Phenol; Photocatalytic activity; Chitosan; Poly(vinyl alcohol); Calcination temperature;

Nano-titania is by far, the most studied material for its photocatalytic application in air and water pollution abatement. In this study, we have demonstrated the advantage offered by using a binary template of PEG and chitosan for the sol–gel synthesis of titania. Nano-titania samples were prepared using PEG, chitosan and the binary combination of these two as templates. XRD showed that all synthesized samples preserved the anatase structure. Titania sample prepared on 1% PEG and 3% chitosan as template (P1-C3 titania) possessed spherical shaped particles with an average particle size of 12.3 nm, a surface area of 82.9 m2/g and uniform dispersion. DRS UV–Vis spectra indicated that, P1-C3 titania showed blue shift in its absorption profile due to decrease in particle size. Consistent with the characteristics, the P1-C3 titania exhibited the highest photocatalytic activity for the degradation of 4-chlorophenol under UV irradiation, in comparison with all the synthesized photocatalytic systems and Degussa-P25. The chitosan bio template is believed to offer controlled growth of titania through Lewis base type interaction with Ti metallic centers in TiO2. Such controlled growth route will be significant in synthesizing custom-made titania for its advanced applications in catalytic processes.
Keywords: Titania; Photocatalysis; Templates; Chitosan–PEG; 4-Chlorophenol;

Enhanced solar water splitting of electron beam irradiated titania photoanode by electrostatic spray deposition by Mukund G. Mali; Hyun Yoon; Seongpil An; Jae-Young Choi; Ha-Yong Kim; Byung Cheol Lee; Byung Nam Kim; Ji Hyun Park; Salem S. Al-Deyab; Sam S. Yoon (205-210).
Surface modifications are often made to titania films to improve its photocatalytic performance in water splitting. We herein introduced electron beam irradiation to enhance the photocatalytic activities of an electro-sprayed titania film for solar water splitting application. The film was fabricated by a facile and scalable electrostatic spraying deposition. According to SEM, X-ray diffraction, and Raman data, electron beam densified the film and improved its crystallinity. Absorbance data indicated that the band gap of the E-beam film reduced, which in turn covered the wider range of absorbed light. These modifications increased oxygen vacancies or defects, which enhanced mobility and separation of electrons and holes. As a result, the E-beam film exhibited a threefold increase in the photocurrent density, compared to that of the non-E-beam film. This electrosprayed titania film was used as a photoanode while the reference and counter electrodes involved in the generation of hydrogen were made of Ag/AgCl and platinum, respectively. The intensity of the UV light illumination used was 1 mW/cm2.
Keywords: Electrostatic spray deposition; Water splitting; Electron beam; TiO2; Thin film;

One-step synthesis of bird cage-like ZnO and other controlled morphologies: Structural, growth mechanism and photocatalytic properties by Shuo Yang; Jian Wang; Xiuyan Li; Hongju Zhai; Donglai Han; Bing Wei; Dandan Wang; Jinghai Yang (211-215).
ZnO nanocages and other nanostructures have been synthesized via a simple one-pot hydrothermal method with different reaction times. It is worth mentioning that this is a completely green method which does not require any other chemicals except that Zn foil served as Zn source in the experiment. X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) and UV–Vis diffuse reflection spectra were used to characterize the crystallinity, morphology and optical property of ZnO structures. Growth mechanisms of ZnO were proposed based on these results. Furthermore, ZnO films with different morphologies and crystal growth habits exhibited different activities to rhodamine B degradation. The influence of the reaction time on the morphology of ZnO films and the effect of the morphologies on the photocatalytic activity are discussed.
Keywords: ZnO; Morphology control; Growth mechanism; Photocatalytic;

Increased photocatalytic activity of tube-brush-like ZnO nanostructures fabricated by using PVP nanofibers as templates by Xinying Chen; Yingjiao Zhai; Jinhua Li; Xuan Fang; Fang Fang; Xueying Chu; Zhipeng Wei; Xiaohua Wang (216-220).
The tube-brush-like ZnO nanostructures were synthesized by hydrothermal method using electrospinning polyvinylpyrrolidone (PVP) nanofibers as templates. The photocatalytic activity of as-grown samples was investigated by photo-degradation of Rhodamine B (RhB). The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV/visible absorption spectroscopy (UV–vis) and photoluminescence (PL) spectroscopy. It was found that the morphologies of the prepared ZnO were tube-brush-like nanostructures. With the grown time increasing, the crystal and the optical properties were improved. In the photocatalytic experiment, the tube-brush-like ZnO nanostructures photocatalytic activity was enhanced the degradation of RhB was up to 98% after 2 h of irradiation. The tube-brush-like ZnO nanostructures showed higher photocatalytic activity because of the special surface morphology.
Keywords: Tube-brush-like ZnO nanostructures; Polyvinylpyrrolidone (PVP); Photocatalytic activity; Rhodamine B (RhB);

Quasi spherical and capsule like ZnO nanostructures have been successfully synthesized via a simple precipitation route without the assistance of external capping agents. The effect of annealing temperature on the properties of ZnO was investigated. In all cases, hexagonal wurtzite crystalline structure of phase pure ZnO was obtained. The crystallinity was found to be gradually increasing with annealing temperature. At low annealing temperatures, more or less spherical ZnO nanoparticles were clearly observed, whereas they tend to grow as nanocapsules with increasing the annealing temperature. The formation of single crystalline nanocapsules was observed at 600 °C. The photoluminescence spectra indicated the annealing dependent emission features, especially in the spectral intensity. The dye pollutant methylene blue was found to be completely degraded under UV light irradiation over the ZnO nano photocatalysts. The highest photoactivity was shown by nanocapsules obtained at 600 °C and was found to be highly reusable.
Keywords: ZnO nanoparticles; Optical studies; Annealing temperature; Crystallinity; Photocatalysis; Hydroxyl radicals;

Zinc oxide (ZnO) and iron doped zinc oxide (Fe/ZnO) nanoflowers were successfully synthesized via a simple hydrothermal process. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering, ultraviolet–visible (UV–vis) diffuse spectroscopy and scanning electron microscopy (SEM), and it was found that the dopant ions replaced some of the crystal lattice zinc ions, and furthermore, Fe3+ and Fe2+ ions coexist. Photocatalytic activities of the catalysts were assessed based on the degradation of rhodamine B (RhB) in aqueous solution under both UV and visible light irradiation (λ  > 420 nm), respectively. All Fe/ZnO samples showed enhanced photocatalytic activity under the irradiation of visible light. On the contrary, Fe/ZnO products displayed poorer performance than that of pure ZnO in the presence of UV light. This phenomenon can be attributed to the coexistence of Fe3+ and Fe2+ in the ZnO host. The photophysical mechanism of the UV and visible photocatalytic activity was investigated with the help of surface photovoltage (SPV) and PL measurements, respectively. The results indicated the influence of coexistence of Fe3+ and Fe2+ in ZnO host on the separation and transfer behavior of the photogenerated charges in the UV and visible regions, which are distinctly different: under the irradiation of UV light, the recombination of the photogenerated electrons and holes was promoted, whereas the separation and transfer of photogenerated electrons and holes was facilitated under the visible light irradiation. The detailed photocatalytic mechanism and the role of Fe on the photodegradation process are discussed.
Keywords: Fe/ZnO; Visible light irradiation; Photosensitive effect; Surface photovoltage;

N-doped ZnO micropolyhedrons were fabricated by calcining the mixture of commercial ZnO (analytical grade) and NH4NO3 at 600 °C for 1.5 h, in which NH4NO3 was utilized as the nitrogen source. The structure, composition, BET specific surface area and optical properties of N-doped ZnO sample were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, wavelength dispersive X-ray fluorescence spectroscopy, field emission scanning electron microscopy, high resolution transmission electron microscopy, N2 adsorption–desorption isotherms, and UV–vis diffuse reflectance spectroscopy. The photocatalytic results demonstrated that the as-synthesized N-doped ZnO microcrystals possessed much higher photocatalytic activity than N-doped TiO2 (which was synthesized by calcining the mixture of P25 TiO2 and NH4NO3 at 600 °C for 1.5 h) and commercial pure ZnO in the decomposition of formaldehyde under visible-light (λ  > 420 nm) irradiation. The present work suggests that NH4NO3 is a promising nitrogen source for one-step calcination synthesis of microcrystalline N-doped ZnO, which can be applied as a visible-light-activated photocatalyst in efficient utilization of solar energy for treating formaldehyde wastewater.
Keywords: N-doped ZnO; Visible-light; Photocatalytic degradation; Formaldehyde;

Microwave-assisted synthesis of self-assembled BiO1.84H0.08 hierarchical nanostructures as a new photocatalyst by Pei Hu; Dongfang Hou; Hongyu Shi; Chaoji Chen; Yunhui Huang; Xianluo Hu (244-249).
Self-assembled hierarchical nanostructures of BiO1.84H0.08 spheres have been successfully synthesized by a rapid, one-pot, low-temperature hydrothermal route under microwave irradiation. The as-prepared hierarchically nanostructured BiO1.84H0.08 possesses a high surface area of 113 m2  g−1. By adjusting the reaction temperature and reactant concentration, the morphology of the as-formed BiO1.84H0.08 nanostructures can be tailored. As a new photocatalyst, the flower-like spherical BiO1.84H0.08 exhibits enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under UV–visible light. The synthetic procedure is simple, efficient, and scalable for mass production. Therefore, the as-formed BiO1.84H0.08 hierarchical nanostructures may offer great potential applications for decomposition of organic contaminants.
Keywords: Microwave irradiation; Photocatalyst; Hierarchical nanostructure; Bi-based oxide;

To overcome the drawback of low solar energy utilization rate brought by general photocatalysts, a novel BiErWO6 photocatalyst with wide spectral responsive property was designed and synthesized by a hydrothermal method. The effects of hydrothermal temperature on the phase structure and the photocatalytic activities of the products were investigated. Due to the wide spectral absorption range, the as-prepared BiErWO6 photocatalyst showed good photocatalytic performance in degradation of rhodamine B (RhB) under simulated solar light. Moreover, the BiErWO6 photocatalyst also exhibited high photocatalytic activity under a green LED (λ  = 520 nm) irradiation. This work provided a new concept for rational design and development of high-performance photocatalysts.
Keywords: BiErWO6; Photocatalyst; Green LED; RhB;

Various 3D N-doped (BiO)2CO3 (N-BOC) hierarchical superstructures self-assembled with 2D nanosheets were fabricated by one-step hydrothermal treatment of bismuth citrate and urea. The as-obtained samples were characterized by XRD, XPS, FT-IR, SEM, N2 adsorption–desorption isotherms and UV–vis DRS. The hydrothermal temperature plays a crucial role in tuning the crystal and morphological structure of the samples. Adjusting the reaction temperature to 150, 180 and 210 °C, we obtained N-doped (BiO)2CO3 samples with corresponding attractive persimmon-like, flower-like and nanoflakes nano/microstructures. The photocatalytic activities of the samples were evaluated by removal of NO under visible and solar light irradiation. The results revealed that the N-doped (BiO)2CO3 hierarchical superstructures showed enhanced visible light photocatalytic activity compared to pure (BiO)2CO3 and TiO2-based visible light photocatalysts. The outstanding photocatalytic performance of N-BOC samples can be ascribed to the doped nitrogen and the special hierarchical structure. The present work could provide new perspectives in controlling the morphological structure and photocatalytic activity of photocatalyst for better environmental pollution control.
Keywords: Hierarchical superstructure; Nitrogen doping; Hydrothermal temperature; Visible light photocatalytic; Air purification;

Preparation and photocatalytic activity of porous Bi5O7I nanosheets by Jun Yang; Longjun Xu; Chenglun Liu; Taiping Xie (265-271).
The porous Bi5O7I nanosheets were successfully prepared by a facile thermal decomposition of BiOI nanosheets, and the pore diameter mainly distributes in 18–30 nm and the most probable distribution emerges at 27 nm.Porous Bi5O7I nanosheets were successfully prepared by a facile thermal decomposition of BiOI nanosheets in air at 500 °C for 2 h. The crystal structure, surface morphology, specific surface area, and optical properties of resulted materials were characterized by XRD, SEM, TEM, nitrogen adsorption–desorption isotherms and UV–vis diffuse reflectance spectroscopy, respectively. Moreover, the photodegradation ability of porous Bi5O7I nanosheets on target pollutant Rhodamine B (RhB) under visible light irradiation (λ  ≥ 400 nm) and simulated sunlight irradiation was investigated. The results indicated that porous Bi5O7I nanosheets were mainly composed of irregular nanosheets. With the layer thickness of 30–50 nm and pore diameter distribution around 25 nm, it belonged to mesoporous material. Compared with BiOI, the photocatalytic activity of porous Bi5O7I nanosheets under visible light was appropriately 2 times than that of BiOI, and 2.3 times under simulated sunlight. The major reasons for the improvement in catalytic performance were the existence of multiple pores and the special band structure.
Keywords: Porous Bi5O7I nanosheets; Photocatalysis; Mesoporous material;

BiPO4/reduced graphene oxide composites photocatalyst with high photocatalytic activity by Yihe Zhang; Bo Shen; Hongwei Huang; Ying He; Bin Fei; Fengzhu Lv (272-277).
The composite photocatalysts composed of BiPO4 and reduced graphene oxide (rGO) were synthesized by a facile hydrothermal method. The BiPO4/rGO composites exhibit much better photocatalytic performance than pure BiPO4.The composite photocatalysts composed of BiPO4 and reduced graphene oxide (rGO) were synthesized by a facile hydrothermal method. Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), transmission electron spectroscopy (TEM), photoluminescence emission spectra (PL) and UV–vis diffuse reflection spectroscopy (DRS) were used to characterize the titled composites. The results showed that the BiPO4 particles can be immobilized on the surface of rGO sheets, and the crystallization phases of BiPO4 were significantly influenced by the amount of graphene. The phase transformation of BiPO4 crystal from hexagonal to monoclinic phase was observed. The introduction of rGO improved the optical properties of BiPO4 and thereby enhancing the utilization of light. Compared with pure BiPO4 under similar synthesis condition, the BiPO4/rGO composites exhibit a much higher photodegradation activity, which was confirmed by photoluminescence (PL) spectra and photocurrent (PC) generation.
Keywords: BiPO4; Reduced graphene oxide; Composites; Photocatalysis;

In this work, various kinds of CdS and CdS/CdSe thin films were fabricated on ITO conductive glass by chemical bath deposition (CBD) and/or electrodeposition (ED) methods. These films were characterized by XRD, XRF, SEM and optical absorption. Their photoelectrochemical properties were also investigated. First, two kinds of CdS thin films were firstly deposited on ITO conductive glass by CBD or ED. It was found that the two kinds of CdS films showed different compositions and crystal structures. The CdS film prepared by CBD is S-rich and has a cubic zinc blende structure, while the CdS film prepared by ED is Cd-rich and has a hexagonal wurtzite structure. Furthermore, CdSe was deposited on the as-obtained CdS films by a galvanostatical ED method, resulting in CdS/CdSe bilayer thin films. The achieved CdS/CdSe bilayer thin films showed enhanced optical absorption than the CdS monolayer thin film. For the photoelectrochemical properties, the CdS/CdSe bilayer thin film also exhibited enhanced photocurrent density and photoconversion efficiency in comparison with the CdS monolayer thin film. In particular, the CdS/CdSe bilayer thin film in which the CdS layer was obtained by ED, showed a maximum photocurrent density of about 6 mA/cm2 and maximum photoconversion efficiency of 3.41%.
Keywords: CdS/CdSe; Electrodeposition; Chemical bath deposition; Photocatalytic; Photoelectrochemical properties;

Optical signal demultiplexing and conversion in the fullerene–oligothiophene–CdS system by Kornelia Lewandowska; Agnieszka Podborska; Przemysław Kwolek; Tae-Dong Kim; Kwang-Sup Lee; Konrad Szaciłowski (285-290).
We report the photoelectrochemical photocurrent switching (PEPS) effect in the system based on a C60 derivatives and nanostructured cadmium sulfide. Rapid and efficient photocurrent switching upon changes of the electrode potential was observed. This process relies on the photocurrent generation by semiconducting particles and interfacial electron transfer reactions governed by the redox chemistry of fullerene derivatives (fullerene–oligothiophene dyads) with molecular oxygen as a final electron acceptor. Surprisingly, fullerene derivatives without thiophene moieties were much less efficient as CdS modifiers. These peculiar photoelectrochemical properties were applied for construction of an optoelectronic logic device.
Keywords: Demultiplexer; PEPS effect; Fullerene–Oligothiophene–CdS system;

One-dimensional (1D) Cd2Ge2O6/CdS core–shell composites were successfully synthesized by a facile ion-exchange method at room temperature. The composition, structure and property of the 1D Cd2Ge2O6/CdS core–shell composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (UV–vis DRS). The photocatalytic activity of the 1D Cd2Ge2O6/CdS core–shell composites was evaluated on the degradation of acid red G solution. The results showed that the 1D Cd2Ge2O6/CdS core–shell composite with 12.7 wt% CdS exhibited a higher photocatalytic activity than the pure CdS under visible light irradiation. Theoretical analyses and scavenger experiment results suggested that the enhanced photocatalytic activity of the 1D Cd2Ge2O6/CdS core–shell composite was mainly attributed to the synergic effect from the well-matched band potentials and 1D core–shell structure.
Keywords: Core–shell; Cd2Ge2O6; CdS; Ion-exchange; Photocatalysis;

Synthesis of CdS/BiOBr composite and its enhanced photocatalytic degradation for Rhodamine B by Wenquan Cui; Weijia An; Li Liu; Jinshan Hu; Yinghua Liang (298-305).
CdS/BiOBr composite photocatalysts were successfully prepared by a facile precipitation method and characterized by XRD, SEM, TEM, EDS, UV–vis and PL. The photocatalytic activities of the samples were evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The effects of CdS content, catalyst dosage, and initial concentration of RhB solution on the photocatalytic degradation were investigated. The results indicated that the CdS/BiOBr composite photocatalysts exhibited strong absorption in the visible light region and possessed excellent photocatalytic activity and stability for RhB degradation. The 40%-loaded CdS/BiOBr composite photocatalyst was found to degrade 97% of RhB under visible light irradiation and showed no apparent decrease in activity after five cycles. The enhancement in both activity and stability were attributed to the enhanced light absorption and effective separation and transfer of photogenerated charges, originating from the well-matched overlapping band-structures and closely contacted interfaces. Experiments using radical scavengers indicated that •O2 and h+ were the main reactive species present in the photosystem. On the basis of the experimental results and estimated energy band positions, the mechanism for the enhanced photocatalytic activity was proposed.
Keywords: CdS/BiOBr; Visible light; Photocatalysis; RhB;

Novel visible-light-driven graphene oxide (GO)/AgBr nanocomposites were synthesized by a facile solution method. The GO/AgBr nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) analysis, UV–vis diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectra (FTIR), and Raman spectra. The results indicated that AgBr nanoparticles were evenly distributed on the surface of GO and the heterostructures were formed. The photocatalytic activity of the as-prepared nanocomposites was evaluated by using Rhodamine B (RhB), Methylene blue (MB) and Methyl orange (MO) as target organic pollutants. The nanocomposites exhibit excellent photocatalytic activity for all of three dyes. Compared with bare AgBr particles, the GO/AgBr nanocomposites show better photocatalytic properties toward RhB pollutants. Additionally, the radical scavengers experiment indicated that O2 radicals was the main reactive species for the RhB degradation under visible light. The increased photocatalytic activity of the GO/AgBr nanocomposites was attributed to the strong coupling between GO and AgBr, which facilitated interfacial charge transfer and inhibited electron-hole recombination. A photocatalytic mechanism of GO/AgBr nanocomposites was also proposed.
Keywords: GO/AgBr composites; Photocatalyst; Photodegradation;

Enhancement of the visible light activity and stability of Ag2CO3 by formation of AgI/Ag2CO3 heterojunction by Changlin Yu; Longfu Wei; Wanqin Zhou; Jianchai Chen; Qizhe Fan; Hong Liu (312-318).
An insurmountable problem for silver-based semiconductor photocatalysts is their poor stability. Here, at room temperature, AgI with different concentrations (5%, 10%, 20% and 30%) were coupled into Ag2CO3, producing a series of novel AgI/Ag2CO3 composite photocatalysts. The effects of AgI addition on the Ag2CO3 catalyst for photocatalytic degradation of methyl orange (MO) under visible light irradiation have been investigated. Some physicochemical technologies like N2 physical adsorption/desorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were applied to characterize these products. Results show that the photocatalytic degradation activity of AgI/Ag2CO3 photocatalyst is much higher than that of pure AgI and Ag2CO3. With the optimal content of AgI (20 wt%), the AgI/Ag2CO3 exhibits the highest photocatalytic degradation efficiency. Its first order reaction rate constant (0.54 h−1) is 20 times of that of AgI (0.026 h−1) and 3.6 times of that of Ag2CO3 (0.15 h−1). The characterizations and theory calculation show that AgI and Ag2CO3 have suitably matched band gap structures. The formation of AgI/Ag2CO3 heterojunction with intimate interface could effectively increase the separation efficiency of the e/h+ pairs and promote the production of OH and O2 •− radicals, which brings about the fast degradation rate of the dye and an increase in photocatalytic stability.
Keywords: AgI; Ag2CO3; Heterojunction; Visible light; Photocatalysis; Methyl orange;

Both α- and β-Ag2WO4 are photoactive for organic degradation in aqueous solutions, and β-Ag2WO4 is more active than α-Ag2WO4 under UV light, but both the catalysts are not stable against photodecomposition to form metallic silver particles.Silver tungstate as photocatalyst for water splitting and dye degradation has been reported, but the catalyst stability is not known. In this work, we find that both α- and β-Ag2WO4 are not stable under UV light for the photocatalytic degradation of phenol and azo-dye X3B in aqueous solutions. Comparatively, β-Ag2WO4 was more photoactive, but less stable than α-Ag2WO4. Solid characterization with X-ray diffraction and scanning electron microscope showed that metallic silver particles were produced with the two catalysts, consequently resulting into decrease in the activity for organic degradation. Measurement of photoluminescence revealed that β-Ag2WO4 had a weaker band gap emission and higher portion of structural defects than α-Ag2WO4. A possible mechanism responsible for the observed difference in photoactivity and stability between the two tungstates is proposed.
Keywords: Silver tungstate; Organic degradation; Photoactivity; Stability;

Dependence of metallic Ag on the photocatalytic activity and photoinduced stability of Ag/AgCl photocatalyst by Jing Tian; Rui Liu; Guohong Wang; Ying Xu; Xuefei Wang; Huogen Yu (324-331).
Recently, Ag/AgCl has been demonstrated to be a stable and highly efficient photocatalytic material. However, considering the strong photosensitive property of AgCl phase without Ag, it is clear that the metallic Ag plays an important role on the photoinduced stability of Ag/AgCl composite, which has a great effect on its photocatalytic performance. In this study, the Ag/AgCl photocatalysts with different amounts of metallic Ag were prepared by a facile hydrothermal method (30–160 °C) to reveal the dependence of metallic Ag on the photoinduced stability and photocatalytic activity of Ag/AgCl photocatalyst. It was found that the amounts of metallic Ag in the Ag/AgCl could be easily controlled by adjusting the hydrothermal temperature, and the Ag amounts (0–9.8 at%) gradually increased with the hydrothermal temperature from 30 to 160 °C. Photocatalytic results indicated that the metallic Ag had a great effect on the photoinduced stability and photocatalytic activity of Ag/AgCl photocatalysts. As for the AgCl-30 photocatalyst (without metallic Ag), with increasing repetitions of photocatalytic reactions, the photocatalytic performance firstly decreased owing to the rapid increase of metallic Ag via the reduction of lattice Ag+ on AgCl surface, while the subsequently stable performance corresponded to the formation of a stable Ag–AgCl composite structure. For the Ag/AgCl (160 °C) photocatalyst, the sample always exhibited a comparable and stable photocatalytic performance due to the initial existing of some metallic Ag (ca. 9.8 at%). Therefore, a certain amount of metallic Ag on the AgCl surface can greatly improve the photoinduced stability of Ag/AgCl photocatalyst in addition to maintaining its stable photocatalytic activity.
Keywords: Photocatalytic activity; Photoinduced stability; Ag/AgCl; Self-stability;

Visible photocatalysis and photostability of Ag3PO4 photocatalyst by Lin Luo; Yuanzhi Li; Jingtao Hou; Yi Yang (332-338).
Ag3PO4 photocatalyst was prepared by precipitation method and characterized by SEM, XRD and diffusive reflectance UV–vis (DRUV–vis) absorption spectra. The gas-phase photodegradation of volatile organic compounds (VOCs) such as benzene and acetone, and the liquid-phase photodegradation of the cationic and anionic dyes on Ag3PO4 were systematically investigated. Both benzene and acetone could not be photodegraded on the Ag3PO4 photocatalyst under the visible irradiation. The Ag3PO4 photocatalyst is efficient for the photodegradation of the aqueous dye solutions, but could not completely photomineralize the dyes to CO2 and H2O. The reason is discussed by comparing the oxidation potential of organic pollutants and the potential of photogenerated holes in Ag3PO4, and measuring the absorption of organic pollutants on Ag3PO4. The photostability of the Ag3PO4 photocatalyst for the photo-degradation of the dyes was tested. The Ag3PO4 photocatalyst itself is photostable in the absence of the scavenger of the photogenerated holes, but is photocatalytically instable in the liquid-phase photodegradation of dyes due to the photoreduction of Ag+ in Ag3PO4 to Ag.
Keywords: Ag3PO4; Visible photocatalytic; Photomineralization; Photostability;

The reduced graphene oxide (RGO) counter electrodes were prepared by drop casting method and followed by heat treatment. The as-prepared RGO counter electrodes were used as substitution for Pt counter electrode in dye-sensitized solar cells (DSSCs). The effects of hydrazine hydrate in graphene oxide (GO) suspension on the performance of RGO counter electrodes were investigated. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that a moderate amount of hydrazine hydrate can enhance the catalytic activity of the RGO film toward the reduction of I3 and decrease the sheet resistance of the film. The efficiency (η) of DSSC based on the RGO counter electrodes with optimum addition of hydrazine hydrate increased from 1.826% to 2.622% under a simulated solar illumination of 100 mW cm−2 (AM 1.5).
Keywords: Hydrazine hydrate; Reduced graphene oxide; Counter electrode; Dye-sensitized solar cell;

Noble-metal-free g-C3N4/Ni(dmgH)2 composite for efficient photocatalytic hydrogen evolution under visible light irradiation by Shao-Wen Cao; Yu-Peng Yuan; James Barber; Say Chye Joachim Loo; Can Xue (344-349).
The noble-metal-free g-C3N4/Ni(dmgH)2 composites show efficient and stable photocatalytic hydrogen evolution under visible light in triethanolamine aqueous solution.We report an economic photocatalytic H2 generation system consisting of earth-abundant elements only by coupling graphitic carbon nitride (g-C3N4) with Ni(dmgH)2 sub-microwires that serve as effective co-catalysts for H2 evolution. This composite photocatalyst exhibits efficient hydrogen evolution under visible-light irradiation in the presence of triethanolamine as electron donor. The optimal coupling of 3.5 wt% Ni(dmgH)2 to g-C3N4 (5 mg composite) allows for a steady H2 generation rate of 1.18 μmol/h with excellent stability. This study demonstrates that the combination of polymeric g-C3N4 semiconductor and small proportion of transition-metal-based co-catalyst could serve as a stable, earth-abundant and low-cost system for solar-to-hydrogen conversion.
Keywords: Photocatalyst; Graphitic carbon nitride; Hydrogen evolution; Water splitting; Nickel-based co-catalyst;

Hydrothermal synthesis method was applied for preparation of cubic-like CuCr2O4 spinel nanoparticles without template. The synthesized cubic-like CuCr2O4 shows excellent photocatalytic activity for degradation of RhB and MB cationic dyes but not for MO anionic dye in the presence of H2O2 under visible light irradiation.CuCr2O4 nanoparticles with cubic-like morphology were prepared via hydrothermal synthesis method without template. The CuCr2O4 samples were characterized by thermogravimetry and differential scanning calorimetry (TG–DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS) and Zeta potentials, respectively. The results indicated that cubic-like CuCr2O4 could be successfully synthesized by calcining the precursor at 600 °C, and the calcination temperature greatly influenced the morphology and optical performance of CuCr2O4. The pH at the point of zero charge (pHpzc) of the CuCr2O4 calcined at 600 °C was about 4.52. The photocatalytic activity of CuCr2O4 was evaluated for degradation of rhodamine B (RhB), methylene blue (MB), and methyl orange (MO) in the presence of H2O2 under visible light irradiation and the effects of the calcination temperature, dosage of photocatalyst, etc., on photocatalytic activity were studied in detail. The photocatalytic results revealed that the CuCr2O4 photocatalyst was of high activity for degradation of RhB (96.8%) and MB (99.5%), but very low activity for degradation of MO (14%). The CuCr2O4 sample calcined at 600 °C possesses the best photocatalytic activity, and the optimal dosage of the CuCr2O4 photocatalyst is 0.4 g/L.
Keywords: Hydrothermal synthesis; CuCr2O4; Photocatalytic activity; Organic dyes;

The magnetite-hydroxyapatite (M-HAP) nanocomposites were prepared by a chemical co- precipitation procedure and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectra (DRS). The ability of the synthesized catalyst for photocatalytic degradation of Acid Blue 25 (AB25), as an organic dye, under UV irradiation was studied. The catalyst was modified employing transition metals (Mn, Fe, Co, Ni, Cu and Zn) trying to improve the catalytic performance of HAP in absence of UV irradiation and in the presence of hydrogen peroxide i.e. a Fenton like reaction. The best results obtained for Cu and Co modified M-HAPs and the effect of operational parameters such pH, amount of catalyst and hydrogen peroxide concentration was studied. In order to investigate the performance of HAP based photocatalyst in visible light region, M-HAP was modified with silver ions. At the end, Langmuir-Hinshelwood kinetic expression used to evaluate and compare the catalytic systems. The strongest degradation activity was observed for Ag-M-HAP/Vis system because of Ag3PO4 formation. Apparent reaction rate constant (K app) by Ag-M-HAP/Vis was 63, 36 and 19 times faster than Cu-M-HAP(II)/H2O2, Co-M-HAP(II)/H2O2 and M-HAP (I)/UV systems, respectively.
Keywords: Hydroxyapatite; Magnetite; Modification; Metal ions; Degradation; Dye pollution;

Preparation of self-cleaning surfaces with a dual functionality of superhydrophobicity and photocatalytic activity by Eun Ji Park; Hye Soo Yoon; Dae Han Kim; Yong Ho Kim; Young Dok Kim (367-371).
Thin film of polydimethylsiloxane (PDMS) was deposited on SiO2 nanoparticles by chemical vapor deposition, and SiO2 became completely hydrophobic after PDMS coating. Mixtures of TiO2 and PDMS-coated SiO2 nanoparticles with various relative ratios were prepared, and distributed on glass surfaces, and water contact angles and photocatalytic activities of these surfaces were studied. Samples consisting of TiO2 and PDMS-coated SiO2 with a ratio of 7:3 showed a highly stable superhydrophobicity under UV irradiation with a water contact angle of 165° and UV-driven photocatalytic activity for decomposition of methylene blue and phenol in aqueous solution. Our process can be exploited for fabricating self-cleaning surfaces with dual functionality of superhydrophobicity and photocatalytic activity at the same time.
Keywords: Superhydrophobicity; Photocatalysis; TiO2; SiO2; PDMS;

Photocatalytic activity of NaTaO3:La prepared under different atmospheres by Zhou Wu; Guoqiang Li; Feng Zhang; Weifeng Zhang (372-375).
NaTaO3:Laprepared under air atmosphere showed the best photocatalytic performance in hydrogen evolution from pure water and methanol solution. Samples under O2 and H2 showed an opposite behavior in both hydrogen evolution.NaTaO3:La photocatalysts were prepared under air, O2 and H2/Ar atmospheres by solid-state reaction method. The photocatalytic activities of these samples were evaluated from the photocatalytic hydrogen evolution from the methanol solution and pure water, and decomposition of Rhodamine B (RhB). NaTaO3:La prepared under air atmosphere showed the best photocatalytic performance in all the evaluation of photocatalytic activity. The sample prepared under H2/Ar atmosphere showed higher activity in pure water splitting than that under O2 atmosphere, which was opposite in H2 evolution reaction and photocatalytic degradation of RhB.
Keywords: Oxides; Photocatalysis; Hydrogen; Water splitting; NaTaO3;