Frontiers of Materials Science (v.12, #3)

In the last decade, the surface plasmon resonance-enhanced solar water splitting (SWS) has been actively investigated for improved hydrogen production. In this mini-review, we briefly introduce the mechanisms for plasmon-enhanced SWS and then review some representative studies related to these mechanisms. In addition, we also briefly discuss how metal oxide geometry affects the SWS activity in combined metal-semiconductor nanostructures. Finally, we summarize the recent discoveries and proposed a future vision for plasmon-enhanced SWS with metal oxide nanostructures.
Keywords: surface plasmon resonance; solar water splitting; nanostructures; noble metals; metal oxides

CoP is a candidate lithiumstorage material for its high theoretical capacity. However, large volume variations during the cycling processes haunted its application. In this work, a four-step strategy was developed to synthesize N-doped carbon nanotubes wrapping CoP nanoparticles (CoP@N-CNTs). Integration of nanosized particles and hollow-doped CNTs render the as-prepared CoP@N-CNTs excellent cycling stability with a reversible charge capacity of 648 mA·h·g−1 at 0.2 C after 100 cycles. The present strategy has potential application in the synthesis of phosphide enwrapped in carbon nanotube composites which have potential application in lithium-ion storage and energy conversion.
Keywords: composites; nanostructures; chemical synthesis; electron microscopy; energy storage

All-conjugated amphiphilic diblock copolymers for improving morphology and thermal stability of polymer/nanocrystals hybrid solar cells by Zhenrong Jia; Xuefeng Xia; Xiaofeng Wang; Tengyi Wang; Guiying Xu; Bei Liu; Jitong Zhou; Fan Li (225-238).
Herein, the ability to optimize the morphology and photovoltaic performance of poly(3-hexylthiophene) (P3HT)/ZnO hybrid bulk-heterojunction solar cells via introducing all-conjugated amphiphilic P3HT-based block copolymer (BCP), poly(3-hexylthiophene)-block-poly(3-triethylene glycol-thiophene) (P3HT-b-P3TEGT), as polymeric additives is demonstrated. The results show that the addition of P3HT-b-P3TEGT additives can effectively improve the compatibility between P3HT and ZnO nanocrystals, increase the crystalline and ordered packing of P3HT chains, and form optimized hybrid nanomorphology with stable and intimate hybrid interface. The improvement is ascribed to the P3HT-b-P3TEGT at the P3HT/ZnO interface that has strong coordination interactions between the TEG side chains and the polar surface of ZnO nanoparticles. All of these are favor of the efficient exciton dissociation, charge separation and transport, thereby, contributing to the improvement of the efficiency and thermal stability of solar cells. These observations indicate that introducing all-conjugated amphiphilic BCP additives can be a promising and effective protocol for high-performance hybrid solar cells.
Keywords: hybrid solar cell; P3HT; ZnO; all-conjugated amphiphilic block copolymer; additive

Catalytically enhanced thin and uniform TaS2 nanosheets for hydrogen evolution reaction by Infant Raj; Yongli Duan; Daniel Kigen; Wang Yang; Liqiang Hou; Fan Yang; Yongfeng Li (239-246).
Though the transition-metal dichalcogenides (TMDs) were proven to have a better performance on the hydrogen evolution reaction (HER), the bulk production of active TMD materials remains a challenging work. This report overcomes those barriers by showing a simple procedure to synthesize TaS2 nanosheets through modifying the arc discharge process. The usage of chloride as the transporting agent reduces the growth period of the formed TaS2 with active edge sites. TaS2 is found to have a uniform thickness (4 nm) with high crystallinity and adopt a 2H polytype (double-layered hexagonal) structure. The as-synthesized TaS2 has superior activity for HER with the potential of 280 mV.
Keywords: hydrogen evolution reaction; TaS2 nanosheets; arc disharge; active edge sites

Novel barium tungstate/nitrogen-doped reduced graphene oxide-graphitic carbon nitride (BaWO4/NRGO-g-C3N4) nanocomposite has been synthesized by a simple one-pot microwave technique. The synthesized nanocomposites are well characterized by diffraction, microscopic and spectroscopic techniques to study its crystal structure, elemental composition, morphological features and optical properties. The material prepared is tested for its performance as an electrocatalyst, photocatalyst and reduction catalyst. The nanocomposite catalyzed the photodegradation of methylene blue (MB) dye in 120 min, reduction of 4-nitro phenol (4-NP) to 4-amino phenol (4-AP) in 60 s, showed an impressive Tafel slope of 62 mV/dec for hydrogen evolution reaction (HER). The observed results suggest that the nanocomposite acts as an efficient multifunctional catalyst. The reported approach provides fundamental insights which can be extended to other metal tungstate-based ternary composites for applications in the field of clean energy and environment in the future.
Keywords: BaWO4/NRGO–g-C3N4 nanocomposites; microwave irradiation; hydrogen evolution reaction; photocatalyst; reduction

A novel Ag3PO4-AgBr-PTh composite loaded on Na2SiO3 was synthesized for enhanced visible-light photocatalytic activity. The photocatalytic activity of the samples was evaluated by photodegrading rhodamine B (RhB) under visible light irradiation. The main reactive species and possible photocatalytic mechanism were also discussed. As a result, the Ag3PO4-AgBr-PTh composite loaded on Na2SiO3 exhibited enhanced photocatalytic activity for RhB compared with Ag3PO4 under visible-light irradiation. Additionally, it was demonstrated that the hole (h+) and superoxide radical (•O 2 ) were the major reactive species involving in the RhB degradation. PTh played vital role for the enhanced photocatalytic activity of Ag3PO4-AgBr-PTh-Na2SiO3 composite, which offered an electron transfer expressway and accelerated the transfer of the electrons from the CB of AgBr into Ag3PO4. This work could provide a new perspective for the synthesis of Ag3PO4-based composites and the improvement of photocatalytic activity of Ag3PO4.
Keywords: Ag3PO4-AgBr-PTh-Na2SiO3 composite; PTh; photocatalytic activity; visible light

A two-step approach to synthesis of Co(OH)2/γ-NiOOH/reduced graphene oxide nanocomposite for high performance supercapacitors by Ke Zhan; Tong Yin; Yuan Xue; Yinwen Tan; Yihao Zhou; Ya Yan; Bin Zhao (273-282).
A two-step approach was reported to fabricate cobaltous hydroxide/γ- nickel oxide hydroxide/reduced graphene oxide (Co(OH)2/γ-NiOOH/RGO) nanocomposites on nickel foam by combining the reduction of graphene oxide with the help of reflux condensation and the subsequent hydrothermal of Co(OH)2 on RGO. The microstructural, surface morphology and electrochemical properties of the Co(OH)2/γ-NiOOH/RGO nanocomposite were investigated. The results showed that the surface of the first-step fabricated γ-NiOOH/RGO nanocomposites was uniformly coated by Co(OH)2 nanoflakes with lateral size of tens of nm and thickness of several nm. Co(OH)2/γ-NiOOH/RGO nanocomposite demonstrated a high specific capacitance (745 mF/cm2 at 0.5 mA/cm2) and a cycling stability of 69.8% after 1000 cycles at 30 mV/cm2. γ-NiOOH/RGO//Co(OH)2/γ-NiOOH/RGO asymmetric supercapacitor was assembled, and maximum gravimetric energy density of 57.3 W∙h/kg and power density of 66.1 kW/kg were achieved. The synergistic effect between the highly conductive graphene and the nanoflake Co(OH)2 structure was responsible for the high electrochemical performance of the hybrid electrode. It is expected that this research could offer a simple method to prepare graphene-based electrode materials.
Keywords: reflux condensation; graphene; cobaltous hydroxide; supercapacitor

Nitrogen-oxygen co-doped corrugation-like porous carbon for high performance supercapacitor by Wang Yang; Wu Yang; Lina Kong; Shuanlong Di; Xiujuan Qin (283-291).
Nitrogen-oxygen co-doped corrugation-like porous carbon (NO-PC) has been developed by direct pyrolysis of formaldehyde-melamine polymer containing manganese nitrate. The melamine, formaldehyde and manganese nitrate act as nitrogen, oxygen source and pore-foaming agent, respectively. NO-PC exhibits favorable porous architecture for efficient ion transfer and moderate heteroatom doping for additional pseudocapacitance, which synergistically enhances the electrochemical performance of the NO-PC-based supercapacitor. The electrode delivers specific capacitance of 240 F/g at 0.3 A/g when tested in 6 mol/L KOH electrolyte, good rate capability (capacitance retention of 83.3% at 5 A/g) as well as stable cycling performance (capacitance remains ~96% after 10000 cycles at 3 A/g). The facile synthesis with unique architecture and chemistry modification offers a promising candidate for electrode material of energy storage devices.
Keywords: nitrogen-oxygen co-doping; porous carbon; supercapacitor

Mesocrystalline TiO2/sepiolite (TiS) composites with the function of adsorption and degradation of liquid organic pollutants were successfully fabricated via a facile and low-cost solvothermal reaction. The prepared TiS composites were characterized by FESEM, HRTEM, XRD, XPS, N2 adsorption-desorption, UV–vis DRS, and EPR. Results revealed the homogeneous dispersion of highly reactive TiO2 mesocrystals on the sepiolite nanofibers. Thereinto each single–crystal–like TiO2 mesocrystal comprised many [001]-oriented anatase nanoparticles about 10–20 nm in diameter. The photocatalytic activity was further evaluated by the degradation of anionic dye (methyl orange) and cationic dye (methylene blue) under the UV-vis light (350≤λ≤780 nm) irradiation. By selecting appropriate experimental conditions, we can easily manipulate the photocatalytic performance of TiS composites. The optimal TiS catalyst (the sepiolite content of 28.5 wt.%, and the reaction time of 24 h) could efficiently degrade methyl orange to 90.7% after 70 min, or methylene blue to 97.8% after 50 min, under UV-vis light irradiation. These results can be attributed to their synergistic effect of high crystallinity, large specific surface area, abundant hydroxyl radicals, and effective photogenerated charge separation.
Keywords: TiO2/sepiolite; mesocrystal; solvothermal; composites; photocatalysis

Influence and its mechanism of temperature variation in a muffle furnace during calcination on the adsorption performance of rod-like MgO to Congo red by Yajun Zheng; Liyun Cao; Gaoxuan Xing; Zongquan Bai; Hongyan Shen; Jianfeng Huang; Zhiping Zhang (304-321).
Calcination temperature plays a crucial role in determining the surface properties of generated MgO, but the influence of temperature variation in a muffle furnace during calcination on its performance is rarely reported. Herein we observed that the temperature in a muffle furnace during calcination demonstrated a gradually increasing trend as the location changed from the furnace doorway to the most inner position. The variation in temperature had a great impact on the adsorption performance of generated rod-like MgO without and/or with involvement of Na2SiO3 to Congo red in aqueous solution. To get a better understanding on the detailed reasons, various techniques including actual temperature measurement via multimeter, N2 physical adsorption, CO2 chemical adsorption and FT-IR spectrometry have been employed to probe the correlation between the adsorption performance of generated MgO from various locations and the inner actual temperature of used muffle furnace as well as their physicochemical properties. In addition, two mechanisms were proposed to elucidate the adsorption process of Congo red over the surface of generated MgO without and/or with presence of Na2SiO3, respectively.
Keywords: magnesium oxide; calcination; muffle furnace; placed location; adsorption performance

The original Taylor principles offer identical intergranular strain equilibrium without stress equilibrium in metals during deformation. In reality, however, the stress and strain equilibria are maintained individually for different grains. As key points, the principles have become a prerequisite predominantly in the current theories, which unreasonably indicate that strains instead of stresses induce grain deformation despite reaching the stress equilibrium by complicated combinations of the activation of slip systems or other crystallographic mechanism via different approaches. Real intergranular equilibria can be traced if mechanical interactions together with the external loading are considered step by step. In this work, several penetrating and non-penetrating slips were used to obtain the necessary elastic and plastic strain tensors of different grains in a natural manner. Without the Taylor principles, the stress and strain equilibria can be reached naturally, simply, easily, reasonably, and individually without complicated calculations. Results of the experimental observation conformed with the predicted deformation texture when certain important engineering stress conditions are included in the simulation. Therefore, the Taylor principles for plastic deformation of polycrystalline metals should now be disregarded.
Keywords: deformation; Taylor principles; stress equilibrium; strain equilibrium; texture