An anti-symmetric dual (ASD) Z-scheme photocatalytic system: (ZnIn2S4/Er3+:Y3Al5O12@ZnTiO3/CaIn2S4) for organic pollutants degradation with simultaneous hydrogen evolution

An anti-symmetric dual (ASD) Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst was prepared by isoelectric point and calcination methods. The photocatalytic activity is estimated via degradation of Acid Orange II as a target organic contaminant with simultaneous hydrogen evolution under simulated solar-light irradiation. The prepared ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst has a high photocatalytic activity, which can be assigned to the enlarged photoresponse range, increased reduction surface and enhanced separation efficiency of photo-induced carriers. Furthermore, the cyclic experiment proves that the prepared ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst still maintains a high photocatalytic activity within five repetitive cycles. Moreover, the mechanism on photocatalytic degradation of organic pollutants with simultaneous hydrogen evolution caused by ASD Z-scheme ZnIn₂S₄/Er³⁺:Y₃Al₅O₁₂@ZnTiO₃/CaIn₂S₄ photocatalyst is proposed. It is wished that this study could provide a promising pathway for effective degradation and rapid hydrogen production.     

V2O5 nanoribbons/N-deficient g-C3N4 heterostructure for enhanced visible-light photocatalytic performance

Visible-light-induced heterostructure photocatalysts have been regarded as promising candidates in clean energy production and environmental treatment of organic pollutants. In this study, we have prepared nanocomposites of V₂O₅/N-deficient g-C₃N₄ (VO/Ndef-CN), which have been characterized by a variety of techniques. The as-synthesized nanocomposites show efficient bifunctional photocatalytic properties toward hydrogen generation and pollutants degradation (dye and antibiotic). The optimized 5VO/Ndef-CN photocatalyst exhibits improved photoactivity for H₂ production (5892 μmol g^?1 h^?1), with a high quantum yield of 6.5%, and fast degradation of organic pollutants, as well as high photocatalytic stability under visible light irradiation. The high photocatalytic efficiency is due to the presence of N defects and S-scheme heterojunction formation, which leads to rapid charge separation, enhanced visible-light absorption, and increased active sites. Furthermore, the possible activity-enhanced mechanism and the photodegradation pathway are proposed based on the experimental and density functional theory (DFT) investigations.     

CoCO3 hierarchical structure embedded on g-C3N4 nanosheets to assemble 3D/2D Z-scheme heterojunction towards efficiently and stably photocatalytic hydrogen production

Structure and interface control of heterojunction is usually a challenging issue to improve the photocatalytic performance. Herein, a new 3D/2D CoCO₃/g-C₃N₄ heterojunction is assembled by embedding hexahedral CoCO₃ on g-C₃N₄ nanosheets. The unique step-like hierarchical structure of CoCO₃, the formed built-in electric field and Z-scheme charge transfer behavior at the interface jointly drive the high-efficient separation of photogenerated carriers to boost the photocatalytic H₂ production. It achieves the optimal H₂ production rate that is almost 2.6 times than g-C₃N₄, apparent quantum efficiency (AQE) of 10.1% at 400 nm and continuous running of 60 h over the 3D/2D CoCO₃/g-C₃N₄ heterojunction. This work endows a fresh structural control strategy for the fabrication of 3D/2D Z-scheme heterojunction to improve the photocatalytic H₂ production performance.     

Rationally construct of CoSx/MoS2/g-C3N4 double heterojunction with promoting the separation of carriers for enhanced photocatalysis

g-C₃N₄ (CN) has attracted extensive attention in photocatalysis field, but its weak visible light absorption and rapid charge recombination limit its application. In this, MoS₂ and CoSx (ZIF67 derivatives) as cocatalyst grew on the surface of semiconductor CN in situ to construct CoSx/MoS₂/CN double heterojunction. Then the activities of photocatalytic hydrogen evolution and degradation MB were researched. The hydrogen production rate of 5%CoSx/MoS₂/CN-2 photocatalyst is 9800 μmol h^?1 g^?1 and is about 6.5 times as great as CN, 46 times than MoS₂ and 98 times than CoSx, respectively. Under natural sunlight and simulated sunlight, the degradation efficiency of MB is 99.95% and 99.50% after 4 h, respectively. Catalyst characterizations have pointed out that CoSx/MoS₂/CN catalyst has abundant active sites and larger specific surface area, which increase absorption of water and oxygen. At the same time, internal electric field and S vacancy enhance electrons transfer rate, which effectively inhibit the recombination of e^?-h⁺. This work provides a new idea into the creation of steady, high-efficiency and continuable photocatalytic catalyst for visible light.     

A novel visible-light responsive photocatalytic fuel cell with a highly efficient BiVO4/WO3 inverse opal photoanode and a MnO2/graphene oxide nanocomposite modified cathode

A highly efficient inverse-opal structured BiVO₄/WO₃ photoanode and a MnO₂/graphene oxide (GO) nanocomposite modified cathode were successfully synthesized in this paper. The optimized BiVO₄/WO₃ inverse opal photoanode achieved a photocurrent density of ∼5.04 mA/cm² at 1.2 V vs. Ag/AgCl under simulated AM 1.5 illumination, which was 2.84 and 2.36 times higher than that of WO₃ inverse opal photoanode and BiVO₄/WO₃ nanoflake photoanode, respectively. The BiVO₄/WO₃ inverse opal photoanode was coupled with the MnO₂/GO modified cathode to build up a novel visible-light responsive photocatalytic fuel cell (PFC) system. The as-established PFC showed outstanding power production performances in comparison with the PFC equipped with a bare MnO₂ modified cathode. For example, in the former PFC system, the maximum power density and the short circuit current density were ∼66.2 μW/cm² and ∼593.5 μA/cm², respectively, for comparison, in the latter PFC, the values were ∼30.1 μW/cm² and ∼255.9 μA/cm², respectively. The degradation experiment for Rhodamine B confirmed successful application of the as-established PFC in pollutant degradation. The mechanism for the significantly enhanced photoelectrocatalytic performances of the PFC was elucidated. The PFC system presented in this paper opened up a new prototype in developing highly efficient devices for energy conversion and environmental protection.     

Interfacially bonded Co-N boosts photocatalytic H2 evolution in a closely coupled CoFe2O4/g-C3N4 composite structure

To create hybrid composites for highly effective photocatalytic hydrogen evolution reactions, the photogenerated charge separation efficiency at the hybrid interface and the surface reaction kinetics at the reactive sites are key factors. In this work, CoFe hydroxide nanosheets prepared by dealloying were first mixed with graphitic carbon nitride (g-C₃N₄) to synthesize a CoFe₂O₄/g-C₃N₄ composite with strong Co-N bonds at the interface by a simple hydrothermal method. It was found that the presence of Co-N bonds between the components in the composites enhances the separation and transfer by photogenerated carriers at the composite interface. Furthermore, the presence of Co-N bonds enhanced the synergistic effect of the hybrid, which significantly boosts their photocatalytic performance in comparison to their counterparts. Under full-spectrum light, the composite photocatalyst has a greater efficiency of photocatalytic water H₂ evolution (6.793 mmol/g⁻¹·h⁻¹) and exceptional stability when compared to pure g-C₃N₄ (0.236 mmol/g⁻¹·h⁻¹) and CoFe₂O₄ (0.088 mmol/g⁻¹·h⁻¹). Under visible irradiation, the photocatalytic activity of the composite (0.556 mmol/g⁻¹·h⁻¹) for H₂ evolution increased by factors of 28.37 and 75.8 when compared to pure g-C₃N₄ and CoFe₂O₄, respectively.     

Construction of dual Z-scheme NiO/NiFe2O4/Fe2O3 photocatalyst via incomplete solid state chemical combustion reactions for organic pollutant degradation with simultaneous hydrogen production

A dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ photocatalyst is prepared via incomplete solid state chemical combustion reaction of Ni(OH)₂ and Fe(OH)₃. The formed perfect interfaces between NiO and NiFe₂O₄ and between NiFe₂O₄ and Fe₂O₃ facilitate the transfers of photo-induced electrons. The photocatalytic degradation of methylene blue and simultaneous production of hydrogen was performed to evaluate the activity of the prepared samples. The dual Z-scheme NiO/NiFe₂O₄/Fe₂O₃ (600–2) photocatalyst obtained by heat treatment of Ni(OH)₂ and Fe(OH)₃ at 600 °C for 2.0 h shows an excellent photocatalytic performance. Additionally, the influences of simulated sunlight irradiation time and methylene blue concentration on the photocatalytic reactions are investigated. Besides, the reusability of sample is assessed via four cycle experiments. Further, a possible mechanism on the photocatalytic reaction is proposed. Maybe, this work would provide an ingenious idea for the construction of dual Z-scheme photocatalyst and the exploration for photocatalytic degradation of organic pollutants with simultaneous hydrogen production.     

Self-generating CeVO4 as conductive channel within CeO2/CeVO4/V2O5 to induce Z-scheme-charge-transfer driven photocatalytic degradation coupled with hydrogen production

The construction of highly efficient Z-scheme photocatalytic system is regarded as a hot research topic in the fields of environmental remediation and renewable energy production. In this work, a novel Z-scheme CeO₂/CeVO₄/V₂O₅ photocatalyst is successfully prepared by using solid phase reaction method. The photocatalytic degradation of organic pollutant (Methylene Blue) with simultaneous hydrogen production is efficiently realized over the prepared Z-scheme CeO₂/CeVO₄/V₂O₅ photocatalysts under visible-light irradiation. The effects of treatment temperatures and treatment times of CeO₂/V₂O₅ composite on the photocatalytic performance of Z-scheme CeO₂/CeVO₄/V₂O₅ photocatalyst are studied. The as-prepared Z-scheme CeO₂/CeVO₄/V₂O₅ (550-3) photocatalyst heat-treated at 550 °C for 3.0 h exhibits the highest photocatalytic performance. It can be ascribed to a moderate amount of CeVO₄ nanoparticles generated between CeO₂ and V₂O₅. The generated CeVO₄ nanoparticles can be used as effective conductive channel to transfer the photo-generated carriers. At the same time, as redox reaction centers it can further accelerate the transfer of photo-generated electrons, effectively enhancing the separation efficiency of photo-generated electron and hole pairs. Furthermore, cyclic test demonstrates that the as-prepared Z-scheme CeO₂/CeVO₄/V₂O₅ (550-3) photocatalyst still maintains a high level of photocatalytic activity within five periods under the same conditions. Moreover, the related photocatalytic mechanism for degradation of organic pollutants with simultaneous hydrogen evolution over the Z-scheme CeO₂/CeVO₄/V₂O₅ (550-3) photocatalyst is proposed. Perhaps, this study affords a simple and novel method to design and develop next generation of highly efficient Z-scheme photocatalysts.     

High performance of proton-conducting solid oxide fuel cell with a layered PrBaCo2O5+δ cathode

A dense BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) electrolyte is fabricated on a porous anode by in situ drop-coating method which can lead to extremely thin electrolyte membrane (10 μm in thickness). The layered perovskite structure oxide PrBaCo₂O_5+δ (PBCO) is synthesized by auto ignition process and initially examined as a cathode for proton-conducting IT-SOFCs. The electrical conductivity of PrBaCo₂O_5+δ (PBCO) reaches the general required value for the electrical conductivity of cathode absolutely. The single cell, consisting of PrBaCo₂O_5+δ (PBCO)/BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY)/NiO-BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) structure, is assembled and tested from 600 to 700 °C with humidified hydrogen (3% H₂O) as the fuel and air as the oxidant. An open-circuit potential of 1.01 V and a maximum power density of 545 mW cm⁻² at 700 °C are obtained for the single cell, and a low polarization resistance of the electrodes of 0.15 Ω cm² is achieved at 700 °C.     

Enhanced degradation of azo dyes wastewater by S-scheme heterojunctions photocatalyst g-C3N4/MoS2 intimately coupled Rhodopseudomonas palustris with chitosan modified polyurethane sponge carrier

With the development of azo dyes in every aspect of life, azo dyes have brought serious harm to human beings and ecological environment. In this study, a new intimately coupling photocatalysis and biodegradation (ICPB) system was reported: The rod-like graphite carbon nitride-molybdenum disulfide (RCM) of S-scheme was prepared by hydrothermal method and loaded onto the exterior surface of chitosan modified polyurethane sponge (CPU), and Rhodopseudomonas palustris (R. palustris) with metabolic versatility, significant survivability and decomposition to toxic and nonbiodegradable organics was combined inside the carrier. The rod-like RCM and egg-like R. palustris in the CPU were observed, the 13.1° and 27.6° characteristic peaks of g-C₃N₄ and 33.4° and 57.6° characteristic peaks of MoS₂ were detected, N–H, NC, C–S–Mo, N–Mo bonds were confirmed, and E_g = 2.42 eV were calculated in RCM, which confirmed the successful preparation of R. palustris/RCM@CPU. The doping ratio of MoS₂ was 6%, RCM dosage was 0.2 g and chitosan doping ratio was 0.5%, R. palustris/RCM@CPU system showed high degradation efficiency. The removal rates of Congo red, methyl orange and carmine were 99.5%, 97.5% and 99.5%, respectively. The significant removal of R. palustris/RCM@CPU system on azo dyes was due to that the RCM of S-scheme produced strong oxidizing superoxide radical (^.O₂⁻), hydroxyl radical (^.OH) and hole (h⁺), and could oxidize azo groups and benzene rings of azo dyes to form alkane compounds, which were mineralized by R. palustris. The close cooperation among CPU adsorption, RCM oxidation and R. palustris mineralization effectively enhanced the degradation efficiency of R. palustris/RCM@CPU system for a variety of azo dyes. This study would propose a new means for the degradation efficiency of azo dye wastewater.     

Synthesis of bimetallic iron ferrite Co0.5Zn0.5Fe2O4 as a superior catalyst for oxygen reduction reaction to replace noble metal catalysts in microbial fuel cell

A low-cost electrochemically active oxygen reduction reaction (ORR) catalyst is obligatory for making microbial fuel cells (MFCs) sustainable and economically viable. In this endeavour, a highly active surface modified ferrite, with Co and Zn bimetal in the ratio of 1:1 (w/w), Co_0.5Zn_0.5Fe₂O₄ was synthesised using simple sol-gel auto combustion method. Physical characterisation methods revealed a successful synthesis of nano-scaled Co_0.5Zn_0.5Fe₂O₄. For determination of ORR kinetics of cathode, using Co_0.5Zn_0.5Fe₂O₄ catalyst, electrochemical studies viz. cyclic voltammetry and electrochemical impedance spectroscopy were conducted, which demonstrated excellent reduction current response with less charge transfer resistance. These electrochemical properties were observed to be comparable with the results obtained for cathode using 10% Pt/C as a catalyst on the cathode. The MFC using Co_0.5Zn_0.5Fe₂O₄ catalysed cathode could produce a maximum power density of 21.3 ± 0.5 W/m³ (176.9 ± 4.2 mW/m²) with a coulombic efficiency of 43.3%, which was found to be substantially higher than MFC using no catalyst on the cathode 1.8 ± 0.2 W/m³ (15.2 ± 1.3 mW/m²). Also, the specific power recovery per unit cost for MFC with Co_0.5Zn_0.5Fe₂O₄ catalysed cathode was found to be 4 times higher as compared to Pt/C based MFC. This exceptionally low-cost cathode catalyst has enough merit to replace costly cathode catalyst, like platinum, for scaling up of the MFCs.     

Performance of double-proveskite YBa0.5Sr0.5Co2O5+δ as cathode material for intermediate-temperature solid oxide fuel cells

Double-proveskite YBa_0.5Sr_0.5Co₂O_5+δ (YBSC) was investigated as potential cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). YBSC material exhibited a good chemical compatibility with the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte up to 950 °C for 2 h. The substitution of Sr for Ba significantly enhanced the electrical conductivity of the YBSC sample compared to undoped YBaCo₂O_5+δ, and also slightly increased the thermal expansion coefficient. At 325 °C a semiconductor-metal transition was observed and the maximum electrical conductivity of YBSC was 668 S cm⁻¹. The maximum power densities of the electrolyte-supported single cell with YBSC cathode achieved 650 and 468 mW cm⁻² at 850 and 800 °C, respectively. Preliminary results suggested that YBSC could be considered as a candidate cathode material for application in IT-SOFCs.