Ternary CdS@MoS2-Co3O4 Multiheterojunction Photocatalyst for Boosting Photocatalytic H2 Evolution

Photoelectrochemical glycerol oxidation to high value-added products over BiVO4/CuWO4 heterojunction photoanodes

Developing high-efficiency, long-term stable photoanodes to harness solar energy for photoelectrocatalytic (PEC) glycerol oxidation into value-added chemicals is pivotal for advancing green chemistry. However, controlling selectivity while achieving high efficiency and stability poses a significant challenge in photoelectrode design. Here, a BiVO4/CuWO4 (abbreviated as BVO/CWO) heterojunction photoanode was synthesized via an electrodeposition method followed by spin-coating. Under AM 1.5G illumination, the BVO/CWO photoanode achieves a glycerol oxidation current density of 1.55 mA∙cm-2 at 1.23 VRHE, maintaining approximately 99 % stability after a 10-hour stability test. The production rate of 1,3-dihydroxyacetone (DHA) for BVO/CWO photoanode reaches 140.3 mmol m-2 h-1 at 1.4 VRHE, representing a nearly 12-fold increase compared to CuWO4 (12.1 mmol m-2 h-1), while the DHA selectivity improves to 50.1 % from 12.5 %. This enhanced performance is attributed to the heterojunction with strong interface interaction within BVO/CWO, which generates a greater photovoltage driving force and improves bulk charge transport efficiency. Introducing the BiVO4 layer on the CuWO4 accelerates interfacial reaction rates and inhibits the photo-corrosion of CuWO4 in strongly acidic conditions. Furthermore, a self-powered system, PEC coupled with a photovoltaic cell (PV-PEC), is developed using a dual-electrode configuration. A PV-PEC device with the BVO/CWO photoanode achieves a DHA productivity of 186.9 mmol m-2 and an H2 productivity of 416.4 mmol m-2 at an operating voltage of 1.5 V over 2.5 h, indicating the application potential of the BVO/CWO photoanode under more realistic conditions.

Carbon Doping Regulates Charge Transfer Paths via a Type-II to S-Scheme Transformation to Improve Photocatalytic Performance

Designing S-scheme heterojunctions with enhanced interfacial interaction is an effective strategy for promoting the separation of photocarriers while maintaining strong photoredox capabilities. However, precisely tailoring the interfacial charge transport pathways between two contacted semiconductors remains a significant challenge due to the similar band alignment in type-II and S-scheme heterostructures. Herein, we report a facile and low-cost carbon doping strategy to smartly tune the charge transfer pathway via a type-II to S-scheme transformation for efficient photocatalytic H2 evolution and H2O2 synthesis. Density functional theory calculations combined with in situ XPS studies demonstrate that the Fermi level of MoO2 shifts from being higher than that of C3N4 to being lower after carbon doping, which drives the inversion of the internal electric field (IEF) direction between MoO2 and C3N4, thus enabling a transition from type-II MoO2/C3N4 heterojunctions to S-scheme C-MoO2/C3N4 heterojunctions. As a result, the optimal S-scheme C-MoO2/C3N4 heterojunctions exhibit a high H2 evolution rate of 16.2 mmol g-1 h-1 and a H2O2 production rate of 877 μmol g-1 h-1, notably surpassing those of the original C3N4 and type-II MoO2/C3N4 heterojunctions. This work provides valuable insights into the fabrication of C3N4 heterostructures and the control of electron migration pathways, thereby creating new possibilities for photocatalysis and optoelectronics applications.

Ultrathin Layered Structure and Oxygen Vacancies Mediated Efficient Charge Separation toward High Photocatalytic Activity in BiOIO3 Nanosheets

Previous bismuth-based photocatalysts usually employ a strong acid solution (e.g., HNO3 solution) to obtain an ultrathin structure toward high photocatalytic activity. In this work, the ultrathin layered BiOIO3 nanosheets are successfully synthesized using just the glucose hydrothermal solution. The high-concentration glucose solution shows the obvious acidity after the hydrothermal process, which leads to the quick decrease in thickness of BiOIO3 nanosheets from ∼45.58 to ∼5.74 nm. The ultrathin structure can greatly improve charge carriers' separation and transfer efficiency. The generation of reductive iodide ions brings about oxygen vacancies in the ultrathin nanosheets, then the defect energy level is formed, causing the decreased band gap and improving the visible light absorption. Compared to thick BiOIO3 nanosheet with little oxygen vacancies, much higher carrier separation efficiency and visible light absorption are achieved in the ultrathin nanosheets with oxygen vacancies, resulting in an excellent photocatalytic performance (0.1980 min-1 for RhB degradation), which is much higher than most other bismuth-based photocatalysts. The superoxide radicals (•O2-) and holes (h+) are the major active species responsible for high photocatalytic activity. This work affords an environmentally friendly strategy to synthesize ultrathin photocatalysts with superior photocatalytic properties.

Construction of core-shell CoSe2/ZnIn2S4 heterostructures for efficient visible-light-driven photocatalytic hydrogen evolution

The use of photocatalysts based on semiconductor heterostructures for hydrogen evolution is a prospective tactic for converting solar energy. Herein, visible-light-responsive three-dimensional core-shell CoSe2/ZnIn2S4 heterostructures were successfully fabricated via in situ growth of ZnIn2S4 ultrathin nanosheets on spherical CoSe2. Without any noble metal co-catalysts, the as-prepared CoSe2/ZnIn2S4 composite achieved attractive photocatalytic hydrogen evolution activity under visible light illumination. Optimal CoSe2/ZnIn2S4 achieved a hydrogen evolution rate of 2199 μmol g-1 h-1, which was 7 times higher than that of pristine ZnIn2S4 and even exceeded that of ZnIn2S4 loaded with platinum. In this distinctive core-shell heterostructure, the presence of CoSe2 could considerably improve the ability to harvest light, quicken the charge transfer kinetics, and avoid the agglomeration of ZnIn2S4 nanosheets. Meanwhile, the experimental results demonstrated that the strong interaction between CoSe2 and ZnIn2S4 at the compact interface could appropriately boost the photogenerated electron-hole pair migration and relieve charge recombination, thus improving photocatalytic hydrogen evolution activity. This work has bright prospects in constructing noble-metal-free core-shell heterostructures for solar energy conversion.