Double S-scheme Cu2-xSe/twinned-Cd0.5Zn0.5S homo-heterojunctions with surface plasmon effects for efficient photocatalytic H2 evolution.

The enhancement of charge separation and utilization efficiency in both the bulk phase and interface of semiconductor photocatalysts, as well as the expansion of light absorption range, are crucial research topics in the field of photocatalysis. To address this issue, twinned Cd0.5Zn0.5S (T-CZS) homojunctions consisting of wurtzite Cd0.5Zn0.5S (WZ-CZS) and zinc blende Cd0.5Zn0.5S (ZB-CZS) were synthesized via a hydrothermal method to facilitate the bulk-phase charge separation. Meanwhile, Cu2-xSe with localized surface plasmon resonance effect (LSPR) generated by Cu vacancies was also obtained through a hydrothermal process. Due to their opposite electronegativity, a solvent evaporation strategy was employed to combine Cu2-xSe and T-CZS by intermolecular electrostatic. After optimization, the photocatalytic hydrogen (H2) evolution rate of 5 wt% Cu2-xSe/T-CZS reached an impressive value of 60 mmol∙h-1∙g-1, which was 4.6 and 66.6 times higher than that of pure Cu2-xSe and T-CZS, respectively. Furthermore, this composites demonstrated a remarkable rate of 0.46 mmol∙h-1∙g-1 under near-infrared (NIR) wavelength (>800 nm). The enhanced performance observed in Cu2-xSe/T-CZS can be attributed to its unique and efficient double S-scheme charge transfer mechanism which effectively suppresses rapid recombination of electron-hole pairs both within the bulk phase and at the surface interfaces; this conclusion is supported by Density Functional Theory (DFT) calculations as well as electron paramagnetic resonance spectroscopy analysis. Moreover, incorporation of Cu2-xSe enables effective utilization ultraviolet visible-near infrared (UV-Vis-NIR) light by the composites while facilitating injection "hot electrons" into T-CZS for promoting photocatalytic reactions. This study provides a potential strategy for achieving efficient solar energy conversion through synergistic integration of non-stoichiometric plasmonic materials with photocatalysts with twinned-twinned structures.

Creating triazine units to bridge carbon nitride with titania for enhanced hydrogen evolution performance.

In this work, a wealth of triazine units was created in carbon nitride through a facile molten salt method to bridge titania and carbon nitride for accelerating charge transportation and enhancing hydrogen production performance. The doping of triazine ring into C3N4 framework results in more exposure of - CN - and - CN bond and forms a homojunction (MCN), which favors photocatalysis by acting as photoresponse and active centers, respectively. Moreover, the triazine units can bridge the hybridized C3N4 and TiO2, forming a stable MCN/TiO2 homo-heterojunction. Attributed to the matched band energy structure of MCN and TiO2 and the structural characteristics of triazine/heptazine heterocyclic, the light response, charge separation and transfer as well as the lifetime of carriers on MCN/TiO2 hybrid are improved significantly. As a result, the MCN/TiO2 homo-heterojunction exhibits excellent activity and stability for photocatalytic hydrogen production performance, up to 2594 µmol∙g-1∙h-1 under simulated solar irradiation, which is 5.5 times higher than that of the bare g-C3N4.