Cow manure biochar assisted twinned Mn0.5Cd0.5S homojunction charge transfer to enhance photocatalytic hydrogen evolution

The twinned structure builds an electric field within the photocatalyst through a unique atomic arrangement, enhancing the separation and transfer efficiency of photogenerated charges. Herein, twinned Mn 0.5 Cd 0.5 S (T-MCS) with a differential band structure, integrating wurtzite (WZ-MCS) and zinc blende (ZB-MCS) phases, was synthesized via hydrothermal synthesis. It was then loaded onto cow manure biochar (CM) for efficient photocatalytic hydrogen evolution. The charge transfer pathways of T-MCS and the composite catalyst were systematically investigated using UV-Vis absorption spectroscopy, photoelectrochemical measurements, and density functional theory (DFT) calculations. T-MCS leverages structural distinctiveness to achieve optimal bulk charge separation, driving exceptional photocatalytic hydrogen production. After reacting under a 300   W Xe-lamp (λ > 420   nm) for 3   h, T-MCS produced 35.7   mmol   g -1 of hydrogen, surpassing ZB-MCS and WZ-MCS by 1.6-fold and 6.7-fold, respectively. In addition, the introduction of CM improves the light absorption efficiency of the composite catalyst, provides more active sites, reduces charge transfer resistance and hydrogen evolution overpotential, and significantly enhances the photoelectrochemical performance of the composite catalyst. Ultimately, T-MCS/CM8 achieved excellent photocatalytic hydrogen evolution performance of 23.2   mmol   g -1 h -1 . This study indicates that the combination of twin crystal homojunctions and biochar with excellent electrochemical properties can promote the transfer and separation of bulk and interfacial charges, and improve the efficiency of photocatalytic hydrogen evolution. This work provides a new strategy for achieving resource recycling and H 2 production.