Bifunctional CdS-MoO₂ catalysts for selective oxidation of lactic acid coupled with photocatalytic H₂ production

The persistent hurdles of charge rapid recombination, inefficient use of light and utilization of sacrificial reagents have plagued the field of photocatalytic hydrogen evolution (PHE). In this research, tiny MoO₂ nanoparticles of 10 nm in diameter were prepared through a straightforward solvothermal approach with a specific ratio of oleylamine and oleic acid as stabilizers. The critical factor in the synthesis process was found to be the ratio of oleylamine to oleic acid. Moreover, a two-phase interface assembly method facilitated the uniform deposition of MoO₂ onto CdS nanorods. Due to the localized plasmonic-thermoelectric effect on the surface of MoO₂ along with its abundant oxygen vacancies, the composite catalyst exhibited outstanding photo-utilization efficiency and an abundance of active sites. The CdS-MoO₂ composite displayed a unique photochemical property in transforming lactic acid into pyruvic acid and generating hydrogen simultaneously. After exposure to artificial sunlight for 4 h, significant values of 4.7 and 3.7 mmol⋅g^-1⋅h^-1 were achieved for hydrogen production and pyruvic acid formation, respectively, exceeding CdS alone by 3.29 and 4.02-fold, while the selectivity of pyruvic acid was 95.68 %. Furthermore, the S-Scheme electron transport mechanism in the composites was elucidated using Electron Paramagnetic Resonance (EPR) spectroscopy, radical trapping experiments, energy band structure analysis, and the identification of critical intermediates in the process of selective oxidation. This work sheds light on the design and preparation of high-performance photocatalysts for biorefining coupled with efficient hydrogen evolution.