Z-Scheme CBO@MoS₂ System for Enhanced H₂O₂ Photosynthesis with Mechanistic Insights

Photocatalysts often have limited light absorption capabilities and suffer from rapid electron hole recombination[1]. This issue can potentially be addressed through suitable band edge line-up of two or more semiconductors, particularly z-scheme systems, which have superior charge separation and light harvesting properties[2]. The present study explores a z-scheme system with CBO (Copper bismuth oxide) and MoS₂(molybdenum sulfide), which have good light harvesting abilities and efficient charge separation. CBO has a narrow bandgap, good light harvesting capability, and high negative conduction band potential[3]. However, pristine CBO has high charge recombination and unfavourable band edge line-up with the water oxidation reaction. MoS₂, a 2D material is recognized as an excellent co-catalyst for advanced oxidative processes with improved light harvesting, efficient interface charge transfer, and separation[4]. CBO@ MoS₂ is synthesized using two step hydrothermal method. The synthesized catalyst is characterized using several techniques, including XRD, Raman, PL, UV-Vis, and TEM. The catalyst has shown a significantly higher H₂O₂ production rate of 1457 µM h^-1 and a current density of -1.6 mA cm^-2 at 0.2 V, both of which are an order of magnitude higher than the pure components. The improved photocatalytic activity of CBO@ MoS₂ is mainly attributed to the efficient separation of the electron-hole pairs due to staggered band alignment and the z-scheme heterojunction that retains the strong redox ability of both CBO and MoS₂. Mechanistic insight in H₂O₂ production is also provided using mott–schottky analysis, scavenger study and kinetic modelling.<br/>References<br/>[1] J. Deng, Y. Ge, C. Tan, H. Wang, Q. Li, S. Zhou, K. Zhang, Degradation of ciprofloxacin using α-MnO₂ activated peroxymonosulfate process: Effect of water constituents, degradation intermediates and toxicity evaluation, Chemical Engineering Journal. 330 (2017) 1390–1400. https://doi.org/10.1016/j.cej.2017.07.137.<br/>[2] Y. Duan, L. Deng, Z. Shi, L. Zhu, G. Li, Assembly of graphene on Ag₃PO₄/AgI for effective degradation of carbamazepine under Visible-light irradiation: Mechanism and degradation pathways, Chemical Engineering Journal. 359 (2019) 1379–1390. https://doi.org/10.1016/j.cej.2018.11.040.<br/>[3] S. Pulipaka, N. Boni, G. Ummethala, P. Meduri, CuO/CuBi₂O₄ heterojunction photocathode: High stability and current densities for solar water splitting, Journal of Catalysis. 387 (2020) 17–27. https://doi.org/10.1016/j.jcat.2020.04.001.<br/>[4] K.F. Mak, C. Lee, J. Hone, J. Shan, T.F. Heinz, Atomically thin MoS₂: a new direct-gap semiconductor, Phys Rev Lett. 105 (2010) 136805. https://doi.org/10.1103/PhysRevLett.105.136805.