Construction of a novel S-scheme CaIn2S4-ZnO/pine cone-derived biochar for enhanced visible-light-induced photocatalytic H2O2 production and antibiotic degradation

The valorization of biomass and engineering of novel efficient carbon-based supports represent a promising way to improve the performance of heterojunction photocatalysts. In this work, a novel S-scheme heterojunction photocatalyst, CaIn2S4-ZnO/biochar derived from a pine cone (CISZ-BC), was synthesized through a hydrothermal-wet impregnation approach. Through a systematic study of critical synthesis parameters, including hydrothermal temperature, reaction time, and biochar loading, the resultant optimized CISZ-BC composite exhibited impressive visible-light-driven photocatalytic performance, with high-efficiency H2O2 production and >95 % degradation of Tetracycline hydrochloride (TCH). The in situ formed S-scheme charge transfer mechanism promoted the efficient separation of the electrons and holes and minimized recombination and high redox potential, which was corroborated by PL, Transient photocurrent, and EIS analyses. Radical trapping experiments and ESR spectroscopy showed that OH and O-2(-) were the main reactive species, leading to H2O2 production and pollutant degradation. LC-MS was also utilized to investigate the degradation pathways of TCH, revealing that the degradation process resulted in a significant reduction in the toxicity index. The composite was stable and recyclable with high photocatalytic activity for six cycles. This study highlights the advantages of biomass valorization in conjunction with designing a tunable photocatalyst to create a sustainable method for environmental remediation and energy applications.