Visible-light-driven photodegradation of methylene blue and doxycycline hydrochloride by waste-based S-scheme heterojunction photocatalyst BiOI/PCN/tea waste biochar.

Herein, we have reported a photocatalytic BiOI, protonated g-CN heterojunction with directional charge transfer channels provided by tea waste biochar to achieve effective e/h pair isolation for the improved degradation of Methylene blue (MB) and Doxycycline hydrochloride (DCHCl). An S-scheme heterojunction was fabricated via the novel method that combined hydrothermal and ultrasonic dispersion, followed by an electrostatic self-assembly route. The as-fabricated BiOI/protonated g-CN/Tea waste biochar heterojunction formed a strong contact at the interface, as supported by the electron microscopic results. As per the adsorption and photocatalytic degradation kinetics study, BiOI/Tea waste biochar/protonated g-CN (40 wt%) heterojunction showed a higher adsorption rate of 41.56% and 32% for MB and DCHCl within 30 min in the dark. Also, 92.02% MB and 90.21% DCHCl degradation rates in 60 and 90 min, respectively, are approximately 43 and 32 times higher than bare BiOI and protonated g-CN photocatalysts. The highest adsorption and degradation rate was achieved owing to the addition of Tea waste biochar and protonated g-CN in a controlled ratio, and the sufficient interfacial contact between BiOI and protonated g-CN is for the improved isolation rate of e/h pairs as evidenced by zeta potential values photoluminescence spectra as well as from scanning and transmission electron microscopy. Moreover, BiOI/Tea waste biochar/protonated g-CN (40 wt%) possessed high stability and recyclability after four consecutive cycles without much altering the degradation ability. Therefore, we believe that the as-fabricated BiOI/Tea waste biochar/protonated g-CN (40 wt%) provides new insight into the highly efficient S-scheme mechanisms significant for accelerating multicomponent photocatalytic redox reactions; while forming an effective visible light responsive candidate for treating wastewater.