Chitin biochar as an effective and low-cost alternative for improving electron charge transfer of supported ZnFe2O4 during catalytic oxidation of high molar mass pollutants

In this work, a novel photocatalyst was prepared by supporting ZnFe2O4 onto chitin biochar. The novelty of this work lies in being the first report of ZnFe2O4 supported on biochar obtained from chitin residues, with a complete investigation of its efficiency carried out in two model pollutant molecules, namely ponceau and methylene blue dyes, using the mechanisms that rule heterogeneous photo-Fenton processes. Different ratios of biochar to metal oxide were tested, and it was observed that the electron/hole recombination rate decreased in the composite with equal amounts of each component, named Zn50B. The catalytic process for ponceau red and methylene blue degradation best fit the first-order kinetic model, with a degradation rate at least 26 times faster than the values reported in the literature, with complete removal after 15 and 60 min, respectively. According to radical scavenging experiments and quantum chemical calculations, the degradation mechanism behind Zn50B efficiency consists on the generation of highly oxidizing •OH(aq) and •O2-(aq) species, and its surface plays a minor role by attracting the studied molecules to near radical-generating active sites. Therefore, Zn50B composite is a promising novel photocatalyst, with proven high stability in up to 8 sequential recycles.