A novel ZnCo2O4/BiOBr p-n/Z-scheme heterojunction photocatalyst for enhancing photocatalytic activity

Abstract

In this study, we developed a novel p-n/Z-scheme heterojunction photocatalyst, ZnCo₂O₄/BiOBr (ZCo/BB), through a straightforward and safe hydrothermal-calcination-solvent thermal method. The composite photocatalyst demonstrated exceptional photocatalytic efficacy, particularly when the mass ratio of ZnCo₂O₄ was 25% (referred to as 25% ZCo/BB). Structural characterization and electrochemical analysis revealed that 25% ZCo/BB exhibited a larger specific surface area and a faster electron transfer rate. Under visible light exposure for 30 min, methylene blue (MB) degradation reached 92%, and the reaction rate constants were 8.2 and 3.7 times higher than those observed for individual ZnCo₂O₄ and BiOBr, respectively. Furthermore, the 25% ZCo/BB demonstrated exceptional photocatalytic stability over four cycles, maintaining over 80% MB degradation after each cycle. The outstanding photocatalytic activity was attributed to the p-n/Z-scheme heterojunction construction, which promoted charge separation and inhibited carrier recombination. In addition, ·OH and h⁺ were the major active species in photocatalysis, and · ${\text{O}}_2^{-}$ was identified as a secondary active species. This work presents an efficient heterojunction photocatalyst for the degradation of organic wastewater.

Keywords: Composite photocatalyst; Mechanism; Methylene blue; Photocatalytic performance; ZnCo2O4/BiOBr; p-n/Z-Scheme heterojunction.