Velvet-Ball-Like S-Scheme FeOOH/ZnMn2O4 Heterojunction for Degradation of Tetracycline Under Visible-Light Irradiation

Abstract

To address the issues of high electron-hole pair recombination rate and low quantum efficiency in the ZnMn₂O₄ (ZMO) photocatalyst, an S-scheme FeOOH/ZnMn₂O₄ (FOH/ZMO) heterojunction composite was constructed by loading FeOOH (FOH) onto ZMO using an impregnation method. The microstructure, optoelectronic properties, and crystal structure of FOH/ZMO were systematically characterized using various characterization methods. The photocatalytic activity of FOH/ZMO was investigated by degrading tetracycline hydrochloride (TC) in simulated wastewater. Characterization results revealed that the FOH/ZMO composite material retained the tetragonal spinel structure of ZMO and formed a unique “velvet-ball-like” morphology. Moreover, FOH was uniformly and closely loaded on the surface of ZMO, and an S-scheme heterojunction structure was successfully constructed at the interface between the two materials. Through the synergistic effects of optimizing the interfacial charge transfer path, retaining highly active redox sites, and promoting the directional separation of carriers, this heterojunction significantly enhanced the photocatalytic activity of FOH/ZMO. Quenching experiments further confirmed that superoxide radicals (·O₂⁻) and hydroxyl radicals (·OH) were the primary reactive species in the degradation process. During the degradation performance tests, FOH/ZMO demonstrated outstanding visible-light catalytic activity. The optimal performance was achieved with 6 wt% FOH loading in FOH/ZMO under conditions of 0.6 g/L catalyst dosage, 20 mg/L initial TC concentration, and pH 7, reaching a degradation efficiency of 98.29% after 100 min of visible-light irradiation. Notably, the catalyst demonstrated excellent magnetic separability. After 4 cycles of use, the catalyst could still maintain a degradation efficiency of 93.79%, demonstrating sound stability. This study not only proposes a novel strategy for designing ZMO-based photocatalysts but also provides valuable insights into the development and practical applications of S-scheme heterojunction materials.

Graphical Abstract