Piezoelectric-induced band tilting: A double-edged sword in the antibiotic degradation process

Abstract

The piezoelectric catalysis is a promising alternative technology for photocatalytic water treatment. However, different energy excitations may draw forth disparate active species generation, which further affects the decomposition path and product toxicity of antibiotics. Here, we developed Zn_xCd_1-xS homojunction (ZCS) as versatile catalysts for decomposing tetracycline (TC) under piezoelectric and photocatalytic conditions, respectively. XRD, TEM, FTIR and XPS results verified the successful fabrication of materials. An oxidative enhancement effect in piezoelectric catalysis was corroborated for the first time. Electrochemistry and ESR characterizations confirmed that, due to the band tilting induced by ultrasound, the valence band of ZCS achieved the redox potential required for hole-driven hydroxyl radical formation, which hardly happened in ZCS-based photocatalysis. Mechanistic studies revealed that piezocatalytic TC degradation relied on the synergistic effect between hydroxyl radical and singlet oxygen, while superoxide radical and holes severally dominated the photocatalytic process. Normalized degradation results demonstrated a superior mineralization capability of piezocatalysis. Photocatalysis directly decomposed TC molecules, whereas piezocatalysis tended to induce polymerization prior to fragmentation, leading to the distinct toxicities of degradation intermediates between piezocatalysis and photocatalysis. This study offers a new avenue for the regulation of reactive species and evoks a new thinking on the toxicity change of hydroxyl radical-induced pollutants.