Enhanced Photocatalytic Degradation of Tetracycline by AgI/BiVO₄ Heterojunction under Visible-Light Irradiation: Mineralization Efficiency and Mechanism

Abstract

Recently, visible-light-driven photocatalysis is of great interest in the environmental pollutant remediation. In the present study, a novel heterostructured photocatalyst AgI/BiVO₄ was synthesized by an in situ precipitation procedure. The AgI/BiVO₄ heterojunctions exhibited excellent photoactivity for the refractory pollutant (tetracycline (TC), a typical antibiotic) decomposition under visible light illumination. The synthetic sample with 1:4 mass ratio of AgI:BiVO₄ possessed the highest photocatalytic performance in all of the as-prepared catalysts. The TC molecules were substantially eliminated (94.91%) within 60 min, and degradation efficiency was considerably better than those of bare BiVO₄ (62.68%) and AgI (75.43%) under identical conditions. Simultaneously, 90.46% of TOC removal was also achieved within 120 min, suggesting that the mineralization was superior and further confirmed by three-dimensional excitation-emission matrix fluorescence spectroscopy (3D EEMs). The XRD, XPS, DRS, and PL measurements revealed that a small amount of Ag nanoparticles was produced at the early photodegradation process. The structure transformation from AgI/BiVO₄ (double-type) to AgI/Ag/BiVO₄ (sandwich-like) improved the corresponding visible-light absorption performance. The self-assembly Z-scheme heterojunction that consisted of AgI, Ag, and BiVO₄ also efficiently accelerated photoinduced electron-hole pairs' separation and ultimately improved the efficiency of TC degradation. The responsible photocatalytic mechanism was discussed in detail on the basis of the reactive species capturing tests and ESR analysis, and the experimental results had been validated that superoxide radicals and holes played a vital role during the photocatalytic process. Furthermore, TC degradation efficiency was not of significant loss after four consecutive cycles, suggesting the excellent photostability of AgI/BiVO₄ nanocomposite. These features demonstrate that the AgI/BiVO₄ heterojunction has great application potential for refractory pollutants' removal from wastewater.