Preparation of a g-C3N4/Ag3PO4 composite Z-type photocatalyst and photocatalytic degradation of Ofloxacin: Degradation performance, reaction mechanism, degradation pathway and toxicity evaluation

In this study, a g-C3N4/Ag3PO4 composite Z-heterojunction photocatalyst was prepared with a simple in situ deposition method, and was first applied to the degradation of Ofloxacin (OFX). When the theoretical g-C3N4 to Ag3PO4 mass ratio was 1:10 (denoted as AC-10), the OFX degradation was optimal, and the degradation efficiency reached 71.9 % within 10 min. Steady state fluorescence emission spectroscopy (PL), electrochemical impedance spectroscopy (EIS), transient photocurrent (I-t) and N2 adsorption-desorption (BET) studies showed that AC-10 had the best charge separation efficiency and highest specific surface area. Additionally, the effects of AC-10 dosage, OFX concentration, pH value, anions, humic acid and water source on the degradation process were also studied. A cycling experiment showed that AC-10 exhibited good stability. Three-dimensional excitation-emission matrix spectroscopy (3D EEMs), LC-MS data and ECOSAR models were used to explore the process for degradation of OFX and predict the biotoxicities of byproducts, and these results indicated that the catalyst was environmentally friendly. In addition, electron spin resonance (ESR) experiments and capture of the active species showed that photogenerated holes (h+) played a major role in the reaction. Finally, the optical properties and the energy band structure of the catalyst were analyzed by UVvis diffuse reflectance spectroscopy (DRS) and Mott-Schottky (M-S) methods, and a Z-type heterojunction charge transfer mechanism was proposed.