Rice Husk Biochar-Based Ag3PO4/g-C3N4 Ternary Photocatalyst for Solar-Light-Driven Tetracycline Degradation: Kinetics, Mechanism and Degradation Pathways

Abstract

The present study involves the preparation of a Ag3PO4/g-C3N4/Rice husk biochar (CAR) heterojunction photocatalyst by adding 30 wt% biochar to the Ag3PO4/g-C3N4 (AC) binary composite (70 wt%). Different composites were prepared with weight ratio of Ag3PO4 and g-C3N4 (1:1, 1:3, and 3:1), while keeping the amount of biochar constant, for the degradation of tetracycline (TC) from water. The material was characterized using XRD, XPS, FESEM, EDS, HRTEM, BET, BJH, FTIR, UV–Vis DRS, and PL, which confirmed its good crystal structure, high surface area, and strong response to sunlight. Among all the prepared samples, the 1:1 composition (CAR11) showed the best photocatalytic activity. It degraded about 96% (0.03549 min-1) of TC (25 ppm) under sunlight within 75 min, while under visible and UV light, the degradation efficiencies were 47.5% and 65.5%, respectively. The effects of different experimental conditions, such as pH, light intensity, catalyst dosage, and reactive species, were also studied to understand the photocatalytic process. The catalyst showed good stability and could be reused for six cycles, maintaining about 81% of its photocatalytic activity. Radical trapping experiments revealed that •O2⁻ radicals were the main reactive species in TC degradation. The degradation intermediates were identified by HRMS analysis, and TOC (76%) and COD (73.2%) measurements confirmed that most of the dye was mineralized into simpler and less harmful products. These results show that the CAR11 exhibited high efficiency and stability for solar-light-driven pollutant degradation.