GNR@CeO2 heterojunction as a novel sonophotocatalyst: Degradation of tetracycline hydrochloride, kinetic modeling and synergistic effects

Abstract

Tetracycline hydrochloride (TCH) is an antibiotic whose presence in aqueous environments, even in trace concentrations, is unsafe for living beings. This work reports the fabrication of a promising sonophotocatalyst, graphene nanoribbon-cerium oxide (GNR@CeO2) heterojunction, for the UV-light driven sonophotocatalytic degradation of TCH. First, GNR@CeO2 heterojunction was fabricated by the simple sonication assisted 1:1 (w/w) doping of cerium oxide (CeO2) nanomaterial onto graphene nanoribbons (GNRs) surface. Further, the GNR, CeO2 and GNR@CeO2 heterojunctions (20 mg L−1 each) were separately investigated as catalysts in the sonocatalytic (40 kHz ultrasound), photocatalytic (390–400 rpm, UV: 365 nm) and sonophotocatalytic (40 kHz ultrasound, 390–400 rpm, UV: 365 nm) processes for the degradation of TCH (70 mL of 20 mg L−1stock). Among the treatment modes, the GNR, CeO2 and GNR@CeO2 heterojunction catalyzed sonophotocatalytic modes recorded the highest TCH removals with 72.9%, 68.3% and 91.2% respectively in 120 min duration. Degradation rates and dynamics obeyed pseudo-first-order kinetics in all the treatment modes. However, GNR@CeO2 catalyzed sonophotocatalytic mode showed the highest degradation rate with the rate constant k = 0.0290 min−1 and correlation coefficient R2 = 0.999, suggesting that the proposed heterojunction acts as effective sonophotocatalyst. The synergy index calculated from the kinetic data also suggests excellent inter-process and inter-catalyst synergy for GNR@CeO2 catalyzed sonophotocatalytic mode. Further, GNR@CeO2 heterojunction also showed high reusability and stability in the sonophotocatalytic process, suggesting that the heterojunction coupled with ultrasound and UV-light serve as practically reliable decontamination system for the removal of TCH in water and wastewaters.