Sunlight mediated enhanced photocatalytic degradation of antibiotics in aqueous medium using silicon doped carbon quantum dots decorated Bi2MoO6 nanoflakes

Abstract

Residual antibiotics in water bodies, including drinking water has led to developing strategies for their removal. Here we report a very efficient method of photocatalytic degradation of tetracycline and ciprofloxacin in an aqueous medium using an optimized batch of silicon doped carbon quantum dot decorated on bismuth molybdate (1.0SiCQDs/Bi2MoO6) nanocomposite as a solar photocatalyst. The photocatalyst is synthesized by the hydrothermal route. Its structural, compositional, morphological, and optical properties are thoroughly characterized. About 97% of tetracycline (TC) and 95% of ciprofloxacin (CIP) are degraded in 90 min of sunlight exposure with a photocatalyst dose of 60 mg per 100 mL, which corresponded to a degradation rate of 0.023 min−1 and 0.025 min−1, respectively. The total organic carbon estimation in the reaction medium after photocatalytic degradation revealed 87.1% and 80.2% mineralization of TC and CIP, respectively. The photocatalytic degradation is attributed to the in-situ generation of reactive oxygen species (ROS), e.g., superoxide radicals, hydroxide radicals, and the role of ROS towards the degradation of tetracycline and ciprofloxacin is confirmed from ROS scavenging studies. The degradation mechanism has been discussed by analyzing the degradation products via ultra-performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UPLC-Q-Tof-MS). The photocatalytic degradation of tetracycline and ciprofloxacin by 1.0SiCQDs/Bi2MoO6 nanocomposites is significantly enhanced as compared to Bi2MoO6 photocatalyst, attributed to interfacial transfer of a photogenerated electron from Bi2MoO6 to SiCQDs, leading to effective charge separation of Bi2MoO6 and the charge carrier mobility.