Narrowing the band gap of TiO2 by co-doping with Mn2+ and Co2+ for efficient photocatalytic degradation of enoxacin and its additional peroxidase like activity: A mechanistic approach

Abstract

This study presents the synthesis of a novel Mn2+ and Co2+ co-doped TiO2 (Mn-Co-TiO2) for the photocatalytic degradation of enoxacin (ENX) under solar light irradiation. The as-synthesized photocatalysts were fully characterized by X-ray diffraction (XRD) analysis, field emission-scanning electron microscopy (FE-SEM), and UV-diffuse reflectance spectroscopy (UV-DRS). The structural appearance of the Mn-Co-TiO2 suggests porous cylindrical type morphology. Moreover, the co-doping of Mn2+ and Co2+ has successfully reduced the band gap of TiO2 from 2.81 eV to 2.10 eV. Applying Langmuir Hinshelwood kinetic model, the photocatalytic degradation of ENX by Mn-Co-TiO2 followed pseudo-first-order kinetics. A total of twelve (12) DPs of ENX were identified by UPLC/MS-MS. The natural water constituents such as CO32−, HCO3−, Cl− and Fe3+ had great influence on the photocatalytic degradation of ENX by Mn-Co-TiO2 under solar light irradiation. The as-synthesized Mn-Co-TiO2 showed appreciable results for the photocatalytic degradation of ENX in synthetic wastewater (SWW) and real wastewater (RWW) samples. Furthermore, the toxicity assessment of ENX and its DPs towards aquatic organisms (i.e., fish, daphnia and green algae) was measured which are helpful for the practical implementation of this technology for wastewater treatment. The Mn-Co-TiO2 materials also showed good peroxidase-like activity towards the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 and followed Michaelis-Menten kinetics.