Solar photocatalytic degradation of metformin by TiO2synthesized using Calotropis gigantea leaf extract

Abstract

A novel TiO2 nanoparticle was prepared through green synthesis using Calotropis gigantea (CG) leaf extract. Morphological analysis showed dispersed spherical CG-TiO2 nanoparticles with an average size of 42 nm. The prepared catalyst was used for the degradation of metformin (a widely used diabetic medicine) by solar photocatalysis. A three-factor central composite design (CCD) was used to explore the effect of independent variables, i.e., pH 3.7, metformin concentration 1.10 mg/L, and catalyst (CG-TiO2) dosage 0.5.2.0 g/L. A maximum metformin degradation of 96.7% was observed under optimum conditions i.e., pH �` 9.7, initial metformin concentration = 9.7 mg/L and catalyst dosage = 0.7 g/L, with i-86% mineralization efficiency. A quadratic model with an error �5% was developed to predict the metformin degradation and the rate of degradation under the optimum conditions followed pseudo-first-order kinetics (k= 0.014/min). CG-TiO2 exhibited higher metformin degradation efficiency (96.7%) compared to P-25 (23.9%) at optimum conditions. The recyclability study indicated effective reuse of the catalyst for up to three cycles. The proposed metformin degradation route is hydroxyl radical (.OH) generation on the CG-TiO2 surface, transfer of .OH to the aqueous phase from CG-TiO2 and subsequent oxidation of metformin in the aqueous phase. � 2021 The Authors.