Solar photocatalytic degradation of metformin by TiO2 synthesized using Calotropis gigantea leaf extract

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 similar to 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)-O-center dot) generation on the CG-TiO2 surface, transfer of (OH)-O-center dot to the aqueous phase from CG-TiO2 and subsequent oxidation of metformin in the aqueous phase.

Automated summary

A novel TiO2 nanoparticle was prepared through green synthesis using Calotropis gigantea (CG) leaf extract, which showed high efficiency in degrading metformin under solar photocatalysis. The proposed degradation route involves hydroxyl radical generation, transfer, and oxidation in the aqueous phase.