A novel TiO2 nanoparticle was prepared through green synthesis using Calotropis gigantea (CG) leaf extract in this study. Morphological analysis showed dispersed spherical CG-TiO2 nanoparticles with an average size of 42 nm. The prepared catalyst was used for metformin (a widely used diabetic medicine) degradation 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, on metformin degradation. A maximum metformin degradation of 96.7% was observed under optimum conditions viz., pH – 9.7, initial metformin concentration – 9.7 mg/L and catalyst dosage – 0.7 g/L, with ∼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 condition 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. Recyclability study indicated effective reuse of the catalyst for up to 3 cycles. The proposed metformin degradation route is hydroxyl radical (•OH) generation on CG-TiO2 surface, transfer •OH to aqueous phase from CG-TiO2 and subsequent oxidation of metformin in the aqueous phase.
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