One-pot biosynthesis of SnO2 quantum dots mediated by Clitoria ternatea flower extract for photocatalytic degradation of rhodamine B

Abstract

In this study, SnO2 quantum dots (QDs) have been successfully biosynthesized using Aparajitha (Clitoria ternatea) flower extract as the green reducing agent and then used as effective photocatalysts for the degradation of rhodamine B (RhB) under UV light irradiation. Clitoria ternatea flower extract contains flavanols and flavonoids, which can serve as reducing agents to convert Sn2+ precursors into Sn° NPs, which are then oxidized to 4–10 nm SnO2 QDs at 400 °C for 2 h. A blue shift in the adsorption wavelength of biosynthesized SnO2 QDs (3.66 eV) in comparison with bulk SnO2 (3.54 eV) is obtained, which can reduce the electron–hole recombination rate of SnO2. In addition, the specific surface area of SnO2 QDs is almost two times higher than that of bulk SnO2, resulting in the acceleration of photocatalytic degradation efficiency and rate of RhB under UVB light irradiation. The photodegradation performance of RhB over SnO2 QDs is highly dependent on several parameters, including H2O2 concentration, catalyst dosage, and pH. The liquid chromatography-mass spectrometric spectra and radical scavenger experiments indicate that the hydroxyl radicals play a crucial role in photodegradation, which can undergo N-deethylation and ring cleavage reactions to produce intermediates of N, N-diethyl-N’-ethylrhodamines, dihydroxybenzoic acid, and maleic acid. Moreover, a possible reaction mechanism for RhB photodegradation over SnO2 QDs is proposed. Results obtained in this study clearly indicate that the extract is an effective bioreagent to develop the green chemistry for the one-pot synthesis of SnO2 QDs photocatalysts for the degradation of pollutants in aqueous solutions.