Green synthesis of CQDs/Ag/talc ternary composite from waste oil tea

Abstract

This study presents a green and facile strategy for synthesizing a novel carbon quantum dots (CQDs)/silver (Ag)/talc ternary composite through the valorization of waste oil tea (WOT) and natural talc. The synthesis involves a three-step process: first, WOT is hydrothermally converted into CQDs; second, these CQDs act as a green reductant to form a CQDs/silver complex in situ at room temperature without any external agents; finally, the CQDs/silver complex is integrated with talc to yield the final composite. In the resulting material, talc serves as a macroscopic support providing a stable layered scaffold, WOT-derived CQDs function as a multifunctional green reductant and molecular bridge while also enhancing adsorption performance, and in situ formed silver nanoparticles (NPs) deliver the core antibacterial functionality. The composite exhibits an enhanced methylene blue adsorption capacity (20.79 mg·g−1) compared to pristine talc, consistent with the Langmuir isotherm and pseudo-second-order kinetics. Moreover, it demonstrates superior broad-spectrum antibacterial activity, achieving >99.98% inhibition against both Escherichia coli and Staphylococcus aureus. This work establishes a successful ‘waste-to-wealth’ and ‘mineral-upgrading’ paradigm based on a CQDs-mediated in situ reduction and chemical anchoring strategy, converting low-value resources into a high-value-added multifunctional material with promising potential for water-purification applications.