Bio-carbon quantum dot modified TiO2 nanocrystals for photocatalytic degradation of PLA and PET microplastics

Abstract

Microplastic pollution is widespread, infiltrating water bodies and soil, entering the food chain, and thereby posing threats to ecosystems and human health. In this study, anatase titanium dioxide (TiO₂) was prepared via a hydrothermal method and subsequently modified with bio-based carbon quantum dots (CQDs). The composite exhibited optimal performance when the concentration of the carbon source (citric acid) was 0.17 M, yielding carbon dots with an observable size of approximately 4.18 nm. The formation of Ti–O–C chemical bonds between the carbon dots and TiO₂ was observed. Compared to pristine TiO₂, the CQDs@TiO₂ composite displayed a reduced bandgap, significantly enhanced light absorption in the visible region, improved photogenerated charge carrier transport, and suppressed non-radiative recombination, leading to a substantial enhancement in photocatalytic performance. The CQDs@TiO₂ photocatalyst was employed for the photodegradation of polyethylene terephthalate (PET) and polylactic acid (PLA) microplastics under visible light irradiation. The results indicated that under illumination at 100 mW cm⁻² in a pH 8 buffer solution, CQDs@TiO₂ effectively catalyzed the degradation of alkali-pretreated PET and PLA microplastic samples, with 48 h degradation rates of 28.9% and 59.8%, respectively. The degradation of both types of plastics primarily relied on the synergistic action of ¹O₂, h⁺, ˙O₂⁻ and ˙OH generated by the photocatalyst, both undergoing a degradation process centered on the cleavage of ester bonds. This study not only demonstrates the superior photocatalytic efficacy of the CQDs@TiO₂ composite but also establishes it as a viable strategy for mitigating the urgent challenge of microplastic pollution under near-natural conditions.