Study on the photocatalytic mechanism and detoxicity of gemfibrozil by a sunlight-driven TiO₂/carbon dots photocatalyst: The significant roles of reactive oxygen species

An environmentally friendly and sunlight-driven photocatalyst is thought to be a promising alternative to conventional water treatment technology. In this study, carbon dots (C-Dots), a newly discovered material with the ability to upconvert light, were decorated to TiO₂ via a facile hydrothermal-calcination synthesis approach. Under simulated sunlight irradiation, a very low C-Dots content of 5.0 wt% resulted in a 2.3 times faster reaction rate for gemfibrozil (GEM) photodegradation than pristine TiO₂. Oxidative species, particularly [rad]OH, were the most important reactive species mediating the photocatalytic degradation of GEM. A notable observation was the higher formation rates of [rad]OH in the TiO₂/C-Dots system than in pristine TiO₂, which was determined via electron spin resonance spectroscopy. Frontier electron density calculations and mass spectrometry were used to verify that the major degradation pathways of GEM contained [rad]OH addition, H abstraction and O₂[rad]⁻ attack. The acute toxicity of the treated solution at two trophic levels first increased slowly and then decreased rapidly as the total organic carbon decreased during photocatalytic degradation. Compared to traditional advanced oxidation processes, TiO₂/C-Dots photocatalytic technology could reduce the generation of toxic by-products. These results highlight the potential application of sustainable sunlight-driven photocatalyst in water purification.