Electrostatic Attraction-Driven Interaction between TiO2 and Colloidal Carbon Quantum Dots for Enhanced Visible Light Photocatalytic Degradation of Tetracycline and Antibacterial Activity Analysis

Developing simple, durable, and efficient photocatalysts is crucial for achieving environmentally friendly treatment of organic pollutants in water. In this study, nanoscale titanium dioxide (TiO 2 ) with a size of approximately 5 nm was synthesized using the sol-gel method, and carbon quantum dots (CQDs) with a size of around 3–5 nm were prepared via a vacuum heating process. The preparation conditions could be controlled to render the TiO 2 surface positively charged and the CQDs surface negatively charged. The combination of TiO 2 with CQDs can form a heterojunction, thereby improving light absorption and the separation efficiency of photogenerated carriers. This enables effective light harvesting and carrier transfer, enhancing the photocatalytic performance. The ζ-potentiometer and electron spin resonance (ESR) measurements confirmed the successful fabrication of high-performance TiO 2 /CQDs composites through electrostatic attraction, forming an interfacial high-speed channel for the transfer of photogenerated carriers. The results demonstrated that the degradation kinetics rate of TiO 2 /CQDs composites reached 0.1345 min − 1 and degraded 98% of tetracycline hydrochloride within 30 min, which is 6.0 and 4.9 times higher than individual TiO 2 and CQDs, respectively. Based on analytical data and experimental results, the photocatalytic mechanism was elucidated, and intermediates along with reactive species were identified to propose possible degradation pathways. Additionally, antimicrobial testing confirmed the nontoxicity of the constructed catalysts and the complete degradation of the pollutants. Graphical abstract