Luminescence properties of CQDs and photocatalytic properties of TiO₂/ZnO/CQDs ternary composites

High-performance fluorescent carbon quantum dots (CQDs) prepared by hydrothermal method using citric acid and polyethyleneimine as raw materials. TiO₂/ZnO/CQDs ternary composites were obtained by compositing different contents of CQDs with TiO₂/ZnO. The phase structure, morphology, photocatalytic performance, and photocatalytic mechanism of ternary TiO₂/ZnO/CQDs were investigated. The result shows that the CQDs synthesized by the hydrothermal method have good whole dispersibility, spherical shape, and particle size of 3–5 nm. When the hydrothermal time is 4 h and the hydrothermal temperature is 220 °C, the fluorescence luminescence performance of the prepared CQDs is the best. The prepared CQDs were loaded on the surface of TiO₂/ZnO to form ternary TiO₂/ZnO/CQDs photocatalysts. The results find that no other new phase is produced by the complex, and the TCZ-1 sample (When the amount of CQDs is 1 mL, the prepared ternary composite photocatalyst.) has a uniform grain size, with an average grain size of about 20 nm. CQDs can reduce the band gap bandwidth of TiO₂/ZnO, and the polar hydrophilic functional groups of CQDs are displayed in the composite, which improves the photocatalytic performance and stability of TiO₂/ZnO. TCZ-1 sample has the best photocatalytic performance, and the photocatalytic degradation rate of methylene blue (MB) solution is 96.7% within 90 min, and after 5 cycles of degradation, it drops to 80.2%, which is improved compared with zinc oxide catalyst.