Visible Light-responsive Photocatalyst Synthesized by Incorporating CQDs into SiO2@TiO2

In recent years, water pollution caused by population growth has become one of the most health-threatening problems. To solve this problem, photocatalytic degradation of organic pollutants using solar energy is expected. Among various photocatalysts, TiO2 has been widely used and studied because of its non-toxicity, low cost, and high chemical stability. However, TiO2 has a wide band gap of 3.2 eV, so only ultraviolet light is available. Since ultraviolet rays account for only about 3~5% of sunlight, research on the effective use of visible light, which accounts for about 45% of sunlight, has been active in recent years. Known major approaches include heterojunction coupling, doping, and dye sensitization. Among them, composites of carbon nanomaterials and TiO2 have been shown to improve optical absorption in visible light. In recent years, carbon quantum dots (CQDs) have attracted attention as a new carbon nanomaterial because of their unique properties. CQDs are non-toxic, inexpensive, and easy to tune. Therefore, it has been applied as a composite material for TiO2 and has been reported to have an optical absorption edge of 419 nm and a band gap of 2.96 eV. In this study, SiO2@TiO2/CQD heterojunction structures were fabricated, and their photocatalytic activity was evaluated using methylene blue. By adjusting the particle size of SiO2@TiO2, the optical wavelength to be reflected can be selected. Among them, SiO2@TiO2 which can reflect optical wavelengths around 400 nm was adjusted to form a structure that allows more efficient optical utilization of TiO2/CQDs.SiO2@TiO2/CQD is a mixture of TiO2 and CQDs coated on the surface of a SiO2 porous structure prepared by the Stover method. This simple preparation method resulted in high surface area, efficient light utilization due to the heterostructure, and efficient charge mobility. As a result, the degradation performance against organic pollutants was shown to be improved.