Carbon quantum dot-sensitized hollow TiO2 spheres for high-performance visible light photocatalysis

Carbon nanosphere templates were prepared hydrothermally using glucose as a carbon source. A coated composite was formed by encapsulating the nanospheres with n-butyl titanate and calcinating the composite according to a controlled temperature programme to remove the carbon nanosphere templates; hollow-structured TiO2 nanospheres were obtained. Then, a TiO2/CQD nanocomposite was prepared with carbon quantum dots (CQDs) by covalent bonding. The structure and morphology of the carbon sphere templates, CQDs, TiO2 nanospheres and composite were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and other characterization techniques. The photocatalytic degradation of a methyl orange (MO) solution by the TiO2/CQD composite nanomaterial was studied. The results showed that the nanocomposites were hollow TiO2 spheres with a diameter of approximately 1.1 μm, a thickness of approximately 50 nm and a specific surface area of approximately 27.9 m2 g−1. The composite exhibited the highest visible light photocatalytic activity when the CQD content was 4.0%. The corresponding apparent first-order rate constant was 0.00429 min−1, which is 2.6 times greater than that of hollow TiO2.