Utilization of Carbon Nanospheres in Photocatalyst Production: From Composites to Highly Active Hollow Structures

Titanium dioxide-carbon sphere (TiO₂-CS) composites were constructed via using prefabricated carbon spheres as templates. By the removal of template from the TiO₂-CS, TiO₂ hollow structures (HS) were synthesized. The CS templates were prepared by the hydrothermal treatment of ordinary table sugar (sucrose). TiO₂-HSs were obtained by removing CSs with calcination. Our own sensitized TiO₂ was used for coating the CSs. The structure of the CSs, TiO₂-CS composites, and TiO₂-HSs were characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The effect of various synthesis parameters (purification method of CSs, precursor quantity, and applied furnace) on the morphology was investigated. The photocatalytic activity was investigated by phenol model pollutant degradation under visible light irradiation (λ > 400 nm). It was established that the composite samples possess lower crystallinity and photocatalytic activity compared to TiO₂ hollow structures. Based on XPS measurements, the carbon content on the surface of the TiO₂-HS exerts an adverse effect on the photocatalytic performance. The synthesis parameters were optimized and the TiO₂-HS specimen having the best absolute and surface normalized photocatalytic efficiency was identified. The superior properties were explained in terms of its unique morphology and surface properties. The stability of this TiO₂-HS was investigated via XRD and SEM measurements after three consecutive phenol degradation tests, and it was found to be highly stable as it entirely retained its crystal phase composition, morphology and photocatalytic activity.