Abstract
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.
Highlights
TiO2 nanoparticles in the excited state are capable of generating free radicals resulting in photoinduced reactions like disinfection [1,2,3,4,5], degradation of various organic pollutants [6,7,8,9], and production of H2, as an alternative green energy source [8,10,11,12]
Carbon sphere templates were synthesized by using ordinary table sugar as carbon source, acetone (Molar Chemicals; 99.96%), and Milli-Q water for their purification
Our own ‘Rutile-H2’ TiO2 and ‘Rutile-H2_calc’ were used as references together with commercial Evonik Aeroxide P25
Summary
TiO2 nanoparticles in the excited state are capable of generating free radicals resulting in photoinduced reactions like disinfection [1,2,3,4,5], degradation of various organic pollutants [6,7,8,9], and production of H2 , as an alternative green energy source [8,10,11,12]. Despite the well-known advantages of TiO2 (it is cheap, chemically stable, and available in large quantities in pure form), it has relatively wide band gap (3.02 eV for rutile and 3.20 eV for anatase [13]). This feature limits the scope of its practical applications as it can only be excited efficiently by UV photons. Over the last three decades, a large number of publications were dedicated to the improvement of the photocatalytic activity and the excitability of TiO2.
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