In Situ Carbon-decorated TiO₂ Photocatalyst: Design, Synthesis, And Catalytic Properties

With the rapid development of modern industrial agriculture, water pollution is becoming more and more serious issue that is hazardous to human health. Photocatalytic technique, as one of the green advanced oxidation technologies, has been widely used in field of environmental pollution treatment, in which Titania (TiO2) photocatalyst has become a hot research topic because of its series of advantages. However, TiO2 photocatalyst holds also some disadvantages such as a low response rate, low quantum yield, poor sunlight absorption and low utilization rate of visible part in sunlight, which substantially hinders their further application. Therefore, the object of this dissertation is to explore the design and preparation of in situ carbon-modified porous/hollow TiO2 photocatalyst with high efficiency as well as its application in environmental pollution treatment, the catalyst not only effectively improve the visible-light photocatalytic efficiency of TiO2, but also can overcome the limitation of carbon-decorated TiO2 prepared via existed methods by using an external carbon precursor. The structure and morphology of the as-synthesized carbon-modified TiO2 photocatalyst were characterized with many details by TEM, SEM, XRD, BET and XPS, the relationship between the structure of the photocatalyst and the photocatalytic activities were discussed deeply.This dissertation used Cationic polystyrene nanoparticles (CPN) prepared by emulsion polymerization as template, and Tetrabutyl titanate (TBT) as titania source, TBT hydrolysate would deposit on the surface of CPN, forming ordered CPN/TiO2 core/shell spheres, finally, the carbon-doped porous TiO2 photocatalyst (C-TiO2) was in situ developed after the removal of CPN template via the calcination of programmed temperature at 450℃. The existence of the carbon element in the as-synthesized C-TiO2 photocatalyst spheres has been proved by elemental analysis (EA) and X-ray photoelectron spectroscopy (XPS), Cls characteristic peak of C-TiO2 at 280.17 eV was observed, this indicated that carbon element substitutionally doped in the place of oxygen in the TiO2 lattice during the carbonization of CPN and formed Ti-C, suggesting the successfully synthesis of carbon-doped porous TiO2 photocatalyst. In addition, the UV-visible diffuse reflectance spectroscopy of C-TiO2 photocatalyst manifested the strong absorption in the visible-light range (400-700nm) in comparison to unmodified P25. The as-prepared carbon-doped porous TiO2 showed the higher photocatalytic activity than commercial P25 in the experiment of the degradation of organic pollutants (methylene blue and rhodamine B) under visible-light irradiation.This dissertation further used cationic polystyrene nanoparticles (CPN) with big particle size prepared by emulsifier-free emulsion polymerization as template and and tetrabutyl titanate (TBT) as titania source, TBT hydrolysate would deposit on the surface of CPN, forming ordered CPN/TiO2 core/shell spheres, finally, the hollow TiO2 photocatalyst (C-TiO2) with high amount of carbon was in situ prepared after the removal of CPN template via the calcination of programmed temperature in nitrogen at 450 ℃. The analysis results of EA and XPS indicated that the carbon amount of as-synthesized C/TiO2 photocatalyst was as high as 20～40%, the BET result demonstrated that the surface area of C/TiO2 was as high as 225.2209 m2/g, far beyond the values of carbon-doped porous C/TiO2 (38.394 m2/g) and commercial P25 (50.2299 m2/g). The UV-visible diffuse reflectance spectroscopy and its corresponding bandgap of C-TiO2 showed that the existence of abundant carbon narrowed the bandgap of C/TiO2 (～2.86 eV), Photocatalytic experiment showed that C/TiO2 manifested superior removal efficiency of methylene blue, far over the corresponding that of commercial P25, as-synthesized carbon-doped titania (C-TiO2), or some representative TiO2 photocatalysts (e.g., blue TiO2, WO3/TiO2, silver modified TiO2, etc). The relationship between the structure of the photocatalyst and the photocatalytic activities indicated that excellently visible-light performance of the as-synthesized C/TiO2 was ascribed to the synergistic effect of narrow bandgap, high amount of carbon, high surface area and suitable shell thickness.Based on above-mentioned results, this dissertation used C/TiO2 with optimal visible-light activity as templates and silver nitrate used as the source of silver nanoparticles, silver ion would be adsorbed onto the surface of C/TiO2 by using the impregnation method, after that, the silver/carbon co-decorated hollow titania photocatalyst (Ag-C/TiO2) was prepared by reduction of silver ion adsorbed via sodium borohydride. TEM, SEM, XPS, ICP-OES and XRD were used to characterize the photocatalyst, this result indicated that C/TiO2 could take full use of negative surface charges so as to promote silver ions to be uniformly deposited on the surface, preparing silver nanoparticles with a small size (<10nm). Whilst the introduction of silver nanoparticles could narrow the bandgap of C/TiO2 (～2.61eV).Photocatalytic experiment showed that as-prepared Ag-C/TiO2 photocatalyst exhibited stronger removal efficiency of methylene blue than C/TiO2 without silver nanoparticles due to synergistic effect of carbon and silver nanoparticles, moreover, as-prepared 2% Ag-C/TiO2 manifested optimal visible-light photocatalytic efficiency when the addition amount of silver nitrate was 2%.The implementation of this dissertation not only prepared three carbon-modified porous/hollow titania visible-light photocatalysts (C-TiO2, C/TiO2, and Ag-C/TiO2), but also constructed a facile method for the in situ synthesis of carbon-modified titania visible-light photocatalysts, building a substantial foundation for the practical application of environmental sewage treatment.