| TiO2 nanomaterial is promising with its large potential and outstanding performance in photocatalyic environmental applications, such as CO2 conversion, water treatment, and air quality control. For many of these applications, the particle size, crystal structure and phase, porosity, and surface area influence the activity of TiO2 dramatically. TiO2 nanomaterials with special structures and morphologies, such as nanospheres, nanowires, nanotubes, nanorods, and nanoflowers are thus synthesized due to their desired characteristics. With an emphasis on the different morphologies of TiO2 and the influence factors in the synthesis, fourteen different TiO2 preparation methods, such as sol-gel method, solvothermal method, reverse micelle method etc., were summarized in the first part. The TiO2 formation mechanism and the advantages and disadvantages of the preparation methods are proposed as well.;The objective of the second part was to convert CO2 to CH 4 using photocatalysis. In this investigation, well-crystallized anatase TiO2 nanoparticles with diameters of ~ 18.4 nm were synthesized by a novel solvothermal method and then Pt/TiO2 nanocomposites with high photocatalytic performance and stability were prepared by photoreduction. The average diameter of the well-dispersed Pt nanoparticles was 1.82 nm. UV-vis absorption spectra showed that the deposition of Pt on TiO2 increased the visible light response ability of the photocatalyst. The photoluminescence (PL) spectra demonstrated that the efficiency of photogenerated charge transfer and separation of Pt/TiO2 was better than that of Pt/P25. The optimal TiO2 calcination temperature was 500 °C, while Pt photodeposition time was 1 h. For the optimized Pt/TiO2 photocatalysts, the CH 4 yield reached 60.1 mumol/(gcat·h), together with a H2 yield of 87.5 mumol/(gcat·h) and an C 2H6 yield of 2.8 mumol/(gcat·h) at 4 h of irradiation. Longer irradiation would result in an increase of H2 output, but not the output of CH4 or C2H6. With 1.0% CO2, the CH4 yield and H2 yield reached 37.7 mumol/(g cat·h) and 97.6 mumol/(gcat·h), respectively. O2 was detected and recorded for a systematic analysis of the relationship between CO2 conversion and water splitting. In addition, the photogenerated electron-hole balance was calculated and an associated reaction mechanism was proposed. |
