Multiple Modifications Of TiO₂ Nanomaterials And Its Photocatalytic Properties

Recently, photocatalytic decomposition of organic pollutants in waste water or air using semiconductors has attracted much attention. Titanium dioxide（ TiO₂） has been considered to be one of the most promising photocatalysts because of its chemical stability, non-toxicity, low cost and superior activity. However, TiO₂ can be activated only under ultraviolet light irradiation（about 4% of the solar energy） due to its large energy band gap（3.2 eV）. Furthermore, TiO₂ also suffers from the rapid recombination of photo- induced electrons and holes. The intrinsic properties of TiO₂ hamper its full potential application. To date, numerous strategies have been developed to promote the photocatalytic activities of TiO₂, such as doping TiO₂ with metal and nonmetal or coupling TiO₂ with narrow band gap semiconductors, noble metal deposition, and so on. Very recently, TiO 2-based multicomposites have generated considerable scientific interest. In this thesis, Cu₂O/graphene/rutile TiO₂ nanorod（CGT）, Fe₂O₃/N-TiO₂ and Cu₂O decorated carbon-incorporated TiO₂ microspheres（Cu₂O/CTMs） were constructed to achieve the multiple modification of TiO₂, aiming to improve its photocatalytic performance. The as-prepared samples were analyzed by a collection of characterizations.The main results are summaried as following:A ternary composite of Cu₂O, graphene and rutile TiO₂ nanorods was prepared using Cu（CH3COO）2·H2O, graphene oxide and TiCl₄ as the starting materials. Graphene/TiO₂ nanorod composites（CG） were obtained by a simple hydrothermal method and then, Cu₂O was coupled onto the surface of graphene/rutile TiO₂ to form Cu₂O/graphene/rutile TiO₂ nanorod（C GT） composites via a chemical bath deposition process. It was found that the introduction of graphene and Cu₂O has little effect on the morphology of TiO₂ nanorods with average dimensions of 140 nm（length）×30 nm（diameter）. A red shift of light absorption edge and more absorption in the visible light region were observed for the resulted ternary samples compared with TiO₂ and graphene/TiO₂ composites. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light irradiation, which showed 2.8 times corresponding enhancement of the degradation efficiency for the ternary composites compared with TiO 2. The highest photocatalytic performance was observed over CGT composites with 0.0025 M concentration of Cu₂O precursor.The nanocomposite of α-Fe₂O₃ and N doped TiO₂（Fe₂O₃/N-TiO₂） was prepared via calcining a homogeneous mixture of titanium nitride（TiN） and ferric hydroxide colloid（Fe（OH）3 gel） at 500 oC in air atmosphere. The as-prepared samples were characterized by XRD, FE-SEM, TEM, UV-DRS, XPS, photoelectrochemical and photocatalytic measurements. The optical absorption investigation indicates superior visible light absorption property was achieved for the resulted Fe₂O₃/N-TiO₂ nanocomposites. Remarkably improved visible light photoelectron-chemical performance was confirmed and the maximum photoconversion efficiency increased about 4.7 times as a result of the modification of TiO₂. Furthermore, the developed Fe₂O₃/N-TiO₂ nanocomposites present enhanced photocatalytic acticity towards the degradation of methylene blue（MB）, as 4.5 times and 1.3 times larger than that of TiO₂（P25） and N-TiO₂, respectively. The results presented here demonstrate the simultaneous modification of TiO₂ with N doping and Fe₂O₃ coupling can significantly enhance the visible light absorption and facilitate the photogenerated carries separation.The composites of Cu₂O decorated carbon- incorporated TiO₂ microspheres（Cu₂O/CTMs） was achieved through a two-step route by preparation of CTMs using a flame assisted hydrolysis method and then deposition of Cu₂O on CTMs by a chemical bath process. A red shift of absorption edge and more visible light absorption was observed for the resulted Cu₂O/CTMs composites in the ultraviolet-visible diffuse reflectance spectroscopy. Their effective visible photocatalytic activity and the effect of deposition amount of Cu₂O on the photocatalytic properties were detec ted by the degradation of methylene blue. The Cu₂O/CTMs composites present enhanced photocatalytic activity towards the degradation of MB, as 1.6 times larger than that of CTMs. And the highest photocatalytic performance was observed over Cu₂O/CTMs with 0.03 M concentration of Cu₂O precursor. This work develops a rapid and facile approach for the fabrication of Cu₂O decorated carbon- incorporated microspheres TiO₂ composites and demonstrates it is an efficient route to improve the photocatalytic activity of TiO₂.