Preparation Of Titanium-Based Compounded/Doped Nanomaterials And Their Photocatalytic Performance

With the increase in environmental pollution, and the yearning of the people building green and pleasant home, there is an urgent need to find a technology to treat the pollutants wih high-efficiency, low prices and the prospects for industrial applications. Semiconductor photocatalysis is one of the most promosing destructive technologies among the advanced oxidation processes (AOPs), because it can make use of solar energy to lead to the total mineralization of most of the organic pollutants that exist in air and aqueous systems. Among the catalysts utilized for photocatalysis, the most competitive nanoparticle is titanium dioxide because of its high oxidative power, photostability, low cost, and nontoxicity. However, the degradation experiments based on TiO2were mainly carried out in suspensions mediated by powder species. In this case, technical problems arising from hard particle-fluid separation after photocatalytic reaction, difficult reuse and costly post processing limit its industrialization. Although, building the heterogeneous systems based on TiO2film or one-dimensional materials with large aspect ratio can effectively solve the problem, low quantum efficiency of the catalyst and limited to UV excitation need further improvement. Therefore, how to improve the photocatalytic property of TiO2-based nanomaterials by inhibiting electron-hole recombination and enhancing the visible light response is still an urgent problem.The innovationes and specific researches in this paper include the following aspects:1. Fabrication of RGO/TiO2films and their photoelectrocatalytic (PEC) performance investigation. In this secton, RGO was obtained by the reduction of graphene oxide (GO) synthesized via Hummers method and creatively applied in photoelectrocatalytic system. GO/TiO2composite prepared by mixing P25and GO was coated on the FTO substrate via a simple doctor-blade technology to prepared GO/TiO2film. RGO/TiO2was obtained when the GO/TiO2film was subjected to the reduction and annealing treatments. The degradation results suggested that the addition of RGO in the composite remarkably enhanced the PEC degradation efficiency. Compared with pure TiO2film, approximately four-fold and five-fold enhancement in the PEC degradation rate toward rhodamine B (RhB) and acid orange Ⅱ (AO-Ⅱ) was obtained over the optimized RGO/TiO2film. PL and EIS measurements suggested that the addition of RGO could inhibit to a large degree the electron-hole recombination on the surface of catalysts and significantly decrease the electronic charge transfer resistance within the film. Furthermore, recycling experiments revealed that the RGO/TiO2film was stable and could be used repeatedly with the retaining of high efficiency and strong adhesion to the substrate even after ten runs.2. Fabrication of visible light response iodine doped TiO2film electrodes and their PEC performance investigation. Iodine-doped TiO2nanocrystallites (I-TNCs) film with extended response to visible light and mesoporous nanocrystalline framework electrodes were firstly prepared with iodine-TiO2nanocrystallites by simple doctor-blade technology and successfully utilized for pollutants removal. The SEM image revealed that film was relatively smooth and no obvious crack was observed. RhB and1-naphthol (1-NP) were selected as the target substances. Under an optimized I/Ti doping ratio of2.5mol%, the PEC performance of the film electrode based on I-TNCs is significantly better, with the RhB degradation efficiency of92%, which was nearly2-fold faster than that of the film electrode based on undoped TNCs. In the1-NP degradation experiment, the main degraded products of1-NP were analyzed by GC-MS and some alcohols and acids were observed, which further confirmed the efficient degradation performance of I-TNCs film electrode. According to the recently published papers, the phenomenon can be ascribed to the following reasons:(i) the presence of iodine causes enhanced light absorption in the interval between400to650nm, which leads to the intensified visible light utilization; and (ii) the introduction of iodine also makes an increase of the specific surface area as well as the number of hydroxyl groups of the catalyst, thus providing favorable conditions for substrate adsorption and degradation.3. A simple hydrothermal method has been firstly developed for syntheses of uniformly decorated Ag/TiO2nanowires without the addition of template or surfactant. It is worth noting that the formation of TiO2nanowires and uniform deposition of silver species on their surface were simultaneously achieved during the hydrothermal treatment. The TEM images demonstrated that the TiO2nanowires process smooth surface with the diameter of50-300nm and lengths up to several micrometers. A typical TEM image of the obtained Ag/TiO2evidenced that Ag species with the diameter of5-10nm were deposited on the surface of TiO2nanowires with little aggregation. Rhodamine B (RhB) and acid orange II (AO-II) were selected as the target substances. The experiments based on the samples subjected to different post treatments, this is, varying the pH of washing solution and the calcining temperature, were carried out and the results revealed that the photocatalytic performance of the samples was largely depended on post treatment processes conducted and the Ag contents. As compared to pure TiO2nanowires, approximately2-fold and4-fold enhancement in the photocatalytic degradation rate toward RhB and AO-II was obtained over the optimized Ag/TiO2nanowires (i.e. pH=1, calcined at600℃, Ag/TiO2=6mol%). The enhanced photocatalytic activity was mainly attributed to existence of the Ag species (Ag2O) on TiO2surface, which could act as an electron acceptor, thus effectively inhibit the photogenerated electron-hole recombination. Besides, the formation of anatase/TiO2(B) interface heterostructure after calcining the Ag/TiO2nanowires facilates the transfor of electron from anatase TiO2to TiO2(B). In this case, the charge recombination was effectively suppressed and thus dye degradation was significantly enhanced.