Synthesis And Performance Study Of Three Typical And Efficient Photocatalysts

Photocatalysis is considered as a promising technology in the field of environmental protection since it has many advantages such as simple degradation process, low energy cost, easy obtaining of photocatalysts, complete degradation of organic pollutant, no secondary pollution and so on. It exhibits the bright application future and great economic and social benefits for controlling the pollutants in water, soil, and air. Moreover, proper photocatalysts could utilize the natural solar energy to yield hydrogen fuel, which is of great significance for the solution of energy crisis. Herein, we have detailedly and systematically investigated three typical photocatalysts (titanium dioxide, titanate nanotubes, and silver orthophosphate) from a material research perspective.TiO2has two serious problems as a photocatalyst. One is that it cannot absorb visible light due to the wide band gap. Aiming at this problem, we synthesized (Mo, C)-codoped anatase TiO2photocatalyst by a sol-gel process, and its structure, chemical composition, chemical state, morphology, and optical absorption property were characterized in detail. As C has two less valence electrons than O, the substitution of C on the O site acts as a double acceptor. Similarly, Mo has two more valence electron than Ti, so they are double donors. In the (Mo, C)-codoped TiO2case, the electrons on the donor levels passivate the same amount of holes on the acceptor levels, so the induced defect bands will not be effective as carrier recombination centers. It is found that both monodoped and (Mo, C)-codoped TiO2exhibited obvious red-shift of absorption edge and better visible-light absorption behavior than pure TiO2-The photocatalytic results indicated that (Mo, C)-codoped TiO2with proper doping concentration showed higher photocatalytic activity than pure, Mo monodoped, and C monodoped TiO2. The other problem of TiO2is its low photocatalytic efficiency. For this case, we synthesized the graphene/rod-shaped TiO2nanocomposite by a novel and facile solvothermal method. The as-prepared graphene and graphene/rod-shaped TiO2nanocomposite were characterized in detail. The photocatalytic activities of graphene/rod-shaped TiO2, graphene/spherical TiO2nanocomposites, and commercial TiO2(P25) were compared. Results indicated that the graphene/rod-shaped TiO2showed higher photocatalytic activity. Among a series of graphene/rod-shaped TiO2nanocomposite samples, the0.48%graphene/rod-shaped TiO2nanocomposite exhibited the best photocatalytic activity, and its photocatalytic reaction rate constant is2.1times of that of P25. Higher BET surface area and the contribution of the reduced charge recombination rate caused by a high electronic mobility of graphene are considered as the reasons for enhanced photocatalytic activity of graphene/rod-shaped TiO2nanocomposite.There are three main shortages in the field of titanate nanotubes:long total hydrothermal reaction time, unclear impression of intermediate products, and wide band gap of titanate nanotubes. Aiming at these problems, we carried out some corresponding investigations. First, the traditional hydrothermal method for synthesis of titanate nanotubes was modified, and the total hydrothermal reaction time of forming a matured network of titanate nanotubes was successfully decreased. Second, the morphological features and structural characteristics of the intermediate products (sheet-like structures) were studied systematically. Results indicated that three types of sheet-like structures, including layered structure, multi-layer nanosheets and single-layer nanosheet, were observed. The structural characteristics of these sheet-like products were determined by high-resolution structure analysis. It is found that the top/bottom surface of these sheet-like structures is the (010) plane of H2Ti3O7. Third, the (B, N)-codoped titanate nanotubes (TNTs) have been prepared via a simple hydrothermal route. Such (B, N)-codoped TNTs showed a decrease in band gap energy as compared with the undoped TNTs, and maintained its nanotube morphology. The codoping of B and N could decrease the number of carrier recombination centers by the charge equilibrium mechanism. The effect of the doping amounts of B and N on the photocatalytic activity of TNTs was studied. Among the as-prepared samples,(1%B,1%N)-codoped TNTs exhibited the best photocatalytic activity, and its photocatalytic degradation ratio is twice as high as that of the undoped TNTs.Ag3PO4as a visible-light active photocatalyst was discovered in the year of2010. Due to its higher photocatalytic activity compared to other visible-light active photocatalysts, the finding of Ag3PO4is considered as a breakthrough in the field of visible-light active photocatalysts. Therefore, it is of great value to detailedly and systematically investigate the Ag3PO4photocatalyst. Nowadays, the research of Ag3PO4photocatalyst is still in the primary stage, and it needs further study. Our work demonstrated that Ag3PO4photocatalyst could be synthesized in the organic N,N-dimethylformamide (DMF) solvent. A series of Ag3PO4and reduced graphite oxide sheets (RGOs) nanocomposites have been fabricated by a facile chemical precipitation approach in DMF solvent without any hard/soft templates. The effect of Ag3PO4/RGOs ratio on the photocatalytic activity was studied. It is found that the Ag3PO4/2.1wt%RGOs showed the best photocatalytic activity, and its photocatalytic reaction rate constant nanocomposite is3and2times of that of pure Ag3PO4nanoparticles for the degradation of methyl orange and methylene blue, respectively. Furthermore, RGOs greatly enhanced the stability of Ag3PO4. On the other hand, we carried out some investigations on the controlled synthesis of Ag3PO4. A novel and rapid strategy has been developed to synthesize the tetrahedral Ag3PO4with the help of surfactant oleic acid. The formation mechanism of tetrahedral Ag3PO4is proposed based on time-dependent experiments. Furthermore, we compared the photocatalytic activities of the obtained tetrahedral Ag3PO4and the reported micro-sized spherical Ag3PO4particles. In addition, it is demonstrated that the morphology of Ag3PO4crystals can be controlled by simply adjusting external experimental conditions such as static and ultrasonic conditions, and various new morphologies, such as branched, tetrapod, nanorod-shaped, triangular prism-shaped Ag3PO4crystals were prepared in the mixture solvents of DMF and H2O. The morphological effect on the photocatalytic activity of the obtained Ag3PO4crystals has been investigated. Photocatalytic results indicated that the branched Ag3PO4and nanorod-shaped Ag3PO4photocatalysts exhibited higher photocatalytic activities than the reported irregular spherical Ag3PO4particles. Among these samples, the branched Ag3PO4crystal with porous structure showed the highest photocatalytic activity among these Ag3PO4crystals with multiform morphologies, and the photocatalytic rate constants of branched Ag3PO4are2.8and4times of that of irregular spherical Ag3PO4for degradation of methylene blue and rhodamine B dye solutions under visible light irradiation, respectively.