| With the continuous development of social economy,the problem of environmental pollution is becoming increasingly serious.Among a large number of control technologies for environmental pollution,the semiconductor photocatalyst represented by TiO2 is an ideal cleaning material for environmental pollution.In this paper,the crystal structure and electrical properties of TiO2 are briefly demonstrated.Moreover,various preparation and modification methods of TiO2 are summarized.Finally,the application of TiO2 in ultraviolet absorption and photocatalysis is introduced.In order to improve the photocatalytic performance of TiO2 and its stability,which is in view of the existing defects of TiO2,the main contents of this paper are as follows:Firstly,SiO2/P25(SP)composites doped with different contents of cerium are prepared by a hydrothermal process at a relatively low temperature in this experiment.The resulting Ce-SiO2/P25(CSP)composites are successfully characterized by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),high resolution transmission electron microscopy(HRTEM),N2-physisorption,UV-vis diffuse reflectance spectroscopy(DRS),and photoluminescence spectroscopy(PL).The photocatalytic activities of the as-obtained catalysts are evaluated for the degradation of organic dyes,including Methylene Blue(MB)and Reactive Red 4(RR4),under visible-light irradiation.The best results are obtained for a cerium loading of 5 mM.The CSP-5 nanoparticle shows 91.86%decomposition of MB and 88.79%decomposition of RR4 in the liquid phase at room temperature under visible-light irradiation in a photoreactor,and the corresponding hydrogen evolution rate is 2.315 mmol g-1,which is more efficient than that of pristine P25.Remarkably enhanced activities towards the photo decomposition of several organic compounds are observed depending on the synergistic effect between silicon and cerium.The Ce-SiO2/P25 structure leads to efficient light harvesting into the visible-light region by forming new energy levels inside the nanoparticles and then electron-hole recombination could be effectively inhibited.The BET surface area measurement is used to provide an insight into the enhanced photocatalytic activity of the CSP composites,which is understood to be because of the relative enhancement of the adsorption of organic molecules on the photocatalyst surface.In addition,the effect of initial pH values on the photocatalytic degradation of different dyes using CSP-5 is investigated.Finally,a good recyclability of CSP-5 is demonstrated compared to that of pristine P25.Herein,the photocatalytic mechanism has been concretely explained.Secondly,Ag nanoparticles are loaded on the suface of TiO2-graphene(P25-GR,PG)nanocomposite to obtain the Ag-TiO2-graphene(Ag-P25-GR,APG)through two-steps hydrothermal method.Using different methods including XRD,XPS,SEM,TEM,UV-vis DRS and PL to characterize the crystalline form,micromophology,suface chemical composition,optical absorption and photoluminescence of the prepared samples.The results show that Ag nanoparticles have been dispersed uniformly on the surface of PG with metallic state.Compared with the single-component materials,the absorption spectra of the ternary APG nanocomposites extend to the visible light region and the charge carrier transportion efficiency is significantly improved.It can be confirmed that the surface plasmon resonance(SPR)has a certain effect on the photocatalytic performance via the experiment for the degradation of organic dye.The optimum load of Ag in APG samples is 2 mM,and the degradation rate of MB and RR4 for APG-2 sample can be up to 86%and 84%respectively.The enhanced photocatalytic performance is based on the existence of graphene and SPR effect,resulting in longer life time of photo?generated electron-hole pairs and faster charge transfer rate.This study provides a theoretical basis for the preparation of highly efficient and stable ternary graphene-based photocatalytic materials. |
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