Research On Preparation And Photocatalytic Activity Of High Effective P25-based Photocatalysts

As environmental pollution being increasingly serious,pollution control and management has become the major issue that needs to be solved.Among various technologies of pollution regulation,titanium dioxide?TiO₂?,as a representative semiconductor photocatalytic material,is an ideal cleaning material for environmental pollution due to its unique properties.The commercial P25 is a kind of TiO₂ powder.These commercial titania nanoparticles have been widely used as photocatalysts in photochemical reactions due to their high photocatalytic activity.Despite many benefits of using TiO₂ to treat water,there are some disadvantages that hinder commercialization.Due to the band gap energy of TiO₂,it can just be activated by UV light of which the portion in sunlight is only 4-5%.Moreover,recombination of photo-generated electronhole pairs also remains to be resolved.In view of the above problems,to improve the photocatalytic activity of titanium dioxide and stability of novel photocatalyst,a serious of commercial P25-based composite photocatalysts are prepared to reduce the recombination rate of photo-generated electron-hole pairs and extend photo-activity of titania into visible light region to improve the utilization efficiency of solar energy.The main studies of this paper are as follows:Firstly.Cu-P25-graphene?CPG?nanocomposite is fabricated through hydrothermal method at relatively low temperature.The technique used for P25-graphene?PG?binary composite is firstly prepared by P25 and graphite oxide?GO?,and then Cu²⁺ ions are impregnated into PG composite.As the results showed,the CPG nanocomposites possess the extended light absorption in visible light and better charge separation capability as compared to the pure P25 and PG system.Moreover,Cu²⁺ content exhibites an obvious influence on photocatalytic activity and the optimal graphene loading content is determined.At the optimal Cu²⁺ ions concentration?4 mM?,the prepared composite?CPG-4?shows the highest photocatalytic activity.The degradation rate of Methylene Blue?MB?for CPG-4 can reach 98.2% under the visible light.The corresponding hydrogen evolution rate of CPG-4 is 7.9 times than that of pure P25.It is concluded that the synergistic effects of Cu²⁺ ions and graphene narrow the band gap of TiO₂ and promote charge separation,which plays significant roles for the enhancement of photoactivity of CPG composite catalysts.The effects of pH values of MB solution for photocatalysts have also been investigated.The results confirm that the optimum pH value is found to be 7.Secondly,the commercially available TiO₂ Degussa P25 is modified using a simple technique to produce a visible-light-active indium and carbon doped P25 catalyst?In₂O₃/C-P25?.The modified photocatalysts have been successfully obtained by thermal heating method.The as-prepared samples are characterized on their structure,morphology and surface chemical composition to prove that indium and carbon ions are incorporated into the TiO₂ matrix for the substitution of indium and carbon for titanium and oxygen respectively in the TiO₂ lattice.The indium and carbon co-doping reduces the energy of photon transition and narrows the band gap of TiO₂.Moreover,the emission region also shows a certain red-shift,which is attributed to the effect of surface states and impurity levels.Also,doping of indium and carbon can inhibit the recombination of excitons and hence further improve the photo-activity of the catalyst,thus the PL intensity of co-doped P25 is significantly reduced.In this section,the photocatalytic activities of all prepared catalysts are evaluated by the degradation of organic dyes including Methylene Blue?MB?and Reactive Red 4?RR4?under visible light irradiation.In₂O₃/CP25 shows the highest degradation rate of organic dye when the loading of In³⁺ ions on P25 is 15%,with an enhancing degree much higher than that of single-component of doping.In addition,the influence of initial pH values on the photocatalytic degradation of MB and RR4 using 15% In₂O₃/C-P25 catalyst is also investigated.The results manifest that the highest degradation of MB is at pH 12 while RR4 is at pH 3,which is due to the influence of isoelectric point of the In₂O₃/C-P25 composite.