Preparation And Photocatalytic Performance Of Ag-N Co-doped TiO₂ Supported Graphene

With the acceleration of industrial process and the rapid increase of population,the problem of water pollution is becoming more and more serious.Taking TiO₂ photocatalyst as representative,the photocatalytic oxidation is recognized as one of the most potential photocatalysts,which is due to generating strong oxidizing active species on the surface of the catalyst and leading to the degradation of water pollutants without secondary pollution under the condition of light excitation.However,owing to the inherent wide band gap and low quantum efficiency of the catalyst,the wider application of TiO₂ was seriously restricted.Aiming at the above problems,the reduced graphene oxide（RGO）was selected as the carrier in paper,the silver and nitrogen are used as target doping for TiO₂.Combined with anaerobic calcination treatment,graphene-loaded titanium dioxide composites（TiO₂/RGO）,silver-doped TiO₂/RGO composites（Ag-N/TiO₂/RGO）,and silver-nitrogen co-doped TiO₂/RGO composites（Ag-N/TiO₂/RGO）were prepared by hydrothermal method.The samples were characterized by XRD,SEM,XPS,Raman,FT-IR and UV-Vis,and so on.The catalytic performance was characterized by using methylene blue（MB）as a simulated pollutant.The main conclusions are as follows:（1）TiO₂/RGO composites with RGO loading of 0.5,1,2,4 wt%were prepared by hydrothermal method using tetrabutyl titanate（TBT）and RGO as raw materials.The results show that the TiO₂ in the TiO₂/RGO sample have mainly anatase phase.The crystal form of TiO₂ will not be affected due to the Graphene loading.However,it can promote the grain refinement and improve the dispersion of TiO₂.Meanwhile,the band gap of TiO₂ turned narrowing due to the loading of graphene and the light absorption edge was shifted from reds to the visible region.Compared with pure TiO₂,the adsorption capacity and degradation efficiency of TiO₂/RGO composites for pollutants were significantly improved.When the graphene loading was 1 wt%,the degradation effect was the best.Under simulated sunlight irradiation for 60 min,85.1%of methylene blue could be degraded,and the photocatalytic degradation rate was about 2.2 times that of pure TiO₂.（2）Ag/TiO₂/RGO composite photocatalysts with 1 wt%reduced graphene oxide loading and 0.5,1,2,4%Ag/TiO₂ mass percentage were prepared by hydrothermal method using Ag NO₃as silver source.The results showed that the TiO₂ in the Ag/TiO₂/RGO sample have anatase phase and presents the sufficient contact among these.The crystal form of TiO₂ cannot be changed with Ag doping,but the growth of TiO₂ particles could be inhibited.Silver doping makes the forbidden band of TiO₂ significantly reduced,and the visible light response range is further expanded.The Schottky barrier formed between the two and the good contact between silver and RGO effectively inhibited the recombination of photogenerated electrons and holes.Compared with TiO₂/RGO composites,Ag/TiO₂/RGO composites have higher photocatalytic activity.When the Ag doping ratio is 2 wt%,the degradation effect is better.Under simulated sunlight irradiation for60 min,92.2%of methylene blue can be degraded,and the photocatalytic degradation rate is about 1.4 times that of pure TiO₂/RGO composites.（3）Ag-N/TiO₂/RGO composites with reduced graphene oxide loading of 1 wt%,silver doping amount of 2 wt%and N/TiO₂ mass percentage of 10,15,20%were prepared by hydrothermal method using CH₄N₂O as nitrogen source.The results show that Ag-N/TiO₂/RGO has a clear layered structure.The TiO₂ in all samples has anatase phase,and the nitrogen doping has mildly effect on the grain size of the composites.Meanwhile,there are two states of chemical adsorption and substitution of TiO₂ lattice oxygen in Ag-N/TiO₂/RGO composites.Compared with TiO₂ and N/TiO₂/RGO,the light absorption edge of Ag-N/TiO₂/RGO composite becomes obviously red shifted.Under simulated sunlight irradiation for 60 min,Ag-N/TiO₂/RGO composites have higher degradation rate than TiO₂ and TiO₂/RGO composites,and the photocatalytic degradation rate further promotes with the increasing of nitrogen doping amount.The degradation rate of Ag-N/TiO₂/RGO composites with 20 wt%nitrogen doping is 41.2%.