Preparation Of GR/TNT Composite Photocatalyst And Study On Its Properties For Degradation Of Phenol And Cr(?) In Water

With the rapid development of modern industry,the pollution of water environment is becoming increasingly serious due to the discharge of organic pollutants and heavy metal ions that are chemically stable,biologically toxic,and difficult to be degraded.Ti O2 is one of the widely used semiconductor photocatalysts,but the disadvantage of Ti O2 is that it can only absorb and use ultraviolet light that accounts for about 4% of the total solar energy.In addition,photo-generated electrons and holes are easily to recombine.Therefore,it will be the key to the application of Ti O2 in actual production is how to solve the recombination rate of photo-generated electrons and holes as well as increase their absorption in the visible light portion,to increase the photocatalytic effect.Compared with Ti O2,titanium dioxide nanotubes(TNT)has improved photocatalytic property and can effectively degrade pollutants in water.Graphene has a large specific surface area,excellent electrical and thermal conductivity,and a high rate of electron migration.Therefore,it has practicalapplication value for improving the performance of photocatalysts.In this paper,P25 was used as the source of titanium,TNT was prepared by concentrated alkali hydrothermal method and calcined;Graphite oxide(GO)was prepared by Hummers method using graphite as raw material,and then ultrasonically converted to graphene oxide.GR/TNT composite photocatalyst was obtained by loading the graphene on TNT while reducing graphene oxide by hydrothermal method.The physicochemical properties of as-prepared GR/TNT composite photocatalyst was characterized and analyzed by XRD,SEM,EDS,FTIR and UV-Vis spectroscopy,and their photocatalytic activity was determined on target pollutants(phenol and Cr(?))under UV and visible light irradiation.The effects of different factors on the degradation of phenol and Cr(?)by GR/TNT were investigated,and the photocatalytic mechanism was analyzed.(1)GR/TNT composite photocatalyst was prepared by using P25 and graphite as raw materials.Characterization resulted indicated that graphene oxide was reduced to GR by hydrothermal method,and combined with TNT through Ti-O-C chemical bond.The band gap of GR/TNT decreased from3.2e V of TNT to 1.38 e V,broadening its visible light absorption range.(2)In the photocatalytic degradation experiment of phenol,when the UV light source was 11 W,2.5% GR/TNT photocatalyst worked well,doping with GR could suppress the recombination rate of photo-generated electrons and holes,thereby increasing the photocatalytic efficiency.The phenol degradationrate could reach 97.04% after 120 min when the dosage of 2.5% GR/TNT photocatalyst was 0.5 g/L,the p H of the solution was 6.5,the phenol concentration was 10 mg/L,and the H2O2 amount was 0.2 m L.In addition,the photocatalytic effect of phenol was better under weakly acidic conditions.The phenol degradation rate could reach 98.17% after 150 min under visible light(500 W)irradiation when the dosage of 2.5% GR/TNT photocatalyst was 0.5g/L,the p H of the solution was 6.5,the phenol concentration was 10 mg/L,and the H2O2 amount was 0.2 m L.Degradation reaction of phenol on GR/TNT composite photocatalyst followed the first-order reaction kinetics(R2?0.95).The appropriate amount of H2O2 could improve the photocatalytic effect of phenol.And GR/TNT had better stability and repeatability.(3)In the photocatalytic degradation experiment of Cr(?),when the UV light source was 250 W,the GR/TNT composite photocatalyst had the best effect while the GR doping amount was 5%.The Cr(?)degradation rate could reach 95.74% after 30 min photoreaction when the dosage of 5% GR/TNT photocatalyst was 0.5 g/L,the p H of the solution was 2,the Cr(?)concentration was 10 mg/L.The p H value was an important factor affecting the degradation rate of Cr(?),The stronger the acidity was,the better the degradation effect was.The Cr(?)degradation rate could reach 99.53% after150 min under visible light(500 W)irradiation when the dosage of 2.5%GR/TNT photocatalyst was 0.5 g/L,the p H of the solution was 2,the Cr(?)concentration was 10 mg/L,and the EDTA amount was 0.2 mmol/L.Degradation reaction of Cr(?)on GR/TNT composite photocatalyst followed the first-order reaction kinetics(R2?0.95).Inorganic anions inhibited Cr(?)reduction rate,whereas the small molecule organic acid could promote the Cr(?)reduction rate.(4)In the photocatalytic degradation experiment of mixed solution of phenol and Cr(?),a 250 W UV lamp was used as the light source.When the dosage of 2.5% GR/TNT was 0.5 g/L,the p H value was 3,and the phenol concentration and Cr(?)concentration was both 10 mg/L,the degradation rate of Cr(?)reached 97.17% after 15 minutes of photoreaction,while under the same condition,the degradation rate of Cr(?)was only 65.42%;after 30 minutes of light reaction,the degradation rate of phenol could reach 96.90%,under the same condition,the degradation rate of phenol was 83.88%.In the process of photocatalytic degradation of mixed solution,Cr(?)reduction and phenol oxidation were synergistic effects.Inorganic anions inhibited the degradation of phenol and Cr(?),EDTA promoted the degradation of Cr(?),and inhibited the degradation of phenol.