Efficiency And Mechanism Of Photocatalytic Treatment For The Heavy Metals By Modified Nano-TiO₂

With the continuous development of industry,the pollution of heavy metal in our country becomes more and more serious.Among them,the wastewater containing chromium has a large amount of emissions and high toxicity.The way to dispose the wastewater containing chromium has become the focus of domestic and foreign scholars.Nano-TiO₂ as a highly efficient photocatalyst,has been widely used in the field of heavy metal wastewater treatment.Because of the low efficiency and the low utilization rate of light,in this paper,the modification of nano-TiO₂ was established.And the application of powder and supported modified TiO₂ were studied.The factors affecting the preparation of TiO₂ were studied by orthogonal experiment.The factors included the concentration ratio of reagents and the calcination temperature.In the condition of FeCl₃ being used as iron source and NH₄F being used as fluoride source,the effect of different Fe and F doping amount on the photocatalytic degradation rate of Cr???were investigated.The chemical reaction kinetic model was established.Scanning electron microscopy,X-ray energy spectrum analysis,and X-ray diffraction were used to characterize and analyze the Fe/F co-doped TiO₂.The experimental results showed that the optimum preparation conditions were as follows,the ratio of tetrabutyl titanate,water,absolute alcohol and glacial acetic acid was 3:5:14:2,the calcination temperature of 450?,and the doping amount of Fe and F was 0.60%?mole ratio?and 2.00%?mole ratio?,respectively.Through the single factor experiments,the effect of powder Fe/F co-doped TiO₂ on photocatalytic degradation rate of Cr???under different reaction conditions was investigated.The experimental results were as follows,with the increase of the Cr???concentration,the photocatalytic degradation decreased and the reaction rate decreased.With the increase of the dosage,the photocatalytic increased at first and then decreased.And with the increase of the original pH,the photocatalytic degradation decreased.When the reaction conditions were that when the concentration of Cr???in the raw water was15mg/L,and the original pH was 6,and the dosage was 1g/L,the photocatalytic degradation rate was up to 55%.The effects of different original pH,HRT and the dosage of formic acid on the operation process of supported Fe/F co-doped TiO₂ reactor were optimized with the single factor experiments and the response surface method.The experimental results showed that with the increase of formic acid dosage,the increase of HRT,the reduction of the original pH,and the decrease of Cr???concentration in the raw water,the photocatalytic degradation increased.When the concentration of Cr???in the raw water was 15mg/L,the optimal working conditions of the supported Fe/F co-doped TiO₂ reactor were obtained with the original pH of 6,HRT of 2h,and the dosage of formic acid of 1g/L.