| TiO2 can effectively degrade aqueous organic compound,however,TiO2 has narrow spectral response range from xx to xx,and thus its photocatalytic activity was limited at other spectral band.Modification of TiO2 was an effective way to expand its spectral response range to visible light and enhance its photocatalysis strength.Different methods have been applied for the synthesis of TiO2.Among them,sol-gel method was popular because of its simple operation and high yield.Recently,the modification of TiO2 was mostly conducted in the sol stage rather than in the gel stage,and few attention has been paid to the application of the intermediate,titanium-based xerogel.This paper systematically studied the modification of TiO2 at different stages of the sol-gel process for visible light responsive photocatalysis.The resultant TiO2 gel exhibited good performance on adsorption and flocculation,which extended the application of TiO2-based materials.Firstly,the surface area and active sites of TiO2 was modified through making mesopores on the surface of TiO2.The increases in surface area and active sites resulted in the enhancement of its photocatalytic performance.Mesoporous TiO2 was usually synthesized by template method in the sol stage.However,mesopores collapse often occurred when the template was removed by calcination.In the study,Zr and Ce were doped and a novel photocatalyst(ZrO2-CeO2-TiO2)was synthesized.The results showed that Zr doping could enhance the thermal stability of the targeted material.After calcination under the temperature ranging from 400? to 600?,mesopores in ZrO2-CeO2-TiO2 all exhibited long-range order.The specific surface area of ZrO2-CeO2-TiO2 was 194 m2/g,which was three times larger than that of TiO2.Ce doping could enhance the visible light response of the resultant material.The photocatalytic performances of four catalysts were evaluated.The removal efficiency of RhB was up to 90%,followed the order that mesopore ZrO2-CeO2-TiO2>mesopore CeO2-TiO2>CeO2-TiO2>TiO2.Furthermore,the effect of the surfactant concentration on the structure and performance of mesopore ZrO2-CeO2-TiO2 was investigated.Under low surfactant concentration,mesopore ZrO2-CeO2-TiO2 exhibited worm-like structure with low degree of crystallinity.As the surfactant concentration increased,the structure of mesopore ZrO2-CeO2-TiO2 became more orderly and the degree of crystallinity was improved.Further increase in the concentration of surfactant caused the decreases in degrees of crystallinity and order.the degrees of crystallinity and order were both considered ideal at optimal surfactant concentration.The photocatalytic performances of mesopore ZrO2-CeO2-TiO2 synthesized under different surfactant concentrations were evaluated by degradation of Acid orange 7(AO7)and the material synthesized under the concentration of 6 ?mol/L surfactant exhibited the best performance.To our knowledge,little study has been done on the modification of TiO2 in the gel stage.TiO2 xerogel was doped by nonmetal(AO7)though adsorption and flocculation,then calcianed 4 h at 400?.In the study,three photocatalysts,NH3-TiO2,Tu-TiO2,AO7-TiO2 were also synthesized by alternative method where modification was made in the sol stage.the structure and performance of the above-mentioned photocatalysts were investigated.The crystal particle was smaller in AC-TiO2(14.1 nm),which also exhibited larger specific surface area(128.2 m2/g),smaller average particle diameter(1.02 ?m)and wider band gap(3.01 eV).Subsequently,the photocatalytic properties of the four materials were evaluated.The results showed that after visible light irradiation for 160 min the removal efficiency of AO7 in AC-TiO2 system was up to 93%,which was significantly higher than that in NH3-TiO2 system(20%).Therefore,modification treatment during the gel process not only expanded the functionality of titanium-based material and extended its life,but also improved its photocatalytic performance.Titanium-based xerogel exhibited sound performance for dye uptake with a maximum adsorption capacity of 736 mg/g according to Langmuir model.Furthermore,titanium-based xerogel removed the dye quickly and the adsorption equilibrium can be achieved within 45 s.The pHpzc of the xerogel was 4.8 and electrostatic interactions were deduced to be the main adsorption mechanism.Because of the leveling effect,the initial pH has little influence on the adsorption capacity of titanium-based xerogel.Similar titanium-based xerogel synthesized by changing the ratio of precursors can also be used as a coagulant for the treatment of dyeing wastewaters.Compared with the conventional Fe salt coagulant,the flocs in titanium-based xerogel system were larger and settling velocity was faster.Complete settlement can be achieved within 1 min,the pH of the treated effluent remained unchanged.The effect of the initial pH and the dosage of coagulant on the alga removal were investigated.The results showed that dye removal efficiency of the studied xerogel under the optimal pH condition was better than that of Fe or Al salt coagulant and the removal efficiency of alga in titanium-based xerogel system was up to 94%.the residual sludge was calcinated and can be used as a photocatalyst for the removal of AO7.After visible light irradiation for 160 min with the photocatalyst,the degradation efficiency of AO7 was up to 85%.This study suggested that the modification of titanium based material in gel stage deserves further investigation,it is expected to expand the application of TiO2 as an environmental functionnal material in the field of water pollution control. |
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