Preparation Of Rare Earth Doped TiO₂/Al₂O₃ And Its Photocatalytic Oxidation Performance In Advanced Treatment Of Pulping Wastewater

The photocatalytic oxidation technology of ozone ultraviolet?UV?combination overcomes the shortcomings of single technology.The core of this technology is to develop a highly efficient,stable catalyst,and to determine the high efficiency and low cost process conditions.In this paper,the preparation of the rare earth metal doped nano titanium dioxide?TiO₂?supported active three oxidation two aluminum?Al₂O₃?composite catalyst,and the removal rate of the wastewater discharge indexes during the treatment of baGdsse slurry wastewater were studied,and the technological conditions of the photocatalytic ozonation wastewater were optimized.The rare earth doped nano TiO₂ was prepared by the sol-gel method.The effect of four different rare earth metals on the photocatalytic oxidation ability of TiO₂ catalyst was investi Gdted with chlorophenol?CP-4?as a model pollutant.It was found that different rare earth metals and different concentrations of rare earth metals had different effects on the activity of TiO₂,and the rare earth mixed with rare earth.The order of sex is:2%La>0.5%Gd>1%Sm>0.5%Ce.The spectral response range of TiO₂ is red shift after rare earth doping,and the size of nano TiO₂ particles decreases with the increase of rare earth doping concentration,but most of it is maintained in 8-15nm.After calcination at 500?,the crystal form of TiO₂ is transformed into anatase with high activity,and XRF data shows that the rate of rare earth metal doping rate can reach 100%.Through the free radical and hole quenching experiments,it is found that the doping of rare earth metal reduces the recombination probability of the photogenerated electron hole in one aspect,and on the one hand,it promotes the ability of ozone to produce·OH.In acidic environment,the photocatalytic ozonation of nano TiO₂ is favorable.When pH is 5,the removal rate of COD_Crr is the highest.The pulping wastewater of a baGdsse plant was treated with the best active2%La-TiO₂ catalyst.The catalyst dosage was 6g/L,the ozone concentration 15mg/L,the UV intensity 45W,and pH were 5,and the removal rate of COD_Cr and TOC in the wastewater was 60.1%and 63.9%,respectively.The active Al₂O₃ was used as the nano 2%La-TiO₂ catalyst carrier and CP-4 as the model pollutant.The effects of different catalyst loading methods and different carrier sizes on the activity of the catalyst were investiGdted.The results show that the smaller the Al₂O₃carrier size,the larger the surface area and pore volume of the catalyst,the more the load2%La-TiO₂,the stronger the catalytic activity.The catalytic effect of 2%La-TiO₂/Al₂O₃ by the ultrasonic assisted sol-gel impregnation roasting method is higher than that of the physical impregnation adsorption method.The catalyst can be completely removed before the catalyst is roasted at 500?.The removal rate of COD_Cr is the highest when the material is increased and the mechanical strength of the catalyst is improved.Through the analysis of XRD,XRF,SEM and BET on the catalyst,TiO₂ is evenly distributed on the surface of Al₂O₃and the inner channel,to a certain extent,the specific surface area and pore volume of Al₂O₃are reduced.The pulping wastewater of a baGdsse plant was treated with the best active2%La-TiO₂/Al₂O₃ catalyst.The catalyst dosage was 10g/L,the ozone concentration 15mg/L,the UV intensity 45W,and pH were 5,and the removal rate of COD_Cr and TOC in the wastewater was 74.3%and 69.4%,respectively.The optimum process conditions for the oxidation of pulping wastewater with the best active 2%La-TiO₂/Al₂O₃ are as follows:the catalyst dosage is 8g/L,the ozone concentration is 20mg/L,the flow 1L/min,the ultraviolet light intensity 45W,the pH value of the reaction30min,the removal rate of COD_Cr and TOC are 83.5%and 84.6%respectively,and AOX from 24.6 to 2.9.The effluent was analyzed by GC-MS and FTIR.After treatment under the best technological conditions,most of the orGdnic matter in the water was degraded,and some of the refractory orGdnic compounds were transformed into intermediates to continue to exist in the water in a new form.Through the recycling of the catalyst,it is proved that2%La-TiO₂/Al₂O₃ has strong stability.The removal rate of COD_Cr in wastewater can still reach more than 70%when used seventh times.The XRD,XRF,SEM and BET analysis of the catalyst after multiple use found that with the increase of the number of use of the catalyst,the 2%La-TiO₂ beGdn to partially fall off and the carrier Al₂O₃ part.The specific surface area and pore volume of the catalyst decrease with the collapse of the channel.