Study On The Zn-Fe Modified Carbon Nanotubes Catalyst And Its PH Adaptability

Deep treatment and reuse of wastewater is an important way to solve the water resources crisis.Catalytic ozonation as an advanced oxidation technology has been widely concerned.Catalytic ozonation technology will be restricted by many factors in the process of practical application,among which the pH value of the solution is the most significant one.The key to the further promotion of catalytic ozonation technology is to develop a catalyst with high pH adaptability and explore the mechanism of its pH adaptability.In this study,supported catalysts of different materials with different active components?iron,zinc,Zn-iron?were prepared,different amounts of ozone and different amounts of catalysts on the catalytic effect were also explored.Then under the condition of the optimal catalytic ozonation to explore the pH adaptability of zinc iron modified carbon nanotubes by using DBP as the model organism.The pH adaptability of CNT-Fe/Zn was studied through the main degradation mechanism,quantitative analysis of the reactive oxygen species?ROS?,the effect of tertiary butyl alcohol and inorganic ions on the catalytic ozonation,active site and the catalyst characterization.Finally,the stability and ecotoxicity of the catalyst were tested.The main conclusions are as follows:?1?Modified carbon nanotubes were optimized and prepared,and the optimal catalyst was characterized.The carbon nanotubes load zinc,iron and zinc-iron were prepared by impregnation calcination method to explore its catalytic ozonation performance.The catalytic performance of CNT-Fe/Zn was better than which of the CNT-Fe and CNT-Zn.The catalytic ozonation degradation of DBP has achieved high removal rate whether it is acidic,alkaline and neutral conditions.The removal rate promoted by CNT-Fe/Zn increases 22%-52%compared with the degradation of DBP under sole ozone conditions in a wide pH range.The catalytic effect of CNT-Fe/Zn was the most significant under pH 4,and the removal rate of DBP could reach 73.21%after 30min.The specific surface area and isoelectric points of CNT-Fe/Zn were 198.7619m²/g and 12.2,respectively.The SEM and XRD characterization confirmed the successful load of the Zn Fe₂O₄.?2?The influencing factors of DBP degradation was studied and the optimal reaction conditions were determined.The ozone dosing quantity affect the catalytic ozone degradation performance of DBP by CNT-Fe/Zn.With the improvement of the ozone dosing quantity,the removal efficiency of DBP rises gradually,but when the ozone dosing quantity is more than 20mg/L,the removal rate of DBP tended to a constant value.Under neutral conditions,when the catalyst dosage was 10 mg/L,20 mg/L,50 mg/L and 100 mg/L,respectively,the removal rates of DBP were 26.21%,35.02%,58.30%and 61.03%,respectively,after 30 min reaction time.The optimum experimental conditions of this study were the ozone dosing quantity 20 mg/L,pH 4,catalyst dosing quantity 50 mg/L based on the experimental effect and economic considerations.After 30 min of reaction,the removal rate of DBP can reach 72.41%after 30 min,which is 53%higher than that of the DBP degradation under sole ozone conditions.?3?The pH adaptive mechanism of CNT-Fe/Zn were explored.The main catalytic mechanism of the system was preliminarily determined by the addition of inorganic anion and tert-butanol?TBA?combining adsorption reaction.The addition of chloride ion,phosphate ion and TBA greatly inhibited the catalytic ozonation process.Among them,the inhibition effect of TBA was the most significant.The contribution rate of adsorption to DBP removal was relatively low,about20%.Therefore,the oxidation of free radicals?hydroxyl radicals?is the main influencing mechanism in this study.According to the ROS quantitative analysis,the addition of catalyst greatly increased the production of hydroxyl radical and hydrogen peroxide in the solution,and the production of both was higher than that of ozone alone.There are a large number of oxygen-containing groups on the surface of CNT-Fe/Zn,in which the concentration of surface hydroxyl has a good linear relationship with the apparent first-order reaction kinetic constant(K_obs),indicating that the surface hydroxyl provides a large number of active sites for the catalyst.Under the co-existence of CNT-Fe/Zn and ozone,the R_ct value of the system was 23.04,which was 5.61 times that of the sole ozone system,indicating that the catalyst greatly improved the ozone utilization rate in the reaction process.Carbon nanotubes have a good synergism with Zn Fe₂O₄.Carbon nanotubes enhance the electron transfer in the reaction process and reduce the exudation of metal ions.The catalyst has good stability and ecological friendliness.In conclusion,under the condition of acidic,neutral and alkaline,carbon nanotubes and franklinite by impregnation calcination method combining,oxygen-containing groups on the surface of CNT-Fe/Zn the metal ions of franklinite provide a large number of active sites for the catalyst activity,promoting the transformation of ozone into hydroxyl radicals.Under acid condition,the generation of large amounts of hydrogen peroxide.Thus the production rate and yield of hydroxyl radical were further increased,so the best effect of catalytic ozonation of DBP was obtained under acidic conditions.