Synthesize Of Mesoporous Ceria Based Materials And Mechanism Of Organic Compounds Degradation

In this thesis,a series of ordered mesoporous ceria（CeO₂）based nano catalytic materials were prepared by microwave-assisted soft template method,and disordered mesoporous CeO₂was prepared by biological template method.By means of X-ray diffraction（XRD）,N₂-adsorption desorption,Scanning Electron Microscopy（SEM）,the regulation of preparation conditions on the morphology,structure and properties of CeO₂ was studied,and the formation mechanism of ordered mesoporous materials prepared by soft template method and disordered mesoporous materials prepared by biological template method was clarified.Meanwhile,the catalytic wet peroxide（CWPO）systems were used to degradate the organic matter in the acrylonitrile wastewater.The catalytic activity,selectivity and stability of the material were evaluated,and the mechanism of the degradation of organic matter by mesoporous CeO₂ based material in CWPO system was clarified.This article consists of five parts as follows:（1）Based on the mechanism of synergism,ordered mesoporous CeO₂ was prepared by microwave-assisted method with cerium nitrate as precursor and PEO-PPO-PEO（F127）as soft template.The mechanism of microwave-assisted soft template method for the formation of mesoporous structure was proposed.The performance and mechanism of mesoporous CeO₂ were revealed by CWPO degradation test of organic matter in acrylonitrile wastewater.Results showed that 5mmol cerium nitrate with 2g F127 reaction for 60min under100℃,then calcination at 550℃for 6h,mesoporous CeO₂ with regular shape and spherical particles was obtained.The specific surface area is 350.1m²/g,and the average pore diameter is 9.06nm.Sulfuric acid can significantly improve the surface acidity of CeO₂.The adsorption mechanism of CeO₂ includes electrostatic and surface complexation,which is chemical adsorption.In the CWPO catalytic degradation test,the COD removal rate of commercial CeO₂ is 35.6%,while that of acidified mesoporous CeO₂ is 89.3%.（2）Based on the oxide doping theory,the mesoporous molecular sieve composite CeO₂-SBA-16 was prepared by microwave assisted heating with cerium nitrate and sodium silicate as raw materials and F127 as template.The prepared CeO₂-SBA-16 was used in microwave assisted wet catalytic oxidation（MW-CWPO）to degrade acrylonitrile wastewater,and its adsorption catalytic performance and mechanism were clarified.Results showed that the specific surface area of the material is 317.5m²/g and the average pore diameter is 6.937nm.The adsorption equilibrium of CeO₂-SBA-16 is achieved in 60 minutes,and the COD adsorption rate is 51.2%.In the catalytic test,when the dosage of CeO₂-SBA-16 is 1.0g,the COD removal rate of acrylonitrile wastewater can reach more than 80%.（3）Based on the principle of plasmon resonance,on the basis of ordered mesoporous CeO₂,Ag/Ag Cl/CeO₂ was prepared by deposition-precipitation and photoreduction.The catalytic performance of Ag/Ag Cl/CeO₂ in the visible light CWPO system（photo-CWPO）was studied,and the mechanism of catalytic action was clarified.Results showed that the specific surface area of Ag/Ag Cl/CeO₂ loaded with 2mmol silver nitrate is 317.5m²/g,the average pore diameter is8.82nm,and the band gap width is 2.9ev.Ag/Ag Cl enhances the adsorption ability of CeO₂ to400～700nm visible light.In the photo-CWPO system,the removal rate of COD increased from51%of single CWPO system to 90.1%of photo CWPO system,and the removal rate of COD still reached 84.8%after the catalyst was reused five times.（4）Based on the principle of biomineralization and biomimetics,disordered mesoporous CeO₂ was prepared with polysaccharide as the biological template.The effects of different template,template concentration and calcination temperature on the structure and morphology of disordered mesoporous CeO₂ were systematically investigated,and the mechanism of synthesis of mesoporous materials with polysaccharide template was revealed.The degradation of acrylonitrile and phenol in microwave-assisted CWPO（MW-CWPO）system was studied to elucidate the mechanism of enhanced catalytic activity of mesoporous CeO₂.Results showed that the three-dimensional disordered mesoporous CeO₂ is prepared with 0.02mol cerium nitrate as the precursor,10%chitosan,1%sodium alginate and 5%starch as the template respectively,and calcinations temperature is 400℃.The specific surface areas of which are 220.37m²/g,256.43m²/g and 210.0 m²/g,and the average pore sizes are 3.66nm,12.87nm and 7.13nm,respectively.In the MW-CWPO degradation experiment,the degradation of acrylonitrile and phenol are completed in 20 minutes.The COD removal rate is in accordance with the second-order kinetic process of Arrhenius empirical model,and the correlation coefficient R² is more than 0.95.（5）Based on the principle of ion doping,Ag/CeO₂ was prepared by soft template method.The influence of Ag doping on the structure and morphology of mesoporous CeO₂ was elucidated.In the continuous flow CWPO reaction system,the way and mechanism of degradation of organic compounds by Ag/CeO₂ were clarified.Results showed that the mesoporous Ag/CeO₂ with regular morphology is obtained by adding 5mmol cerium nitrate and2mmol silver nitrate into 2g F127,and reacting under 100℃for 60min and calcining at 550℃for 6h.The specific surface area is 297.2m²/g and the average pore diameter is 8.57nm.In CWPO system with Ag/CeO₂ as catalyst,the COD removal rate is 93.4%,which is about 10%higher than that of CeO₂ catalyst.In CWPO system,the catalysis of Ag/CeO₂ is the result of Lewis acid position,alkali position and unique redox property of CeO₂.There are 101 figures,21 tables and 190 references in this paper.