Study On The Controllable Preparation Of Porous Bimetal Oxides And Their Performance In Catalytic Ozonation

In recent years,the catalytic ozonation technology has been widely studied in the treatment of refractory organic pollutant wastewater,and has been gradually promoted in practical industrial wastewater treatment.In catalytic ozonation,the decomposition of ozone can be accelerated using a catalyst,to generate abundant reactive oxygen species with no selectivity and strong oxidizing ability to efficiently treat organic wastewater.Therefore,designing efficient,cheap and environmentally friendly catalysts is a key to improve catalytic ozonation performance.In this thesis,aiming at improving mass transfer and reducing ion leaching of metal oxide catalysts,two novel porous bimetal oxide catalysts were developed to improve the catalytic ozonation activity and stability by means of regulating the structure and metal valence states of the catalyst.CuOx/Al2O3 with a layered mesoporous structure and Co3-xMnxO4 with a three-dimensional hierarchical porous structure were studied in detail in catalytic ozonation of two typical pollutants,and the relationship between the structure and performance of the catalysts and the reaction mechanism were discussed in depth.The main contents progress of the thesis are summarized as follows.In the first part of the thesis,we used the layered MIL-53(Al)as the carrier and precursor,and introduced the copper source through the impregnation method.Subsequently,a series of novel CuOx/Al2O3 catalysts were prepared by adjusting the concentration of the precursor solution and calcination temperature.The preparation method not only realizes the high dispersion of copper species,but also promotes the formation of multivalent copper.The reducing gas generated by the thermal decomposition of the organic ligands of MIL-53(Al)facilitates the formation of lowvalent copper.The obtained catalysts exhibited a layered mesoporous structure,in which highly dispersed and multivalent active copper species were stabilized.In a typical sample,the copper species are distributed in the interlayer of Al2O3 with a size of 2～5 nm,and it exists in complex valence states of Cu0,Cu+ and Cu2+(31.3%,40.9%and 27.8%,respectively).With the increase of calcination temperature(500～650℃),the content of the low-valent copper(Cu0/+)gradually increased(up to 72.2%),but decreased to 58.4%as the calcination temperature was further increased to 800℃.Cu0/+ is more favorable to for the catalytic ozonation to degrade sodium oxalate,and Cu+ is found to be the main active site.The catalyst with Cu a content of 1.2 wt%and calcined at 650℃ exhibits excellent catalytic ozonation performance with 100%removal of 50 mg L-1 sodium oxalate within 15 min.During the reaction,the electron transfer between the multivalent copper sites promoted ozone decomposition to generate free hydroxyl radicals(·OH)for the efficient degradation of sodium oxalate.In the second part of the thesis,a series of three-dimensional hierarchical porous cobalt-manganese spinel phase oxides(Co3-xMnxO4)were prepared by adjusting the molar ratio of the metal ions and calcination temperature using histidine as the ligand and foaming agent.The introduction of histidine makes the material have a hierarchical pore(abundant mesopores and macropores)structure.The cobalt-manganese spinel can improve its reducibility and surface Lewis acid sites compared with single metal oxides.Changing the molar ratio of cobalt to manganese affects the content of surface Lewis acid sites and the valence distribution of surface Mn.The content of Lewis acid sites of Co3-xMnxO4-400 is not directly related to the catalytic activity,but the average oxidation state of Mn has a negative linear correlation with the catalytic activity,the higher the average oxidation state of Mn,the worse the catalytic performance.The typical sample Co1.5Mn1.5O4-400 exhibits excellent catalytic ozonation performance with 100%removal of 50 mg L-1 carbamazepine within 3 min and 70%TOC removal within 60 min.In the process of catalytic ozonation,the main reactive oxygen species are surface hydroxyl radicals(·OHsurface),singlet oxygen(1O2)and hydrogen peroxide.The combination of cobalt and manganese in the form of spinel can significantly reducing the leaching of manganese ions during the reaction.The surface hydroxyl groups on the catalyst and the electron transfer between Co and Mn in different valence states may synergistically promote the decomposition of ozone,thereby generating reactive oxygen species and achieving efficient degradation and mineralization of pollutants.We have successfully developed two novel catalysts through novel preparation methods,which are layered mesoporous Al2O3 loaded with low-valent CuOx and CoMn spinel with three-dimensional hierarchical porous structure.The valence distribution of Cu in CuOx/Al2O3 catalyst can be controlled by adjusting the calcination temperature,and Cu+is the main active copper species.The average oxidation state of Mn in Co3xMnxO4 can be regulated by adjusting the molar ratio of Co to Mn,and the lower the average oxidation state of Mn,the higher the catalytic activity.In addition,the CuOx/Al2O3 with layered mesoporous structure and CoMn spinel with the threedimensional hierarchical porous structure can not only enhance the mass transfer,but also significantly reduce the leaching of metal ions during the reaction process.This thesis can provide ideas for the preparation of Cu-Al and Co-Mn based catalysts,and can provide some support for the development of catalytic ozonation technology for organic wastewater treatment.