Preparation Of Zinc-containing Composite Metal Catalysts And Their Heterogeneous Photocatalytic Ozone Degradation Of Organic Pollutants In Water

With the rapid development of society,the problems of human health and ecological balance caused by organic pollutants in the environment have become the focus of social attention.Heterogeneous photocatalytic ozonation technology is a combination of photocatalytic technology and ozonation technology,which has the potential to efficiently degrade pollutants.In this system,the surface characteristics of different types of catalysts are different,so the catalytic effects and pollutant degradation capabilities exhibited in heterogeneous photocatalytic ozonation technology are different.Therefore,the selection and preparation of suitable catalysts has become the focus of research.In this paper,different metal-doped ZnS binary nanocomposite catalysts and TiO₂/ZnO/Mg?OH?₂ ernary nanocomposite catalysts were prepared.Through a series of characterization tests and catalytic performance analysis of these two types of catalysts,the internal electron transfer mechanism of these two catalysts in the application of heterogeneous photocatalytic ozonation technology was obtained,which fundamentally promoted their application in the purification of wastewater by heterogeneous photocatalytic ozonation technology.Through the free radical capture experiment and reading related literature,the synergistic mechanism and main active substances between O₃,UV and catalyst are studied,which provided the theoretical basis for the application of this technology.This paper has obtained some valuable research results,mainly as follows:?1?The application of different metal?Cu,Ag,Bi,Ga or In?doped ZnS binary nanocomposite catalysts to heterogeneous photocatalytic ozonation was studied.The doped metal enters into the ZnS nanolattice respectively,and affect the partial structure of ZnS particles.The absorption intensity of the metal-doped ZnS catalyst in the ultraviolet region is significantly higher than that of ZnS,which is conducive to the formation of more electron-hole pairs under the 254 nm UV lamp.Cu/ZnS has the narrowest band gap,which promotes electron transfer rates.Ag/ZnS,Bi/ZnS,Ga/ZnS,and In/ZnS have more valence bands than ZnS,which promotes the oxidation capacity of the holes.The catalytic performance of metal doped ZnS is better than that of ZnS.The internal electron transfer mechanism of metal doped ZnS is as follows:schottky junction is formed between ZnS and doped metal,which can be used as electron trap to effectively capture electrons and inhibit the combination of electron-hole pairs.Cu/ZnS can achieve almost complete degradation of 4-CP and mineralization rate of 72.69%within 18 minutes,it has the best catalytic performance and good cycle stability.?2?The application of TiO₂/ZnO/Mg?OH?₂ ternary nanocomposite catalysts to heterogeneous photocatalytic ozonation was studied.The synthesized ternary nanocomposite is a spherical structure coated with TiO₂ and Mg?OH?₂ on the surface of ZnO.With the increase of calcination temperature,Mg?OH?₂ will undergo dehydration condensation reaction to form MgO,which increase the specific surface area,pore volume and pore size of the material.The absorption intensity of TiO₂/ZnO/Mg?OH?₂ in the ultraviolet region is significantly higher than that of ZnO,which makes it easier to absorb the ultraviolet with the wavelength of 254 nm.TiO₂/ZnO/Mg?OH?₂ ternary nanocomposites have a narrower band gap than a single catalyst,which promotes the electron transfer rates.The TiO₂/ZnO/Mg?OH?₂?TZM-400?synthesized at a calcination temperature of 400°C can achieve almost complete degradation of 1,4-D and mineralization rate of 84.37%within 40 minutes,it has the best catalytic performance and good cycle stability.The internal electron transfer mechanism of TZM-400 is:?a?when the photoexcited electrons in the valence band?VB?of Mg?OH?₂ transferred to the conduction band?CB?,the electrons were first transferred to CB of ZnO and then to CB of TiO₂;?b?the photoexcited electrons of Mg?OH?₂ were directly transferred to the CB of TiO₂;?c?the holes in the VB moved in the opposite direction.At the same time,MgO with excellent adsorption performance adsorbs more pollutants and active materials to the surface of the catalyst to promote the reaction.1,4-D will eventually be degraded into CO₂,H₂O and a small amount of organic acids:formic acid,acetic acid and oxalic acid.?3?In the process of heterogeneous photocatalytic ozonation system degradation of pollutants,the synergistic mechanism between O₃,UV and catalyst is mainly divided into the following four parts:the catalyst generates electrons?e^-?-holes?h⁺?pair under the action of UV;O₃ generates·OH and·O₂^-under the action of e^-;O₃ generates·OH and·O₂^-under the action of UV;water molecules in solution generate·OH under the action of h⁺.In the application of pollutant degradation,e^-and·OH play a key role.