Removal Of NO_x By Zr-MOF During Photocatalytic Oxidation

Due to the large-scale use of fossil fuels,a large amount of gases are discharged into the atmosphere in a short period of time,causing the deterioration of the atmospheric environment gradually.Low levels of nitrogen oxides?NOx?can cause serious damage to many organs of human body.Photocatalysis is a new technology that uses light to drive semiconductor catalysts with suitable band gap for a series of redox reactions.Due to the unique properties of depth reaction at room temperature,convenient operation and environmentally friendly,it has been used as an efficient method to remove NOx of low concentrations.The selection of photocatalyst mainly focused on low specific surface area materials such as metal oxides,bismuth salts,carbonitride polymers,etc.So far,the efficiency and stability of NOx removal under visible light are relatively low,and often associated with high levels of toxic byproducts?NO₂?.This thesis mainly studied the application of metal-organic framework materials with photocatalytic activity in NOx removing,and focused on the following issues: improve the separation efficiency of photo-generated electrons and holes,enhance the activity and stability of the catalyst,and suppress the generation of NO₂ in the catalytic process.The main research contents of this paper are divided into the followingparts:1.Microwave-assisted synthesis of N-GDY/NH₂-UIO-66?Zr?composite materials for visible light catalytic oxidation to remove NOxA microwave-assisted synthesis method was used to construct an in-situ N-doped graphyne?N-GDY?and NH₂-UIO-66?Zr?into a composite material,and studied its photocatalytic removal of NOx.The high hole transporting properties of graphyne can accelerate the migration of photogenerated holes from NH₂-UIO-66?Zr?to graphyne,which greatly reduces the recombination rate of photogenerated electrons and holes.The photocatalytic activity of the composites is more than twice higher compared to that of pure NH₂-UIO-66?Zr?.Under visible light?? ? 420 nm?,N-GDY/NH₂-UIO-66?Zr?presents high photocatalytic oxidation activity of NOx removing?removal rate up to 74%?and high stability,and at the same time,it can inhibit the generation of a large amount of toxic by-products?NO₂?to control the concentration of NO₂ in a low range.2.Microwave-assisted synthesis of nitro-modified UIO-66?Zr?for visible light catalytic oxidation of NOxThe "pre-functionalization" strategy was adopted,and the nitro group was modified into the UIO-66?Zr?backbone by microwave-assisted solvothermal method.The electron-withdrawing property of nitro increase the material's ability to adsorb the electron-rich gas NO.At the same time,nitro is a chromophore and can form a conjugate with the electron cloud on the benzene ring to deepen the color of the material which can affect the light absorption performance of the catalysts.With the increase of the amount of modified nitro in the skeleton,the colors of the prepared materials are continuously deepened,and the band gap narrowed from 3.91 e V to 2.71 e V.The catalyst's absorption of light was successfully extended from the ultraviolet region to visible light area.UIO-66?Zr?modified with different nitro content was used for photocatalytic removal of NOx.As the amount of nitro modification gradually increased,the activity of photocatalytic removal of NOx showd a clear increasing trend.When the nitro groups are modified on every links in the backbone,the catalyst activity reaches the maximum?the removal rate is as high as 76 %?.And maintain high catalytic stability.3.Research on the inhibition of NO₂ formation during the photocatalytic oxidation of NOxIn this section,Metal-Organic Frameworks materials with visible light?? ? 420 nm?catalytic activity are used for the study of photocatalytic oxidation to remove NOx under wet and dry conditions,respectively.?NH₂-UIO-66?Zr?,NH₂-MIL-125?Ti??has significantly lower activity in removing NOx than it does under humid conditions.The electron-withdrawing group?-NO₂?-modified UIO-66?Zr?has nearly twice as much photocatalytic activity under dry conditions compared with,while the formation of NO₂ during photocatalytic oxidation to remove NOx.The catalytic activity of UIO-66-NO₂ is much higher than that of NH₂-UIO-66?Zr?and NH₂-MIL-125?Ti?under dry conditions.Studies have shown that MOF modified by electron-withdrawing groups is more active than NO donors in removing NOx under dry conditions,and a small amount of adsorbed water in the NO₂-UIO-66(Zr channel can promote NOx oxidation.The large specific surface area of the Metal-Organic Framework is used to enrich the low concentration of NO in the atmosphere while relying on itself to adsorb trace amounts of H2 O from the air,thereby achieving efficient removal of NO and completely suppressing the production of toxic by-products?NO₂?.