| Methylamine（CH3NH2）is a typical nitrogen contained odor which caused serious impact on people’s life.Owing to the advantages of eco-friendly,efficient and simple to operate,the photocatalytic degradation method has great potential in methylamine degradation.In this study,nano-TiO2（Evonik Degussa P25）was used as the substrate for surface modification to improve the degradation efficiency of methylamine.A series of surface modifications,such as acid-base modification,surface morphology regulation and precious metal Pt loading were carried out on TiO2substrate.Based on the analysis of physical and chemical properties and in situ infrared spectroscopy（DRIFT）,the influences of experimental atmosphere were explored and the photocatalytic degradation process of methylamine were proposed.（1）H3PO4/TiO2、H2SO4/TiO2 and Na OH/TiO2 catalysts were prepared by a simple impregnation method.Under dry conditions,the removal efficiencies of methylamine were 75.1%,74.2%,63.9%and 49.5%,respectively.The results show acid-base modification could broaden the absorption range of light spectrum,reduce the resistance of charge migration,and promote the migration and separation of photogenerated electrons and holes.Furthrermore,acid modification is helpful to enhance the adsorption capability of methylamine.Considering the removal efficiency of methylamine and the characterization of catalyst,phosphoric acid modification achieved the best performance.The methylamine degradation efficiency of H3PO4/TiO2 can reach up to 85%under the condition of 10%relative humidity.（2）DRIFTS spectra were used to investigate the photocatalytic degradation process of methylamine.Based on the anyalysis of DRIFTS spectra,the methylamine may be degraded by the following pathways:a.the broking of C-N bondtook place firstly,then·CH2 and NH3 were oxidized into CO2,NO,NO3-and other products;b.·CH2NH2 generated through CH3NH2 dehydrogenated,followed by oxidized to amide and NCO by·O2-and·OH,then hydrolyzed to NH3 and carboxylic acid,finally degraded to CO2 and NO3-.By-products such as nitromethane may produce in the photochemical reactions between free radicals and gas phase products.The addition of a small amount of water vapor may promote the generation of·OH and the oxidation of·CH2 and·CH3,thus inhibit the formation of by-products in the photochemical reaction.（3）TiO2 nanotubes（TNTs）were prepared by hydrothermal method with nano-TiO2 as substrate and applied to the photocatalytic degradation of methylamine.The effect of calcination temperature on the degradation performance of methylamine was studied.The degradation efficiency of TNTs-350 obtained by calcination at350℃is the best,and the degradation efficiency of methylamine can reach more than85%.The results of DRIFT spectra showed that CH3NH2 experienced the intermediate process of-NCO and-COOH on the surface of TNTs-350,and finally degraded into CO2、NH3,NO3-and other products.Adding a small amount of water vapor can promote the reaction process.（4）In order to further improve the photocatalytic degradation efficiency of methylamine,different forms of Pt（Pt0,Pt Ox and Pt Clx）were loaded on TNTs-350catalyst by impregnation,calcination and reduction methods,respectively.The experimental results showed that the adsorption capacity of methylamine was enhanced when Pt element was loaded in the form of Pt Clx,and the photocatalytic degradation of methylamine was promoted on the Pt Clx/TNTs-350.Pt0 and Pt Ox loading will reduce the adsorption capacity of methylamine of TNTs-350,resulting in a decline in degradation efficiency.The optimal Pt loading of Pt Clx/TNTs-350catalyst is 0.5%,and the degradation efficiency of methylamine can reach more than95%.Physical and chemical characteristics analysis showed that the doping of Pt Clx on the surface of TNTs can construct a new electron transfer channel,promote the separation of photogenerated electrons and holes,and generate more·OH,·O2-free radicals to participate in the reaction,thus improving the photocatalytic degradation efficiency of methamine. |
