Photocatalytic Degradation Of Gaseous Methylamine By TiO₂ Based Thin Films

Air pollution is becoming more and more serious and complex.As a major component of air pollution,the effective degradation of volatile organic compounds?VOCs?has attracted widespread attention.Methylamine belongs to common nitrogen-containing pollutant,which has a significant impact on the atmospheric environment and human health.The photocatalytic degradation of methylamine is of great significance to the degradation of other VOCs,especially to organic amines.Photocatalytic technology is an efficient and environmentally friendly method for VOCs purification.Among many photocatalysts,TiO₂ has been applied in water purification,air purification and deodorization due to its excellent photocatalytic performance and good stability.However,TiO₂ is a semiconductor with wide band gap?3.0-3.2eV?,which makes it only responsive to ultraviolet light and unable to utilize the abundant visible energy in sunlight.Consequently,semiconductor composite was used to modify TiO₂,in order to broaden its range of light response and inhibit the recombination of photo-generated electron holes,so as to improve the photocatalytic efficiency of TiO₂ in the range of visible light.The details are as follows:?1?First of all,TiO₂ film was successfully fabricated on stainless wire mesh by a modified dip coating method.The photocatalyst was characterized by X-ray diffraction,scanning electron microscope and contact angle analyzer.A batch airtight photo-reactor was specifically designed and constructed for this work.The products and reaction mechanism of photocatalytic degradation of methylamine were studied.?2?The effects of these parameters on photocatalytic degradation efficiency and kinetics of gaseous methylamine were investigated by varying the pulling times,relative humidity and intensity of illumination of ultraviolet.As a result,the optimum preparation parameters and reaction conditions were obtained.Through experimental analysis,it is found that the photocatalytic degradation rate increased with the increase of pulling times,but decreased beyond a certain pulling times of three.It matched well with the Langmuir–Hinshelwood?L–H?kinetic model.There was an optimum concentration of water vapor in the degradation of methylamine.As for the effect of intensity of illumination,it was found that conversion of methylamine increased with it.In repetitive experiments,the prepared catalyst exhibited excellent stability.?3?C₃N₄ was modified on the surface of TiO₂ film/stainless steel mesh by calcination.The crystal structure,surface morphology and band gap of the composite film were characterized and analyzed by X-ray diffraction,scanning electron microscope,transmission electron microscope and UV-Vis.The photocatalytic degradation experiments of gaseous methylamine indicated that the C₃N₄/TiO₂ composite film possessed excellent photocatalytic activity in the visible light range,mainly due to the narrow band gap of C₃N₄?².66eV?,which effectively broadened range of light response of the composite film.Meanwhile,the formation of heterojunctions reduces the recombination of photo-generated electron hole pairs,which further improved the photocatalytic performance of the composite film.The composite film also owned high stability,which made it possible for practical applications.