Research On The Impact Of Absorption Spectrum Expansion On NO Photocatalvtic Oxidation Performace

As one of the major air pollutants,nitrogen oxides?NO_x?emitted from combustion of fossil fuels are in high concentration and mainly removed by selective catalytic reduction?SCR?.However,this method is not a suitable for the removal of low concentration NO_x in tunnel or underground garage.Whereas,photocatalytic oxidation of NO has mild reaction conditions and low operation cost,which exhibits good application potential for the removal of low concentration NO_x.To enhance photocatalytic oxidation of NO,Fe₃O₄@SiO₂ as photothermal agent was added into photocatalysts to facilitate the photocatalytic oxidation process.Furthermore,Bi/BiOI/black TiO₂ heterojunction and La/BiOI with expanded absorption spectrum and good photocatalytic oxidation capability for NO were developed to utilize solar light more efficiently,and the promotion mechanism was discussed.Firstly,P25/Fe₃O₄@SiO₂ was prepared by a facile solid-solid mixing method.Then the effects of SiO₂ shell,the amount of Fe₃O₄@SiO₂,the NIR absorption capability of Fe₃O₄@SiO₂ and the impact of photothermal effect on photocatalytic performance were studied.Experimental result showed that for the optimized P25/Fe₃O₄@SiO₂,an activity enhancement of 36%was reached compared to that of pure P25.SiO₂ shell could proctect Fe₃O₄ during photocatalytic process.Based on the characterization,the promotion mechanism from photothermal effect was proposed as follows.Fe₃O₄@SiO₂ absorbed the infrared light,transferred it to thermal energy based on photothermal effect,and then accelerated the photocatalytic performance of P25.Furthermore,the enhancement of NO oxidation capability was also observed when Fe₃O₄@SiO₂ mixed with other photocatalysts such as ZnO,g-O₃N₄ and BiOI,et al.Secondly,Bi/BiOI/black TiO₂ heterojunction was prepared via a calcination reduction approach and the amount of precusor,P25 and BiOI,was optimized.Studies demonstrated that the photocatalytic oxidation efficiency of NO of the optimized Bi/BiOI/black TiO₂ reached 70%with good stability under the illumination of simulated sunlight.Due to the surface plasmon resonance?SPR?effect of Bi and the heterostructure of Bi/BiOI/black TiO₂,the absorption spectrum of Bi/BiOI/black TiO₂ was expanded and the photoexcited photons and holes were separated efficiently.Moreover,in Bi/BiOI/black TiO₂,·O₂-and ·OH were generated as active species,responsible for the NO photocatalytic oxidation process.As a result,photocatalytic performance of Bi/BiOI/black TiO₂ was promoted.Finally,La doped 3D BiOI was prepared using a one-step solvothermal method and an impregnation method.The effect of preparation method,the kind of La precursor and the amount of La were invertigated and the preparation conditions were optimized.Experimental results showed that La/BiOI prepared by the solvothermal method exhibited higher photocatalytic activity than by the impregnation method and La/BiOI prepared from La?NO₃?₃ was more efficient than from La?Ac?3 or LaCl₃.In addition,the optimized 0.3%La/BiOI reached a high photocatalytic activity of 74%under visible light illumination and the photocatalyst exhibited stable performances.The doping of La led to a red-shift of light adsorption spectrum and enhanced the separation of photoexcited photons and holes.At the same time,lots of ·OH responsible for the photocatalytic oxidation of NO were generated.As a consequence,the doping of La enhanced the photocatalytic capability of BiOI.