Studies On Catalytic Degradation Of Typical Small Molecule HC Compounds In Air At Room Temperature

With the rapid development of human society,the increasingly prominent environmental problems have become the key issue of restricting the development of human society.Nowadays,the human beings are facing the threat of environmental pollution,especially air pollution.Recently,the negative impact of the HC compounds emissions is attracting more attention.As one of the three major pollutants in the car exhaust,the HC compounds would react with the nitrogen oxides to form photochemical smog and haze,which eventually cause adverse health effects.Therefore,removing the HC compounds from air has attracted widespread attention.In this paper,we choose ethylene and methane as the typical HC compounds,and explore the degradation methods of the HC compounds under room temperature.The main contents include the following:1.A series of photocatalysts such as g-C3N4,CdS,Cu2O,BiVO4,Ag3PO4,WO3,SrTiO3,TiO2 were prepared and their activity for photocatalytic oxidation of C2H4 were examined.According to the experiment results and previous reports,we suggest that an appropriate semiconductor photoxcatalyst for photocatalytic oxidation of C2H4 should satisfy the following criteria:Firstly,the conduction band(CB)minimum should be more negative than the reduction potential of O2(O2 + e-?·O2-,-0.33 eV vs.Normal Hydrogen Electrode,NHE);Secondly,the valence band(VB)maximum should be more positive than the oxidation potential of OH-(OH + h+?·OH,+2.59 eV vs.NHE);Finally,the bandgap should be larger than 2.92 eV This means an approprate semiconductor photocatalyst can only absorb ultraviolet(UV)light,so exploring a semiconductor photocatalysts for highly efficient oxidation of ethylene under visible light illumination remains a challenging task.Inspired by natural photosynthesis of plants,it could be possible to design an efficient photocatalyst for removing ethylene under irradiation by fabricating a Z-scheme configuration with two narrow bandgap semiconductors.Finally,two types of Z-scheme photocatalysts g-C3N4-Ag3P04 and In2O3-Ag-Ag3PO4 wrere fabricated and their performance on the photodegradation of C2H4 under visible light illumination were examined.2.In order to catalytic oxidation of ethylene under low-temperature conditions,we analyzed the thermodynamics and dynamics of the reaction C2H4 + O2?CO2 + H2O,and suggest that nano metal particles could be a good catalysis.In consideration of the deactivation may be caused by the adsorption of produced water on the catalyst surface,we choose the hydrophobic materials as the supports of catalysts.According to the above description,we fabricated a series of catalysts with different mass percentage of Pt nanoparticles supported on hydrophobic multi-walled carbon nanotubes(MCNTs)[1-Pt-MCNTs,2-Pt-MCNTs,3-Pt-MCNTs]and examined their performance for ethylene oxidation.This results revealed that the Pt nanoparticles supported on hydrophobic MCNTs exhibited the highest activity and demonstrated excellent durability in prolonged reaction time and recycle use.The conversion of 200 ppm ethylene over 3-Pt-MCNTs at 0 ? was 100%.The conversion of 200 ppm ethylene with 3-Pt-MCNTs remained 100%for more than 120 h at 25 ?.3.Given the high C-H bond energy(434 kJ·mol-1)and the non-polar nature of the CH4 molecule,it is very difficult to active the C-H bond of CH4.In order to photocatalytic oxidation of methane under room-temperature,we used the built-in electric field of the polar ZnO semiconductor and Zn2+-O2-ion pairs in the nonpolar plane of ZnO to active the C-H band of methane.As we know,the complete photocatalytic reaction process including three steps:photon absorption,separation of charge,surface reaction.To improve the pegrformance of photocatalytic oxidation of CH4,we propose the folLowing materials design strategies:(?)nano silver decoration may function as both a co-catalyst and a light-harvesting medium;(?)the polar structure readers fast separation and transportation of photo-generated electrons and holes;(?)rich defective surfaces benefit surface adsorption and reactions.Ag decorated ZnO photocatalysts were fabricated and examined for methane oxidation.The experimental results show that a nanoscale ZnO can efficiently oxidize methane under simulated sunlight irradiation and nano silver decoration further improves the activity to a high level even under visible light illumination.