Molecular Adsorption And Reaction On Single Crystal Wurtzite ZnO(000(?)) Polar Surfaces Studied By UHV-FTIRS

As the atmospheric pollution becomes more and more serious,it is extremely urgent to find advanced technologies to to solve environmental problems.Since Professors Fujishima and Honda had found that water can be photolyzed to form H2 and O2 on the TiO2 electrode,using the photocatalytic technology to solve the problems of air pollution and energy shortage have attracted widespread attention.Although photocatalytic technology has a wide range of application prospects,many photocatalysts have problems such as weak catalytic selectivity,short lifetime,and low stability.Therefore,to achieve industrialization and practical application of photocatalytic technology,we need to further research on photocatalytic mechanism.Therefore,the studies on molecular adsorption and reaction on catalst surfaces are critical in understanding the catalytic mechanism.Among the oxide catalysts,ZnO has attracted much attention in the fields of heterogeneous catalysis,optoelectronic devices,and gas sensing materials.ZnO and ZnO-based compound catalysts are widely used in various chemical production fields.The present study focused on the non-polar ZnO surfaces,however,few studies have been conducted on the polar ZnO surface due to the unstability.Obviously,it is more interesting to research on the polar surface of ZnO,which could broaden the selection range of ZnO catalysts.In this thesis,by using a new-designed state-of-the-art ultrahigh vacuum-Flourier transform infrared spectrometer(UHV-FTIRS)system,we systematically studied adsorption and co-adsorption of CO and CO2 molecules on polar ZnO surfaces such as wurtzite single crystal Zn0(000(?))-(1 X 3)reconstituted surfaces and adsorption of CO2 on ZnO(000(?))-H(1×1)hydroxylated surfaces.The main results are as follows:1.On Zn0(000(?))-(1×3)reconstructed surfaces,The CO2 molecule linearly adsorbed on the oxygen vacancy surface along the oxygen vacancy row with the C atom bond to the Zn2+ ion.The CO2 binding energy on the surface is higher and the desorption temperature is about 160 K.We also given the corresponding molecular adsorption model for this configuration.2.On the hydroxylated ZnO(000(?))-H(1×1)surface,CO2 is tiltedly adsorbed on the hydrogen atom.For this configuration,we gave the corresponding molecular adsorption model.The annealing results indicate that the adsorption energy of CO2 on the hydroxylated surface is lower than that on the oxygen vacancies.3.On the ZnO(000(?))-(1×3)reconstructed surface,CO can only adsorb on oxygen vacancies along the oxygen vacancies row,with the C atom bind to the Zn2+cation at oxygen vacancies.The binding energy of CO on such surface is very high and the desorption temperature is about 250 K.4.For the co-adsorption of CO and CO2 on the ZnO(000(?))-(1×3)reconstructed surface,CO tends to occupy the adsorption site preferentially,while CO2 can only adsorb on the site that CO is not occupied.The adsorption binding energy of CO2 at the surface is significantly weakened,due to the influence of adsorbed CO and the resulting desorption temperature of CO2 is only 130 K.