Photothermocatalytic Degradation Of Gaseous Pollutants By Oxides And Oxyhalides

Due to the advantages of high efficiency and energy saving,photocatalytic technology has been of important application prospects in environmental purification.At present,visible light-driven catalytic oxidation of gaseous pollutants is one of the important topics in photocatalytic research.Further,it is found that photothermal synergistic catalysis can mutually promote photoreaction and thermal reaction,and hence accelerate the surface reaction rate,which has become a hot topic in recent years.The key to realize photothermal synergistic catalysis is the design of photothermocatalytic materials.In this thesis,by means of the construction of oxygen vacancies and the loading of surface cocatalyst,the blue light induced photocatalytic properties of M_xO/TiO₂?M=Cr,Cu,Co?and oxygen vacancy type BiOCl-OV catalysts were studied.By comparing the photocatalytic and photocatalytic properties,the design rules of efficient photothermocatalysts were explored,which could provide more references for the design of photothermocatalytic materials in the future.Specific research contents are as follows:?1?.The impregnation method is used to synthesize Cr_xO/TiO₂ with different loading content of Cr_xO.Structural characterization showed that titanium dioxide itself contained a small amount of oxygen vacancies,and the loading of Cr_xO could broaden the visible absorption range of titanium dioxide and promote the separation of photogenerated electron holes.By comparing the photocatalytic and photothermocatalytic degradation of acetaldehyde under blue light,it was found that TiO₂ with a small amount of oxygen vacancies had more significant oxidation ability under blue light photocatalysis.The effect of the loading amount of surface cocatalyst on the catalytic activity was further compared.It was found that the photocatalytic activity was the highest when the loading amount of Cr_xO was 0.3wt%.However,the photothermocatalytic activity was the highest when the loading of Cr_xO is 3wt%,which reveals that a small amount of oxygen vacancies and surface cocatalyst are more conducive to photothermal synergistic catalysis.?2?.Four cocatalyst including Co_xO,Cu_x O,Cr_xO and Pt were loaded on the surface of TiO₂.Transient photovoltage spectroscopy showed that Co_xO and Cr_xO promote hole transfer,while CuxO and Pt promote electron transfer.The effects of different cocatalysts on the catalytic performance were compared.It was found that under photocatalysis,the enhancement of the catalytic performance of TiO₂ by electron transfer cocatalyst was better than that by hole transfer cocatalyst.On the contrary,under photothermalcatalysis,the enhancement of the catalytic performance by hole transfer cocatalyst is better than that of the electron transfer cocatalyst.The main reason for the difference is that under photothermal catalysis,the hole transfer cocatalyst promotes the collection and utilization of holes,accelerates the rate of water oxidation by hole,and balances with the rate of oxygen reduction by electrons,thus significantly improving the oxidation ability of the catalyst.?3?.BiOCl nanosheets were synthesized by hydrothermal method.By UV irradiation,the oxygen vacancy can be introduced and further tuned over BiOCl?BiOCl-OV?.Photocatalytic and photothermalcatalytic degradation of NO_x show that large amount of oxygen vacancies tend to lead to the recombination of electron and holes,which decrease the degradation of NO_x.However,a small amount of oxygen vacancies is beneficial to the enhancement of photo-thermal catalytic oxidation of NO,resulting from that a small amount of oxygen vacancies provide more adsorption sites for NO and intermediate product NO₂,and photothermal synergy accelerates the rate of surface reaction with electron and hole,respectively.Meanwhile,the presence of oxygen vacancies is beneficial to the transformation of NO₂ to the final product NO₃^-and ultimately to the enhancement of the mineralization capacity of NO.