Preparation, Characterization And Photothermo-catalytic Property Of Nanostructured CeO₂

Air pollution from volatile organic compounds (VOCs) have been a serious environmental problem for these decades. The method of Control the volatile organic compounds (VOCs) emission has become an important issue because they are not only hazardous to human health but also harmful to the environment. CeO2 as a new photocatalytic materials began to get attention in Air Treatment.In this paper, the CeO2 photocataly are prepared. They are characterized with XRD, Raman, BET, TEM, DRUV-vis, and photoelectrochemical measurement. under the photothermocatalytic, thermocatalytic and photocatalytic condition, The catalyst for VOC of catalytic degradation performance are researched. The main contents of this dissertation are listed as follows:The mesoporous nanorod-like ceria with high BET surface area of 121 m2/g is prepared by a facil method, microwave assisted hydrolysis of Ce(NO3)3.6H2O in presence of urea. XRD analysis reveals that the ceria sample was indexed to the pure fluorite cubic structures. The average crystal size of ceria is-7 nm。its absorption edge significantly shifts to visible region with a band gap of as low as 2.75 eV due to the presence of Ce3+. The rate constant (kptc=6.9x10-2 min-1) of the photothermocatalytic oxidation is 9.2 times higher than that for the alone photocatalytic oxidation at near room temperature. kptc is 3.7 times higher than (kpc+ ktc). These beneficial effects promote catalytic efficiency for gas-phase purification of organic contaminants such as benzene, hexane and actone. The mesoporous nanorod-like ceria also exhibits an excellent stability for the photothermocatalytic oxidation. After 30 cycles each of which lasts one hour, its photothermocatalytic activity almost remains unchanged. It also shows high efficient photothermocatalytic activity for the gas-phase purification of other organic contaminants such as Toluene acetone and hexaneIt has been widely accepted that the oxidation of hydrocarbon on metal oxide follows a mechanism called the Mars-van Krevelen redox cycle, the hydrocarbon is first oxidized by the lattice oxygen in the CeO2, and then the CeO2-x is re-oxidized later by gaseous oxygen, under the photothermocatalytic oxidation in the presence of O2, the photogenerated electrons in the ceria conduction band with UV- Vis irradiation induce the generation of active oxygen species (e.g.O2-).the significant enhancement of oxygen ion conduction in the mesoporous nanorod-like ceria with increasing temperature can greatly improve separation efficiency of photogenerated electrons and holes by UV-vis photons and thus the reduced ceria (CeO2-x) is re-oxidized both by gaseous oxygen and the active oxygen species rather than just by gaseous oxygen in the thermocatalytic oxidation. The high efficient separation of holes and electrons generated with the co-excitation of both UV-vis irradiation and thermal energy from a Hg lamp is beneficial to the formation of more hole trapped lattice oxygen ions and active oxygen species, which accelerates the redox cycle of CeO2/CeO2-x, thus results in the high synergetic photothermocatalytic efficiency.