Photocatalytic Degradation Of Gaseous Benzene Over Palygorskite Supported Bismuthate

In this paper,a series of composite materials were prepared by hydrothermal method and sol-gel method using palygorskite?Pa?supported bismuth compounds?Bi₂WO₆,BiVO₄,Bi₂MoO₆?.The structure,morphology and optical absorption properties of the samples were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,diffuse reflection spectrometer?DRS?,photoluminescence?PL?,nitrogen adsorption-desorption measurement?BET?and X-ray photoelectron spectroscopy?XPS?.The photocatalytic activity of the samples was tested by the degradation rate of gaseous benzene under 365 nm ultraviolet light,and cyclic experiment to test catalyst stability.The mechanism of photocatalytic degradation of gaseous benzene by the composite catalyst was investigated experimentally,and the mineralization rate was calculated by measuring the amount of CO₂ produced.Main conclusions were shown as follow:?1?The Bi₂WO₆/Pa composite catalysts with high photocatalytic activity and stability were prepared by hydrothermal method.The catalyst was dispersed at the bottom of the glass tube and its photocatalytic activity was tested by degrading gaseous benzene.When benzene initial concentration was 50 mg/m³,over Bi₂WO₆/Pa with mass ratio was 8:2,calcined temperature was 250°C and the precursor pH value was 3,the benzene degradation efficiency reached 68.2%and the mineralization efficiency reached 62.7%after 2 h 365 nm UV light irradiation.Compared with pure Bi₂WO₆,the high activity of composite catalyst could be attributed to its large specific surface area and lower photoinduced electron-hole recombination rate.Photo-generated holes?h⁺?and superoxide radicals??O₂^-?played a dominant role in the process of the photocatalytic degradation of benzene.?2?The Bi₂WO₆/Pa materials were synthesized by sol-gel method,and the catalyst was evenly coated on the inner wall of the glass tube.The photocatalytic activity was tested by degrading gaseous benzene.The optimum condition of composite catalyst was Bi₂WO₆/Pa with mass ratio of 0.7:1 and calcined at 450°C.In the case of 0.3 g dose catalysts,the benzene initial concentration 100 mg/m³ and after 2 h 365 nm UV irradiation,the degradation rate reached 70.5%and the mineralization was 64.3%.Compared with the Bi₂WO₆/Pa composite catalyst prepared by hydrothermal method,the particle size of the samples prepared by the sol-gel method was significantly reduced,the specific surface area was increased,and the absorption of visible light was enhanced.It was found through mechanism research that h⁺and?O₂^-were the main active species of benzene degradation.?3?The BiVO₄/Pa composite catalyst was synthesized by sol-gel method,and the photoactivity of the photocatalyst was tested by degrading gaseous benzene.The optimum preparation conditions for the composite catalyst were:mass ratio of BiVO₄/Pa of 4:6 and calcination temperature of 550°C.The benzene initial concentration 100 mg/m³ and after 365 nm UV irradiation 2 h,the degradation rate and the mineralization of gaseous benzene reached 72.2%and 66.5%,respectively.Through the sample structure and the photocatalytic performance,it could be deduced that the improvement of photocatalytic efficiency was due to Pa acted as a carrier to increase the specific surface area of the catalyst while also accepting photogenerated electrons from BiVO₄.The h⁺and?O₂^-played an important role in the degradation of benzene.?4?Bi₂MoO₆/Pa composite photocatalysts were successfully prepared by sol-gel method.The results showed that Bi₂MoO₆/Pa composite photocatalyst has the highest photocatalytic activity when the mass ratio of Bi₂MoO₆ and Pa was 8:2 and the calcinations temperature was 450°C,the degradation rate and the mineralization of gaseous benzene with 100 mg/m³ reached 67.4%and 61.6%after 2 h.In this reaction system,h⁺and·O₂^-and·OH played a major role in the degradation of benzene.