Preparation Of Zinc Cobaltate Photocatalyst And Its Performance In Degradation Of Toluene

Volatile organic compounds（VOCs）can seriously affect indoor air quality and human health,and the implementation of effective treatment of emergent VOCs has become particularly urgent.Photocatalytic oxidation technology has great prospect in the purification treatment of VOCs due to its moderate reaction conditions（normal temperature and pressure）,low energy consumption,strong oxidizing ability and environmental friendliness.Regarding photocatalytic technology,the two key factors affecting the photocatalytic activity of the photocatalyst are the spectral response range and quantum efficiency.As a photocatalyst material,spinel zinc cobaltate possesses characteristics of visible-light response,stable structure and chemical stability,low cost,availability and non-toxicity.It has been widely used in the field of organic pollutants purification.In this dissertation,the zinc cobaltate catalyst and its composites with different morphologies were prepared by self-sacrificial template method and co-precipitation pyrolysis method.The differences in physical and chemical properties of the as-prepared materials were analyzed and compared by implementing various characterization techniques.The catalytic activity of different catalysts was evaluated by photocatalytic degradation of gaseous toluene and the degradation mechanism of the photocatalytic process were inferred.The obtained results of the thesis work are introduced as follows:（1）Hollow porous Zn_xCo_3-xO₄ nanocubes and ZnCo₂O₄ nano particulate catalysts were prepared by self-sacrificial template method and co-precipitation pyrolysis method,respectively.Through the characterization of the crystal structure,size morphology,elemental composition and optical properties of the two catalysts,it was found that Zn_xCo_3-xO₄nanocubes have relatively larger specific surface area,higher visible light absorption capacity and improved separation efficiency of photogenerated carriers.Under the irradiation of visible light for 6 h,the degradation rate of toluene over hollow porous Zn_xCo_3-xO₄ was about 78%,which was 13%higher than that of the ZnCo₂O₄ nanoparticles under the same reaction conditions.The in-situ FTIR spectra and EPR techniques were used to analyze the photocatalytic degradation of gaseous toluene.It was found that during the degradation reaction,intermediate products such as benzaldehyde and benzoic acid,and final products such as CO₂ and H₂O were produced,and the reactive species directly generated in the photocatalytic system involved h⁺and·O₂^─.（2）The Zn_xCo_3-xO₄ and rGO/Zn_xCo_3-xO₄ catalytic materials systems were prepared in situ using a sacrificial template method.By XRD,SEM,TEM,Raman,XPS and EDX characterizations,it was found that the introduction of rGO did not affect the formation of Zn_xCo_3-xO₄ crystal structure.Compared with pure Zn_xCo_3-xO₄ material,the surface of rGO/Zn_xCo_3-xO₄ was rougher,and a thin wrinkled rGO layer could be observed on the outer wall of Zn_xCo_3-xO₄.The characterization results of DRS showed that rGO/Zn_xCo_3-xO₄ showed relatively higher light energy absorption.Through the photocatalytic degradation of gaseous toluene,it was observed that the degradation efficiency of rGO/Zn_xCo_3-xO₄ after 6 h exposure to visible light was about 82%,which is 9%higher than that of pure Zn_xCo_3-xO₄ under the same experimental conditions.