Fabrication Of CDs-ZIF-67 Photocatalysts For Gaseous Toluene Adsorption-degradation Properties

Volatile organic pollutants(VOCs)are important precursors for ozone and atmospheric particulates formation.It have extensive sources and cause serious environmental problems like photocatalytic smog.VOCs are ubiquitous indoor air pollutants which may cause severe threats to human and other living things.Visible-light-driven photocatalytic oxidation is a promising strategy to decompose VOCs to harmless substances because of its advantages of excellent catalytic efficiency,environment friendly and low pollutants selectivity.However,there are still some problems in semiconductor photocatalytic technology such as weak visible light absorbability and low efficiency of photo-induced electron and hole separation.These disadvantages limited the application of photocatalytic technology to VOCs treatment.Therefore,a novel photocatalyst CDs-ZIF-67 were synthesized by introducing glucose as the precursor of carbon dots into the microporous structure of ZIF-67.Additionally,properties of as-prepared photocatalyst and adsorption-photocatalytic degradation activities were discussed in detail.The research contents and results are as follows:(1)Through the various characterization analysis,the framework of ZIF-67 remain stable while the carbon dots were produced by the glucose calcinations process in the micropores of ZIF-67.The size of carbon dots was controlled by the ZIF-67 structure.The rich micropores on the surface of ZIF-67 provide the sample good adsorption capacity.The light adsorbing ability was promoted because of the introduction of carbon dots.With the increased of the concentration of carbon quantum dots in the ZIF-67 structure,the fluorescence emission intensity decreased.The efficiency of photo-induced electron and hole separation was improved,which was beneficial to the photocatalytic reaction.(2)The adsorption experiment of CDs-ZIF-67 with benzene aqueous solution revealed that CDs-ZIF-67 sample exhibited high-efficient for benzene adsorption capacity at the concentration of 100-300 mg/L at room temperature.The adsorption capacity of CDs-ZIF-67 is higher at lower benzene aqueous concentration.The study of adsorption kinetics revealed that the adsorption behavior of CDs-ZIF-67 on benzene aqueous solution conformed to the pseudo-second-order reaction kinetics.The results indicated that the adsorption process includes chemical adsorption process.The reaction rate of adsorption was determined by a variety of factors.(3)During the adsorption-photocatalytic degradation experiment of CDs-ZIF-67 with gaseous toluene,the adsorption process lasted for 15 min to reach adsorption equilibrium.The degradation rate of gaseous toluene with CDs-ZIF-67 photocatalyst in 6 h could reach 74% under visible light irridiation.The photocatalytic degradation activities of the samples were obviously improved after ZIF-67 doped with carbon dots.According to in situ FT-IR analysis,a series of intermediates such as benzyl alcohol,benzaldehyde and benzoic acid were generated during the photocatalytic degradation of gaseous toluene.Some of these intermediates were finally decomposed to CO2 and H2 O.