Preparation Of Lanthanum-nitrogen Codoped Titanium Dioxide And Its Photocatalytic Activity For Chlorobenzene Conversion

Recently,the harm to the environment and human caused by volatile organic pollutants(VOCs)had aroused more and more attention.Chlorobenzene(CB)was one of the important VOCs.Due to the structure stability of benzene ring,it was difficult to be degraded by the conventional biological techniques.Meanwhile,because of higher hydrophobicity,it was difficult to transfer between gas and water phase.Therefore,the traditional biofiltration was improper for treatment of this kind compound.The reasonable pretreatment technology has received more and more attentions in order to effectively solve these problems.Ti02 photocatalyst,with the advantages of high catalytic activity,good stability,strong oxidation ability and less secondary pollution production,could transform high hydrophobicity and high poisonous pollutants directly to water soluble and easily biodegradable compounds.With a result,it could provide a possibility for sequent biotreatment.Lanthanum-nitrogen co-doped TiO2 nanotubes were prepared by a combination of sol-gel and hydrothermal method using the Box-Behnken of response surface method to design the experiment.It obtained the best proportion of catalyst(1.33La/0.54N-Ti(0.52))by the analysis of response surface.It indicated that[La],[N]and[(NH4)2CO3]had significant impacts,and[(NH4)2CO3][N]had significant interaction on the conversion of CB.Thrpugh XRD,TEM,BET,UV-vis and FTIR analysis,it indicated that the as-prepared catalyst had nanotubes structure(the diameter was 6-8nm)and the bigger specific surface(395.5m2/g).This catalyst with mixture crystal(anatase and rutile)structure could strongly respond 365nm wavelength,and the redshift of maximum absorption wavelength was near visible light region.With the best prepared photocatalyst,the best CB conversion efficiency could reach 93.3%when the RH was 10%and residence time was 60s.When CB initial concentration increased to 150 mg/m3,the conversion efficiency decreased to 85%.The photocatalytic conversion of CB was according with the Langmuir-Hinshelwood mode,and it suggested that the catalytic action controlled the conversion rate.The deactivated catalyst could be regenerated by the UV365 irradiation 3h and the conversion efficiency could be restored to nearly 80%.GC/MS was used to analyze the generated intermediates.It was found that CB was mainly transformed to p-clorophenol and 3-chlorphenol firstly,and then 4-Hydroxybenzoic acid and other small organic compounds.Three possible degradation pathways were established and the pathway of CB—p-clorophenol/p-clorophenol—4-hydroxybenzoic acid—small molecular substances was speculated as a main conversion pathway.The analysis of solubility and poisonousness of intermediates indicated that the solubility increased and the poisonousness reduced.All the results suggested that the prepared photocatalyst could be used in the pretreatment before the biological treatment.