Photocatalytic Degradation Of Benzene And Toluene With Heteropolyacid Composite Catalysts

Heteropolyacids as eco-friendly catalysts represented by12-tungstophosphoric acid are unique and versatile catalysts since they possessbifunctional catalytics of strong acidity and high redox ability, thereby they havea widely usein many fields. However, heteropolyacids have very low surfaceareas and high solubility, and these properties make some difficulties in catalystrecovery and catalyst life. Therefore, it is necessary to further study aboutmodified and supported heteropoly acid to improve its applicability.In this work, TiO₂and attapulgite （ATP） clay which is inexpensive naturalnano-structural material as potential candidates of carrier materials due to theirunique structure.HPA loaded TiO₂and ATP by sol-gel method. The compositecatalysts were characterized with XRD, SEM and BET to determine theirstructural, morphological and photocatalytic properties. The influences ofdifferent prepartion parameters on the photocatalytic ability wereinvestigated.The mechanisms of photocatalytic degradation and dynamics forbenzene series （BTEX） on the surface of ATP/HPA and HPA/TiO₂were studied.Studied. The effects of water vapor, oxygen and nitrogen concentration on thephotocatalytic degradation of benzene and toluene were investigated.The resultsare as follows.Tungstophosphate acid （PW） loaded TiO₂by sol-gel method andcharacterized by XRD, SEMand BET. The activity of the catalyst was evaluatedby investigation the photocatalytic degradation of benzene and toluene. Resultsindicated that the most favorable parameters for preparation of PW/TiO₂weremole ratio of0.0085:1, calcination temperature of350℃, calcination time of2h.Under these optimized conditions, after1-hour illumination, the degradationefficiency of1106.9mg/m3of benzene were13.5%, the degradation efficiencyof113.8mg/m3of toluene was50.7%. The study also showed that PW/TiO₂exhibited greater photocatalytic activity than TiO₂orPW.Tungstophosphate acid loaded attapulgite （PW/ATP） by sol-gel method andcharacterized by XRD, SEM and BET. The activity of the catalyst was evaluatedby investigation the photocatalytic degradation of benzene and toluene. Resultsindicated that the most favorable parameters for preparation of PW/ATPwere load of40%, calcination temperature of500℃,calcination time of3h.Underthese optimized conditions, after1-hour illumination, the degradation efficiencyof210.8mg/m³of benzene were26.3%, the degradation efficiency of153.2mg/m³of toluene was27.3%.The study also showed that PW/ATPexhibitedgreater photocatalytic activity than ATPorPW.The effects of water vapor, oxygen and nitrogen on the photocatalyticdegradation efficiency of benzene and toluene was investigated. The resultsshowed that ambient O₂could be an important condition for benzene andtoluenedegradation with photocatalytic.The degradation efficiencies ofbenzeneand toluene were higher than in presence of N₂or water vapor. The electrongenerated from TiO₂is trapped by HPA first in the PW/TiO₂system, followed byelectron transfer from PW to oxygen or water. Thus, electron directly to O₂orH2O to yield free strong oxidizing O₂-or OH radical species, these radicalspecies reacted with benzene and toluene, which resulted in the degradation ofbenzene and toluene.UV excitation of PW inducedelectrons and holes in the PW/ATPsystem, the photodegradation of benzene and toluene was mainly mediated throughthe generation of O₂-orOH radical species. O₂-orOH radical specieswere thedominant photooxidant in PW/TiO₂andPW/ATPmediated photocatalysis.Inpresence of N₂, the photodegradation of benzene and toluenewas mainly mediatedthrough the generation of electrons and holesby PW/TiO₂andPW/ATP.