Studies On Adsorption-Photocatalytic Degradation Of Indoor VOC By Using TiO₂/ACF Composite

On account of its high efficiency,convenience,non-pollution,etc.,adsorption-photocatalytic method has a broad application prospect in the field of indoor volatile organic compounds'?VOC?control.Activated carbon fiber?ACF?and TiO₂ are excellent adsorbent and photocatalyst,respectively.Loading TiO₂ particles onto ACF surfaces by appropriate method and forming TiO₂/ACF composite can comprehensively utilize the strong adsorptivity of ACF and high photocatalytic activity of TiO₂,which can effectively degrade indoor VOC.However,with respect to the adsorption-photocatalytic degradation of indoor VOC by using TiO₂/ACF composite,some problems are existing:most experimental systems differ from actual gas purification environment definitely;the immobility of TiO₂/ACF composite is usually poor;discussions of influencing factors on VOC degradation rate are defective,etc.Based on the above issues,in order to make simulated air purification environment more closer to reality,a closed-cycle experimental system was designed and built.The environmental chamber and photocatalytic reactor were amplified properly,black light lamp with low power was chosen as the illuminant,and the simulated pollution sources,frequency converter system,automatic starting and stopping device,thermoregulating and conditioning devices,as well as measuring systems were configured to the closed-cycle system.Afterwards,using AlPO₄ as binding agent,P25 nano-TiO₂ particles were loading onto the ACF surfaces by adhesive method to prepare TiO₂/ACF composite filter,and the properties of TiO₂/ACF were investigated by means of XRD,TG,BET,etc.Finally,typical indoor VOC such as formaldehyde and xylene were selected as model pollutants,degradation effects of preparing composites by different adsorbent substrates were compared in the closed-cycle system.Meanwhile,influences of initial concentration,face velocity and relative humidity on the adsorption-photocatalytic degradation of gaseous xylene by using TiO₂/ACF composite,as well as the corresponding analysis of photocatalytic reaction kinetics were studied.After the analysis of experimental results,several conclusions can be obtained:?1?The XRD patterns of ACF,TiO₂,TiO₂/ACF samples indicate that P25 nano-TiO₂particles were well loading onto ACF surfaces by the cohesive action of AlPO₄;average grain size of TiO₂ in the composite and pure TiO₂ are respectively 15.6nm,19.7nm;crystal structure of P25 nano-TiO₂ is almost unchanged when AlPO₄ is used as the binding agent.?2?The TG patterns of ACF,TiO₂/ACF samples indicate that pyrolysis temperature of the viscose-based ACF is at about 550?,and the TiO₂/ACF composite filter has a high thermal stability.?3?The nitrogen adsorption-desorption isotherms of ACF,TiO₂,TiO₂/ACF samples indicate that large amounts of microporous structures exist in ACF and TiO₂/ACF composite.The pore structure of TiO₂/ACF is similar to the slit pore,which is produced by layered structure.Thus,it can be drawn that nano-TiO₂ particles are effectively loading onto the layered structure of ACF.In addition,specific surface area of the TiO₂/ACF composite is slightly decreased than ACF while the composite prepared by adhesive method still has a large value(S_BET=672.843m²/g).?4?Comparing the degradation of low concentration formaldehyde and xylene when using different adsorbent substrates such as wooden honeycomb activated carbon,coconut shell activated carbon,viscose-based ACF,we find that the degradation rate of TiO₂/ACF is the highest,no matter for polar molecule as formaldehyde,or non-polar molecule as xylene,which both can reach about 80%in 2 hours.?5?The influence law of initial concentration on adsorption-photocatalytic degradation of xylene by TiO₂/ACF at different velocities present differently.When V=0.15m/s,degradation rate of xylene firstly rises and then declines with the increasing of initial concentration;when V=0.3m/s,variation of initial concentration has little influence on the degradation of xylene.After the analysis of photocatalytic reaction kinetics at different initial concentrations when V=0.15m/s,we can conclude that photocatalytic degradation process of gaseous xylene by using TiO₂/ACF in closed-cycle system is basically fitting to L-H first order reaction kinetics model.?6?Under the condition that C₀=24mg/m³,T=24?,RH=30%,adsorption rate of xylene gas firstly rises and then declines with the increasing of face velocity in the period of adsorption,which reaches the maximum value when V=0.3m/s.In the period of photocatalytic reaction,by analyzing photocatalytic reaction kinetics at different face velocities,we find that influence law of velocity on photocatalytic degradation rate is consistent with the adsorption rate's,and then the corresponding degradation equation,apparent first order reaction rate constant,etc.are obtained by linear fitting.In general,the adsorption-photocatalytic degradation effect of xylene by using TiO₂/ACF is the optimum when V=0.3m/s.?7?Under the condition that C₀=38mg/m³,V=0.3m/s,T=24?,adsorption efficiency of xylene gas is the best when RH=30%in the period of adsorption,as relative humidity increases,adsorption rate of xylene declines gradually.In the period of photocatalytic reaction,by analyzing photocatalytic reaction kinetics at different relative humidities,we find that over lowering or excessive humidity is both unfavorable for the proceeding of photocatalytic degradation,and the photocatalytic degradation rate of gaseous xylene reaches the maximum when RH=50%,of which the corresponding apparent first order reaction rate constant k'equals to 0.347h^-1.In general,the adsorption-photocatalytic degradation rate of gaseous xylene by using TiO₂/ACF is the optimum when RH=30%-50%,which can reach more than 90%in 5 hours.