Carrier Transport Path Regulation On TiO₂ Interface For Photocatalytic Degradation Of VOCs

As the important precursors of secondary organic aerosols,volatile organic compounds（VOCs）have bocome one of the major air pollutants in China.Although photocatalysis is a potential VOCs treatment technology,current photocatalytic degradation efficiency of VOCs needs to be further promoted to meet industrial needs.It is widely accepted that the transport of carriers to the adsorbed molecules is the rate-limiting step of photocatalysis.In order to regulate the interfacial carrier transport path and imporove the photocatalytic degradation and mineralization efficiency of VOCs,we employed Sn doping,TiO₂ quantum dot（QD）,and Pd and TiO₂ dual quantum dots methods to construct localized reaction sites on the surface of TiO₂nanoparticles.By utilizing the atmospheric surface photovoltage system built in-house and other material characterization methods,we explored the effects of local surface sites on the separation and interfacial transport of carriers.The specific results are as follows:（1）When only water was present,Sn doping enhanced the transmission of photogenerated electrons to surface water molecules.When both water and toluene existed,they captured photogenerated electrons and holes,respectively.Therefore,Sn doping was shown to effectively improve the separation,migration and utilization of photogenerated carriers and might promote the direct interaction between toluene and photogenerated holes.Besides,Sn doping increased the specific surface area of TiO₂ and provided abundant acid sites.Under 50%humidity conditions,the photocatalytic degradation zero-order reaction rate constant of Sn doped TiO₂ for toluene was 2.3 times that of the blank TiO₂ nanoparticles.（2）The heterogeneous interface between TiO₂ quantum dots and TiO₂ nanoparticles,which was constructed by a dipping method,changed the local electric field and increased the accumulation of holes in the TiO₂ quantum dots.The quantum size effect made the valence band maximum of TiO₂ quantum dots lower than that of TiO₂ nanoparticles,which further enhanced the oxidation ability of the material.In addition,the TiO₂ quantum dots and the Ti and O atoms of the surrounding TiO₂ nanoparticles formed a local catalytic site,which improved the separation efficiency of electron-hole pairs.Under 50%humidity conditions,the the photocatalytic degradation zero-order reaction rate constant of TiO₂ quantum dots modified TiO₂ for toluene was 2.7 times that of the control TiO₂ nanoparticles.（3）Local reduction-oxidation reaction sites were constructed on the surface of the Pd and TiO₂ dual quantum dots modified TiO₂ nanoparticles by using a photoreduction method.Pd quantum dots and TiO₂ quantum dots synergistically enhanced the carrier interface transport efficiency at the TiO₂ interface by inducing the transfer of photogenerated electrons to O₂ and the transfer of photogenerated holes to toluene,respectively.Under 50%humidity conditions,the photocatalytic degradation zero-order reaction rate constant of Pd and TiO₂ dual quantum dots modified TiO₂ nanoparticles for toluene was 4.4 times that of the control TiO₂ nanoparticles.