TiO₂ Activity Enhancement Through The Synergistic Effect Of Photonic Crystals With Double PBGs And The CdS Quantum Dots

Titanium oxide?TiO₂?,as an important semiconductor photocatalytic material,has been attracting worldwide attention in environmental cleanup,solar cells and photolysis of water,owing to its good photocatalytic performance,high chemical stability,low toxicity,availability and low price,etc.However,TiO₂ as a photocatalytic material has two shortcomings: one is its quick recombination of ultraviole-light-excited electron-hole pairs,the other is the low light absorption rate caused its large electronic bandgap?EBG?.Therefore,in this paper,we put forward the research topic that TiO₂ activity enhancement through the synergistic effect of photons localization of photonic crystals?PCs?with double PBGs and the CdS quantum dots?QDs?effect,the research content and results are as follows:To begin with,CdS QDs sensitized TiO₂ membrane was synthesized through doping the TiO₂ membrane with CdS QDs by chemical bath deposition method?CBD?.The photodegradation of gaseous CH3CHO?acetaldehyde?was used as probe reaction to test the photocatalytic activity of the prepared membranes under visible light irradiation,and the results showed that the CdS QDs sensitization can enhance the photocatalytic activity of TiO₂ membrane,with the acetaldehyde degradation rate constant?k?on CdS QDs/TiO₂ membranes being 2.82 times of that on plain TiO₂ membranes.Firstly,CdS QDs extended the light absorption to the visible region,thus enhancing the photocatalytic activity.Secondly,the heterojunction between CdS and TiO₂ promoted the transfer of photo-generated electrons,which inhibited the recombination of photogenerated carriers,thus improving the quantum efficiency and photocatalytic activity.Secondly,TiO₂/SiO₂ opal composite membranes were fabcricated by spin-coating a layer of nc-TiO₂ onto the SiO₂ opal layer,and the photodegradation of acetaldehyde was used as probe reaction.The results showed that the enhancement factors for TiO₂/SiO₂-380 membranes was 1.57 compared with nc-TiO₂/SiO₂-dis,which benefited from the photons localization of PCs when the PBG of the SiO₂ PCs overlapping with the absorption edge of TiO₂.Once again CdS QDs/TiO₂/SiO₂ opal composite membrane was prepared by coupling SiO₂ opal layer onto the CdS QDs/TiO₂ membrane,and the PBG of the SiO₂ opal PCs layer was designed at the EBG of the CdS QDs.The photodegradation of gaseous CH3 CHO was used as probe reaction.The results showed that acetaldehyde degradation rate constant on CdS QDs/TiO₂/SiO₂ opal composite membrane reached four times of that on plain TiO₂ membrane.The light harvesting efficiency of CdS QDs sensitized TiO₂ membrane in the visible light region can be improved through the light reflection effect and photons localization at the PBG of photonic crystal,thus improving the photocatalytic activity.Finally,we prepared the PCs with double PBGs through room temperature floating self-assembly and the vertical deposition technique.Then coupling a photonic crystal with double-PBGs onto a CdS quantum dots sensitized TiO₂ layer to prepare a composite membrane.One of the PBGs was designed at the age of the EBG of TiO₂,and the another PBG designed at the age of the EBG of the CdS QDs.The gaseous CH3 CHO was used as probe reaction to evaluate the photocatalytic activity of the composite membranes under the while light irradiation.The results showed that enhancement factors for CdS QDs/TiO₂/SiO₂-380,CdS QDs/TiO₂/SiO₂-460 and CdS QDs/TiO₂/SiO₂ opals with double PBGs were 1.27,1.75 and 2.07 in comparison with the control of CdS QDs/TiO₂/SiO₂-dis.To find out its cause,on the one hand the coupling effect of the PBG of PC and the EBG of CdS QDs improved the light harvesting efficiency of CdS QDs/TiO₂ in the visible light region,on the other hand the synergistic effect of PCs with double PBGs and CdS QDs significantly improved the photocatalytic activity of TiO₂.