| TiO2 has been regarded as as one of the most useful photocatalytic and photoelectric materials,but its optical response is limited in ultraviolet light with wavelength shorter than 387 nm.Although considerable efforts have been made to enhance the light harvest of TiO2,such as doping and semiconductor coupling,the light-harvesting effect is limited.In recent years,photonic crystal?PC?--a new kind of materials was found to have good effect on the enhancement of light harvest of TiO2.However,as the research on the enhancement of light harvest through PCs is on its initial stage,the mechanism of PCs' light-harvesting effect is still ambiguous,and how the PCs' photonic band gap?PBG?,periodicity,and its spatial distribution effect on light harvest of TiO2 is yet to be investigated.To address these problems,the nc-TiO2/SiO2 Opal composite films were fabricated by coupling SiO2 Opal PCs to the nc-TiO2 film,and gaseous degradation of acetaldehyde was used as probe reaction to investigate the effect of PCs on the light harvest of nc-TiO2.Contents of the research are as follows:1.The effect of PCs PBG on light-harvesting enhancement of nc-TiO2 was studied.In this work,a series of SiO2 Opals with different PBGs were fabricated via the room temperature floating self-assembly?RTFSA?technique.The PBG of the SiO2 Opal was tuned by the size of SiO2 microspheres constructing the SiO2 Opal.It was found that the nc-TiO2/SiO2 Opal composite film,with the PBG of the SiO2 Opal PCs overlapping with the absorption edge of TiO2,exhibited the highest photocatalytic activity,which was 1.5 times that of the film of nc-TiO2 coated on a disordered porous SiO2 film.The farther the photonic PBG away from the absorption edge of TiO2,the lower the photocatalytic activity of the composite films.When PBG of SiO2 Opal was completely outside of the absorption edge of TiO2,the photocatalytic enhancement was not found.2.The effect of PCs periodicity on light-harvesting enhancement of nc-TiO2 was conducted.The periodicity of SiO2 Opal PCs layer was tuned by the concentration of silica suspension in vertical deposition.It was found that the photocatalytic enhancement factor increased with the SiO2 Opal PCs periodicity,indicating that,the more the periodicity of the PCs,the stronger the effect of its photon localization.However,when the PCs periodicity was more than 35,the enhancement factor tended asymptotically to a stationary value.3.The effect of spatial distribution of photon localization on light-harvesting enhancement of nc-TiO2 was investigated by inserting a SiO2 spacer with various thicknesses between the SiO2 Opal PCs and nc-TiO2.It was shown that the photocatalytic activity decreased with the gap distance between the nc-TiO2 catalytic layer and the PCs layer?i.e.the thickness of the SiO2 spacer?,and when the gap distance was larger than 2.9 ?m,the PCs layer could no longer enhance the photoactivity of the nc-TiO2.The effect of the photon localization of PCs can exist outside the PCs,and weakens with the distance away from the surface of the PCs.4.The effect of photon localization of PCs on the enhanced visible light harvest of TiO2 was investigated.SiO2 Opal SiO2 Opal was coupled with CdS QDs/nc-TiO2 and its photocatalytic performance was investigated.It was shown that the photoactivity of CdS QDs sensitized TiO2 was enhanced by 1.76 times when the PBG of SiO2 Opal was overlapping with the absorption edge of CdS QDs.5.The effect of PCs,which had double PBGs?designated as SiO2 Opal-DPBG?on the enhanced light harvest of TiO2,was investigated.The results showed that when one PBG of SiO2 Opal-DPBG was at the EBG of the CdS QDs?400500 nm?and another PBG was at EBG of TiO2?380 nm?,the photocatalytic activity of the composite film was 2.11 times of that of the film of CdS QDs/nc-TiO2 coated on a disordered porous SiO2 film.This was attributed to the enhanced light harvest of nc-TiO2 at 380 nm and the enhanced light harvest of CdS QDs at 465 nm,and both of the enhancements were induced by the SiO2 Opal-DPBG PCs. |
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