光子晶体与上转换发光协同作用提高二氧化钛光催化性能规律及机理研究

TiO2 has been regarded as an most useful photo-catalytic material due to its high stability and efficiency, low toxicity, low price and availability. However, the wide electronic band-gap (EBG=3.2 eV) of anatase TiO2 limits its utilization in ultraviolet light with wavelength less than 387nm which occupies just 4% of sunlight. Extensive efforts have been made to enhance the energy harvesting efficiency of TiO2. Through sensitization by CdS quantum dots, the absorption edge of TiO2 can be extended to the visible light region, but the utilization of visible light is still limited and the near infrared light which occupies 47% of sunlight is still underused. On the one hand, up-conversion luminescence is considered to be one of the effective methods to raise the utilization of near-infrared light. On the other hand, the effect of stop band reflection and photon localization of photonic crystal on enhancing the light absorption is remarkable. But in terms of photo-catalyst, inverse opal photonic crystals are more used for the bigger specific surface area. However the light at the stop band of inverse opal photonic crystals will be reflected and can’t propagate in photonic crystals. so the reflected light at band gap of photonic crystals can’t be used. To improve the utilization of sunlight on TiO2, SiO2 opal photonic crystals membrane is used as the band gap reflector to enhance the light harvesting at stop band of photonic crystals. Furthermore, the preparation of SiO2 opal photonic crystals is far easier than that of inverse opal photonic crystals. In the study, the SiO2 opal photonic crystals is coupled with up-conversion luminescence materials, then composited with TiO2 photo-catalyst sensitized by CdS quantum dots. The photo-catalytic degradation of acetaldehyde on CdS/TiO2/Up-converter/SiO2 opal composited photo-catalysts is used as the probe reaction. The project is to research the rule of the coupling of photonic crystals and Up-converter on enhanced photo-catalytic performance of Titania materials.

二氧化钛作为最有前景的半导体光催化剂，其最大的缺点在于光催化活性高的锐钛矿二氧化钛只能吸收波长小于387nm的紫外光，虽然通过CdS量子点可将二氧化钛吸收边延伸到可见光区但其光利用率仍有限，而且，太阳光中约47%的近红外光未得到利用，而上转换发光被认为是提高近红外光利用率的有效方法之一。另外，光子晶体带隙效应和光局域效应在增强光吸收方面效果显著，而在光催化领域，由于反opal光子晶体具有更大的比表面，人们多采用单层反opal光子晶体。但因为在光子带隙频带内的光无法在反opal光子晶体内传播，导致这部分光无法被利用。为提高TiO2对太阳光的利用率，本项目利用制作容易的SiO2 Opal光子晶体膜作为带隙反射层，将之与上转换发光材料耦合，以CdS量子点敏化的TiO2为光催化剂，光催化降解乙醛为探针，研究光子晶体与上转换发光效应协同作用增强半导体催化剂光吸收率的相关规律。

光催化活性高的锐钛矿二氧化钛只能吸收波长小于387nm的紫外光，因此其光利用率有限，目前大部分研究集中于提高二氧化钛可见光利用率，而对于太阳光中约47%的近红外光的利用却少有研究。为利用太阳光中的近红外光，上转换发光被认为是最具有应用前景的方法之一。但目前的上转换发光剂的量子效率通常较低，而利用光子晶体提高上转换量子效率近年来颇受关注。本项目将SiO2 Opal光子晶体与稀土掺杂的NaYF4（RE3+：NaYF4）上转换发光材料耦合，以CdS量子点敏化的TiO2（CdS QDS-TiO2）为光催化剂，光催化降解罗丹明B为探针，研究了光子晶体与上转换发光协同作用增强半导体催化剂光吸收率的相关规律。研究结果表明当光子晶体的带隙位置分别与TiO2的吸收边及CdS QDS的吸收边吻合时，利用SiO2 Opal的带隙反射与光局域效应，可同时增强TiO2在紫外光区和可见光区的光吸收，其全光光催化性能提高了2.11倍。而当CdS QdS-TiO2与NaYF4：Yb,Tm上转换发光材料复合后，由于NaYF4：Yb,Tm可以发出CdS QdS-TiO2可以吸收的紫外光及可见光，所得的复合催化剂在近红外光下也显示出一定的催化性能，在全光下复合粒子的光催化性能是TiO2的11.2倍。而通过将SiO2 Opal光子晶体与RE3+：NaYF4上转换发光材料复合，当光子晶体的带隙与上转换粒子的发射峰吻合，此时NaYF4:Yb/Tm和NaYF4:Yb/Er的发光强度分别提高了34.71倍和23.13倍。这项工作为太阳能电池、环境光催化和光通信等太阳能利用领域的采光强化提供了宝贵的信息，为光子晶体、上转换材料及光催化剂的制备与应用提供了一定的指导，另外对实现全光响应光催化剂的制备与应用具有促进作用。