Photocatalytic degradation of volatile chlorinated organic compounds on CuffiO_2 films prepared by size-controlled Cu deposition

在甲酸钠存在下，用光还原法制备了沉积铜的二氧化钛(CuTiO2)薄膜。当初始Cu2+浓度小于50 mg L 1时，薄膜的透过率随辐照时间的增加而降低。在辐照6h后，扫描电子显微镜显示薄膜上的铜颗粒大多为0.51±0.04μm，而在100或150 mg的L溶液中辐照，在透过率下降之前有诱导期。扫描电子显微镜照片显示，在诱导期内，铜颗粒孤立沉积，厚度为(2.6±0.5)μm，且有较大的空隙。这些事实提出了两种制备铜/二氧化钛薄膜的方法。通过改变初始铜(II)浓度小于50 mg L(方法A)或改变诱导期内铜(II)浓度大于100 mg L(方法B)的照射时间，可以验证薄膜上负载的铜量。比较了两种方法制备的CuTiO2薄膜在500℃焙烧条件下对亚甲基蓝的光催化降解活性。在无空气吹扫条件下，B法制备的薄膜具有比纯二氧化钛更高的光催化活性。这一发现归因于薄膜的较高透过率和铜颗粒作为电子陷阱的作用，从而抑制了空穴和电子之间的复合。用B方法制备的CuTiO2光催化降解气相中的三氯乙烯(TCE)，但随着光照时间的增加，TCE的转化率急剧下降。这一事实表明，副产物的积累显著影响了铜/二氧化钛薄膜的性能。

Cu-deposited TiO_2 (Cu/TiO_2) films were prepared by photoreduction of Cu(II) in the presence of sodium formate. With the initial Cu(II) concentrations less than 50 mg L 1, the transmittance of the films decreased with an increase in the irradiation time. After the irradiation for 6 hrs, the scanning electron microscopy (SEM) indicated that the most of the Cu particles on the films were 0.51±0.04 μm. On the other hand, when irradiation was conducted in 100 or 150 mg L^<-1> Cu(II) solution, induction periods were observed before the transmittance decreased. The SEM images of the films indicated that Cu particles of 2.6±0.5 μm were deposited isolatedly with much open space in the induction periods. These facts proposed two methods to fabricate the Cu/TiO_2 films. The Cu amounts loaded on the film can be verified by changing the initial Cu(II) concentration less than 50 mg L^<-1> (method A), or changing the irradiation time within the induction period under the Cu(II) concentration above 100 mg L^<-1> (method B). The photocatalytic activities of the Cu/TiO_2 films prepared by both methods followed by calcination at 500℃ were compared in the degradation of methylene blue in aqueous solutions. The films prepared by method B showed a higher photocatalytic activity than a pure TiO_2 under no purging with air. This finding is attributable to higher transmittance of the films and function of the Cu particles as the electron trap which leads to suppression of the recombination between holes and electrons. Photocatalytic degradation of trichloroethylene (TCE) in the gas phase was also performed on the Cu/TiO_2 films prepared by method B. However, the TCE conversion decreased drastically with an increase in the irradiation time. This fact suggests that the accumulation of the by-products significantly affected the performance of the Cu/TiO_2 films.