TiO_2薄膜的Ag改性及光催化活性

Silver Modification of TiO_2 Thin Films and Their Photocatalytic Activity

用光化学沉积法对纳米TiO2薄膜进行了Ag改性,用漫反射紫外-可见光谱、扫描电子显微镜和X射线光电子能谱分析了Ag-TiO2薄膜的光谱特征、表面形貌和表面组成.以苯酚为模拟污染物,在不同波长光源及有氧和无氧条件下考察了Ag-TiO2薄膜的光催化活性.结果表明,当银沉积量大于0.0150mg/cm2时,Ag-TiO2薄膜对紫外光的吸收发生了明显的蓝移,同时在346nm附近出现了小的吸收峰且该峰随着银沉积量的增加逐渐向长波方向移动.沉积在TiO2薄膜表面的银颗粒大小不均匀,主要以单质银的形式存在,也生成了部分Ag2O;相对于TiO2薄膜,Ag-TiO2薄膜表面吸附氧的含量明显增大.Ag-TiO2薄膜的光吸收特性对其催化活性影响较大.在低压汞灯及有氧参与的条件下,银沉积量为0.0523mg/cm2的Ag-TiO2薄膜的催化活性最高,其反应速率常数是TiO2薄膜的1.16倍.Ag+更易沉积在较大n值的Ag簇上,其颗粒大小不可能完全均匀.Ag-TiO2薄膜的光吸收特性、Ag簇的大小以及Ag对O2的吸附作用是决定Ag-TiO2薄膜催化活性的主要因素.

Silver-modified TiO2 thin films were prepared by the photodeposition method, and their optical characteristics, distribution and size of silver clusters on the surface, and surface states were analyzed by diffuse reflectance ultraviolet-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The photocatalytic activity of the films was tested using phenol degradation as the model reaction under the irradiation with ultraviolet light of different wavelengths in the presence or absence of oxygen. The resuits showed that when the Ag loading exceeded 0.015 0 mg/cm^2, a remarkable blue shift of the absorption band of the Ag-TiO2 thin films was observed. In addition, the minor absorption peak around 346 nm appeared and shifted toward the long wavelength with increasing Ag loading. Silver particles photodeposited on the surface of the films were nonuniform and existed mainly as Ag^0 with a little Ag2O. The content of O2 adsorbed on the surface of Ag-TiO2 was increased remarkably in contrast to that of the pure TiO2 thin films. The photocatalytic activity of the Ag-TiO2 thin films was greatly affected by their light absorption character. When irradiation by a low pressure mercury lamp in the presence of oxygen, the Ag-TiO2 thin films reached the maximum activity at a Ag loading of 0. 052 3 mg/cm^2, and the first-order rate constant was 1.16 times that of the TiO2 thin films. These results indicated that Ag ＋ preferably deposited on silver clusters with a large n value, and the photocatalytic activity of the Ag-TiO2 thin films was mainly affected by their light absorption character, the size of silver clusters, and the adsorption ability of silver clusters to O2.