紫外吸收光谱法研究ZnO/碳纳米管复合材料催化降解偶氮染料

以Zn(NO₃)₂和酸化多壁碳纳米管为原料采用水热法合成了ZnO/碳纳米管复合材料，产物经X射线粉末衍射(XRD)和透射电子显微镜(TEM)表征，表明六方晶相的ZnO颗粒大小约为28 nm。紫外吸收光谱研究表明, 该复合材料在太阳光照下具有较高的光催化降解偶氮染料的活性。探究了光照时间﹑催化剂用量﹑染料浓度以及不同的染料结构等因素对催化效率的影响，结果表明随光照时间的延长，偶氮染料位于400 nm的特征峰强度逐渐减弱，且偶氮染料的降解呈准一级的反应。该复合材料对三种染料：酸性橙﹑酸性大红﹑酸性嫩黄的溶液都具有较好的降解能力，反应速率分别为0.09，0.28，0.22 mg· L-1·min-1,此光催化降解速率的差异是由于偶氮染料分子中有机官能团的不同所造成。当选用最优条件时，该复合材料可以迅速降解染料，且经过五次循环后，其催化效率仍高于50％。

Study on Photocatalytic Decomposition of Azo-Dyes by ZnO/Carbon Nanotubes Composites by UV-Vis Spectroscopy

ZnO/carbon nanotubes composites were prepared by hydrothermal treatment of the mixture of zinc nitrate and acid-treated multiwalled carbon nanotubes and characterized by transmission electron microscope (TEM) and X-ray powder diffraction (XRD). The TEM image indicated that ZnO nanoparticles with a diameter about 28 nm covered the carbon nanotubes. The XRD pattern shows that ZnO nanoparticles attached to the MWNTs exhibit a hexagonal phase. The diffraction peaks can be assigned to (100), (002), (101), (102), (110), (103), (200), (112) and (201) planes of the crystalline ZnO, respectively. The average size of the crystalline ZnO, calculated from the half-width of the (100) diffraction peak by the Scherrer equation, is 27.8 nm, which accords with the TEM observation. The ZnO/carbon nanotubes composites were used as a photocatalyst under sunlight for the decomposition of azo-dye, which was studied by UV-Vis spectroscopy. The effects of the illumination time, catalyst amount, initial dye concentration and the different structures of the dye on the photocatalytic process were investigated. It was noted that the intensity of the absorption peak corresponding to the azo-dye decreased rapidly at 400 nm during the photolysis process and the decomposition of azo-dye was a quasi-first order reaction. The decomposition rates for azo-dyes such as acid orange, Acid bright red, Acid light yellow are 0.09, 0.28 and 0.22 mg x L(-1) x min(-1), respectively, which maybe resulted from their different functional groups. It can be stated that the complete removal of color, after selection of optimum operation parameters, can be achieved in relatively short time by using ZnO/carbon nanotubes composites. After recycling 5 times, the catalyst still has more than 50% efficiency.