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光催化技术在环境净化方面,尤其是降解有机污染物应用上表现出潜在价值.可见光响应型光催化剂具有优异的光吸收特性和高的光催化活性,因而备受人们关注并被大量研究.Pb_3Nb_2O_8光催化剂由于其自身的稳定性以及对可见光响应的能力是一种潜在的高效光催化材料.但是,有报道表明Pb_3Nb_2O_8光催化剂对可见光降解有机物活性较低,这主要归因于它较小的比表面积以及较高的电子-空穴复合率.为了解决这个问题,本文采用蒸发自组装技术制备了大比表面积的介孔Pb_3Nb_2O_8,采用光沉积方式在介孔Pb_3Nb_2O_8上负载了均匀分散的纳米Ag颗粒,并对不同焙烧温度、载Ag量以及进一步的热处理对光催化活性的影响作了深入研究.XRD结果表明,在400℃和500℃焙烧条件下获得的样品属于Pb_3Nb_2O_8相,600℃焙烧使得介孔Pb_3Nb_2O_8发生相变.氮气吸附-脱附表征表明,升高焙烧温度使样品比表面积从最大69 m~2/g(400℃)减小到19 m~2/g(600℃).透射电子显微镜分析结果表明,所获得样品具有蠕虫状介孔孔道结构,并且Ag纳米颗粒均匀分散在介孔Pb_3Nb_2O_8表面.紫外-可见吸收光谱表明,介孔Pb_3Nb_2O_8的吸收边拖尾到530-550 nm,担载Ag之后光吸收发生显著变化,光吸收拓展到700 nm.光催化活性测试采用可见光催化氧化脱氢异丙醇气体至丙酮反应.结果表明,在420 nm以上可见光照射下,1 h内的光催化反应过程中,采用高温固态反应制备的Pb_3Nb_2O_8上丙酮生成速率为2.9 ppm/min,而介孔Pb_3Nb_2O_8催化剂上最高可达55.5 ppm/min.介孔Pb_3Nb_2O_8负载Ag之后,400℃焙烧的介孔Pb_3Nb_2O_8光催化活性显著提高,降解速率达120.7 ppm/min.通过介孔Pb_3Nb_2O_8和固相合成Pb_3Nb_2O_8的光催化活性对比发现,大比表面积样品的光催化活性显著提高.这可归结为大的比表面积提供了大量的催化反应活性位点,从而提高了光催化反应活性,此外介孔材料的孔壁结构为纳米结构,有利于光生电子-空穴传输到表面参加反应.担载Ag后介孔Pb_3Nb_2O_8的光催化活性进一步提高,主要是因为助催化剂Ag纳米颗粒促进了光生电子-空穴分离,延长了载流子寿命,从而提高了光催化活性.
Photocatalytic technology has shown potential value in the environmental purification, especially the application of degrading organic pollutants. Visible light-responsive photocatalyst has attracted much attention and been studied extensively due to its excellent light-absorbing properties and high photocatalytic activity.Pb_3Nb_2O_8 The photocatalyst is a potentially efficient photocatalytic material due to its own stability and its ability to respond to visible light.However, it has been reported that the Pb 3 Nb 2 O 8 photocatalyst has a low activity on visible light degradation of organic compounds, mainly due to its smaller ratio Surface area and high electron-hole recombination rate.In order to solve this problem, the mesoporous Pb_3Nb_2O_8 with large specific surface area was prepared by evaporation self-assembly technique, and the uniformly dispersed nano-Ag particles were loaded on the mesoporous Pb_3Nb_2O_8 by photo-deposition , And the effect of different calcination temperature, Ag loading and further heat treatment on the photocatalytic activity was studied.XRD results show that the samples obtained at 400 ℃ and 500 ℃ are Pb_3Nb_2O_8 phase calcined at 600 ℃, Pb_3Nb_2O_8 phase transition occurred.Nitrogen adsorption - desorption characterization showed that increasing the calcination temperature of the sample The specific surface area decreased from 69 m ~ 2 / g (400 ℃) to 19 m ~ 2 / g (600 ℃) .The results of transmission electron microscopy showed that the samples obtained had worm-like mesoporous pore structure and Ag nanoparticles Uniformly dispersed on the surface of mesoporous Pb_3Nb_2O_8.The UV-Vis absorption spectra showed that the absorption edge of mesoporous Pb_3Nb_2O_8 was traced to 530-550 nm, the absorption of light changed significantly after loading Ag, and the light absorption was extended to 700 nm. The photocatalytic oxidation of dehydrogenation of isopropanol to acetone using visible light was performed.The results showed that the formation rate of acetone on Pb_3Nb_2O_8 prepared by high temperature solid-state reaction was 2.9 ppm / min, and up to 55.5 ppm / min on the mesoporous Pb_3Nb_2O_8 catalyst.The photocatalytic activity of the mesoporous Pb_3Nb_2O_8 calcined at 400 ℃ increased significantly after the mesoporous Pb_3Nb_2O_8 was loaded with the degradation rate of 120.7 ppm / min.The mesoporous Pb_3Nb_2O_8 and the solid The photocatalytic activity of Pb3Nb2O8 synthesized by the phase comparison shows that the photocatalytic activity of the sample with a large specific surface area is significantly increased, which can be attributed to the fact that a large specific surface area provides a large number of catalytic reactive sites, High photocatalytic activity, in addition the mesoporous material pore structure of the nanostructures conducive to photogenerated electron-hole transport to the surface to participate in the reaction.After carrying Ag mesoporous Pb 3 Nb 2 O 8 photocatalytic activity further increased, mainly because of help Ag nanoparticles promoted the photogenerated electron-hole separation, prolonging the lifetime of carriers and increasing the photocatalytic activity.