【作者】 熊轶超；

【导师】 王安杰；

【作者基本信息】 大连理工大学 ， 化学工程与技术， 2012， 硕士

【摘要】 半导体光催化技术是一种新兴、高效、节能的现代绿色环保技术,是光催化剂在光辐射的作用下将水和空气中的有机污染物降解为无毒或者毒性较低的物质。Ti02作为最有潜力的半导体光催化剂之一,因其较强的氧化能力、低廉的价格、稳定的化学性能以及无毒性,被广泛应用于多种有机污染物的降解。但是,Ti02多相光催化技术,由于其光能利用率和量子效率均较低,给其实际应用带来了困难。所以,通过各种改性方法减小TiO2禁带能来提高可见光利用率,同时减少光生电子-空穴对的复合从而提高其量子效率,一直是TiO2光催化技术努力的方向。本论文通过沉积贵金属和掺杂非金属两种方法改性纳米TiO2,达到增强其光催化性能的目的。一般来说,贵金属的功函数(Φm)高于TiO2的功函数(Φs)(4.33-4.85eV),因此当贵金属沉积在TiO2表面时,光生电子将从TiO2颗粒迁移到贵金属表面,这样有效分离了光生电子-空穴对,有利于光催化反应的进行。为此,本文首先以商品级TiO2DegussaP-25为原料,采用等离子体法制备了金属Pt和Pd分别沉积以及共沉积的TiO2,分别标记为Pt/TiO2、Pd/TiO2和PtPd/TiO2。同时,采用传统热法,即程序升温还原(TPR)法制备了Pt和Pd分别沉积的TiO2催化剂,标记为Pt/TiO2(T)和Pd/Ti02(T)。对上述两种催化剂,在可见光下以20ppm亚甲基蓝溶液为底物进行光催化降解实验,并对这两种催化剂进行了氮气物理吸附、ICP、UV-Vis等表征。结果表明,与未改性的P-25相比,Pt/TiO2和Pd/TiO2的催化活性有显著提高；且当贵金属的担载量相同时,等离子体法制备的催化剂,比传统热法制备的催化剂表现出较高的催化活性。在介质阻挡放电(DBD)等离子体发生器中,以H2S/H2的混合气体为放电介质,对商品级二氧化钛Degussa P-25进行放电处理,制备出了淡黄色的S掺杂的TiO2,标记为S-TiO2。同时,采用传统热法,在同样的混合气体中对P-25进行处理,得到的催化剂标记为S/TiO2。对上述两种催化剂,在可见光下以20ppm亚甲基蓝溶液为底物进行光催化降解实验,并对两种改性催化剂进行了XRD、XPS和UV-Vis表征。结果表明,与未改性的P-25相比,等离子体法制得的S-TiO2表现出较高的催化活性；而热法处理得到的S/TiO2催化活性较P-25并未有所提高。XRD结果表明,两种改性方法并未明显改变TiO2的晶粒尺寸和晶相比例。通过UV-Vis表征发现,等离子法制得的S-TiO2与P-25相比,对可见光的吸收显著增强。同时计算结果显示,P-25带隙能为3.0eV,而S-TiO2的带隙能降低为2.7eV。XPS结果显示,采用等离子体法成功地将S元素以负价态的形式掺杂进入了TiO2表面,使得TiO2表面羟基数量减少,氧空穴数量增加。基于上述两种改性方法的良好效果,本文接理来进行了上述两种方法的结合。先利用浸渍法制备出沉积贵金属Pt和Pd的氧化物形式的Ti02,再利用H2S/H2等离子体进行非金属S的掺杂和贵金属的还原,一步得到S-Pt/TiO2和S-Pd/TiO2催化剂,同时考察了这些催化剂降解有机染料亚甲基蓝的光催化活性。通过对比发现,同时沉积了贵金属和掺杂了非金属的二氧化钛,与只沉积贵金属或者只掺杂了非金属的相比,光催化活性并没有提高,这可能是因为贵金属发生了S中毒,从而降低了催化剂的催化活性。更多还原

【Abstract】 Photocatalytic technology, as a modern green environmental protection technology, is novel, highly effective and energy-efficient. It takes semiconductor as the catalysts and decomposes organic pollutant in water and the air into low toxicity or non-toxic substance under the radiation of the light. TiO2, as one of the most popular photocatalysts for decomposing various environmental pollutants, has received much attention due to its non-toxicity, low-cost, photostability, and chemical inertness. Although it has great potential, some problems still hinder practical application of TiO2, such as the low photo-quantum efficiency and low photocatalytic activity under visible light. Therefore, visible-light-active TiO2has been developed by reducing the band gap; meanwhile, to decrease the recombination of photogenerated electrons and holes has been another key point in modification of TiO2. In this paper, the modified TiO2photocatalysts have been synthesized by different procedures to improve their photocatalytic efficiency under visible light.Noble metal, serving as a Schottky-barrier to trap the charge carriers, is usually used to modify the TiO2surface to improve the photocatalytic efficiency. As a result, the second chapter of the paper illuminated modification of TiO2by loading platinum (Pt) and palladium (Pd) via H-plasma reduction (PR) method, which is easier and faster than conditional temperature programmed reduction (TPR). The catalysts were characterized by Nitrogen adsorption-desorpotion, ICP and UV-Vis. The photodecomposition of methylene blue in aqueous solution by all the samples above was also investigated respectively. The results showed that photoactivity of all the noble metal loaded TiO2(denoted as Pt/TiO2, Pd/TiO2, PtPd/TiO2) prepared by PR method were much enhanced, compared to the catalysts prepared by TPR method and Degussa P-25.Yellowish S-doped Degussa P-25(S-TiO2) powders were prepared via a H2S/H2plasma method in a dielectric barrier discharge (DBD) reactor. The other catalyst synthesized by thermal treatment of P-25with the H2S/H2mixture (S/TiO2) was used for comparison. The photocatalytic performances of the catalysts were evaluated by the degradation of a20ppm aqueous solution of a reactive dyestuff, Methylene Blue, under the visible light. The catalysts were characterized by XRD, XPS and UV-Vis. The results indicated that the activity of S-TiO2was much higher than that of P-25, while that of S/TiO2was not significantly improved. The XRD revealed that neither the structure nor the crystal phase ration of P-25 was influenced by the treatments with H2S/H2. The UV-Vis showed that the visible-light absorption of S-TiO2was higher than that of P-25. The band-gap energy of P-25was calculated to be3.0eV, while that of S-TiO2decreased to2.7eV. As evidenced XPS, the negative-valence S was incorporated on the surface of TiO2after the H2S/H2plasma treatment, leading to a decrease in the surface of OH groups and increase in the oxygen vacancies.On the basis of the above two kinds of modification, this paper took a combination of them to get a novel kind of photocatalyst. First, TiO2loaded metallic oxide were made with deposition-precipitation (DP) method, and then, they were treated by H2S (10%)/H2-plasma in order to dope S in the TiO2lattice and reduce metallic oxide on TiO2. In the end, a novel kind of catalyst were obtained and denoted as S-Pt/TiO2and S-Pd/TiO2. The photodecomposition of methylene blue in aqueous solution by all the samples above was also investigated respectively. In contrast to those catalysts only loaded noble metal or doped S, these novel catalysts showed worse photocatalytic activity under visible light.更多还原