【作者】 陈代梅；

【导师】 姜忠义；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 二氧化钛（TiO₂）由于具有化学性质稳定、抗光腐蚀、无毒和成本低等优点,在光电转化和光催化领域具有广阔的应用前景。然而,TiO₂的禁带宽度较大（3.0-3.2 eV）,只能被波长小于387nm的紫外光激发,且光生电子和空穴易复合,因此限制了其在光催化领域的广泛应用。为了增强TiO₂可见光吸收和提高TiO₂光催化效率,本论文采用溶胶-凝胶法制备了一系列B、C、N、C-N掺杂TiO₂,采用高温分解法制备了N-F共掺杂TiO₂,采用吸附法制备了锌卟啉修饰的N掺杂TiO₂。通过TG-DTA、XRD、TEM、XPS、FT-IR和UV-Vis光谱等手段来考察非金属掺杂TiO₂的组成和结构,并研究了其光催化特性。第一,采用溶胶-凝胶法制备了B-TiO₂,并对其结构和催化特性进行了研究。研究结果表明:掺杂的B元素以B³⁺的形式进入了TiO₂晶格的间隙,形成了Ti-O-B结构;B元素的存在可有效抑制TiO₂颗粒的生长,促进TiO₂从锐钛矿向金红石的相转变。但当B掺杂量过大时会在TiO₂颗粒表面形成B2O3,从而抑制TiO₂相转化;采用NADH的再生体系来评价B-TiO₂在紫外光下的光催化活性,发现其光催化活性均高于未掺杂TiO₂,这是由于B掺杂提高了TiO₂的禁带宽度和紫外光吸收。当B和Ti的原子比达到5 at.%时,再生效率最高,达到了94%。第二,采用溶胶-凝胶法制备了C-N-TiO₂,并对其结构和光催化特性进行了研究。研究结果表明:N原子取代TiO₂晶格中氧原子,形成了N2p能带,从而降低TiO₂的禁带宽度,提高TiO₂对可见光的吸收。而C原子不能进入TiO₂晶格,而是在TiO₂颗粒表面形成活性炭和碳氧化合物的复合物薄层,该薄层有类似染料敏化剂的作用,可增强可见光吸收;C和N掺杂均可抑制TiO₂颗粒的生长,其中,C掺杂作用更明显;采用亚甲基蓝降解体系比较不同掺杂量的C-TiO₂、N-TiO₂和C-N-TiO₂在可见光下的光催化活性,由于掺杂的C和N元素的协同效应,C-N-TiO₂表现出比单掺杂TiO₂更高的可见光催化活性。第三,采用高温煅烧（NH4）2TiF6法制备了N-F-TiO₂,并对其结构和光催化特性进行了研究。研究结果表明:随着煅烧温度升高和煅烧时间延长,（NH4）2TiF6先分解为NH4TiOF3和TiOF2,而后逐渐转变成锐钛矿型N-F-TiO₂。硼酸作为氧源可促进TiO₂的形成,提高TiO₂的结晶度和产率;N和F原子取代了TiO₂晶体中的氧原子,且掺杂效率比溶胶-凝胶法高。此外,掺杂N原子提高了TiO₂的可见光吸收,掺杂F原子增加了TiO₂的表面酸性和活性位点,因此N和F共同掺杂会产生协同效应;亚甲基蓝可见光催化降解实验表明,所合成的N-F-TiO₂表现比商业化产品Degussa P25更高的光催化活性。第四,采用吸附法制备了锌卟啉修饰的N-TiO₂,并对其结构和光催化特性进行了研究。研究结果表明:由于羧基的存在,ZnTCPP（四羧基苯基锌卟啉）和TiO₂发生配合形成C-O-Ti键,使得ZnTCPP更容易吸附在N-TiO₂的表面;亚甲基蓝可见光催化实验表明,由于吸附的染料分子和N掺杂的协同效应,ZnTCPP修饰的TiO₂表现出比N-TiO₂和ZnTCPP修饰的纯TiO₂更高的光催化活性。更多还原

【Abstract】 Titanium dioxide （TiO₂） has been considered as one of the most promising materials for its application in photocatalysis and photoelectric conversion because of its high chemical stability, corrosion resistance, non-toxicity and low cost etc. However, the wide band gap （3.0-3.2eV, only absorbing the UV light ofλ<387nm） and the easy recombination of photoinduced electrons and holes result in a low efficiency of photocatalysis and seriously limit the practical application of TiO₂. In order to improve the photocatalytic activity or extend the optical absorption to the visible light region, in this dissertation, a sol-gel method was developed to prepare the B-TiO₂, C-TiO₂, N-TiO₂ and C-N-TiO₂ nanopaticles, the dye adsorption was employed to prepare the N-doped TiO₂ modified by Zn porphyrins, and a pyrolysis method using （NH4）2TiF6 as the precursor was introduced to prepare the N-F-TiO₂, respectively. The chemical composition and structural properties of these nonmetals doping TiO₂ nanoparticles were investigated by TG-DTA, XRD, TEM, XPS, FT-IR and UV-Vis spectroscopy, and their photocatalytic activity were studied in detail.Firstly, TiO₂ nanoparticles only doped with B element were prepared by a sol-gel method, and their structure and photocatalytic properties were studied. The results showed that B³⁺ was likely to weave into the interstitial TiO₂ structure, forming the chemical environment like Ti-O-B. The doping of boron ions could efficiently inhibit the grain growth and facilitate the anatase-to-rutile transformation prior to the formation of diboron trioxide phase. When the B amount is high enough to form the diboron trioxide, the doping of boron ions could inhibit the anatase-to-rutile transformation. The photocatalytic activity of the B-doped TiO₂ nanoparticles was evaluated by the photoregeneration of nicotinamide adenine dinucleotide （NADH） under UV-Vis light. All B-doped TiO₂ nanoparticles calcined at 500oC showed higher photocatalytic activity than pure TiO₂ sample due to the increase of band gap and absorption in the UV range. When the molar ratio of B to Ti was 5%, the TiO₂ nanoparticles could photocatalytically reproduce 94% NADH.Secondly, C-N-codoped TiO₂ nanoparticles were prepared by a sol-gel method, and their structure and photocatalytic properties were studied. The results revealed that N atoms could incorporate into the lattice of anatase through substituting the sites of oxygen atoms and induce N2p state, which can narrow the band gap of TiO₂ and enhance the visible light absorption, while most of C atoms could form a mixed layer of deposited active carbon and carbonate species on the surface of TiO₂, which can act the role of photosensitiser like the organic dyes and widen the region of visible light absorption. The doping of C and N atoms could suppress the crystal growth of TiO₂, and the effect of C doping was more pronounced than that of N doping. The photocatalytic activity of resulting C-TiO₂, N-TiO₂ and C-N-TiO₂ samples with different C and N content were evaluated by methylene blue degradation under visible light irradiation. It was found that C-N-TiO₂ nanomaterials exhibited the highest photocatalytic activity, which could be attributed to the synergistic effect of doped C and N atoms.Thirdly, N-F-codoped TiO₂ nanoparticles were prepared by pyrolysis of （NH4）2TiF6, and their structure and photocatalytic properties were studied. The results demonstrated that, with the increase of calcination temperature and time, （NH4）2TiF6 was decomposed into NH4TiOF3 and TiOF2 firstly, and then transformed into anantase N-F-codoped TiO₂. H3BO3 as oxygen source can promote the formation of anantase TiO₂, increase the crystallinity and productivity of TiO₂. N and F atoms replaced oxygen sites of anatase TiO₂, meanwhile, the amount of doping N and F of N-F-TiO₂ prepared by this approach was greater than those prepared by the sol-gel approach. N doping enhanced the visible light absorption, and F doping led to the enhancement of surface acidity and active sites. So, there is the synergetic effect of doped N and F atoms together. The photocatalytic activity of N-F-TiO₂ was evaluated by methylene blue degradation under visible light. It was found that N-F-TiO₂ exhibited higher photocatalytic activity than Degussa P25.Finally, N-TiO₂ nanoparticles sensitized by dye were prepared by direct adsorption of Zn porphyrin onto the surface of N-TiO₂, and the characterization and photocatalytic properties of these TiO₂ nanoparticles were carried out. The results showed the ZnTCPP was chemisorbed on the surface of TiO₂ through a C-O-Ti bond, while the ZnTPP was physically adsorbed. Therefore, it was easier for ZnTCPP to adsorb on the surface of N-TiO₂ than ZnTPP. The photocatalytic activity of N-TiO₂ sensitized by ZnTCPP was evaluated by methylene blue degradation under visible light. It was found that N-TiO₂ sensitized by ZnTCPP exhibited higher photocatalytic activity than N-TiO₂ and undoped TiO₂ sensitized by ZnTCPP due to the synergistic effect of adsorbed dye and doped N atoms.更多还原