| 共掺杂TiO2光催化剂的制备及性能研究 | |
| Alternative Title | Investigation on Fabracation and Properties of Co-Doped TiO2 Photocatalysts |
| 沈艳芳 | |
| Subtype | 博士 |
| Thesis Advisor | 杨柯 |
| 2009-02-18 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料加工工程 |
| Keyword | 光催化 Tio2 共掺杂 可见光 |
| Abstract | TiO2光催化剂因其光催化效率高、化学稳定性强、无毒性和成本低等优异的物理、化学性能，在能源和环保领域有着巨大的潜在应用价值。目前，其在太阳能染料敏化电池（DSSC）、自清洁材料、杀菌材料和环境污染治理等方面的应用已初具规模。然而，由于TiO2是一种宽禁带的半导体，只有波长短、能量高的紫外光才能被TiO2吸收，这就极大地限制了TiO2的广泛应用。在当今这一能源短缺、环境污染严重的时代，人类千方百计地利用自然能源，尤其是绿色清洁、取之不尽、用之不竭的太阳能。如果能够设法改变TiO2的能带结构，使其在可见光，尤其是太阳光的照射下即可被激发，则TiO2光催化剂将会在能源和环境领域得到广泛应用，为人类带来无尽的福音。近年来，世界各国很多科学家们都将TiO2光催化的研究重点转移到了对其可见光化的研究领域。为了使TiO2吸收可见光，研究者采用了各种各样的方法，包括金属离子掺杂、半导体耦合、表面超强酸化、制备特殊形貌（如介孔材料）和染料敏化等。其中，Asahi在2001年的《Science》杂志上报道，通过N、C、S等非金属元素的掺杂，可以使TiO2吸收可见光，在提高其可见光光催化性能的同时还不降低其在紫外光下的光催化效率，这就使TiO2可见光化的研究向前迈进一步。目前，大多数研究者都将精力集中在如何通过掺杂各种非金属来扩展TiO2对可见光的吸收范围，同时能够显著提高其在可见光下的光催化性能。然而，就目前的报道来看，仅通过掺杂非金属元素对提高TiO2的可见光吸收性能和光催化性能的作用是有限的，这可能是由于仅靠一种非金属来取代晶格氧原子或钛原子的数量还很有限。因此，一些研究者开始转向金属-非金属或非金属-非金属二元共掺杂改性TiO2的研究。研究结果表明，多数二元共掺杂体系的可见光光催化效果比单一掺杂体系要好。在充分调研前人工作的基础上，本论文将工作侧重点放在(W, N)、(Ta, N)和(Nb, N)二元共掺杂TiO2和(P, Mo, N)三元共掺杂TiO2的制备，以及催化剂物理、化学和催化性能的系统研究上。其中，(Ta, N)、(Nb, N)和(P, Mo, N)掺杂TiO2的体系均系自主创新。本论文的主要工作包括： 采用包括溶胶-凝胶和机械合金化两步法制备了(W, N)二元共掺杂的纳米TiO2光催化剂。研究结果证明，(W, N)二元共掺杂的纳米TiO2光催化剂的紫外-可见吸收光谱明显地向可见光区移动，并且在可见光区有两个吸收边；掺杂后的TiO2光催化剂禁带宽度减小，对可见光产生响应。光催化实验的结果表明，(W, N)二元共掺杂的纳米TiO2光催化剂在可见光下的光催化性能要显著高于仅有W掺杂的TiO2和Degussa P25。 采用湿化学法一步合成(W, N)二元共掺杂的纳米TiO2光催化剂，对其物理、化学、光学和催化性能进行了系统研究。结果表明，掺杂使TiO2光催化剂的紫外-可见吸收光谱向可见光区发生了红移，表明掺杂后的催化剂的禁带宽度减小，对可见光产生响应。采用亚甲基蓝和磺基水杨酸两种有机物来考察(W, N)二元共掺杂的纳米TiO2光催化剂在可见光下的光催化性能。结果表明，(W, N)二元共掺杂的纳米TiO2光催化剂在可见光下的光催化性能得到显著提高，超过了W掺杂的TiO2和Degussa P25。 利用机械合金化法制备了(Ta, N)二元共掺的纳米TiO2光催化剂，并通过后续的400℃、N2气氛中热处理来去除未反应完全的氮源——尿素，同时促进了TiO2的晶化。XRD分析表明，在机械合金化的过程中生成了新相Ta3N5。紫外-可见吸收光谱表明，(Ta, N)二元共掺的纳米TiO2光催化剂吸收范围红移至可见光区，并且其吸收光谱上有两个明显的吸收台阶。降解亚甲基蓝的实验结果表明，(Ta, N)二元共掺的纳米TiO2光催化剂的可见光催化活性和对亚甲基蓝的COD去除率均超过P25，其中以样品TN181-cal.的光催化活性最高。降解磺基水杨酸的实验结果表明，样品TN181-cal.的光催化活性最高。对(Ta, N)二元共掺杂提高TiO2的可见光催化活性的机理进行了分析，认为二元共掺杂在TiO2的禁带中引入N的杂质能级，Ta的杂质能级和氧空位的能级可以有效地减小禁带宽度；同时，Ta3N5的生成，使其能够与TiO2发生耦合作用。 采用机械合金化法制备了(Nb, N)二元共掺杂的TiO2光催化剂，并通过后续的热处理使没有反应完全的氮源分解，同时使TiO2和掺杂形成的产物NbN得到进一步晶化。对(Nb, N)二元共掺杂的TiO2光催化剂进行了全面的性能表征，研究结果表明，在机械合金化过程中形成了新相——窄禁带半导体NbN。少量NbN的存在能起到耦合剂的作用，可以将可见光诱导产生的光生电子传递到TiO2的导带上，有助于光催化效率的提高。紫外-可见光谱的研究结果表明，(Nb, N)二元共掺杂的TiO2光催化剂的光吸收范围红移至可见光区。(Nb, N)二元共掺杂的TiO2光催化剂在可见光下光催化降解亚甲基蓝和磺基水杨酸的实验中均显示出较好的光催化性能，样品对亚甲基蓝的COD去除率均超过P25，最高为P25的2.75倍。Nb和N的共掺杂在TiO2的能带中引入了新的杂质能级，包括N的掺杂能级、Nb的掺杂能级和氧空位的掺杂能级，能够有效地减小TiO2的禁带宽度，使其在可见光的作用下即可被激发。此外，形成的NbN会起到耦合修饰TiO2的作用，发挥其作为窄禁带半导体的优势，将可见光激发产生的光生电子直接传递至TiO2的导带，参与光催化反应。 采用无机盐磷钼酸铵作为掺杂元素的来源，通过溶胶-凝胶法一步制得了(P, Mo, N)三元共掺杂的纳米TiO2光催化剂，再通过后续的热处理使催化剂得到晶化。紫外-可见吸收光谱表明，(P, Mo, N)三元共掺杂可以有效地使TiO2光催化剂的吸收光谱发生红移，而且使TiO2对可见光的吸收量大大增加。(P, Mo, N)三元共掺杂的纳米TiO2光催化剂在可见光下可以有效地降解有机工业染料亚甲基蓝和有机物磺基水杨酸。对亚甲基蓝的降解实验表明，(P, Mo, N)三元共掺杂的纳米TiO2的降解效率要高于Mo掺杂的TiO2和P25；其中样品(P, N)-0.3Mo-TiO2的光催化效率最高，在4个小时内可将溶液中的亚甲基蓝降解完全，而且COD去除率表明亚甲基蓝几乎被完全矿化。对磺基水杨酸的降解实验表明，(P, Mo, N)三元共掺杂的纳米TiO2的降解效率高于Mo掺杂的TiO2和P25。分析了P、Mo和N三元共掺杂提高TiO2可见光催化效率的机理，认为P、Mo和N三元共掺杂可以在TiO2的禁带中引入一些杂质能级，而当MoO3形成后，还能与TiO2耦合，起到传递光生载流子和协同催化的作用。因此，P、Mo和N三元共掺杂比单一掺杂更能有效地提高TiO2在可见光下的光催化活性。其创新点在于，选取适当的掺杂源——磷钼酸铵，通过溶胶-凝胶一步即实现了P、Mo和N三种元素的共掺杂，原材料易于获得，操作步骤简单，过程易于控制，有望实现工业化。 |
| Other Abstract | TiO2 photocatalysts have great potential applications in both energy and environment fields for their high photo-activities, high chemical stabilities, avirulence and cheapness. So far, applications of TiO2 photocatalysts in dye sensitized solar cells (DSSC), self-cleaning materials, anti-virus materials and environment purifications have been reported. However, the band gap of TiO2 is as large as 3.0 to 3.2 eV, meaning only the high-energy light (such as ultraviolet light) can be absorbed by TiO2. It is a great problem to restrict the wide applications of TiO2 photocatalysts. Today, people in the earth have to face two urgent problems---energy scarceness and environment pollution, and they are trying to make use of the solar energy, which is clean, plentiful and economical. If something can be done to minimize the band gap of TiO2, visible light (the main part of solar spectra) can be absorbed by TiO2, which will make the wide application of TiO2 photocatalysts into realization and give evangel to all human beings. In recent years, scientists begin to change the research focus to how to make TiO2 sensitive to the visible light. A great variety of methods have been tried, including doping with metal ions, coupling with other semiconductors, acidizing the surfaces, sensitizing with dyes, and so on. In 2001, Asahi et al. fabricated N-doped TiO2 photoctalysts and investigated their activities under visible light by photodegradation of methylene blue and acetone. It revealed that N-doping can enhance the photoactivity of TiO2 under visible light with no reduction of photoactivity under ultraviolet light, which is a milestone in the research and development of TiO2. Nowadays a lot of researchers are focusing on the non-metal doping to improve the photoactivity of TiO2 under visible light. However, doping with only one non-metal element is limited to improve the visible-light sensitivity and photocatalytic activity of TiO2, according to the present reports. A possible reason is that the oxygen atoms or titanium atoms replaced by the doped non-metal atoms are not too much. As a result, some researchers begin to investigate the metal-nonmetal or two non-metal elements binary co-doped TiO2 photocatalysts. Most of the results showed that the photocayalytic activities under visible light of binary co-doped TiO2 photocatalysts are better than the unitary doped TiO2. Based on these previous reports, this dissertation was focused on the investigation of (W, N), (Ta, N), (Nb, N) and (P, Mo, N) co-doped TiO2 photocatalysts. Among them, (Ta, N), (Nb, N) and (P, Mo, N) co-doped TiO2 photocatalysts are firstly fabricated and studied. The main work in this dissertation is as follows: (W, N)-binary co-doped TiO2 photocatalysts were fabricated by a two-step method combining with sol-gel and mechanical alloying (MA) methods. Physical, chemical, optical and photocatalytical properties of the (W, N)-binary co-doped TiO2 photocatalysts were analyzed. The experimental results revealed that (W, N)-binary co-doped TiO2 photocatalysts can be sensitized by visible light, and their UV-Vis spectra are red-shifted to the visible light region for the reduced band gap by doping. (W, N)-binary co-doped TiO2 photocatalysts showed enhanced photocatalytic activities under visible light, which are higher than those of W-doped and P25 TiO2. (W, N)-binary co-doped TiO2 photocatalysts were also synthesized through a sol-gel method, and their physical, chemical, optical and photocatalytical properties were investigated. It was shown that co-doping with W and N can make TiO2 absorb visible light to some extent. Both methylene blue (MB) and sulfosalicylic acid (SSA) were used to evaluate the photocatalytic activities of the (W, N)-binary co-doped TiO2 photocatalysts under visible light. Enhanced photocatalytic activities under visible light were observed for the (W, N)-binary co-doped TiO2 photocatalysts, which are also higher than W-doped and P25 TiO2. MA method was employed to prepare (Ta, N) and (Nb, N)-binary co-doped TiO2 photocatalysts. Heat-treatment in N2 atmosphere at 400℃ was also used to wipe off the un-reacted N source and promote the development of crystals. New phases, Ta3N5 and NbN, were found to be formed during the MA process, which are considered as narrow band gap semiconductors. Ta3N5 and NbN can act as couplants of TiO2, because they can be sensitized by visible light and can deliver the photo-generated electrons to the conduction band of TiO2. Both (Ta, N) and (Nb, N)-binary co-doped TiO2 photocatalysts can absorb visible light to some extent, and they both exhibit enhanced photocatalytic activities under visible light in photodegradation of MB and SSA. Possible mechanisms for the enhanced photocatalytic activities of both (Ta, N) and (Nb, N)-binary co-doped TiO2 photocatalysts were also proposed based on the experimental results. At last, (P, Mo, N)-ternary co-doped TiO2 photocatalysts were prepared by a one-step sol-gel method, in which ammonium molybdophosphate, (NH4)3H4[P(Mo2O7)6]•xH2O, was employed as the doping source of P, Mo and N. Physical, chemical, optical and photocatalytical properties were studied. It was found that ternary doping of P, Mo and N can red-shift the onset of the absorption spectra to the visible light region, and the amount of the absorptance is enlarged. (P, Mo, N)-ternary co-doped TiO2 photocatalysts showed greatly enhanced photocatalytic activities under visible light in both the MB and SSA photodegradations, and the photodegradation rates are much higher than Mo-doped and P25 TiO2. For example, the (P, N)-0.3Mo-TiO2 sample could completely photodegrade and mineralize MB in the solution within 4 hours irradiation. A possible mechanism for the enhanced photoactivities was suggested. The innovation of the present work is that ternary co-doping with P, Mo and N can be realized by a sol-gel method, which is advantageous for improving the photoactivities of TiO2 under visible light. Meanwhile, the fabrication method is easily-operated and controlled, which is promising in application in future. |
| Pages | 149 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17221 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 沈艳芳. 共掺杂TiO2光催化剂的制备及性能研究[D]. 金属研究所. 中国科学院金属研究所,2009. |
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