【作者】 李辉；

【导师】 夏正斌；

【作者基本信息】 华南理工大学 ， 化学工程， 2015， 硕士

【摘要】 利用半导体纳米催化剂将太阳能转换成化学能是解决当前能源危机的一个有效途径。在所有半导体材料中,Ti O2因其具有良好的光催化活性、热和化学稳定性好、无毒且价格低廉的优点而被广泛研究并应用于光催化制氢、降解有机污染物、染料敏化太阳能电池、传感器、电化学电容器以及生物医学领域。与Ti O2纳米颗粒相比,阳极氧化法制备的一维Ti O2纳米管阵列(TNTs)具有高长径比、大比表面积的特点,并可为光生电子的分离和传输提供一个垂直的路径,从而具有更优异的光电化学性能。然而,宽带隙的Ti O2只能响应紫外光和Ti O2表面的光生电子和空穴复合较快这两大问题极大地限制了TNTs在光电化学领域的应用。因此,通过改进TNTs的制备方法并对其进行合理的改性来提高TNTs的光电化学活性具有极为重要的意义。本论文采用一种新的、温和的含有BF4-刻蚀离子的电解液制备了TNTs,并研究了形貌和结构对TNTs光电催化性能的影响。此外,本文还通过Ti3+自掺杂、石墨烯量子点的负载以及采用Cd S纳米晶和还原石墨烯构建全固态Z型复合光催化剂等技术,拓宽了TNTs的光谱响应范围,促进了光生电子/空穴对的分离与传输,从而极大地提高了光电催化效率。本文的主要研究内容如下:(1)在一种含新型离子BF4-的有机电解液中研究了不同电位对纳米管表面形貌和光电催化性能的影响。结果表明,与传统的F-类似,BF4-在阳极氧化过程中也能作为刻蚀离子来形成高度有序的Ti O2纳米管阵列。阴离子BF4-在高电场时易分解成F-离子,所以高电位条件下形成单壁Ti O2纳米管阵列(SW-TNTs)而低电位下形成双壁Ti O2纳米管阵列(DW-TNTs)。由于双壁结构具有更大的比表面积和更好的光吸收,所以DW-TNTs比SW-TNTs表现出更优异的光电化学性能。(2)采用一种含BF4-的新型电解液,通过两步阳极氧化法制备了管壁极为光滑且氟-硼共掺杂的Ti O2纳米管阵列(BF-TNTs)。结果表明,在相同较高水含量的情况下,基于BF4-的电解液得到的是具有“光滑”管壁结构的纳米管,而基于传统的F-的电解液则得到的是“波纹”管壁结构的Ti O2纳米管(F-TNTs)。在阳极氧化过程中,BF4-的部分分解使得非金属元素氟和硼共掺杂于Ti O2纳米管阵列中。因此,BF-TNTs比F-TNTs表现出更好的光电化学性能。(3)采用一种微波辅助Na BH4化学还原法制备了Ti3+自掺杂Ti O2纳米管(MR-TNTs)。紫外-可见漫反射光谱结果表明,MR-TNTs的光谱吸收范围由紫外光区拓展到了可见光区,电化学阻抗谱图表明还原过程产生的Ti3+有利于MR-TNTs的电导性和电荷转移。样品MR-TNTs在可见光区的光电流密度是未改性TNTs的8倍,且在AM1.5条件下其最优的饱和光电流密度和光电转化效率分别为3.05 m A/cm-2(1.23 V vs.RHE)和1.66%,这是目前掺杂TNTs光电极体系的最高值。入射光子-电流转换效率在紫外光区和可见光区均有增加。另外,MR-TNTs比未用超声辅助的化学还原法制备的Ti O2纳米管(R-TNTs)具有更好的光电化学稳定性,这是由于自掺杂的Ti3+主要存在于体相而不是在表面。(4)通过连接分子结合和电泳沉积的复合技术制备了同轴异质石墨烯量子点敏化Ti O2纳米管阵列(EPD-GQDs/TNTs)。结果表明,在电泳沉积过程,硅烷连接分子作为极好的媒介将GQDs与TNTs通过共价键连接起来,从而防止GQDs在管口的堵塞并形成了均匀的GQDs层附着在内管壁。通过改变电泳沉积时间,可以控制TNTs内壁GQDs合适的沉积层厚度。与未改性的Ti O2纳米管阵列和通过传统的浸渍-沉降方法制备的GQDs敏化Ti O2纳米管阵列(IP-GQDs/TNTs)相比,EPD-GQDs/TNTs的光电化学水分解性能和光催化有机染料降解活性显著增强,这归因于其宽的光吸收范围,光生载流子的快速分离以及稳定性。(5)采用电泳沉积(EPD)和连续离子层吸附-反应(SILAR)的复合技术制备了含Cd S纳米晶、还原氧化石墨烯和Ti O2纳米管阵列的三元纳米复合物(Cd S/RGO/TNTs)。与纯TNTs、RGO/TNTs和Cd S/TNTs相比,三元复合物Cd S/RGO/TNTs表现出更高的可见光光电化学活性,这得益于外部的Cd S层充当敏化剂来捕获可见光光子,中部的RGO层不仅可以作为电子媒介和传输体来抑制光生载流子的复合,也可以作为绿色敏化剂来强化可见光吸收,内部带隙变窄的TNTs可以收集从Cd S和RGO的热电子去参与后续的氧化还原反应。更多还原

【Abstract】 Using semiconductor nanocatalysts to convert the solar energy to chemical energy is an effective way to solve the current energy crisis. Among all of semiconductors, Ti O2 has been extensively studied and used in the fields of photocatalysis for hydrogen and organic pullutants degradation, dye-sensitized solar cells, sensors, electrochemical capacitors and biomedicine due to its excellent photocatalytic activity, thermal and chemical stability, non-toxocity and low-cost. Compare to the bulk particulate Ti O2, the one-dimensional Ti O2 nanotube arrays(TNTs) prepared by anodization method possess high aspect ratio, large surface area, and provide a perpendicular pathway for photogenerated electrons separation and transfer, which lead to superb photoelectrocatalytic performance. However, the wide bandgap of Ti O2 which only responses to UV light and relatively fast recombination of photogenerated electron-holes on the surface of catalyst siganificantly limit the photoelectrocatalytic applications of TNTs. Hence, improving the preparation methods of TNTs and reasonably modifying their properties are important in enhancing the photoelectrocatalytic activity of TNTs. In this thesis, a new and gentle BF4- contained electrolyte is employed to fabricate TNTs and the influences of their morphologies and structures on photoelectrocatalytic activity are also investigated. In addition, Ti3+ self-doped, nano-gold and graphene quantum dots loading and Z-scheme hybrid photocatalyst constructed by Cd S nanocrystallites and reduced graphene oxide are used to extend the sprectrum responsive range and boost the separation and transfer of photogenerated electron-holes, thus greatly improve photoelectrocatalytic efficiency. The details are presented as below:The influences of different potentials on morphologies and structures of naontubes and photoelectrocatalytic performance in a new BF4- contained organic electrolyte are studied. The results show that the BF4-, similar to the conventional F-, can also act as the etching ions to form the highly ordered Ti O2 nanotube arrays in the anodization process. The anion BF4- are easily decomposed to release the fluorion ions into the electrolyte under high electric field and thus single-walled Ti O2 nanotube arrays(SW-TNTs) are formed at high potentials but double-walled Ti O2 nanotube arrays(DW-TNTs) are formed at relatively low potentials. The DW-TNTs show more excellent photoelectrocatalytic performance than the SW-TNTs due to larger specific area and better light absorption of double-walled structure.Extremely smooth and boron-fluorine co-doped Ti O2 nanoube arrays(BF-TNTs) are prepared by two-steps anodization method in a new BF4- contained electrolyte. The results show that the “smooth” walls nanotubes are obtained in the contained electrolyte while the “rippled” walls nanotubes(F-TNTs) are formed in the conventional under the same condition of relatively high water content. The non-metal boron and fluorine elements which may come from the partial decomposition of BF4- are doped into the Ti O2 nanotubes arrays during the anodization process. As a result, the BF-TNTs exhibit better photoelectrocatalytic activity than the F-TNTs.A microwave-assisted chemical reduction method with Na BH4 is employed to prepare bulk abundant Ti3+ self-doped Ti O2 nanotube arrays(MR-TNTs). The optimized saturation photocurrent density and photoconversion efficiency of the MR-TNTs under simulated solar illumination are measured to be 3.05 m A/cm2 and 1.66%, respectively, which are the highest values ever reported for doped TNTs photoelectrodes. Moreover, the MR-TNTs exhibit much more stable PEC performance than the Na BH4 treated TNTs(R-TNTs) without microwave assistance, which is attributed to the self-doped Ti3+ mainly exist in the bulk rather than on the surface.A coaxial heterogeneous graphene quantum dots sensitized Ti O2 nanotube arrays(EPD-GQDs/TNTs) is prepared by a coupling technique of linker molecules binding and electrophoretic deposition(EPD). The silane linker molecules act as a superb medium for integrating GQDs and TNTs by covalent amide linkage, thus preventing GQDs clogging on the tube entrances and forming an uniform GQDs layer tightly attached to the inside tube walls during the following EPD process. By adjusting the time of EPD, appropriate thickness of the deposited GQDs in the internal tube walls of TNTs can be controlled. Compared to the pristine TNTs and GQDs/TNTs prepared by conventional impregnation-precipitation method(IP-GQDs/TNTs), the EPD-GQDs/TNTs exhibit significantly enhanced photoelectrochemical water splitting activity and photocatalytic organic dye decomposition performance for their broad photo-absorption range, fast separation of photogenerated charge and stability.Ternary nanocomposite photoelectrodes composed of Cd S nanocrystallites, reduced graphene oxide(RGO) and Ti O2 nanotube arrays(TNTs) are prepared by a coupling technique of electrophoretic deposition(EPD) and successive ionic layer adsorption and reaction(SILAR). Compare to pure TNTs, RGO/TNTs, and Cd S/TNTs, the ternary Cd S/RGO/TNTs hybrids show much higher visible-light-driven photoelectrochemical and photocatalytic activity due to that the outer layer of Cd S acts as sensitizer for trapping substantial photons from the visible light, the middle layer of RGO not only serves as electrons mediator and transporter for suppressing the recombination of photogenerated carriers, but also plays as a green sensitizer for enhancing visible light absorption, and the inner TNTs with narrowed band gap collect the hot electrons form the Cd S and RGO to participate subsequent redox reaction for hydrogen production and organic pollutants degradation.更多还原