【作者】 王雪芹；

【导师】 孟令辉； 黄玉东； Flemming Besenbacher；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2015， 博士

【摘要】 Ti O2基半导体催化剂具有催化活性高、氧化性强、耐光腐蚀性、无毒、成本低等优点,在光催化领域中受到越来越多的关注。Ti O2基半导体催化剂的微观形貌、晶型结构、光学特性等物理性能的对其光催化性能有着至关重要的影响。然而,对于不同结构Ti O2纳米材料物理性能与其光催化活性之间关系的研究还不尽详实。本文针对上述问题,系统性地研究了Ti O2纳米颗粒的粒径和结晶度大小对其光催化降解苯酚性能的影响,并研究了Ti O2纳米管的微观形貌对其光催化及光电催化性能的影响,通过对Ti O2纳米管进行负载改性,用简单工艺制备出了成本低廉、稳定性好、催化活性高的光催化裂解水产氢催化剂。研究结果对提高Ti O2基纳米材料的催化性能具有现实的指导意义及应用价值。针对Ti O2纳米颗粒的粒径和结晶度不易单独控制的问题,采用超临界流体合成方法制备了一系列具有不同粒径和结晶度的锐钛矿纳米颗粒,其中粒径系列样品的粒径由6.6nm提高到了26.6nm,结晶度保持在82%左右,结晶度系列样品的结晶度由12.6%提高到82.0%,粒径大小均为~9.2nm;选用苯酚为模型分子,研究了粒径和结晶度大小对Ti O2纳米颗粒光催化性能的影响,结果表明,Ti O2纳米颗粒粒径的增大可明显提高其光催化降解苯酚的反应效率,而结晶度的变化对其光催化活性几乎没有影响;通过对苯酚降解反应过程中中间产物的生成与降解速率进行跟踪研究发现,Ti O2纳米颗粒粒径的提高可有效抑制中间产物对苯二酚和苯醌之间的氧化还原反应,避免两者相互转化时消耗光生自由基,提高了光生电子的有效利用率。Ti O2纳米管具有结构规整、比表面积大、催化活性高等优点,其催化性能与其表观形貌有很大的关系。采用电化学阳极氧化法,通过调整制备过程中的工艺参数,如电解液中F-浓度、氧化电压、氧化温度和氧化时间等制备了一系列Ti O2纳米管,研究了各因素对其微观形貌以及光电催化性能的影响。结果表明,F-的存在是Ti O2纳米管形成的关键所在,F-浓度的提高有利于Ti O2纳米管的形成及生长,而过高的F-浓度会导致Ti O2纳米管长度及其表面规整度下降,氧化电压、氧化温度、氧化时间的变化均会影响其长度、管径和表面规整度,适宜的阳极氧化条件为:F-浓度150mmol/L、氧化电压50V、氧化温度20℃、氧化时间120min,此时可制备出规整度高、表面清洁、长度约为4.5μm、管径115nm的Ti O2纳米管;经过对具有不同形貌的Ti O2纳米管的光电催化性能以及光催化降解Rh B的性能进行研究可知,Ti O2纳米管长度、管径和表面规整度的提高有利于提高其对紫外光的吸收利用率,并可提高光生电子-空穴对的有效分离和转移效率;而Ti O2纳米管表面杂质颗粒或丝束状物质的出现为光生电子-空穴对的再结合提供了更多的活性中心,不利于催化反应的进行。为了进一步提高Ti O2纳米管在光催化裂解水反应中的催化活性,采用紫外光照辅助电化学沉积的方法制备了Ti O2纳米管负载Ni Mo Zn复合纳米颗粒。结果表明,Ni Mo Zn复合纳米颗粒中少量Zn的加入有利于促进产氢过程中的电子转移过程,从而提高了催化活性,而过量Zn的加入反而抑制了其电子转移过程以及质子吸附过程,适宜的Zn含量为1%~3%;紫外光照可明显改善Ti O2纳米管表面的可浸润性,使其由超疏水状态变为亲水性;经紫外光照辅助电化学沉积15s后,Ni Mo Zn纳米颗粒均匀的负载在Ti O2纳米管管壁内外,其光催化产氢效率提高了近8%。更多还原

【Abstract】 Titanium dioxide(Ti O2) has attracted great attention in heterogeneous photocatalysis applications due to its high reactivity, strong oxidizing power, long-term stability and non-toxicity. It has been found that the photocatalytic performance of Ti O2 is mostly governed by their microstructure, polymorph composition and optical properties, etc. However, how the physical properties of the Ti O2-based nanomaterials influence their photocatalytic performances are not fully understood yet. Here, we investigated the influence of crystallite size and crystallinity of Ti O2 nanoparticles on the photodegredation of phenol systematically, and also the microstructure of Ti O2 nanotubes. The Ti O2 nanotubes was further doped by Ni Mo Zn alloy nanoparticles to prepare an earth-abundant, long-term stability and high reactivity photocatalyst for water splitting hydrogen evolution. Such studies are essential for the design of efficient photocatalyst toward large-scale application of photocatalysis.Two series of crystallite size and crystallinity controlled pristine anatase nanoparticles have been synthesized under supercritical water-isopropanol conditions. Photocatalytic degradation of phenol was carried out to evaluate the influence of crystallite size and crystallinity on the performance of anatase. We discovered that the reactivity of anatase nanoparticles is independent of the crystallinity. In contrast, increasing the crystallite size from 6.6 nm to 26.6 nm resulted in an enhancement of the photocatalytic performance. By tracking the evolution of phenolic intermediates and analyzing the reaction kinetics we revealed how the crystallite size influences the photo-decomposition of phenol. When small anatase nanoparticles were used as photocatalysts, phenol was selectively oxidized to benzoquinone, and then it subsequently underwent a rapid redox reaction wherein photo-generated readicals were inefficiently consumed. Conversely, hydroqu inone was found to be the dominant intermediate product in the phenol decomposition when using large anatase nanoparticles. In this case, the rates of hydroquinone-benzoquinone redox reactions were significantly suppressed, which facilitated the full decomposition of phenol and phenolic compounds.The self-organized Ti O2 nanotubes, which was characterized by high specific surface area and excellent electronic property, has attracted considerable interest over the past decade. Here we prepared a series of Ti O2 nanotubes by varying the concentration of F- in the electrolyte, the oxidation potential, temperature and oxidation time. The micromorphology of the Ti O2 nanotubes and the corresponding photocatalytic and photoelectrocatalytic performance were further studied. The results showed that, the presence of F- in the electrolyte was essential for the formation of Ti O2 nanotubes. Both the length and the diameter of the Ti O2 nanotubes increased as the increasing of F- concentration. However, excessive F- in the electrolyte will over-etch the Ti O2 nanotube surface, which resulted in shorter and irregular arrays. Meanwhile, the potential, temperature and oxidation time varied the length, tube diameter and the regularity of the Ti O2 nanotubes. The optimized conditions for preparing Ti O2 nanotubes was the F- concentration of 150 mmol/L, the potential of 50 V, the temperature of 15 ℃, the time of 120 min. By investigating the micromorphology of Ti O2 nanotubes on their photocatalytic and photoelectrocatalytic performance, we found that the increasing of the tube length, diameter and regularity improve the UV absorption of Ti O2 nanotubes and the charge transfer efficiency. While, the surface impurities will act as the recombination center of photo-generated electron and hole pairs, which will depress the photocatalytic reactivity of Ti O2 nanotubes.To further improve the photocatalytic performance of Ti O2 nanotubes for water splitting hydrogen evolution reaction, the Ni Mo Zn alloy nanoparticles was deposited onto the Ti O2 nanotube surface using the UV-assistant electro-deposition method. We found that, the catalytic performance of Ni Mo Zn alloy nanoparticles was mostly governed by its Zn concentration. The addition of small amount of Zn(1~3 at%) will significantly enhance its electrocatlaytic performance by improving the charge transfer process during the water splitting reaction. However, excessive Zn in the alloy nanoparticles not only depresses the charge transfer process, but also inhibits the proton adsorption process. The UV light irradiation remarkably improves the wetability of Ti O2 nanotubes, which is beneficial for the electro-deposition of Ni Mo Zn alloy nanoparticles. After deposition of 15 s, the Ni Mo Zn alloy nanoparticles loaded onto the Ti O2 nanotubes surface uniformly. And the photon to current conversion efficiency of the doped Ti O2 nanotubes was ~8% higher than previously.更多还原