【作者】 吴亚惠；

【导师】 蔡伟民；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2011， 博士

【摘要】 利用可再生能源（如太阳能）治理水污染和大气污染的方法在过去几十年得到了迅速的发展,其中光催化技术是最为安全和环境友好的方法。光催化净化技术的核心是光催化材料,TiO₂纳米薄膜是一种成本低、安全无毒、稳定性好且易回收的光催化材料,在环境污染治理中具有十分广泛的应用前景。众所周知,纳米薄膜的形貌对其多样化的性能和相应的应用有重要影响;因此,制备具有一定形貌的纳米TiO₂薄膜,可以有效地提高其光催化性能。本文采用原位化学氧化法在钛金属表面原位生成了不同结构和形貌的TiO₂纳米薄膜,并对薄膜进行了表征和光催化降解性能的研究。围绕以上内容,主要开展了以下几方面工作:（1）采用氢氧化钠和双氧水的混合氧化液,在80℃的水热反应釜中与金属钛片反应24小时,再经过酸洗和热处理,制备了低维结构的钛基TiO₂纳米线网络状薄膜。纳米线网络结构的形成过程为:钛片部分溶解在氧化液中形成钛酸钠溶胶,通过溶解-沉积过程逐渐生长形成钛酸钠盐纳米线,再经过酸洗热处理最终形成TiO₂纳米线网络状结构。通过光催化降解苯酚溶液测试该纳米线薄膜的光催化性能,结果表明,这种TiO₂纳米线网络状薄膜表现出良好的光催化降解性能并具有很好的稳定性,2小时候苯酚的降解率达到75.9%。薄膜的网络状结构和锐钛矿晶型是其具有良好光催化性能的主要原因。（2）用双氧水氧化液直接与钛片反应,并通过进一步的水热后处理制备了钛基TiO₂纳米花状薄膜。在氧化反应过程中,钛基底上形成了无定形的TiO₂纳米花状结构,水热处理使得无定形TiO₂晶化并形成锐钛矿/金红石混合晶相。通过光催化降解甲基橙测试样品的光催化活性,结果表明与没有经过水热反应直接煅烧的样品相比,水热反应得到的TiO₂薄膜光催化活性提高了两倍。研究了水热反应温度与时间对薄膜性质的影响,结果表明提高水热反应的温度或者延长水热反应的时间可以提高薄膜的结晶度,从而提高薄膜的光催化效率。在此基础上,以尿素为原料,通过焙烧热解的方法对TiO₂纳米花薄膜进行表面改性。研究发现不同焙烧温度下改性的薄膜,带隙宽度都有不同程度的降低。将薄膜用于光催化降解甲基橙,结果表明,无论是在可见光下还是全谱照射下,改性后的TiO₂纳米花薄膜的光催化降解性能均有所提高。其中350℃改性TiO₂薄膜表现出最佳的可见光活性,可见光下光照3小时甲基橙的降解率达到72.8%,DRS测试表明其带隙宽度降至2.4 eV。XPS分析结果表明改性TiO₂薄膜的可见光光催化活性可以归因于尿素热解在薄膜表面形成的胺类聚合物的敏化作用。（3）在双氧水中加入不同量的过氧钨酸溶胶,再将钛片加入其中进行原位化学氧化反应,制备了钨掺杂的一维纳米TiO 2薄膜。所制备的纳米TiO₂薄膜呈纳米花、纳米网或者纳米孔状结构。溶胶加入量不同,薄膜中的钨含量不同,钨元素掺杂进入了TiO₂的晶格中形成Ti-O-W键。Ti-O-W键是通过过氧钛酸和过氧钨酸在反应体系中的缩合沉积形成的。DRS测试表明掺杂了钨的TiO₂薄膜的吸收边红移,禁带宽度均小于3.1eV。将掺杂改性薄膜光催化降解甲基橙测试其光催化性能,结果表明掺杂了钨的薄膜光催化降解性能远优于纯TiO₂薄膜,可见光下光照3小时甲基橙的降解率最高能达到19.3%,全谱照射3小时后,最优条件下掺杂样品对甲基橙的降解率达到91.3%,光催化降解速度是未掺杂样品的4.3倍。更多还原

【Abstract】 Development of the effective methods aimed at removal of pollutants from water and air by using the renewable energy sources e.g. solar energy becomes a subject of the intensified research over the last decades. One of the most safe and environmentally friendly chemical methods is photocatalysis. The key to the photocatalysis purifying technology is the photocatalysis material. Titanium dioxide nanofilms, as photocatalysts, possess advantages such as low cost, innocuity safety, well stability and easily recovery. Therefore they are promising materials for applications in pollution control. It is well known that the morphologies of nanofilms are demonstrated to have great effects on their widely varying properties and corresponding potential applications. Therefore, the fabrication of TiO₂ nanofilms with special morphologies could effectively improve their photocatalytic activity. In the present work, we synthesized various TiO₂ nanofilms by in situ chemical oxidation method. Meanwhile, the properties and photocatalytic degradation activities were investigated. In this dissertation, our investigations are carried out as follows:（i） When Ti sheets were treated with an aqueous mix-solution of sodium hydroxide and hydrogen peroxide in a reaction kettle for 24 h at 80℃and then with HCl aqueous solution and heat treatment, low-dimensional titania nanowires network films were prepared. The formation process is that the oxidative solution causes partial dissolution of the Ti sheets to form an amorphous sodium titanate sol, which gradually form sodium titanate nanowires through dissolution precipitation mechanism. TiO₂ nanowires were finally obtained after the treatment by HCl aqueous solution and the heat treatment. The TiO₂ nanofilms can be applied to photodegrade phenol solution. The film prepared shows excellent photocatalytic performance and stability and the phenol removal is as high as 75.9% after 2 h irradiation. The excellent photocatalytic activity must be attributed to the synergetic effect of the net-like anatase structure.（ii） Ti sheets were directly treated with hydrogen peroxide and further hydrothermal treatment was conducted. Nanoflower films on Ti substrates were obtained by these steps. The oxidation step ensured the formation of flower-like amorphous TiO₂ on titanium surface. The hydrothermal step facilitated the crystallization of amorphous titanium oxide and the formed films possess both anatase and rutile phases. The photocatalytic activity was evaluated by decomposing methyl orange in water. Compared with the traditional annealed sample without hydrothermal treatment, the rate of degradation tripled. The effects of hydrothermal temperature and time are also investigated. The photocatalytic activitivies of the flower-like films are improved with the increasing hydrothermal temperature or prolonged hydrothermal time for the higher crystallinity.Further study focuses on the modification of the nanoflower films through roasting the films with urea. The study showed that the band-gap of the modified TiO₂ thin films is reduced in varying degrees. The photocatalytic activity was also investigated by photocatalytic degradation of methyl orange. Photocatalytic results showed that the photocatalytic efficiency under visible light or full spectrum light illumination was enhanced after modification. The modified TiO₂ film which roasted at 350℃showed the best activity under the visible light irradiation. 72.8% methyl orange was degraded in 3 hours. DRS test showed that the band-gap was down to 2.4eV. XPS results indicated that the visible light photocatalytic activity is due to the effect of the polymer formed during urea pyrolysis process.（iii） Different amount of peroxotungstic acid sol was added in peroxide dioxide and Ti sheets were reacted with these mixed oxidation solution. W-doped TiO₂ nanostructured films were synthesized in situ on Ti substrate by this one-pot process. According to our data analysis, the films showed typical nanoflower, nanoweb or nanopore morphologies. Tungsten content in the films changes with the amount of additional sol Tungsten is doped into the TiO₂ lattice to form Ti-O-W bond, which is obtained by the condensation of peroxo titanic acid and peroxotungstic acid. The absorption edge of the films, measured by a UV-Vis spectrophotometer, was observed to shift toward longer wavelengths when tungsten was incorporated to the TiO₂ films. The band gap energy was less than 3.1 eV for W-doped TiO₂ systems and the band gap of grown TiO₂ is 3.1eV. Furthermore, photocatalytic activity of the films was also examined by measuring the decomposition rate of methyl orange under both visible and full-septrum irradiations. It was observed that the W-doped layers were more photoactive as compared to as-synthesized pure TiO₂ layers. Under the visible light irradiation, the degradation rate could reach up to 19.3% in 3 hours. For the film prepared under optimum condition, the methyl orange removal is as high as 91.3% after 3 h full spectrum light illumination and the speed of degradation is 4.3 times higher than undoped TiO₂ films.更多还原