【作者】 海洋；

【导师】 余家国；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2011， 硕士

【摘要】 能源与环境是二十一世纪人类面临和亟待解决的两大世界性的问题。由于化石燃料(煤、石油、天然气)的不断枯竭,以及燃烧化石燃料带来的日益严重的环境污染等全球性问题,开发新型的、环境友好的和可再生无污染的新能源引起世界各国的广泛关注。氢能源由于其高的燃烧值、燃烧产物是水以及无环境污染等优点,被看做是在未来的一种理想的替代能源。太阳能由于其取之不尽用之不竭、清洁无污染、可再生等优点,必将对未来新型能源的开发起着举足轻重的作用。自从1972年日本科学家Fujishima和Honda在Ti02电极上发现光催化分解水以来,太阳光诱导光催化反应被普遍认为是一种将太阳能转化为氢能源的有效途径。因此采用半导体化合物进行直接的光催化来分解水产氢受到了人们的普遍关注。本论文采用Ni(OH)2和CuO复合Ti02半导体来提高Ti02的光催化分解水产氢的活性。首先,以P25和硝酸镍为前驱体,通过一步简单的沉淀法成功制备了Ni(OH)2纳米簇改性Ti02的纳米复合光催化剂(Ni(OH)2-TiO2)。在甲醇溶液中,通过测试光催化分解水产氢的活性,研究了Ni(OH)2纳米簇的沉积量对催化剂分解水产氢活性的影响。这一研究结果表明在经过Ni(OH)2纳米簇的改性后,Ti02的光催化产氢活性得到了大大的提高。在试验中找出了Ni(OH)2的最佳沉积量为0.23mol%,这时的光催化产氢速率为3056μmolh-1g-1,对应的量子效率是12.4%,这一结果超过了纯Ti02的223倍。Ti02光催化产氢活性的明显提高是因为Ni(OH)2纳米簇在Ti02表面上的沉积。光催化活性提高的机理是因为Ni2+/Ni的电极电势的位置(Ni2++2e-=Ni,Eo=-0.23V)要比锐钛矿Ti02的导带位置(-0.26 V)稍微低一些,同时又要比H+/H2的电极电势的位置(2H++2e-=H2,Eo=-0.00V)高一些。这就使得Ti02导带的电子可以转移到Ni(OH)2上,将Ni2+的颗粒还原为Ni0,而Ni0的作用就是协助电荷的分离同时作为光催化产氢的助催化剂,从而提高了光催化分解水产氢的活性。CuO改性的TiO2 (CuO-TiO2)光催化剂在甘油的水溶液中成功实现了有效的光催化分解水产氢和甘油的降解。以P25(德国Degussa公司)和硝酸铜为前驱体,采用溶液浸渍法和煅烧法成功的将CuO纳米簇沉积在了Ti02的表面。对最后得到的CuO-TiO2纳米复合光催化剂做了以下的表征：X射线衍射分析、紫外-可见漫反射光谱分析、X射线光电子能谱分析、N2吸附脱附、投射电子显微分析和荧光光谱分析。采用低功率的紫外发光二激光(LED灯)作为光催化分解水产氢的光源。CuO对光催化产氢的影响做了较为详细的研究,结果表明CuO纳米簇可以作为有效的助催化剂来提高Ti02光催化分解水产氢的活性。CuO的最佳沉积为1.3 wt%,在0.1M甘油溶液中的产氢速率为2061μmol h-1g-1,此时的量子效率达到了13.4%,这一数值超过了纯的Ti02活性的129倍。CuO纳米簇的量子尺寸效应被认为是改变了CuO在CuO-TiO2复合光催化剂中导带和价带的能带位置,这将有助于电子的转移,从而提高了催化剂光催化产氢的活性。这一研究使用CuO纳米簇来代替贵金属做助催化剂用来光催化产氢的同时也提供了一种方法通过量子尺效应来提高催化剂的光催化产氢活性。更多还原

【Abstract】 Energy and environment are two significant global issues to the humanity in 21st century. The exhaustion of fossil fuels (such as coal, oil and natural gas) and the global environmental contamination caused by fossil fuels encourage all the countries in the word to develop a novel, environmental-friendly and renewable energy resource. Hydrogen has been considered as an attractive and ideal candidate for the energy carrier of the future because of its high combustion energy and free environmental pollution. Because solar energy is greatly abundant, clean and especially renewable, it will play an important role in the development of new energy sources. Since Fujishima and Honda firstly reported the photoelectrochemical water splitting on a TiO2 electrode, sunlight induced the photocatalytic reactions are widely identified as one of the most promising routes for converting solar energy to hydrogen energy. In view of this, direct photocatalytic production of hydrogen via water splitting reaction over various kinds of oxide semiconductors has received much attention to develop the sustainable source of hydrogen energy. In this work, Ni(OH)2 and CuO facilitate the separation of photogenerated charge carriers and thus enhance the photocatalytic H2-production activity of TiO2.Ni(OH)2 cluster-modified TiO2 (Ni(OH)2/TiO2) nanocomposite photocatalysts were fabrication by a simple precipitation method using Degussa P25 TiO2 powder (P25) as support and Ni(NO3)2 as precursor. The effect of Ni(OH)2 cluster loading content on the photocatalytic hydrogen production rates of the as-prepared samples in methanol aqueous solution was investigated. The results showed that the photocatalytic H2-production activity of TiO2 was significantly enhanced by loading Ni(OH)2 clusters. The optimal Ni(OH)2 loading content was found to be 0.23 mol%, giving H2-production rate of 3056μmolh-1g-1 with quantum efficiency (QE) of 12.4%, exceeding that on pure TiO2 by more than 223 times. This high photocatalytic H2-production activity is due to the deposition of Ni(OH)2 clusters on the surface of TiO2. The enhanced mechanism is because the potential of Ni2+/Ni (Ni2++2e-=Ni, E°=-0.23 V) is slightly lower than conduction band (CB) (-0.26 V) of anatase TiO2, meanwhile higher than the reduction potential of H+/H2 (2H++2e-= H2, E°=-0.00 V), which favors the electron transfer CB of TiO2 to Ni(OH)2 and the reduction of partial Ni2+to Ni0. The function of Ni0 is to help the charge separation and to act as co-catalyst for water reduction, thus enhancing the photocatalytic H2-production activity.Efficient hydrogen production and decomposition of glycerol were achieved on CuO-modified titania (CuO-TiO2) photocatalysts in glycerol aqueous solutions. CuO clusters were deposited on the titania surface by impregnation of Degussa P25 TiO2 powder (P25) with copper nitrate followed by calcination. The resulting CuO-TiO2 composite photocatalysts were characterized by X-ray diffraction (XRD), UV-visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The low-power ultraviolet light emitting diodes (UV-LED) were used as the light source for photocatalytic H2-production reaction. A detailed study of CuO effect on the photocatalytic H2-production rates showed that CuO clusters can act as an effective co-catalyst enhancing photocatalytic activity of TiO2. The optimal CuO content was found to be 1.3 wt%, giving H2-production rate of 2061μol h-1 g-1 (corresponding to the apparent quantum efficiency (QE) of 13.4% at 365 nm), which exceeded the rate on pure TiO2 by more than 129 times. The quantum size effect of CuO clusters is deemed to alter its energy levels of the conduction and valence band edges in the CuO-TiO2 semiconductor systems, which favors the electron transfer and enhances the photocatalytic activity. This work shows not only the possibility of using CuO clusters as a substitute for noble metals in the photocatalytic H2 production but also demonstrates a new way for enhancing hydrogen production activity by quantum size effect.更多还原