磷酸盐修饰对纳米TiO₂光电化学性质影响研究

【作者】 周佳；

【导师】 井立强；

【作者基本信息】 黑龙江大学 ， 物理化学， 2011， 硕士

【摘要】 TiO₂半导体材料光电化学分解水制氢以及光催化降解污染物等方面的潜在应用而引起了广泛的关注。但是光生载流子复合效率较高这个瓶颈因素限制了TiO₂光电化学方面的应用,大量研究都尝试克服这个瓶颈因素,而其中表面修饰是比较有效的改性方法之一。基于以上分析,本论文开展通过磷酸以及磷酸盐修饰TiO₂来提高其光生载流子分离状况,进而改善光电化学性质的研究。重点利用瞬态吸收光谱（TAS）等技术揭示磷酸修饰对光生电荷分离、传输等动力学过程的影响,从而揭示影响光电化学的本质原因。主要涉及两方面工作:采用简单的溶液浸渍法实现磷酸对纳米TiO₂的表面修饰。适量磷酸修饰提高了纳米TiO₂薄膜电极光电流密度。基于不同pH值电解液的I-V曲线的测试,揭示了磷酸修饰使得TiO₂表面产生负电荷是其光电流密度提高的关键。瞬态吸收光谱测试结果证实了磷酸修饰使得TiO₂光生载流子的寿命延长,这与其表面携带负电荷有关。光生载流子寿命的延长意味着光生电子-空穴的分离效率得到有效提高,这深入地解释了磷酸修饰能够提高纳米TiO₂薄膜电极光电流密度,预示着光电化学分解水析氢的性能将得到提高。采用简单的溶液浸渍法实现磷酸钴对纳米TiO₂的表面修饰。适量磷酸钴的修饰显著地提高了TiO₂薄膜电极光电流密度。基于电化学数据及电化学测试结果,认为低价钴离子有利于光生空穴的捕获,进而在较低的析氧电位下与水发生氧化反应,从而解决了由于光生空穴与水反应需要较长时间而导致的光生电子-空穴分离效率较差的瓶颈问题。表面光电压谱（SPS）进一步证明低价钴离子能够有效地捕获光生空穴。基于不同制备条件下样品的I-V曲线测试结果,证明无定型低价钴离子具有捕获光生空穴的作用。此工作的研究为设计合成高性能的TiO₂基光电材料提供一些可借鉴的方法与思路,为进一步洞察研究光电化学分解水以及光催化降解污染物提供思路,为丰富TiO₂光电化学理论提供一些重要的实验依据。更多还原

【Abstract】 The photoelectrochemical properties of TiO₂ have been widely studied since the low cost and high stability of TiO₂, and the energetics of the valence and conduction bands of TiO₂ which are suitable for contamination oxidation to purify the environment and proton reduction to solve the energy problem, respectively. The practical use of TiO₂ as water splitting and pollutant control materials is, however, limited due to the high energy of the band gap transition. This limits the absorption of TiO₂ to the UV region. A low quantum yield for photo carriers following the absorption of UV photons further limits the use of TiO₂ for photoelectrochemical water splitting. Numerous studies have attempted to overcome these shortcomings and to increase photoelectrochemical efficiency. In this paper TAS has been used to explore separation and transmission of nc-TiO₂ which is modified by phosphate and cobalt phosphate, and then the mechanism has been deeply penetrated.Phosphoric acid modification nanosized TiO₂ has been prepared by a sample impregnation method. The results show that an appropriate amount of cobalt phosphate modification could improve the photoelectrochemical activity of nc-TiO₂, which is attributed to the surface negative charge on the surface of TiO₂ after acid modification. The TAS results shows that phosphoric acid modification prolongs the life of carrier, and this is attributed to the surface negative charge on the surface of TiO₂, then the separation rate of photo electrons and photo holes are improved. The results were favorable to reveal the reason of the enhancement of photoelectrochemical current density of TiO₂ film electrode which corresponding to water splitting has been improved.Cobaltous phosphate modification nanosized TiO₂ has been prepared by a sample impregnation method.The results show that an appropriate amount of cobalt phosphate modification could improve the photocatalytic activity of nc-TiO₂, which is attributed to its holes have been trapped by low price cobalt ions, so that recombination of the holes and the electrons can be inhibited. The low price cobalt ions can be oxidized by holes to form high price cobalt ions, and high price cobalt ions oxidize water directly to form oxygen, which can promote the separation of photogenerated electron-hole pairs.This study has provided some reference methods and ideas for designing and synthesizing high performance TiO₂ based photoelectrochemical material and provided some important experimental basis for enrich the theory of TiO₂ photocatalytic technology.更多还原