Nanocrystalline TiO2 studied by optical, FTIR and X-ray photoelectron spectroscopy:: correlation to presence of surface states
Nanocrystalline TiO2 studied by optical, FTIR and X-ray photoelectron spectroscopy:: correlation to presence of surface states
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DOI：
10.1016/s0040-6090(99)00722-1
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发表时间：
2000-01-10
期刊：
影响因子：
2.1
通讯作者：
Sastry, M
中科院分区：
文献类型：
--
作者：
Kumar, PM;Badrinarayanan, S;Sastry, M
纳米二氧化钛已通过两种不同的方法在有机介质中合成，产生了两种不同的结构相，即金红石相和锐钛矿相。这些差异体现在用于研究纳米粒子的不同表征技术中。紫外 - 可见光谱显示与吸收峰相关的粒径约为2.5纳米，这与透射电子显微镜（TEM）估计的2.5 - 5.0纳米相符。掠入射X射线衍射表明，对于所考虑的不同方法，存在金红石相和锐钛矿相以及Ti₂O₃的覆盖层。尽管从吸收曲线来看跃迁性质存在差异，但直接跃迁得到了证实。两种颗粒结构的光致发光（PL）光谱分别在314纳米和399纳米处显示出明显的红移峰（距激发态0.81电子伏特），并且还揭示了最大PL信号周围的振动特征。此外，在两种情况下都在617.5纳米处观察到Ti³⁺（PL）态，这是一个由俄歇过程控制的特征。傅里叶变换红外（FTIR）研究揭示了Ti - O氧化物物种之间的微弱复合振动，以及通过（OH）基团的掺入而产生的额外不饱和位点（Ti³⁺），这在块状二氧化钛中是看不到的。因此，为了实现配位饱和（八面体位置），由Ti - 6(3⁺) - OH以及Ti - 4(4⁺) - O（四面体）组成的表面是必要的。掠入射X射线衍射研究表明存在TiO₂的金红石相以及Ti的低价氧化物相（Ti₂O₃）。TiO₂薄膜的X射线光电子能谱（XPS）证实了氧化物相以及低价态的存在。XPS和FTIR光谱通过羟基的掺入证实了低价态（Ti²⁺，Ti³⁺）配位饱和的吸附位点的存在。随着粒径减小，这些位点会增多，为额外的配位开辟了途径，从而带来重要的应用。在这种情况下，Ti₂O₃覆盖层使二氧化钛表面达到饱和。与文献报道相比，数据中观察到了细微的差异。（C）2000爱思唯尔科学股份有限公司。保留所有权利。
Nanophase TiO2 has been synthesized in an organic medium by two different routes, yielding two different structural phases viz. rutile and anatase. These differences are reflected in the different characterization techniques used to study the nanoparticles. UV-vis spectroscopy shows absorption-peak related particle sizes of similar to 2.5 nm and agrees with transmission electron microscopy (TEM) estimates of 2.5-5.0 nm. Grazing incidence X-ray diffraction shows rutile and anatase phase with an overlay of Ti2O3 for the different routes considered. Differences in the nature of the transition from absorption plots not withstanding, a direct transition is confirmed. Photo-luminescence (PL) spectra for the two particulate structures shows prominent red shifted peaks at 314 nm and 399 nm, respectively (0.81 eV from the excitation), and also reveals vibrational features around the maximum PL signal. In addition a Ti3+ (PL) state is observed at 617.5 nn for both cases, a feature governed by the Auger process. Fourier transform infrared (FTIR) studies reveal weak complex vibrations between the Ti-O oxide species and also additional unsaturated sites (Ti3+) through incorporation of (OH) groups, not otherwise seen in bulk titania. A surface consisting of Ti-6(3+)-OH for coordinative saturation (octahedral site), along with Ti-4(4+)-O (tetrahedral) is thus necessary. Grazing incidence X-ray diffraction studies shows the presence of the rutile phase of TiO2 and also a sub-oxide phase of Ti (Ti2O3) X-ray photoemission spectre (XPS) of thin films of TiO2 confirms the oxide phase and also the presence of sub-valence states. The XPS and FTIR. spectra confirm the presence of adsorbed sites for coordinative saturation of sub-valence states (Ti2+, Ti3+), through hydroxyl incorporation. These sites are amplified as the particle size is reduced, opening avenues for additional coordination, leading to important applications. In this case, a Ti2O3 overlay saturates the surface of titania. Subtle differences are observed in the data vis-a-vis literature reports. (C) 2000 Elsevier Science S.A. All rights reserved.