Investigation of the formation process of photodeposited Rh nanoparticles on TiO2 by in situ time-resolved energy-dispersive XAFS analysis.
Investigation of the formation process of photodeposited Rh nanoparticles on TiO2 by in situ time-resolved energy-dispersive XAFS analysis.
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DOI：
10.1021/la1022906
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发表时间：
2010-07
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通讯作者：
Junya Ohyama;K. Teramura;S. Okuoka;S. Yamazoe;Kazuo Kato;T. Shishido;Tsunehiro Tanaka
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文献类型：
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作者：
Junya Ohyama;K. Teramura;S. Okuoka;S. Yamazoe;Kazuo Kato;T. Shishido;Tsunehiro Tanaka
利用原位时间分辨能量色散x射线吸收精细结构（DXAFS）分析揭示了在液固悬浮状态下，以甲醇为牺牲氧化剂，在RhCl(3)水溶液中，在tio2(2)光催化剂上，Rh（3+）离子直接还原为Rh金属并形成Rh纳米粒子的过程。通过对各x射线吸收近边结构（XANES）光谱的最小二乘拟合，对对应于Rh(0)和Rh（3+）的真实光谱进行线性组合，估计了Rh金属颗粒和Rh（3+）前驱体的组分。金属铑的含量随光照射时间的增加呈线性增加，在光照射90 min后达到饱和。通过扩展XAFS （EXAFS）光谱傅里叶变换（FT）中2.45 A处的Rh-Rh散射曲线拟合，确定了配位数（Rh-Rh对）。配位数随光照射时间线性增加，在光照射90 min后达到恒定值10。该值低于Rh箔（12）。这表明在TiO(2)上形成了细小的Rh金属纳米颗粒。此外，ICP测定的Rh（3+）的减少率与XANES光谱估计的Rh金属颗粒比例的增加率和FT-EXAFS光谱评估的配位数（Rh-Rh对）的增加率一致。这一结果有力地支持了电荷分离产生的电子在某一时刻以恒定速率将Rh（3+）前体还原为Rh金属粒子的事实。Rh颗粒的生长不是渐进式的，而是在表面上依次出现具有均匀大小的Rh颗粒。
The photodeposition process of Rh metal nanoparticles on a TiO(2) photocatalyst from RhCl(3) aqueous solution in the presence of methanol as a sacrificial oxidant, which consists of the direct reduction of Rh(3+) ions to Rh metal and the formation of Rh nanoparticles, was uncovered by in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis in a liquid-solid suspension state. The fractions of Rh metal particles and Rh(3+) precursor were estimated by the least-squares fitting of each X-ray absorption near-edge structure (XANES) spectrum by a linear combination of authentic spectra corresponding to Rh(0) and Rh(3+). The fraction of Rh metal linearly increased with photoirradiation time and saturated after 90 min of photoirradiation. The coordination number (Rh-Rh pair) was evaluated by the curve fitting of the Rh-Rh scattering at 2.45 A in the Fourier transforms (FT) of extended XAFS (EXAFS) spectra. The coordination number linearly increased with photoirradiation time and attained a constant value of 10 after 90 min of photoirradiation. This value is lower than that for the Rh foil (12). These suggest the formation of fine Rh metal nanoparticles on TiO(2). In addition, the diminution rate of Rh(3+) as determined by ICP analysis was in good agreement with the increased rates for the fraction of Rh metal particles estimated by XANES spectra and the coordination number (Rh-Rh pair) evaluated by FT-EXAFS spectra. This result strongly supports the fact that electrons generated by charge separation reduce the Rh(3+) precursor to an Rh metal particle at a moment in time and at a constant rate. The Rh particles do not grow in incremental steps, but Rh particles with a uniform size appear one after another on the surface.