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首页> 外文期刊>Chemistry: A European journal >Kinetic and mechanistic investigations of the light induced formation of gold nanoparticles on the surface of TiO _2
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Kinetic and mechanistic investigations of the light induced formation of gold nanoparticles on the surface of TiO _2

机译：TiO _2表面光诱导金纳米颗粒形成的动力学和机理研究

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The kinetics of the formation of gold nanoparticles on the surface of pre-illuminated TiO _2 have been investigated using stopped-flow technique and steady state UV/Vis spectroscopy. Excess electrons were loaded on the employed nanosized titanium dioxide particles by UV-A photolysis in the presence of methanol serving as hole scavenger, stored on them in the absence of oxygen and subsequently used for the reduction of Au ~(III) ions. The formation of gold nanoparticles with an average diameter of 5 nm was confirmed after mixing of the TiO _2 nanoparticles loaded with electrons with aqueous solution of tetrachloroaureate (HAuCl _4) by their surface plasmon absorbance band at 530 nm, as well as by XRD and HRTEM measurements. The rate of formation of the gold nanoparticles was found to be a function of the concentration of the gold ions and the concentration of the stored electrons, respectively. The effect of PVA as a stabilizer of the gold nanoclusters was also studied. The observed kinetic behavior suggests that the formation of the gold nanoparticles on the TiO _2 surface is an autocatalytic process comprising of two main steps: 1) Reduction of the gold ions by the stored electrons on TiO _2 forming gold atoms that turn into gold nuclei. 2) Growth of the metal nuclei on the surface of TiO _2 forming the gold particles. Interestingly, at higher TiO _2 electron loading the excess electrons are subsequently transferred to the deposited gold metal particles resulting in "bleaching" of their surface plasmon band. This bleaching in the surface plasmon band is explained by the Fermi level equilibration of the Au/TiO _2 nanocomposites. Finally, the reduction of water resulting in the evolution of molecular hydrogen initiated by the excess electrons that have been transferred to the previously formed gold particles has also been observed. The mechanism of the underlying multistep electron-transfer process has been discussed in detail.
机译：使用停止流技术和稳态紫外/可见光谱研究了在预照射的TiO _2表面上金纳米颗粒形成的动力学。在存在作为空穴清除剂的甲醇的存在下，通过UV-A光解将过量的电子负载在所用的纳米二氧化钛颗粒上，在没有氧气的情况下将其存储在其上，随后用于还原Au〜（III）离子。通过载有电子的TiO _2纳米颗粒与四氯金酸酯水溶液（HAuCl _4）的表面等离子体吸收带在530 nm处以及XRD和HRTEM混合，证实了平均粒径为5 nm的金纳米颗粒的形成。测量。发现金纳米颗粒的形成速率分别是金离子浓度和所存储电子浓度的函数。还研究了PVA作为金纳米簇稳定剂的作用。观察到的动力学行为表明，在TiO _2表面上形成金纳米颗粒是一种自动催化过程，包括两个主要步骤：1）通过TiO _2上存储的电子还原金离子，形成金原子，金原子变成金核。 2）金属核在形成金颗粒的TiO _2表面上的生长。有趣的是，在较高的TiO _2电子负载下，过量的电子随后转移到沉积的金金属颗粒上，导致其表面等离激元带“漂白”。 Au / TiO _2纳米复合材料的费米能级平衡解释了表面等离激元带中的这种漂白。最后，还观察到水的减少导致由已经转移到先前形成的金颗粒中的过量电子引发的分子氢的放出。潜在的多步电子转移过程的机理已经详细讨论。

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