Photoreduction of Methylviologen in Saponite Clay: Effect of Methylviologen Adsorption Density on the Reaction Efficiency
Photoreduction of Methylviologen in Saponite Clay: Effect of Methylviologen Adsorption Density on the Reaction Efficiency
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DOI：
10.1007/s42860-019-00047-8
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发表时间：
2019-12
影响因子：
2.2
通讯作者：
T. Fujimura;T. Shimada;R. Sasai;S. Takagi
中科院分区：
文献类型：
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作者：
T. Fujimura;T. Shimada;R. Sasai;S. Takagi
确定固态主体材料中分子的光化学反应效率的机制并对其进行估计是很困难的。本研究的目的是测量由 MV2+ 和皂石（一种 2:1 粘土矿物）组成的半透明混合膜中甲基紫罗碱阳离子自由基 (MV+·) 的光生效率。 MV+• 是MV2+ 的单电子还原物质。 MV+·是通过这些薄膜的紫外线照射产生的。 MV2+的荧光强度和MV+•的光生效率取决于MV2+的负载水平。当MV2+的负载水平较高（皂石阳离子交换容量（缩写为%CEC）的75%）时，由于自荧光猝灭反应，其荧光显着降低，并且与低吸附密度的薄膜（10%CEC，φ=1.1×10–2）相比，MV+·的光生效率相对较高（量子产率φ=3.5×10–2）。此外，当MV2+的负载水平非常低(0.13％CEC)时，没有观察到自荧光猝灭反应并且不产生MV+·。根据这些观察，皂石中自猝灭反应和MV+·形成的主要机制之一是激发的MV2+和邻近的基态MV2+分子之间的电子转移反应。
To identify the mechanisms for and to estimate the photochemical reaction efficiency of molecules in solid-state host materials is difficult. The objective of the present research was to measure the photogeneration efficiency of the methylviologen cation radical (MV+•) hosted in a semi-transparent hybrid film composed of MV2+and saponite, a 2:1 clay mineral. MV+• is the one-electron reduced species of MV2+. MV+• was generated by UV irradiation of these films. The fluorescence intensity of MV2+and the photogeneration efficiency of MV+• depended on the loading level of MV2+. When the loading level of MV2+was high (75% of the cation exchange capacity (abbreviated as % CEC) of saponite), its fluorescence was reduced considerably because of the self-fluorescence quenching reaction, and the photogeneration efficiency of MV+• was relatively high (quantum yield φ = 3.5×10–2) compared to that of films with low adsorption density (10% CEC, φ = 1.1×10–2). Furthermore, when the loading level of MV2+was very low (0.13% CEC), a self-fluorescence quenching reaction was not observed and MV+• was not generated. From these observations, one of the principal mechanisms of the self-quenching reaction and MV+• formation in saponite is the electron transfer reaction between excited MV2+and adjacent MV2+molecules in the ground state.