Inoguchi Shota, Fukami Kazuhiro, Amano Ken-Ichi, Kitada Atsushi, Murase Kuniaki
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan.
Faculty of Agriculture, Meijo University, Nagoya, Aichi 468-8502, Japan.
ACS Omega. 2020 Oct 8;5(41):26894-26901. doi: 10.1021/acsomega.0c04127. eCollection 2020 Oct 20.
The ion enrichment behavior due to surface-induced phase separation and the concomitant phase transition of electrolyte solutions between a liquid and a solid confined within nanopores of porous silicon is examined using concentrated aqueous solutions. We performed open-circuit potential measurements and differential scanning calorimetry (DSC) while varying the concentration of aqueous tetraethylammonium chloride (TEACl) solution. Open-circuit potential measurements revealed that the local OH concentration within the nanopores increases as the bulk TEACl concentration increases. DSC measurements indicated that TEA cations are enriched within the nanopores and an extremely high concentration of TEA remarkably increases the local OH concentration. This increase in the local pH should realize the selective precipitation of metal hydroxides within the nanopores. However, such precipitation was not observed in our investigations using aqueous solutions containing zinc cations. The experimental results suggest that ionic species within the nanopores of porous silicon are more stable than those in a bulk solution due to the formation of ion pairs with enhanced stability as well as kinetic factors that increase the activation energy for precipitation.
使用浓水溶液研究了多孔硅纳米孔内表面诱导相分离导致的离子富集行为以及电解质溶液在液体和固体之间伴随的相变。我们在改变四乙基氯化铵（TEACl）水溶液浓度的同时进行了开路电位测量和差示扫描量热法（DSC）。开路电位测量表明，随着本体TEACl浓度的增加，纳米孔内的局部OH浓度升高。DSC测量表明，TEA阳离子在纳米孔内富集，并且极高浓度的TEA显著提高了局部OH浓度。局部pH值的这种升高应该会实现纳米孔内金属氢氧化物的选择性沉淀。然而，在我们使用含锌阳离子水溶液的研究中未观察到这种沉淀。实验结果表明，由于形成了稳定性增强的离子对以及增加沉淀活化能的动力学因素，多孔硅纳米孔内的离子物种比本体溶液中的离子物种更稳定。
