Department of Plant Science and Landscape Architecture, University of Connecticut, 1376 Storrs Road, Storrs, Connecticut 06269-4067, United States.
Environ Sci Technol. 2012 Jan 3;46(1):300-6. doi: 10.1021/es2033394. Epub 2011 Dec 5.
Recent experimental research into the adsorption of various cations on zeolite minerals has shown that nanopore channels of approximately 0.5 nm or less can create an effect whereby the adsorption of ions, especially those that are weakly hydrated, can be significantly enhanced. This enhanced adsorption occurs due to the removal of hydrating water molecules which in turn is caused by the nanopore channel's small size. A new adsorption model, called the nanopore inner-sphere enhancement (NISE) effect, has been proposed that explains this unusual adsorption mechanism. To further validate this model a series of nuclear magnetic resonance (NMR) spectroscopy studies is presented here. NMR spectra were gathered for Na adsorbed on three zeolite minerals of similar chemical composition but differing nanoporosities: zeolite Y with a limiting dimension of 0.76 nm, ZSM-5 with a limiting dimension of 0.51 nm, and mordenite with a limiting dimension of 0.26 nm. The NMR experiments validated the predictions of the NISE model whereby Na adsorbed via outer-sphere on zeolite Y, inner-sphere on ZSM-5, and a combination of both mechanisms on mordenite. The strong Na adsorption observed in these nanoporous minerals conflicts with sodium's general designation as a weak electrolyte.
最近对沸石矿物吸附各种阳离子的实验研究表明，直径约为 0.5nm 或更小的纳米孔道可以产生一种效应，使离子的吸附，特别是那些弱水合的离子的吸附得到显著增强。这种增强的吸附是由于去除了水合水分子，而这又是由纳米孔道的小尺寸引起的。因此，提出了一种新的吸附模型，称为纳米孔内球增强（NISE）效应，该模型解释了这种不寻常的吸附机制。为了进一步验证该模型，本文提出了一系列核磁共振（NMR）光谱研究。为三种化学组成相似但纳米孔隙率不同的沸石矿物吸附的 Na 收集了 NMR 谱：沸石 Y 的极限尺寸为 0.76nm，ZSM-5 的极限尺寸为 0.51nm，丝光沸石的极限尺寸为 0.26nm。NMR 实验验证了 NISE 模型的预测，即 Na 通过沸石 Y 的外球吸附、ZSM-5 的内球吸附以及丝光沸石上两种机制的组合吸附。在这些纳米多孔矿物中观察到的强 Na 吸附与钠通常被指定为弱电解质的性质相矛盾。
