Ding Hao, Khan Sana T, Zeng Songshan, Sun Luyi
Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, United States.
Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, United States.
Inorg Chem. 2021 Jun 7;60(11):8276-8284. doi: 10.1021/acs.inorgchem.1c00968. Epub 2021 May 25.
The exfoliation of microcrystalline α-zirconium phosphate (α-ZrP) in an organic solvent is very difficult to achieve. Surprisingly, the addition of tetra(-butyl)ammonium hydroxide (TBAOH) into a methanol dispersion of a nanosized α-ZrP brings about the complete exfoliation of nanosheets. To understand the mechanism, we examined the stepwise intercalation/exfoliation of the nanosized α-ZrP using TBAOH in four different solvents (water, methanol, ethanol, and butanol). Propionate groups on the edge of the nanosized α-ZrP prevent TBA cations from entering the galleries. Due to the formation of unstable solvent-intercalated α-ZrP with an increased interlayer distance in methanol and ethanol, TBA cations can overcome the steric hindrance and move into nanosheet layers to exchange with solvent molecules. However, the movability of the cations into the center of the galleries is preferred at a certain interlayer distance range, which leads to exfoliation of α-ZrP in methanol but intercalation only in ethanol. In water, in the beginning, neither intercalation nor exfoliation by TBA cations occurs. An additional amount of TBAOH causes the deformation of propionate groups and removes the barriers on the edges, followed by late intercalation and then exfoliation. On the other hand, butanol, as the solvent, is bulky and effectively limits the intercalation behavior of TBA cations. The weaker polarity of ethanol and butanol, compared with water and methanol, lowers the ion interactions in the solvent, which is another reason why they do not lead to exfoliation.
在有机溶剂中实现微晶α-磷酸锆（α-ZrP）的剥离非常困难。令人惊讶的是，将四丁基氢氧化铵（TBAOH）添加到纳米尺寸α-ZrP的甲醇分散液中会使纳米片完全剥离。为了理解其机理，我们研究了在四种不同溶剂（水、甲醇、乙醇和丁醇）中使用TBAOH对纳米尺寸α-ZrP进行逐步插层/剥离的过程。纳米尺寸α-ZrP边缘的丙酸根基团阻止TBA阳离子进入层间。由于在甲醇和乙醇中形成了层间距增加的不稳定溶剂插层α-ZrP，TBA阳离子可以克服空间位阻并进入纳米片层与溶剂分子进行交换。然而，在一定的层间距范围内，阳离子向层间中心移动更有利，这导致α-ZrP在甲醇中剥离而在乙醇中仅发生插层。在水中，一开始TBA阳离子既不发生插层也不发生剥离。额外添加的TBAOH会导致丙酸根基团变形并消除边缘的障碍，随后发生后期插层，然后剥离。另一方面，丁醇作为溶剂体积较大，有效地限制了TBA阳离子的插层行为。与水和甲醇相比，乙醇和丁醇的极性较弱，降低了溶剂中的离子相互作用，这是它们不会导致剥离的另一个原因。
