Center for Materials Science , Zewail City of Science and Technology , October Gardens , Giza 12578 , Egypt.
Department of Sciences, University College Groningen , University of Groningen , 9718 BG Groningen , Netherlands.
Inorg Chem. 2019 Nov 18;58(22):15078-15087. doi: 10.1021/acs.inorgchem.9b01611. Epub 2019 Oct 29.
The remarkable water stability of Zr-carboxylate-based metal-organic frameworks (MOFs) stimulated considerable interest toward their utilization in aqueous phase applications. The origin of such stability is probed here through pH titration and p modeling. A unique feature of the Zr(μ-OH)(μ-O)(RCO) cluster is the Zr-bridging oxo/hydroxyl groups, demonstrating several p values that appear to provide for the water stability at a wide range of pH. Accordingly, the tunability of the cage/surface charge of the MOF can feasibly be controlled through careful adjustment of solution pH. Such high stability, and facile control over cage/surface charge, can additionally be augmented through introducing chemical functionalities lining the cages of the MOF, specifically amine groups in the UiO-66-NH presented herein. The variable protonation states of the Zr cluster and the pendant amino groups, their H-bond donor/acceptor characteristics, and their electrostatic interactions with guest molecules were effectively utilized in controlled experiments to demonstrate high uptake of model guest molecules (137 mg/g for Cr(VI), 1275 mg/g for methylene blue, and 909 mg/g for methyl orange). Additionally, a practical form of the silica-supported MOF, UiO-66-NH@SiO, constructed in under 2 h reaction time, is described, generating a true platform microporous sorbent for practical use in demanding applications.
Zr-羧酸基金属-有机骨架（MOFs）的出色水稳定性激发了人们对其在水相应用中的利用产生了浓厚的兴趣。通过 pH 滴定和 p 模型探究了这种稳定性的起源。Zr(μ-OH)(μ-O)(RCO) 簇的一个独特特征是 Zr 桥接的氧/羟基基团，具有多个似乎在广泛的 pH 值范围内提供水稳定性的 p 值。因此，MOF 的笼/表面电荷的可调性可以通过仔细调节溶液 pH 值来实现。这种高稳定性和对笼/表面电荷的易于控制，可以通过在 MOF 的笼中引入化学官能团来进一步增强，具体来说，就是本文中所展示的 UiO-66-NH 中的胺基团。Zr 簇和侧挂氨基的可变质子化状态、它们的 H 键供体/受体特性以及它们与客体分子的静电相互作用，在控制实验中得到了有效利用，以证明对模型客体分子（Cr(VI) 为 137mg/g，亚甲基蓝为 1275mg/g，甲基橙为 909mg/g）的高吸收能力。此外，还描述了一种在 2 小时反应时间内构建的二氧化硅负载 MOF（UiO-66-NH@SiO）的实用形式，它生成了一种真正的微孔吸附剂平台，可用于苛刻应用中的实际使用。
