Tunable Low–Relative Humidity and High–Capacity Water Adsorption in a Bibenzotriazole Metal–Organic Framework

Materials capable of selectively adsorbing or releasing water can enable valuable applications ranging from efficient humidity and temperature control to the direct atmospheric capture of potable water. Despite recent progress in employing metal–organic frameworks (MOFs) as privileged water sorbents, developing a readily accessible, water-stable MOF platform that can be systematically modified for high water uptake at low relative humidity remains a significant challenge. We herein report the development of a tunable MOF that efficiently captures atmospheric water (up to 0.78 g water/g MOF) across a range of uptake humidity (27–45%) employing a readily accessible Zn bibenzotriazolate MOF, CFA-1 ([Zn5(OAc)4(bibta)3], H2bibta = 1H,1H′-5,5′-bibenzo­[d]­[1,2,3]­triazole), as a base for subsequent diversification. Controlling the metal identity (zinc, nickel) and coordinating nonstructural anion (acetate, chloride) via postsynthetic exchange modulates the relative humidity of uptake, facilitating the use of a single MOF scaffold for a diverse range of potential water sorption applications. We further present a fundamental theory dictating how continuous variation of the pore environment affects the relative humidity of uptake. Exchange of substituents preserves capacity for water sorption, increases hydrolytic stability (with 5.7% loss in working capacity over 450 water adsorption–desorption cycles for the nickel-chloride-rich framework), and enables continuous modulation for the relative humidity of pore condensation. This combination of stability and tunability within a synthetically accessible framework renders Ni-incorporated M5X4bibta3 promising materials for practical water sorption applications.

可选择性吸附或释放水的材料，可支撑一系列极具应用价值的场景，涵盖高效温湿度调控以及直接从大气中捕获饮用水。尽管近年来金属有机框架 (metal–organic frameworks, MOFs) 作为优质水吸附材料取得了诸多进展，但开发一种易于合成、兼具水稳定性，且可通过系统修饰实现低相对湿度下高水吸附量的MOF平台，仍是一项重大挑战。本研究报道了一种可调控的MOF，其可在27%~45%的吸附湿度区间内高效捕获大气中的水分（最高可达0.78 g水/g MOF）；该材料以易于合成的二苯并三唑锌基MOF CFA-1（化学式为[Zn5(OAc)4(bibta)3]，其中H2bibta = 1H,1H′-5,5′-二苯并[d][1,2,3]三唑）作为基础骨架，用于后续功能修饰。通过后合成交换调控金属节点种类（锌、镍）与配位非结构阴离子（乙酸根、氯离子），可调节水吸附的相对湿度阈值，使得单一MOF骨架即可适配多种潜在的水吸附应用场景。本研究还提出了一套基础理论，用以阐释孔道环境的连续变化如何影响水吸附的相对湿度阈值。取代基交换不仅保留了水吸附容量，还提升了材料的水解稳定性（富镍-氯离子骨架在450次水吸附-脱附循环后工作容量仅损失5.7%），同时可实现孔道冷凝相对湿度的连续调控。这种兼具稳定性与可调控性、且易于合成的骨架特性，使得掺杂镍的M5X4bibta3成为极具应用前景的实用型水吸附材料。