(631d) A Hydrogen-Bonded Supramolecular Coordinating Complex for Copper Removal from Aqueous Solutions with Unprecedentedly Fast Kinetics

Copper, one of the most widely used heavy metals, is extremely toxic to human health if present in large amounts despite its essential role in human physiology. Albeit a plethora of explored MOFs, relatively few structures have been sought for stable, affordable yet highly effective copper removal from water streams. Few MOFs have been studied either as copper adsorbents or detective sensors. Among them, zeolitic imidazolate framework (ZIF8)was reported to perform an extremely high Cu(II) ions adsorption capacity (up to ~800 mg/g) which makes it one of the current state-of-the-art adsorbents for copper ions removal. However, ZIF8 did not perform well at pH < 3. Adsorbents that are specifically designed to target given ions of interest must be made available and affordable for pragmatic large-scale separation. Compared to frameworks built upon coordination bonds and covalent bonds (e.g. MOFs, covalent organic frameworks – COFs), hydrogen-bonded frameworks have received less attention due to a preconceived notion of a lack of stability due to the non-covalent interacting network. However, recent studies have shown potentials for these material families in selective separation thanks to their flexibility, reversibility and capability for guest-host interaction.

Herein, we demonstrate the synthesis, characterization, and mechanistic understandings of copper adsorption behaviors of a new water-stable copper scavenger with unprecedentedly fast sorption kinetics, relatively high sorption capacity, selective performance at low pH and scalability. In essence, by coupling coordination chemistry and supramolecular assembly, a new crystal material was formed in aqueous medium through the combination of metal-ligand coordination and non-covalent interactions such as inter- and intra-molecular hydrogen bonds. The material structure and behaviors in water environment were studied experimentally and computationally. Performed on our first model ion-of-interest, copper, with immense promise compared to ZIF8, we envision that such a synthetic strategy may pave the way for further interesting functional crystalline structures to be emerged and readily translated to macroscopic platforms.