Tuning the Chemical Environment within the UiO-66-NH2 Nanocages for Charge-Dependent Contaminant Uptake and Selectivity

Ahmed H Ibrahim; Worood A El-Mehalmey; Rana R Haikal; Mohamed E A Safy; Muhamed Amin; Hassan R Shatla; Stavros G Karakalos; Mohamed H Alkordi

doi:10.1021/acs.inorgchem.9b01611

Tuning the Chemical Environment within the UiO-66-NH₂ Nanocages for Charge-Dependent Contaminant Uptake and Selectivity

Inorg Chem. 2019 Nov 18;58(22):15078-15087. doi: 10.1021/acs.inorgchem.9b01611. Epub 2019 Oct 29.

Authors

Ahmed H Ibrahim¹, Worood A El-Mehalmey¹, Rana R Haikal¹, Mohamed E A Safy¹, Muhamed Amin², Hassan R Shatla¹, Stavros G Karakalos³, Mohamed H Alkordi¹

Affiliations

¹ Center for Materials Science , Zewail City of Science and Technology , October Gardens , Giza 12578 , Egypt.
² Department of Sciences, University College Groningen , University of Groningen , 9718 BG Groningen , Netherlands.
³ College of Engineering and Computing, Swearingen Engineering Center , University of South Carolina , Columbia , South Carolina 29208 , United States.

PMID: 31661254
DOI: 10.1021/acs.inorgchem.9b01611

Abstract

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 pK_a modeling. A unique feature of the Zr₆(μ₃-OH)₄(μ₃-O)₄(RCO₂)₁₂ cluster is the Zr-bridging oxo/hydroxyl groups, demonstrating several pK_a 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-NH₂ 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-NH₂@SiO₂, constructed in under 2 h reaction time, is described, generating a true platform microporous sorbent for practical use in demanding applications.