Linker mediated enhancement in reusability and regulation of Pb(II) removal mechanism of Cu-centered MOFs

Abstract

Our study demonstrates improved hydrolytic stability of Cu-centered MOFs through linker selection, resulting in enhanced and selective Pb(II) removal with contrasting removal mechanisms. A simple one-pot solvothermal process was employed to synthesize Copper 1,3,5-Benzene-Tricarboxylic Acid (Cu-BTC) MOF, Copper Imidazolate (Cu-Im) MOF and Copper Nicotinic Acid (Cu-NA) MOF, respectively. The synthesis of these MOFs was confirmed using characterization techniques such as XPS, XRD, FTIR and ICP-OES. Water stability studies using experimental and modelling approaches demonstrated that substituting the 1,3,5-benzene-tricarboxylic acid linker with either imidazolate or nicotinic acid, enhanced the hydrostability of the Cu-centered MOF from under 2 h to over 48 h, while showing a high Pb(II) adsorption capacity of 492 mg g-1. This improved hydrostability was observed across acidic and basic pH and at elevated temperatures. The improved stability of Cu-Im significantly enhanced its reusability and showed Pb(II) adsorption for 3 cycles, with 99.5 % removal efficiency at the end of the 3rd cycle and a desorption efficiency of 92.7 %. The experimental data obtained were substantiated with modelling studies (density functional theory) to gain insights into the 2D structure of Cu-Im and compare the hydrolytic stability of Cu-BTC and Cu-Im. Cu-Im, when tested on textile effluent showed a Pb(II) removal efficiency of 99 % within 2 h of treatment. This study opens up the possibility of using linker selection and design as a strategy to enhance the hydrostability of Cu-centered MOFs and in the process improve its applicability for environmental remediation applications.