Modulated synthesis of thiol-functionalized fcu and hcp UiO-66(Zr) for the removal of silver(i) ions from water

Abstract

In recent years there has been a developing interest in the capture of Ag(I) ions from wastewater. In this work we present the synthesis and characterization of two modified thiol-containing UiO-66 metal–organic frameworks (MOFs) capable of removing Ag(I) from aqueous solution. Mercaptoacetic acid (HMAc) was used as a modifier and incorporated as mercaptoacetate into the MOFs. The modulation of the UiO-66 synthesis with HMAc represents an easy and low-cost method for the introduction of thiol groups into the UiO-66 framework, while preserving the general UiO-66 properties like porosity and stability. The usage of very high equivalents of HMAc in relation to ZrCl₄ led to reproducible formation of the rare hexagonal close packed (hcp) topology of UiO-66 instead of its common face-centered cubic (fcu) packing. The materials showed a maximum uptake for Ag(I) from aqueous solutions of over 84 mg g⁻¹ for the fcu structure and 36 mg g⁻¹ for the hcp structure. The uptake follows a Langmuir type behavior for both topologies. Uptake kinetics indicates a pseudo second-order rate law for the initial uptake before diffusion control takes over.