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

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.