Green synthesis of Zr-based metal–organic framework hydrogel composites and their enhanced adsorptive properties

Abstract

Metal–organic frameworks (MOFs) have emerged as promising candidates for a wide range of applications due to their high surface area and customizable structures, however, the minimal external hydrophilicity of MOFs has limited their biomedical implementations. Structuring of MOFs within polymer frameworks is an approach used to create hybrid materials that retain many of the MOF characteristics (e.g. high adsorption capacity) but expand the range of mechanical and surface properties as well as form factors accessible. Using this approach, hybridizing MOFs with hydrophilic hydrogels can give rise to materials with improved hydrophilicity and biocompatibility. Here, we describe the synthesis of the first Zr-based MOF-hydrogel hybrid material (composite 3) using a green chemistry approach, in which only water was used as the solvent and relatively low temperature (50 °C) was applied. Using methylene blue (MB) as a probe molecule, composite 3 exhibited greater adsorption capacity than the MOF or the hydrogel alone in aqueous solution at most tested pH values (all except pH 13). At an initial MB concentration of 0.0096 mg mL⁻¹ (30.014 μM) and neutral pH conditions, this new hybrid presented the highest loading of MB among similar materials (MB adsorbed = 4.361 ± 0.092 mg MB per g Zr, partition coefficient = 0.172 ± 0.004 mg g⁻¹ μM⁻¹) and largely retained its adsorption capacity under varied conditions (pH 1–13 and 0.2–1.0 M NaCl), rendering possible applications in drug delivery and the removal of tumor contrast agent/dye with minimal leakage due to its broad chemical stability.