In situ synthesis of metal-organic frameworks on sulfonated cellulose nanofibrils

The intrinsic fragility and inferior processibility of metal-organic frameworks (MOFs) particles often restrict their functional application despite their high surface area and porous structure. We investigated the feasibility of sulfonated cellulose nanofibrils (SCNF) as a biopolymer template to hybridize MOFs. SCNF was synthesized through periodate oxidation followed by bisulfite sulfonation. The sulfonate groups increased electronegativity and enhanced the dispersibility of the cellulose fibers. More importantly, the negatively charged sulfonates could serve as anchors for metal ions to initiate the in situ growth of MOFs along the surface of cellulose fibers. We have achieved the synthesis of three types of SCNF/MOF hybrids, namely, SCNF/ZIF-8, SCNF/ZIF-67, and SCNF/HKUST-1. These hybrids can be formed as free-standing aerogels, exhibiting remarkably high surface areas and flexibility for applications. The assessment of the adsorptive efficiency of the SCNF/ZIF-8 hybrid indicates that the hybrid material exhibited a notably higher adsorption capacity for methylene blue versus the SCNF control. DFT calculation provides further insights into the underlying adsorption mechanisms, revealing that the sulfonates on the SCNF and the nitrogen atoms in the ZIF-8 ligands primarily contributed to the affinity for methylene blue. SCNF offers a versatile and robust biopolymer substrate for templating a wide array of MOFs with promising applications as adsorbents and beyond.