Removal of copper ions by cellulose nanocrystal-based hydrogel and reduced adsorbents for its catalytic properties

Removal of copper ions (Cu(II)) efficiently from water is crucial for water environment security. We use sustainable, low-cost, renewable cellulose derivatives (carboxymethylcellulose sodium (CMC-Na)) and polyvinyl alcohol (PVA) as the matrix, and cellulose nanocrystals (CNCs) as the functional addition. The CNC/CMC-Na/PVA hydrogel was prepared by the physical cross-linking method. Static adsorption experiments proved that CNC/CMC-Na/PVA hydrogel has a greater adsorption potential (108 mg/g) towards Cu(II). At the same time, the adsorption of Cu(II) on CNC/CMC-Na/PVA hydrogels is spontaneous and endothermic, and obeys the pseudo-second-order model with intra-particle diffusion. Furthermore, the primary adsorption mechanisms had been electrostatic attraction and surface complexation. Importantly, CNC/CMC-Na/PVA hydrogel has efficient absorbability and preferable reusability in actual water samples. Furthermore, the copper nanoparticles (Cu NPs) adsorbed on the surface of CNC/CMC-Na/PVA hydrogels were reduced with NaBH₄ in situ to realize the secondary utilization in CNC/CMC-Na/PVA hydrogels supported by Cu NPs. It is found that the material can be used as a catalyst to efficiently catalyze the conversion of HMF to BHMF (99%). Consequently, we provide insights into the hydrogel preparation that would possibly be promising novel adsorbents for the elimination of heavy-ion from sustainable water purification.