A covalent organic framework-enhanced hydrogel based on carboxylated cellulose nanofibers and water hyacinth carbon for efficient capture of dyes and heavy metal ions.

To remediate dye and heavy metal contamination in industrial wastewater, a novel ternary hydrogel adsorbent (COF@CCNF/WHC) was fabricated via radical polymerization using water hyacinth-derived carbon (WHC), carboxylated cellulose nanofibers (C-CNF) and covalent organic framework (COF). Compared with conventional biomass carbon and pure COF, this hydrogel suppresses powder agglomeration and improves separation performance, achieving high-efficiency water purification and providing a viable solution for the sustainable strategy of "treating waste with waste." Multiple characterizations verified that the composite maintained the core structures of each component, exhibiting better thermal stability than single materials. Its equilibrium swelling ratio reached approximately 480%, providing sufficient space for adsorption. Adsorption results revealed that the adsorption of methylene blue (MB), crystal violet (CV), Pb2+, and Cu2+ followed the pseudo-second-order kinetic and Langmuir isotherm models, with maximum adsorption capacities of 1054.10 mg g-1, 1069.50 mg g-1, 1602.06 mg g-1, and 982.95 mg g-1, respectively, outperforming most reported adsorbents. COF@CCNF/WHC performed best under neutral to weakly alkaline conditions; coexisting ions and humic acid reduced its adsorption efficiency. It retained high removal efficiency after five adsorption-desorption cycles with excellent reusability. The adsorption mechanisms include electrostatic attraction, hydrogen bonding, and π-π interactions. This work provides a novel material for wastewater treatment and a sustainable strategy for biomass waste resource utilization.