A preassembled framework nanocellulose hydrogel inspired by biological systems in nature and ion-imprinted polymers for efficient removal of Cu(II).

• A pre-assembled framework structure hydrogel (Cu2+-CNF hydrogel) was developed. • Explained the formation mechanism of the pre-assembled framework in Cu2+-CNF hydrogel. • Cu2+-CNF hydrogel exhibited excellent adsorption properties and mechanical properties. • Propose a general strategy for the pre-assembly of framework hydrogels. Hydrogels can effectively address various adsorption requirements as a multifunctional adsorbent material with a three-dimensional spatial network. However, conventional hydrogels, typically synthesized using the one-pot method, often exhibit a heterogeneous internal structural arrangement, leading to non-uniform stress distribution when interacting with heavy metal ions. This has resulted in the structural disruption of conventional hydrogels in the adsorption of heavy metal ions, and they exhibit low adsorption performance, low cycling performance, and non-selective adsorption. Herein, a preassembled framework structure hydrogel (Cu2+-CNF hydrogel) was developed by introducing template ions (Cu2+), which have been coordinated with monomers (Acrylic acid and Acrylamide), into a network of cellulose nanofibrils (CNFs) polymers. The obtained Cu2+-CNF hydrogel exhibited excellent adsorption properties(Cu2+-CNF hydrogel, 402 mg/g) compared to those prepared by the one-pot method(CNF hydrogel, 129 mg/g). In addition, the Cu2+-CNF hydrogel has superior selective adsorption property and tensile strain properties (CNF hydrogel: 20 % to Cu2+-CNF hydrogel: 100 %) at higher swelling ratios (CNF hydrogel: 2313 wt% to Cu2+-CNF hydrogel: 8379 wt%). Even after multiple folding or repeated adsorption–desorption cycles, the integrity of the structure and adsorption function can still be maintained. This work provides a general strategy for preparing a new type of nanocellulose hydrogel. [ABSTRACT FROM AUTHOR]