Carboxymethyl cellulose/polyvinyl alcohol/covalent organic framework composite hydrogel beads for the removal of heavy metal ions from aqueous solutions

Sodium carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) composite hydrogels were used as the host material, and two types of composite hydrogel beads (CPCB-TPB and CPCB-TAPT) were prepared by simple blending with hydrophobic 4-[3,5-bis(4-aminophenyl) phenyl] aniline / 2,5-divinylterephthalaldehyde (TPBDVA-COF) and hydrophilic 2,4,6-tris(4-aminophenyl)-1,3,5-triazine / 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (TAPT-TP-COF) as fillers. These beads were designed for the removal of Ni(II) from wastewater. The study investigated the effects of COFs with different functional groups on the mechanical properties and adsorption characteristics of the hydrogel carriers, and optimized the preparation process of the adsorbents. Experimental results demonstrated that the adsorption behavior of both adsorbents conformed to the pseudosecond-order kinetic model and the Langmuir isotherm model. Notably, the hydrogel beads containing TAPTTP-COF with hydrophilic functional groups exhibited higher mechanical strength and adsorption capacity. The maximum adsorption capacities calculated from the experimental data were 403.58 mg/g for CPCB-TAPT and 325.96 mg/g for CPCB-TPB. The adsorbents primarily interacted with Ni2 + through electrostatic attraction and coordination complexation. Both adsorbents maintained excellent adsorption performance after five adsorption-desorption cycles.