Fabrication of carboxylated cellulose nanocrystal/sodium alginate hydrogel beads for adsorption of Pb(II) from aqueous solution

Carboxylated cellulose nanocrystal-sodium alginate (CCN-Alg) hydrogel beads were easily prepared through a cross-linking method. The structure and properties of the composite beads were characterized by TEM, FTIR, SEM, XPS, thermogravimetric analysis (TGA), and zeta potential measurement. A high ratio of 76% of the Pb(II) ion was adsorbed within the first 2 h, and the adsorption equilibrium was nearly reached after 3 h. The experimental isotherm could be fitted by the Langmuir model, yielding an extreme adsorption capacity of 338.98 mg g−1. The adsorption process followed a pseudo-second-order kinetic model, and thermodynamic analyses confirmed that the adsorption is a spontaneous and exothermic process. Regeneration tests with acid treatment indicated that the CCN-Alg beads performed well in repeated Pb(II) adsorptions, as they could maintain an adsorption capacity of 223.2 mg g−1 after five repeated cycles. These results indicate that these CCN-Alg beads are a potentially effective and sustainable adsorbent for application in wastewater treatment.