Facile synthesis of Zr(IV)-crosslinked carboxymethyl cellulose/carboxymethyl chitosan hydrogel using PEG as pore-forming agent for enhanced phosphate removal

Zr(IV)-crosslinked carboxymethyl cellulose/carboxymethyl chitosan hydrogels were prepared using polyethylene glycol (PEG) as pore-forming agent. The hydrogels exhibited porous structure and the pore size increased with the PEG content. The obtained hydrogels were used as adsorbents for removal of phosphate from aqueous solutions. The hydrogel prepared with most amount of PEG displayed largest adsorption amount of phosphate. This result might be attributed to improvement of surface area and pore volume caused by introduction of PEG, which could boost exposure of adsorption sites in the hydrogel and enhance the diffusion of phosphate into interior of the hydrogel. The phosphate adsorption achieved equilibrium within 400 min and the removal process followed pseudo-second-order kinetic model. The maximum adsorption capacity was reached at pH = 2.0, and the adsorption capacity gradually increased with temperature. In the presence of coexisting anions, SO42− ions exerted much more negative effect on phosphate adsorption than Cl− and NO3− ions. The phosphate adsorption mechanism was related to electrostatic interaction, ligand exchange and ion exchange. Moreover, the hydrogel exhibited relatively stable adsorption capacity after six adsorption/desorption cycles. The present study presented a facile method for preparing an excellent hydrogel adsorbent for phosphate removal from aqueous solutions.