Hydrogel composites containing nanocellulose as adsorbents for aqueous removal of heavy metals: design, optimization, and application

In this study, hydrogel composites based on chitosan-g-poly(acrylic acid) matrices filled with cellulose nanowhiskers (CNWs) were prepared, and their ability to adsorb Pb(II) and Cu(II) ions from the water was investigated. A factorial design approach was performed to examine the effect of some selected parameters on the adsorption process. The optimized conditions revealed that the highest adsorption of Pb(II) (818.4 mg/g) and Cu(II) (325.5 mg/g) is obtained within 30 min, at pH 4.0, using 20 mg of the hydrogel composite containing 10 w/w-% of CNWs. As assessed, functional groups available in the hydrogel matrix and CNWs act as coordination sites for the adsorption. The Langmuir type I isotherm fitted the experimental adsorption data indicating monolayer formation drive the adsorption process. The maximum adsorption capacity of the hydrogel composite prepared in this study concerning the two selected metals was comparable or better than those reported to other similar adsorbent materials. Also, adsorption kinetics followed the pseudo-second-order model. Desorption studies indicate that the post-utilized hydrogel composite can be regenerated and reused again in new adsorption processes without a dramatic loss of efficiency. The results presented here shed light on some essential aspects related to the design and application of hydrogel composites containing nanocellulose in the adsorption process. Moreover, these findings may be helpful to obtain adsorbent materials for practical applications.