Amine-functionalized cellulose nanofiber-sodium alginate-Fe(III) porous hollow beads for the efficient removal of Cr(VI)

To date, highly toxic heavy metal ions from wastewater seriously deteriorate the aquatic environment safety. This study proposes an adsorbent that can be adopted to remove heavy metal ions by combining environmentally friendly cellulose nanofibers (CNFs), sodium alginate (SA), and amino-rich polyethyleneimine using a ferric chloride- and glutaraldehyde-mediated crosslinking process and yielding a porous hollow bead (CS-Fe@PEI). The bead has a hollow porous structure according to SEM and a high nitrogen content of 13.85 wt% with numerous active adsorption sites, which are beneficial to the adsorption of heavy metal ions. Chromium was chosen as the main model pollutant for batch adsorption experiments. CS-Fe@PEI has excellent adsorption capacity of 526.32 mg/g for Cr(VI) at 298 K, which conforms with the Langmuir isotherm and pseudo-second-order model. The stable hollow structure allowed the regeneration of the CS-Fe@PEI beads for more than six cycles after Cr(VI) adsorption. According to FT-IR, Zeta, and XPS analyses, the beads effectively adsorbed the pollutants by electrostatic interaction, reducing the hypertoxic Cr(VI) to Cr(III). Furthermore, the beads also possessed a superior adsorption capacity for heavy metal cations (Cu(II), Cd(II), Ni(II), and Pb(II)). These results demonstrated that the fabricated CS-Fe@PEI beads were an efficient and reusable adsorbent, with a high potential for removing heavy metal ions from industrial wastewater.