Hollow polyethyleneimine/carboxymethyl cellulose beads with abundant and accessible sorption sites for ultra-efficient chromium (VI) and phosphate removal

Novel millimeter-scale hollow polyethyleneimine/carboxymethylcellulose beads were facilely prepared by simply adjusting the usage of polyethyleneimine for surface modification of preformed solid carboxymethylcellulose beads, which were gradually transformed into hollow beads during the glutaraldehyde mediated cross-linking process. Taking advantage of the hollow structure and porous shells which possess abundant, accessible sorption sites, this newly designed bead-like sorbent exhibited very high adsorption capacity for Cr(VI) and phosphates, for which the exceptional value of 535.39 mg/g and 150.65 mg/g was achieved under fitting conditions, respectively, and both of them much superior to most reported studies. Most importantly, the adsorption capacity for Cr(VI) and phosphate over the typical sorbent remained at high levels even after 6 and 22 cycles, respectively, which is another feature of the hollow bead-like sorbent. Based on various characterization results like SEM-EDX, FT-IR, TGA, zeta potential, XPS, etc., it showed that the adsorption mechanism of Cr(VI) over as-fabricated hollow bead-like sorbents could be mainly correlated to the electrostatic attraction and reduction manner, while the adsorption process of phosphate was mainly due to the electrostatic interaction. By its millimeter-sized shape with surface accessible sorption sites, the column adsorption testing revealed that the Thomas model fitted well with the phosphate adsorption process. Given its controllable fabrication process, excellent adsorption performance, and exceptional mechanical properties, this newly designed millimeter-scale hollow bead-like sorbent has promising applications in the field of anionic pollutant removal.