Preparation of PEI/CS aerogel beads with a high density of reactive sites for efficient Cr(vi) sorption: batch and column studies

Abstract

In view of the sustainable character and high-density of reactive sorption sites, a new kind of poly(ethylenimine)/chitosan (PEI/CS) aerogel beads were successfully synthesized using controllable sol–gel and freeze drying methods, with the aim of using them for efficient Cr(VI) removal from aqueous acid solutions. Compared with the reported CS-based sorbents for hexavalent chromium [Cr(VI)], not only is the synthetic process used simple but the bead-like samples could be easily separated from solutions for recycling. Structural characterization and batch experiments were compared to illustrate the adsorption performance of the aerogel beads which were synthesized using various processes. Out of the three samples (CS–glutaraldehyde (GA), CS–GA–PEI and CS/PEI–GA beads), the one referred to as CS–GA–PEI exhibited the highest adsorption capacity and the maximum amount of Cr(VI) removal was 402.9 mg g⁻¹ at pH 2.0 and 298 K. The pseudo-second-order and Langmuir model preferably fitted the adsorption process best. After five cycles of desorption–regeneration tests, more than 80% of Cr(VI) could still be removed by these newly designed CS–GA–PEI beads. Adsorption mechanisms could be explained using electrostatic attraction and reduction reaction theories, on the basis of comprehensive analysis. More importantly, taking advantage of the micrometer sized particles and three-dimensional network that developed, fixed-bed column tests were also conducted on the resultant bead-like sample, which also exhibited excellent sorption performance under testing conditions. These superiorities of CS–GA–PEI beads make them a potential candidate for use in remediating the pollution caused by Cr(VI) ions.