Hexavalent chromium adsorption onto crosslinked chitosan and chitosan/β-cyclodextrin beads: Novel materials for water decontamination

Abstract

The primary aim of the present research was the development and testing of novel synthesized crosslinked beads consisting of plain chitosan and/or with β-cyclodextrin as hexavalent chromium adsorption agents. Their effectiveness was evaluated in batch experiments, whereby the effects of pH, initial hexavalent chromium concentration, initial adsorbent concentration, and temperature were investigated. Between the two beads, chitosan/β-cyclodextrin provided higher hexavalent chromium removal efficiency than the chitosan beads. Further, it achieved higher amount of adsorbed hexavalent chromium in the majority of the experiments. The adsorption was exothermic and more spontaneous at low temperature (15 °C). The optimum hexavalent chromium removal conditions were identified at pH = 4, initial concentration of adsorbent 20 g/L, and temperature of 15 °C; at high initial concentrations of hexavalent chromium (75 and 100 mg/L) a decrease in the removal efficiency was observed. The maximum reported adsorption capacity was 400.00 and 555.56 mgCr(VI)/gadsorbent for plain chitosan and chitosan with β-cyclodextrin beads produced by crosslinking, respectively. Moreover, the adsorption of hexavalent chromium onto both beads was revealed to follow the kinetic model of pseudo-second. Both the adsorption and the characterization of the beads were evaluated prior and after the adsorption process by FTIR and SEM analyses. Finally, the synthesized beads provided satisfactory regeneration results after four adsorption/desorption cycles. Therefore, they constitute a promising novel class of adsorbents for the efficient decontamination of aqueous streams with concentrations of hexavalent chromium that exceed legislation limits.