Novel crosslinked chitosan for enhanced adsorption of hexavalent chromium in acidic solution

To increase acid resistance, a water soluble diepoxy compound [1,2: 7,8-diepoxyoctane (DEO)] as a new crosslinker was successfully used to crosslink chitosan beads (CS). The effects of crosslinking conditions (temperature, time, pH, and DEO concentrations) on weight loss and hexavalent chromium [Cr(VI)] adsorption performance of cross-linked chitosan beads (CS-DEO) in acidic solution were investigated. The prepared crosslinked chitosan beads were characterized by BET, SEM, TGA, XRD, and FT-IR analysis. Based on SEM images, morphological surface changes were observed after DEO treatment. TGA analysis results showed that thermal decomposition temperature of chitosan improved upon the crosslinking treatment. The XRD patters demonstrated that crosslinking reaction resulted in a slight reduction in the absorbent crystallinity. Furthermore, the prepared CS-DEO beads were stable in acidic solution and could efficiently adsorb Cr(VI). The CS-DEO beads cross-linked in 6 g/L of DEO solution at pH 10 and 50 degrees C for 5 h showed no weight loss but had high Cr(VI) adsorption capacity of 325.2 mg/g at pH 2.0, much higher than other reported chitosan-based adsorbents. The kinetic study of CS-DEO followed the pseudo-second-order kinetics. The adsorption isotherm of Cr(VI) on the CS-DEO beads could be fitted well by the Freundlich equation. Moreover, the prepared CS-DEO beads could be easily regenerated at least five times using 1 mol/L NaOH solutions without significant reduction in the Cr(VI) removal performance. DEO is a proper and favorable crosslinker for chitosan-based adsorbents. The prepared CS-DEO beads can be considered as a suitable and efficient adsorbent for Cr(VI) ions in aqueous solutions.