Preparation of aminated cross-linked chitosan beads for efficient adsorption of hexavalent chromium.

Novel chitosan-based adsorbent (CS-DEO-SP) was successfully prepared by cross-linking and amination using diepoxyoctane (DEO) and spermine (SP) sequentially for the enhanced adsorption of Cr(VI) from aqueous solutions. The optimal CS-DEO-SP beads were prepared with 1.5 mg/L of SP for 5 h at 50 °C. The prepared beads exhibited heterogeneous and porous surfaces. The increased surface area (79.6%), pore volume (86.0%), and pore size (31.2%) of the modified adsorbent evidenced the successful modification of chitosan beads. The adsorption kinetics of Cr(VI) ions onto the prepared CS-DEO-SP beads was well fitted by the pseudo-second-order model (R > 0.97), and the adsorption isotherms adapted well with the Freundlich model (R > 0.96). The experimental data revealed that the adsorption of Cr(VI) ions on the CS-DEO-SP beads was extremely dependent on solution pH, and the maximum adsorption capacity of 358.1 mg/g was achieved at acidic condition (pH 2.0). After the regeneration of spent CS-DEO-SP beads using 1.0 mol/L NaOH, the adsorption capacity of reused adsorbent gradually declined within five consecutive adsorption cycles. Overall, the prepared CS-DEO-SP beads showed excellent stability in acidic solution and Cr(V) adsorption performance and thus can be used as an efficient adsorbent for eliminating Cr(VI) ions from acidic metal-plating wastewater.