New absorbents, polyacrylamide/chitosan quaternary ammonium salt semi-interpenetrate network hydrogels[(PAAm/HACC semi-IPN), (s-IPN 1.5), and (s-IPN 3)], were successfully prepared via in situ polymerization by thermal synthesis for the removal of humic acid (HA) from aqueous solution. The materials were characterized by SEM, FT-IR, and XRD. The adsorption behaviors of adsorbents for HA were investigated as a function of pH, ionic strength, contact time, initial HA concentration, and temperature. The results showed that s-IPN 3 outperformed s-IPN 1.5. The adsorption capacity of the adsorbent for HA decreased with an increase in solution pH and decrease of temperature, and low ionic strength was conducive to the adsorption of HA. The adsorption kinetics fitted to a pseudo-second-order kinetic model and the adsorption isotherms could be described by the Sips isotherm model. The impressive maximum adsorption capacity could reach 238.08 mg·g-1 at the condition of pH=7.0, ionic strength=0.01 mol·L-1, and T=298 K. The adsorbent could remove HA from aqueous solution efficiently.
Keywords: adsorption; chitosan quaternary ammonium salt; humic acid; interpenetrate network hydrogel; polyacrylamide.