Synthesis of magnetic chitosan nanoparticle and its adsorption property for humic acid from aqueous solution

Abstract

In this study, a novel magnetic chitosan nanoparticle (MCNP) was first prepared by one-step in situ co-precipitation at low temperature and normal atmosphere to remove humic acid (HA) from aqueous solution. Modern characterization analysis showed that MCNP was quasi-spherical in shape with a size of 10nm, and the chemical crosslinking occurred mainly on the hydroxyl groups in chitosan. The increase in solution pH from 4 to 10 caused an obvious decrease in equilibrium adsorption capacity of HA from 29.3 to 7.4mg/L due to the changes of surface charge of MCNP and structural morphology of HA molecules. The adsorption process was attachment-limited under low pH conditions, and both transport-limited and attachment-limited under high pH conditions. The effect of ionic strength was complicated at different initial HA concentrations. Low ionic strength significantly improved adsorption performance and enhanced the interactions between adsorption sites and HA molecules, whereas high ionic strength might weaken adsorption ability because of the negative effects of screening enhanced and competitive adsorption. Common ions existed in neutral natural water sources would not have negative effects on HA removal. The adsorption mechanisms during adsorption process were electrostatic attraction and hydrogen bonding. Regeneration studies indicated that MCNP could be recyclable for a long term. This research extended the potential applicability of MCNP to a great extent and provided a convenient approach to efficiently remove HA from water.