Chitosan and low-cost fly ash-based alkali-activated materials have gained wide attention as adsorbents for the removal of aqueous heavy metal contaminants. Both materials are sustainable and feature unique properties along with their limitations. In this work, we investigated the synergistic effect of hybrid adsorbents prepared from both types of material. The chitosan functionalizes the alkali-activated inorganic material, whereas the inorganic component provides enhanced physicomechanical properties, leading to a cost-efficient adsorbent. Two types of alkali-activators, NaOH and Na2SiO3, were employed to generate two sets of hybrid adsorbents with varying chitosan content (0-to-2 %mass). The effect of chitosan dosage on aqueous Pb (II) and Zn (II) sorption efficiency was investigated. The addition of chitosan resulted in improved overall efficiency of the adsorbents. The hybrid adsorbents exhibited 98-100% removal efficiencies for both metals, but a higher performance is recorded for Zn compared to Pb. Compared to NaOH-activated materials, Na2SiO3-activated materials exhibited higher BET surface area, better overall sorption performance, and more noticeable improvement by chitosan addition. Mechanistic investigation reveals that the sorption processes are chemisorption controlled, and the sorption kinetic data follows a pseudo-second-order model.

Chitosan modified alkali-activated inorganic material for aqueous heavy metal sorption

ACS Spring 2022

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