Dual-network design to enhance the properties of agar aerogel adsorbent by incorporating in situ ion cross-linked alginate

Natural and synthetic adsorbents are used to remove contaminants from polluted waters. In particular, polymer-based aerogels are promising but their adsorption capacity and dimensional stability should be improved. Here we propose a new design strategy to prepare a dual-network aerogel, consisting of physical cross-linked agar and Ca2+ cross-linked sodium alginate as the first and second networks, respectively. After introducing cross-linked sodium alginate into the agar matrix, the morphology of the agar aerogel transformed from a distinct layered structure to a co-continuous network. The swelling degree ratio of the agar aerogel is reduced, and the dimensional stability was improved by introducing ion cross-linked sodium alginate into the agar matrix. The aerogels were used as adsorbents to remove methylene blue from aqueous solutions. The adsorption capacity of the agar aerogel was remarkably improved by adding sodium alginate due to the increase in electrostatic attraction and adsorption site.