Preparation of CO2/N2-switchable hydrogel beads and adsorption, desorption, regeneration for Cu(Ⅱ)

CO2/N2-stimulated compounds have been widely used in separation field. However, their application as adsorbent for heavy metal ions removal remains a huge challenge. In this work, chitosan was incorporated into alginate matrix to form composite hydrogel beads with CO2/N2-switchable responsibility. A systematic adsorption test for Cu2+ was conducted and the prepared CTS-SA@calcium hydrogel beads presented an adsorption capacity of 125 mg·g−1. Moreover, these hydrogel beads can be desorbed effectively by bubbling CO2 and then be regenerated effectively by bubbling N2. The desorption is attributed to the amion-rich chitosan, which could be reacted with carbonic acid in water, while the regeneration is attributed to the transition of amino groups from protonated/cationic form to non-protonated/neutral form. This switched adsorption - desorption - regeneration cycle can be repeated several times. Compared with the traditional desorption using strong acids, this CO2/N2-switchable desorption - regeneration strategy holds a great potential for adsorbent regeneration and practical wastewater treatment.