Porous alginate aerogel beads for effective and rapid heavy metal sorption from aqueous solutions: Effect of porosity in Cu2+ and Cd2+ ion sorption

Calcium alginate porous aerogel beads were prepared by sc-CO2 drying, characterized and for the first time evaluated for their performance on metal ion sorption in comparison with their non-porous xerogel analogues. The aerogels were mainly mesoporous, also containing micropores and macropores with BET surface area of 419 m2 g−1. The material exhibited enhanced sorption capacity with 20% higher degree of active site saturation after sorption compared to the xerogel beads and sorption values reaching 126.82 mg g−1 for Cu2+ and 244.55 mg g−1 for Cd2+. The sorption kinetics exhibited a significant decrease in sorption time, with 99% removal achieved 600–800 min earlier than for xerogel beads. This behaviour indicates increased functional groups accessibility combined with increased flexibility due to the effect of porosity, facilitating chain rearrangement during ion exchange. A multistage mechanism for heavy metal sorption kinetics was suggested by the results of both Weber–Morris and film diffusion models.

► Ca-alginate porous aerogel beads evaluated for the first time on metal sorption.
► Significantly enhanced sorption properties over non-porous xerogel beads.
► More efficient, 20% higher degree of active site saturation after sorption.
► Faster sorption, 99% removal achieved 600–800 min earlier.
► Multistage mechanism proposed for heavy metal sorption kinetics.