Alginate versus Chitosan for Templating Growth and Shaping HKUST-1 as Porous CO2-Adsorbent Beads

Abstract

This study aims at elucidating the role of the polysaccharide skeleton (alginate versus chitosan) during the growth and shaping of HKUST-1 as porous beads. Although the two biopolymers afford an open porous hydrogel network, the freeze-drying step was crucial with water medium being inappropriate to preserve the crystalline framework of HKUST-1. Alternatively, drying in ethanol circumvented this drawback by keeping intact the structure of HKUST-1. However, a contrasting behavior was observed in the resulting polysaccharide@HKUST-1 beads, as HKUST-1 grown in alginate underwent a dramatic collapse, whereas self-standing, open porous microspheres could be obtained using the chitosan templating route. The resulting chitosan@HKUST-1 cryogel displays an enhanced CO₂ capture (2.67 mmol.g⁻¹) compared to its analogs shaped by alginate, making consequently chitosan a better option for structuring MOF-based adsorbents.