Alginate-reinforced poly(3-hydroxybutyrate)/ poly(hydroxybutyrate-co-hydroxyvalerate) aerogel monoliths fabricated by phase separation as environmental floating adsorbents

Abstract

Poly(3-hydroxybutyrate) (PHB)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) aerogel monoliths were prepared via nonsolvent induced phase separation and then sequentially immersed in ethanol and sodium alginate (ALG) solutions. The resulting composite aerogels contained up to a 52 wt% fraction ALG, causing a remarkable increase in their compressive modulus and collapse strength from 0.3 MPa and 33 kPa to 4 MPa and 406 kPa, respectively, i.e., by 13/12 times. An increase in the ALG contents in the composite aerogels allowed them to effectively adsorb both water and soybean oil, according to pseudo-second-order adsorption kinetics. The highly porous composite aerogel acted as an efficient floating adsorbent for a cationic dye (i.e., methylene blue (MB)) in water. MB adsorption was found to be strongly dependent on ALG contents in the adsorbent, as well as operating parameters such as the initial concentration, pH, and temperature of MB solutions. MB adsorption is best described by the Langmuir isotherm and follows pseudo-second-order kinetics. Ca²⁺-crosslinking of ALG further increased compressive strength but significantly decreased MB adsorption capability following pseudo-first-order kinetics, implying a slow internal diffusion step for MB adsorption due to its tightened network structure relative to noncrosslinked adsorbents.

Keywords: Adsorbent; Aerogel; Alginate; Phase separation; Poly(3-hydroxybutyrate); Poly(hydroxybutyrate-co-hydroxyvalerate).