Green crosslinking with oxidized sodium alginate for enhanced Mo(VI) adsorption in alginate-based membranes

The use of green and nontoxic crosslinking agents in material synthesis is both important and challenging. In this study, oxidized sodium alginate (OSA) was synthesized via sodium periodate oxidation and used for the preparation of sodium alginate/polyethyleneimine membranes. FTIR confirmed the presence of aldehyde groups after the oxidation of sodium alginate. In addition, the appearance of the Schiff base structure of the OSA membrane indicated that crosslinking was successful. SEM revealed the roughness and porosity of the surfaces of OSA membranes, which were favourable for the adsorption of Mo(VI). XPS indicated that adsorption was potentially related to the coordination reactions of amino groups on PEI and to electrostatic attraction. Permeation characterization revealed that the membrane had excellent mechanical strength and durability. The maximum adsorption amount calculated via the Sips equation was 452.112 mg g^-1 at 50 °C. The adsorption process followed pseudo-second-order kinetics and was spontaneous, as confirmed by thermodynamic analysis. Competing ions, simulated of industrial wastewater and cyclic desorption experiments confirmed the good practical application of this material. Overall, the OSA membrane showed good performance in removing and recovering Mo(VI) from aqueous solutions, and OSA was determined to be a green crosslinker comparable to glutaraldehyde (GA).