Alkaline resistant tunable superaerophobic bio-based chitosan/dialdehyde starch hydrogels

Abstract

Development of bio-based materials with advanced properties is required to replace synthetic and per-and polyfluoroalkyl-based ingredients, particularly for applications involving solid-liquid-gas interfaces. To enable alkaline-resistant materials with tunable aerophobicity, bio-based chitosan/dialdehyde starch hydrogels were prepared through covalent Schiff base crosslinking. Chitosan molecular weight (250-1800 kDa) and concentration (1.5-4.0% w/v) were varied at fixed crosslinker content (1.0% w/v) to investigate the effect on network formation, viscoelasticity and functionality. Rheological analysis shows that systems with low chitosan content require long gelation times (>30 min) to form viscous materials with storage moduli of 1 Pa and internal porous structure (10-100 mu m). In contrast, highly concentrated chitosan gels formed rapidly (<4 min) reaching up to 150 Pa, indicating improved structural strength. Swelling experiments on freeze-dried hydrogels at pH 6.8, 10, and 12 showed water absorption with swelling ratios ranging from 5000 to 1300%, depending on composition. Most systems maintained structural stability over the 7-day swelling test, undergoing limited degradation in alkaline conditions (pH 12). Aerophobicity was evaluated by measuring contact angles of bubbles on submersed (in water or pH 12) hydrogels, which range from 130 to 170 degrees, increasing with both chitosan concentration and molecular weight. The material features were demonstrated for electrode development, improving performance at higher overpotentials (-0.67 V) and increasing alkaline water-splitting efficiency by 15%. The prepared materials thus provide alkaline resistance and tunable properties offering potential for various applications, including gas-evolving electrode coatings, alkaline electrolyzer membranes, anti-corrosion coatings, pollutant absorption, environmental remediation, and sensing technologies.