Superabsorbent Polymers Cross-linked with AlCl₃: Synthesis, Characterization, and Potential for Sustainable Agriculture

Superabsorbent polymers with robust water retention capacity have significant potential for next-generation agricultural amendments to enhance crop productivity. Herein, we report the facile synthesis of superabsorbent polymer (SAP) cross-linked with aluminum chloride (AlCl₃) as an inorganic cross-linker. Fourier transform infrared (FTIR) spectroscopy confirmed coordination complexation between Al³⁺ cations and the hydroxyl functional groups of polyvinyl alcohol (PVA) and the carboxylate functional groups of potassium polyacrylate (KPA). Scanning electron microscopy (SEM) revealed a porous, interconnected interior network with pore sizes of 10–50 μm. Thermogravimetric analysis (TGA) evidenced controlled thermal degradation behavior up to 400 °C. By optimizing AlCl₃ cross-linker concentrations at 0.2 g for KPA and 0.6 g for PVA, extremely high swelling capacities up to 966% and 428% respectively were attained, demonstrating the profound impact of cross-linking density on hydrophilicity. When applied to soil growing onions at 1% w/w, the tailored SAPs increased moisture retention by 57%, regulated water release, and increased onion bulb yield by 29% compared to unamended soil. This work expands the fundamental knowledge on the synthesis and characterization of cross-linked superabsorbents with potential benefits for next-generation sustainable agriculture as well as various medical and environmental remediation applications.