Synthesis of superabsorbent hydrogel based on crosslink agent silica nanoparticles vinyl from rice husk

Abstract Indonesia, one of the world’s largest rice producers, faces significant environmental challenges due to the disposal of rice husk waste, which is often burned and contributes to air pollution. Rice husk ash contains a high silica content (86.90–97.30%), which can be utilized to synthesize silica nanoparticles (nanosilica) and further employed as crosslinking agents in the production of superabsorbent hydrogels. In this study, superabsorbent hydrogels were synthesized via an addition polymerization process using vinyl silica nanospheres (VSNp) as the crosslinking agent, acrylic acid as the monomer, and ammonium persulfate (APS) as the initiator. The prepared hydrogels were characterized in terms of absorption capacity, swelling ratio in 0.9% NaCl and 5% urea solutions, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to examine their surface morphology. The results demonstrated the highest absorption capacity of 115,822% in sample C2 (0.1 g of initiator and 0.1 g of crosslink agent), with maximum swelling ratios of 10,502% in NaCl and 93,766% in urea solutions. FTIR analysis confirmed the presence of siloxane groups and the disappearance of C = C bonds, indicating successful hydrogel formation. SEM images revealed a complex three-dimensional fibrous and network structure, while XRD results showed enhanced crystallinity with the incorporation of VSNp, marked by a diffraction peak at 2θ = 20.8° with an intensity of 973 cps.