Sustainable xanthan-based superabsorbent hydrogel with enhanced durability for repeated nitrate remediation in drinking water

This study focuses on synthesizing and characterizing a superabsorbent hydrogel based on xanthan cross-linked with glycerin. The synthesis tests revealed that the swelling percentage of the hydrogel is greatly influenced by the mass ratios of glycerin-to-xanthan and water-to-xanthan, as well as the curing temperature. The resulting hydrogels exhibited swelling ratios ranging from 52 to 229% after 120 min of immersion in water. Nitrogen adsorption-desorption analysis indicated a specific surface area of 63.78 m²/g, a total pore volume of 0.42 cm³/g, and an average mesopore diameter of 26.2 nm for the dried hydrogel. Scanning electron microscopy revealed macropores ranging from 50 to 400 μm on the as-synthesized hydrogel's outer surface. Thermal durability tests showed a mass loss of 0.5% to 1% when the optimal hydrogel was exposed to temperatures between 40 and 160 °C for 1 h, highlighting its high thermal stability. In the nitrate removal tests, the optimal absorbent demonstrated a nitrate removal percentage exceeding 92.4% after 70 min for initial nitrate concentrations of 100, 150, and 200 mg/L, using an absorbent dose of 1 g/L at pH 5. Reusability assessments indicated that the absorbent could maintain approximately 85% of its initial performance after 10 regeneration cycles. The Langmuir isotherm model provided a better fit for the equilibrium nitrate absorption data, with a maximum absorption capacity of 370.37 mg/g. Overall, this study highlights the potential of xanthan-based superabsorbent hydrogel as an eco-friendly and reusable absorbent for nitrate removal from drinking water.