Carboxyl-Functionalized Lotus Cellulose Fiber-Based Superabsorbent Hydrogel for Efficient Water and Fertilizer Management

To address challenges associated with the water–food nexus under climate change and population growth, a multifunctional cellulose-based superabsorbent hydrogel (L-CF/CMCAA-1ATP) was developed by incorporating carboxyl-functionalized lotus cellulose fibers (L-CF) derived from waste lotus stems via deep eutectic solvent extraction and spray drying into a carboxymethyl cellulose/acrylic acid/attapulgite hydrogel network. Under optimized conditions, the L-CF/CMCAA-1ATP hydrogel exhibited an equilibrium swelling capacity of 1979 g/g in deionized water and retained 74.37% of absorbed water after 250 min at 75 °C. Soil application significantly improved water-holding capacity (40.11% to 56.55%) and maintained 34.41% water retention after 21 days. Additionally, cumulative nitrogen, phosphorus, and potassium losses were reduced by 28.84%, 28.56%, and 42.23%, respectively, after five leaching cycles, with DFT calculations indicating that nutrient retention arises from hydrogen-bonding interactions with carboxyl, hydroxyl, and siloxane groups in the hydrogel network. Agricultural assays demonstrated enhanced maize growth, with chlorophyll content increasing by 21.56% compared with the control. Cell viability remained above 95% at all tested concentrations, confirming low cytotoxicity. These results demonstrate that the L-CF/CMCAA-1ATP superabsorbent hydrogel combines excellent water absorbency, water retention, nutrient conservation, plant growth promotion, and low in vitro cytotoxicity, highlighting its potential as a waste-valorization approach for utilizing agricultural residues and improving water and nutrient management in agriculture.