Next-Generation Fertilizers: A TiO₂-Chitosan Composite Superabsorbent as a Sustained Release N-Fertilizer

This work aims to develop a sustained-release fertilizer by synthesizing a TiO₂-chitosan composite superabsorbent. For this purpose, chitosan was modified with TiO₂ nanoparticles, and terephthalaldehyde was used as a cross-linker. The reaction follows the Schiff base condensation mechanism. Confirmatory characterization of the synthesized material was done using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy-energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. Thermal gravimetric analysis-differential scanning calorimetry was performed to study the thermal behavior of the synthesized material. Rheology was performed for the mechanical studies. The superabsorbent showed excellent swelling behavior. The swelling was studied in different environments; a swelling percentage of 706.6% was observed at room temperature, categorizing the synthesized hydrogel as a superabsorbent. The urea loading at different pHs was also investigated, and a loading capacity of 90% was observed at an acidic pH. Finally, the release of fertilizer from the loaded hydrogel in different media was studied using UV-visible spectrophotometry. Various mathematical models were applied, and the results were fitted to the Korsmeyer-Peppas model. At pH 4, the highest correlation coefficient of 0.89 and an n-value of 0.27 were obtained, showing that the release corresponds to Fickian diffusion. Further, to compare the urea-loaded hydrogel with pure urea, a real-time experiment on the germination of Brassica oleracea var. viridis (Kashmiri saag) seeds was performed and a germination index of 274.69% was observed in the case of urea-loaded hydrogel. According to the results, the synthesized superabsorbent showed excellent controlled release in acidic medium and could be employed in soil for agricultural purposes.