Urea–Lignin/Chitosan Nanocomposite as Slow-Release Nanofertilizer

Urea is a universal fertilizer, but its use efficiency hardly exceeds 30–35%, and more than 70% is lost to the environment, causing eutrophication in aquatic systems. This research focuses on encapsulating urea molecules using a lignin-chitosan composite. The nanocomposite was developed as a suitable carrier for entrapping nitrogenous fertilizer. Coconut coir contains plenty of lignin, which was extracted using the organosolv process by using ethanol as a solvent. Organosolv lignin (OSL) yielded spherical lignin nanoparticles (LNPs) via the solvent displacement method. Finally, a nitrogen source was loaded into the chitosan/lignin nanocomposite fertilizer (lignorea), which consists of LNPs, chitosan, and a cross-linker. The nanocomposite was characterized using PSA, SEM, TEM, UV–vis, FTIR, and XRD. The morphology of the OSL and LNPs was examined under SEM (626 ± 40 nm) and TEM (26 ± 9 nm). The noncrystallinity of both lignin and crystallinity after entrapment in nanocomposite was validated by XRD. The specific functional group pertaining to the lignin backbone had aromatic vibrations at 1511 cm–1 (OSL) and 1507 cm–1 (LNPs), and the presence of an amide peak after loading N was observed in FTIR. The lignin samples have their corresponding spectral absorbance at 281 and 288 nm wavelengths obtained in UV–vis. The size and stability of the extracted OSL and LNPs were verified by a particle size analyzer and zeta potential, respectively. The compatibility and interactions of the developed nanofertilizer were confirmed with molecular modeling and simulation. The developed nanofertilizer has total nitrogen of 30–35% which slowly releases up to 15 days in the soil. The study clearly suggests that lignin with chitosan served as a perfect template to hold and release N in a regulated pattern that collectively contributes to improved N use efficiency.