Hydrothermal synthesis of nanohydroxyapatite-activated carbon composites and its slow-release performance for urea

Urea is the most widely used nitrogen-based fertilizer, but its excessive application leads to nutrient loss through leaching and evaporation. This study presents a nanohydroxyapatite (nHA)-activated carbon (AC) composite synthesized via hydrothermal method as a slow-release material (SRM) for urea. The composites of nHA-AC (HC) enhances urea adsorption and release control. Structural and functional group of composites were confirmed by XRD and FTIR, while TEM revealed nHA nanorods coating the surface of AC. Furthermore, zeta potential and surface area of HC showed a better properties than pure nHA. The composite HC1 (nHA:AC = 75:25) showed the best performance, releasing only 17% of urea over 240 min and adsorbing 0.54 g_urea/g_SRM (36.2%). These results highlight the potential of HC1 as an efficient slow-release fertilizer to improve nutrient use efficiency in agriculture.