In-Situ Anchoring of Hydroxyapatite Nanorods on Waste Orange Peel-Derived Phosphorylated Carbon Spheres for Enhanced Fertilizer Stability

Nanohydroxyapatite (nHA) is a highly promising candidate for sustainable agriculture due to its excellent biocompatibility and environmental friendliness. However, their practical application has long been hindered by poor dispersibility. Herein, we develop an in situ approach that couples phosphorylated carbon sphere (PCS) formation from waste orange peels with concurrent nHA nucleation, creating nHA/PCS composites as a root exudate-triggered nanofertilizer. Density functional theory (DFT) calculations show weak binding energy at the nHA/PCS-nHA interface, thereby inhibiting nHA nanorods agglomeration. Compared to commercial nanohydroxyapatite (nCHA), nHA/PCS demonstrates superior interface stability and sustained-release properties. The nHA/PCS treatment significantly enhances lettuce seedling growth by improving root architecture and stimulating oxalic acid secretion, increasing leaf fresh weight by 60.95% compared to that with nCHA treatments. As a scaffold, the PCS matrix chemically anchors nHA nanorods for a controlled release in response to root exudates. This work presents an innovative strategy for engineering stable nanofertilizer delivery systems.