Hybridizing Mg–Fe Layered Double Hydroxide with Pectin Natural Polymer for Organic Ligand-Responsive Phosphate Release: An Innovative Controlled-Release Phosphorus Fertilizer

Phosphorus (P) is vital for plant growth, but its agricultural use is limited by soil fixation and environmental loss. This study developed an organic ligand-responsive phosphate release system by hybridizing magnesium–iron-layered double hydroxides (Mg–Fe LDH) with pectin from apple and citrus (pectin-A/C). Structural properties and phosphate (PO4) release of LDH hybrids with different concentrations of metal precursors (0.5LDH-A/C, 2.5LDH-A/C) were evaluated. All hybrids exhibited higher PO4 sorption than pristine Mg–Fe LDH, with 2.5LDH-A reaching 118.2 mg g–1. Phosphate release kinetics showed that 0.5LDH-A/C provided slow release up to 1056 h, while 2.5LDH-A/C released 87.7% PO4 with 4 mM citrate, responding to organic ligands. Synchrotron spectroscopy revealed that Fe substitution in LDH layers and Fe(III)-P species was the key influencing PO4 release. The slow-release behavior of 0.5LDH-A/C and the ligand responsiveness of 2.5LDH-A/C highlight their potential to enhance sustainable agriculture by improving fertilizer efficiency, ensuring food security, and minimizing environmental impact.