Synthesis and characterization of eco-friendly Ca-Al-LDH loaded with phosphate for agricultural applications

Controlled-release phosphate carriers based on hydrocalumite-like Layered Double Hydroxides (Ca-Al-LDHs) have been synthesized to serve as a P-source for Bradyrhizobium elkanii growth. [Ca-Al]-LDHs loaded with different phosphate contents were prepared by structural reconstruction (SR) and ion exchange (IE) and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), adsorption experiments, solid-state nuclear magnetic resonance (NMR) and thermal analysis (TG/DTG). [Ca-Al-PO43 −]-LDHs comprising similar crystalline phases were formed regardless the phosphate uptake route. However, phosphate loadings were found to be higher in [Ca-Al-PO43 −]-LDH obtained by IE rather than by SR. This was related to differences in specific surface area between precursors used in each route. [Ca-Al]-LDH IE-33.10 mM significantly increased the growth of Bradyrhizobium elkanii, a nitrogen-fixing symbiotic bacterium widely used in crop (mainly soybean) plantations. Once [Ca-Al-PO43 −]-LDHs are eco-friendly materials, they have enormous potential to be used in leguminous crops and raise agriculture production.