The role of nanoparticle structure and morphology in the dissolution kinetics and nutrient release of nitrate-doped calcium phosphate nanofertilizers

Francisco J Carmona,Norberto Masciocchi,Federica Bertolotti,Antonietta Guagliardi,José M Delgado-López,Gloria B Ramírez-Rodríguez,Gregorio Dal Sasso,Jan Skov Pedersen

doi:10.1038/s41598-020-69279-2

Francisco J Carmona, Norberto Masciocchi + Show 6 more

Open Access

https://doi.org/10.1038/s41598-020-69279-2

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Abstract

Bio-inspired synthetic calcium phosphate (CaP) nanoparticles (NPs), mimicking the mineral component of bone and teeth, are emergent materials for sustainable applications in agriculture. These sparingly soluble salts show self-inhibiting dissolution processes in undersaturated aqueous media, the control at the molecular and nanoscale levels of which is not fully elucidated. Understanding the mechanisms of particle dissolution is highly relevant to the efficient delivery of macronutrients to the plants and crucial for developing a valuable synthesis-by-design approach. It has also implications in bone (de)mineralization processes. Herein, we shed light on the role of size, morphology and crystallinity in the dissolution behaviour of CaP NPs and on their nitrate doping for potential use as (P,N)-nanofertilizers. Spherical fully amorphous NPs and apatite-amorphous nanoplatelets (NPLs) in a core-crown arrangement are studied by combining forefront Small-Angle and Wide-Angle X-ray Total Scattering (SAXS and WAXTS) analyses. Ca2+ ion release rates differ for spherical NPs and NPLs demonstrating that morphology plays an active role in directing the dissolution kinetics. Amorphous NPs manifest a rapid loss of nitrates governed by surface-chemistry. NPLs show much slower release, paralleling that of Ca2+ ions, that supports both detectable nitrate incorporation in the apatite structure and dissolution from the core basal faces.

Highlights

Bio-inspired synthetic calcium phosphate (CaP) nanoparticles (NPs), mimicking the mineral component of bone and teeth, are emergent materials for sustainable applications in agriculture
CaP NPs appear in the form of very thin nanoplates (NPLs) of a highly structurally defective and calcium-deficientapatite phase crystallizing in the hexagonal P63/m space group[7], likely grown from an amorphous metastable precursor[11,12]
By a joint forefront analysis of small angle X-ray scattering (SAXS) and wide angle X-ray total scattering (WAXTS) data, we provide a structural, microstructural and morphological characterization at the atomic-tonanometre detail level, and discuss the NPs dissolution, incorporation of N O3– ions in the crystal lattice and release tests in relation to the structural and morphological model

Summary

Introduction

Bio-inspired synthetic calcium phosphate (CaP) nanoparticles (NPs), mimicking the mineral component of bone and teeth, are emergent materials for sustainable applications in agriculture. Synthetic CaP NPs prepared in close to physiological conditions or mimicking bone mineral structure or function (so called “biomimetic”) are remarkably biocompatible, non-toxic and biodegradable[13,14,15] They show high chemical and thermal stability, aptitude to either cation or anion doping, high adsorption capacity for organics (drugs and proteins), and pH-responsive solubility that opens the way to a controlled release of calcium and phosphate ions[6]. Solubility of hydroxyapatite [the most thermodynamically stable CaP, possessing the Ca5(PO4)3(OH) formulation in ideal crystals of geological o rigin30] is of high relevance, with important implications in bone/teeth (de)mineralization p rocess[6,31,32,33,34,35] This is a highly complex process, controlled by many diverse factors (pH, ionic strength, Ca/P ratio, NPs size, structural defects and ionic substitutions)[28,35,36]. These findings strongly suggest that size and defects of apatite do play an active role

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