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

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. ca 2+ 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 ca 2+ ions, that supports both detectable nitrate incorporation in the apatite structure and dissolution from the core basal faces. Biomineralization, the process by which living organisms generate organic/inorganic hybrids with unique properties, has long been used as an unceasing stimulus for the development of materials with new functionalities 1,2. Among them, calcium orthophosphate (CaP) nanoparticles (NPs), the most important inorganic constituents of bone and teeth, have attracted a great deal of attention 3-6. In vertebrates, CaP NPs appear in the form of very thin nanoplates (NPLs) of a highly structurally defective and calcium-deficient (hydroxy)apatite phase crystallizing in the hexagonal P6 3 /m space group 7 (or subtle deformation thereof 8-10), likely grown from an amorphous metastable precursor 11,12. 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 13-15. Additionally, 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. Owing to these remarkable properties, CaP has been used

Nanotechnology in plants: recent advances and challenges

“…12 In addition to providing a controlled release rate of nutrients, these strategies can contribute to improving the solubility and bioavailability of elements, reducing loss rate and increasing the absorption efficiency and absorption rate of nutrients in crops. [13][14][15] Controlled-release capacity of N has been reported for several urea-containing NPs, including urea-montmorillonite nanocomposites (230 nm average size particle of clay material), 16 ureacoated zeolite NPs (1-2 mm zeolite size) 17 and urea-modified hydroxyapatite NPs (150 nm average length). 18 Zeolite and hydroxyapatite-based NPs (mean sizes of 583 nm and 22 nm, respectively) have been also used to apply P with positive results in peanut (Arachis hypogaea) and wheat (Triticum aestivum).…”

Towards a more sustainable viticulture: foliar application of N‐doped calcium phosphate nanoparticles on Tempranillo grapes

“…urea), are widely used, and possess the intrinsic disadvantage of being rapidly lost in the environment by water runoff, leaching or even decomposition to volatile ‘greenhouse’ gases; on the other site of the spectrum, highly insoluble bulk hydroxyapatite, Ca 5 (PO4) 3 (OH), of geological or synthetic origin does not release significant amounts of phosphorus nutrients, and, being made of larger crystals, cannot be decorated to a reasonable extent by surface‐bound urea. These evidences prompt the identification and preparation of new materials, where chemical doping, solubility and dissolution rates can be tuned to optimise (multi)nutrient release 20,21 . For this goal, biodegradable calcium phosphate nanoparticles have been proposed as promising phosphorus 22–26 and N 7,20,27 fertilisers.…”

“…These evidences prompt the identification and preparation of new materials, where chemical doping, solubility and dissolution rates can be tuned to optimise (multi)nutrient release. 20,21 For this goal, biodegradable calcium phosphate nanoparticles have been proposed as promising phosphorus [22][23][24][25][26] 26 and N 7,20,27 fertilisers. These biodegradable nanoparticles can be also used as carriers for the controlled delivery of agrochemicals, such as humic substances 28 or urea.…”

Recent Developments in the Application of Nanomaterials in Agroecosystems

“…These types of fertilizers can also be prepared by the encapsulation of nutrients within the nanomaterials [31][32][33]. Nano-fertilizers can improve the yield and quality of crops with increased nutrient usage efficiency, while lessening the production cost and thereby resulting in a sustainable agriculture [34][35][36][37][38]. The use of pesticide is a common practice in agriculture and several studies have been carried out for the advancement of effective pesticides [39][40][41][42].…”