Availability of Fe in soil to plants is closely related to the presence of humic substances (HS). Still, the systematic data on applicability of iron-based nanomaterials stabilized with HS as a source for plant nutrition are missing. The goal of our study was to establish a connection between properties of iron-based materials stabilized by HS and their bioavailability to plants. We have prepared two samples of leonardite HS-stabilized iron-based materials with substantially different properties using the reported protocols and studied their physical chemical state in relation to iron uptake and other biological effects. We used Mössbauer spectroscopy, XRD, SAXS, and TEM to conclude on iron speciation, size, and crystallinity. One material (Fe-HA) consisted of polynuclear iron(III) (hydr)oxide complexes, so-called ferric polymers, distributed in HS matrix. These complexes are composed of predominantly amorphous small-size components (<5 nm) with inclusions of larger crystalline particles (the mean size of (11 ± 4) nm). The other material was composed of well-crystalline feroxyhyte (δ'-FeOOH) NPs with mean transverse sizes of (35 ± 20) nm stabilized by small amounts of HS. Bioavailability studies were conducted on wheat plants under conditions of iron deficiency. The uptake studies have shown that small and amorphous ferric polymers were readily translocated into the leaves on the level of Fe-EDTA, whereas relatively large and crystalline feroxyhyte NPs were mostly sorbed on the roots. The obtained data are consistent with the size exclusion limits of cell wall pores (5-20 nm). Both samples demonstrated distinct beneficial effects with respect to photosynthetic activity and lipid biosynthesis. The obtained results might be of use for production of iron-based nanomaterials stabilized by HS with the tailored iron availability to plants. They can be applied as the only source for iron nutrition as well as in combination with the other elements, for example, for industrial production of "nanofortified" macrofertilizers (NPK).
Natural polyelectrolytes, humic substances, are suggested to control in situ growth of feroxyhyte nanoparticles of a highly reduced mean size and with enhanced colloidal stability in salt solutions. The feroxyhyte is formed as 2-5 nm thick and 20 6 20 nm wide nanoflakes due to the blocking of developing facets of feroxyhyte and constraints caused by diffusion limitations of ionic constituents across partially charged branches of humic substances.
ExperimentalHigh-purity FeCl 2 ?4H 2 O was purchased from ABCR GmbH&Co (Germany). Potassium humate was purchased from ''Sakhalinsky Humates'' (groups of companies, Russia). According to manufacturer's information, potassium humate was produced by alkaline extraction from leonardite.
An overview of key stages in nanotechnology progress and the world nanoindustry market development has been carried out. A comprehensive analysis of patents, including the growth rate of numbers of patent applications from 2001 to 2014; patent distributions between countries, institutes, and companies; and a compilation of main areas in patent protection is given. The main part of the review is devoted to trends in three primary clusters in nanoindustry: nanomaterials, nano(opto)electronics, and nanomedicine. Characteristics of the most interesting products and technologies in the main fields of interest are presented, including classification, market value, and main applications.
Superparamagnetic iron oxide γ-Fe 2 O 3 (maghemite) nanoparticles (SPION) encapsulated into water-soluble microspheres of rock salt were synthesized via a new aerosol spray pyrolysis procedure. Humic acids (HA) were employed to stabilize the aqueous suspensions of γ-Fe 2 O 3 nanoparticles released upon dissolution of the NaCl matrix. The effect of HA on the surface charge of maghemite-based colloids was studied in pH range of 3 -10. Humic polyanions compensate positive charges on a hydrated γ-Fe 2 O 3 surface resulting in strongly negative ζ-potential (< −40 mV) of colloid even in acidic environment. In neutral and alkaline environment, ζ-potential of maghemite-based colloid drops below −55 mV; thus, HA should effectively stabilize the nanoparticle colloid over the whole pH range studied. Meanwhile, bare maghemite SPION at pH 3 -6 have ζ-potential in the +20 mV to −20 mV range (isoelectric point at pH 4.35), which is insufficient for electrostatic stabilization of the suspensions. The absence of embryotoxicity of HA-stabilized nanoparticles was demonstrated.
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