Iron oxide nanoparticles for plant nutrition? A preliminary Mössbauer study

One of the most important micronutrients for plants is iron. We have prepared iron(III) oxyhydroxide and magnetite nanoparticles with the aim to use them as possible nutrition source for plants. The iron(III)-oxide/oxyhydroxide nanoparticles prepared under our experimental conditions as colloidal suspensions proved to be 6-line ferrihydritenanoparticles as verified by XRD,TEM/SAED and Mössbauer spectroscopy measurements. 57Fe Mössbauer spectra of magnetite nanoparticles prepared under different preparation conditions could be analyzed on the basis of a common model based on the superposition of four sextet components displaying Gaussian-shaped hyperfine magnetic field distributions

Iron uptake from manufactured nanomaterials: obscured mechanism, controversial effect

Transition metals in nanomaterials such as iron, manganese or zinc are essential microelements for plants. When these metals are present in suboptimal concentration for the plants, deficiency syndromes develop that causes reduced crop production or poor fruit quality. Low mineral content of plant products has a major role in human malnutrition. Most stable Fe-chelates for the correction of Fe deficiency are not biodegradable and expensive so applying manufactured nanomaterials may serve as a cheap and eco-friendly alternative. Newly designed, transition metal containing nanomaterials stabilized in colloid suspension have been characterised and then applied in hydroponic cultures to cucumber model plants in a wide range of concentration. The uptake and distribution of the elements from the nanomaterials and their utilization were investigated by microXRF mapping, ICP-MS, enzyme activity tests, gene expression measurements and the changes in some basic physiological parameters were followed. Nanoferrihydrite and nano-Mn-Zn-ferrite colloid suspensions with 3-8 nm particle size applied in 0.01-0.02 mM concentration and at slightly acidic pH proved to be a good source of Fe, Mn and Zn in various experimental conditions. Mn-Zn-ferrite has also been tested at pH 7.5 and Fe deficient cucumber plants showed a significant recovery after 3 days of application in terms of chlorophyll concentration and photosynthetic efficiency but not at pH 8.5. Mn and Zn deficient plants also showed recovery upon addition of the ferrite. Ferric chelate reductase assays showed that it is not the normal reduction-based uptake pathway that plays a role in the iron utilization of these nanoparticles. Analysis of root ferric chelate reductase expression pointed out a quick utilisation of Fe content of the nanoferrihydrite particles. Elevated concentrations of the nanoferrite at the millimolar range as compared to equal concentrations of micronutrient salts proved to be significantly less toxic. However, another nanomaterial, an insoluble nano FeCo powder applied to the nutrient solution of cucumber in high concentration causes severe chlorosis due to cobalt toxicity, pointing on that the composition of the nanoparticles is highly important for their bioactivity. Keywords: nanomaterial, ferrite, ferrihydrite, fertilizer, ferric chelate reductase, toxicity This work was supported by the National Research, Development and Innovation Office, Hungary (NKFIH) K115784, 115913, 124159 and VEKOP-2.3.3-15-2016-00008. Á. Solti was also supported by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences (BO/00207/15/4)

Cation distribution and related properties of MnxZn1−xFe2O4Mn_{x}Zn_{1−x}Fe_{2}O_{4} spinel nanoparticles

MnxZn1xFe2O4 (x = 0.05...0.9) nanoparticles prepared via solegel hydrothermal process were investigatedby X-ray powder diffractometry (XRPD), transmission electron microscopy (TEM), 57Fe Mössbauerspectroscopy (MS), electron paramagnetic resonance spectroscopy (EPR), X-ray absorption near edgestructure spectroscopy (XANES) and magnetic hysteresis measurements. XRPD measurements revealed anon-monotonic dependence of the cubic lattice parameter on the Mn concentration, which is interpretedas being the result of a corresponding variation in the inversion degree (concentration of Fe ions on theoccupied tetrahedral lattice sites) of the studied spinels. XANES measurements indicated that the averageoxidation state of Mn ions decreases with the applied Mn concentration, in contrast with Fe ions thatwere found to be exclusively in the 3+ oxidation state by MS measurements. EPR spectra recorded as afunction of temperature enabled the determination of the characteristic anisotropy energy barrier of thesuperparamagnetic particles, and contributed to the clarification of peculiarities of the corresponding57Fe Mössbauer spectra. On the basis of the observed results the interdependences among the samplestoichiometry, the cubic cell parameter, the particle size, the inversion degree, the magnetic orderingtemperature and the effective magnetic anisotropy are discussed