New Sustainable, Scalable and One-Step Synthesis of Iron Oxide Nanoparticles by Ion Exchange Process

This work introduces an innovative, sustainable, and scalable synthesis of iron oxides nanoparticles (NPs) in aqueous suspension. The method, based on ion exchange process, consists of a one-step procedure, time and energy saving, operating in water and at room temperature, by cheap and renewable reagents. The influence of both oxidation state of the initial reagent and reaction atmosphere is considered. Three kinds of iron nanostructured compounds are obtained (2-lines ferrihydrite; layered-structure iron oxyhydroxide δ-FeOOH; and cubic magnetite), in turn used as precursors to obtain hematite and maghemite NPs. All the produced NPs are characterized by a high purity, small particles dimensions (from 2 to 50 nm), and high specific surface area values up to 420 m²/g, with yields of production >90%. In particular, among the most common iron oxide NPs, we obtained cubic magnetite NPs at room temperature, characterized by particle dimensions of about 6 nm and a surface area of 170 m²/g. We also obtained hematite NPs at very low temperature conditions (that is 2 h at 200 °C), characterized by particles dimensions of about 5 nm with a surface area value of 200 m²/g. The obtained results underline the strength of the synthetic method to provide a new, sustainable, tunable, and scalable high-quality production.

Characterization of an active ingredient made of nanoscale iron(oxyhydr)oxide for the treatment of hyperphosphatemia

Kidney disease is one of the main non-communicable diseases. Every year millions of people worldwide die from kidney dysfunction. One cause is disturbances in the mineral metabolism, such as abnormally high phosphate concentrations in the blood, medically referred to as hyperphosphatemia. A new active ingredient based on nanoscale iron(oxyhydr)oxide with particle sizes below 3 nm surrounded by an organic coating has been developed for a more effective treatment. The examination of the structural properties of these particles within this study promises to gain further insights into this improved effectiveness. More than half of the active ingredient consists of organic substances, the rest is mostly iron(oxyhydr)oxide. Analyzes by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) show that the organic molecules act as stabilizers and lead to ultrasmall iron(oxyhydr)oxide cores with a size of 1.0–2.8 nm. The nanoparticles coated with the organic molecules have an average size of 11.7 nm. At 4.2 K, the nanoparticles display a magnetic hyperfine field of 45.5 T in the Mössbauer spectrum, which is unusually low for iron(oxyhydr)oxide. The material is also not ferrimagnetic. Combining these results and taking into account the composition of the nanoparticles, we identify low crystalline ferrihydrite as the most likely phase in the iron(oxyhydr)oxide nuclei. At the same time, we want to emphasize that a final identification of the crystal structure in iron(oxyhydr)oxides can be impeded by ultrasmall particle sizes. In summary, by a combinatorial characterization, we are able to observe extraordinary properties of the ultrasmall nanomaterial, which is the basis for the investigation of the high phosphate-binding efficacy of this active ingredient.

The combination of different analytical methods, supported by TEM, DLS, SAXS, Mössbauer spectroscopy, and SQUID, allows more accurate characterization of a new nanoscale active ingredient based on iron(oxyhydr)oxide against hyperphosphatemia.

Microwave-Assisted Synthesis of Water-Dispersible Humate-Coated Magnetite Nanoparticles: Relation of Coating Process Parameters to the Properties of Nanoparticles

Nowadays, there is a demand in the production of nontoxic multifunctional magnetic materials possessing both high colloidal stability in water solutions and high magnetization. In this work, a series of water-dispersible natural humate-polyanion coated superparamagnetic magnetite nanoparticles has been synthesized via microwave-assisted synthesis without the use of inert atmosphere. An impact of a biocompatible humate-anion as a coating agent on the structural and physical properties of nanoparticles has been established. The injection of humate-polyanion at various synthesis stages leads to differences in the physical properties of the obtained nanomaterials. Depending on the synthesis protocol, nanoparticles are characterized by improved monodispersity, smaller crystallite and grain size (up to 8.2 nm), a shift in the point of zero charge (6.4 pH), enhanced colloidal stability in model solutions, and enhanced magnetization (80 emu g⁻¹).

From green chemistry and nature-like technologies towards ecoadaptive chemistry and technology

Nature-like technologies can be considered as a logical development of green chemistry principles implemented to design novel materials and processes aimed at mimicking and reproducing natural life-sustaining mechanisms on molecular level. Humic substances which penetrate throughout the entire environment and represent from 50 to 90% of organic matter in soil and water ecosystems, play multiple life-sustaining functions on Earth. To name a few, HS regulate transport and availability of biogenic elements to plants, immobilize and mitigate toxicity of hazardous elements in the contaminated ecosystems, protect plants from non-specific abiotic stresses, play key role for fertility of soils determining water-retention and structure. Here we represent a novel platform for nature-inspired synthesis of soft and hybrid (nano)materials aimed at their use for soil and water clean up, carbon sequestration, soil fertility restoration. It is based on a smart use of natural hyperbranched polyelectrolytes – humic substances, which possess multiple functional groups including carboxyl, hydroxyl, amide, and others. Multiple functional groups of HS make them amenable both for classical chemical modification as well as for producing interpolyelectrolyte complexes. In this work, we present both approaches for manufacturing silicon-containing humic derivatives and supramolecular complexes with acquired new property – self-adhesion to both inorganic and bio-surfaces. The synthesis is conducted using humic materials from different sources and functional organosilanes. Self-assembly of the supramolecular silicon-humic systems occurs with formation of humic-silsesquioxane networks capable to adhere to mineral surfaces. This process is similar to immobilization of organic coatings to mineral surfaces. We have shown how this process can be realized in the ground waters for the purposes of the environmental clean up. We have also proposed to use the silicon-humic complexes for improving humus content of soils and for reconstructing soil restoration processes both in the lab and in the field. Another field of our research is synthesis of iron-containing humics-stabilized nanoparticles (NPs), which can be used as a source for plants nutrition instead of synthetic iron chelates. The idea is based on the natural phenomenon that in soils, water-stable sols of iron-containing NPs are formed due to complexing with HS, which can bind large amounts of poorly ordered iron (hydr)oxides providing for stabilization of colloidal iron in the form of NPs. It has been numerously shown that the presence of HS improves iron acquisition by plants in soils, but there was no systematic study so far with respect to a relationship between size and crystallinity of humics-stabilized iron-containing NPs and their availability to plants. We have conducted such a study and could establish conditions when humics-stabilized NPs could be taken up by plants with similar efficiency as FeEDTA. The presented data demonstrate good prospects for a use of green humics-based materials in nature-like technologies. We also hope that these studies will give rise to new branch of chemistry and technology which can be called ecoadaptive chemistry and technology.

Key Roles of Size and Crystallinity of Nanosized Iron Hydr(oxides) Stabilized by Humic Substances in Iron Bioavailability to Plants

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).

Hierarchical Formation Mechanism of CoFe2O4 Mesoporous Assemblies

The development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by β-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of Fe(III) ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the β-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule.

Gas Slug Microfluidics: A Unique Tool for Ultrafast, Highly Controlled Growth of Iron Oxide Nanostructures

The use of nanomaterials in real life applications is often hampered by our inability to produce them in large quantities while preserving their desired properties in terms of size, shape, and crystalline phase. Here we present a novel continuous method to synthesize nanostructures with an unprecedented degree of control regarding their properties. In particular, the excellent properties of microreactors for chemical synthesis are enhanced by the introduction of gas slugs of tailored composition. Slug dynamics accelerate mixing, reduce processing times (from hours in batch processes to minutes or even seconds), and, depending on the gas atmosphere used, allows one to accurately control the crystalline phase and shape of the resulting nanostructures. Inert (N2), oxidizing (O2), or reducing (CO, H2) gases were used, leading to different morphologies and crystalline structures in a high yield, highly reproducible fabrication process.