Structure evolution of nanoparticulate Fe2O3

Unveiling the role of inorganic nanoparticles in Earth's biochemical evolution through electron transfer dynamics

This article explores the intricate interplay between inorganic nanoparticles and Earth's biochemical history, with a focus on their electron transfer properties. It reveals how iron oxide and sulfide nanoparticles, as examples of inorganic nanoparticles, exhibit oxidoreductase activity similar to proteins. Termed "life fossil oxidoreductases," these inorganic enzymes influence redox reactions, detoxification processes, and nutrient cycling in early Earth environments. By emphasizing the structural configuration of nanoparticles and their electron conformation, including oxygen defects and metal vacancies, especially electron hopping, the article provides a foundation for understanding inorganic enzyme mechanisms. This approach, rooted in physics, underscores that life's origin and evolution are governed by electron transfer principles within the framework of chemical equilibrium. Today, these nanoparticles serve as vital biocatalysts in natural ecosystems, participating in critical reactions for ecosystem health. The research highlights their enduring impact on Earth's history, shaping ecosystems and interacting with protein metal centers through shared electron transfer dynamics, offering insights into early life processes and adaptations.

Inorganic Fe-O and Fe-S oxidoreductases: paradigms for prebiotic chemistry and the evolution of enzymatic activity in biology

Oxidoreductases play crucial roles in electron transfer during biological redox reactions. These reactions are not exclusive to protein-based biocatalysts; nano-size (<100 nm), fine-grained inorganic colloids, such as iron oxides and sulfides, also participate. These nanocolloids exhibit intrinsic redox activity and possess direct electron transfer capacities comparable to their biological counterparts. The unique metal ion architecture of these nanocolloids, including electron configurations, coordination environment, electron conductivity, and the ability to promote spontaneous electron hopping, contributes to their transfer capabilities. Nano-size inorganic colloids are believed to be among the earliest 'oxidoreductases' to have 'evolved' on early Earth, playing critical roles in biological systems. Representing a distinct type of biocatalysts alongside metalloproteins, these nanoparticles offer an early alternative to protein-based oxidoreductase activity. While the roles of inorganic nano-sized catalysts in current Earth ecosystems are intuitively significant, they remain poorly understood and underestimated. Their contribution to chemical reactions and biogeochemical cycles likely helped shape and maintain the balance of our planet's ecosystems. However, their potential applications in biomedical, agricultural, and environmental protection sectors have not been fully explored or exploited. This review examines the structure, properties, and mechanisms of such catalysts from a material's evolutionary standpoint, aiming to raise awareness of their potential to provide innovative solutions to some of Earth's sustainability challenges.

A stable and strongly ferromagnetic Fe17O10- cluster with an accordion-like structure

Isolated clusters are ideal systems for tailoring molecule-based magnets and investigating the evolution of magnetic order from microscopic to macroscopic regime. We have prepared pure Fe_n^- (n = 7-31) clusters and observed their gas-collisional reactions with oxygen in a flow tube reactor. Interestingly, only the larger Fe_n^- (n ≥ 15) clusters support the observation of O₂-intake, while the smaller clusters Fe_n^- (n = 7-14) are nearly nonreactive. What is more interesting is that Fe₁₇O₁₀^- shows up with prominent abundance in the mass spectra indicative of its distinct inertness. In combination with DFT calculations, we unveil the stability of Fe₁₇O₁₀^- within an interesting acordion-like structure and elucidate the spin accommodation in such a strongly ferromagnetic iron cluster oxide.

A versatile chemical vapor synthesis reactor for in situ x-ray scattering and spectroscopy

We describe a versatile reactor system for chemical vapor synthesis of nanoparticles, which enables in situ investigations of high temperature gas phase particle formation and transformation processes by x-ray scattering and x-ray absorption spectroscopy. The system employs an inductively heated hot wall reactor as the energy source to start nanoparticle formation from a mixture of precursor vapor and oxygen. By use of a modular set of susceptor segments, it is especially possible to change solely the residence time of the gas mixture while keeping all other process parameters (temperature, gas flow, pressure) constant. Corresponding time-temperature profiles are supported by computational fluid dynamics simulations. The operation of the system is demonstrated for two example studies: tin oxide nanoparticle formation studied by small angle x-ray scattering and iron oxide nanoparticle formation by x-ray absorption spectroscopy.

Advances in magnetic films of epsilon-iron oxide toward next-generation high-density recording media

Iron oxide magnets, which are composed of the common elements iron and oxygen, are called ferrite magnets. They have diverse applications because they are chemically stable and inexpensive. Epsilon-iron oxide (ε-Fe2O3) is a polymorph that shows an extremely large coercive field as a magnetic oxide. It maintains its ferromagnetic ordering even when downsized to a single nano-sized scale (i.e.,<10 nm). Due to these characteristics, ε-Fe2O3 is highly expected to be used for high-density magnetic recording media in the big data era. Here, we describe the recent developments of magnetic films composed of metal-substituted ε-iron oxide, ε-MxFe2-xO3 (M: substitution metal), toward the next-generation of magnetic media.

Synthesis and characterization of new surface modified magnetic nanoparticles and application for the extraction of letrozole from human plasma and analysis with HPLC-fluorescence

Acetic acid-functionalized magnetic nanoparticles modified by (3-amino-propyl)-tri-ethoxy silane was synthesized and used as a new solid-phases adsorbent. Infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy (EDX), vibrating sample magnetometer (VSM) and Electrophoretic Light Scattering (ELS) were used to characterize the modified nanoparticles. The molecular interaction between letrozole and nanoparticles (NPs) was studied using density functional theory (DFT) calculations. The developed nanoparticles were applied for dispersive solid-phase extraction of letrozole (an anticancer drug) from human plasma. Extracted letrozole was quantified using an isocratic HPLC/FL method. The extraction efficiency was optimized using one experiment at a time optimization method based on the adsorbent quantity, sample pH, adsorption time, desorption time, and elution solvent type/volume. The analysis method was fully validated according to the FDA guideline for bioanalytical method validation. The linear quantification range was 0.01-1 μg/mL and the lower limit of quantification (LLOQ) was 0.01 μg/mL. Plasma samples of 6 patients were analyzed and the measured letrozole concentrations range was 0.04-0.31 μg/mL. The newly synthesized magnetic nanoparticles were used successfully for the extraction of letrozole from spiked and clinical plasma samples. The developed method is a precise and simple method that is suitable for pharmacokinetic studies and clinical applications.

Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension

Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properties more and more with decreasing the nanoparticle size. In particular, the saturation magnetization reduces, revealing a spin canting effect. Moreover, a large effective magnetic anisotropy is measured at low temperature together with an exchange bias effect, a behavior that we related to the existence of a highly disordered glassy magnetic phase.

Crystal Structure and Magnetic Properties of ϵ-Rux Fe2-x O3 Nanosize Hard Ferrite

A new series of metal-substituted ϵ-iron oxides, ϵ-Ru_x Fe_2-x O₃ (x=0 (1), 0.005 (2), and 0.014 (3)) nanoparticles (average size=20 nm) is synthesized by sintering iron oxide hydroxide with ruthenium hydroxide in a silica matrix. The samples are characterized by inductively coupled plasma mass spectrometry, and energy dispersive X-ray spectroscopy (EDS) of transmission electron microscope. The X-ray diffraction pattern shows that ϵ-Ru_x Fe_2-x O₃ has an orthorhombic crystal structure with a space group of Pna2₁ and the Rietveld analyses show that Ru is doped selectively at the regular octahedral C site among the four non-equivalent Fe sites (A, B, C, and D site). Magnetization vs. temperature plots show that the Curie temperature (T_C ) depends on x, and T_C =498 K for 1, 497 K for 2, and 496 K for 3. Magnetization vs. external magnetic field plots indicate that the coercive field (H_c ) increases from 17.7 kOe (1) to 20.3 kOe (3). This increment of 15 % on H_c is attributed to the single ion anisotropy of the magnetic spin on Ru^III (4d⁵ , S=1/2).

Effect of hydrogenation on the structure and magnetic properties of an iron oxide cluster

Hydrogenation of an iron oxide particle influences the geometrical topology and total magnetic moment and invokes different superexchange mechanisms.

The stability and unexpected chemistry of oxide clusters

The stability of Fe_mO_n clusters is determined by second energy differences.

Strain Effect on Electronic Structure and Work Function in α-Fe₂O₃ Films

We investigate the electronic structure and work function modulation of α-Fe₂O₃ films by strain based on the density functional method. We find that the band gap of clean α-Fe₂O₃ films is a function of the strain and is influenced significantly by the element termination on the surface. The p_x and p_y orbitals keep close to Fermi level and account for a pronounced narrowing band gap under compressive strain, while unoccupied d_z₂ orbitals from conduction band minimum draw nearer to Fermi level and are responsible for the pronounced narrowing band gap under tensile strain. The spin polarized surface state, arising from localized dangling-bond states, is insensitive to strain, while the bulk band, especially for p_z orbital, arising from extended Bloch states, is very sensitive to strain, which plays an important role for work function decreasing (increasing) under compressive (tensile) strain in Fe termination films. In particular, the work function in O terminated films is insensitive to strain because p_z orbitals are less sensitive to strain than that of Fe termination films. Our findings confirm that the strain is an effective means to manipulate electronic structures and corrosion potential.

Predicting size-dependent emergence of crystallinity in nanomaterials: titania nanoclusters versus nanocrystals

Bottom-up and top-down derived nanoparticle structures refined by accurate ab initio calculations are used to investigate the size dependent emergence of crystallinity in titania from the monomer upwards. Global optimisation and data mining are used to provide a series of (TiO₂)_N global minima candidates in the range N = 1-38, where our approach provides many new low energy structures for N > 10. A range of nanocrystal cuts from the anatase crystal structure are also considered up to a size of over 250 atoms. All nanocrystals considered are predicted to be metastable with respect to non-crystalline nanoclusters, which has implications with respect to the limitations of the cluster approach to modelling large titania nanosystems. Extrapolating both data sets using a generalised expansion of a top-down derived energy expression for nanoparticles, we obtain an estimate of the non-crystalline to crystalline crossover size for titania. Our results compare well with the available experimental results and imply that anatase-like crystallinity emerges in titania nanoparticles of approximately 2-3 nm diameter.

Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity

We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe(3+) ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.

A comparative study of small 3d-metal oxide (FeO)n, (CoO)n, and (NiO)n clusters

Geometrical and electronic structures of the 3d-metal oxide clusters (FeO)_n, (CoO)_n, and (NiO)_n are computed using density functional theory with the generalized gradient approximation in the range of 1 ≤ n ≤ 10.