Role of aliphatic ligands and solvent composition in the solvothermal synthesis of iron oxide nanocrystals

Colloidal synthesis of the mixed ionic-electronic conducting NaSbS2 nanocrystals

Solution-based synthesis of mixed ionic and electronic conductors (MIECs) has enabled the development of novel inorganic materials with implications for a wide range of energy storage applications. However, many technologically relevant MIECs contain toxic elements (Pb) or are prepared by using traditional high-temperature solid-state synthesis. Here, we provide a simple, low-temperature and size-tunable (50-90 nm) colloidal hot injection approach for the synthesis of NaSbS2 based MIECs using widely available and non-toxic precursors. Key synthetic parameters (cationic precursor, reaction temperature, and ligand) are examined to regulate the shape and size of the NaSbS2 nanocrystals (NCs). FTIR studies revealed that ligands with carboxylate functionality are coordinated to the surface of the synthesized NaSbS2 NCs. The synthesized NaSbS2 nanocrystals have electronic and ionic conductivities of 3.31 × 10-10 (e-) and 1.9 × 10-5 (Na+) S cm-1 respectively, which are competitive with the ionic and electrical conductivities of perovskite materials generated by solid-state reactions. This research gives a mechanistic understanding and post-synthetic evaluation of parameters influencing the formation of sodium antimony chalcogenides materials.

Controlling Cation Distribution and Morphology in Colloidal Zinc Ferrite Nanocrystals

This paper describes the first synthetic method to achieve independent control over both the cation distribution (quantified by the inversion parameter x) and size of colloidal ZnFe₂O₄ nanocrystals. Use of a heterobimetallic triangular complex of formula ZnFe₂(μ₃-O)(μ₂-O₂CCF₃)₆(H₂O)₃ as a single-source precursor, solvothermal reaction conditions, absence of hydroxyl groups from the reaction solvent, and the presence of oleylamine are required to achieve well-defined, crystalline, and monodisperse ZnFe₂O₄ nanoparticles. The size of the ZnFe₂O₄ nanocrystals increases as the ratio of oleic acid and oleylamine ligands to precursor increases. The inversion parameter increases with increasing solubility of the precursor in the reaction solvent, with the presence of oleic acid in the reaction mixture, and with decreasing reaction temperature. These results are consistent with a mechanism in which ligand exchange between oleic acid and carboxylate ligands bound to the precursor complex influences the degree to which the reaction produces a kinetically trapped or thermodynamically stable cation distribution. Importantly, these results indicate that preservation of the triangular Zn-O-Fe₂ core structure of the precursor in the reactive monomer species is crucial to the production of a phase-pure ZnFe₂O₄ product and to the ability to tune the cation distribution. Overall, these results demonstrate the advantages of using a single-source precursor and solvothermal reaction conditions to achieve synthetic control over the structure of ternary spinel ferrite nanocrystals.

Influence of water concentration on the solvothermal synthesis of VO2(B) nanocrystals

Phase and length control of VO2(B) nanocrystals afforded by manipulating the ratio of toluene to water.

Evaluation of electrochemical properties of nanostructured metal oxide electrodes immersed in redox-inactive organic media

This paper describes analysis of dropcast nanocrystalline and electrochemically deposited films of NiO and α-Fe₂O₃ as model metal oxide semiconductors immersed in redox-inactive organic electrolyte solutions using electrochemical impedance spectroscopy (EIS). Although the data reported here fit a circuit commonly used to model EIS data of metal oxide electrodes, which comprises an RC circuit nested inside a second RC circuit that is in series with a resistor, our interpretation of the physical meaning of these circuit elements differs from that applied to EIS measurements of metal oxide electrodes immersed in redox-active media. The data presented here are most consistent with an interpretation in which the nested RC circuit represents charge transfer between the metal oxide film and the underlying metal electrode, and the non-nested RC circuit represents the resistance and capacitance associated with formation of a charge-compensating double-layer at the exposed interface between the metal electrode and electrolyte solution. Applying this interpretation to analysis of EIS data collected for metal oxide films in organic media enables the impact of film morphology on electrochemical behavior to be distinguished from the effects of the intrinsic electronic structure of the metal oxide. This distinction is crucial to the evaluation of nanostructured metal oxide electrodes for electrochemical energy storage and electrocatalysis applications.

Cation Distribution in Spinel Ferrite Nanocrystals: Characterization, Impact on their Physical Properties, and Opportunities for Synthetic Control

Metal oxide materials that adopt the spinel crystal structure, such as metal ferrites (MFe₂O₄), present tetrahedral (A) and octahedral [B] sublattice sites surrounded by oxygen anions that provide a relatively weak crystal-field splitting. The formula of a metal ferrite material is most precisely described as (M_1-xFe_x)[M_xFe_2-x]O₄, where the parentheses and square brackets denote the tetrahedral and octahedral sites, respectively, and x is the inversion parameter quantifying the distribution of M²⁺ and Fe³⁺ cations among these sites. The electronic, magnetic, and optical properties of spinel ferrites all depend on the magnitude of x, which, in turn, depends on the relative sizes of the cations, their charge, and the relative crystal-field stabilization afforded by tetrahedral or octahedral coordination. Compared to bulk spinel ferrites, the large surface-area-to-volume ratio of spinel ferrite nanocrystals provides additional structural degrees of freedom that enable access to a broader range of x values. Achieving synthetic control over the degree of inversion in addition to the size and shape is critical to tuning the properties of spinel ferrite nanocrystals. In this Forum Article, we review physical inorganic methods used to quantify x in spinel ferrite nanocrystals, describe how the electronic, magnetic, and optical properties of these nanocrystals depend on x, and discuss emerging strategies for achieving synthetic control over this parameter.

Solvothermal synthesis of α-Fe2O3 polyhedrons and its application in an immunochromatographic strip test for the detection of foodborne pathogen Listeria monocytogenes

The immunochromatographic strip test (ICST) is a powerful on-site detection technology due to its unique advantages of simplicity, rapidity, and readability by the naked eye. Here we illustrate the potential of α-Fe₂O₃ polyhedrons as a novel visual label, which exhibit advantages of high stability and economy, for the detection of Listeria monocytogenes (L. monocytogenes) as a model foodborne pathogen. A low-cost and simple one-step solvothermal approach was developed for the synthesis of α-Fe₂O₃ polyhedrons; the average diameter of the α-Fe₂O₃ polyhedrons is about 200 nm. The crystal structure and morphology of α-Fe₂O₃ polyhedrons were characterized by x-ray diffraction and transmission electron microscope. α-Fe₂O₃ polyhedrons were immunized with anti-L. monocytogenes antibody to prepare an antibody-colloidal α-Fe₂O₃ polyhedron ICST. Visual detection can be obtained directly by the naked eye within 10 min. The detection limit of L. monocytogenes by α-Fe₂O₃ polyhedron ICST assay was 3.8 × 10⁶ and 5.6 × 10⁶ CFU/ml of pure culture and artificially spiked orange juice drink sample, respectively. Results indicated that the antibody-colloidal α-Fe₂O₃ polyhedron ICST is a rapid, simple, and low-cost assay. This approach showed great potential in the application of foodborne pathogen detection concerning food safety.

Magnetic Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Heterometallic trinuclear oxo-centered clusters as single-source precursors for synthesis of stoichiometric monodisperse transition metal ferrite nanocrystals

Solvothermal reactions of M_IIFe2III(μ₃-O)(μ₂-O₂CR)₆(H₂O)₃ (R = CF₃, M = Fe, Co, Ni, Cu, Zn) clusters produce monodisperse, phase-pure MFe₂O₄ nanocrystals.