Adaptation of the Crystal Structure to the Confined Size of Mixed-oxide Nanoparticles

Chemical composition and crystal structure are central to defining the functional properties of materials. But when a material is prepared in the form of nanoparticles, the structure and, as a consequence, the composition will also frequently change. Understanding these changes in the crystal structure at the nanoscale is therefore essential not only for expanding fundamental knowledge, but also for designing novel nanostructures for diverse technological and medical applications. The changes can originate from two thermodynamically driven phenomena: (i) a crystal structure will adapt to the restricted size of the nanoparticles, and (ii) metastable structural polymorphs that form during the synthesis due to a lower nucleation barrier (compared to the equilibrium phase) can be stabilized at the nanoscale. The changes to the crystal structure at the nanoscale are especially pronounced for inorganic materials with a complex structure and composition, such as mixed oxides with a structure built from alternating layers of several structural blocks. In this article the complex structure of nanoparticles will be presented based on two examples of well-known and technologically important materials with layered structures: magnetic hexaferrites (BaFe12O19 and SrFe12O19) and ferroelectric Aurivillius layered-perovskite bismuth titanate (Bi4Ti3O12)

Synthesis of Lanthanum-Strontium Magnanites by a Hydroxide-Precursor Co-Precipitation Method in Solution and in Reverse Micellar Microemulsion

Nanostructured lanthanum-strontium manganites have been synthesized using two different co-precipitation approaches, one in bulk solution, and the other in reverse micelles of CTAB/1-hexanol/1-butanol/water microemulsion. In both cases, precursor cations were precipitated by alkali precipitating agents. The properties of the material synthesized by using these two methods were compared in order to reveal potential advantages of microemulsion-assisted approach. The influence of the annealing conditions on the properties of synthesized manganites was investigated by using X-ray diffraction, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis and magnetic measurements

Multi-reaction kinetic modeling for the peroxidase-aldolase cascade synthesis of a D-fagomine precursor

Altres ajuts: Acord transformatiu CRUE-CSICThe feasibility of a peroxidase-aldolase cascade reaction for the synthesis of therapeutically-valuable iminocyclitols is discussed herein. A two-enzyme system consisting of chloroperoxidase (CPO) and D-fructose-6-phosphate aldolase (FSA) was evaluated for the synthesis of a D-fagomine precursor (preFagomine) from a N-Cbz-3-aminopropanol. An in-depth, systematic, step-by-step kinetic modeling of seven reactions and two inactivation decays was proposed to elucidate the reaction mechanism, prepare suitable stabilized biocatalysts, and find the optimal conditions for its application. The model described accurately the data and predicted the outcome at different experimental conditions. The inactivation of FSA caused by CPO was identified as the main bottleneck in the reaction. A two-step reaction approach and the use of immobilized enzymes on magnetic nanoparticle clusters and functionalized agarose carriers increased the stability of FSA, with an 1839-fold higher preFagomine formation per mol of enzyme in comparison to a one-pot reaction using soluble enzymes

Novel Ba-hexaferrite structural variations stabilized on the nanoscale as building blocks for epitaxial bi-magnetic hard/soft sandwiched maghemite/hexaferrite/maghemite nanoplatelets with out-of-plane easy axis and enhanced magnetization

Atomic-resolution scanning-transmission electron microscopy showed that barium hexaferrite (BHF) nanoplatelets display a distinct structure, which represents a novel structural variation of hexaferrites stabilized on the nanoscale. The structure can be presented in terms of two alternating structural blocks stacked across the nanoplatelet: a hexagonal (BaFeO) R block and a cubic (FeO) spinel S block. The structure of the BHF nanoplatelets comprises only two, or rarely three, R blocks and always terminates at the basal surfaces with the full S blocks. The structure of a vast majority of the nanoplatelets can be described with a SR∗S∗RS stacking order, corresponding to a BaFeO composition. The nanoplatelets display a large, uniaxial magnetic anisotropy with the easy axis perpendicular to the platelet, which is a crucial property enabling different novel applications based on aligning the nanoplatelets with applied magnetic fields. However, the BHF nanoplatelets exhibit a modest saturation magnetization, M, of just over 30 emu g. Given the cubic S block termination of the platelets, layers of maghemite, γ-FeO, (M), with a cubic spinel structure, can be easily grown epitaxially on the surfaces of the platelets, forming a sandwiched M/BHF/M platelet structure. The exchange-coupled composite nanoplatelets exhibit a remarkably uniform structure, with an enhanced M of more than 50 emu g while essentially maintaining the out-of-plane easy axis. The enhanced M could pave the way for their use in diverse platelet-based magnetic applications

Biotransformation of copper oxide nanoparticles by the pathogenic fungus Botrytis cinerea

The effects of copper (Cu) on microorganisms have been studied for decades due to its strong antimicrobial activity. Nowadays, emerging technologies are developing new antimicrobial compounds such as CuO and Cu nanoparticles (NPs), or products with their inclusions. In this study two plant pathogenic fungi, Alternaria alternata and Botrytis cinerea, were exposed to Cu in either ionic (Cu2+) or microparticle (MP, CuO) or nanoparticle (NP, Cu or CuO) form, in solid and liquid culturing media. B. cinerea proved to be resistant to CuO and Cu NPs and CuO MPs in comparison to A. alternata as shown by pronounced growth and lower levels of lipid peroxidation. B. cinerea grown in the presence of CuO and Cu NPs and CuO MPs on solid medium formed a blue compound at the fungal/ culturing medium interface, followed by a Cu depletion zone. The blue compound was characterized as Cu-oxalate by Cu-K EXAFS. In B. cinerea, pronounced activity of catechol-type siderophores and/or organic acid secretion apparently induces leaching and mobilization of Cu ions from the CuO MPs, CuO and Cu NPs and their further complexation with extracellularly secreted oxalic acid. As such, the pathogenic fungus B. cinerea may be used for copper extraction and/or purification and synthesis of different materials

Design and fabrication of magnetically responsive nanocarriers for drug delivery

Magnetically-assisted delivery of therapeutic agents to the site of interest, which is referred to as magnetic drug targeting, has proven to be a promising strategy in a number of studies. One of the key advantages over other targeting strategies is the possibility to control remotely the distribution and accumulation of the nanocarriers after parenteral administration. However, preparation of effective and robust magnetically responsive nanocarriers based on superparamagnetic iron oxide nanocrystals (SPIONs) still represents a great scientific challenge, since spatial guidance of individual SPIONs is ineffective despite the presence of high magnetic field gradient. A strategy to overcome this issue is the clustering of SPIONs to achieve sufficient magnetic responsiveness. In this mini-review, we address current and future strategies for the design and fabrication of magnetically responsive nanocarriers based on SPIONs for magnetically-targeted drug delivery, including the underlying physical requirements, the possibility of drug loading, and the control of drug release at the targeted site

Magnetic Properties of Mn-Doped Amorphous SiO2 Matrix

Samples of Mn-doped amorphous SiO2 matrix with manganese concentration 0.7 and 3 at.% have been prepared by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10 - 20 nm in size. Two types of Mn-rich particles are dispersed in silica matrix, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility reveals that dominant magnetic phase at higher temperatures is lambda-MnO2. At temperatures below T-C = 43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of lambda-MnO2. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the AC magnetic susceptibility in the sample with 3 at.% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature T-C. The low-temperature maximum in the zero-field-cooled magnetization observed for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments in the geometrically frustrated Mn sublattice of the lambda-MnO2 crystal structure.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

The formation and characterization of nanocrystalline phases by mechanical milling of biphasic calcium phosphate/poly-L-lactide biocomposite

Biphasic calcium phosphate/poly-L-lactide granules of 150-200 mu m sizes were subjected to high-energy mechanical milling in a planetary ball mill for up to 480 minutes. Characterization of the material obtained was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), environmentally scanning electronic microscopy (ESEM), transmission electron microscopy (TEM) and infrared spectroscopy (IR). These techniques confirmed that mechanical milling induced significant changes in the biocomposite structure and properties. The most significant changes are reduction of the HAp crystallites size from 99.8 to 26.7 nm and beta-TCP from 97.3 to 29.6, as well as crystallinity of PLLA phases. Homogeneous phase distribution (arrangement) is obtained by extending the duration of mechanical milling

STRUCTURE AND CHARACTERIZATION OF (x)Ni0.7Zn0.3Fe2O4 – (1-x)BaTiO3 COMPOSITES

Multiferroic composites with formula Ni0.7Zn0.3Fe2O4 - BaTiO3 (x = 0.1, 0.3, 0.5, 0.7, 0.9) were prepared by mixing chemically obtained NZF and BT powders in the planetary mill for 24 h. NiZnFe2O4 (NZF) powder was prepared by auto-combustion method starting from nickel, zinc and iron nitrates. Barium titanate (BT) powder was prepared with the same method. The optimization of sintering process was performed. One series of powders were pressed and sintered at 1170 °C, while the others were sintered at 1120 °C. X-ray measurements confirmed the presence of NZF, BT phases and the traces of barium ferrite phase. The microstructures of the ceramics show (Fig. 1.) the formation of grains with different shape and size. The formation of polygonal (NZF grains), rounded (BT grains) and plate like grains (barium ferrite phase) was noticed. The magnetic analyses showed that in the composites due to existence of ferroelectric phase a dilution effect appears

PROPERTIES OF PbZr0.52Ti0.48O3 - NiZnFe2O4, CoFe2O4 MULTIFERROIC COMPOSITES OBTAINED BY AUTO-COMBUSTION SYNTHESIS

Nickel zinc ferrite (NZF), cobalt ferrite (CF) and barium titanate (BT) nanosized powders were synthesised by auto-combustion method. Multiferroic composites with the formula xPbZr0.52Ti0.48O3+(1-x)CoFe2O4 and xPbZr0.52Ti0.48O3+(1-x)Ni0.7Zn0.3Fe2O4 (x=0.8 and 0.9) were prepared from nickel zinc ferrite, cobalt ferrite and barium titanate powders by mixing in planetary ball mill for 24 h. Pellets were sintered at different temperatures in order to obtain dense, two phased composites. XRD data indicated the formation of well crystallized structure of PZT and NZF/CF phase in the composite ceramics. SEM micrographs revealed a uniform grain distribution of both phases without any secondary phases. Magnetic measurements of all sintered composites were carried out and presented in Figure 1. All the composite samples exhibit typical ferromagnetic hysteresis loop, indicating the presence of the order magnetic structure. Saturation magnetization moment decreases with increasing PZT content, because of non-magnetic PZT phas