Nano-sized Precursors Research Articles

Synthesis of hard and tough calcium stabilized α-sialon/SiC ceramic composites using nano-sized precursors and spark plasma sintering

Silicon carbide (SiC)-reinforced calcium (Ca)-α-sialon ceramic composites were synthesized using nano-sized precursors and spark plasma sintering at 1500 °C for 30 min by adding 10, 20 and 30 wt % of SiC particles into the sialon matrix. Almost complete densification was achieved for all processed samples. The second-phase SiC particles were found to be homogeneously dispersed in the α-sialon matrix. The effect of the amount of loaded SiC on the mechanical properties of the ceramic composites was studied. A remarkable combination of hardness and toughness values, specifically 24.53 GPa (HV10) and 11.0 MPa m1/2, respectively, was obtained for the composite ceramic containing 30 wt% SiC, whereas hardness and fracture toughness values of only 21.1 GPa (HV10) and 7.3 MPa m1/2, respectively, were obtained for the monolithic α-sialon ceramic. The increase in fracture toughness was fairly attributed to the crack deflection, crack bridging and grain pullout mechanisms caused by the finely dispersed SiC particles.

Ultrahigh Oxygen Reduction Reaction Electrocatalytic Activity and Stability over Hierarchical Nanoporous N-doped Carbon

Hierarchical nanoporous N-doped carbon ZNC-1000 was prepared by facile pyrolysis of well-designed nanosized ZIF-8 precursor with optimized reaction temperature and time. It possesses large surface areas leading to sufficient exposed electrochemical active sites. Meanwhile, its moderate graphitization degree and suitable nanosized hierarchical porosity distributions would lead to the sufficient interaction between O2 and the electrocatalyst surface which would benefit the transports of electrons and the electrolyte ions for ORR. As an electrocatalyst for oxygen reduction reaction, the ZNC-1000 presents a better catalytic property than the commercial Pt/C with 6/1 mV positive shifts for onset/half-wave potentials and 1.567 mA cm−2 larger for limiting current density respectively. The stability of ZNC-1000 is also much better than that of Pt/C with negative shifts of 0/−2 mV (vs 5/31 mV) for onset/half-wave potentials and 6.0% vs 29.2% loss of limiting current density after 5000 cycles of accelerated durability test, as well as the relative current of 87.5% vs 40.2% retention after 30,000 s continuous chronoamperometric operation.

Photocatalytic degradation of methylene blue by nanostructured Fe/FeS powder under visible light

The photocatalytic performance of mechano-thermally synthesized Fe/FeS nanostructures formed from micron-sized starting materials was compared with that of a thermally synthesized nanostructure with nano-sized precursors in this paper. The properties of as-synthesized materials were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), diffuse reflectance spectroscopy (DRS), and ultraviolet-visible (UV-Vis) spectroscopy. The effects of irradiation time, methylene blue (MB) concentration, catalyst dosage, and pH value upon the degradation of MB were studied. Magnetic properties of the samples showed that both as-synthesized Fe/FeS photocatalysts are magnetically recoverable, eliminating the need for conventional filtration steps. Degradation of 5 ppm of the MB solution by mechano-thermally synthesized Fe/FeS with a photocatalyst dosage of 1 kg/m3 at pH 11 can reach 96% after 12 ks irradiation under visible light. The photocatalytic efficiency is higher in alkaline solution. The kinetics of photocatalytic degradation in both samples is controlled by a first-order reaction. However, the rate-constant value in the thermally synthesized Fe/FeS photocatalyst sample is only 1.5 times greater than that of the mechano-thermally synthesized one.

Nano-sized metabolic precursors for heterogeneous tumor-targeting strategy using bioorthogonal click chemistry in vivo

Herein, we developed nano-sized metabolic precursors (Nano-MPs) for new tumor-targeting strategy to overcome the intrinsic limitations of biological ligands such as the limited number of biological receptors and the heterogeneity in tumor tissues. We conjugated the azide group-containing metabolic precursors, triacetylated N-azidoacetyl-d-mannosamine to generation 4 poly(amidoamine) dendrimer backbone. The nano-sized dendrimer of Nano-MPs could generate azide groups on the surface of tumor cells homogeneously regardless of cell types via metabolic glycoengineering. Importantly, these exogenously generated ‘artificial chemical receptors’ containing azide groups could be used for bioorthogonal click chemistry, regardless of phenotypes of different tumor cells. Furthermore, in tumor-bearing mice models, Nano-MPs could be mainly localized at the target tumor tissues by the enhanced permeation and retention (EPR) effect, and they successfully generated azide groups on tumor cells in vivo after an intravenous injection. Finally, we showed that these azide groups on tumor tissues could be used as ‘artificial chemical receptors’ that were conjugated to bioorthogonal chemical group-containing liposomes via in vivo click chemistry in heterogeneous tumor-bearing mice. Therefore, overall results demonstrated that our nano-sized metabolic precursors could be extensively applied to new alternative tumor-targeting technique for molecular imaging and drug delivery system, regardless of the phenotype of heterogeneous tumor cells.

Nano‑calcium phosphate bone cement based on Si-stabilized α-tricalcium phosphate with improved mechanical properties

This study aimed to develop nano‑calcium phosphate cement (nCPC) and evaluate the effect of nanosized precursors on mechanical, physical and handling properties (injectability and setting time) as well as conversion rate of nano-reactants into nano-hydroxyapatite (nHA). In this study, while alpha tricalcium phosphate (α-TCP, 98wt%) and HA (2wt%) were applied as the powder phase, 2.5wt% NaH2PO4 solution was used as liquid phase of cement. Before nano-CPC preparation, Si-stabilized α-TCP nanopowder with particle size of 10±3.6nm was firstly synthesized in a two-step process of sol-gel followed by mechanical alloying. Moreover, HA nanopowder with particle size of 32±3.6nm was synthesized using sol-gel process. Our results revealed that after 3days of immersion in ringer's solution, reactants almost completely converted to nHA. Moreover, the initial and final setting time of nano-CPC was obtained 6.3±2.1min and 14.3±4.0min, respectively. Furthermore, injectability of this formulation was reached 87.90±2.60%. In addition, our results confirmed that the compressive strength and modulus of nano-CPC enhanced with increasing immersion time in ringer's solution from 9.50±1.27MPa and 0.38±0.07GPa (at 1day) to 18.70±2.23MPa and 0.57±0.15GPa (at 5days), respectively. Finally, in order to evaluate cellular responses to nano-CPC, MG63 cells were cultured on it and cell morphology and cytotoxicity were evaluated. Results revealed that nano-CPC enhanced proliferation and spreading of osteoblast like cells compared to control (tissue culture plate) which could be due to both appropriate physical and chemical properties of nano-CPC which stimulate cell proliferation. Our findings suggest the formation of an injectable nano-CPC with appropriate mechanical, physical and degradation rate which can potentially utilized for filling bone defects.

Preparation of high performance Bi2Sr2Co1.8Ox thermoelectric materials from nanosized precursors

ABSTRACTBi2Sr2Co1.8Ox thermoelectric (TE) materials were prepared by three different synthesis methods producing nanosized precursors: coprecipitation (with ammonium carbonate or oxalic acid) and attrition milling, which were compared with those obtained by the classical solid state method. Microstructure has shown that precursors produced by coprecipitation and attrition milling methods produced nanometric precursors much smaller than the typical sizes produced by the solid state route. The TE properties are in agreement with the microstructural features, leading to lower resistivity in all the samples, compared with the solid state ones, while Seebeck coefficient is practically unchanged in all cases. As a consequence, maximum power factor values of around four times higher than those obtained in the classical solid state method have been determined. Moreover, the highest power factor value at 650°C is higher than the best results obtained in as-grown textured materials produced by the laser floating zone technique.

Photoluminescence of silica monoliths prepared from cold sintering of nanometric aerosil precursors under high pressure

Blue photoluminescent silica monoliths were obtained by cold sintering of nanosized precursors under high pressure. The samples were prepared from hydrophobic and hydrophilic fumed silica AEROSIL® precursors which were placed inside a soft capsule of hBN and pressed at 7.7GPa. Practically no photoluminescence (PL) emission was observed for the nanometric powdered precursors while a relatively intense emission was measured for the sintered monoliths, which was dependent on the excitation wavelength (2.47–5.63eV). The emission was observed in the range between 2.0 and 3.5eV for all samples with the peak at ~2.7eV for excitation between 3.26–3.44eV. The blue band is probably related to the defects produced during the cold sintering process related to plastic deformation and internal stress of the monolith. The intensity of PL spectra of the monoliths obtained from the hydrophilic precursor (A200) was higher than the intensity of the spectra observed for the monoliths obtained from hydrophobic precursors (R974, R816 and R812) probably due to the presence of the carbon groups at the surface of the hydrophobic precursors, hindering the cold sintering process.

Microstructural and electromagnetic study of low temperature fired nano crystalline MgCuZn ferrite with Bi2O3 addition

The present study investigates electromagnetic properties, as well as microstructural and thermal stability, of low temperature fired MgCuZn ferrite with the addition of various amounts of Bi2O3. To achieve better performance at low sintering temperature, ceramic specimens were fabricated using nano-sized precursor powders through the nitrate-citrate auto-combustion method. X-ray diffraction study shows the formation of single phase spinel structure without any impurity phases. Compared with the additive-free sample, the addition of Bi2O3 increases the density of all specimens. Scanning electron microscopy micrographs of samples indicate that Bi2O3 content significantly affects densification through grain growth promotion. Excessive amounts of Bi2O3, however, lead to abnormal grain growth. Moreover, the sample with 0.25wt% Bi2O3 shows the highest density and grain shape uniformity as well as the lowest porosity. Dynamic magnetic properties were studied in a frequency range of 1–90MHz, using an impedance analyzer. Results reveal that the sample with a low amount of additive (0.25wt%) has the highest saturation magnetization, initial permeability (at 1MHz), and quality factor, whereas it's Curie temperature slightly decreases. With the further increase of Bi2O3 content, however, the initial permeability and saturation magnetization of samples deteriorate gradually.

Development of a single-phase Ca-α-SiAlON ceramic from nanosized precursors using spark plasma sintering

Nitrogen-rich Ca-α-SiAlON ceramics were synthesized using nanosized precursors via spark plasma sintering process for various holding times (10, 20, 30min) at relatively low temperatures of 1500°C and 1600°C. The effects of the experimental conditions, namely sintering time and temperature, on the densification and mechanical properties of the processed α-SiAlON were investigated. All of the conditions yielded nearly completely densified ceramics. A remarkable combination of hardness and toughness was obtained for the samples at either sintering temperature; and these values were greatest after 30min sintering time, with Vickers hardness values of 21.6GPa and 20.5GPa and fracture toughness values of 7.3MPa√m and 9.7MPa√m for sintering temperatures of 1500°C and 1600°C, respectively. The differences in the mechanical properties of these samples were related to differences in the phases formed during the sintering process.

Pulverization of oxide powders utilizing thermal treatment in ammonia-based atmosphere

A new pulverization process utilizing thermal treatment in controlled atmosphere was developed. The samples, including SrTiO3 single crystals, TiO2 single crystals and BaTiO3 ceramic, were pulverized into nano-sized powder by heating in gas stream containing air and ammonia (NH3) at high temperature. Although the detailed mechanism for this pulverization process is still unclear but it is evident that thermal treatment in NH3 based atmosphere containing small fraction of air (5–10%) causes not sintering but pulverization. Efficient synthesis of an oxynitride compound, LaTiO2N, was demonstrated by using nano-sized La2Ti2O7 precursor prepared by utilizing this new powder preparation process.

Reactivity Improvement of Dicalcium Phosphate Dihydrate with Fluoride for Its Removal from Waste and Drinking Water

Dicalcium phosphate dihydrate (DCPD) reacts with fluoride ion in an aqueous solution and forms stable fluoroapatite (FAp). This reaction requires a lag time to form nano-sized precursor, hydroxyapatite (HAp)-like calcium phosphate, on DCPD surface. This long lag time prevents DCPD from applying as an effective fluoride removal agent from waste water. The purpose of this study is to improve the reactivity of DCPD with fluoride ion by HAp-coating on the DCPD surface by soaking it in the simulated body fluid (SBF) under various DCPD/SBF ratios and soaking periods. The results showed the HAp-coating on DCPD by soaking in the SBF reduced the lag time to be negligible with increasing in amount of HAp up to 2 % in mass to the DCPD; however, further HAp formation had no affects on improvement of the reactivity.

Mg(OH)2 nanoparticles produced at room temperature by an innovative, facile, and scalable synthesis route

Nanoparticles form the fundamental building blocks for many exciting applications in various scientific disciplines. However, the problem of the large-scale synthesis of nanoparticles remains challenging. An original, eco-friendly, single step, and scalable method to produce magnesium hydroxide nanoparticles in aqueous suspensions is here presented. The method, based on an exchange ion process, is extremely simple and rapid (few minutes). It employs cheap or renewable reactants, operates at room temperature and does not require intermediate steps (washings/purifications) to eliminate undesired compounds. Moreover, it is possible to regenerate the exchange material and to reuse it for new operation of synthesis, according to a cyclic procedure, providing potential aptitudes of scalability of nanoparticles production. Some of the synthesis parameters are varied, and structural and morphological features of the produced nanoparticles, after few seconds from the beginning of the synthesis up to the ending time, are investigated by means of several techniques, such as X-ray diffraction (profile fitting and Rietveld refinement), transmission electron microscopy, infrared spectroscopy, thermal analyses, and surface area measurements. In any case, pure and stable suspensions are produced, characterized by crystalline and mesoporous Mg(OH)2 nanoparticles, with lamellar morphology. In particular, the nanolamellas appeared constituted by a superimposition of hexagonally plated and crystalline nanosized precursors (2–3 nm in dimensions), crystallographically oriented.

Synthesis of Nanostructured Molybdenum Carbide as Catalyst for the Hydrogenation of Levulinic Acid to γ-Valerolactone

The effect of the morphology and size of unsupported molybdenum carbide (β-Mo2C) was investigated in the selective hydrogenation of levulinic acid to γ-valerolactone (GVL) in aqueous phase. Nanostructured β-Mo2C was synthetized by two different approaches: (i) using multiwalled carbon nanotubes (CNT) as both hard template and source of carbon and; (ii) using 1D nanostructured α-MoO3 as precursor. Depending on the type of synthesis used, the morphology of the resulting β-Mo2C was different. Well-oriented β-Mo2C nanoparticles with a fibril morphology were formed when CNTs were used as hard template and source of carbon at 700 °C for 6 h under inert environment, while well-defined β-Mo2C 1D nanostructures were formed after carburization of the nano-sized α-MoO3 precursor at 650 °C/2 h under 20 % (v/v) CH4/H2 atmosphere. The catalytic performance of the materials was investigated at 30 bar H2 and 180 °C in a batch reactor and compared with a Mo2C synthesized by temperature-programmed carburization of commercial MoO3. The β-Mo2C 1D nanostructures presented a relatively higher activity than the others probably as a result of more exposed active sites, confirmed by the higher CO chemisorption uptake. All of the catalysts were highly selective to GVL (>85 %). Deep hydrogenation products such as 1,4 pentanediol and methyltetrahydrofuran were observed in minor amounts, underlining the hydrogenation potential of molybdenum carbide based materials.

Synthesis of CuAlO2 from chemically precipitated nano-sized precursors

A study was carried out on the synthesis of CuAlO2 at temperatures below 1000°C, using a simple approach based on mechanical mixing of chemically precipitated CuO and Al(OH)3 nanoparticles. Synthesis of precursor powders was achieved at low temperatures (<100°C) via precipitation from their corresponding aqueous solutions. After drying at room temperature, precursors were mixed in equimolar ratios by a combination of ball milling and sonication. Green pellets were obtained by filtration casting of the mixed powder slurry followed by dry compaction. X-ray diffraction study showed that the single phase CuAlO2 samples with high crystallinity formed only after 5h of firing at 900°C under flowing nitrogen. Electron microscopy images revealed a loosely packed microstructure with high surface area consisting of nanosized grains after the heat treatment. The achieved relative density was 45% of the theoretical density. The crystallite size was estimated to be 39nm and the specific surface area of the sintered sample was measured as 9.67m2/g. The bandgap was calculated as 3.07eV with a transmittance of 60% in the visible region. The measured electrical conductivity was 4×10−3mS/cm at room temperature and showed an increase with increasing measurement temperature, which indicates semiconducting behavior. The conductivity was shown to increase by an order of magnitude with a higher degree of densification by sintering at 1150°C.

Fabrication and characterization of nanostructured thermoelectric FexCo1-xSb3

Abstract A novel synthesis route for the fabrication of p-type nanostructured skutterudite, FexCo1-xSb3 in large quantity is reported. This scalable synthesis route provides nano-engineered material with less impact on the environment compared to conventional synthesis procedures. Several Fe substituted compositions have been synthesized to confirm the feasibility of the process. The process consists of a nano-sized precursor fabrication of iron and cobalt oxalate, and antimony oxides by chemical co-precipitation. Further thermochemical processes result in the formation of iron substituted skutterudites. The nanopowders are compacted by Spark Plasma Sintering (SPS) technique in order to maintain nanostructure. Detailed physicochemical as well as thermoelectric transport properties are evaluated. Results reveal strongly reduced thermal conductivity values compared to conventionally prepared counterparts, due to nanostructuring. P-type characteristic was observed from the Seebeck measurements while electrical conductivity is high and shows metallic behavior. The highest TE figure of merit of 0.25 at 800 K has been achieved, which is strongly enhanced with respect to the mother compound CoSb3. This suggests the promise of the utilized method of fabrication and processing for TE applications with improved performance.

The effect of non-magnetic Al3+ ions on the structure and electromagnetic properties of MgCuZn ferrite

A series of Al substituted MgCuZn ferrite powders with composition Mg0.3Cu0.2Zn0.52AlxFe1.98−xO3.99 (0.00≤x≤0.06) have been synthesized with nano-sized precursor powders through the nitrate–citrate auto-combustion route. These powders were calcined, compacted and sintered at 900°C for 4h. X-ray diffraction patterns show the formation of cubic spinel structure. Infrared spectra indicate two fundamental absorption bands corresponding to the tetrahedral and octahedral complexes, respectively. A significant increase in density and grain size is observed with increasing Al content. The room temperature saturation magnetization increases for x=0.015 and then decreases for further increase in Al substitution. The initial permeability increases with the Al content attributed to the increase in the grain size and density. Curie temperature is found to be dependent on the Al concentration and it decreases due to decrease in the number of super-exchange interactions between Fe3+ ions in the tetrahedral and octahedral sites.

Role of subcolloidal (nanosized) precursor species in the early stage of the crystallization of zeolites in heterogeneous systems.

A critical analysis was carried out for the purpose of understanding the role of subcolloidal (nanosized) (alumino)silicate precursor species in the early stage of crystallization of zeolites in heterogeneous systems (hydrogels). The formation and evolution of these subcolloidal species in both the solid and the liquid phases were investigated by various experimental methods such a scanning electron microscopy (SEM, FE-SEM), transmission electron microscopy, atomic force microscopy, particle size analysis, pH measurement, atomic absorption spectroscopy, and dynamic light scattering, after careful separation of intermediates from reaction mixture by two-step centrifugation treatment. The results revealed that a chain of processes (i) the formation of low-molecular-weight (LMW) silicate species, by dissolution of Al-enriched amorphous silica, and their aggregation into about 3 nm sized primary precursor species (PPSs), (ii) the formation of larger (∼3 to ∼15 nm sized) silicate precursor species (LSPSs) by a rapid aggregation/coalescence of PPSs, (iii) the formation of "gel" (primary amorphous precursor) by a random aggregation of LSPSs at room temperature, and (iv) the formation of the worm-like particles (secondary amorphous precursor) occurred in the solid phase during heating of the reaction mixture (hydrogel) from room temperature to 170 °C. It is interesting that almost the same processes occur in the liquid phase but with decreased rate according to the relative low concentration of LMW silicate species. With the above described findings, it is highly expected that the manipulation of crystallization pathway through controlling the formation/evolution of precursor species in the initial stage of the process can be achieved.

Size, crystal structure and morphology changes of IATO nanoparticles effect on its optical property

Controlling and changing size, crystal structure and morphology of antimony and tin-doped indium oxide (IATO) nanoparticles can effectively influence their specific optical properties. Nanocube-like, nanorod-like and nanosphere-like IATO nanoparticles have been fabricated from 20 to 200 nm in diameter by sintering as-prepared precursors with distinct crystallographic structures and morphologies. These nano-sized precursors are either cubic In(OH)3 or orthorhombic InOOH with different crystallographic sizes and shapes due to the use of different solvents (deionized water, absolute ethyl alcohol and ethylene glycol) in hydrothermal synthesis process. Characterization and comparison of experimental samples have detailedly demonstrated that desired optical properties of IATO nanoparticles should be attained by appropriate change of size, crystal structure and morphology of IATO nanoparticles.

Crystal-phase control of molybdenum carbide nanobelts for dehydrogenation of benzyl alcohol

Belt-shaped molybdenum carbides in α- and β-phases were synthesized by reducing and carburizing a nano-sized α-MoO3 precursor with hydrocarbon-hydrogen mixtures at appropriate temperatures; the β-Mo2C nanobelts with a higher fraction of coordinatively unsaturated Mo sites were more active than the α-MoC1-x nanobelts in dehydrogenation of benzyl alcohol to benzaldehyde.

Carbon-coated single-crystalline LiFePO4 nanocomposites for high-power Li-ion batteries: the impact of minimization of the precursor particle size

In this work, a high-energy ball mill technique is designed to deal with bulk precursors and achieve particle size minimization. A large amount of the nano-sized precursor is achieved in a narrow particle size distribution of ca. 95 nm. We confirm that the dimensional size of the precursor has a significant influence on the final LiFePO4 particle size and that small grains of the precursor probably form single-crystalline nanoparticles during the calcination process. After carbothermal reduction, the carbon-coated single-crystalline LiFePO4 nanocomposites (nano-CS–LFP) are easily synthesized. Benefiting from the decreasing particle size, the specific surface area of nano-CS–LFP is up to 48.0 m2 g−1, which implies a higher interfacial contact area between the active particles and the electrolyte, as well as an increase in its capacitance capability. Besides, cyclic voltammetry curves of nano-CS–LFP reveal a better capability of reversible reactivity and a lower polarization. Galvanostatic charge–discharge results exhibit excellent rate performance with a discharge capacity of ca. 100 mA h g−1 at 10 °C and a stable cycling property with a capacity retention of ca. 90% after 1000 cycles. In addition, the rapid charge–discharge test over 60 seconds indicates an excellent pulse performance with a high current in a short time period. The combination of the merits of carbon coating and particle size minimization is responsible for the above improvements. Finally, this facile preparation strategy is favorable for the industrial production of economical LiFePO4 materials from lab synthesis.