Search

An efficient ligand-induced MOF-on-MOF strategy is proposed to fabricate hollow ZIF-67@PBA heterostructures. By manipulating the Co2+/Zn2+ ratio in the precursor ZIF-67, the catalyst Co x Fe-ZP can be conveniently obtained after pyrolysis, showing satisfactory electrocatalytic oxygen evolution. [Display omitted] There is significant anticipation for high-efficiency and cost-effective non-precious metal-based catalysts to advance the industrial application of the anodic oxygen evolution reaction (OER) for hydrogen production. This study introduces an efficient strategy that utilizes ligand-induced metal–organic framework (MOF) building blocks for the synthesis of hollow binary zeolitic imidazolate frameworks 67 (ZIF-67) and Prussian blue analogues (PBAs) (ZIF-67@PBA) heterostructures through a hybrid MOF-on-MOF approach. Manipulating the Co2+/Zn2+ ratio in the precursor ZIF-67 allows for the convenient synthesis of the final product, denoted as Co x Fe-ZP, after pyrolysis, where the inclusion of Zn effectively modulates the distribution of Co in the catalyst. The resulting Co x Fe-ZP catalysts exhibit a positive synergistic effect between hollow graphitic carbon nanomaterials and Fe-doped Co nanoparticles. The optimal Co 0.3 Fe-ZP catalyst demonstrates satisfactory OER performance, achieving an overpotential of 302 mV at 10 mA cm−2 and a small Tafel slope of 60.0 mV dec−1. Further analysis of the activation energy confirms that the enhanced OER activity of Co 0.3 Fe-ZP can be reasonably attributed to the combined influence of its morphology and composition. This study demonstrates a ligand-induced method for examining the morphology and electrochemical properties of grown binary MOF-on-MOF heterostructures for OER applications. [ABSTRACT FROM AUTHOR]

Transition metal and nitrogen doped carbons (M-N-C) catalysts present significant potential as substitutes for platinum-carbon (Pt/C) in catalyzing oxygen reduction reaction (ORR). Hence, we employ an epitaxial growth strategy to prepare Zn/Co-ZIF@ZIF-8 crystals with core-shell structure. Subsequent pyrolysis and acid etching produce highly porous cobalt-doped nitrogen materials for ORR investigation. The resulting Co-NC@NC catalyst demonstrates a graded porous structure alongside remarkable conductivity, possessing a specific surface area measuring 623 m2 g−1. It showcases heightened ORR activity with a half-wave potential (E 1/2) of 0.886 V, superior kinetic performance (illustrated by an extremely low Tafel slope measuring 45.98 mV/dec), and strengthened stability (with mere 25 mV day after 40,000 cycles) when contrast with Pt/C catalysts in 0.1 M KOH. Additionally, it exhibits notable activity and stability in acidic environments. These remarkable attributes are attributable to the graded structure, which facilitates rapid mass transfer, a high electrochemically active area that exposes highly dispersed active sites, and a conductive carbon skeleton network that promotes electron transfer. • Ion exchange-epitaxial strategy synthesizes core-shell cobalt nanoparticles. • Graded porous structure enhances active sites and accelerates mass transfer. • Catalyst shows excellent ORR stability and activity in all pH environments. • Catalyst exhibits 25 mV E 1/2 decay after 40000 cycles of ADT. [ABSTRACT FROM AUTHOR]

Electromagnetic pollution and heat dissipation problems are becoming increasingly worthy of attention due to the rapid development of electronic devices, which puts forward an urgent demand for microwave absorbers with excellent thermal management performance. Herein, high-performance Co/carbon nanofiber (Co/CNF) microwave absorbers with high thermal conductivity were fabricated by facile step-by-step method. The microwave absorption properties can be readily tuned by adjusting the content and size of Co nanoparticles through concentration gradient adsorption. Benefiting from the formation of dielectric and magnetic coupling network, Co/CNF composites possess intensive dipole polarization, interface polarization, and magnetic loss. The optimal Co/CNF composites exhibit outstanding microwave absorption performance with a minimum reflection loss (RL) of −53.0 dB at 11.44 GHz, and a maximum effective absorption bandwidth (EAB) of 5.5 GHz. In addition, the thermal conductivities of the Co/CNF-natural rubber (Co/CNF-NR) composites are significantly improved. This work may inspire the exploration of high-efficiency heat-conduction microwave absorbers based on CNF.

• The adsorption strength of Co n (n = 1–5) clusters with same size on three ZrO 2 surfaces follows the order: m- ZrO 2 (−111) > t -ZrO 2 (101) > c -ZrO 2 (111). • It is thermodynamically favourable for the nucleation of Co n clusters on c -ZrO 2 (111) and t -ZrO 2 (101) surfaces, but it is opposite on m -ZrO 2 (−111) surface. • More Co-Zr bonds and electron transfer of the Co 5 cluster on m -ZrO 2 (−111) surface lead to overlap between Co d-orbital and Zr d-orbital. • The AIMD simulations not only confirmed the stable Co 5 structures of DFT calculation, but also predicted the morphology of large Co 13 clusters on ZrO 2 surfaces under realistic reaction conditions, consistent with the experimental SAM images. The optimization of structure-dependent activity of supported metal catalysts has driven the dynamic determination of the morphology of Co nanoparticles on ZrO 2 using atomic-level simulations. Density functional theory (DFT) calculations combined with ab initio molecular dynamics (AIMD) simulations were used to investigate the surface structure, nucleation mechanism and morphology evolution of Co n clusters supported on different ZrO 2 facets. As the size of the Co n (n = 1–5) cluster increases, the competition between Co-Co bonding and the interaction of Co n clusters with the ZrO 2 surface further promotes the nucleation of larger clusters. Co atoms prefer to nucleate into large clusters on both c -ZrO 2 (111) and t -ZrO 2 (101) surfaces, but this behavior is unfavorable on the m- ZrO 2 (-111) surface. The analysis of electric properties suggests that the types of hybrid orbitals and the number of electron transfer accounts for the difference in energies of Co n clusters on ZrO 2 surfaces. Further, the AIMD simulations verified the stable structure of small Co 5 cluster obtained by DFT, and predicted the morphology of large Co 13 clusters on ZrO 2 surfaces under realistic reaction conditions, consistent with the experimental SAM images. Our work provides an intuitive understanding of structure and morphology evolution of catalysts for the targeted design of catalysts to achieve the desired activity and explore more reaction possibilities. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we developed a highly selective detector towards the antibiotic drug chloramphenicol (CAP) using Co nanoparticle, which are grown in situ on N‐doped carbon nanotube polyhedra (Co@NCNP), which are obtained by a pyrolysis strategy derived from core‐shell ZIF‐8@ZIF‐67. Physical characterization verified that metal‐organic framework (MOFs)‐derived Co@NCNP nanocomposites present a nanotube structure on their mesoporous polyhedron surface. As a result, the as‐prepared Co@NCNP can be used as a sensitive electrochemical sensor for chloramphenicol detection, and the modified electrode is also studied by electrochemical methods such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). When compared with single ZIF‐67‐derived electrode, the Co@NCNP displays a higher electrocatalytic activity in the presence of chloramphenicol. Moreover, an excellent performance with a linear response range of 5–268.83 μM and a low detection limit of 0.5 μM (S/N=3) is observed for the Co@NCNP modified electrode. Finally, the fabricated chloramphenicol sensor achieves a good anti‐interference ability, stability, excellent repeatability, and remarkable reproducibility. The sensor also could be applied in human serum to determine of chloramphenicol with a satisfactory result. [ABSTRACT FROM AUTHOR]

Carbon nanofibers with various contents of Co nanoparticle were synthesized by a two step process of electrospinning and subsequent heat treatment. The thermal stability,phase composition,microstructure and electromagnetic characteristics of the carbon nanofibers were characterized by differential scanning calorimetry-thermogravimmetric analysis (DSC-TGA),X-ray diffraction(XRD),scanning electron microscope(SEM) and vector network analyzer(VNA),and the microwave absorption performance was studied.The results indicate that the crystallinity of composite nanofibers is moderate when the carbonization temperature is 800℃.The amorphous carbon is partially converted into graphite and CoAc2 completely reduces to face-centered cubic structured Co nanoparticle. The fiber is intact and beads-on-string structure exists in the fiber networks. The electromagnetic characteristics of the carbon nanofibers significantly improve by the doping of Co. The Carbon nanofibers containing 7%(mass fraction) as fillers with thickness of 1.5mm exhibit maximum effective absorption bandwidth of 4.5GHz, and it is obviously improved compared to pure carbon nanofibers.

Cost efficient bifunctional air cathodes possessing high electrocatalytic activity are of great importance for the development of secondary Zn‐air batteries. In this work, cobalt nanoparticles are encapsulated within a 3D N‐doped open network of carbon tubes (Co@N‐CNTs) by a molten‐salt synthesis procedure conducted at a high temperature. Physical characterization demonstrates that Co@N‐CNTs are comprised of Co particle inserted carbon tubes with mesoporous tube walls, providing significant active surface area for electrochemical reactions. High electrocatalytic activity of Co@N‐CNTs towards both oxygen evolution and oxygen reduction reactions is due to its well‐developed active surface and a synergistic effect between N‐doped carbon and Co nanoparticles. Both primary and secondary Zn‐air battery cells assembled using Co@N‐CNTs as an air cathode show higher electrochemical performance than similar cells containing commercial Pt/C and Pt/C +RuO2, making the newly developed material a promising alternative to existing metal‐based air cathodes. [ABSTRACT FROM AUTHOR]

Hierarchical carbon skeletons derived from natural wood can be employed as the substrates to fabricate self-supported catalysts. The typically three sections (cross section, radial section, and tangential section) of wood would significantly affect the electrocatalytic performance. Therefore, the correlations between anisotropy structure of wood derived hierarchical carbon skeletons and oxygen evolution reaction (OER) performances was systematically investigated. The cross-sectional wood-derived carbon decorated with Co nanoparticles requires an overpotential of 370 mV to deliver 50 mA cm−2 superior to those of radial-sectional and tangential-sectional counterparts. The cross-section of wood derived carbon skeleton possesses higher content of Co nanoparticles, which is accounted for the enhanced OER catalytic activity. This work highlights the critical contribution of anisotropy of carbon skeletons in promoting the OER properties and provides a new paradigm for designing advanced electrocatalysts. [Display omitted] • Three carbonized wood electrodes were fabricated through one step carbonization. • Higher loading Co nanoparticles endowed Co/C-CW with enhanced OER activity. • Co/C-CW required an overpotential of 370 mV to achieve 50 mA cm−2. [ABSTRACT FROM AUTHOR]

The hydrogenation of nitrogen‐containing heterocyclic precursors in aqueous medium is quite challenging, especially at low temperature and without imposing molecular hydrogen pressure. In the light of the edges of metal nanoparticles (NPs) possess high selective activity, but most of the exposed metal surface does not. Hence, to influence the activity of the entire NPs surface, the use of zeolitic imidazolate frameworks (ZIFs) to obtain the metal NPs encapsulated in the carbon tubes which has been applied frequently. Herein, we design and synthesize a series of metal catalysts encapsulated in N‐doped carbon nanotubes (NCT), which disperse on the hollow N‐doped carbon framework (HNC), via pyrolysis ZIF‐67, ZIF‐67@ZIF‐8, and ZIF‐8@ZIF‐67 step by step. The catalyst of Co@NCT/HNC shows outstanding activity of hydrogenation of quinoline under mild conditions, due to the synergistic effects between Co NPs, NCT and HNC, such as the NCT make the hydrogen reach the surface of the reactant rapidly, and the encapsulated structure can enormously prevent the metal aggregating. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cobalt-entrapped, nitrogen-doped mesoporous carbon materials have been prepared using melamine formaldehyde resin (MF resin) as precursor and CoCl 2 as template. A fraction of CoCl 2 can be reduced to Co nanoparticles and wrapped by the nitrogen doped carbon. Meanwhile, the ratio of MF resin to CoCl 2 is an important parameter determining the mesoporous structures of the final products. The surface area of the obtained material decreases with the increase in the ratio of MF resin to CoCl 2 . Electrocatalytic tests show that the obtained catalysts are highly active for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm −2 at 171 and 186 mV under acidic and alkaline conditions, respectively. Additionally, these catalysts also show good long-term stabilities. [ABSTRACT FROM AUTHOR]

The Co@N-C nanocatalysts derived by direct carbonization of Co-containing metal organic framework (MOF) structure under N 2 flow have been prepared for their application as catalyst in reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) assisted by NaBH 4 . Under inert gas treatment, we obtained Co 0 phase-based nanocatalyst which inherited their former MOF precursor morphology. The resultant nanocatalysts were denoted as Co@N-C 600, 700, 800 corresponding to the respective carbonization temperatures and each was characterized using powder X-Ray diffraction (PXRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), surface area-porosity and transmission electron microscopy (TEM). We found that Co@N-C 700 presented the desired properties with largest surface area (262.800 m 2 /g), high crystallinity with better Co nanoparticle dispersed on the C-N matrix and sufficient amount of Co per gram of nanocatalyst without obvious particle aggregation. All of the nanocatalysts could catalyze 1.25 mM 4-NP to 4-AP per mg catalyst per second which is comparatively remarkable performance compared to previous reposts. Most importantly, as predicted Co@N-C 700 possessed the highest catalytic activity with 6 times consecutive catalytic reactions in successfully reducing 100% 4-NP to 4-AP. The catalytic activity was speculated due to the Co nanoparticle as catalytic active site worked synergistically with C-N matrix as conductive layer which could provide and transport electrons for catalytic reduction reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-N-CNT-CF is fabricated by growth Co-MOF and a straightforward CVD process. • DFT results confirm Co@G and N-CNT provide multitudinous lithiophilic sites. • Co-N-CNT-CF substrate exhibits outstanding electrochemical performance. Lithium (Li) metal is an impeccable candidate anode for satisfying the energy density requirements of next-generation Li batteries. However, Li dendritic growth and fragile solid-elecrolyte interphase (SEI) caused by the high reactivity between Li and electrolyte are the primary challenges for its large-scale applications. Herein, a bifunctional lithiophilic hierarchical substrate composed of high-density nitrogen-doped carbon nanotubes and Co nanoparticles encapsulated in graphene (Co@G) decorated carbon fibers (Co-N-CNT-CF) can modulate the structural dimensions and hierarchy of Li nucleation/growth and alleviate Li volume expansion, achieving the homogeneous Li plating/stripping behavior. Density functional theory (DFT) calculations and experimental results confirm the highly lithiophilicity of the substrate, which exhibits a low Li nucleation overpotential, enhanced Coulombic efficiency (CE), small voltage hysteresis, and ultrastable lifespan without dendritic formation. As coupled with the thick LiFePO 4 and LiCoO 2 (∼2 mA h cm−2) cathodes, the Co-N-CNT-CF@Li composite anode (N/P = 3) enables a high reversible capacity, high Li utilization, and improved cycle stability. This work engineers a hierarchical structure of the three-dimensional (3D) lithiophilic carbon substrate for realizing highly reversible, dendritic-free Li metal anodes. [ABSTRACT FROM AUTHOR]

• Co@N-doped carbon was prepared by pyrolysis of ZIF-8@ZIF-67 to modify CdSe QDs. • The k of Cr(VI) reduction over 2%Co@C/CdSe is 33.9 times higher than that of CdSe. • The best H 2 evolution rate of 2%Co@C/CdSe is 139 times larger than that of CdSe. • Enhanced charge separation and light absorption is responsible for high activity. Solar-driven water splitting is regarded as one promising green way to produce H 2. Photo-reduction of hexavalent chromium (Cr(Ⅵ)) to hypotoxic Cr(III) can control the Cr(VI)-induced pollution. A key in these processes is to develop a photocatalyst with high specific surface area, good light absorption and efficient charge carrier separation. A Co-encapsulated N-doped carbon (Co@NC) was prepared by pyrolysis ZIF-8@ZIF-67 precursor to modify CdSe quantum dots (QDs). The obtained catalyst was used to reduce Cr(Ⅵ) and split water under visible light irradiation. Modification CdSe with Co@NC made obtained Co@NC/CdSe possessing enhanced visible-light absorption and photoexcited charge separation. The optimal 2%Co@NC/CdSe exhibited the excellent Cr(Ⅵ) reduction performance with a rate constant of 0.28 min–1 in the absence of sacrificial agent, as well as high H 2 evolution rate of 6.48 mmol g–1 h–1 in 10% lactic acid solution. The H 2 O 2 and electrons were the active species to reduce Cr(VI). This work gives a beneficial insight for improving the photocatalytic activity of QDs. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon based non-precious metals and carbon-based materials have been widely demonstrated as promising electrocatalysts on oxygen reduction reaction. Nevertheless, how to control synthesize electrocatalysts effectively by employing a general path is still a great challenge. In this paper, we propose a facile strategy to grow Co nanoparticles/N-doped carbon nanotube hetero-structure from Co-based complexes with excellent electrocatalytic activity. By using different ligands (oleylamine, p-phenylenediamine, and 2-methylimidazole), Co-based complexes or metal-organic framework with the special morphologies were prepared and taken as templates for the Co nanoparticles/N-doped carbon nanotubes growing at high temperature. The as-prepared Co nanoparticles/N-doped carbon nanotubes perform high activity and excellent capacity on the electrocatalysis of oxygen reduction reaction. The onset potential and half-wave potential is measured as 0.92 V RHE and 0.84 V RHE respectively, which is very closed to the performance of commercial Pt/C(20%). Besides, the different Co-complexes with special morphologies are used as template for growing N-doped carbon nanotubes encapsulated Co nanoparticles and their corresponding electrocatalysis shows that the as-prepared Co nanoparticles/N-doped carbon nanotubes performance high capabilities on electrocatalysis of oxygen reduction reaction. The facile strategy for growing N-doped carbon nanotubes provides a possibility path to fabricate electrode on different substrate with excellent performance. [Display omitted] • The electrocatalysis of the Co NPs/CNTs performed high activities and good durability, which were closed to the previous reported results and the performance of commercial Pt/C. • The as-prepared Co NPs/CNTs heterostructures prepared with varies of Co complexes were testified with similar structure, doping element, defects and chemical valences. • The Co NPs/CNTs heterostructures were prepared by growing CNTs with the original morphologies remaining, which providing a general and effected path to prepared Co NPs/CNTs with controlled morphologies. [ABSTRACT FROM AUTHOR]

Abstract: A reconstruction technique for off-axis electron holography not requiring Fourier transformation is presented. Background intensity and amplitude modulation recorded in a hologram are normalized using an envelope function, and a cosine-function image corresponding to interference fringes is retrieved from the hologram. A reconstructed phase image is then calculated from the retrieved cosine image. After phase unwrapping, the phases due to carrier frequency and Fresnel diffraction from the biprism are removed using a reference hologram, and the corrected phase image is obtained. One advantage of this method is that the spatial resolution does not rely on the interference fringe spacing. Another advantage is that the phase image has no artifacts due to windowing of the sideband, which occurs in the usual Fourier-transformation method. Details of the calculation process and demonstrations of the method using a latex sphere particle and self-assembled Co nanoparticles are described. [Copyright &y& Elsevier]

• The CoMoO 4 /Co 2 Mo 3 O 8 with rich-oxygen vacancies (V o) incorporated by Co nanoparticles is designed. • The Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o is helpful for H* adsorption and interfacial electron transferring. • The vacancies can optimize the binding energy of intermediates on CoMoO 4 /Co 2 Mo 3 O 8 interfaces. • The Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o shows excellent HER electrocatalytic performance. Realizing synergetic effect of multiple factors is critical to develop an optimal catalyst. Bimetallic oxides have shown great potential for catalytic hydrogen evolution from water splitting in alkaline media because their oxygen species are beneficial for water adsorption and can get unique d electron configurations to optimize the binding strength of intermediates. Here bimetallic oxide heterointerface CoMoO 4 /Co 2 Mo 3 O 8 with rich-oxygen vacancies (V o) incorporated by the monodisperse small-size cobalt (Co) nanoparticles (Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o) is designed for hydrogen evolution reaction (HER) in alkaline media. The charge redistribution occurs at the CoMoO 4 /Co 2 Mo 3 O 8 interface because of incorporation of Co, and this will be helpful for H* adsorption and interfacial electron transferring. Meanwhile, the rich-oxygen vacancies can well optimize the binding energy of intermediate species on CoMoO 4 /Co 2 Mo 3 O 8 interface and thus will facilitate the sluggish HER in alkaline media. Because of the synergistic effects of metallic Co, CoMoO 4 /Co 2 Mo 3 O 8 interfaces and rich-oxygen vacancies, the Co@CoMoO 4 /Co 2 Mo 3 O 8 -V o catalyst shows superior electrocatalytic activity for HER in alkaline media with a low overpotential of 60 mV at 10 mA cm−2, a small Tafel slop of 52 mV dec-1, and excellent durability with ∼ 2% degradation after 24 h test. This work will provide a new strategy to enhance HER catalytic performance of bimetallic oxides in alkaline media. [ABSTRACT FROM AUTHOR]

Electrocatalyst is the pivotal component promoting the kinetics of oxygen reduction reaction in aqueous metal-air batteries. However, the content of increased bond as the active species is usually limited by the metal loading, tiny pore canal, insufficient nitrogen further restraining the electrocatalytic effectiveness of single-atom catalysts in oxygen reduction reaction (ORR). Herein, Co, N-dual doped carbon (Co/NNC) is prepared by a versatile strategy of the combination approach of SiO 2 template with extra nitrogen source. Based on ZIF-67 prepared with the assistance of SiO 2 template, the extra nitrogen source was introduced in the high-temperature pyrolysis procedure. The material characterizations of XRD, SEM, HRTEM, BET, Raman and XPS are conducted to synthetically analyze the functional role of extra nitrogen source. Moreover, the Co/NNC with increased Co-N x active sites is employed into two aqueous metal-air batteries of Zn-air and Mg-air batteries, which exhibits excellent performances especially in the aspects of discharge specific capacity, discharge stability and power density. [Display omitted] 1 SiO 2 template and extra nitrogen source are combined to prepare Co/NNC. 2 Extra nitrogen source boosts the Co-N x content of Co/NNC derived from ZIF-67. 3 In aqueous metal-air batteries, Co/NNC shows superior capacity performance than Pt/C. [ABSTRACT FROM AUTHOR]

The ternary Co/SiO x /N-C catalyst is synthesized by a facile method and characterized by the 3D tomography technique, which is considered as oxygen electrocatalysts for rechargeable Zn-air batteries. • The utilization of biomass through simple and low-cost procedures is provided. • Well-dispersed cobalt nanoparticles are synthesized on the SiO x /N-C framework. • The structure has been characterized through 3D TEM tomography. • The framework enhances the catalytic activity and stability of the Co systems. • The Zn-air battery with a CR900 air catalyst shows cycling durability for 400 h. Well-dispersed cobalt nanoparticles (NPs) are synthesized on a silicon oxide/nitrogen-doped carbon framework derived from sustainable bamboo leaves through in situ pyrolysis of cobalt silicate/nitrogen-doped carbon. The three-dimensional (3D) transmission electron microscopy (TEM) tomography technique reveals the detailed distribution of Co NPs on the framework. The framework ensures a fine distribution, provides an interconnected conductive network, and improves the catalytic activity and stability of the ternary Co catalysts. Consequently, the optimized CR900 electrocatalyst exhibits superior electrochemical activity, including a low overpotential of 263 mV at 10 mA cm−2 and a half-wave potential of 0.81 V for OER and ORR, respectively. Furthermore, the Zn-air battery with the CR900 catalyst displays a maximum power density of 138.2 mW cm−2 and prominent cycling durability after 400 h. Furthermore, we provide insights into the scalable synthetic strategy of metal or alloy-based catalysts towards high-performance rechargeable metal-air batteries. [ABSTRACT FROM AUTHOR]

We outline the method for evaluation of the particle size distribution of the magnetic nanoparticles from the hysteresis loop measurements. We apply the method to study the ultrafine Co particles filling the porous silica gel matrix (SiO2). The influence of the technological conditions of the sample preparation onto particle size distribution function is demonstrated. [Copyright &y& Elsevier]

Exchange anisotropy was studied by SQUID magnetometry on an array of monodisperse colloidal nanoparticles consisting of a 7–8 nm diameter FCC Co core covered with a 2–2.5 nm thick FCC CoO shell. Temperature-dependent measurements of the exchange bias field show that the exchange anisotropy vanishes when a magnetic field was applied during cooling below 150 K. The suppression of exchange anisotropy is due to uncompensated interfacial antiferromagnetic spins. [Copyright &y& Elsevier]

Abstract: Magnetic properties and thermal stability of cobalt nanoparticles encapsulated in SiO2 prepared with the reversed micelle technique with various w were investigated. The average diameters of the Co nanoparticles and SiO2 capsules were about 2.9 and about 5.2nm. The magnetization curves of Co nanoparticles exhibit superparamagnetic nature. After annealing up to 673K in vacuum, the magnetization increases by a factor of 2.4 and the average diameter of the Co particles increases by a factor of 1.3, although shape and size of the SiO2 capsules were kept. [Copyright &y& Elsevier]