Supported Ag catalysts on silica and corundum have been synthesized applying an improved impregnation technique. The resulting Ag particle sizes can be divided into three categories concerning: (I) ...bulk-like, (II) nanoparticles of 1–6 nm, and (III) in situ created Ag clusters below 1 nm. Ag nanoparticles and bulk-like Ag are investigated concerning their pretreatment dependence for CO oxidation showing that harsher pretreatment conditions need to be applied for smaller particle sizes, based on their tendency to form Ag2CO3. A particle size effect for Ag in oxidation reactions is investigated using CO oxidation as a test reaction. The CO oxidation performance is increasing with decreasing particle size with Ag clusters showing the highest activity. A novel method based on the adsorption of ethylene (C2H4) as sensor molecule is further used to discriminate the silver–oxygen (Ag–O) interaction strength of bulk-like Ag, Ag nanoparticles, and Ag clusters, showing a distinct Ag–O chemistry for the three individual particle size regimes. By application of C2H4 breakthrough curve measurements, the available Ag surface area is determined which enables a correlation of Ag surface area and CO oxidation rate. Correlations of Ag–O interaction strength, Ag surface area, and CO oxidation activity are discussed within the scope of this work.
This account article treats with spatially non-uniform degradation events of Pt/C cathode catalysts in polymer electrolyte fuel cells involving the formation and dissolution of positively charged Pt ...ions and detachment of metallic Pt nanoparticles/clusters, which were visualized by the same-view nano XAFS and STEM-EDS imaging technique under humid N
2
atmosphere.
AuPt nanoparticles clusters (NPCs) were electrodeposited on multiwalled carbon nanotubes (MWCNTs). The as-prepared AuPt NPCs@MWCNTs nanocomposites exhibited considerably enhanced electrocatalytic ...activity than Pt NPs@MWCNTs for methanol oxidation in acid medium. In comparison with Pt NPs@MWCNTs, a remarkable resistance to CO poisoning and a higher If/Ib value (the ratio of the forward scan oxidation peak current (If) and reverse scan oxidation peak current (Ib)) was achieved by AuPt NPCs@MWCNTs electrocatalyst, which is attributable to the unique NPCs nanostructure with enlarged electrochemical active surface areas. These results demonstrated the potential of AuPt NPCs@MWCNTs, which can be considered as an efficient electrocatalyst for methanol oxidation in direct methanol fuel cells.
The scope of Wurtz coupling and catalytic dehydrocoupling methods for the synthesis of functional polysilanes of compositions, RR’Si
n
(linear), (PhMeSi)
x
-co-(RSi)
1 − x
n
(branched) and RSi
n
...(network) R = Et
3
SiCH
2
CH
2
, 2-Fu/2-ThMe
2
SiCH
2
CH
2
(Fu = Furyl, Th = Thienyl),
n
-Hex or Ph; R’ = H or Me is presented. By virtue of
σ
-delocalized silicon backbone and variable HOMO–LUMO band gap energies, these polymers are found to be promising candidates as reducing agents for Ag(I) ions in toluene/
cyclo
-hexane and provide a simple approach for ‘size-controlled’ synthesis of silver nanoparticles (AgNPs) as well as fluorescent polymer–silver nanocomposites.
Graphical Abstract
Synthetic methods for a few linear, branched and network polysilanes bearing thienyl/furyl substituted sila–alkyl side chains are described. These polymers are useful precursors for
in situ
reduction of Ag(I) ions and afford stable polymer–silver nanoassemblies with control over the size domains. Photoluminescence properties of these nanoassemblies are also reported.
CuO nanostructures materials were prepared by thermal process using carbon charcoal assisted. The copper powder and copper sheet were mixed and covered with carbon charcoal. The starting materials ...and Si substrates were put in the furnace and heated at various temperatures under atmosphere of nitrogen gas. The prepared products were characterized by scanning electron microscope and X-ray diffraction technique and then studying for changing of the electrical resistance with temperature. The results revealed that the nanostructures of material consisting of CuO and Cu2O phase and the electrical resistance was changed with temperature.
We report a theoretical discussion on the magnetocaloric effect (MCE) of ferromagnetic Gd nanoparticles arranged in large eccentricity ellipsoidal clusters. We focus on micrometer-sized clusters of ...uniformly packed Gd nanoparticles, with the external field parallel to the major axis of the ellipsoidal cluster. We have replicated the bulk results for small nanoparticle spatial density. However, for large nanoparticle density, the MCE is strongly influenced by the nanoparticle's dipolar interaction. At low temperatures, the dipolar field strengths can reach a few Teslas, and there are two distinct regimes. For high external field strengths, the MCE is normal, and the dipolar interaction causes an up-shift of the temperature for the peak of the isothermal entropy change Δ S . For low external field strengths, the MCE is normal for temperatures above the cluster Curie temperature. In contrast, we found an inverse MCE for low temperatures due to the nucleation of an antiferromagnetic pattern, where neighboring lines along the ellipsoid major axis are magnetized in opposite directions.
In this paper, a core–shell nanocomposite of clusters of superparamagnetic iron oxide nanoparticles coated with poly(dopamine) (SPION clusters@PDA) is fabricated as a magnetic field-directed ...theranostic agent that combines the capabilities of highly sensitive magnetic resonance imaging (MRI) and photothermal cancer therapy. The highly concentrated SPION cluster core is suitable for sensitive MRI due to its superparamagnetic properties, and the poly(dopamine) coating layer can induce cancer cell death under near-infrared (NIR) laser irradiation because of the photothermal conversion ability of PDA. MRI scanning reveals that the nanocomposite has relatively high r2 and r2(*) relaxivities, and the r2(*) values are nearly threefold higher than the r2 values because of the clustering of the SPIONs in the nanocomposite core. Due to the rapid response to magnetic field gradients, enhanced cellular uptake of our nanocomposite mediated by an external magnetic field can be achieved, thus producing significantly enhanced local photothermal killing efficiency against cancer cells under NIR irritation.
FePt nanoparticles (NPs) and colloidal nanoparticle clusters (CNCs) have been synthesized by the reduction of platinum acetylacetonate (Pt(acac)
2
) combined with thermal decomposition of iron ...pentacarbonyl (Fe(CO)
5
) and compared to pure Pt NPs and CNCs for the catalytic activity of the oxygen reduction (ORR). The formation of NPs and CNCs has been carried out controlling injection temperature of the precursors and the surfactants during the synthesis. The size of the NPs and the CNCs formed is around 3 and 38 nm, respectively. High electrocatalytic performance of the FePt CNCs in comparison with that of nanoparticles and nanocluster of platinum has been obtained for the reduction reaction (ORR) in basic medium. The ORR is carried out by a four-electron charge transfer. The increase in the activity of the CNC structures formed by FePt nanoparticles can be attributed to the alloy formation that produces surface and electronic changes of the Pt atoms and to the structure of the CNCs obtained.
Graphical Abstract
Polarization curves of (a) CNCs FePt, (b) NPs FePt, (c) CNCs Pt, and (d) NPs Pt and their morphology.
We report a theoretical discussion on the magnetocaloric effect (MCE) of ferromagnetic Gd nanoparticles arranged in large eccentricity ellipsoidal clusters. We focus on micrometer-sized clusters of ...uniformly packed Gd nanoparticles, with the external field parallel to the major axis of the ellipsoidal cluster. We have replicated the bulk results for small nanoparticle spatial density. However, for large nanoparticle density, the MCE is strongly influenced by the nanoparticle's dipolar interaction. At low temperatures, the dipolar field strengths can reach a few Teslas, and there are two distinct regimes. For high external field strengths, the magnetocaloric effect is normal, and the dipolar interaction causes an up-shift of the temperature for the peak of the isothermal entropy change \Delta S , For low external field strengths, the MCE is normal for temperatures above the cluster Curie temperature. In contrast, we found an inverse MCE for low temperatures due to the nucleation of an antiferromagnetic pattern, where neighboring lines along the ellipsoid major axis are magnetized in opposite directions.
PDF
