Transition particle size dependence

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Fig. 4.35. Particle size-dependent bistability and hysteresis. On model system I (500-nm EBL-fabricated particles), the CO oxidation shows a perfectly stable bistability behavior. On the time scale accessible by the experiment (>10 s), we can arbitrarily switch between the two states by pulsing either pure CO or O2 (a and d). For the model system II (6-nm particles), a very slow transition toward a single global state is observed in the transition region between the CO- and O-rich reaction regimes (b and e). This behavior is assigned to fluctuation-induced transitions, which are accelerated by the presence of defect sites. For the smallest particles of the model system III (1.8 nm), a globally monostable kinetics is rapidly established under all conditions (c and f). For all experiments, the total flux of CO and O2 beams at the sample position was equivalent to a local pressure of 10" Pa. The surface temperature in (a-c) was 400 K and in (d-f) 415 K (from [147])...

Optical properties of copper nanoparticles are quite remarkable because the energy of the dipolar mode of surface collective electron plasma oscillations (surface plasmon resonance or SPR) coincides with the onset of interband transition. Therefore, optical spectroscopy gives an opportunity to study the particle-size dependence of both valence and conduction electrons. The intrinsic size effect in metal nanoparticles, caused by size and interface damping of the SPR, is revealed experimentally by two prominent effects a red shift of the surface plasmon band and its broadening. 

The dichroism in natural fibers with incorporated metal nanoparficles was found to depend strongly not oidy on the element employed [50] but also on the particle size [51], which was calculated from the full-width at half-maximum of X-ray diffraction patterns, yielding values between 5 and 14 nm in ramie, hemp, bamboo, silk, viscose silk, acetate rayon, and wool fibers [51]. As an example of a particle-size-dependent dichroism, a color transition between perpendicular and parallel orientation of polarization plane and long fiber axis in ramie fibers appeared from straw yellow to indigo blue for gold particles of 8.5-nm diameter and from claret red to green at 12.3-nm diameter [51]. 

As illustrated in Figure 10.28 in heterogeneous catalysis for nanosized metal particles, one distinguishes three types of transition-metal particle-size-dependent behavior. When activation of a-type CH bonds is rate controlhng, the rate of reaction normalized per surface atom, TOF (turn over frequency) tends to increase with a decrease in particle size. This is the behavior according to curve II. It is due to the relative increase in the fraction of more reactive coordinatively unsaturated surface atoms. 

Figure 7.1. The influence of particle size on property (a) The transition temperature of zirconia particles between the monoclinic and the tetragonal modification. There is a considerable hysteresis and the transition temperature drops with particle size, (b) The size dependence of the lattice constant of iron particles, (c) The particle size dependence of the melting point of a few metals. Their bulk melting points are given at the right-hand side of the graph.

To test this hypothesis of particle size dependent reduction rates, the Cu L3M4,5M4,5 XAES regions were examined before and after exposure of the substrates to the soft X-rays. Figure 16B shows Auger spectra of the Cu L3M4,5M4,5 transition of 0.010 M and 0.0040 M Cu(ac)2 prepared surfaces corresponding to the largest and smallest CuO particle sizes, respectively. Spectra a of both samples were taken immediately after initial X-ray irradiation and b after 50 additional min of exposure to... 

Transition metal nitrate hydrates are industrially favored precursors for the preparation of supported metal (oxide) catalysts because of their high solubility and facile nitrate removal. The final phase and particle size depend on the experimental conditions, as reported for both supported and unsupported metal nitrates [1-3]. Several authors report that decreasing the water partial pressure during the decomposition of unsupported nickel nitrate hexahydrate, via vacuum or a high gas flow, increases the final NiO surface area [3, 4], The low water partial pressure results in dehydration of the nickel nitrate hydrate to anhydrous nickel nitrate followed by decomposition to NiO. Decomposition at higher particle pressures, however, occitrred through the formation of intermediate nickel hydroxynitrates prior to decomposition to NiO. Thus, NiO obtained via intermediate nickel hydroxynitrate species showed a poorer siuface area (1 m /g) compared to NiO obtained via anhydrous nickel nitrate species (10 mVg) [4]. 

Experimentally, tire hard-sphere phase transition was observed using non-aqueous polymer lattices [79, 80]. Samples are prepared, brought into the fluid state by tumbling and tlien left to stand. Depending on particle size and concentration, colloidal crystals tlien fonn on a time scale from minutes to days. Experimentally, tliere is always some uncertainty in the actual volume fraction. Often tire concentrations are tlierefore rescaled so freezing occurs at ( )p = 0.49. The widtli of tire coexistence region agrees well witli simulations [Jd, 80]. 

Rate of polymerization. The rate of polymerization for homogeneous systems closely resembles anionic polymerization. For heterogeneous systems the concentration of alkylated transition metal sites on the surface appears in the rate law. The latter depends on the particle size of the solid catalyst and may be complicated by sites of various degrees of activity. There is sometimes an inverse relationship between the degree of stereoregularity produced by a catalyst and the rate at which polymerization occurs. 

A classical issue in transition-metal catalysis is the dependence of catalytic activity on changes in the particle size of the metal clusters in the nanosize region [14]. 

The size-dependent features of the electronic structure have been explored, with special emphasis on the evolution of the valence band DOS of transition and noble metals as the particle size increases. 

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