Size Dependence Of Nanoparticles Research Articles

Ultra small Gd 2O 3 nanoparticles: Absorption and emission properties

In this paper, we report a facile method for synthesis of ultra small (1–3 nm) gadolinium oxide (Gd 2O 3) nanoparticles using citric acid (CA) as a capping agent. The dependence of nanoparticle (NP) size on the ratio between CA and gadolinium (Gd) is investigated. Absorption properties of the ultra small Gd 2O 3 NPs in UV region have four characteristic peaks at 312 nm, 274 nm, 253 nm and 228 nm. Finally, we show that the Gd 2O 3 nanoparticles synthesized by this method induce triplet emission (phosphorescence) from CA and EG in the NIR region.

Studies on metal oxide nanoparticles catalyzed sodium aluminum hydride

This paper reports the catalytic activity of several metal oxide nanoparticles such as TiO2, CeO2, La2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3 and Gd2O3 for NaAlH4. TiO2 was found to be the most effective catalyst. In order to find the size dependence of TiO2 nanoparticles on the catalytic activity, TiO2 nanoparticles of different sizes such as 5 nm, 25 nm, 150 nm and 200 nm have been used. TiO2 nanoparticles lower the desorption temperature of sodium alanate (NaAlH4) from ∼ 473 K to ∼373 K. Using 5 nm and 25 nm TiO2 catalysts ∼3 wt% hydrogen could be released within 5–7 min at 423 K. TiO2 (25 nm) catalyst lowers the activation energy of NaAlH4 to 67 kJ/mol H2, as compared to 119 kJ/mol H2 for the pristine material. This is better than Ti nanoparticles catalyst of similar size which lowers the activation energy up to 77 kJ/mol H2. The long-term reversible characteristics of 25 nm TiO2 admixed NaAlH4 up to 35 cycles and the phase structural features of the cycled samples are discussed.

Origin of the size dependence of Au nanoparticles toward molecular oxygen dissociation

Density functional theory calculations using a plane-wave basis set and a generalized gradient approach exchange-correlation potential have been carried out to study the dissociation of molecular oxygen by Au nanoparticles and its dependence with particle size. The analysis of the energy related data shows that the reactivity is dominated by the energy barrier height from adsorbed O2 to the dissociated state and by the stability of molecular oxygen on the nanoparticle. The energy barrier is found to be only slightly dependent on the particles size where large variations are found for the adsorption energy of the O2 molecule on the different nanoparticles. A careful analysis of the electronic structure shows that the driving force for O2 adsorption by these nanoparticles is the existence of a clear gap between occupied and unoccupied states for the naked particle. This allows accommodating bonding states with O2 below the Fermi level resulting in a strong interaction. On the contrary, the Au nanoparticles with a more metallic electronic structure have necessarily to accommodate bonding and antibonding states below the Fermi level with a concomitant weaker interaction with O2.

Elementary processes at nanoparticulate photocatalysts

The paper is a mini review on the authors own work related to laser induced processes at metal nanoparticle/oxidic support systems. A number of aspects will be addressed ranging from the nano particle size dependence on the efficiency of the photochemical process, the influence of low coordination sites of the nano particles and dynamical processes such as energy transfer between adsorbates, light induced particle changes or spill over processes. The paper reviews nano and femtosecond laser experiments as well as quantum state resolved experiments. Results will be compared to typical findings from simple oxidic supports and metal single crystals. This review may be of interest for future photocatalyst development for applications such as solar fuel synthesis and related problems.

Damage production in nanoparticles under light ion irradiation

Modifying the properties of nanoparticles by ion irradiation leads to sputtering and defect production, possibly enhanced by the high surface-to-volume ratio of the irradiated objects. By molecular-dynamics simulations, we address the size dependence of platinum nanoparticles' response to light ion irradiation and show that in contrast to irradiation by heavier ions the sputtering yield does not depend on the particle size. In contrast, very high vacancy concentrations can be obtained in nanoparticles, the maximal concentration depending on the particle size. The evolution of vacancy concentration and sputtering upon irradiation are rationalized in terms of a kinetic model based on single knock-on events.

Non-Resonant Third-Order Nonlinearity of Nanometric and Subnanometric Silver Particles in Aqueous Solution

We have measured and analyzed the behavior of the nonlinear refractive index of silver spheres in water in a non-resonant femtosecond excitation regime. Two different diameter silver nanosphere (0.65 and 9 nm) suspensions were used in the experiments. Thermal and nonthermal contributions to the nonlinear properties of the samples were determined exploring a novel high sensitivity thermal managed eclipse Z-scan technique. The dependence of nonthermal third order nonlinear susceptibility of the colloid with the silver nanoparticles filling factor was described using the generalized Maxwell-Garnett model. The nanoparticle size dependence of the colloid nonlinear refractive index was observed.

Size Dependence of CuO Nanoparticles Synthesized by Wet Chemical Method

Copper Oxide nanoparticles with a particle size ranging from 80 nm-300 nm were prepared by a wet chemical procedure. Copper carbonate hydroxide and Sodium Hydroxide were used as raw materials. Copper hydroxide was generated as a precursor which was thermally decomposed to CuO nanoparticles. The size of the nanoparticles is directly proportional to the concentration of the copper carbonate hydroxide reagent. The nanoparticles were characterized using AFM, XRD and UV Vis Spectrometry.

Microwave dielectric properties of NiFe2O4 nanoparticles ferrites

AbstractNickel ferrite (NiFe2O4) was synthesized by the micelles mixing method, using lyophilized coconut oil. The method leads to the formation of ferrite nanoparticles. Nickel ferrite was prepared in coconut oil suspension and annealed during 4 h, at 400, 600, 800, 1000, and 1200°C. The X‐ray diffraction (XRD) was applied to investigate the nanoparticle size dependence on the annealing temperature. Complex permittivity measurements were carried out in cavity resonators at 5.0 and 9.0 GHz, using the small perturbation theory. The main result is that the real part of the permittivity decreases with increasing annealing temperatures (3.6–2.4), while the imaginary part of the permittivity varies only for the lowest annealing temperatures, remaining low for the other samples (about 10−3). The X‐ray diffractograms indicates that the nanoparticle size increase with annealing temperature, allowed the correlation between the nanoparticle size and the observed microwave dielectric response. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1341–1343, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22402

Resonance energy transfer from a fluorescent dye to a metal nanoparticle

A quantum mechanical theory of the rate of excitation energy transfer from a fluorescent dye molecule to the surface plasmonic modes of a spherical metal nanoparticle is presented. The theory predicts the distance dependence of the transfer rate to vary as 1/d(sigma), with sigma=3-4 at intermediate distances, in partial agreement with the recent experimental results. Förster's 1/d(6) dependence is recovered at large separations. The predicted rate exhibits nontrivial nanoparticle size dependence, ultimately going over to an asymptotic, a(3) size dependence. Unlike in conventional fluorescence resonance energy transfer, the orientational factor is found to vary between 1 and 4.

Size dependence, nucleation, and phase transformation of FePt nanoparticles

Monolayers of chemically prepared FePt nanoparticles were deposited on silicon nitride membrane windows, and annealed under different conditions. Hysteresis loops showed a bimodal distribution of switching fields. The size dependence determined from transmission electron microscopy was correlated with the magnetic switching field distribution, assuming that all particles above a threshold size d* had high anisotropy. This simplified model yielded a common value of d*, independent of the annealing conditions. The dependence of d* on the initial particle size indicated the importance of grain boundaries as nucleation sites, and supports the hypothesis that the fcc-to-fct phase transformation is kinetically limited.

Dynamic susceptibility investigation of biocompatible magnetic fluids: The surface coating effect

In this study room-temperature dynamic susceptibility measurements were used to investigate magnetite nanoparticles surface-coated with dextran and dimercaptosuccinic acid, both dispersed as biocompatible magnetic fluids. Multicomponent susceptibility curves were associated with the presence of monomers and dimers in the sample. Transmission electron microscopy data have been used to support the analysis carried out with the susceptibility data. The field dependence of the peak position of the imaginary component of the dynamical susceptibility was analyzed within the picture of an asymmetric double-well potential for the relaxation of the magnetic moment associated with the magnetite nanoparticle. The nanoparticle size dependence of the susceptibility peak position was taken into account in the data analysis. Nanoparticle-size parameters obtained from the analysis of the susceptibility data of the two samples (3.7 and 6.1nm) are in very good agreement with the values obtained from the fitting of the electron microscopy data (3.1 and 5.6nm).

Transdermal delivery of mixnoxidil with block copolymer nanoparticles

We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration of minoxidil in vitro and in vivo. Self-assembled 40- and 130-nm nanoparticles, both containing minoxidil, were prepared by solvent evaporation of poly(ε-caprolactone)-block-poly(ethyleneglycol) and were applied onto the skin of both hairy and hairless guinea pigs in the Franz diffusion cell. In hairy guinea pig skin, the permeation of the minoxidil that incorporated in 40-nm nanoparticles was 1.5-fold higher in the epidermal layer and 1.7-fold higher in the receptor solution than that of 130-nm nanoparticles. Nanoparticle size dependence on the permeation behavior of minoxidil was not observed for hairless guinea pig skin in either the epidermal layer or the receptor solution. Phospholipid liposomes and ethanol–water admixture, on the other hand, containing the same amount of minoxidil did not show differences in the amount of permeation irrespective of the existence of hair follicles. Confocal microscopy coupled with in vivo and in vitro skin permeation results demonstrated that nanoparticles containing solutes penetrated mainly via shunt routes like hair follicles, resulting in skin absorption of solutes.

Transdermal delivery of mixnoxidil with block copolymer nanoparticles

We evaluated the effect of hydrodynamic size of self-assembled nanoparticles on skin penetration of minoxidil in vitro and in vivo. Self-assembled 40- and 130-nm nanoparticles, both containing minoxidil, were prepared by solvent evaporation of poly(ε-caprolactone)-block-poly(ethyleneglycol) and were applied onto the skin of both hairy and hairless guinea pigs in the Franz diffusion cell. In hairy guinea pig skin, the permeation of the minoxidil that incorporated in 40-nm nanoparticles was 1.5-fold higher in the epidermal layer and 1.7-fold higher in the receptor solution than that of 130-nm nanoparticles. Nanoparticle size dependence on the permeation behavior of minoxidil was not observed for hairless guinea pig skin in either the epidermal layer or the receptor solution. Phospholipid liposomes and ethanol–water admixture, on the other hand, containing the same amount of minoxidil did not show differences in the amount of permeation irrespective of the existence of hair follicles. Confocal microscopy coupled with in vivo and in vitro skin permeation results demonstrated that nanoparticles containing solutes penetrated mainly via shunt routes like hair follicles, resulting in skin absorption of solutes.

Nanoparticles produced by laser ablation of solids in liquid environment

The formation of Ti, Si, Ag and Au nanoparticles under laser ablation of metal targets in liquid environment (H 2O, C 2H 5OH, C 2H 4Cl 2) is reported. The use of a high-repetition-rate Cu vapor laser (wavelength 510.5 nm, pulse duration 20 ns, repetition rate 15 kHz) allows high rate of nanoparticles formation as a sol. The nanoparticles are characterized by X-ray diffraction (XRD), UV–visible transmission spectrometry, high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). The nanoparticle size dependence on both the laser fluence and the nature of the liquid is studied. In some cases, nanoparticles of compounds are formed via reaction of the metal with the liquid.