Surface Effects In Nanoparticles Research Articles

Tertiary amine ionic liquid incorporated Fe3O4 nanoparticles as a versatile catalyst for the Knoevenagel reaction

In order to develop a functional ionic liquid catalyst with good stability and excellent catalytic effect on the organic reactions under alkaline conditions, a magnetic nanocatalyst of tertiary amine ionic liquid incorporated Fe3O4 was prepared and applied in the Knoevenagel reaction, the catalyst exhibits good stability and excellent catalytic performance in the Knoevenagel reaction, short reaction time and excellent yields of Knoevenagel products were obtained. In addition, the catalyst can be separated rapidly under the external magnetic force and reused for 8 times without significant loss of activity. Through the activity comparison of the catalyst and the FTIR, XRD, TG, VSM, SEM, TEM, and BET analysis, the excellent catalytic effect of the catalyst may be attributed to the synergistic effect of the catalytic action of tertiary amine, ionic liquid structure and the small size and strong surface effect of nanoparticles.

Ratiometric Afterglow Nanothermometer for Simultaneous in Situ Bioimaging and Local Tissue Temperature Sensing

Simultaneous in situ bioimage tracing and temperature sensing have been two of the foci of modern biomedicine that have given birth to designing novel luminescent nanothermometers with dual functions. To minimize the disadvantages of existing approaches, like the surface effect of nanoparticles, autofluorescence, and/or the thermal effect described herein, a bifunctional (simultaneous in vivo bioimaging and local tissue temperature sensing) ratiometric afterglow nanothermometer has been realized in the physiological temperature range (298–325 K) based on persistent luminescent Cr3+ (with d electron configuration)-doped zinc gallogermanate nanoparticles. The contributions of the radiative 2E → 4A2 and 4T2 → 4A2 transitions of surface and interior Cr3+ to the near-infrared afterglow dual emissions are modeled, and the measured thermal sensitivities (0.043–0.047 K–1) for detecting the temperature of a human serum albumin solution are 1 order of magnitude higher than those using an upconverting luminescent na...

Surface effect induced Cu-Cu bonding by Cu nanosolder paste

Based on surface effect of nanoparticles, excellent Cu-Cu bonding was achieved by sintering of Cu nanosolder paste. The surface melting behavior of nanoparticles and the bonding process was investigated at the temperature of 250°C to 400°C under the protection of Argon/Hydrogen gas mixtures. The antioxidative Cu nanoparticles were synthesized with high yield by an efficient method for the preparation of solder paste. The bonding achieved by thermo-compression shows great tolerance to experimental environment and the roughness of bonding substrates. The largest shear strength in this study could exceed 35MPa, which is suitable for high-density packaging of three-dimensional integrated circuits.

A single-molecule approach to ZnO defect studies: Single photons and single defects

Investigations that probe defects one at a time offer a unique opportunity to observe properties and dynamics that are washed out of ensemble measurements. Here, we present confocal fluorescence measurements of individual defects in ZnO nanoparticles and sputtered films that are excited with sub-bandgap energy light. Photon correlation measurements yield both antibunching and bunching, indicative of single-photon emission from isolated defects that possess a metastable shelving state. The single-photon emission is in the range of ∼560–720 nm and typically exhibits two broad spectral peaks separated by ∼150 meV. The excited state lifetimes range from 1 to 13 ns, consistent with the finite-size and surface effects of nanoparticles and small grains. We also observe discrete jumps in the fluorescence intensity between a bright state and a dark state. The dwell times in each state are exponentially distributed and the average dwell time in the bright (dark) state does (may) depend on the power of the exciting laser. Taken together, our measurements demonstrate the utility of a single-molecule approach to semiconductor defect studies and highlight ZnO as a potential host material for single-defect based applications.

Supported Ag nanoparticles as trace iodide adsorbent from acetic acid

Ag nanoparticles (AgNPs) were used as adsorbent to remove trace iodide from acetic acid. Under identical conditions, AgNPs adsorbent with 0.5 wt % Ag has the same performance as commercial adsorbent with 10 wt % Ag+. In addition, Ag loss of AgNPs adsorbent is remarkably lower than that of commercial adsorbent. The Ag content in AgNPs adsorbent affects its adsorption performance, and the optimal content is 1.0 wt %. Saturated AgNPs adsorbent can be regenerated by hydrogen reduction and reused with satisfying performance. The properties of AgNPs adsorbent are based on surface effect of nanoparticles, differing from commercial Ag+ type adsorbents. In a word, AgNPs adsorbent is of high efficiency, low Ag loss and easy recycling, thus making it “green adsorbent” for removing iodide from acetic acid.

In vitro biological effects of magnetic nanoparticles

Magnetic nanoparticles (MNPs) have great potential for a wide use in various biomedical applications due to their unusual properties. It is critical for many applications that the biological effects of nanoparticles are studied in depth. To date, many disparate results can be found in the literature regarding nanoparticle-biological factors interactions. This review highlights recent developments in this field with particular focuses on in vitro MNPs-cell interactions. The effect of MNPs properties on cellular uptake and cytotoxicity evaluation of MNPs were discussed. Some employed methods are also included. Moreover, nanoparticle-cell interactions are mediated by the presence of proteins absorbed from biological fluids on the nanoparticle. Many questions remain on the effect of nanoparticle surface (in addition to nanoparticle size) on protein adsorption. We review papers related to this point too.

Influence of Nano-CaCO<sub>3</sub> on Mechanical Property of PALC

The influence of Nano- CaCO3 on the mechanical property of PALC was studied in the paper. And the mechanism of Nano- CaCO3 modified cement-based materials was also discussed by means of X-ray diffraction and SEM. The results shows that the PALC with 2% of added Nano-CaCO3 by weight of cement has an optimum splitting strength, in which the increase of splitting strength are about 15.2%,20.4% and 19.7% at 3days,7days and 28 days. The reasons for causing the above results are because Nano-CaCO3’s filling effect of micro-particle, surface effect of nano-particles as well as micro-nucleus effect.

Stoichiometry of BaTiO3 nanoparticles

Barium titanate nanoparticles with various nominal Ba/Ti ratios were prepared through direct synthesis from solution (DSS) and further annealed at different temperatures. Their deviation from stoichiometry was studied through XRD analysis, and a large deviation from stoichiometry has been observed. The grain size we studied ranges from 50 nm to 1 μm. For the as-prepared particles, the grain size is about 50 nm, and the maximum excess of Ti is over 15%. For the samples annealed at 800 °C, the grain size is increased to 100 nm, and the maximum excesses of Ba and Ti are 8 and 9%, respectively. The defects formed during synthesis and surface effect of nanoparticles are both estimated for their contributions to the deviation from stoichiometry, and the defects have been found to be mainly responsible for the large deviation observed.

Transparent magnetic composites of ZnFe2O4 nanoparticles in silica

Uniformly dispersed zinc ferrite nanoparticles were successfully synthesized in a silica matrix with both the magnetic properties and optical transparency designed in the visible wavelength region. The phases and morphologies of these zinc ferrite particles were examined using x-ray diffraction, Raman spectroscopy and transmission electron microscopy. A much lower formation temperature of ZnFe2O4 in nanocomposites was observed in this study compared to in conventional ceramic processing. The particle size of zinc ferrite was found to vary with the initial drying temperature, suggesting that a well-established silica network provides more confinement to the growth of ZnFe2O4 particles. The magnetic properties, measured at both 78 K and room temperature, exhibit strong dependence on the particle size, and are related to the unusual cation distribution and the surface effect of nanoparticles. The optical properties of the nanocomposites can be adjusted by varying the concentration of the zinc ferrite nanoparticles. Their absorption coefficient remains below 400 cm−1 in the red visible light region.

Finite-size versus surface effects in nanoparticles

We study the finite-size and surface effects on the thermal and spatial behaviours of the magnetisation of a small magnetic particle. We consider two systems: (1) A box-shaped particle of simple-cubic structure with either periodic or free boundary conditions. This case is treated analytically using the isotropic model of D-component spin vectors in the limit D→∞, including the magnetic field. (2) A more realistic particle (γ-Fe 2O 3) of ellipsoidal (or spherical) shape with open boundaries. The magnetic state in this particle is described by the anisotropic classical Dirac–Heisenberg model including exchange and dipolar interactions, and bulk and surface anisotropy. This case is dealt with by the classical Monte Carlo technique.

Surface effects in nanoparticles: application to maghemite -Fe O

We present a microscopic model for nanoparticles, of the maghemite ($\gamma $% -Fe$_{2}$O$_{3}$) type, and perform classical Monte Carlo simulations of their magnetic properties. On account of M\"{o}ssbauer spectroscopy and high-field magnetisation results, we consider a particle as composed of a core and a surface shell of constant thickness. The magnetic state in the particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions and bulk and surface anisotropy. We consider the case of ellipsoidal (or spherical) particles with free boundaries at the surface. Using a surface shell of constant thickness ($\sim 0.35$ nm) we vary the particle size and study the effect of surface magnetic disorder on the thermal and spatial behaviors of the net magnetisation of the particle. We study the shift in the surface ``critical region'' for different surface-to-core ratios of the exchange coupling constants. It is also shown that the profile of the local magnetisation exhibits strong temperature dependence, and that surface anisotropy is reponsible for the non saturation of the magnetisation at low temperatures.