Understanding the growth of Eu(2)O(3) nanocrystal films made via electrophoretic deposition

Quantitatively controlled electrophoretic deposition of nanocrystal films from non-aqueous suspensions

This study presents a novel method to correlate the mass and charge transfer kinetics during the electrophoretic deposition of nanocrystal films by using a purpose-built double quartz crystal microbalance combined with simultaneous current-measurement. Our data support a multistep process for film formation: generation of charged nanocrystal flux, charge transfer at the electrode, and polarization of neutral nanocrystals near the electrode surface. The polarized particles are then subject to dielectrophoretic forces that reduce diffusion away from the interface, generating a sufficiently high neutral particle concentration at the interface to form a film. The correlation of mass and charge transfer enables quantification of the nanocrystal charge, the fraction of charged nanocrystals, and the initial sticking coefficient of the particles. These quantities permit calculation of the film thickness, providing a theoretical basis for using concentration and voltage as process parameters to grow films of targeted thicknesses.

Survival and reduction in foodborne bacteria using methyl cellulose film doped with europium oxide nanoparticles

The study validated the efficacy of methyl cellulose films doped with different concentration of Eu2O3 nanoparticles to inactivate foodborne pathogens. Eu2O3 nanoparticles were added to the methyl cellulose solution with different weight percentages (0.0, 0.5, 0.75, 1.0, 1.25, and 1.5 wt%). X-ray diffraction patterns for the prepared films were studied. A significant lower count of E. coli, S. typhimurium, and S. aureus (p ≤ .05) inoculated in MC films doped with Eu2O3 nanoparticles compared with pure MC film could be achieved. The findings acquired verify the impact of prepared MC films doped with Eu2O3 nanoparticles on the test strains.

Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties

Monoclinic-type tetragonal LaPO₄ :Eu (core) and LaPO₄ :Eu@LaPO₄ (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO₄ and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications.

Effect of surface coating on optical properties of Eu(3+)-doped CaMoO4 nanoparticles

A simple polyol method has been used for the synthesis of CaMoO4:Eu (core), CaMoO4:Eu@CaMoO4 (core/shell) and their silica coated CaMoO4:Eu@CaMoO4 (core/shell/shell) nanoparticles. X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), UV/Vis absorption and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. XRD patterns and FT-Raman spectra showed that these nanoparticles have a scheelite-type tetragonal structure without the presence of deleterious phases. These nanoparticles were easily dispersed in water, producing a transparent colloidal solution. The optical energy band-gap decreases after core/shell formation due to increase the crystalline size. The photoluminescence (PL) spectra of the as-synthesized core, core/shell and core/shell/shell nanoparticles measured with an excitation source wavelength of 325nm showed that the emission intensity was increases after shell formation around the surface of core nanoparticles.

Toward dynamic control over TiO2 nanocrystal monolayer-by-monolayer film formation by electrophoretic deposition in nonpolar solvents

The controlled electrophoretic deposition of monolayers and ultrathin films of 4.0 nm TiO(2) nanocrystals from stable, nonpolar solvent-based suspensions is reported. Stable suspensions were prepared in hexane, and the electrophoretic mobility of the nanocrystals was enhanced by a combination of a liquid-liquid extraction followed by mechanical surfactant removal by high-speed centrifugation. The controlled evolution of the density of TiO(2) nanocrystal monolayers was studied by transmission electron microscopy and optical transmittance spectroscopy. Ultrathin films were assembled while maintaining monolayer-by-monolayer growth and uniform density of the film. A time-dependent, equivalent circuit model has been proposed to characterize the electrophoretic current that was recorded during our experiments. Further, we demonstrate that the proposed model, coupled with the mobility, provides a means to estimate the deposition rate and, hence, the time necessary to fabricate a submonolayer, a monolayer, and multilayers of nanocrystals.

Transferable graphene oxide films with tunable microstructures

This report describes methods to produce large-area films of graphene oxide from aqueous suspensions using electrophoretic deposition. By selecting the appropriate suspension pH and deposition voltage, films of the negatively charged graphene oxide sheets can be produced with either a smooth "rug" microstructure on the anode or a porous "brick" microstructure on the cathode. Cathodic deposition occurs in the low pH suspension with the application of a relatively high voltage, which facilitates a gradual change in the colloids' charge from negative to positive as they adsorb protons released by the electrolysis of water. The shift in the colloids' charge also gives rise to the brick microstructure, as the concurrent decrease in electrostatic repulsion between graphene oxide sheets results in the formation of multilayered aggregates (the "bricks"). Measurements of water contact angle revealed the brick films (79°) to be more hydrophobic than the rug films (41°), a difference we attribute primarily to the distinct microstructures. Finally, we describe a sacrificial layer technique to make these graphene oxide films free-standing, which would enable them to be placed on arbitrary substrates.