246 research outputs found
Reversing Ostwald Ripening
The phenomenon of Ostwald Ripening is generally considered a limiting factor
in the monodisperse production of nanoparticles. However, by analysing the free
energy of a binary AB solution with precipitated A particles we show that there
is a region in the parameter space of component concentrations and interaction
energies where smaller particles are more stable than bigger ones. The strong
binding of B species to surfaces of A particles significantly decreases the
particle effective surface energy, making it negative. The global minimum of
free energy in such a system is thus reached when mass is transferred from
bigger particles to the smaller ones, such that all particles become identical
in size. The process of mass transfer is opposite to Ostwald ripening, and can
be used for generating monodisperse arrays of nanoparticles.Comment: 11 pages and 4 figures of the main text plus 4 pages and 1 figure
supporting materia
Hyperstoichiometric Interaction Between Silver and Mercury at the Nanoscale**
Breaking through the stoichiometry barrier: As the diameter of silver particles is decreased below a critical size of 32?nm, the molar ratio of aqueous HgII to Ag0 drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1 (see figure). Therein, around 99?% of the initial silver is retained to rapidly form a solid amalgam with reduced mercury
Silver activation on thin films of Ag-ZrCN coatings for antimicrobial activity
Nowadays, with the increase of elderly population and related health problems, knee and hip joint prosthesis are being widely used worldwide. However, failure of these invasive devices occurs in a high percentage thus demanding the revision of the chirurgical procedure. Within the reasons of failure, microbial infections, either hospital or subsequently-acquired, contribute in high number to the statistics. Staphylococcus epidermidis (S. epidermidis) has emerged as one of the major nosocomial pathogens associated with these infections. Silver has a historic performance in medicine due to its potent antimicrobial activity, with a broad-spectrum on the activity of different types of microorganisms. Consequently, the main goal of this work was to produce Ag-ZrCN coatings with antimicrobial activity, for the surface modification of hip prostheses.
Thin films of ZrCN with several silver concentrations were deposited onto stainless steel 316 L, by DC reactive magnetron sputtering, using two targets, Zr and Zr with silver pellets (Zr + Ag target), in an atmosphere containing Ar, C2H2 and N2. The antimicrobial activity of the modified surfaces was tested against S. epidermidis and the influence of an activation step of silver was assessed by testing samples after immersion in a 5 % (w/v) NaClO solution for 5 minutes.
The activation procedure revealed to be essential for the antimicrobial activity, as observed by the presence of an inhibition halo on the surface with 11 at. % of Ag. The morphology analysis of the surface before and after the activation procedure revealed differences in silver distribution indicating segregation/diffusion of the metallic element to the films surface.
Thus, the results indicate that the silver activation step is responsible for an antimicrobial effect of the coatings, due to silver oxidation and silver ion release.IF acknowledges the financial support of FCT-Fundacao para a Ciencia e a Tecnologia through grant SFRH/BD/71139/2010.This research is partially sponsored by FEDER funds through the program COMPETE-Programa Operacional Factores de Competitividade and by Portuguese national funds through FCT-Fundacao para a Ciencia e a Tecnologia, under the projects ANTIMICROBCOAT-PTDC/CTM/102853/2008 and in the framework of the Strategic Projects PEST-C/FIS/UI607/2011, and PEST-C/EME/UI0285/2011.The authors thank the FCT Strategic Project PEST-OE/EQB/LA0023/2013 and the Project "BioHealth-Biotechnology and Bioengineering approaches to improve health quality", Ref. NORTE-07-0124-FEDER-000027, co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER. The authors also acknowledge the project "Consolidating Research Expertise and Resources on Cellular and Molecular Biotechnology at CEB/IBB", Ref. FCOMP-01-0124-FEDER-027462
Uptake of Toxic Metal Ions from Water by Naked and Monolayer Protected Silver Nanoparticles: An X-ray Photoelectron Spectroscopic Investigation
where MSA is mercaptosuccinic acid). The particles were of 30 and 8 nm diameter, respectively. We observed that the metal ions interact with both the core of the nanoparticles and the functional groups of the capping agents. We study the effects of interaction using spectroscopic and microscopic techniques such as ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffractio
Facile and Rapid Synthesis of a Dithiol-Protected Ag<sub>7</sub> Quantum Cluster for Selective Adsorption of Cationic Dyes
We report a facile and rapid (less
than 15 min) synthesis of atomically
precise, dithiol-protected, silver quantum cluster, Ag<sub>7</sub>(DMSA)<sub>4</sub> (DMSA: meso-2,3-dimercaptosuccinic acid), through
a modified solid state route. The as-synthesized cluster exhibits
molecular optical absorption features with a prominent λ<sub>max</sub> at ∼500 nm. Composition of the cluster was confirmed
using various spectroscopic and microscopic techniques such as electrospray
ionization mass spectrometry (ESI MS), X-ray photoelectron spectroscopy
(XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy
(FTIR), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), and energy dispersive analysis of X-rays (EDAX).
Clusters supported on neutral alumina have been shown as better adsorbents
for selective adsorption of cationic dyes (over anionic dyes) from
water. This selectivity for cationic dyes was evaluated by zeta potential
(ζ) measurements. The efficiency of clusters for removal of
dyes is very high when compared to nanoparticles (NPs) protected with
ligands (citrate and mercaptosuccinic acid (MSA)) possessing similar
chemical structures as that of DMSA. The higher efficiency of clusters
for the removal of dyes is attributed to their smaller size and large
surface area compared to the NPs in addition to favorable electrostatic
interactions between the clusters and cationic dyes. Adsorption of
dyes (cationic and anionic) was enhanced when dye molecules contain
hydrogen bond forming functional groups. Supported clusters have been
reused up to five cycles without the loss of activity once the adsorbed
dye is extracted using suitable solvents
- …