80 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
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
Understanding the Degradation Pathway of the Pesticide, Chlorpyrifos by Noble Metal Nanoparticles
Application of nanoparticles (NPs) in environmental remediation
such as water purification requires a detailed understanding of the
mechanistic aspects of the interaction between the species involved.
Here, an attempt was made to understand the chemistry of noble metal
nanoparticle–pesticide interaction, as these nanosystems are
being used extensively for water purification. Our model pesticide,
chlorpyrifos (CP), belonging to the organophosphorothioate group,
is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl
thiophosphate at room temperature over Ag and Au NPs, in supported
and unsupported forms. The degradation products were characterized
by absorption spectroscopy and electrospray ionization mass spectrometry
(ESI MS). These were further confirmed by ESI tandem mass spectrometry.
The interaction of CP with NP surfaces was investigated using transmission
electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy,
and X-ray photoelectron spectroscopy (XPS). XPS reveals no change
in the oxidation state of silver after the degradation of CP. It is
proposed that the degradation of CP proceeds through the formation
of AgNP–S surface complex, which is confirmed by Raman spectroscopy.
In this complex, the P–O bond cleaves to yield a stable aromatic
species, TCP. The rate of degradation of CP increases with increase
of temperature and pH. Complete degradation of 10 mL of 2 ppm CP solution
is achieved in 3 h using 100 mg of supported Ag@citrate NPs on neutral
alumina at room temperature at a loading of ∼0.5 wt %. The
effect of alumina and monolayer protection of NPs on the degradation
of CP is also investigated. The rate of degradation of CP by Ag NPs
is greater than that of Au NPs. The results have implications to the
application of noble metal NPs for drinking water purification, as
pesticide contamination is prevalent in many parts of the world. Study
shows that supported Ag and Au NPs may be employed in sustainable
environmental remediation, as they can be used at room temperature
in aqueous solutions without the use of additional stimulus such as
UV light
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