The complex process of nanoparticle formation in an aqueous solution
is governed by kinetics and thermodynamic factors. This paper describes
a room-temperature growth kinetic study and evaluation of thermodynamic
activation parameters of monodispersed silver nanoparticles (AgNPs)
synthesized in alkaline medium by chemical reduction method using
AgNO
3
as a source of Ag
+
ions and tannic acid
(TA) as a reductant (reducing agent) as well as a capping or stabilizing
agent in the absence of any other external stabilizer. A simple and
conveniently handled reaction process was monitored spectrophotometrically
to study the growth kinetics in an aqueous solution as a function
of the concentration of silver ion, hydroxide ion, and TA, respectively.
The neutral nucleophilic group donates the electron density via a
lone pair of electrons to Ag
+
ions for the reduction process,
i.e., for the nucleation of AgNPs colloid. Also, a few silver ions
form a silver oxide, which also facilitates the nucleation center
to enhance the growth of AgNPs colloid. The decrease and increase
in rate constant on varying the TA concentration showed its adsorption
onto the surface of metallic AgNPs and stabilized by polygalloyl units
of TA and were the main elements to control the growth kinetics. Consequently,
stabilized TA-mediated AgNPs are formed using the electron donated
by quinone form of TA followed by a pseudo-first-order reaction. Apart
from this, nanoparticles formed were characterized using UV–visible
spectrophotometry, Fourier transform infrared spectroscopy, field
emission scanning electron microscopy, energy-dispersive X-ray spectroscopy,
transmission electron microscopy, and powder X-ray diffraction techniques
to confirm its formation during the present kinetic study.
Here, in the present
study, silver nanoparticles (SNPs) in the
size range 6–10 nm have been synthesized by a chemical reduction
method using nicotinamide (NTA), an anti-inflammatory agent, and cetyltrimethylammonium
bromide (CTAB), a good stabilizing agent, to preparing the nanoparticles
in the 6–10 nm size range. Kinetic studies on the formation
of SNPs have been performed spectrophotometrically at 410 nm (strong
plasmon band) in aqueous medium as a function of [AgNO
3
], [NTA], [NaOH], and [CTAB]. The plot of ln(
A
∞
–
A
t
) versus time exhibited a straight line and the pseudo-first-order
rate constants of different variables were calculated from its slope.
On the basis of experimental findings, a plausible mechanism was proposed
for the formation of SNPs colloid. From the mechanism, it is proved
that the reduction of silver ions proceeded through the formation
of silver oxide in colloidal form by their reaction with hydroxide
ions and NTA after performing their function and readily undergo hydrolysis
to form nicotinic acid as a hydrolysis product with the release of
ammonia gas. The preliminary characterization of the SNPs was carried
out by using a UV–visible spectrophotometer. The detailed characterization
of SNPs was also carried out using other experimental techniques such
as Fourier transform infrared spectroscopy (FTIR), field-emission
scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy
(EDS), transmission electron microscopy (TEM), and powder X-ray diffraction
(PXRD). SNPs show a remarkable catalytic activity of up to 90% for
the reduction of the cationic dye methylene blue.
For the very first
time, a detailed kinetic study for the preparation
of silver nanoparticles (silver NPs) by neuroleptic agent gabapentin
(GBP) in the absence of a stabilizer has been reported in this investigation.
This paper is devoted to the preparation of silver nanoparticles by
a chemical reduction method in which gabapentin acts as both a reductant
and a stabilizer, and AgNO3 is used as a source of Ag+ ions and NaOH for maintaining the alkaline medium. A UV–visible
spectrophotometer is used to monitor the progress of the reaction
kinetics in an aqueous medium by changing the concentration of different
variables such as AgNO3, NaOH, and gabapentin at 40 °C.
It is found that the reaction rate follows a pseudo-first-order reaction.
The thermodynamic activation parameters were also studied at five
different temperatures (303, 308, 313, 318, and 323 K) and used in
the support of the proposed mechanistic scheme for the formation of
silver nanoparticles. The prepared silver nanoparticles were characterized
using different techniques: UV–visible spectrophotometry, Fourier
transform infrared spectroscopy, field emission scanning electron
microscopy, energy-dispersive X-ray spectroscopy, transmission electron
microscopy, and powder X-ray diffraction. The average particle size
was observed in the range of 5–45 nm.
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