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We present a plausible mechanism of formation, encapsulation, and stabilization of gold nanoparticles (GNPs) in presence of poly(vinyl pyrrolidone) (PVP) in 1-butanol in support of UV-visible, Raman, Fourier transform infrared spectroscopy (FTIR), zetapotential, X-ray photoelectron spectrum (XPS), and transmission electron microscopy. A surface plasmon resonance band at 533 nm in the UV-visible spectrum reveals formation of *20 nm spherical GNPs in the non-hydrocolloid. In the FTIR spectrum, selective enhancement in the intensity of C-H stretching and red-shift in the C=O band suggests that PVP encapsulate GNP by an interaction between PVP and GNP that occurs via O-atom of pyrrolidone ring. Raman and XPS spectrum well supports the findings of FTIR spectrum. Zeta potential of -15.22 mV at 7.5 pH found in PVP-capped GNP strongly recommends the role of electrosteric effect towards the observed colloidal stability. Microscopic image demonstrates a thin coating of amorphous PVP layer around GNPs in a core-shell structure. Probing the mechanism of formation, encapsulation, and stabilization of GNP could provide essential information for development of bimetallic NPs for catalytic applications.

The study of the interaction between poly(vinylpyrrolidone) (PVP) and gold (Au) nanoparticles (NPs) in a colloid is of special interest for possible applications in the field of catalysis, biosensing, and biomedicine. A strong optical absorption arising from Au NPs at 532 nm in Au-PVP colloids is ascribed to surface plasmon resonance. The X-ray photoelectron spectroscopic results confirm reduction of the Au 3+ ion to Au 0 . A noticeable decrease in the binding energies of the Au4f doublet peak of the Au NP with PVP as compared to the bulk Au atom implies interfacial interaction between the Au NP and PVP molecules. A marked enhancement in vibrational band intensities of C-H (2,961, 2,936, and 2,872 cm −1 ) stretching, C-N (1,463 cm −1 ) stretching, and CH 2 (1,381 cm) bending vibrations in the pyrrolidone ring of PVP molecules reveals a charge-transfer-type interaction between the PVP molecules and surface of the Au NP. A significant decay of the emission band intensity (approximately 85%) in the π ← π* band of the PVP molecules at approximately 392 nm in the presence of Au NPs suggests non-bonding (n) electron transfer from the O atom of the pyrrolidone ring of PVP molecules to the electron-deficient Au NP. A negative zeta potential of (−) 15.2 mV reveals accumulation of n-electrons of the O atom of the carbonyl group of PVP molecules on the surface of the Au NP. Transmission electron microscopic images of PVP-capped Au NPs corroborate the spectroscopic results.

In this article, we report a facile one-step chemical synthesis of gold (Au) nanoparticles (GNPs) from a new precursor salt i.e., gold hydroxide in the presence of poly(vinyl pyrrolidone) (PVP) polymer. The non-aqueous dispersion of GNPs was comprehensively characterized by UV-Visible, FTIR, zeta potential, and transmission electron microscope (TEM). A strong surface plasmon resonance band at 529 nm in the UV-Visible spectrum confirms the formation of GNPs in the Au colloid. The FTIR spectroscopic results showed that PVP molecules get chemisorbed onto the surface of GNP via O-atom of carbonyl group. A negative zeta potential of (-)16 mV reveals accumulation of nonbonding electrons of O-atom of carbonyl group of PVP molecules on the nanosurface of GNP. TEM images demonstrate a core-shell nanostructure with an Au-crystalline core covered by a thin amorphous PVP-shell. PVP-capped GNPs could be a potential candidate for bio-sensing, catalysis, and other applications.

Herein, we report a facile green synthesis of Cu 2 O nanoparticles (NPs) using copper sulfate as precursor salt and hydrazine hydrate as reducing agent in presence of bio-surfactant (i.e. leaves extract of arka -a perennial shrub) at 60 to 70°C in an aqueous medium. A broad band centered at 460 nm in absorption spectrum reveals the formation of surfactant stabilized Cu 2 O NPs. X-ray diffraction pattern of the surfactant stabilized NPs suggests the formation of only Cu 2 O phase in assistance of a bio-surfactant with the crystallite size of ∼8 nm. A negative zeta potential of −12 mV at 8.0 pH in surfactant stabilized Cu 2 O NPs hints non-bonding electron transfer from O-atom of saponin to the surface of NP. Red-shift in the vibrational band (Cu-O stretching) of Cu 2 O from 637 cm −1 to 640 cm −1 in presence of bio-surfactant suggests an interfacial interaction between NPs and O-atoms of -OH groups of saponin present in the plant (i.e. Calotropis gigantea) extract. From X-ray photoelectron spectroscopy spectra, a decrease in binding energy of both 2p 3/2 and 2p 1/2 bands in Cu 2 O with saponin molecules as compared to bulk Cu atom reveals a charge transfer interaction between NP and saponin surfactant molecules. Transmission electron microscopy images show crystalline nature of Cu 2 O NPs with an fcc lattice.

In this article, a possible mechanism of solubilizing C 60 molecules through poly (vinyl pyrrolidone) PVP is described in exploring its diverse biological, cosmetical, and medicinal activities. Markedly enhanced (~ three times) absorbance, molar extinction coefficient, or oscillator strength in a   * band in the C(sp 2 ) electron transitions of C 60 molecules at 299 nm confers an effective surface adsorption of chromophoric groups of PVP molecules on the carbon surface. High resolution transmission electron and field emission scanning electron microscopic images in C 60 -PVP nanofluids clearly show adsorption of an amorphous PVP surface layer (35-37 nm thickness) on the C 60 nanosurface. An intense dynamic light scattering band measuring an average hydrodynamic length of 306 nm attributes to PVP encapsulated C 60 molecules. An average zetapotential (-) 17.8 mV at 6.5 pH describes PVP molecules aided accumulation of n-electrons on the C 60 surface. Raman and Fourier transform infrared bands show distinctly enhanced intensity in the C=O and C-N stretching vibrations of lactam rings in presence of C 60 molecule as a result of a charge transfer coupling of PVP functional groups with the C 60 nanosurface. A nearly 11% decrease in emission band intensity in the n  n* band of the PVP molecules at 393 nm upon addition of Downloaded by [University of Leeds] at 01:36 06 July 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 4.0 µM C 60 molecules exhibit n-electrons transfer from O-atom of pyrrolidone ring to electron deficient carbon nanosurface in surface modified C 60 molecules.

We study the quenching of fluorescence intensity of 40 g/L poly(vinyl pyrrolidone) PVP molecules by varying the content of gold nanoparticles (GNPs) from 1 to 5 lM in 1-butanol. A profound exponential decay of the emission band intensity in the p / np* band of the PVP molecules at *392 nm upon gradual addition of the GNPs demonstrates an existence of an excited state interaction of NPs with the PVP molecules in a gold colloid in 1-butanol. Such quenching is caused by the non-bonding electron transfer from the O-atom of carbonyl group of the PVP molecules to the surface of the GNP. X-ray photoemission spectroscopy (XPS) study corroborates the spectroscopic results. A linear Stern-Volmer plot with a quenching constant of 2.23 9 10 6 M -1 reveals dynamic quenching in a non-aqueous NF. A mechanism of fluorescence quenching was proposed in support of XPS and images taken from hybrid nanostructure using transmission electron microscope. Study on quenching of fluorescence intensity of PVP fluorophore in the presence of GNPs is useful for optoelectronic devices and biosensors.

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