X-ray photoelectron spectrum in surface interfacing of gold nanoparticles with polymer molecules in a hybrid nanocomposite structure

Abstract

In situ Au3+--> reaction and dispersion of the resulting gold in the form of nanoparticles (NPs) in a reactive polymer medium, such as poly(vinyl alcohol) (PVA) molecules in hot water, are explored to devise a composite Au-PVA structure of self-standing films. The Au-NPs (0-2 wt%) tailor a violet to purple to a yellowish color of films from a colorless base polymer. A distinct surface interface (of thickness 2-5 nm) from the core (20-30 nm diameter) is resolved in transmission electron microscope images. The x-ray photoelectron spectrum (XPS) in the 81-91 eV range accounts for the effect which causes asymmetric shapes of the 4f(7/2) and 4f(5/2) Au bands. In a model structure, the asymmetry arises in the contribution of the surface Au atoms, which extend a chemical bridging with surface O atoms from the PVA molecules in a surface layer. A similar asymmetry also arises in C 1s and O 1s bands in the counterpart PVA molecules at 287.79 and 532.35 eV, respectively. At Au content as large as 2 wt%, no separate XPS band arises on a negligibly small fraction of surface Au atoms when Au-NPs have been grown in thin laminates (or cuboids and prisms).

Inquiring the mechanism of formation, encapsulation, and stabilization of gold nanoparticles by poly(vinyl pyrrolidone) molecules in 1-butanol

“…5c) implies that N-atoms of pyrrolidone ring do not interact directly with GNP (Frens 1973;Xian et al 2012;Zhou et al 2009). However, shifting of O1s peak to higher binding energy owing to decrease in the electron density around O-atom of carbonyl group confirms that an interaction between GNP and PVP occurs only via O-atom of C=O group (Frens 1973;Tripathy et al 2009;Xian et al 2012;Zhou et al 2009). …”

“…The peak of O1s (as shown in Fig. 5b (Tripathy et al 2009). Almost unchanged in the N1s peak position of N-atom of pyrrolidone group in presence of GNP (as shown in Fig.…”

“…to Au 0 valance state in the reaction medium (Abyaneh et al 2007;Tripathy et al 2009;Zhou et al 2009). Decrease in binding energy of both 4f 7/2 and 4f 5/2 band in GNP with PVP molecules as compared to bulk Au atom reveals a charge transfer interaction between GNP and PVP polymer molecules (Abyaneh et al 2007;Tripathy et al 2009;Zhou et al 2009). A similar effect has also been reported in PVPcapped GNP and Au metallized polycarbonate Patnaik and Li 1998).…”

“…In presence of electron-deficient Au 3? ion, the nucleophilic agent (i.e., enol form of PVP) can easily donate the lone-pair electron present on the O-atom of hydroxyl group and readily form Au-O-C bond in a weak polymer-metal coordinated complex (d) (Ram and Fecht 2011;Tripathy et al 2009). As the thermodynamically stable keto form usually predominates at equilibrium in a keto-enol tautomerism, suitable rearrangement in (d) results in formation of Au atom along with PVP (keto form) and 1-butanol.…”

“…Soon after the pioneer work of Helcher (1718) on the synthesis of GNPs in presence of a polysaccharide, scientists and academia felt that polymers could be used as efficient stabilizing/reducing agent in the development of inorganic-organic nanostructure materials of various morphologies and sizes of ones interest (Hoppe et al 2006;Goy-López et al 2010;Xian et al 2012;Zhou et al 2009). In the synthesis of metal NPs, the most commonly used polymers include poly(vinyl alcohol), poly(vinyl pyrrolidone) PVP, and poly (ethylene glycol) (Hoppe et al 2006;Goy-López et al 2010;Tripathy et al 2009;Xian et al 2012;Zhou et al 2009). On the other hand, the increased interest on the use of PVP as capping/reducing/nucleating agent has been increased a lot owing to its non-toxicity, good biodegradability, excellent film forming ability and easy processability, superb stabilizing ability, mild reducing ability, and outstanding solubility in various polar solvents (Alexandridis 2011;Hoppe et al 2006;Xian et al 2012;Zhou et al 2009).…”