N-Methyl-2-pyrrolidone as a Reaction Medium for Gold(III)-Ion Reduction and Star-like Gold Nanostructure Formation

Abstract

The efficiency of a wet chemical route to synthesize gold nanostructures with tunable size and shape significantly depends on the applied solvent and the interaction of solvent molecules with other species such as gold ions. The ability of the organic solvent N -methyl-2-pyrrolidone (NMP) as a suitable medium for application in star-like gold nanostructure (AuNS) synthesis with a tunable morphology at ambient conditions has been investigated. The time-dependent analysis of the UV–vis absorption spectra of Au III Cl 4 – in a pure NMP solution illustrates the role of NMP as simultaneous complexing and reducing agents. Kinetic studies indicate that Au III Cl 4 – in NMP solution is reduced to Au I Cl 2 – , with no need to use another reducing agent, any external energy sources, or solvent pretreatment. This is because Au I species stay stable in this solution unless poly(vinylpyrrolidone) (PVP) catalyzes their disproportionation. Morphological studies by transmission electron microscopy (TEM) specify the high-yield synthesis of AuNS with monocrystalline spikes in a concentrated NMP solution by PVP. This study illustrates that the presence of seeds, as another agent to catalyze the disproportionation of Au I species, makes it possible to synthesize AuNS in varying concentrations of PVP in this medium. The role of PVP concentration and the presence of seeds in the formation kinetics, morphology, and optical properties is systematically discussed. The results achieved through this study develop a straightforward and safe procedure for AuNS synthesis in high yield in a water-miscible organic polar solvent with tunable morphology and optical properties. Considering the high capability of NMP to dissolve various types of polymers and hydrophobic ligands, synthesizing AuNS in this solvent opens a window to a practical and easy way to fabricate gold-based nanomaterials with fascinating optical properties.

Growing Gold Nanostars on 3D Hydrogel Surfaces

“…At a low pH, ascorbic acid is only capable of reducing Au 3+ to Au + (which form Au­(III)­Cl 4 – and Au­(I)­Cl 2 – in solution, respectively). The final reduction to Au 0 and the formation of nanoparticles may thus occur either by spontaneous disproportionation of Au­(I)­Cl 2 – into Au­(III)­Cl 4 – and Au 0 , or via a redox reaction with the gel . When performing both single-step and preloaded in situ growth on unmodified gelatin substrates (chemical structure shown in Figure A), AuNSt coatings were also produced with no other changes to the synthetic procedure (Figures D,E and S16).…”

“…The final reduction to Au 0 and the formation of nanoparticles may thus occur either by spontaneous disproportionation of Au(I)Cl 2 – into Au(III)Cl 4 – and Au 0 , or via a redox reaction with the gel. 75 When performing both single-step and preloaded in situ growth on unmodified gelatin substrates (chemical structure shown in Figure 3 A), AuNSt coatings were also produced with no other changes to the synthetic procedure ( Figures 3 D,E and S16 ). This result is relevant because it indicates that these syntheses may be broadly translatable to other biocompatible materials containing peptide bond structures ( e.g ., collagen), and peptide or protein-based hydrogels), which would significantly expand the applicability of in situ growth.…”

Elucidating impact of solvent and pH in synthesizing silver nanoparticles via green and chemical route

“…At higher ammonia concentrations, complete inhibition of nanoparticle formation occurred. Furthermore, propanol, being a less polar solvent than ethanol and containing a longer carbon chain, exhibited reduced overall polarity, preventing the dissociation of precursor ionic compounds and, consequently, nanoparticle formation [45][46][47][48] (Fig. 3a, Table 1a).…”

An additive‐free electrosynthesis of gold micro‐stars for sensitive electroanalysis of N‐Acetyl‐L‐cysteine compared to conventional gold nanoparticles

“…Anisotropic gold nanostructures are materials of interest due to their widespread applications in health, energy, and the environment. [1][2][3][4][5][6] Among different anisotropic gold nanostructures, gold nanostars have been successfully used in catalysis, [7,8] surface-enhanced Raman scattering, [9][10][11][12][13] photothermal therapy, [14][15][16] direct elec-acid [17,19,24,25] in either the absence or presence of surfactants such as sodium dodecyl sulfate, [9] poly(N-vinylpyrrolidone), [10,23,26] cetyltrimethylammonium bromide, [12,16,[27][28][29] lauryl sulfobetaine, [30] etc. and a singlestep method by using catechol, [31] hydroquinone, [11] hydroxylamine, [32,33] 2-[4-(2-hydroxyethyl)−1-piperazinyl] ethanesulfonic acid, [14] etc.…”

“…The utilization and application of the anisotropic gold nanostructures including star shapes are highly influenced by their method of synthesis. [ 21–23 ] Gold nanostars may be prepared in solution through a multi‐step (i.e., seed mediation followed by growth) method by using silver nitrate and ascorbic acid [ 17,19,24,25 ] in either the absence or presence of surfactants such as sodium dodecyl sulfate, [ 9 ] poly( N ‐vinylpyrrolidone), [ 10,23,26 ] cetyltrimethylammonium bromide, [ 12,16,27–29 ] lauryl sulfobetaine, [ 30 ] etc. and a single‐step method by using catechol, [ 31 ] hydroquinone, [ 11 ] hydroxylamine, [ 32,33 ] 2‐[4‐(2‐hydroxyethyl)−1‐piperazinyl] ethanesulfonic acid, [ 14 ] etc.…”