Facile Photochemical Syntheses of Conjoined Nanotwin Gold-Silver Particles within a Biologically-Benign Chitosan Polymer

Abstract

A simple photochemical method for making conjoined bi-metallic gold-silver (Au/Ag) nanotwins, a new breed of nanoparticles (NPs), is developed. To the best of our knowledge, the photochemical method resulted in distinct, conjoined, bimetallic nanotwins that are different from any well-established alloyed or core-shell nanostructures in the literature. The conjoined Au-Ag NPs possessed surface plasmon resonance (SPR) properties of both metals. The bimetallic nanostructures possessing distinctive optical properties of both metals were obtained using Au NPs as seeds in the first step, followed by the addition of a silver precursor as feed in the second step during a photochemical irradiation process. In the first step, small, isotropic or large, anisotropic Au NPs are generated by photoinduced reduction within a biocompatible chitosan (CS) polymer. In the second step, a silver precursor (AgNO3) is added as the feed to the AuNPs seed, followed by irradiation of the solution in the ice-bath. The entire photochemical irradiation process resulting in the formation of bimetallic Au-AgNPs did not involve any other reducing agents or stabilizing agents other than the CS polymer stabilizer. The small, conjoined Au-Ag bi-metallic NPs exhibited SPR with peak maxima centering at ~400 nm and ~550 nm, whereas the large conjoined nanoparticles exhibited SPR with peak maxima centering at ~400 nm, 550 nm, and 680 nm, characteristic of both gold and silver surface plasmons in solution. The tunability in the SPR and size of the bimetallic NPs were obtained by varying the reaction time and other reaction parameters, resulting in average sizes between 30 and 100 nm. The SPR, size, distribution, and elemental composition of the bi-metallic NPs were characterized using UV-Vis absorption, electron microscopy, and energy dispersive X-ray spectroscopy (EDS) studies.

Photochemical Synthesis of Gold and Silver Nanoparticles—A Review

“…These bimetallic NPs may form spheres [ 137 ], decahedrons [ 134 ], mixed nanostructures [ 138 ], and nanodendrites [ 139 ]. In terms of composition, these NPs can consist of alloys [ 137 , 140 ], nanotwins [ 137 , 141 ], core-shell structures [ 136 , 142 , 143 , 144 , 145 , 146 , 147 ], and hollow NPs [ 148 ].…”

“…These hybrids were tested for surface-enhanced Raman spectroscopy (SERS) applications. Besides, Korir et al obtained Au–Ag nanotwins via a two-step photochemical process in the presence of 1% chitosan [ 141 ]. First, Au seeds were synthesized starting from chloro(dimethyl sulfide)gold(I) (the precursor) under a medium-pressure mercury vapor lamp (Source 1: 40–48% UV + 40–43% visible) irradiation for 60–90 min or under UVA irradiation for 6 min.…”

Green Synthesis of Silver Nanoparticles by Low-Energy Wet Bead Milling of Metal Spheres

“…As an example, this aspect finds important applications in heat transfer technology [17], where nanofluids as heat carriers need to combine a low toxicity with an efficient stabilization against agglomeration for a wide range of temperature and fluid-dynamics conditions [18]. Nowadays, many reagents derived from plant extracts, pigments, yeast, and enzymes have been used as reductants for the synthesis of zerovalent NPs [19], with more positive results in cases of precursors containing noble metals like gold, platinum, palladium, silver [20], and other elements of weakly electropositive properties [21]. Top-down chemical methods, though representing a cost-effective alternative strategy for the production of inorganic nanoparticles, are still confined to a narrow field, probably owing to a lack of control on particle diameters, whose broad distribution adversely affects the quality of the final product.…”

Nanoparticles Synthesis in Wet-Operating Stirred Media: Investigation on the Grinding Efficiency

“…For this reason, research is increasingly pushing towards the development of new approaches that are cheaper, intrinsically safer, and more environmentally sustainable. Such a goal can be achieved by adopting new procedures [ 10 ] that generally refer to ‘green nanotechnology’ [ 11 ], in which reagents derived from plant extracts, pigments, yeast, and enzymes are employed [ 12 , 13 , 14 ].…”