Water and Organic Solvent Dispersible Gold Nanorods that are pH Responsive

Abstract

Shape-controlled gold nanorods are prepared in the presence of a capping agent, cetyltrimethylammonium bromide (CTAB), which controls their morphology and dispersibility in water. To control their dispersibility between water and another organic solvent, a pH-responsive amphiphile C18AA was introduced on gold nanorods instead of CTAB. The C18AA-capped gold nanorods were dispersed in both water and chloroform. These gold nanorods were pH-responsive depending on the extent of C18AA deprotonation observed: deprotonation of the terminal amine above pH 9.5 increases the hydrophobicity of the nanorods, resulting in them being more soluble in chloroform than in water. C18AA-capped gold nanorods can transfer from the water phase to the organic phase by changing the pH from 9.0 to 12.5. The morphology of the nanorods did not change as a result of ligand-exchange, or phase transfer, due to the stabilizing effect of the C18AA capping molecule. C18AA-capped gold nanorods can also be transferred to the water phase by evaporating the chloroform.

Morphological Stability and Catalytic Performance of Supported and Unsupported Dendritic Gold Nanowire Catalysts

“…The properties of metal nanocrystals are strongly dependent on their size and shape; therefore, an effective synthesis technique is essential to obtain nanocrystals with the desired properties . Recently, there have been many reports on the fabrication of shape‐controlled metal nanocrystals, such as cubes, flowers, rods, and wires . Thermodynamics predicts that noble metal atoms should nucleate and grow into spherical decahedral or icosahedral nanoparticles covered with the (111) crystal facet, because the interfacial free energy (γ) is γ(111) < γ(100) < γ(110) and the surface area per volume of spherical nanoparticles is lower than that of shape‐controlled nanocrystals .…”

“…Moreover, a truncated octahedron enclosed by a mixture of (111) and (100) crystal facets is the most stable structure for large nanoparticles as this achieves the lowest surface area per volume . Therefore, the preparation of shape‐controlled nanocrystals such as cubes, rods, and wires that were covered with a large amount of (100) and (110) facets were conducted using capping agents with selective adsorption properties …”

pH‐Responsive Supported and Unsupported Gold Nanocrystals

“…Over the past few decades, the continuous development of new routes for the synthesis of NCs has resulted in the availability of NCs with desired sizes, size distributions, shapes and compositions . Recently, the preparation and application of NCs that respond to external stimuli, such as light, temperature and pH, have become attractive . It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems .…”

“…Recently, the preparation and application of NCs that respond to external stimuli, such as light, temperature and pH, have become attractive . It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems . External‐stimuli‐responsive NCs have often been prepared using capping agents that respond to external stimuli .…”

“…It is known that external‐stimuli‐responsive NCs are applied in sensors, photochromic paper, and novel NC recovery systems . External‐stimuli‐responsive NCs have often been prepared using capping agents that respond to external stimuli . However, the external‐stimuli‐responsive capping agent can only be used to prepare specific external‐stimuli‐responsive metal NCs due to the low stability of metal NCs.…”