Reaction–Diffusion Assisted Synthesis of Gold Nanoparticles: Route from the Spherical Nano-Sized Particles to Micrometer-Sized Plates

Szabolcs Farkas,Dezső Horváth,László Janovák,Viktória Hornok,Ágota Tóth,Gábor Schuszter,Ágota Deák,Hideki Nabika,Gábor Holló,István Lagzi,Masaki Itatani

doi:10.1021/acs.jpcc.1c08404

Abstract

The design of nanoparticles of desired sizes and shapes and 2D nanostructured materials is challenging and important due to their unique physical and chemical properties. One of the most common methods for the generation of metal nanoparticles is the wet synthetic route in which metal ions are reduced and the formed particles are stabilized in the liquid phase. Here we show a facile and powerful method to synthesize gold nanoparticles in a solid agarose gel utilizing the diffusion of reagents using the Turkevich method at room temperature. Our technique yields particles spatially separated by their sizes and shapes (spheres and plates) in the gel column. We have achieved 4 orders of magnitude difference in the sizes of the synthesized particles with a linearly increasing trend in the function of their spatial position. We have also generated micrometer-sized nanoplates with triangle, truncated triangle, or hexagon shapes attaining almost the length-to thickness ratio of 500, representing the magnificent power of the reaction–diffusion assisted synthesis.

Highlights

The synthesis of metal nanoparticles (NPs) and their selfassembly into nanostructured materials have gained much attention in the past few decades due to their unique chemical, optical, magnetic, and electronic properties.[1−5] They have been widely used in various applications ranging from catalysis[6−8] to nanomedicine[9−13] to electronics.[14−16] The most common technique to prepare metal NPs is the wet chemical synthesis method in a bulk phase, in which a metal salt and reducing as well as stabilizing agents have been used in the aqueous phase.[17]
The agarose concentration was reduced to the value at which no formation of AuNPs was observed at room temperature, and the gel matrix was solid enough to provide a medium for convectionfree mass transport of the reagents realized solely by diffusion
We have demonstrated a general and facile method to synthesize AuNPs of various sizes and shapes separated spatially in a hydrogel matrix by their average size utilizing the effect of the diffusion of the reagents on the particle growth

Summary

INTRODUCTION

The synthesis of metal nanoparticles (NPs) and their selfassembly into nanostructured materials have gained much attention in the past few decades due to their unique chemical, optical, magnetic, and electronic properties.[1−5] They have been widely used in various applications ranging from catalysis[6−8] to nanomedicine[9−13] to electronics.[14−16] The most common technique to prepare metal NPs is the wet chemical synthesis method in a bulk phase, in which a metal salt and reducing as well as stabilizing (capping) agents have been used in the aqueous phase.[17] The redox reaction produces metal atoms from metal ions, and they form nuclei (nucleation step), which can grow producing nanometer-sized particles (growth step).[18,19] The stabilizing agent adsorbing onto the surface of the formed particles inhibits further particle growth and produces a stable dispersion of NPs.[20] The oldest wet synthesis route to generate spherical gold nanoparticles (AuNPs) is the Turkevich method.[21] It is based on the reduction of a gold salt by citrate at elevated temperature (usually T > 70 °C), where citrate plays a role as a reducing and stabilizing agent as well. The obtained library of nanoparticles contains spatially separated spherical AuNPs with the size of 20−30 nm and gold nanoplates (triangle, truncated triangle, and hexagon) of sizes ranging from a few hundred nanometers to 70 μm

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES