Shape Changes from Polygonal Gold Nanocrystals to Spherical Nanoparticles Induced by Bubbling N2 or O2 Gas in Polyol Synthesis of Gold Nanostructures

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  • Md Jahangir Alam
    Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University
  • Masaharu Tsuji
    Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University
  • Mika Matsunaga
    Institute for Materials Chemistry and Engineering, Kyushu University

Abstract

<jats:title>Abstract</jats:title> <jats:p>Effects of gas bubbling in the polyol synthesis of Au nanostructures through reducing HAuCl4 have been studied in an oil-bath heating at 150 °C. Under bubbling N2, mixtures of polyhedral particles such as octahedra, triangular or hexagonal plates, and decahedra were major products (99%), besides a small amount of spherical nanoparticles (1%). Polyhedral particles were slowly transformed to monodispersed spherical particles with an average diameter of 245 ± 21 nm with increasing the heating time and the yield of spherical particles increased to 40% after heating for 60 min. When the bubbling gas was switched from N2 to O2, polygonal particles prepared under bubbling N2 were rapidly etched and converted efficiently to spherical particles (96%) with an average size of 119 ± 40 nm. It was found that not only O2 dissolved in ethylene glycol but also by-products like Cl− anions produced in the supernatant participate in the shape changes of Au nanocrystals. The transformation of Au nanostructures under bubbling N2 or O2 was discussed in terms of gas bubbling induced Ostwald ripening, shape-selective oxidative etching by O2/Cl−, and grain-rotation-induced grain coalescence (GRIGC) and fusion mechanisms.</jats:p>

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