Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures

In these decades, Au nanostructures have been demonstrated to be promising nanomaterials in catalysis, detection and biomedicine. The merit of these applications manly arises from the expression of properties with strong correlations to their shape and size. Thus, well control of Au nanostructures i...

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Main Author: Xia, Jing
Other Authors: Dong Zhili
Format: Theses and Dissertations
Language:English
Published: 2018
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Online Access:http://hdl.handle.net/10356/75887
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Institution: Nanyang Technological University
Language: English
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spelling sg-ntu-dr.10356-758872023-03-04T16:47:19Z Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures Xia, Jing Dong Zhili Hu Xiao School of Materials Science & Engineering Han Ming Yong DRNTU::Engineering::Materials::Nanostructured materials In these decades, Au nanostructures have been demonstrated to be promising nanomaterials in catalysis, detection and biomedicine. The merit of these applications manly arises from the expression of properties with strong correlations to their shape and size. Thus, well control of Au nanostructures in shape and size is important in improving their properties and applications. To synthesize morphology-controlled Au nanostructures, well understanding of their growth mechanism is crucial. Therefore, the main objective of this thesis is to prepare anisotropic Au nanostructures and understand their growth mechanism behind. Colloidal growth of Au nanostructures has been exploring for decades via chemical reduction of AuCl4-. The intermediate process is very difficult to investigate during the fast reduction of Au3+ to Au0, and thus it is of importance to explore the slow reduction for study of intermediate process with a series of weak reducing agents possessing typical aldehyde groups (i.e., HCOH, HCOOH, HCONH2, HCOCH3 and HCON(CH3)2). The binding energies of Aun+ (n = 3, 1 and 0) to ligands are simulated to exhibit binding different affinities to starting, intermediate and final Au species. In an optimized slow reaction in which ligands show stronger binding affinities to Au+ than Au3+ and Au0, intermediate process that the formation and disproportionation of Au+ is demonstrated. For example, formic acid has much stronger binding affinity to Au+ than Au3+ so that intermediate Au+ is able to be captured during the slow reduction of Au3+. Upon the disproportionation of Au+ to Au0 and Au3+, the binding affinity of ligands to different Au facets and Au0 is crucial in controlling growth of anisotropic Au nanostructures. The adsorption of various ligands causes substantially decreased surface energies on different Au planes. There are much higher energies on {110} planes compared to the other two {111} and {100} planes with certain ratios in these energies, leading to morphological growth of Au nanoplates by various organic ligands. Meanwhile, ligands with stronger binding energies to Au0 have stronger effect in controlling the anisotropic growth of Au nanostructures. Furthermore, Ag, Pd and Pt nanosheets are successfully prepared via this facile synthetic method. In addition, using the as-prepared Au nanoplates as templates, ultrathin Au nanosheets with average thickness of ~1.5 nm and bimetallic nanostructures maintaining the plate-like shape are also produced. Doctor of Philosophy (MSE) 2018-07-10T07:38:27Z 2018-07-10T07:38:27Z 2018 Thesis Xia, J. (2018). Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures. Doctoral thesis, Nanyang Technological University, Singapore. http://hdl.handle.net/10356/75887 10.32657/10356/75887 en 190 p. application/pdf
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic DRNTU::Engineering::Materials::Nanostructured materials
spellingShingle DRNTU::Engineering::Materials::Nanostructured materials
Xia, Jing
Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
description In these decades, Au nanostructures have been demonstrated to be promising nanomaterials in catalysis, detection and biomedicine. The merit of these applications manly arises from the expression of properties with strong correlations to their shape and size. Thus, well control of Au nanostructures in shape and size is important in improving their properties and applications. To synthesize morphology-controlled Au nanostructures, well understanding of their growth mechanism is crucial. Therefore, the main objective of this thesis is to prepare anisotropic Au nanostructures and understand their growth mechanism behind. Colloidal growth of Au nanostructures has been exploring for decades via chemical reduction of AuCl4-. The intermediate process is very difficult to investigate during the fast reduction of Au3+ to Au0, and thus it is of importance to explore the slow reduction for study of intermediate process with a series of weak reducing agents possessing typical aldehyde groups (i.e., HCOH, HCOOH, HCONH2, HCOCH3 and HCON(CH3)2). The binding energies of Aun+ (n = 3, 1 and 0) to ligands are simulated to exhibit binding different affinities to starting, intermediate and final Au species. In an optimized slow reaction in which ligands show stronger binding affinities to Au+ than Au3+ and Au0, intermediate process that the formation and disproportionation of Au+ is demonstrated. For example, formic acid has much stronger binding affinity to Au+ than Au3+ so that intermediate Au+ is able to be captured during the slow reduction of Au3+. Upon the disproportionation of Au+ to Au0 and Au3+, the binding affinity of ligands to different Au facets and Au0 is crucial in controlling growth of anisotropic Au nanostructures. The adsorption of various ligands causes substantially decreased surface energies on different Au planes. There are much higher energies on {110} planes compared to the other two {111} and {100} planes with certain ratios in these energies, leading to morphological growth of Au nanoplates by various organic ligands. Meanwhile, ligands with stronger binding energies to Au0 have stronger effect in controlling the anisotropic growth of Au nanostructures. Furthermore, Ag, Pd and Pt nanosheets are successfully prepared via this facile synthetic method. In addition, using the as-prepared Au nanoplates as templates, ultrathin Au nanosheets with average thickness of ~1.5 nm and bimetallic nanostructures maintaining the plate-like shape are also produced.
author2 Dong Zhili
author_facet Dong Zhili
Xia, Jing
format Theses and Dissertations
author Xia, Jing
author_sort Xia, Jing
title Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
title_short Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
title_full Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
title_fullStr Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
title_full_unstemmed Ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
title_sort ligand-controlled preparation and fundamental understanding of anisotropic gold nanostructures
publishDate 2018
url http://hdl.handle.net/10356/75887
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