Galvanic replacement reactions (GRRs) have been established as one of the most powerful and versatile methods for fabricating hollow-structured nano-/micro materials with well-defined and tunable shape and size. Two key aspects of GRRs are (a) to develop facile method(s) for the fabrication of structurally well-defined and redox-active templates and (b) to explore the applications of GRRs in various modes, including both reductive and oxidative modes GRRs as well as non-conventional modes such as heterogeneous conversion of hard templates to soft hollow structured capsules. The main goal of this thesis is to study these two aspects of GRRs.

The first major contribution of this thesis is the development of an unconventional electrochemical method, square-wave voltammetry (SWV), for th...[ Read more ]

Galvanic replacement reactions (GRRs) have been established as one of the most powerful and versatile methods for fabricating hollow-structured nano-/micro materials with well-defined and tunable shape and size. Two key aspects of GRRs are (a) to develop facile method(s) for the fabrication of structurally well-defined and redox-active templates and (b) to explore the applications of GRRs in various modes, including both reductive and oxidative modes GRRs as well as non-conventional modes such as heterogeneous conversion of hard templates to soft hollow structured capsules. The main goal of this thesis is to study these two aspects of GRRs.

The first major contribution of this thesis is the development of an unconventional electrochemical method, square-wave voltammetry (SWV), for the fabrication of structurally-well-defined size-tunable reductive GRR template, Cu₂O. Each and every experimentally-adjustable parameter in SWV was studied on its effect to the electrodeposited and shape-preserving Cu₂O nano-/microcrystals. To the best of our knowledge, this work represents the first systematic study of SWV in size-tunable and shape-invariant deposition of nanocrystals without employing any organic surfactant and surface capping agent. The deposited Cu₂O nanocubes were used as the reductive templates to fabricate Cu₂O@Ag core-shell structures by GRR for single particle surface-enhanced Raman spectroscopy (sp-SERS).

The second major contribution of this thesis (Chapters 3~7) is the fabrication and applications of a hitherto unstudied strong solid oxidant, silver oxide nitrate ([Ag⁺(NO₃^-@Ag₆O₈)]), in GRRs.

For the first time the measurement of the standard reduction potential of [Ag⁺(NO₃^-@Ag₆O₈)](s)/Ag⁺(aq) redox couple was reported, establishing that [Ag⁺(NO₃^-@Ag₆O₈)] is indeed the most potent crystalline oxidant in aqueous phase under ambient condition known to date. It was shown that [Ag⁺(NO₃^-@Ag₆O₈)] mesocrystals in uniform size and shape could be conveniently fabricated by SWV in aqueous solution without using any organic additives.

A new mode of GRR, hetero-GRR, was reported together with a systematic exploration of the fabrication of various polymeric meso-capsules, including polyaniline (PANI), polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) in different reaction media, such as aqueous solution, aprotic organic solvent, and also under solvent-free condition.

A key question in the applications of [Ag⁺(NO₃^-@Ag₆O₈)] mesocrystals in GRRs, namely its chemical stability and lifetime in various reaction media, was addressed for the first time by single particle micro-Raman spectroscopy (sp-μRaman). By using sp-μRaman technique, we measured the stability and lifetime of structurally well-defined single [Ag⁺(NO₃^-@Ag₆O₈)] mesocrystal in aqueous solution, aprotic organic solvent, dry air, and at different temperature. This study paved the way for the applications of [Ag⁺(NO₃^-@Ag₆O₈)] in GRRs under various reaction conditions.

Finally, we systematically investigated the size-tunable range under shape-invariance (Chapter 6) and the shape-tunable range under symmetry-invariance for [Ag⁺(NO₃^-@Ag₆O₈)] mesocrystals fabricated by various electrochemical deposition methods, especially SWV. It was demonstrated that the size of [Ag⁺(NO₃^-@Ag₆O₈)] cubic mesocrystals can be tuned by galvanostatic method while the shape of [Ag⁺(NO₃^-@Ag₆O₈)] could be tuned under O_h-preserving symmetry by potentiostatic method without using any organic surfactants or surface capping agent.