Fabrication of Cubic Nanocages and Nanoframes by Dealloying Au/Ag Alloy Nanoboxes with an Aqueous Etchant Based on Fe(NO₃)₃ or NH₄OH

Abstract

This paper describes a two-step procedure for generating cubic nanocages and nanoframes. In the first step, Au/Ag alloy nanoboxes were synthesized through the galvanic replacement reaction between Ag nanocubes and an aqueous HAuCl 4 solution. The second step involved the selective removal (or dealloying) of Ag from the alloy nanoboxes with an aqueous etchant based on Fe (NO 3 ) 3 or NH 4 OH. The use of a wet etchant other than HAuCl 4 for the dealloying process allows one to better control the wall thickness and porosity of resultant nanocages because there is no concurrent deposition of Au. By increasing the amount of Fe(NO 3 ) 3 or NH 4 OH added to the dealloying process, nanoboxes derived from 50-nm Ag nanocubes could be converted into nanocages and then cubic nanoframes with surface plasmon resonance (SPR) peaks continuously shifted from the visible region to 1200 nm. It is also possible to obtain nanocages with relatively narrow SPR peaks (with an FWHM as small as 180 nm) by controlling the amount of HAuCl 4 used for the galvanic replacement reaction and thus optimization of the percentage of Au in the alloy nanoboxes.Hollow nanoparticles of noble metals have unique physical and chemical characteristics that differentiate them from many other types of nanostructured materials. 1 They have also been recognized for a range of applications, including catalysis, 2 optical sensing, 3 drug delivery, 4 biomedical imaging, 5 as well as photothermal cancer treatment. 6 Among various synthetic routes, the one based on galvanic replacement reaction has proven to be the most effective in generating hollow nanostructures from a number of noble metals. 1,7 It has been demonstrated that bimetallic alloy hollow nanostructures composed of Ag and Au, Pd, or Pt could be conveniently prepared by reacting Ag nanostructures with a compound containing a less reactive noble metal such as Au, Pd, or Pt. In particular, Au/Ag nanoboxes (nanostructures with hollow interiors) and nanocages (nanostructures with hollow interiors and porous walls) with tunable surface plasmon resonance (SPR) peaks can be routinely synthesized by reacting Ag nanocubes with HAuCl 4 in an aqueous solution. By increasing the amount of HAuCl 4 added to a suspension of Ag nanocubes, the nanocubes can be controlled to evolve from solid objects into cubic nanoboxes and then nanocages. As a well-established example, the SPR peaks of *Corresponding author. E-mail: xia@chem.washington.edu. gold hollow nanoboxes and nanocages can be readily tuned from the visible to the near-infrared (NIR) region by varying the wall thickness relative to the overall dimension. 8 NIH Public AccessAlthough the protocol based on the galvanic replacement reaction with HAuCl 4 works well for Ag nanostructures of a variety of shapes, it has a drawback that limits our ability to achieve a tight control over the wall thickness and porosity for the resultant nanocages. In the early stage of the reaction (or when a relatively small amount of HAuCl 4 is added), Ag atoms are dissolved fr...

Gold Nanocages for Biomedical Applications

“…For example, we have very recently demonstrated the ability to selectively etch Ag from alloyed Au-Ag nanoboxes. [33] This process decouples the dealloying of silver from the deposition of gold, generating Au nanocages with thinner and more porous walls and further red-shifted SPR peaks than previous methods. (A) A schematic illustration of the two-step protocol used to conjugate antibodies to the surface of Au nanocages.…”

Hollow metal nanostructures for enhanced plasmonics: synthesis, local plasmonic properties and applications

“…As the deposition of precursor atoms takes place on the surface of the NC, the final hollow NC retains the shape and dimensions of the original template [86,94], which allows the control of the morphology of the hollow structure [95]. Thus, Xia group has widely studied how Ag nanocubes synthesized by using a polyol process and then oxidized by an aqueous HAuCl 4 solution generate uniform Au nanoboxes or nanocages [64,[96][97][98][99]. Similarly, Ag nanowires have been widely exploited as templates for the preparation of hollow nanotubes via the GRR [86,97,[100][101][102][103][104].…”

Face the Edges: Catalytic Active Sites of Nanomaterials

“…Ag nanosphere is prepared at the beginning of the reaction, then galvanic etching by AuCl 4 − could change the morphologies and compositions, and finally Ag‐Au NFs are produced (Figure 9c). Such alloying‐dealloying process could finely control the final morphologies, comparing to the direct etching process to get NFs, though both of them may form NFs as final products under suitable conditions 144, 145, 146…”