Anti-galvanic Reduction Research Articles

Mechanism Insight into Metal Exchange between Au25(SR)18-/Ag25(SR)18- Clusters and Metal Ions from Ab Initio Molecular Dynamics Simulations.

The metal exchange reaction has emerged as an efficient method to synthesize ligand-protected alloy nanoclusters with precise compositions and structure. However, the understanding of the mechanism of these metal exchange processes is quite limited. Herein, the dynamic process of metal exchange of Au25(SR)18- and Ag25(SR)18- (R = CH3) nanoclusters with metal ions (Au+, Ag+, Cu2+, Cu+, Cd2+, and Hg2+) is investigated using ab initio molecular dynamics simulations. Computational results unveiled a multifaceted nature of the metal exchange process, dictated by several variables, including thermodynamic stability, electrochemical activity, metal affinity to ligand, and the coordination mode of metal ions. As a result of these factors, metal ions may either directly exchange with Au or Ag atoms on the icosahedral core surface by a "knock-off" mechanism or be stably adsorbed at the core-motif interface of Au25(SR)18- and Ag25(SR)18- nanoclusters. Meanwhile, we also discovered that counterions can promote adsorbed Ag and Cu atoms to diffuse into the gold core. Finally, the driving force of the galvanic reduction and antigalvanic reduction reactions is discussed. The formation of a more stable core-doping product nanocluster is the major driving force of metal exchange reactions.

Tuneable Plasmonic Resonances Of A Dynamic Thin Film Of Ultrasmall Nanocrystals Modified In the Anti-Galvanic Reduction Process.

Ultrasmall gold nanoparticles (NPs) have revolutionized nanotechnology as they are an excellent starting substrate for the synthesis of organic-inorganic hybrid materials with photonic or energy conversion applications, often with a responsive nature. However, ultrasmall NPs do not sustain plasmonic resonances, preventing their use in plasmon-related applications. In the presented work, we show a method of chemical modification of ultrasmall gold nanoparticles in order to fabricate dynamically controlled plasmonic thin films. For this purpose, we used the Anti-Galvanic Reduction process (AGR) to modify the surface of small gold nanoparticles, inducing plasmonic properties without notable size increases. Au@Ag NPs are then modified with liquid crystal-like organic ligands. The obtained NPs can assemble into densely packed films with long-range order and temperature-dependent structural properties. Namely, we detect two, fully reversible phase transitions between the hexagonal and cubic symmetries. The combination of AGR and organic surface modifications enabled us to demonstrate the possibility of managing plasmonic properties in the thin film of ~2 nm diameter metallic NPs.

Single-Atom-Kernelled Nanocluster Catalyst.

To propose the concept of single-atom-kernelled nanocluster, we synthesized a Pd-based trimetal nanocluster with a single-Ag atom-kernel for the first time by introducing some steric hindrance factors and employing a joint alloying strategy that combines the coreduction with an antigalvanic reduction (AGR). Although the AGR-derived Pd-based trimetal nanoclusters with single-silver atom kernels have low contents of gold, they show higher activity and selectivity than those of the bimetal precursor nanocluster in the electrocatalytical reduction of CO2 to CO. Furthermore, it is revealed that the kernel single atoms from both Au4Pd6(TBBT)12 and Au3AgPd6(TBBT)12 are not the active sites for catalysis, but greatly influence the catalytical performance by effecting the electronic configuration. Thus, it is demonstrated that the single-atom-kernelled nanocluster can not only improve the precious metal utilization (even to 100%) but also better the properties and provide insight into the structure-property correlation for metal nanoclusters.

New Routes for Multicomponent Atomically Precise Metal Nanoclusters.

Atomically precise metal nanoclusters (NCs), protected by a monolayer of ligands, are regarded as potential building blocks for advanced technologies. They are considered as intermediates between the atomic/molecular regime and the bulk. Incorporation of foreign metals in NCs enhances several of their properties such as catalytic activity, luminescence, and so on; hence, it is of high importance for tuning their properties and broadening the scope of applications. In most of the cases, enhancement in specific properties was observed upon alloying due to the synergistic effect. In the past several years, many alloy clusters have been synthesized, which show a tremendous change in the properties than their monometallic analogs. However, controlling the synthesis and tuning the structures of alloy NCs with atomic precision are major challenges. Various synthetic methodologies have been developed so far for the controlled synthesis of alloy NCs. In this perspective, we have highlighted those diverse synthetic routes to prepare alloys, which include co-reduction, galvanic reduction, antigalvanic reduction, metal deposition, ligand exchange, intercluster reaction, and reaction of NCs with bulk metals. Advancement in synthetic procedures will help in the preparation of alloy NCs with the desired structure and composition. Future perceptions concerning the progress of alloy nanocluster science are also provided.

Hard‐Sphere Random Close‐Packed Au47Cd2(TBBT)31 Nanoclusters with a Faradaic Efficiency of Up to 96 % for Electrocatalytic CO2 Reduction to CO

AbstractMetal nanoclusters have recently attracted considerable attention, not only because of their special size range but also because of their well‐defined compositions and structures. However, subtly tailoring the compositions and structures of metal nanoclusters for potential applications remains challenging. Now, a two‐phase anti‐galvanic reduction (AGR) method is presented for precisely tailoring Au44(TBBT)28 to produce Au47Cd2(TBBT)31 nanoclusters with a hard‐sphere random close‐packed structure, exhibiting Faradaic efficiencies of up to 96 % at −0.57 V for the electrocatalytic reduction of CO2 to CO.

Hard-Sphere Random Close-Packed Au47 Cd2 (TBBT)31 Nanoclusters with a Faradaic Efficiency of Up to 96 % for Electrocatalytic CO2 Reduction to CO.

Metal nanoclusters have recently attracted considerable attention, not only because of their special size range but also because of their well-defined compositions and structures. However, subtly tailoring the compositions and structures of metal nanoclusters for potential applications remains challenging. Now, a two-phase anti-galvanic reduction (AGR) method is presented for precisely tailoring Au44 (TBBT)28 to produce Au47 Cd2 (TBBT)31 nanoclusters with a hard-sphere random close-packed structure, exhibiting Faradaic efficiencies of up to 96 % at -0.57 V for the electrocatalytic reduction of CO2 to CO.

Cysteamine-capped gold-copper nanoclusters for fluorometric determination and imaging of chromium(VI) and dopamine.

Highly emissive cysteamine-capped gold-copper bimetallic nanoclusters (CA-AuCu NCs) with a quantum yield of 18% were synthesized via one-pot anti-galvanic reduction. The CA-AuCu NCs were characterized by HR-TEM, XPS, FTIR, MALDI-TOF mass spectrometry, DLS, and zeta potential analyses. The NCs are shown to be viable fluorescent probes for Cr(VI) ions and dopamine (DA) via quenching of the blue fluorescence, typically measured at excitation/emission wavelengths of 350/436nm. During DA recognition, a dark brown color appears, which is distinguishable from that of Cr(VI) detection. The aggregation induced quenching due to electron transfer was demonstrated by photoluminescence, HR-TEM, FTIR, DLS, and zeta potential interrogations. In buffer of pH7, response is linear in the 0.2 ~ 100μM for Cr(VI) and from 0.4 ~ 250μM for DA. The respective detection limits are 80 and 135nM. The method was applied to the determination of both Cr(VI) and DA in (spiked) tap, lake and sea water, and in human urine samples. The low toxicity of CA-AuCu NCs was validated by the MTT assay, and their responses to Cr(VI) ions and DA was also proven by Raw 264.7 cell imaging. Graphical abstractCysteamine capped Au-Cu nanoclusters (CA-AuCu NCs) were synthesized via one-pot anti-galvanic reduction and utilized in sensing of Cr(VI) ions and dopamine (DA) with demonstrated real/urine and cell imaging applications.

The Effect of an Antigalvanic Reduction of Silver on Gold for the Stability of a Self-Assembled Alkanethiol Monolayer and Chemical Lift-Off Lithography

The effects of silver antigalvanic reduction (Ag AGR) on the structure of alkanethiol self-assembled monolayers (SAMs) on gold with regard to the ordered structure and surface coverage were studied using electrochemical methods. In this paper, we report the structure changes as well as the chemical lift-off lithography (CLL) performance of SAMs dependent on chain lengths, namely, 1-butanethiol, 6-mercapto-1-hexanol, and 11-mercapto-1-undecanol. Cyclic voltammetry of the redox probe and linear sweep voltammetry of the reductive desorption demonstrated that the structure of SAMs with Ag AGR pretreatment are more ordered, resulting from higher surface coverage and stronger molecular interaction. Meanwhile, the influence of Ag AGR on the CLL efficiency behaved differently depending on the SAM chain lengths in both electrochemistry and AFM imaging. In general, the formation of alkanethiol SAMs on Ag AGR/Au has enabled a facile method, which possesses a great potential on the quality control of the SAMs system.

Reactive Ag+ Adsorption onto Gold

Proposed mechanisms of monolayer silver formation on gold nanoparticle (AuNP) include AuNP-facilitated under-potential reduction and antigalvanic reduction in which the gold reduces Ag+ into metallic atoms Ag(0). Reported herein is the spontaneous reactive Ag+ adsorption onto gold substrates that include both as-obtained and butanethiol-functionalized citrate- and NaBH4-reduced gold nanoparticles (AuNPs), commercial high-purity gold foil, and gold film sputter-coated onto silicon. The silver adsorption invariably leads to proton releasing to the solution. The nominal saturation packing density of silver on AuNPs varies from 2.8 ± 0.3 nmol/cm2 for the AuNPs preaggregated with KNO3 to 4.3 ± 0.2 nmol/cm2 for the AuNPs prefunctionalized with butanethiol (BuT). The apparent Langmuir binding constant of the Ag+ with the preaggregated AuNPs and BuT-functionalized AuNPs are 4.0 × 103 M–1 and 2.1 × 105 M–1, respectively. The silver adsorption has drastic effects on the structure, conformation, and stability of the...

Anti-Galvanic Reduction of Silver Ion on Gold and Its Role in Anisotropic Growth of Gold Nanomaterials

The role of silver ions in the seed-mediated growth of gold nanostructures has been investigated. Silver submonolayer or monolayer on specific facet of gold is assumed in previously suggested mechanism owing to underpotential deposition (UPD) of silver by ascorbic acid having weak reducing power. Silver overpotential deposition by ascorbic acid, however, is confirmed by electrochemical stripping voltammetry, whereas submonolayer of silver on gold is spontaneously formed by anti-galvanic reduction in the absence of ascorbic acid. In the presence of cetyltrimethylammonium bromide (CTAB), silver overpotential deposition by ascorbic acid does not occur, but submonolayer of silver is formed on gold surface. Adsorption of silver and CTAB on gold dramatically hindered the electron transfer by the oxidation of ascorbic acid on gold, which reduces gold ions to metallic gold in seed-mediated growth. These results provide the evidence to the in-depth observation of mechanism in seed-mediated growth where the blockin...

Adding two active silver atoms on Au₂₅ nanoparticle.

Alloy nanoparticles with atomic monodispersity is of importance for some fundamental research (e.g., the investigation of active sites). However, the controlled preparation of alloy nanoparticles with atomic monodispersity has long been a major challenge. Herein, for the first time a unique method, antigalvanic reduction (AGR), is introduced to synthesize atomically monodisperse Au25Ag2(SC2H4Ph)18 in high yield (89%) within 2 min. Interestingly, the two silver atoms in Au25Ag2(SC2H4Ph)18 do not replace the gold atoms in the precursor particle Au25(SC2H4Ph)18 but collocate on Au25, which was supported by experimental and calculated results. Also, the two silver atoms are active to play roles in stabilizing the alloy nanoparticle, triggering the nanoparticle fluorescence and catalyzing the hydrolysis of 1,3-diphenylprop-2-ynyl acetate.

Ion-precursor and ion-dose dependent anti-galvanic reduction.

Controlling alloy nanoparticles with atomic monodispersity is challenging, and the recently revealed anti-galvanic reduction (AGR) provides a unique solution to this challenge. Herein we demonstrate that AGR is ion-precursor and ion-dose dependent, which offers novel strategies to tune the composition, structure and properties of nanoparticles by varying the ion-precursor and ion-dose in the AGR reaction.

A novel biosensor for copper(ii) ions based on turn-on resonance light scattering of ssDNA templated silver nanoclusters.

A new ultrasensitive biosensor for copper(ii) ions was developed based on turn-on resonance light scattering (RLS) of ssDNA templated silver nanoclusters through anti-galvanic reduction (AGR). In our experimental assay, ultra-small size fluorescent C-rich ssDNA templated silver nanoclusters (C-rich ssDNA-Ag NCs) exhibit direct reduction of copper(ii) ions to elemental copper (Cu0) and the resulting Cu0 formed copper nanoparticles on the surface of C-rich ssDNA-Ag NCs spontaneously. The process produced Ag/Cu alloy nanoparticles with larger diameters, turning-on RLS signal of C-rich ssDNA-Ag NCs. As the concentration of Cu2+ ions increased, the RLS signal of C-rich ssDNA-Ag NCs gradually enhanced. The present method achieves the detection of Cu2+ ions in a linear range of 5 × 10-9 M to 7.5 × 10-7 M with a detection limit of 2 nM. Moreover, RLS spectrum, TEM image, fluorescence spectrum, X-ray photoelectron spectroscopy (XPS), and MALDI-TOF mass spectrometry were carried out for investigating the mechanism of the biosensor. The present strategy of constructing a biosensor based on AGR of metal nanoclusters paves a new way to design novel RLS probes.

Chemico‐Physical Synthesis of Surfactant‐ and Ligand‐Free Gold Nanoparticles and Their Anti‐Galvanic Reduction Property

Galvanic reduction (GR) is a classic reaction. In simple terms, metals can reduce less reactive (or more noble) metal ions, while the opposite--metals reduce more reactive (or less noble) metal ions--should not occur. However, recently we found that anti-galvanic reduction (AGR) occurred to thiolated gold and silver nanoparticles. However, the essential issue whether the occurrence of AGR requires the assistance of reductive thiolate ligands or not still remained unanswered. In this work, by using a novel protocol (chemical reduction and physical ablation), we synthesized surfactant- and ligand-free gold nanoparticles. We found that these as-prepared nanoparticles can reduce silver ions and copper ions, thus illustrating that AGR is not dependent on reductive ligands. Further experiments demonstrated that AGR is applicable to other metal (such as Pt and Pd) nanoparticles and that the AGR process is size-dependent. Finally, it was found that the Raman scattering signals of Rhodamine 6G are distinctly enhanced on the gold nanoparticles that had been reacted with silver ions, which indicates the use of AGR for tuning the property of nanoparticles.

Synthesis of thiolated Ag/Au bimetallic nanoclusters exhibiting an anti-galvanic reduction mechanism and composition-dependent fluorescence.

We report a direct one-pot approach, employing 11-mercaptoundecanoic acid (11-MUA) as a reducing and capping agent, for the preparation of fluorescent Ag/Au bimetallic nanoclusters (Ag/AuNCs) from HAuCl4 and AgNO3 in basic aqueous solution at room temperature. Unlike the monocomponent 11-MUA-AgNCs with negligible fluorescence, the as-prepared 11-MUA-Ag/AuNCs exhibit similar average diameters of ∼1.8 nm but much stronger and tunable fluorescence by varying the concentration ratios of AgNO3 to HAuCl4 in the synthesis. The quantum yield of the 11-MUA-Ag/AuNCs can reach 6.81% at a Ag-to-Au molar ratio of 1 : 2, nearly 3-fold higher than the monocomponent 11-MUA-AuNCs (2.38%) of similar sizes. More importantly, the occurrence of the reaction between Ag(+) ions and Au(0) of 11-MUA-AuNCs (which is opposite to the classic galvanic theory) and the coexistence of Ag(0) and Au(+) in the final NC products, are revealed by thorough analysis of XPS data. The anti-galvanic reduction, that is, metal ions are replaced by less reactive metals, has been further demonstrated through the reaction between the as-obtained purified monocomponent 11-MUA-AuNCs and Ag(+) ions. Direct electrochemical insights into the anti-galvanic reduction mechanism were provided by cyclic voltammetry characterizations of the NCs, and the universality of the anti-galvanic reduction was tested by preparing thiolated Pt/Au bimetallic NCs using platinum instead of silver in our synthetic system.

An anti-galvanic reduction single-molecule fluorescent probe for detection of Cu(ii)

An anti-galvanic reduction method using [Ag62S13(SBut)32]4+ nanoclusters as the metal ion probe for detecting Cu2+ is reported here. We found [Ag62S13(SBut)32]4+ can reduce more reactive Cu2+ with a quantitative relationship. The single molecule fluorescence imaging shows that Ag62 NCs could be used as a single molecule probe for detecting Cu2+.

Anti‐Galvanic Reduction of Thiolate‐Protected Gold and Silver Nanoparticles

Unexpected: Anti-galvanic reduction (AGR), that is, metal ions are reduced by more-noble metals, was found in small thiolated gold (see figure) and silver nanoparticles! These findings are not only unexpected considering the classic galvanic theory, but also provide a facile and mild method to make alloys on the nanoscale or tune the compositions, structures, and properties of nanostructures that are otherwise difficult to obtain.