Spectroscopic evidence for electrochemical effect of mercury ions on gold nanoparticles

Tuning Chemical Interface Damping: Competition between Surface Damping Pathways in Amalgamated Gold Nanorods Coated with Mesoporous Silica Shells

The mechanism of mercury (Hg) amalgamation in gold nanorods coated with a mesoporous silica shell (AuNRs@mSiO2) and the effect of chemical treatments on the localized surface plasmon resonance (LSPR) spectral changes in single amalgamated AuNRs@mSiO2 remains unclear. In this study, we investigated Hg amalgamation and inward Hg diffusion in single AuNRs@mSiO2 without structural deformation via dark-field scattering spectroscopy and X-ray photoelectron spectroscopy. Then, we investigated the chemisorption of thiol molecules on single amalgamated AuNRs@Hg-mSiO2. Unlike previous studies on single AuNRs, the thiolation on single AuNRs@Hg-mSiO2 resulted in a redshift and line width narrowing of the LSPR peak within 1 h. To determine the chemical effect, we investigated the competition between two surface damping pathways: metal interface damping (MID) and chemical interface damping (CID). When we exposed amalgamated AuNRs@Hg-mSiO2 to 1-alkanethiols with three different carbon chain lengths for 1 h, we observed an increase in the line width broadening with longer chain lengths owing to enhanced CID, demonstrating the tunability of CID and LSPR properties upon chemical treatments. We also investigated the competition between the two surface damping pathways as a function of the time-dependent Au-Hg surface properties in AuNRs@Hg-mSiO2. The 24-h Hg treatment resulted in increased line width broadening compared to the 1-h treatment for the same thiols, which was attributed to the predominance of CID. This was in contrast to the predominance of MID under the 1-h treatment, which formed a core-shell structure. Therefore, this study provides new insights into the Hg amalgamation process, the effect of chemical treatments, competition between surface decay pathways, and LSPR control in AuNRs@mSiO2.

Photo-assisted simultaneous electrochemical detection of multiple heavy metal ions with a metal-free carbon black anchored graphitic carbon nitride sensor

The simultaneous detection of multiple heavy metal ions in solution is an important yet highly challenging problem. In this work, a metal-free g-C₃N₄/carbon black (CB) composite electrode was synthesized by a one-step thermal polycondensation method and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet visible light spectroscopy. In addition, the photoelectrochemical response of the g-C₃N₄/CB nanocomposite to Cd²⁺, Pb²⁺ and Hg²⁺ both separately and as a mixture of the three analytes was investigated by differential pulse anodic stripping voltammetry. The g-C₃N₄/CB electrode demonstrated an excellent sensing performance to Cd²⁺, Pb²⁺ and Hg²⁺ in the range of 0-700 nM, 0-300 nM and 0-500 nM, respectively, with limits of detection (LOD) of Cd²⁺, Pb²⁺, and Hg²⁺ of 2.1, 0.26 and 0.22 nM, respectively. The LOD of the combined solution of the three analytes was slightly higher at 3.3 nM. Additionally, the metal-free g-C₃N₄/CB photoelectrochemical sensor exhibited excellent electrochemical stability and electrode reproducibility. Finally, g-C₃N₄/CB sensor also showed satisfactory results in the detection of trace analyte ions in real environmental systems. This work provides a novel and promising approach in the simultaneous detection of multiple heavy metal ions in solution for practical applications.

How Stabilizers and Reducing Agents Affect the Formation of Nanogold Amalgams

The influence of mercury on the morphology and formation mechanism of gold amalgams in the presence of different reducing agents (ascorbic acid and sodium borohydride) was systematically studied. In the presence of cetyltrimethylammonium bromide (CTAB), chemical reducing agents not only reduced mercury ions in the solution but also replaced the CTAB molecules on the surface of the gold nanorod. The stability of the reducing agents in the colloidal system and the combining capacity of the reducing agent to the gold nanoparticles can affect the alloying process of mercury and gold, thereby forming a rod-shaped or spherical gold amalgam. Once CTAB was removed, a similar transformation process occurs between the gold nanorods and mercury. In addition, without the presence of a stabilizer, mercury that cannot be dispersed undergoes Ostwald ripening growth, which causes the gold amalgam nanoalloys to form a tip-to-tip structure as a result of mercury enrichment because of the weak shielding effects occurring at the tips of the gold nanorods. After the CTAB molecules were substituted with ascorbic acid and alkylthiol molecules, the question of whether the shielding effect weakened or disappeared was also investigated. By investigation, this research found that, in comparison to the blocking effect of CTAB molecules, the binding ability of the reducing agent to gold plays a dominant role in the nanoamalgam formation process.

Co-assembled gold nanorod@tripeptide core-shell nanospheres for aqueous Hg2+ removal

The construction of peptide and metal nanoparticles hybrid is attractive to explore their synergistic properties and applications extensively. However, it remains a challenge to fabricate a well-defined and size-controllable short peptide/Au nanoparticles hybrid. Here, we report a facile and flexible co-assembly strategy for the construction of tripeptide coated Au nanorods (AuNRs). The tripeptide (Phe-Phe-Cys, FFC) grows via covalently crosslinking to form spheres. The size of the core@shell nanospheres can be controlled by modulating the amount or size of AuNRs. Especially, the concentration of AuNRs fixes the amount of seeds, which further affect the local concentration of FFC on the surface of AuNRs seed, leading to a narrower diameter of hybrid compared to FFC spheres. Moreover, owing to their synergistic effects, this hybrid exhibits a good adsorption capacity of Hg²⁺ from aqueous solutions by electrostatic interaction and forming into Au/Hg amalgam. This strategy could be extended to the fabrication of other biomolecules and metal nanoparticle hybrids with diverse functions.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm^-2 with a small Tafel slope of 56.23 mV dec^-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

Single-Atom Switching as a General Approach to Designing Colorimetric and Fluorogenic Probes for Mercury Ions

By performing a single-atom replacement within common fluorophores, we have developed a facile and general strategy to prepare a broad-spectrum class of colorimetric and fluorogenic probes for the selective detection of mercury ions in aqueous environments. Thionation of carbonyl groups from existing fluorophore cores results in a great reduction of fluorescence quantum yield and loss of fluorescence emission. The resulting thiocaged probes are efficiently desulfurized to their oxo derivatives in the presence of mercury ions, leading to pronounced changes in chromogenic and fluorogenic signals. Because these probes exhibit high selectivity, excellent sensitivity, good membrane-permeability, and rapid responses towards mercury ions, they are suitable for visualization of mercury in both aqueous and intracellular environments.