Nanoporous silver fabricated with pretreated Ag-Al alloy toward surface enhanced Raman sensing

Nanoporous silver (NPS), characterized by its three-dimensional bi-continuous interpenetrating ligament channel structure, is a good candidate for surface enhanced Raman scattering (SERS), attributed to its exceptional surface-to-volume ratio and significant SERS enhancement capabilities. Here, we have successfully fabricated NPS through the dealloying ofα-terpineol (α-TPN) coated Ag55Al45alloy. The resultingα-NPS exhibits uniform ligaments and nanopore sizes, maintaining high SERS performance even after being exposed to air for more than one month. The pretreatment of precusor alloy withα-TPN is crucial not only for the formation of nanoporous structure but also for ensuring the long term stability ofα-NPS. Specifically,α-TPN functions as a surfactant, facilitating atomic diffusion to achieve a superior interconnected NPS. Furthermore, during the dealloying process, the carbonization ofα-TPN serves as a protective layer, effectively inhibiting the oxidation of silver.

Refinement of nanoporous copper by dealloying the Al-Cu alloy in NaOH solution containing sodium dodecyl sulfate

This work reports the refinement of nanoporous copper (NPC) ligaments by introducing the sodium dodecyl sulfate (SDS) surfactant in the dealloying process. The Al₈₀Cu₂₀ (at%) alloy precursor is chemically dealloyed in a mixed solution of NaOH and SDS surfactant, producing NPC with a hierarchical microstructure. Micron-scaled skeletons that build up higher level networks consist of geometrically similar nano-scaled bi-continuous ligament-pore networks at the lower level. It has been found that the size of the ligaments in the lower level networks reduces from ∼32 nm to ∼24 nm with increasing SDS concentration to 1 mM. Further increasing the SDS concentration to 5 mM only leads to a slight ligament size decrease to ∼21 nm. Remarkably, nano-sized cones are formed on the lower level network surface in the dealloying solution containing 1 mM SDS, and the cone number greatly rises when the SDS concentration increases to 5 mM. The surface diffusivity of Cu adatoms is evaluated based on the experimental data, and the refinement of the ligament as well as the formation of cones are associated with the decreased surface diffusivity and the retarded Cu adatom motions with the addition of SDS. Quantum chemical calculations and molecular dynamics simulations are performed to model the adsorption behavior of SDS. It has been found that the SDS-substrate interaction increases with the number of SDS molecules before SDS reaches saturation.

Combining physical vapor deposition structuration with dealloying for the creation of a highly efficient SERS platform

Nanostructured noble metal thin films are highly studied for their interesting plasmonic properties. The latter can be effectively used for the detection of small and highly diluted molecules by the surface-enhanced Raman scattering (SERS) effect. Regardless of impressive detection limits achieved, synthesis complexity and the high cost of gold restrict its use in devices. Here, we report on a novel two-step approach that combines the deposition of a silver-aluminum thin film with dealloying to design and fabricate efficient SERS platforms. The magnetron sputtering technique was used for the deposition of the alloy thin film to be dealloyed. After dealloying, the resulting silver nanoporous structures revealed two degrees of porosity: macroporosity, associated to the initial alloy morphology, and nanoporosity, related to the dealloying step. The resulting nanoporous columnar structure was finely optimized by tuning deposition (i.e., the alloy chemical composition) and dealloying (i.e., dealloying media) parameters to reach the best SERS properties. These are reported for samples dealloyed in HCl and with 30 atom % of silver at the initial state with a detection limit down to 10^-10 mol·L^-1 for a solution of rhodamine B.

Silver Foams with Hierarchical Porous Structures: From Manufacturing to Antibacterial Activity

The development of porous materials with hierarchical porous structures is currently of great interest. These materials exhibit properties representative of different pore scales and thus open up the possibility of being used in new applications. In this paper, a method for the preparation of silver foams with hierarchical porous structures is discussed. Here, the replication method, which is typically used to produce coarse-pore foams, is merged with dealloying, which is commonly used to manufacture small-pore foams. For this purpose, packed NaCl particles (hard template) were infiltrated with 75%Al-25%Ag alloy (whose so-called soft template is the Al-rich phase). Both the hard and soft templates were removed by water dissolution and dealloying with HCl or NaOH solutions, respectively. Extensive characterization of the resulting materials revealed pores ranging from a few nanometers to hundreds of micrometers. The materials were characterized by their antibacterial performance against Gram-positive and Gram-negative bacteria and showed significantly higher activity than both silver foams prepared by sintering pure Ag particles and silver nanofoams produced by chemical dealloying. The combinations of pores of different sizes and the resulting high internal specific surface area have a decisive influence on the antibacterial capacity of these new materials.

Vapor phase dealloying-driven synthesis of bulk nanoporous cobalt with a face-centered cubic structure

The VPA–VPD strategy successfully realizes the fabrication of bulk nanoporous FCC-Co because of the temperature effect and size influence.

Bimetallic nanoporous Pd-Ag prepared by dealloying with polyvinylpyrrolidone and their electrocatalytic properties

Bimetallic nanoporous Pd-Ag solid solution alloys with hierarchical structure were prepared by dealloying melt-spun Al-Pd-Ag ribbons in a 10 wt% H₃PO₄ solution. Electrocatalytic properties of nanoporous Pd-Ag alloys were measured in comparison with the nanoporous Pd without Ag. Experimental results showed that the nanoporous Pd-Ag alloys displayed electrocatalytic properties superior to their Ag-free counterparts. In particular, the optimised composition was revealed to be Pd/Ag = 3/2 in atomic ratio in the precursor with fixed 85 at% Al alloys, which yielded in a peak current density in the nanoporous Pd-Ag alloy two times that of the pure Pd one. The electrocatalytic activity of nanoporous Pd-Ag alloy with refined microstructure was further increased up to three times of the pure Pd one by adding 1 mM polyvinylpyrrolidone (PVP) into the H₃PO₄ solution. The underlying mechanism of refinement was related to a restriction effect on the free diffusion of Pd and Ag under adsorption of the PVP macromolecules. The significant improvement in the electrocatalytic properties was attributed to the dual promotion by the electron transfer from PVP to Pd-Ag and by a synergistic effect between Pd and Ag.

Structure analysis of precursor alloy and diffusion during dealloying of Ag-Al alloy

Nanoporous silver (NPS) was fabricated by dealloying Ag-Al alloy ribbons with nominal compositions of 30, 35 and 40 at% Ag (corresponding to hypoeutectic composition, eutectic composition and hypereutectic composition, respectively). The microstructures of the Ag-Al precursor and as-dealloyed samples were observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM) as well as via focused ion beam (FIB) technique. We concluded that with the increase in Ag content from 30 to 40 at%, the diameter of ligament increased from 70 ± 15 nm to 115 ± 35 nm. Due to the method of crystalline solidification and the distribution of α-Al(Ag) and γ-Ag2Al phases, the as-dealloyed Ag35Al65 alloy exhibited a homogeneous ligament/pore structure, whereas the microstructures of Ag30Al70 and Ag40Al60 showed thinner and coarser ligament structures, respectively.

Nanoporous foam fabricated by dealloying AgAl thin film through supercritical fluid corrosion

In this research, nanoporous silver foams are fabricated through dealloying Ag₃₅Al₆₅ (as atomic percentage, at%) thin films in supercritical (SC) carbon dioxide.

Mesoporous Ni60Fe30Mn10-alloy based metal/metal oxide composite thick films as highly active and robust oxygen evolution catalysts †

A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ~350 mV overpotential to oxidize water with a current density of 10 mA/cm2 in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA/cm2 at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (~10 nm) results in a high BET surface area (43 m2/g) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ~3×104 cm2 of catalytic area per cm2 of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.

Preparation of nanoporous molybdenum film by dealloying an immiscible Mo–Zn system for hydrogen evolution reaction

Nanoporous Mo film was prepared by dealloying immiscible Mo–Zn system and it shows superior catalytic activity towards hydrogen evolution reaction than smooth Mo foil.

Self-grown Ni(OH)(2) layer on bimodal nanoporous AuNi alloys for enhanced electrocatalytic activity and stability

Au nanostructures as catalysts toward electrooxidation of small molecules generally suffer from ultralow surface adsorption capability and stability. Here, we report Ni(OH)2 layer decorated nanoporous (NP) AuNi alloys with a three-dimensional and bimodal porous architecture, which are facilely fabricated by a combination of chemical dealloying and in situ surface segregation, for the enhanced electrocatalytic performance in biosensors. As a result of the self-grown Ni(OH)2 on the AuNi alloys with a coherent interface, which not only enhances adsorption energy of Au and electron transfer of AuNi/Ni(OH)2 but also prohibits the surface diffusion of Au atoms, the NP composites are enlisted to exhibit significant enhancement in both electrocatalytic activity and stability toward glucose electrooxidation. The highly reliable glucose biosensing with exceptional reproducibility and selectivity as well as quick response makes it a promising candidate as electrode materials for the application in nonenzymatic glucose biosensors.