Nanoporous Silver Research Articles

New Electrochemical Approach for Synthesis of Nanoporous Silver

Cu-Ag alloy films were electrodeposited on Au substrates to serve as precursor alloys for synthesizing finely-structured nanoporous Ag (NPS) structures. Two innovative approaches, surface limited redox replacement (SLRR) and defect mediated growth (DMG) along with overpotential deposition (OPD), were comparatively utilized to fabricate Cu-Ag alloy films. The electrolyte for these novel approaches contained Pb2+ ions to serve either as a sacrificial metal to be replaced by the co-depositing Cu and Ag (in SLRR) or as mediating metal to facilitate the 2D growth of both alloy constituents (in DMG). The resulting alloy films from both approaches displayed superior uniformity and miscibility compared to the OPD alloy, as evidenced by electrochemical scanning electron microscopy (SEM) and X-ray diffraction characterization routines. In a subsequent step, NPS structures were generated through the de-alloying of as-deposited Cu-Ag alloys, as illustrated by SEM imaging that revealed ligament and pore sizes with a thickness in the ballpark of 40 nm. Also, surface area measurements done by a Pb underpotential deposition assay suggested a surface enhancement ratio nearly five times higher than that of flat Ag. Furthermore, various de-alloying potentials were assessed to determine the optimal de-alloying potential for the best outcome of the de-alloying process.

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 of α-terpineol (α-TPN) coated Ag55Al45 alloy. The resulting α-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 with α-TPN is crucial not only for the formation of nanoporous structure but also for ensuring the long term stability of α-NPS. Specifically, α-TPN functions as a surfactant, facilitating atomic diffusion to achieve a superior interconnected NPS. Furthermore, during the dealloying process, the carbonization of α-TPN serves as a protective layer, effectively inhibiting the oxidation of silver.

Effect of precursor composition and heat-treatment on the morphology and physical properties of Ag nanosponges

Nanoporous silver (np-S) was prepared by free corrosion dealloying of a series of Ag–Al thin films containing between 25 and 73 at.% Al. It was found that precursor composition had an important influence on the nanostructures and morphologies of the np-S. In particular the size of the Ag ligaments systematically decreased from 32 to 13 nm as the Al content was increased over the series. In contrast, there was only a weak effect on pore size, which remained in the range 11–15 nm, with the maximum occurring at about 55 at.% Al. There was however a significant increase in the density of the pores as the Al content of the precursor was increased. The electrical resistivity of the np-S increases with the decrease in ligament size, changing from about 3 × 10−8 Ω m for sponges with ligaments of about 32 nm diameter rising to 30 × 10−8 Ω m for the sponge with the 13 nm ligaments. The surface area of the np-S was estimated by the electrochemical capacitance in KNO3 solutions and was estimated to increase by an order of magnitude compared to a smooth Ag surface. There was a systematic change in the optical properties of the sponges, with a trend towards less metallic behaviour as the ligament size decreased and pore density increased. These changes culminated in the sponge prepared from the 73 at.% Al precursor having non-metallic characteristics with regard to visible and near-infrared light. The volume fraction of metal was estimated to be of the order of 40 ± 5%. Prior annealing of the precursor inhibited dealloying.

Plastron effect enhanced electrochemical CO2 reduction activity over hydrophobic three-dimensional nanoporous silver.

The electrochemical reduction of CO2 on catalyst surfaces is hindered by the inefficient mass transfer of CO2 in aqueous solutions. In this study, we employed an electrochemical reduction approach to fabricate a hydrophobic three-dimensional nanoporous silver catalyst with a plastron effect, aiming to enhance the CO2 diffusion. The resulting catalyst exhibited an exceptional performance with the FECO peaking at 95% at -0.65 V (vs. RHE) and demonstrated remarkable stability during continuous electrolysis for 48 hours. Control experiments, together with Tafel analysis, EIS measurements, and contact angle results, confirmed that the notable enhancement of performance was attributed to the hydrophobic porous structure that facilitated efficient storage and rapid mass transfer of low-solubility CO2 gas reactants.

Reusable Wrinkled Nanoporous Silver Film Fabricated by Plasma Treatment for Surface-Enhanced Raman Scattering Applications.

A nanoporous silver film (npAgF), a promising structure for surface-enhanced Raman spectroscopy (SERS), can be fabricated by using successive O2 and Ar plasma treatments on a planar silver film. The common dealloying method for producing an npAgF involves annealing at high temperatures to produce an alloy film, as well as harsh etching using corrosive chemicals. By contrast, the plasma-based method can be applied directly to various functional substrates to produce more sophisticated npAgF structures. Herein, we report a facile fabrication method for a wrinkled npAgF (w-npAgF) for SERS applications using a thermally contractible polystyrene substrate. The w-npAgF had 3D wrinkles of the nanoporous structure and showed approximately 8 times higher SERS enhancement than did the flat npAgF. Moreover, the w-npAgF could be reused for multiple SERS measurements of different molecules by mild O2 and Ar plasma treatments after each use, in which the O2 plasma effectively removed the adsorbed organic molecules and the Ar plasma reduced silver oxide to pristine silver for subsequent SERS measurements. The wrinkled nanoporous structure was maintained after multiple mild plasma treatments for reuse. The simplicity of plasma-based fabrication and high sensitivity of w-npAgFs are promising features for the green production of low-cost and reusable 3D SERS substrates.

Pore evolution and size effect of nanoporous silver on SERS for malachite green detection

The nanoporous silver (NPS) films with the average pore size ranging from 51 to 246 nm were synthesized by dealloying co-sputtered AgxAl100-x (x = 30–56 at%) precursor films in 1 M HCl for 30–120 min. The structure of the NPS films, the dissociation of Al, and the aggregation of Ag were evaluated by field emission scanning electron microscopy as a function of dealloying time. The results showed that the pore size first decreased as the dealloying time increased, followed by pore coarsening, regardless of the relative density of NPS films. The finite-difference time-domain (FDTD) simulation further indicated that the smaller the nanopores, the higher the hot-spot area and surface electric field. As the average pore size of NPS film decreased to 51 nm, the enhanced Raman intensity of rhodamine 6G (R6G) using the NPS film as substrate was at least two orders higher than that using pure Ag film. Meanwhile, the detection limit of malachite green, a wildly used chemical in aquaculture, was 10-5 M with the enhancing factor 1.58 × 105.

Wettability of Nanoporous Silver Fabricated by Electrochemical Dealloying

Wettability of Nanoporous Silver Fabricated by Electrochemical Dealloying

A review on the design of nanostructure-based materials for photoelectrochemical hydrogen generation from wastewater: Bibliometric analysis, mechanisms, prospective, and challenges

Years of study have shown that creating a commercial photoelectrode to solve particular bottlenecks, such as low charge separation and injection efficiency, short carrier diffusion length and lifespan, and poor stability, requires the employment of a variety of components. Developing photovoltaic-electrolysis, photocatalytic, and photoelectrochemical approaches to accelerate hydrogen production from solar energy has been highly competitive. Photoelectrochemical water splitting utilizing nanoporous materials is one of the promising approaches to produce hydrogen more efficiently, cost-effectively, and on a long-term basis. Nanoporous materials have been highly used in photoelectrochemical water-splitting systems and are crucial in numerous applications. Those materials have a porous structure and excellent conductivity, enabling the deposition of transition metal atoms and electrochemically active chemicals on a large active surface area. However, there remains a dearth of review articles exploring the application of nanoporous materials in photoelectrochemical reactions. Therefore, this review provides bibliometric statistics and various perspectives on a range of nanoporous materials, including indium, nickel, gold, copper, lead, silver, aluminum, silicon, tin, iron, zinc, titanium, bismuth vanadate, cadmium sulfide, and zeolites. Additionally, this review offers a comprehensive assessment of worldwide studies on utilizing nanoporous materials in photoelectrochemical cells. We show how morphological modifications to materials may improve charge transfer and, as a consequence, overall power conversion efficiency.ke The superior catalytic performance of nanostructures with varying levels of complexity has been discovered in photoelectrochemical reactions. Finally, significant issues and future research directions in the domains are discussed.

Tunable lipid-coated nanoporous silver sheet for characterization of protein-membrane interactions by surface-enhanced Raman scattering (SERS)

Membrane environments affect protein structures and functions through protein-membrane interactions in a wide range of important biological processes. To better study the effects from the lipid’s hydrophilic and hydrophobic interaction with protein on different membrane regions, we developed the lipid-coated nanoporous silver sheets to provide tunable supported lipid monolayer/bilayer environments for in situ surface-enhanced Raman vibrational spectroscopy (SERS) characterizations. Under the controllable surface pressure, lipid monolayer/bilayer was coated along the microscopic curved surface of nanoporous silver sheets to serve as a cell membrane mimic as well as a barrier to avoid protein denaturation while empowering the high SERS enhancements from the underlying metallic bases allowing detection sensitivity at low physiological concentrations. Moreover, we fine-tuned the lipid packing density and controlled the orientation of the deposited lipid bilayers and monolayers to directly monitor the protein structures upon interactions with various membrane parts/positions. Our results indicate that lysozyme adopted the α-helical structure in both hydrophilic and hydrophobic interaction with lipid membrane. Interestingly, alpha-synuclein folded into the α-helical structure on the negatively charged lipid heads, whereas the hydrophobic lipid tails induced the β-sheet structural conversion of alpha-synuclein originated from its unstructured monomers. These direct observations on protein hydrophilic and hydrophobic interaction with lipid membrane might provide profound insights into the formation of the β-sheet-containing alpha-synuclein oligomers for further membrane disruptions and amyloid genesis associated with Parkinson’s disease. Hence, with the controllability and tunability of lipid environments, our platform holds great promise for more general applications in investigating the influences from membranes and the correlative structures of proteins under both hydrophilic and hydrophobic effects.Graphical

Hydrophobic Nanoporous Silver with ZIF Encapsulation for Nitrogen Reduction Electrocatalysis

Electrochemical nitrogen reduction reaction (ENRR) offers a sustainable alternative to the environmentally hazardous Haber-Bosch process for producing ammonia. However, it suffers from an unsatisfactory performance due to its limited active sites and competitive hydrogen evolution reaction. Herein, we design a hydrophobic oleylamine-modified zeolitic imidazolate framework-coated nanoporous silver composite structure (NPS@O-ZIF). The composite achieves a high ammonia yield of (41.3 ± 0.9) μg·h-1·cm-2 and great Faradaic efficiency of (31.7 ± 1.2)%, overcoming the performances of NPS@ZIF and traditional silver nanoparticles@O-ZIF. Our strategy affords more active sites and accessible channels for reactant species due to the porous structure of NPS cores and restrains the evolution of hydrogen by introducing the hydrophobic molecule coated on the ZIF surfaces. Hence, the design of the hydrophobic core-shell composite catalyst provides a valuably practical strategy for ENRR as well as other water-sensitive reactions.

Highly efficient electrochemical ammonia synthesis using superhydrophobic nanoporous silver

This work presents a unique electrocatalyst of superhydrophobic nanoporous silver, achieving superior ENRR enhancement with high faradaic efficiency of 31.1%.

Nanoporous black silver film with high porosity for efficient solar steam generation

Nanoporous black silver film with high porosity for efficient solar steam generation

Indium decorated nanoporous Ag as an efficient catalyst for enhanced CO2 electroreduction

Development of bimetallic nanoporous structures is of great importance for their energy and environmental applications due to their superior catalytic properties resulting from their higher surface-to-volume ratio, excellent surface reaction sites, as well as numerously rich microstructural properties. Herein, indium-modified nanoporous silver (np-Ag-In) was prepared by alloying-dealloying technique. The microstructure of the sample before and after the reaction was characterized by scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM).The XPS spectra showed a shift of d-band centers in Ag–In which could enhance the catalytic activity. Besides, Faraday efficiency of np-Ag-In to generate CO reached ∼94% at −0.8 V vs. RHE, while the geometric current density (jtot) was as high as 15mA/cm2, which is 21% higher than that of np-Ag (12.3mA/cm2). The improved catalytic performance could be attributed to the synergistic effects through tuning of properties and surface composition restructuring. This work sheds light into the relationship between the fine structure of the surface and the electrocatalytic performance in CO2 reduction.

A novel dealloying strategy for fabricating nanoporous Ag via ζ′-AgGa alloy

A mild strategy for fabricating nanoporous silver (np-Ag) pieces was reported via preparation of Ag–Ga alloys in relatively low temperature and subsequent electrochemical dealloying in nitric acid (HNO3) aqueous solution. After selectively etching Ga out of the Ag–Ga alloy, a typical three-dimensional (3D) bicontinuous nanoporous structure with a pore size of ∼67.21–159.33 nm was observed. A series of studies have shown that the addition of sodium dodecyl sulfate (SDS) results in minimum pore size. The coarsen exponent (n) is 1.61, and the activation energy was calculated to be 27.04 kJ mol−1. The ζ′-AgGa alloy prepared at low temperature can be used as the precursor for the preparation of fine np-Ags, and this method provides a new strategy for the industrial production of dealloyed np-Ag.

Nanoporous silver nanorods as surface-enhanced Raman scattering substrates

Structures with dense nanopores are desirable as surface-enhanced Raman scattering (SERS) sensing substrates because the nanopores can behave as both analyte containers and SERS-active sites (known as hot spots). Inspired by the dealloying process to prepare nanoporous structures through selectively removing active metals from their alloy, we developed a method to prepare nanoporous Ag nanorods through chemical reduction of the electrodeposited Ag7O8NO3 nanorods using a strong reducing agent (e.g., NaBH4). The length and the thickness of the Ag7O8NO3 nanorods could be controlled by the electrodeposition voltage and time. Nitrogen and oxygen elements were immediately removed from Ag7O8NO3 nanorods by the reducing agent, leaving behind a tremendous number of nanopores with a mean size of 20 nm, which can efficiently trap and enrich analytes. Meanwhile, the densely packed nanopores can behave as SERS hot spots to provide strong SERS enhancement. The nanoporous Ag nanorods as SERS substrates were used to sensitively detect adenine, spike glycoprotein, and polychlorinated biphenyls pollutants, as well as identify different types of bacteria. The simple fabrication process and the outstanding SERS performance of the nanoporous Ag nanorods make them promising candidates for SERS applications towards trace detection of pollutants, narcotics, food additives, and biomolecules.

Morphological features of micro- and nanoporous silver and copper films synthesized by the substitution reaction method

The results of a study of the structural features of thin silver and copper films synthesized by the chemical substitution reaction are presented. Silver films were obtained by immersing copper substrates in a solution of silver nitrate. Copper films were synthesized by immersing iron and tin-plated iron substrates in a copper sulfate solution. The study of the morphology and composition of the synthesized layers was carried out using a scanning electron microscope. It has been shown that metal nanoporous layers up to 1 μm thick are formed on the substrates as early as 2-3 s after the start of the reaction. The layers consist of microcrystalline hexagonal plates and micro- and nanodendrites. As the reaction time increases, the layers become denser. In this case, the minimum pore size is 20 nm. The synthesized nanoporous films can be used for photocatalytic decomposition of water and enhancement of Raman scattering. Keywords: morphology, porous film, silver, copper, substitution reaction.

Effect of dealloying parameters on HER electrocatalytic performance of nanoporous silver

Effect of dealloying parameters on HER electrocatalytic performance of nanoporous silver

Effect of high temperature oxidation on dealloying mechanism of Ag-Cu alloy

Nanoporous silver (NPS) with a three-dimensional (3D) bicontinuous ligament/pore structure can be fabricated in different ways and with different treatments. Thermal treatments before or after dealloying can have a considerable impact on the dealloying process. High-temperature oxidation (HTO) has been researched as a method to tune the process of NPS fabrication. In this work, X-ray diffraction and X-ray photoelectron spectroscopy characterizations were used to identify the phase after HTO and dealloying. Copper oxide was found in the precursor alloy after HTO, which could be the key factor that would influence the mechanism of NPS fabrication. Scanning electron microscopy and transmission electron microscopy were executed to characterize the pathway of forming NPS and research the difference between HTO specimens and the as-cast sample. This demonstrated that, compared to the free corrosion pathway, the diffusion method of Ag atoms was different under HTO pretreatment, which was the predominant factor causing a larger 3D bicontinuous ligament/pore structure. Finally, the microstructure of the final NPS pretreated with HTO for 3 min was much more homogeneous than that of the others, and when the pretreatment time of HTO reached 5 min, the ligament/pore structure almost collapsed.

A simple and reliable approach for the fabrication of nanoporous silver patterns for surface-enhanced Raman spectroscopy applications

The fabrication of plasmonic nanostructures with a reliable, low cost and easy approach has become a crucial and urgent challenge in many fields, including surface-enhanced Raman spectroscopy (SERS) based applications. In this frame, nanoporous metal films are quite attractive, due to their intrinsic large surface area and high density of metal nanogaps, acting as hot-spots for Raman signal enhancement. In this paper, we report a detailed study on the fabrication of nanoporous silver-based SERS substrates, obtained by the application of two successive treatments with an Inductively Coupled Plasma (ICP) system, using synthetic air and Ar as feeding gases. The obtained substrates exhibit a quite broad plasmonic response, covering the Vis–NIR range, and an enhancement factor reaching 6.5 times, 10^7, estimated by using 4-mercaptobenzoic acid (4-MBA) as probe molecule at 532 nm. Moreover, the substrates exhibit a quite good spatial reproducibility on a centimeter scale, which assures a good signal stability for analytical measurements. Globally, the developed protocol is easy and cost effective, potentially usable also for mass production thanks to the remarkable inter-batches reproducibility. As such, it holds promise for its use in SERS-based sensing platforms for sensitive detection of targets molecules.

Effects of pre-oxidation conditions on microstructure evolution and hydrogen evolution reaction performance of nano-porous Ag

A novel strategy was developed to fabricate nano-porous silver (NPS) with a three-dimensional bi-continuous open porous structure. A high temperature oxidation (HTO) craft and a strong oxidant-assisted low-temperature oxidation method were used to tune the dealloying of AgXCu(1-X) ribbons. The NPS fabricated from the Ag15Cu85 ribbon by the HTO pretreatment exhibited a ligament size of ∼841 nm after 1 h of dealloying. However, the NPS fabricated from the Ag15Cu85 ribbon by the H2O2 craft exhibited a ligament size of ∼61 nm after 1 h of dealloying. In addition, the NPS fabricated by the strong oxidant-assisted dealloying craft exhibited an ultrahomogeneous ligament pore structure and a higher Tafel slope in regard to its hydrogen evolution reaction.