Search

Silver and its alloys undergo tarnishing with time, which is a black stain on the surface due to the formation of Ag2S. Developing a tarnish resistant Ag alloy was attempted by alloying Ag with elements that form a passive oxide layer on the surface. Germanium is proven to provide better tarnish resistance to sterling Silver alloy (92.5 wt% pure) which is available under the trade name of Argentium©. The present work investigates the tarnish resistance behavior of sterling silver alloy (92.5 wt% pure) containing various additions of Copper, Zinc, and Germanium. The alloys were prepared by melting and casting route, followed by Passivation Heat Treatment (PHT) to create a stable and continuous oxide layer. The temperature for PHT was optimized using thermogravimetry analysis (TGA) of the alloys prepared. Accelerated tarnish test was carried out to investigate the tarnishing behavior of alloy samples obtained before and after PHT. The samples were characterized using XRD, SEM-EDX, and micro-Raman Spectroscopy. The change in reflectance of the samples after tarnish test is determined using UV–Visible reflectance spectroscopy. The mechanism behind the tarnish resistance was derived using Density Functional Theory (DFT) by comparing sulphur (S2) and Oxygen (O2) adsorption energies (BE) of the alloying elements. The lower value of S2(BE)/O2(BE) indicates better oxidation and tarnish resistance. The ratio ranges between 222 % (Pure Ag) and 132 % (for Ag-4.2Cu-2.8Zn-1.4Ge) and the p-p between Ge and O has contributed to the reduction in the ratio.

We report a novel approach for surface-enhanced Raman spectroscopy (SERS) detection in digital microfluidics (DMF). This is made possible by a microspray hole (μSH) that uses an electrostatic spray (ESTAS) for sample transfer from inside the chip to an external SERS substrate. To realize this, a new ESTAS-compatible stationary SERS substrate was developed and characterized for sensitive and reproducible SERS measurements. In a proof-of-concept study, we successfully applied the approach to detect various analyte molecules using the DMF chip and achieved micro-molar detection limits. Moreover, this technique was exemplarily employed to study an organic reaction occurring in the DMF device, providing vibrational spectroscopic data.

Surface Enhanced Raman Scattering (SERS) is emerging as a potent analytical tool for the detection of various pollutants in complex environments due to its distinctive vibrational fingerprint ability and pronounced detection sensitivity. Precautious of adverse blue-green economies and ecological impacts, sustainable generation of SERS active substrates and analyte casting matrices are getting prioritized. Herein, gold nanoflowers (AuNFs) of ∼75 ± 15 nm were initially biofabricated using an expended cell culture medium as a one-step synthesis cumstabilization strategy. Then the heavy architecture of multi-faceted AuNFs with deep pits and edges, that acted as hotspots for enhancing the localized electromagnetic fields, was utilized for the direct SERS detection of commonly used carcinogenic herbicides collected from agro-farms at nanomolar regimes with 0.44 ppm and 0.27 ppm for Glyphosate and amino methyl phosphonic acid, respectively. Such a low level detection is superior by 8.33% when compared to the reported values. Computational finite-difference time-domain (FDTD) simulations affirmed the enhanced SERS effect from the multi-faceted nanostructure of AuNFs with structural heterogeneities that provide numerous hotspots to amplify the localized electromagnetic field. More eminently, fish scale derived biotemplate through AuNF-analyte drop casting contributed to the exceptional intensities, attributed to the naturally grooved hierarchically porous hydrophilic lamellar structures contact angle of 73°. Overall, the adapted bioengineering of SERS substrate is safe, robust, affordable and reproducible, fostered by bioderived durable biomatrix offering potent sustainable SERS detection of various biomedically and environmentally relevant molecules.

An electrochemical approach to enable surface-enhanced Raman spectroscopy (SERS) detection in continuous microflow is presented. This is achieved by the integration of a silver electrode as SERS substrate in a microfluidic chip device. By the application of actuation pulses of about 4 V, otherwise irreversibly adsorbed analytes are stripped off, which enables quasi-real-time SERS detection in a continuous microflow. The approach opens up a way for in situ SERS monitoring of compounds in microflow with high application potential in microseparation techniques like HPLC and lab-on-a-chip devices.

A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.

In heterogeneous catalysis, characterization of heterogeneous metal interfaces of bimetallic catalysts is a crucial step to elucidate the catalytic performance and is a key to develop advanced catalysts. However, analytical techniques such as X-ray photoelectron spectroscopy can only work in vacuum conditions and are difficult to use for in situ analysis. Here, we present efficient and convenient core–shell nanoparticle-enhanced Raman spectroscopy to explore the in situ electronic structures of heterogeneous interfaces (Au@Pd and Au@Pt core–shell NPs) by varying the shell thickness. The experimental observations reported here clearly show that Pd donates electrons to Au, while Pt accepts electrons from Au at the heterogeneous interfaces. This conclusion gains further support from ex situ X-ray photoelectron spectroscopy results. The Au core greatly affects the electronic structures of both the Pd and Pt shells as well as catalytic behaviors. Finally, the as-prepared core–shell nanoparticles were used to demonstrate their improved catalytic properties in real electrocatalytic systems such as methanol oxidation and oxygen reduction reactions.