Добірка наукової літератури з теми "Dealloyed nanoprous gold (NPG)"

Volatile organic compounds (VOCs) are prevalent in daily life, from the lab environment to industrial applications, providing tremendous functionality but also posing significant health risk. Moreover, individual VOCs have individual risks associated with them, making classification and sensing of a broad range of VOCs important. This work details the application of electrochemically dealloyed nanoporous gold (NPG) as a VOC sensor through measurements of the complex electrical frequency response of NPG. By leveraging the effects of adsorption and capillary condensation on the electrical properties of NPG itself, classification and regression is possible. Due to the complex nonlinearities, classification and regression are done through the use of a convolutional neural network. This work also establishes key strategies for improving the performance of NPG, both in sensitivity and selectivity. This is achieved by tuning the electrochemical dealloying process through manipulations of the starting alloy and through functionalization with 1-dodecanethiol.

Potentiometric redox sensing in solutions containing multiple redox molecules was evaluated using in-house constructed nanoporous gold (NPG)-platinum (Pt) and unmodified NPG electrodes. The NPG-Pt electrode was fabricated by electrodepositing Pt into the nanoporous framework of a chemically dealloyed NPG electrode. By varying the concentration of the Pt salt and the electrodeposition time, different amounts of Pt were introduced. Characterization by SEM shows the pore morphology doesn’t change with the addition of Pt and XPS indicates the electrodes contain ∼2.5–24 wt% Pt. Open-circuit potential (OCP) measurements in buffer and solutions containing ascorbic acid, cysteine, and/or uric acid show that the OCP shifts positive with the addition of Pt. These results are explained by an increase in the rate of the oxygen reduction reaction with the addition of Pt. The overall shape of the potentiometric titration curves generated from solutions containing one or more bioreagents is also highly dependent on the amount of Pt in the nanoporous electrode. Furthermore, the generation of OCP vs Log [bioreagent] from the results of the potentiometric experiments shows an ∼2-fold increase in sensitivity can result with the addition of Pt. These results indicate the promise that these electrodes have in potentiometric redox sensing.

In this study, we report nanoporous gold (NPG) as an economic, efficient, and stable alternative electrocatalyst for methanol electro-oxidation. The said sample was successfully prepared from an Fe-rich metastable Au33Fe67 supersaturated solid solution acting as the precursor, which was formed into ribbons by the phenomenon of rapid solidification using melt-spinning technique. The as-quenched ribbon was then chemically dealloyed in 1 M HCl at 70 °C for different durations of time. A homogeneous, free-standing, and mechanically stable NPG sample was obtained with tunable ligament shape and size. The morphology and composition were characterized by using SEM with EDS, while the structure by XRD. The sample was examined as an electrocatalyst for methanol electro-oxidation profiting off its large surface area; cyclic voltammetry (CV) was the technique employed for electrochemical studies. In a basic solution of methanol and KOH, the sample displays a low peak potential of 0.47 V vs. Ag/AgCl for methanol electro-oxidation with a high peak current density of 0.43 mA/cm2. In addition, it demonstrates outstanding stability and high poisoning tolerance. It is noteworthy that the fabrication process of the NPG sample from start to end was intentionally opted to be sustainable, cost-effective, rapid, and feasible. The usage of critical raw materials was avoided. As a whole, the properties and results put forth by the NPG sample make it an inexpensive, sustainable, and excellent alternative as an electrocatalyst for methanol electro-oxidation.

Grain boundary formation during coarsening of nanoporous gold (NPG) is investigated wherein a nanocrystalline structure can form by particles detaching and reattaching to the structure. MicroLaue and electron backscatter diffraction measurements demonstrate that an in-grain orientation spread develops as NPG is coarsened. The volume fraction of the NPG sample is near the limit of bicontinuity, at which simulations predict that a bicontinuous structure begins to fragment into independent particles during coarsening. Phase-field simulations of coarsening using a computationally generated structure with a volume fraction near the limit of bicontinuity are used to model particle detachment rates. This model is tested by using the measured NPG structure as an initial condition in the phase-field simulations. We predict that up to ∼5% of the NPG structure detaches as a dealloyed Ag75Au25 sample is annealed at 300 °C for 420 min. The quantity of volume detached is found to be highly dependent on the volume fraction and volume fraction homogeneity of the nanostructure. As the void phase in the experiments cannot support independent particles, they must fall and reattach to the structure, a process that results in the formation of new grain boundaries. This particle reattachment process, along with other classic processes, leads to the formation of grain boundaries during coarsening in nanoporous metals. The formation of grain boundaries can impact a variety of applications, including mechanical strengthening; thus, the consideration and understanding of particle detachment phenomena are essential when studying nanoporous metals.