PdAg Bimetallic Nanoalloy-Decorated Graphene: A Nanohybrid with Unprecedented Electrocatalytic, Catalytic, and Sensing Activities

Synthesis of AgNPs from leaf extract of Naringi crenulata and evaluation of its antibacterial activity against multidrug resistant bacteria

The biosynthesis of AgNPs using a methanolic extract of Naringi crenulata is described in this study. UV-visible spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), particle size analyzer (PSA), scanning electron microscope (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to characterize the synthesized AgNPs. The UV-visible spectrum revealed a sharp peak at 420 nm, which represents silver's strong Plasmon resonance. FTIR and XRD confirmed the functional groups (N-H stretch, alkanes, O-H stretch, carboxylic acid, N-H bend, C-X fluoride, and C-N stretch) and face-centered cubic crystalline structure of synthesized AgNPs. SEM and TEM analyses revealed that the synthesized nanoparticles had a spherical morphology with an average diameter of 32.75 nm. The synthesized AgNPs have antibacterial activity against multidrug-resistant bacteria pathogens such as Vibrio cholerae, Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, and Klebsiella pneumoniae. AgNPs can be synthesized using a methanolic extract of Naringi crenulate, and the resulting particle may have wide range of biological applications.

Supramolecular confinement pyrolysis to carbon-supported Mo nanostructures spanning four scales for hydroquinone determination

Metal nanostructures with high atom utilization, abundant active sites, and special electron structures should be beneficial to the electrochemical monitoring of hydroquinone (HQ), a highly toxic environmental pollutant. However, traditional nanostructures, especially non-noble metals generally suffer from severe aggregation, or consist of a mixture of nanoparticles and nanoclusters, resulting in low detection sensitivity. Herein, we precisely control the size of Mo-based nanostructures spanning four scales (viz. Mo₂C nanoparticles, Mo₂C nanodots, Mo nanoclusters and Mo single atoms) anchored on N, P, O co-doped carbon support. The detection sensitivity of four samples toward the HQ follows the orders of Mo single atoms＞Mo₂C nanodots＞Mo nanoclusters＞Mo₂C nanoparticles. The catalytic ability of four catalysts is investigated, also showing the same order. The supported Mo single atoms show superior electro-sensing performance for HQ with wide linear range (0.02-200 μM) and low detection limit (0.005 μM), surpassing most previously reported catalysts. Moreover, the coexistence of dihydroxybenzene isomers of catechol (CC) and resorcinol (RC) does not interfere with the detection of HQ on the Mo single-atom sensor. This work opens up a polyoxometalate-based confinement pyrolysis approach to constructing ultrafine metal-based nanostructures spanning multiple-scales for efficient electrochemical applications.

Free-Standing, Interwoven Tubular Graphene Mesh-Supported Binary AuPt Nanocatalysts: An Innovative and High-Performance Anode Methanol Oxidation Catalyst

Pt-based alloy or bimetallic anode catalysts have been developed to reduce the carbon monoxide (CO) poisoning effect and the usage of Pt in direct methanol fuel cells (DMFCs), where the second metal plays a role as CO poisoning inhibitor on Pt. Furthermore, better performance in DMFCs can be achieved by improving the catalytic dispersion and using high-performance supporting materials. In this work, we introduced a free-standing, macroscopic, interwoven tubular graphene (TG) mesh as a supporting material because of its high surface area, favorable chemical inertness, and excellent conductivity. Particularly, binary AuPt nanoparticles (NPs) can be easily immobilized on both outer and inner walls of the TG mesh with a highly dispersive distribution by a simple and efficient chemical reduction method. The TG mesh, whose outer and inner walls were decorated with optimized loading of binary AuPt NPs, exhibited a remarkably catalytic performance in DMFCs. Its methanol oxidation reaction (MOR) activity was 10.09 and 2.20 times higher than those of the TG electrodes with only outer wall immobilized with pure Pt NPs and binary AuPt NPs, respectively. Furthermore, the catalyst also displayed a great stability in methanol oxidation after 200 scanning cycles, implying the excellent tolerance toward the CO poisoning effect.

Mechanistic insight into the electrocatalytic performance of reduced graphene oxide supported palladium, silver and palladium-silver nanodeposits toward electro-dehalogenation of halocarbons in room temperature ionic liquids

Herein, we report the results from our extensive voltammetric investigations designed to explore, assess and explain the electrocatalytic performance of reduced graphene oxide supported metal nano-deposits toward the electro-dehalogenation of halocarbons in room temperature ionic liquids (RTILs). Specifically, we investigated the electro-reductive dechlorination of the model halocarbon, carbon tetrachloride over glassy carbon electrode (GCE) and palladium-graphene (Pd-Gr), silver-graphene (Ag-Gr) and palladium-silver-graphene (PdAg-Gr) nanocomposites in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf₂]). Analysis of the voltammetric data in light of Marcus-Hush formulation reveals that the electro-reductive cleavage of the C-Cl bond of CCl₄ over GCE in [BMIM][NTf₂] follows a sticky dissociative electron transfer (SDET) pathway. The significantly stronger interaction energy between electrogenerated Cl^- and CCl₃˙ (radical) fragments in RTILs makes electroreduction of CCl₄ in [BMIM][NTf₂] much easier than in organic solvents. The activation-driving force relationship for electro-catalytic dechlorination of CCl₄ over Pd-Gr was observed to follow a modified sticky dissociative electron transfer model wherein apart from the ion-radical interaction, the adsorptive interaction of chlorinated species with the electrocatalytic surface needs to be taken into consideration to account for the apparent activation energy-driving force dependence. Interestingly the activation energy-driving force relationships for the electroreduction of CCl₄ over Ag-Gr and PdAg-Gr were observed to fit a modified stepwise ET (MSET) pathway. In the MSET pathway, the adsorption and the implied free energy change of the electroreducible halocarbon significantly alter the solvent re-organization energy and the inherent barrier for the heterogeneous ET process. The adsorptive interaction and hence the electrocatalytic performance of PdAg-Gr were observed to be more than that observed for Ag-Gr. This is attributed to the Ag to Pd charge transfer in the PdAg-Gr nanodeposits. Our results besides underlining the positive influence of RTILs in facilitating the electroreductive detoxification of halocarbons, very well establish the mechanistic basis for the electrocatalytic performance of graphene based nanodeposits toward electrodehalogenation of halocarbons.

Electrochemical reduction of CO2 to ethylene on Cu/Cu x O-GO composites in aqueous solution

Here, we present fabrication of Graphene oxide (GO) supported Cu/Cu x O nano-electrodeposits which can efficiently and selectively electroreduce CO2 into ethylene with a faradaic efficiency (F.E) of 34% and a conversion rate of 194 mmol g-1 h-1 at -0.985 V vs. RHE. The effect of catalyst morphology, working electrode fabricational techniques, the extent of metal-GO interaction and the oxide content in Cu/Cu x O, was studied in detail so as to develop a protocol for the fabrication of an active, stable and selective catalyst for efficient electro-production of ethylene from CO2. Moreover, a detailed comparative study about the effect of the GO support, and the nature of the cathodic collection substrate used for the electro-deposition is presented.

Next-Generation Multifunctional Carbon-Metal Nanohybrids for Energy and Environmental Applications

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, Cu₂O, MoS₂, TiO₂, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nanohybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water-environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., H₂O splitting and CO₂ conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.