Evaluation of reduced-graphene-oxide-supported gold nanoparticles as catalytic system for electroreduction of oxygen in alkaline electrolyte

Facile Synthesis of Low-Cost Copper-Silver and Cobalt-Silver Alloy Nanoparticles on Reduced Graphene Oxide as Efficient Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media

Copper-silver and cobalt-silver alloy nanoparticles deposited on reduced graphene oxide (CuAg/rGO and CoAg/rGO) were synthesized and examined as electrocatalysts for oxygen reduction reaction (ORR) and hydrogen peroxide reduction reaction (HPRR) in alkaline media. Characterization of the prepared samples was done by transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction analysis (XRD), and scanning electron microscopy with integrated energy-dispersive X-ray spectroscopy (SEM-EDS). CuAg/rGO and CoAg/rGO nanoparticles diameter ranged from 0.4 to 9.2 nm. The Ag loading was ca. 40 wt.% for both electrocatalysts, with that for Cu and Co being 35 and 17 wt.%, respectively. CoAg/rGO electrocatalyst showed a Tafel slope of 109 mV dec⁻¹, significantly lower than that for CuAg/rGO (184 mV dec⁻¹), suggesting faster ORR kinetics. Additionally, a higher diffusion current density was obtained for CoAg/rGO (−2.63 mA cm⁻²) than for CuAg/rGO (−1.74 mA cm⁻²). The average value of the number of electrons transferred during ORR was 2.8 for CuAg/rGO and 3.3 for CoAg/rGO electrocatalyst, further confirming the higher ORR activity of the latter. On the other hand, CuAg/rGO showed higher peak current densities (−3.96 mA cm⁻²) for HPRR compared to those recorded for CoAg/rGO electrocatalyst (−1.96 mA cm⁻²).

Effect of Graphene vs. Reduced Graphene Oxide in Gold Nanoparticles for Optical Biosensors-A Comparative Study

Aiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobilization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV-Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.

Electrocatalysis of gold-based nanoparticles and nanoclusters

Gold (Au)-based nanomaterials, including nanoparticles (NPs) and nanoclusters (NCs), have shown great potential in many electrocatalytic reactions due to their excellent catalytic ability and selectivity. In recent years, Au-based nanostructured materials have been considered as one of the most promising non-platinum (Pt) electrocatalysts. The controlled synthesis of Au-based NPs and NCs and the delicate microstructure adjustment play a vital role in regulating their catalytic activity toward various reactions. This review focuses on the latest progress in the synthesis of efficient Au-based NP and NC electrocatalysts, highlighting the relationship between Au nanostructures and their catalytic activity. This review first discusses the parameters of Au-based nanomaterials that determine their electrocatalytic performance, including composition, particle size and architecture. Subsequently, the latest electrocatalytic applications of Au-based NPs and NCs in various reactions are provided. Finally, some challenges and opportunities are highlighted, which will guide the rational design of Au-based NPs and NCs as promising electrocatalysts.

Graphene Oxide Decorated Nanometal-Poly(Anilino-Dodecylbenzene Sulfonic Acid) for Application in High Performance Supercapacitors

Graphene oxide (GO) decorated with silver (Ag), copper (Cu) or platinum (Pt) nanoparticles that are anchored on dodecylbenzene sulfonic acid (DBSA)-doped polyaniline (PANI) were prepared by a simple one-step method and applied as novel materials for high performance supercapacitors. High-resolution transmission electron microscopy (HRTEM) and high-resolution scanning electron microscopy (HRSEM) analyses revealed that a metal-decorated polymer matrix is embedded within the GO sheet. This caused the M/DBSA⁻PANI (M = Ag, Cu or Pt) particles to adsorb on the surface of the GO sheets, appearing as aggregated dark regions in the HRSEM images. The Fourier transform infrared (FTIR) spectroscopy studies revealed that GO was successfully produced and decorated with Ag, Cu or Pt nanoparticles anchored on DBSA⁻PANI. This was confirmed by the appearance of the GO signature epoxy C⁻O vibration band at 1040 cm-1 (which decreased upon the introduction of metal nanoparticle) and the PANI characteristic N⁻H stretching vibration band at 3144 cm-1 present only in the GO/M/DBSA⁻PANI systems. The composites were tested for their suitability as supercapacitor materials; and specific capacitance values of 206.4, 192.8 and 227.2 F·g-1 were determined for GO/Ag/DBSA⁻PANI, GO/Cu/DBSA⁻PANI and GO/Pt/DBSA⁻PANI, respectively. The GO/Pt/DBSA⁻PANI electrode exhibited the best specific capacitance value of the three electrodes and also had twice the specific capacitance value reported for Graphene/MnO₂//ACN (113.5 F·g-1). This makes GO/Pt/DBSA⁻PANI a very promising organic supercapacitor material.

One-pot facile simultaneous in situ synthesis of conductive Ag–polyaniline composites using Keggin and Preyssler-type phosphotungstates

Two heteropolytungstate structures, Keggin (H₃PW₁₂O₄₀) and Preyssler (H₁₄[NaP₅W₃₀O₁₁₀]), were used to synthesize conductive silver nanoparticle–polyaniline–heteropolytungstate (AgNPs–PAni–HPW) nanocomposites. During the oxidative polymerization of aniline, heteropolyblue was generated and served as the reducing agent to stabilize and distribute AgNPs within “PAni–Keggin” and “PAni–Preyssler” matrixes as well as on their surfaces. The prepared nanocomposites and AgNPs were characterized using UV-visible (UV-Vis) and Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), pore size distribution BET, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). UV-Vis results showed different stages of the formation of metal NPs embedded in the polymer–HPW composites, and FT-IR spectra presented characteristic bands of PAni, Keggin and Preyssler anions in the composites confirming no changes in their structures. The presence of AgNPs and an intensely crystalline matrix were confirmed by the XRD pattern. The BET surface areas were found to be 38.426 m² g⁻¹ for “AgNPs–PAni–Keggin” and 29.977 m² g⁻¹ for “AgNPs–PAni–Preyssler” nanocomposites with broad distributions of meso-porous structure for both nanocomposites. TEM and SEM images confirmed that the type of heteropolyacids affected the size of AgNPs. This is the first report that uses Keggin and Preyssler-type heteropolytungstate to synthesize “AgNPs–PAni–HPW” nanocomposites in an ambient condition through a low-cost, facile, one-pot, environmentally friendly and simultaneous in situ oxidative polymerization protocol.

Two heteropolytungstate structures, (a) Keggin (H₃PW₁₂O₄₀) and (b) Preyssler (H₁₄(NaP₅W₃₀O₁₁₀]), have been used to synthesize conductive silver nanoparticle–polyaniline–heteropolytungstate, (AgNPs–PAni–HPW) nanocomposites.