Nanocomposite for methanol oxidation: synthesis and characterization of cubic Pt nanoparticles on graphene sheets

Nanozyme-mediated cascade reaction system for electrochemical detection of 1,5-anhydroglucitol

Diabetes is one of metabolic diseases affecting major human health. The early diagnosis and treatment of diabetes have significant benefits. 1,5-anhydroglucitol (1,5-AG) accurately reflects a patient's average blood glucose level for the past 3-7 days and becomes a promising marker for real-time detection of diabetes. In this study, a novel biosensor for determination 1,5-AG is constructed using reduce graphene oxide-carboxymethylated chitosan-hemin@platinum nanocomposites (rGO-CMC-H@Pt NCs) nanozyme and pyranose oxidase (PROD) enzyme as the electrochemical biosensing platform. The rGO-CMC-H@Pt NCs nanozyme has good electro-conductibility, high specific surface area, and admirable peroxide-like catalysis effect to enhance the electrochemical response. 1,5-AG is catalyzed by PROD and produces hydrogen peroxide (H₂O₂), which in turn can be decomposed by rGO-CMC-H@Pt NCs and produce a current signal recorded by differential pulse voltammetry (DPV) technique. Under optimal conditions, the response currents have a linear relationship in the 1,5-AG concentration of 0.1-2.0 mg/mL with R² of 0.9869. The sensitivity is 2.1895 μA/μg·mL^-1 and the limit of detection (LOD) is 38.2 μg/mL (S/N = 3). In addition, the specificity, reproducibility, stability and recovery (94.5-107.6%) of 1,5-AG biosensors all exhibit good performance. Therefore, the designed 1,5-AG biosensor has a good effect and can be used for the diagnosis of diabetes.

Characterization of Au and Bimetallic PtAu Nanoparticles on PDDA-Graphene Sheets as Electrocatalysts for Formic Acid Oxidation

Nanocomposite materials of the Au nanoparticles (Au/PDDA-G) and the bimetallic PtAu nanoparticles on poly-(diallyldimethylammonium chloride) (PDDA)-modified graphene sheets (PtAu/PDDA-G) were prepared with hydrothermal method at 90 °C for 24 h. The composite materials Au/PDDA-G and PtAu/PDDA-G were evaluated by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) for exploring the structural characterization for the electrochemical catalysis. According to TEM results, the diameter of Au and bimetallic PtAu nanoparticles is about 20-50 and 5-10 nm, respectively. X-ray diffraction (XRD) results indicate that both of PtAu and Au nanoparticles exhibit the crystalline plane of (111), (200), (210), and (311). Furthermore, XRD data also show the 2°-3° difference between pristine graphene sheets and the PDDA-modified graphene sheets. For the catalytic activity tests of Au/PDDA-G and PtAu/PDDA-G, the mixture of 0.5 M aqueous H2SO4 and 0.5 M aqueous formic acid was used as model to evaluate the electrochemical characterizations. The catalytic activities of the novel bimetallic PtAu/graphene electrocatalyst would be anticipated to be superior to the previous electrocatalyst of the cubic Pt/graphene.

Electrocatalytic Polysulfide Traps for Controlling Redox Shuttle Process of Li-S Batteries

Stabilizing the polysulfide shuttle while ensuring high sulfur loading holds the key to realizing high theoretical energy of lithium-sulfur (Li-S) batteries. Herein, we present an electrocatalysis approach to demonstrate preferential adsorption of a soluble polysulfide species, formed during discharge process, toward the catalyst anchored sites of graphene and their efficient transformation to long-chain polysulfides in the subsequent redox process. Uniform dispersion of catalyst nanoparticles on graphene layers has shown a 40% enhancement in the specific capacity over pristine graphene and stability over 100 cycles with a Coulombic efficiency of 99.3% at a current rate of 0.2 C. Interaction between electrocatalyst and polysulfides has been evaluated by conducting X-ray photoelectron spectroscopy and electron microscopy studies at various electrochemical conditions.

Synthesis and characterizations of Ni-NiO nanoparticles on PDDA-modified graphene for oxygen reduction reaction

We are presenting our recent research results about the Ni-NiO nanoparticles on poly-(diallyldimethylammonium chloride)-modified graphene sheet (Ni-NiO/PDDA-G) nanocomposites prepared by the hydrothermal method at 90°C for 24 h. The Ni-NiO nanoparticles on PDDA-modified graphene sheets are measured by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) pattern for exploring the structural evidence to apply in the electrochemical catalysts. The size of Ni-NiO nanoparticles is around 5 nm based on TEM observations. The X-ray diffraction (XRD) results show the Ni in the (012), (110), (110), (200), and (220) crystalline orientations, respectively. Moreover, the crystalline peaks of NiO are found in (111) and (220). The thermal gravimetric analysis (TGA) result represents the loading content of the Ni metal which is about 34.82 wt%. The electron spectroscopy for chemical analysis/X-ray photoelectron spectroscopy (ESCA/XPS) reveals the Ni(0) to Ni(II) ratio in metal phase. The electrochemical studies with Ni-NiO/PDDA-G in 0.5 M aqueous H2SO4 were studied for oxygen reduction reaction (ORR).

Immobilization of carbon nanotubes on functionalized graphene film grown by chemical vapor deposition and characterization of the hybrid material

We report the surface functionalization of graphene films grown by chemical vapor deposition and fabrication of a hybrid material combining multi-walled carbon nanotubes and graphene (CNT-G). Amine-terminated self-assembled monolayers were prepared on graphene by the UV-modification of oxidized groups introduced onto the film surface. Amine-termination led to effective interaction with functionalized CNTs to assemble a CNT-G hybrid through covalent bonding. Characterization clearly showed no defects of the graphene film after the immobilization reaction with CNT. In addition, the hybrid graphene material revealed a distinctive CNT-G structure and p-n type electrical properties. The introduction of functional groups on the graphene film surface and fabrication of CNT-G hybrids with the present technique could provide an efficient, novel route to device fabrication.

The microwave-assisted ionic liquid nanocomposite synthesis: platinum nanoparticles on graphene and the application on hydrogenation of styrene

The microwave-assisted nanocomposite synthesis of metal nanoparticles on graphene or graphite oxide was introduced in this research. With microwave assistance, the Pt nanoparticles on graphene/graphite oxide were successfully produced in the ionic liquid of 2-hydroxyethanaminium formate [HOCH2CH2NH3][HCO2]. On graphene/graphite oxide, the sizes of Pt nanoparticles were about 5 to 30 nm from transmitted electron microscopy (TEM) results. The crystalline Pt structures were examined by X-ray diffraction (XRD). Since hydrogenation of styrene is one of the important well-known chemical reactions, herein, we demonstrated then the catalytic hydrogenation capability of the Pt nanoparticles on graphene/graphite oxide for the nanocomposite to compare with that of the commercial catalysts (Pt/C and Pd/C, 10 wt.% metal catalysts on activated carbon from Strem chemicals, Inc.). The conversions with the Pt nanoparticles on graphene are >99% from styrene to ethyl benzene at 100°C and under 140 psi H2 atmosphere. However, ethyl cyclohexane could be found as a side product at 100°C and under 1,520 psi H2 atmosphere utilizing the same nanocomposite catalyst.