Cuprous oxide nanoparticles dispersed on reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Cuprous oxide (Cu(2)O) nanoparticles dispersed on reduced graphene oxide (RGO) were prepared by reducing copper acetate supported on graphite oxide using diethylene glycol as both solvent and reducing agent. The Cu(2)O/RGO composite exhibits excellent catalytic activity and remarkable tolerance to methanol and CO in the oxygen reduction reaction.     

Study on the application of reduced graphene oxide and multiwall carbon nanotubes hybrid materials for simultaneous determination of catechol,hydroquinone, p-cresol and nitrite

In this paper, the reduced graphene oxide and multiwall carbon nanotubes hybrid materials (RGO–MWNTs) were prepared and a strategy for detecting environmental contaminations was proposed on the basis of RGO–MWNTs modified electrode. The hybrid materials were characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and N₂ sorption–desorption isotherms. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the RGO–MWNTs, the simultaneous measurement of hydroquinone (HQ), catechol (CC), p-cresol (PC) and nitrite (NO₂⁻) with four well-separate peaks was achieved at the RGO–MWNTs modified electrode. The linear response ranges for HQ, CC, PC and NO₂⁻ were 8.0–391.0 μM, 5.5–540.0 μM, 5.0–430.0 μM and 75.0–6060.0 μM, correspondingly, and the detection limits (S/N = 3) were 2.6 μM, 1.8 μM, 1.6 μM and 25.0 μM, respectively. The outstanding film forming ability of RGO–MWNTs hybrid materials endowed the modified electrode enhanced stability. Furthermore, the fabricated sensor was applied for the simultaneous determination of HQ, CC, PC and NO₂⁻ in the river water sample.     

A new method for the voltammetric determination of nitrite

A voltammetric method is presented for the determination of nitrite by use of a carbon-paste electrode chemically modified with an anion-exchanger. Because it is possible to accumulate nitrite on the electrode surface, trace nitrite concentrations down to 1 ng/ml can be determined.     

Simultaneous determination of adrenaline,uric acid,and cysteine using bifunctional electrocatalyst of ruthenium oxide nanoparticles

In this study, ruthenium oxide nanoparticles were electrochemically deposited on the surface of a glassy carbon electrode (RuON-GCE). Electrochemical studies indicate that a modified electrode (RuON-GCE) plays the role of an excellent bifunctional electrocatalyst for the oxidation of adrenaline (AD) and uric acid (UA) in two different potentials. The charge transfer coefficient (α) and the heterogeneous charge transfer rate constant (k′) between the analytes and the electrodeposited nanoparticles were determined using cyclic voltammetry experiments. Through a different pulse voltammetric (DPV) method, the plot of the electrocatalytic current versus AD and UA concentrations emerged to be constituted of two linear segments with different sensitivities. Furthermore, the detection limits of AD and UA were estimated. In DPV, RuON-GCE could separate the oxidation peak potentials of AD, UA, and cysteine (Cys) present in the same solution though, at the bare GCE, the peak potentials were indistinguishable. Finally, the modified electrode activity was studied for the electrocatalytic determination of AD in an injection solution and UA in a human urine sample. The results were found satisfactory.     

Synthesis and characterization of graphene and ordered mesoporous TiO2 as electrocatalyst for the determination of azo colorants

Ordered mesoporous TiO₂, synthesized by soft template method, coupled with graphene was used to modify a carbon paste electrode. The graphene layer was very thin and the mesoporous TiO₂ particles were nano-scale, as confirmed by scanning electron microscopy and transmission electron microscopy. Graphene and mesoporous TiO₂ displayed remarkable enhancement effect and greatly increased the oxidation signals of two azo colorants, i.e., Ponceau 4R and Allura Red. The influence of electrolyte, scan rate, amount of graphene and mesoporous TiO₂, accumulation potential, and time on the signal enhancement of Ponceau 4R and Allura Red was discussed, and therefore, a novel and sensitive electrochemical method was developed for the detection of Ponceau 4R and Allura Red. The linear range was wider than two order of magnitude for both of Ponceau 4R and Allura Red. The limit of detection for Ponceau 4R and Allura Red was 1.35 and 0.34 nM, respectively. Finally, this method was successfully applied in soft drink and sausage samples, which was confirmed by high-performance liquid chromatography technique.     

8-aminoquinoline functionalized graphene oxide for simultaneous determination of guanine and adenine

The nanocomposite graphene oxide/8-aminoquinoline (GAQ) was prepared as modified electrode material for simultaneous determination of guanine and adenine. The prepared GAQ was characterized by SEM, TEM, FTIR, Raman, and UV-vis, which confirmed that the 8-aminoquinoline had been functionalized by covalent modification. The differential pulse voltammetry (DPV) proved the electrochemical properties of the GAQ, which exhibited good electrocatalytic activity and prominent synergistic effect for sensitive determination of guanine and adenine. The guanine and adenine both were detection by DPV showed good linearity with linear range covering 0.1–160 μM, and the detection limits (LOD) (S/N = 3) both were estimated to be 0.033 μM for guanine and adenine, respectively.     

Synthesis and characterization of a novel binuclear iron phthalocyanine/reduced graphene oxide nanocomposite for non-precious electrocatalyst for oxygen reduction

Binuclear iron phthalocyanine/reduced graphene oxide(bi-Fe Pc/RGO) nanocomposite with good electrocatalytic activity for ORR in alkaline medium was prepared in one step. High angle annular dark field image scanning transmission electron microscopy(HAADF-STEM) and energy dispersive X-ray spectroscopy element mapping results show bi-Fe Pc was uniformly distributed on RGO. An obvious cathodic peak located at about-0.23 V(vs. SCE) in CV and an onset potential of-0.004 V(vs. SCE) in LSV indicate the as-prepared bi-Fe Pc/RGO nanocomposite possesses high activity which is closed to Pt/C for ORR. The ORR on bi-Fe Pc/RGO nanocomposite follows four-electron transfer pathway in alkaline medium. Compared with Pt/C, there is only a slight decrease(about 0.02 V vs. SCE) for bi-Fe Pc/RGO nanocomposite when the methanol exists. The excellent activity and methanol tolerance in alkaline solutions proves that bi-Fe Pc/RGO nanocomposite could be considered as a promising cathode catalyst for alkaline fuel cells.     

A glassy carbon electrode modified with gold nanoparticle-encapsulated graphene oxide hollow microspheres for voltammetric sensing of nitrite

Reduced graphene oxide hollow microspheres (rGO HMS) were encapsulated with gold nanoparticles (AuNPs) by spray drying. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the AuNP/rGO HMS. When placed on a glassy carbon electrode (GCE), it exhibits excellent electrochemical catalytic properties towards the oxidation of nitrite. The electrocatalytic properties were studied using various electrochemical techniques. Compared to AuNP-decorated graphene sheet based electrodes documented in the literature, the one presented here provides a larger surface area. This enhances the catalytic activity towards nitrite. The electrode, typically operated at a working potential of 0.82 V (vs. SCE), has a linear response in the 5.0 μM to 2.6 mM nitrate concentration range, and a detection limit as low as 0.5 μM (at an S/N ratio of 3).

Open image in new window

Graphical abstract Schematic presentation of the synthesis of graphene hollow microspheres encapsulated with of gold nanoparticles (AuNP/rGO HMS) through a spray drying technique. The material was applied to the electrochemical determination of nitrite.

     

Nitrogen-enriched carbon powder prepared by ball-milling of graphene oxide with melamine: an efficient electrocatalyst for oxygen reduction reaction

A simple strategy for the production of an efficient platinumfree electrocatalyst for the oxygen reduction reaction was demonstrated. Nitrogen-enriched carbon powder was synthesized by a solid-phase method consisting of grinding graphene oxide and melamine in a planetary ball mill without any solvents and high-temperature processing. Based on XPS and IR spectroscopy data, it was assumed that the high electrocatalytic activity of the obtained material is due to the presence of nitrogen atoms and quinone groups on its surface.     

Stabilization of high-performance oxygen reduction reaction pt electrocatalyst supported on reduced graphene oxide/carbon black composite

Oxygen reduction reaction (ORR) catalyst supported by hybrid composite materials is prepared by well-mixing carbon black (CB) with Pt-loaded reduced graphene oxide (RGO). With the insertion of CB particles between RGO sheets, stacking of RGO can be effectively prevented, promoting diffusion of oxygen molecules through the RGO sheets and enhancing the ORR electrocatalytic activity. The accelerated durability test (ADT) demonstrates that the hybrid supporting material can dramatically enhance the durability of the catalyst and retain the electrochemical surface area (ECSA) of Pt: the final ECSA of the Pt nanocrystal on the hybrid support after 20?000 ADT cycles is retained at >95%, much higher than the commercially available catalyst. We suggest that the unique 2D profile of the RGO functions as a barrier, preventing leaching of Pt into the electrolyte, and the CB in the vicinity acts as active sites to recapture/renucleate the dissolved Pt species. We furthermore demonstrate that the working mechanism can be applied to the commercial Pt/C product to greatly enhance its durability.     

A sensitive nitrite sensor using an electrode consisting of reduced graphene oxide functionalized with ferrocene

A composite consisting of chitosan containing azidomethylferrocene covalently immobilized on sheets of reduced graphene oxide was drop-casted on a polyester support to form a screen-printed working electrode that is shown to enable the determination of nitrite by cyclic voltammetry and chronoamperometry. Both reduction and oxidation of nitrite can be accomplished due to the high electron-transfer rate of this electrode. Under optimal experimental conditions (i.e. an applied potential of 0.7 V vs. Ag/AgCl in pH 7.0 solution), the calibration plot is linear in the 2.5 to 1450 μM concentration range, with an ~0.35 μM limit of detection (at a signal-to-noise ratio of 3). The sensor was successfully applied to the determination of nitrite in spiked mineral water samples, with recoveries ranging between 95 and 101 %.

Open image in new window

Graphical abstract We describe the design of ferrocene-functionalized reduced graphene oxide electrode and its electrocatalytic properties towards the determination of nitrite. Compared to a reduced graphene oxide electrode, the sensor exhibits enhanced electrocatalytic activity towards both oxidation and reduction of nitrite.

     

Fluorescent aptasensor for the determination of Salmonella typhimurium based on a graphene oxide platform

We report on an aptamer with high affinity against Salmonella typhimurium (S. typhimurium) and selected from an enriched oligonucleotide pool by a whole-cell SELEX process in a method for the fluorimetric determination of S. typhimurium using a graphene oxide platform. In the absence of target, the fluorescence was fairly weak as result of the FAM-labeled aptamer adjacent to graphene oxide. If, however, the fluorophore is released from the graphene oxide due to the formation of the target/aptamer complexes, fluorescence intensity is substantially increased. Under the optimum conditions, the assay displays a linear response to bacteria in the concentration range from 1?×?10³ to 1?×?10⁸ CFU·mL^?1, with a detection limit of 100 CFU·mL^?1. The method is selective in that fluorescence is not much enhanced in case of other bacteria. This aptasensor displays higher sensitivity and selectivity than others and is believed to possess a large potential with respect to the rapid detection of bacteria.

Electrografting of amino-TEMPO on graphene oxide and electrochemically reduced graphene oxide for electrocatalytic applications

4-Amino-2,2,6,6-tetramethyl-1-piperridine N-oxyl (4-amino-TEMPO), an electroactive nitroxide radical, was attached to the surface of graphene oxide (GO) and electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode by a simple, rapid and green electrografting method. The electroactive interfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The calculated surface coverage for 4-amino-TEMPO is up to 1.55 × 10^− 9 mol·cm^− 2. The modified electroactive interface exhibited excellent electrocatalytic activity towards the electro-oxidation of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂).     

Ultrasonic route synthesis,characterization and electrochemical study of graphene oxide and reduced graphene oxide

Research on Chemical Intermediates - In this study, an efficient route for graphene oxide (GO) and reduced GO (RGO) synthesis was developed by using an ultrasonic probe and bath alternatively. RGO...     

氧化石墨烯和石墨烯在催化领域中的应用研究进展

石墨烯具有独特的二维平面结构,其导电性能好,比表面积大,耐酸碱,耐高温.基于石墨烯的优异特性,本文作者从材料的合成和结构等方面对石墨烯基催化剂的研制及其催化性能进行了评述.介绍了石墨烯催化体系的类型和机理,对石墨烯催化中存在的问题进行了简单分析,并对石墨烯在催化领域的应用前景进行了展望.     

Photometric determination of nitrite

A new sensitive colour reaction for nitrite determination is presented. The method is based on the reaction of nitrite with p-aminobenzoic acid to form a diazonium ion, which is coupled with 8-hydroxyquinoline, in alkaline medium, to form a reddish-orange water-soluble azo dye. Diazotization and coupling are very fast and control of temperature is unnecessary. Moreover, the colour is stable and its intensity is in direct proportion to nitrite concentration over a wide range.     

Fluorometric determination of nitrite

A sensitive, simple and rapid fluorometric procedure for the determination of nitrite is described. It is based on the reaction of nitrite with 2,3-diaminonaphthalene in acidic solution to form 1-[H]-naphthotriazole, a highly fluorescent compound in alkaline medium. The detection limit is approximately 0.5 ng ml in the test sample (1% relative fluorescence intensity). Application of the method to analysis of a milk sample was tested with aliquots spiked with known amounts of nitrite.