Seungwon Jeon

Reductive determination of hydrogen peroxide with MWCNTs-Pd nanoparticles on a modified glassy carbon electrode

This paper introduces the use of multi walled carbon nanotubes (MWCNTs) with palladium (Pd) nanoparticles in the electrocatalytic reduction of hydrogen peroxide (H(2)O(2)). We have developed and characterized a biosensor for H(2)O(2) based on Nafion(®) coated MWCNTs-Pd nanoparticles on a glassy carbon electrode (GCE). The Nafion(®)/MWCNTs-Pd/GCE electrode was easily prepared in a rapid and simple procedure, and its application improves sensitive determination of H(2)O(2). Characterization of the MWCNTs-Pd nanoparticle film was performed with transmission electron microscopy (TEM), Raman, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and amperometry (at an applied potential of -0.2V) measurements were used to study and optimize performance of the resulting peroxide biosensor. The proposed H(2)O(2) biosensor exhibited a wide linear range from 1.0 μM to 10 mM and a low detection limit of 0.3 μM (S/N=3), with a fast response time within 10s. Therefore, this biosensor could be a good candidate for H(2)O(2) analysis.

Urea derivative of calix[4]diquinone: HSO4− ion selective receptor

Abstract Urea derivative of calix[4]diquinone 3 has been synthesized in two steps via urea formation and oxidation of 1 . Anion-ligand interactions were studied by 1 H NMR and electrochemical analysis and showed a good affinity between receptor 3 and HSO 4 − .

Poly(vinyl chloride) membrane cesium ion-selective electrodes based on lipophilic calix[6]arene tetraester derivatives.

New lipophilic tetraesters of calix[6]arene and calix[6]diquinone are investigated as cesium ion-selective ionophores in poly(vinyl chloride) membrane electrodes. For an ion-selective electrode based on calix[6]arene tetraester I, the linear response is 1x10(-6)-1x10(-1) M of Cs(+) concentrations. The selectivity coefficients for cesium ion over alkali, alkaline earth and ammonium ions are determined. The detection limit (log a (Cs (+))=-6.31) and the selectivity coefficient (log k (Cs (+),Rb (+))(pot )=-1.88) are obtained for polymeric membrane electrode containing calix[6]arene tetraester I.

High catalytic activity of electrochemically reduced graphene composite toward electrochemical sensing of Orange II

Orange II, an azo dye, is sometimes illegally used as a red dye in food products despite its adverse health effects if consumed. Therefore, the determination of low concentrations of Orange II is an important target. An Orange II sensor was prepared using electrochemically reduced graphene oxide grafted with 5-amino-1,3,4-thiadiazole-2-thiol-Pt nanoparticles (denoted as ERGO-ATDT-Pt) onto a glassy carbon electrode (GCE) and investigated for Orange II detection in 0.1M acetate buffer solution (ABS at pH 4.5) with prominent reversible redox peaks. A wide linear range of 1×10(-)(8)-6×10(-)(7)M with a low detection limit of 3.4×10(-)(10)M (s/n=3) was found for Orange II detection. This developed ERGO-ATDT-Pt/GCE sensor showed good selectivity, excellent stability and better response to the real sample analysis with excellent recovery.

Different length linkages of graphene modified with metal nanoparticles for oxygen reduction in acidic media

This paper reports the chemical synthesis and experimental characterization of various graphene oxide (GO)-supported platinum (Pt) and palladium (Pd) nanoparticle (NP) catalysts. To investigate the relationship between the linker length and the catalytic activities of the metal-decorated GO catalysts, six samples were prepared with three different linker molecules, HS(CH2)2SH, HS(CH2)3SH and HS(CH2)4SH (denoted as GO-l-NPs), and two different metal NPs, Pt and Pd. All GO-l-NP catalysts were tested in oxygen reduction reaction (ORR) using electrochemical techniques such as cyclic voltammetry (CV) and rotating ring disk electrode (RRDE) hydrodynamic voltammetry to quantitatively obtain the ORR kinetic constants and the reaction mechanisms on a glassy carbon electrode (GCE) in 0.5 M H2SO4 solution. All GO-l-NPs/GCE electrodes showed significantly improved ORR activity and mechanisms. GO-l-NPs were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that Pt and Pd were successfully attached onto the GO surface. A more positive potential catalytic ORR was observed in the modified GO-l-NPs with longer chain linker lengths in both cases.

A novel δ-MnO2 with carbon nanotubes nanocomposite as an enzyme-free sensor for hydrogen peroxide electrosensing

We have reported the synthesis and application of a δ-MnO2 with carbon nanotubes (δ-MnO2/CNTs) nanocomposite as an enzyme-free sensor for the detection of H2O2 through an electroreduction reaction, where δ-MnO2 serves as the catalytic center and CNTs as the highly conductive base material. The δ-MnO2/CNTs nanocomposite was synthesized via a simple and single-step hydrothermal process in alkaline solution without using any surfactants or templates. The electrochemical properties of the δ-MnO2/CNTs on a glassy carbon electrode were investigated by cyclic voltammetry, and amperometry. It was found that, under optimized conditions, the sensor fabricated electrode provides linear amperometric responses for H2O2 in a large concentration range from 0.05 to 22 mM and a detection limit of 1 μM with a comparatively high sensitivity of 243.9 μA mM−1 cm−2. In addition, the δ-MnO2/CNTs modified GCE exhibits excellent selectivity, and good reproducibility for H2O2 detection. It is promising that the proposed H2O2 sensor can be used as an effective tool to measure the H2O2 in practical samples.

Electrochemistry of a urea-functionalized calix[4]diquinone sulfate-anion selective receptor

Abstract A new class of neutral ligands is synthesized and studied for the binding properties with anions by electrochemical methods. The binding of calix[4]diquinone 1 with HSO 4 − causes a large negative shift of the electrode potentials of the calix[4]diquinone. This novel neutral anion receptor 1 binds anions through hydrogen-bonding and shows high selectivity for HSO 4 − over H 2 PO 4 − , Cl − , and CH 3 CO 2 − . The selectivity of HSO 4 − over H 2 PO 4 − , Cl − , and CH 3 CO 2 − may be attributed to the stronger hydrogen-bonding with the urea moiety, and also with the quinone moiety of 1 receptor, and also the greater compatibility of the cavity of 1 with tetrahedral HSO 4 − .

Anion Recognition by Urea Derivatives of Anthraquinone: Dihydrogen Phosphate Ion Selective Neutral Receptors

Three urea derivatives of anthraquinone were synthesized and they showed a high selectivity for dihydrogen phosphate ions.

Electrocatalytic reduction of dioxygen by quadruply aza bridged closely interfaced cofacial bis(5,10,15,20-tetraphenylporphyrin)s in various pH solutions

Abstract The electrocatalytic reduction of dioxygen is investigated by cyclic voltammetry and chronoamperometry at a glassy carbon electrode and a carbon microelectrode adsorbed with cobalt porphyrins in dioxygen-saturated aqueous solutions of various pH. The reduction potential ( E p ) of dioxygen at chemically modified electrodes shows dependence on pH. Electrochemical reduction of dioxygen at monomeric Co-1 or dimeric Co 2 -2 modified electrodes establishes a pathway of 2e − reduction to form hydrogen peroxide, but it carries out 4e − reduction of dioxygen to water at the electrode adsorbed with dimeric Co 2 -3 or Co 2 -4 in all pH solutions. The electrocatalytic pathway of dioxygen reduction by cofacial biscobalt porphyrins is independent of pH, but the E p of dioxygen reduction is dependent on pH. Theelectrochemical reduction of dioxygen is irreversible and diffusion controlled.

New Approach for Porous Chitosan?Graphene Matrix Preparation through Enhanced Amidation for Synergic Detection of Dopamine and Uric Acid

Amide-functionalized materials have emerged as promising nonprecious catalysts for electrochemical sensing and catalysis. The covalent immobilization of chitosan (CS) onto graphene sheet (GS) (denoted as CS–GS) has been done via higher degree of amidation reaction to develop an electrochemical sensing matrix for simultaneous determination of dopamine (DA) and uric acid (UA). The enhanced amidation between CS and GS has not been reported previously. However, electrochemical results have revealed that the CS–GS enhances the electrocatalytic performance in terms of the oxidation potential and peak current due to the higher degree of amide functionalization compared to that of CS/GS, which has a lower amidation. Differential pulse voltammetry-based studies have indicated that the CS–GS matrix works at a lower detection limit (0.14 and 0.17 μM) (S/N = 3) and over a longer linear range (1–700 and 1–800 μM), with a comparatively higher sensitivity (2.5 and 2.0 μA μM–1 cm–2), for DA and UA, respectively. In addition, the CS–GS matrix demonstrates good selectivity toward the detection of DA and UA in the presence of a 10-fold higher concentration of AA and glucose. The as-prepared three-dimensional porous CS–GS also endows selective determination toward DA and UA in various real samples.