Gold nanoparticles/over-oxidized poly-eriochrome black T film modified electrode for determination of arsenic.

A glassy carbon electrode, modified with gold nanoparticles/over-oxidized poly-eriochrome black T film, was fabricated for sensitive determination of As(III) by stripping voltammetry in an acidic medium. The electrode surface properties were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The electrode demonstrated a good response towards As(III), with a detection of 0.077 µM and good linearity in the range of 0.1 to 10 µM (R2 = 0.9977). For the determination of As(III), the fabricated electrode was placed in different mineral water samples, acidified with 0.75 M HCl solution, spiked with various concentrations of As(III). Spiked recoveries for mineral water samples were obtained in the range of 100.3%-105.0%. The relative standard deviations were lower than 4.0%.

Sensitive determination of hydrazine using poly(phenolphthalein), Au nanoparticles and multiwalled carbon nanotubes modified glassy carbon electrode.

This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton-Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25-13 µM at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 µM. A modified electrode was applied to naturel samples for hydrazine determination.

Highly improved electrocatalytic oxidation of dimethylamine borane on silver nanoparticles modified polymer composite electrode.

Dimethylamine borane (DMAB) is a promising fuel alternative for fuel cell applications. In this work cyclic voltammetric behavior of DMAB was investigated on the polymerized aminophenol film decorated with Ag nanoparticles in alkaline media. The polymer film was formed on the glassy carbon electrode by electrochemical technique and then, the surface was modified with Ag nanoparticles. The surface of the modified electrode was identified by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy techniques. The developed electrode has displayed high electrocatalytic activity for DMAB oxidation in alkaline media depending on the supporting electrolyte concentration. Experimental parameters such as cycle number used in electropolymerization of p-aminophenol, deposition of Ag nanoparticles and supporting electrolyte were optimized.

Metal organic frameworks in electrochemical and optical sensing platforms: a review.

Metal-organic frameworks (MOFs) are porous coordination polymers (CP) produced by metal-based nodes and multitopic organic ligands. Based on their porous and microcrystalline powder structures, they have initially been used for storage, catalysis and separation. Then, because of their advantageous properties like ease of the tailoring, they also have been applied in areas like chemical sensing, biological applications, etc. The CPs were combined with molecules such as organic dyes, small biomolecules, nanomaterials like nanoparticles, nanowires, nanofibers and polymers and as a result, composite MOFs have been produced. By this way, better mechanical stability, conductivity, and catalytic performance were obtained. This review (with 135 refs.) summarizes the progress made in the past years in the field of electrochemical and optical sensing based on the use of MOFs. Following an introduction into the field, large sections cover MOF based sensors exploiting (a) carbon nanomaterials (with subsections on carbon nanotubes, graphene and its derivatives), (b) metal/metal oxide MOFs; including gold, silver, copper and/or copper oxide nanoparticle and other metal/MOF composites. Enzyme mimicking MOFs are discussed next. In this context, after the brief information about focused MOFs, the nanomaterial/MOF composites were discussed and related examples were presented. Graphical abstract MOF structures in Sensing Systems.

Simultaneous determination of theophylline and caffeine on novel [Tetra-(5-chloroquinolin-8-yloxy) phthalocyanato] manganese(III)-Carbon nanotubes composite electrode.

This work reports the synthesis of new symmetrically substituted manganese(III) phthalocyanine (2eOHMnPc) (2) containing tetra 5-chloroquinolin-8-yloxy group at the peripheral position for the first time. Manganese(III) phthalocyanine (2) was synthesized by cyclotetramerization of 4-(5-chloroquinolin-8-yloxy)phthalonitrile (1) in the presence of corresponding metal salt (manganese(II) chloride). This peripherally substituted phthalocyanine complex (2) was purified by column chromatography and characterized by several techniques such as IR, mass and UV-Visible spectral data. This novel synthesized phthalocyanine was mixed with multiwalled carbon nanotubes in order to prepare the novel catalytic surface on glassy carbon electrode for theophylline and caffeine detection in acidic medium. The novel composite electrode surfaces were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. Individual and simultaneous determination of theophylline and caffeine were studied by differential pulse voltammetry. The detection limits were individually calculated for theophylline and caffeine as 6.6 × 10-9 M and 5.0 × 10-8 M, respectively. In simultaneous determination, LODs were calculated for theophylline and caffeine as 8.1 × 10-9 M and 3.0 × 10-7 M, respectively. The practical applicability of the proposed modified electrode was tested for the determination of theophylline and caffeine in green tea, cola and theophylline serum.

Polymer Film Supported Bimetallic Au-Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media.

ABSTRACT: Ammonia borane is widely used in most areas including fuel cell applications. The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles. The glassy carbon electrode was firstly covered with polymeric film electrochemically and then, Au, Ag, and Au-Ag nanoparticles were deposited on the polymeric film, respectively. The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloyed Au-Ag bimetallic nanoparticles are formed. Electrochemical measurements indicate that the developed electrode modified by Au-Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media. The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane. Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions.

Photoelectrocatalytic oxidation of NADH in a flow injection analysis system using a poly-hematoxylin modified glassy carbon electrode.

A stable electroactive thin film of poly-hematoxylin (poly-HT) was successfully prepared on a glassy carbon electrode (GCE) surface by recording successive cyclic voltammograms of 0.3 mM HT, in a phosphate buffer solution (pH 7.0) containing 0.1 M NaNO3, in the potential range of -0.5 to +2.0 V vs. Ag/AgCl. The deposition of HT on GCE surface can be explained through the electropolymerization process. This poly-HT modified electrode exhibited a good electrocatalytic activity towards the NADH oxidation in a phosphate buffer solution (pH 7.0), and led to a significant decrease in the overpotential by more than 320 mV compared with the bare GCE. In order to perform the photoelectrocatalytic determination of NADH in a flow injection analysis (FIA) system, a home-made flow electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed. Flow rate of carrier solution, transmission tubing length, injection volume and applied potential for the amperometric and photoamperometric FIA studies were optimized as 1.3 mL min(-1), 10 cm, 100 µL and +300 mV vs. Ag/AgCl, respectively. The currents obtained from amperometric and photoamperometric measurements in FIA system at optimum conditions were linearly dependent on the NADH concentration and linear calibration curves were obtained in the range of 1.0×10(-7)-1.5×10(-4) M and in the range of 1.0×10(-7)-2.5×10(-4) M NADH, respectively. The relative standard deviation (RSD) of six replicate injections of 6.0×10(-5) M NADH was calculated as 2.2% and 4.3% for the amperometric and the photoamperometric method, respectively. The limit of detection was found to be 3.0×10(-8) M for the photoamperometric determination of NADH.

Cu nanoparticles incorporated polypyrrole modified GCE for sensitive simultaneous determination of dopamine and uric acid.

Cu nanoparticles have been electrochemically incorporated polypyrrole film that was used for modification of the glassy carbon electrode surface. The performance of the electrode has been characterized by cyclic voltammetry and atomic force microscopy. The electrode has shown high electrocatalytic activity towards the oxidation of dopamine (DA) and uric acid (UA) simultaneously in a phosphate buffer solution (pH 7.00). The electrocatalytic oxidation currents of UA and DA were found linearly related to concentration over the range 1x10(-9) to 1x10(-5)M for UA and 1x10(-9) to 1x10(-7)M for DA using DPVs method. The detection limits were determined as 8x10(-10)M (s/n=3) for UA and 8.5x10(-10)M (s/n=3) for DA at a signal-to-noise ratio of 3.

Voltammetric behavior of copper(I)oxide modified carbon paste electrode in the presence of cysteine and ascorbic acid.

The electrochemical behavior of a copper(I)oxide (Cu(2)O) modified carbon paste electrode (MCPE) was investigated in different buffer solutions and in the presence of ascorbic acid (AA) and cysteine (RS). Working conditions such as pH, mineral oil, and modifier ratio were optimized. Voltammetric results revealed that RS forms rather stable complexes with Cu(I) which has a high electrocatalytic reduction peak current at -0.65V versus SCE in borate buffer (pH 9.2). In the case of AA, a complexation occurred with Cu(II) species at the electrode surface, rather than Cu(I). The electrocatalytic reduction peak current of the Cu(II)-AA complex was observed at -0.07V in phosphate buffer at pH 6.9. Linear responses were observed in the range 2.0x10(-9) to 3.0x10(-8)M with a 0.9954 correlation coefficient for RS and 1.0x10(-9) to 2.0x10(-8)M with a 0.9961 correlation coefficient for AA.