Samiei foroushani, M.,
Niroumand, N.,
Karimi shervedani, R.,
Yaghoobi, F.,
Kefayat, A.,
Torabi, M. Publication Date: 2019
Bioelectrochemistry (15675394)130
A multifunctional nanocomposite theranostic system is constructed of manganese oxide (Mn3O4) nanoparticles (NPs), as a tumor diagnostic agent, in conjunction with polyacrylic acid (PAA), as a pH-sensitive drug delivery agent, and methotrexate (MTX), as a model of targeting agent and anticancer drug. Physicochemical characteristics of the Mn3O4@PAA/MTX system is studied in detail by several techniques, including X-ray and Auger photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The system performance is studied based on (i) in-vitro MRI measurements to support efficiency of the Mn3O4@PAA NPs as a diagnostic agent, (ii) drug release performance of the Mn3O4@PAA/MTX NPs at pHs of 5.4 and 7.4 through in-vitro method to evaluate application of the NPs as pH-sensitive nanocarriers for MTX, and (iii) impedance spectroscopy measurements to show Mn3O4@PAA/MTX NPs affinity for capturing of cancer cells. The results show that (i) Mn3O4@PAA NPs can be used as a contrast agent in MRI measurements (r1 ≅ 6.5 mM−1 s−1), (ii) the MTX, loaded on Mn3O4@PAA NPs, is released faster and more efficient at pH 5.4 than 7.4, and (iii) the GC-Mn3O4@PAA/MTX electrode system captures the 4T1 cells 3.32 times larger than L929 cells. © 2019
Publication Date: 2006
Talanta (00399140)69(3)pp. 741-746
Fabrication and application of a voltammetric sensor based on gold 2-mercaptobenzothiazole self-assembled monolayer (Au-MBT SAM) for determination of silver ion is described. Preliminary experiments were performed to characterize the monolayer. The surface pKa determined for the MBT monolayer is 7.0. This value was obtained by impedimetric titration of the monolayer in the presence of Fe(CN)6 3-/4- as a redox probe. The extent of surface coverage was evaluated as 1.52 × 10-9 mol cm-2 based on charged consumed for reductive desorption of the monolayer in the 0.50 M NaOH solution. Then the sensor was used for determination of Ag(I) by square wave voltammetry. The parameters affecting the sensor response, such as pH and supporting electrolyte, were optimized. A dynamic calibration curve with two linear parts was obtained in the concentration ranges of 5 × 10-8-8 × 10-7 and 1 × 10-6-1 × 10-5 M of Ag(I). The detection limit adopted from cathodic striping square wave voltammetry was as 1 × 10-8 M for n = 7. Furthermore, the effect of potential interfering ions on the determination of Ag(I) was studied, and an appropriate method was used for the elimination of this effect. © 2005 Elsevier B.V. All rights reserved.
Publication Date: 2024
Journal of Materials Science (15734803)59(17)pp. 7218-7234
This paper presents the nickel–cobalt nanoprickly particles (PNi2Co3) composited with graphene nanosheets (GNs) and carbon nanotubes (CNT), prepared via the one-pot hydrothermal method (PNi2Co3/GNs/CNT), as an efficacious nonprecious metal bifunctional electrocatalyst for both oxygen evolution and reduction reactions (OER/ORR). The study employs a comprehensive methodology, incorporating cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) analysis to characterize and assess the materials and electrochemical properties investigated in the article. The primary objective was to successfully prepare a bifunctional electrocatalyst, and the PNi2Co3/GNs/CNT material achieved this goal. It exhibited superior OER activity, durability, and resistance to crossover effects, by an overpotential (η) of 480 mV and a Tafel slope of 61 mV dec−1, significantly higher than those obtained for RuO2 nanoparticles (η = 970 mV, Tafel slope = 85 mV dec−1). A similar trend was observed for ORR, where the PNi2Co3/GNs/CNT displayed high activity with an n = 3.93, close to the activity of a Pt/C (20 wt%), commercial catalyst with n = 4. Careful analysis of the EIS results via suitable models, in conjunction with Tafel data, revealed that the enhanced activity originates mainly from two factors: (a) the large surface area of the Ni–Co nanoprickly alloy and graphene sheets, where the CNTs (as a spacer) helped graphene nanosheets to avoid restacking and decreasing the surface area, and (b) the synergistic effect between Ni–Co nanoprickly and carbon components (GNs and CNT) of the composite. Graphical abstract: (Figure presented.). © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.
Publication Date: 2017
Electrochimica Acta (00134686)244pp. 230-238
Non-precious metal electrocatalysts with high activity towards hydrogen evolution reaction (HER) are desirable regarding renewable energy devices such as fuel cells and water electrolysis. However, fabrication of new materials for this purpose remains a main challenge. Here, a binder-free nanocomposite, prickly nickel nanostructured/reduced graphene oxide nanosheets, is constructed via electroless-deposition on cupper surface covered with a fresh prelayer of nickel (Cu-Nifpl-PNiNS/RGONs) for the first time. Then, the fabricated system is tested successfully for the HER in alkaline solutions. Structure and activity of the composite are characterized quantitatively by surface techniques and electrochemical methods. The results show that the hedgehog-like prickly nickel nanostructures wrapped in the RGONs cloth are formed, pinning the PNiNS/RGONs into the Cu-Nifpl surface, resulting in exceptional stability and activity for the Cu-Nifpl-PNiNS/RGONs system. In effect, the composite has shown excellent structural stability against disintegration by ultrasound waves; and electrocatalytic activity towards the HER as η20 = −57 mV, Tafel slope = −43 mV dec−1 and j0 = 1.05 mA cm−2, quite close to −22 mV, −40 mV dec−1 and 5.88 mA cm−2, obtained in the same conditions for commercial Pt/C, respectively. The remarkable increase in electrocatalytic activity was found to be originated partially from increase in the surface roughness and mainly from synergetic chemical coupling effects between PNiNS and RGONs. © 2017 Elsevier Ltd
Publication Date: 2014
Electrochimica Acta (00134686)142pp. 51-60
Sulfur doped graphene nanosheets (S-GNs) are synthesized by using graphene oxide (GO) as carbon source and sodium polysulfide as sulfur source, and then, annealing the prepared precursors (S-GO) at different temperatures up to 1000 °C. The structure and morphological characteristics of the fabricated composites are investigated by Field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical methods. Electrochemical results show that S-GNs has high catalytic activity toward oxygen reduction reaction (ORR) in an alkaline electrolyte in comparison with GNs. To improve the characteristics of S-GNs and prevent agglomeration of the particles, the S-GNs-1000-CB is fabricated by mixing the S-GNs-1000 with the carbon black (CB). The results show that CB particles inserted between S-GNs layers function as spacers and prevent the restacking of S-GNs during drying, and thus, most probably promote the diffusion of O2 molecules through S-GNs and enhance the ORR rate. The S-GNs-1000-CB composites show excellent electrocatalytic activity in alkaline solutions over all the studied (catalyst) samples. Our findings demonstrate that S-GNs-1000-CB is an appropriate catalyst for ORR in alkaline solutions, and could be a good candidate for replacement of the precious Pt based catalysts for this goal. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Analytica Chimica Acta (00032670)825pp. 34-41
Gold electrode surface is modified via covalent attachment of a synthesized thiol functionalized with 8-hydroxyquinoline, p-((8-hydroxyquinoline)azo) benzenethiol (SHQ), for the first time. The behavior of the nanostructured electrode surface (Au-SHQ) is characterized by electrochemical techniques including cyclic and differential pulse voltammetry (CV and DPV), and electrochemical impedance spectroscopy (EIS). The modified surface is stable in a wide range of potentials and pHs. A surface pKa of 6.0±0.1 is obtained for Au-SHQ electrode using surface acid/base titration curves constructed by CV and EIS measurements as a function of pH. These results helped to determine the charge state of the surface as a function of pH. The gold modified electrode surface showed good affinity for sensing the Al(III) ion at pH 5.5. The sensing process is based on (i) accumulation and complex formation between Al(III) from the solution phase and 8HQ function on the Au electrode surface (recognition step) and (ii) monitoring the impedance of the Au-SHQ-Al(III) complex against redox reaction rate of parabenzoquinone (PBQ) (signal transduction step). The PBQ is found to be a more suitable probe for this purpose, after testing several others. Thus, the sensor was tested for quantitative determination of Al(III) from the solution phase. At the optimized conditions, a linear response, from 1.0×10-11 to 1.2×10-5M Al(III) in semi-logarithmic scale, with a detection limit of 8.32×10-12M and mean relative standard deviation of 3.2% for n=3 at 1.0×10-7M Al(III) is obtained. Possible interferences from coexisting cations and anions are also studied. The results show that many ions do not interfere significantly with the sensor response for Al(III). Validity of the method and applicability of the sensor are successfully tested by determination of Al(III) in human blood serum samples. © 2014 Elsevier B.V.
Publication Date: 2009
Sensors and Actuators B: Chemical (0925-4005)137(1)pp. 195-204
Comparative electrochemical study of glucose oxidase (GOx) immobilized on gold electrodes modified by three types of mercaptocarboxylic acid self-assembled monolayers (SAMs), including 3-mercaptopropionic acid (MPA), 3-mercaptosuccinic acid (MSA), and thiodisuccinic acid (TDSA), is reported. GOx was immobilized on SAMs via anhydride route to prepare (Au-MPA-GOx), (Au-MSA-GOx), and (Au-TDSA-GOx) biosensors. Steps of formation and analytical performance of the prepared biosensors were traced by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). While partial surface coverage (θ) of gold by thiols showed the following order Au-MPA(θ = 36%) > Au-MSA(θ = 30%) > Au-TDSA(θ = 24%), inverse effect was observed for slopes (activities) of the calibration curves for glucose determination as Au-MPA-GOx < Au-MSA-GOx < Au-TDSA-GOx. This matter was explained based on advantages of multi-branch carboxylic acids (i.e. TDSA) allowing immobilization of more enzymes even with less surface coverage (24%) by thiols. Data obtained by CA and EIS methods for the entire of the study were in good agreement. © 2008 Elsevier B.V. All rights reserved.
Publication Date: 2016
Electrochimica Acta (00134686)187pp. 646-654
Comparative electrochemical behavior of three types of proteins; cytochrome c (Cyt c), Agaricus Bisporus laccase (LacAB) and glucose oxidase (GOx) immobilized on gold mercaptopropionic acid self-assembled monolayer via three different methods, including (a) covalent attachment by using EDC/NHS organic activators, (b) electrostatic interactions, and (c) covalent-coordinate binding by using Zr(IV) ion glue is investigated. Immobilization steps and electrochemical behavior of the immobilized proteins are traced by means of cyclic and differential pulse voltammetry (CV and DPV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results indicate that characteristics of the immobilized systems including; surface coverage, electrocatalytic activity and stability of the proteins are considerably affected by type of the bond formed between electrode and protein (the immobilization method), and nature of the protein. Immobilization via Zr(IV) ion resulted in higher activities for metalloproteins, i.e. Cytc with Heme active center and LacAB with T copper active center, while EDC/NHS method was more efficient for GOx having FAD cofactor. The experimental data will be presented and discussed from which the efficient immobilizing method for each case is introduced. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2007
Electrochimica Acta (00134686)52(24)pp. 7051-7060
Comparative electrochemical behavior of self-assembled monolayers (SAMs) of three heteroaromatic thiols, 2-mercaptobenzoxazole (MBO), 2-mercaptobenzothiazole (MBT), and 2-mercaptobenzimidazole (MBI) are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the electrode/solution interface are considerably and differently affected by thiols constructing the SAMs. The consumed charges for reductive desorption of SAMs, which is criterion for the amount of chemically adsorbed thiol, are significantly different for these three SAMs, specially for MBT, implying that SAM of MBT is formed through both sulfur atoms; the thiol sulfur and skeleton sulfur of the thiazole ring. Desorption potentials of the SAMs have shown the following order for strength of gold-sulfur bond: MBT > MBO > MBI. Activity of the three SAMs as pH-sensitive interfaces was also investigated and their surface-pKa values derived from the EIS measurements showed this order for acidic strength of SAMs: MBO > MBT > MBI. This is the same order expected due to the difference in electronegativity of the O, S, and N heteroatoms, and confirms that the most electron-rich ring imidazole is attached to the benzene ring of MBI. A comparison of the interfacial charge transfer resistance variation as a function of gold immersion time in thiols solution reveals that kinetics of Au-MBT assembly is different from those of two others and confirms formation of Au-MBT SAM via both sulfur atoms of MBT. © 2007 Elsevier Ltd. All rights reserved.
Publication Date: 2018
Biosensors and Bioelectronics (0956-5663)117pp. 794-801
Construction of hybrid systems that combine the cancer treatment and diagnosis agents on a single platform, known as theranostic systems, have received great attentions in the field of nanobiomedicine. Here, construction and characterization of a new multifunctional hybrid theranostic system based on RGO, PDA, BSA, DTPA-Mn(II), and MTX constituents, is presented. Accordingly, GO is partially reduced and simultaneously functionalized by dopamine, leading to reduced graphene oxide/polydopamine, RGO-PDA system; and then, the bovine serum albumin protein (BSA) is grafted onto this system. The obtained system, RGO-PDA-BSA, is further decorated with diethylenetriaminepentaacetic acid-Mn(II) as diagnostic system and methotrexate as anticancer drug. Physicochemical characteristics of the RGO-PDA-BSA-DTPA-Mn(II)/MTX system are studied by Fourier transform infrared spectroscopy, atomic force microscopy, and electrochemical methods. The capturing ability of the prepared system for the cancer cells is evaluated through electrochemical impedance spectroscopy (EIS) and by using the 4T1 cancer cells in comparison with L929 normal cells. The EIS results indicate that a degree of selectivity as 6.23 for GC-RGO-PDA-BSA-DTPA-Mn(II)/MTX electrode system toward 4T1 cells, which is larger than that obtained for this system toward the L929 cells. Similar analysis performed using the GC-RGO-PDA-DTPA-Mn(II)/MTX system (having no BSA) indicate that the selectivity degree of the system is increased only by a factor of 1.6, implying that presence of BSA has increased the selectivity of the system for 4T1 cells by a factor of four. This behavior supports the crucial role of BSA in this process for 4T1 cells. Finally, the drug release study of RGO-PDA-BSA-DTPA-Mn(II)/MTX system is performed successfully at pH 7.4. © 2018 Elsevier B.V.
Publication Date: 2016
Electroanalysis (15214109)28(4)pp. 874-880
5-amino-1,10-phenanthroline-Fe(II) complex is immobilized onto GC electrode and used for determination of DNA bases. Modifications are traced by electrochemical methods. All DNA bases are electroactive on the modified electrode. The Ips increased linearly with increase of DNA bases concentration. A wide response range was observed for each base (~4 orders for guanine (GA) and adenine (A); and ~2.5 orders for thymine (T) and cytosine (C)) with DLs of 0.15, 4.44, 133.0 and 230.0nM, respectively. The electrode was applied for determination of calf-thymus DNA bases. The value obtained for [(GA+C)/(A+T)], 0.78, is in good agreement with standard value, 0.77. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2019
Electrochimica Acta (00134686)327
Owing to the growing significance of hydrogen as a non-polluting fuel, design and construction of low-cost, efficient and highly stable electrocatalysts are required for its production by means of water electrolysis. Herein, a general strategy is introduced to fabricate a new type of electrocatalysts based on bimetallic core@shell structure formed on nitrogen-doped nanoporous carbon for electrocatalytic hydrogen evolution reaction (HER). Accordingly, a nickel metal organic framework, Ni‒MOF, synthesized by using benzene-1,3,5-tricarboxylic acid (H3BTC) as the carbon source and 2-methyl-imidazole as the carbon and nitrogen source, is employed, and the nickel/nitrogen−doped nanoporous carbon composite, Ni/NNPC system, is synthesized by the direct carbonization of Ni‒MOF system, i.e. annealing the system in argon atmosphere without using any carbon precursor additive. Then, the outer layers of nickel in Ni/NNPC system are replaced by Pt via galvanic reaction to synthesize the nanostructured system, Ni metal core@Pt thin layer shell, Ni@Pt/NNPC. The step-by-step synthesis of the system and formation of core@shell was supported by several surface analysis techniques. The fabricated materials were transferred onto a glassy carbon (GC) electrode and studied for the HER. The electrochemical results revealed a large electrocatalytic activity for the GCE/Ni@Pt/NNPC system toward the HER in both alkaline and acidic media, compared with GCE, GCE/Ni−MOF and GCE/Ni/NNPC. Tafel slopes of 43.78 and 46.73 mV dec−1, and overpotentials of −33.80 and −76.32 mV (vs RHE) at 20 mA cm−2 (η20) were observed on GCE/Ni@Pt/NNPC electrode in the alkaline and acidic media, under the same conditions, respectively. The observed activity is attributed to (i) the increased electrochemically active surface area, (ii) the cooperative action or synergistic effect between the Pt thin layer shell and the Ni metal core as well as between the Ni@Pt nanoparticles and the NNPC platform, and (iii) effective pore structures of the Ni@Pt/NNPC system. © 2019 Elsevier Ltd
Publication Date: 2018
Bioelectrochemistry (15675394)122pp. 149-157
A new strategy is developed for construction of the mixed molecular nanostructures from folic acid (FOA), a targeting agent, and deferrioxamoine-Ga(III), (DFO-Ga(III)), a theranostic agent, on gold-mercaptopropionic acid surface, Au-MPA. The strategy is focused to achieve a system in which all the active constituents of FOA; i.e., pteridine rings, p-aminobenzoeic acid, and the glutamic acid, having high affinity for folate receptor overexpressed on cancer cells; remain unreacted in adjacent to DFO-Ga(III), Au-MPA-[DFO-Ga(III)]‖-[FOA]. For this purpose, the –NH2 groups of FOA and DFO-Ga(III) were attached covalently and separately to –COOH of Au-MPA surface allowing all the active groups of FOA to be available for drug delivery purposes. The data obtained through several electrochemical and surface analysis techniques, supported successful construction of the designed mixed molecular nanostructures system. In addition, the results showed that the system is stable, and Ga(III) ion does not leave DFO-Ga(III) complex. The prepared surface was successfully tested for capturing of the breast cancer cells 4 T1 as a model. The measurements showed a rapid uptake kinetics (t1/2 of ~6.0 min) and efficient accessibility of the system by the cancer cells; the Rct was significantly increased in the presence of 4 T1 cells compared with blank PBS (ΔRct ~420 kΩ). © 2018 Elsevier B.V.
Publication Date: 2006
Analytical Chemistry (15206882)78(14)pp. 4957-4963
Fabrication and electrochemical characterization of a novel nanosensor for determination of Cu2+ in subnanomolar concentrations is described. The sensor is based on gold cysteamine self-assembled monolayer functionalized with salicylaldehyde by means of Schiff's base formation. Cyclic voltammetry, Electrochemical impedance spectroscopy (EIS), and electrochemical quartz crystal microbalance were used to probe the fabrication and characterization of the modified electrode. The sensor was used for quantitative determination of Cu2+ by the EIS in the presence of parabenzoquinone in comparison with stripping Osteryoung square wave voltammetry (OSWV). The attractive ability of the sensor to efficiently preconcentrate trace amounts of Cu2+ allowed a simple and reproducible method for copper determination. A wide range linear calibration curve was observed, 5.0 × 10-10-5.0 × 10-6 and 5.0 × 10-10-5.0 × 10-6 M Cu2+, by using the EIS and OSWV, respectively. Moreover, the sensor presented excellent stability with lower than 10% change in the response, as tested for more than three months daily experiments, and a high repeatability with relative standard deviations of 6.1 and 4.6% obtained for a series of eight successive measurements in 5.0 × 10-7 M Cu2+ solution, by the EIS and OSWV, respectively. © 2006 American Chemical Society.
Publication Date: 2006
Sensors and Actuators B: Chemical (0925-4005)115(2)pp. 614-621
A monolayers of cysteamine (CA) was prepared on a polycrystalline gold electrode through self-assembly procedure to produce a gold cysteamine self-assembled monolayers (Au-CA SAMs) modified electrode. Characterization of the modified electrode was performed by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was used to evaluate pKa of the adsorbed CA on the gold surface, and a value of 7.6 was obtained for the Au-CA surface pKa. The charged terminal groups of monolayers served for determination of dopamine (DA) in the presence of high concentration of ascorbic acid (AA) using differential pulse voltammetry (DPV). Well-separated DA and AA voltammetric waves (∼330 mV) were observed at the Au-CA SAMs electrodes in an acidic solution. A calibration curve with two linear parts was obtained for DA, 6.00 × 10-6 to 3.84 × 10-4 M and 3.36 × 10-4 to 9.50 × 10-3 M, with correlation coefficients 0.997 and 0.992, respectively. The detection limit for DA was found to be 2.31 μM in the presence of 1.0 mM AA. The apparent charge transfer rate constants (kapp) of AA and DA were evaluated by using EIS measurements on the modified electrode as 44.0 cm s-1 × 10-8 cm s-1 and 2.45 cm s-1 × 10-8 cm s-1, respectively. © 2005 Elsevier B.V. All rights reserved.
Publication Date: 2014
Bioelectrochemistry (15675394)98pp. 53-63
Direct electrochemistry of cytochrome c (Cyt c) is achieved via Zr(IV) ion as an immobilization matrix to interface Cyt c on gold surface via thiol self-assembled monolayers. Steps of surface modification and electrocatalytic activity of the immobilized Cyt c are followed by voltammetry, impedance spectroscopy, chronoampetrometry, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The results indicate that the native structure of Cyt c is conserved during the immobilization process. The immobilization method is rather simple, effective and free of immobilizing activators and reagents. Direct electron transfer rate constant and surface coverage of the immobilized Cyt c are found as 8.62(±1.98) s-1 and 1.15(±0.38)×10-11molcm-2, respectively. Bioactivity studies of the immobilized Cyt c toward oxidation of the ascorbic acid (AA) substrate show a linear response, from 10.0μM to 1.30mM AA, with a detection limit of 5.0(±1.8) μM AA and mean relative standard deviations varied from 13.7% to 3.7% for n=4 at each point. A value of 1.6(±0.8) mM AA is found for the Michaelis-Menten constant of Au-MPA-Zr(IV)-Cyt c toward AA for the first time. The tightly immobilized Cyt c maintains its bioactivity for more than 32days storage at 4°C. © 2014 Elsevier B.V.
Publication Date: 2012
Bioelectrochemistry (15675394)84pp. 25-31
Direct electrochemistry of a new laccase enzyme immobilized on gold and its application as a biosensor for dopamine (DA) are investigated by voltammetry and electrochemical impedance spectroscopy. The sensor demonstrated a redox adsorption behavior with E 0'=+180mV vs. Ag/AgCl for immobilized Agaricus bisporus laccase (LacAB) enzyme. The MPA platform was assembled on Au with and without utilization of ultrasounds. Excellent results were obtained by using the enzyme electrode fabricated based on MPA assembled with sonication. The LacAB immobilized in this condition showed a large electrocatalytic activity for oxidation of DA. Accordingly, a third-generation (mediator free) biosensor was constructed for DA. The DA concentration could be measured in the linear range of 0.5 to 13.0 and 47.0 to 430.0μmolL -1 with correlation coefficients of 0.999 and 0.989, respectively, and a detection limit of 29.0nmolL -1. The biosensor was successfully tested for determination of DA in human blood plasma and pharmaceutical samples. © 2011 Elsevier B.V.
Publication Date: 2008
Electrochimica Acta (00134686)53(12)pp. 4185-4192
Electrocatalytic activity of a new catalyst toward the oxidation reaction of hydroquinone as a model compound is described. The catalyst was formed by immobilizing metal cations on the topside of a gold-5-amino-2-mercaptobenzimidazole, self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+: Cu2+, Ag+) electrode. Preparation steps and the electrocatalytic activity of the catalyst were studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS data were approximated by appropriate electronic equivalent circuit models from which kinetic parameters, such as charge transfer resistance, double layer capacitance, and apparent rate constant (kapp), were estimated. Excellent activity was observed for Au-5A2MBI-Ag+ SAM with the following order: Au-5A2MBI-Ag+ > Au-5A2MBI-Cu2+ > Au-5A2MBI, after testing many modified electrodes. The increased activity originates from a modification of the Au-5A2MBI structure by mediating the effect of Ag+. This behavior was understood from significant increases in the kapp without significant changes in the double layer capacitance. © 2008 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Electroanalysis (15214109)28(9)pp. 1957-1969
Electrocatalytic activities of graphene nanosheets/Nile blue nanocomposite, synthesized and adsorbed simultaneously on the glassy carbon (GC−GNs−NB) electrode, are investigated. The nanocomposite was characterized by ATR−FTIR, FESEM and voltammetry. Activity of the electrode toward reduction of H2O2 and oxidation of NO2 − was studied electrochemically. Values of 1.95 and 0.730 mM are found for the Michaelis−Menten constant of the electrode toward H2O2 and NO2 −, respectively. Wide dynamic response ranges were observed for the electrode, with DLs of 0.22 μM H2O2 and 1.1 μM NO2 −. Effect of interferences was studied. The sensor was successfully tested for H2O2 and NO2 − contents in real samples, respectively. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2008
International Journal of Hydrogen Energy (03603199)33(10)pp. 2468-2476
Kinetics of hydrogen evolution reaction (HER) was studied in 1 M NaOH at 298 K on nickel-phosphorous-carbon (Ni81 P16 C3) composite electrode. Evaluation of the electrode activities was carried out by steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The kinetic parameters obtained by Tafel curves revealed that Ni-P composites modified by incorporation of carbon from L-lysine source during the electroplating process were active toward the HER. Thus, to study more precisely the electrode activities, the EIS measurements were performed. A surface roughness factor (Rf) more than three orders of magnitude was obtained for the Ni81 P16 C3 electrode. The HER rate constants were estimated using Tafel-impedance data assuming the Volmer-Heyrovský path. Analysis of the Rf in conjunction with the values obtained for rate constantans showed that the increase in activity of the electrode was originated by 18% from increase in Rf and by 82% from increase in the intrinsic activity (synergetic effect). Microstructure and composition of the electrodes were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and elemental microanalysis (EDX). Besides the good electrocatalytic activity, excellent chemical and electrochemical stability was observed for Ni81 P16 C3 composite electrode toward the HER. © 2008 International Association for Hydrogen Energy.
Publication Date: 2008
Journal of New Materials for Electrochemical Systems (14802422)11(4)pp. 259-265
Nickel-phosphorus-codeposited graphite carbon (Ni-P-Cg) materials have been studied by means of electrochemical and mi-crostructural techniques. Steady-state polarization Tafel curves showed that the Ni-P-C electrodes were active toward the HER. The activity of the Ni-P-Cg materials was depended on the electrode composition and the best activity was obtained on Ni 83P12C5 electrode (n250 = -242.4±2.1 mV), which was subjected to annealing at 400 °C in argon atmosphere. EIS measurements revealed that the electrodes were active and the source of the activity was originated mainly from improvement in electronic structure of the catalyst, and partially from increase in the surface roughness caused by the heat treatment process mentioned above. Furthermore, the Volmer-HeyrovsĶý mechanism was determined for the HER and the latter was the rate-determining step. © J. New Mat. Electrochem. Systems.
Publication Date: 2005
Journal of New Materials for Electrochemical Systems (14802422)8(3)pp. 213-220
The aqueous suspended RuCl3 was coated into the pores of microporous Ni-Zn-P alloy and thermally decomposed at 400°C in an open furnace to produce composite electrodes (Ni-Zn-P-RuO2). The microporous alloy was prepared via a three-step layer-by-layer galvanostatic deposition. The electrocatalytic behavior of the electrode was investigated in the hydrogen evolution reaction (HER), by steady state polarization Tafel curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) in 1M NaOH solution at 25°C. The kinetics as Tafel slopes, double layer capacitances, and charge transfer resistances towards the HER were evaluated. The electrode is characterized by (i) a large real surface area of three orders of magnitude obtained from CV and EIS measurements, and (ii) high physical and electrochemical stability of RuO2 dispersed into the surface. The poisoning effect of cyanide ion on the HER was also studied by EIS. This study allowed us to select properly data for kinetics approximation. © J. New. Mat. Electrochem. Systems.
Publication Date: 2009
Journal Of The Iranian Chemical Society (1735207X)6(1)pp. 104-112
Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+:Cu2+ or Ag+) for electrocatalytic determination of hydroquinone (H2Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H2Q concentrations were linear from 1.0 × 10-5 to 4.0 × 10-4 M (r=0.998) for Au-5A2MBI, from 1.0 × 10-5 to 6.0 × 10-4 M (r=0.998) for Au-5A2MBI-Cu2+, and from 2.0 × 10-6 to 2.0 × 10-5 M (r=0.996) and 1.0 × 10-4 to 1.0 × 10-3 M (r=0.991) for Au-5A2MBI-Ag+ SAM modified electrode. The respective detection limits were found as 6.5 × 10-6, 4.6 × 10-6 and 1.8 × 10-7 M. Both Cu2+ and Ag+ ions were found to have a good electrocatalytic effect on the oxidation of H2Q; however, Ag+ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag+ SAM electrode was used as a suitable sensor for determination of H2Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.
Publication Date: 2007
Journal Of The Iranian Chemical Society (1735207X)4(2)pp. 221-228
Electrochemical characterization and application of nickel ruthenium dioxide (Ni-RuO2) as a pH sensor for the determination of petroleum oil acid number is described. The sensor consists of RuCl3 thermally decomposed onto the upper side of a polycrystalline nickel electrode at 400°C in an open furnace. The advantages of the sensor are: (i) easy preparation, (ii) fast response in a large pH range, (iii) high physical and chemical stability, and (iv) excellent reproducibility as determined by the reproducible linear variation of charge transfer resistance (Rct) as a function of overpotential (η) obtained by electrochemical impedance spectroscopy (EIS), and the Nernstian slope of the electrode potential in a wide range of pH (1.5-12.5) obtained by potentiometric measurements. The potentiometric selectivity coefficients of the sensor toward some anions and cations were evaluated in aqueous solution. The characterized Ni-RuO2 pH sensor was successfully tested for the determination of petroleum oil acid number.
Publication Date: 2007
Sensors and Actuators B: Chemical (0925-4005)126(2)pp. 415-423
A new method is developed, for direct coupling of enzymes on gold thiol self-assembled monolayers, based on glucose oxidase as a model enzyme and gold mercaptosuccinic anhydride self-assembled monolayer as a platform. The immobilization method is simple and fast, and enzyme is immobilized very close to the gold electrode surface. Preparation steps and the biosensor response to glucose are monitored by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The relative differences between the slopes and intercepts of the current and conventional methods, using EDC/NHS activators for immobilization, are 10 and 8% for five-time measurements of each calibration curve obtained by chronoamperometry. The EIS data are approximated based on appropriate electronic equivalent circuit models and charge transfer resistances (Rct) are extracted from which a wide range linear calibration curve is obtained using 1/Rct versus glucose concentration. In addition, the analytical method is improved based on the EIS abilities allowing decreasing data acquisition time by a factor of 15. © 2007 Elsevier B.V. All rights reserved.
Publication Date: 2010
Electroanalysis (15214109)22(9)pp. 969-977
A new sensor, gold-6-amino-2-mercaptobenzothiazole (6A2MBT), was fabricated via a self-assembly procedure. Electrochemical properties of the monolayer were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent antifouling property against the oxidation products of DA, allowed us to construct a dynamic calibration curve with two linear parts, 1.00 10-6 to 3.72 10-4 and 3.72 10-4 to 6.42 10-4 M DA, with correlation coefficients of 0.997 and 0.992 and a detection limit of 1.57 10-7 M DA by using differential pulse voltammetry (DPV), respectively. Finally, the performance of the Au-6A2MBT modified electrode was successfully tested for electrochemical detection of DA in a pharmaceutical sample. © 2010 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim.
