Papers by Shokoufeh Rastgar
Journal of Electroanalytical Chemistry, 2014
Herein, we present the large scale fabrication of carbon nanotubes (CNT) electrodes supported on ... more Herein, we present the large scale fabrication of carbon nanotubes (CNT) electrodes supported on flexible polymeric sheets by subsequent multilayer inkjet printing of a silver layer for electrical connection, CNT layers as active electrode material and an insulation layer to define a stand-alone CNT active electrode area with high accuracy. Optical and electrochemical characterization using several redox mediators demonstrates the reproducibility of the electrode surfaces and their functionality even with a single inkjet printed CNT layer. These electrodes are targeted to the clinical sector for the determination of the antioxidant power (AOP) of biologically relevant fluids by pseudo-titration voltammetry. As a proof-ofconcept, the AOP of ascorbic acid solutions and biological samples such as erythrocyte concentrates (ECs) from different blood donors were determined demonstrating the potential use of the presented CNT sensors on ECs for blood transfusion purposes and the clinical sector.
Electrochimica Acta, 2012
ABSTRACT The electrochemical reduction of tinidazole (TNZ) is studied on gold-nanoparticle/carbon... more ABSTRACT The electrochemical reduction of tinidazole (TNZ) is studied on gold-nanoparticle/carbon-nanotubes (AuNP/CNT) modified glassy carbon electrodes using the linear sweep voltammetry. An electrochemical procedure was used for the deposition of gold nanoparticles onto the carbon nanotube film pre-cast on a glassy carbon electrode surface. The resulting nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry. The effect of the electrodeposition conditions, e.g., salt concentration and deposition time on the response of the electrode was studied. Also, the effect of experimental parameters, e.g., potential and time of accumulation, pH of the buffered solutions and the potential sweep rate on the response is examined. Under the optimal conditions, the modified electrode showed a wide linear response toward the concentration of TNZ in the range of 0.1–50 μM with a detection limit of 10 nM. The prepared electrode was successfully applied for the determination of TNZ in pharmaceutical and clinical samples.
Advanced Materials Interfaces, 2020
tree of printing technologies which also comprise the contact printing techniques, such as roll-t... more tree of printing technologies which also comprise the contact printing techniques, such as roll-to-roll printing, [6] microcontact printing, [7] nanoimprint [8] technique, and so on. Traditional IJP techniques, such as piezoelectric IJP and thermal-bubble IJP, are typical drop-on-demand (DOD) printing techniques. The principle of IJP is based on the utilization of the transient high pressure, generated either by the rapid transform of the micropiezoelectric crystal attached to the ink chamber (piezoelectric IJP) or by the rapid expansion of a microbubble within the chamber (thermal-bubble IJP), to eject ink drops out of a small orifice. For both traditional IJP techniques, the viscosity of the inks should not excess several tens mPa s to ensure printability. [9] Currently, three strategies are normally adopted by IJP for printing viscous inks. The first strategy reduces the viscosity of the ink to a value accepted by the traditional IJP techniques (normally by heating the ink during printing). Now, inkjet nozzles integrated with heating component are commercially available. This strategy is limited since many inks cannot be heated, for instance, inks containing temperature sensitive materials which might be destroyed irreversibly by high temperature or the viscosity cannot be further reduced below the acceptable value even after heating. The second strategy is based on an increase of the transient pressure within the chamber in order to fiercely eject the viscous ink and give the ink sufficient momentum for the detachment of a drop and its subsequent flying. A typical method is the valve-based printing technique, [10] in which a piston, driven by piezostack, [11-13] electromagnetic coil [14] or pressure [15] is used to generate the extremely high pressure in the chamber. More often, viscosity reducing and pressure increasing are adopted at the same time [10b,16] for handling inks with extremely high viscosity, for instance, silica gel, adhesive, sealant and so on. [17,18] The third strategy is utilizing external forces generated by other mechanisms and devices outside the ink chamber/pipeline, to print/dispense the viscous inks without reducing the viscosity or increasing the pressure within the chamber/pipeline. This strategy is represented by the well-known electro-hydrodynamic printing (also known as e-jet printing), [19] and the recently developed acoustophoretic printing technique. [20] For the e-jet printing, high voltage is applied between the conductive nozzle and the opposite conductive printed surface (or a conductive substrate beneath the insulating printed surface). In today's era, the inkjet printing (IJP) technique plays important roles in the fabrication of mechanical, electronical, and even biological devices. However, the current IJP techniques are incapable of handling viscous inks, which greatly hinder the extensive industrial application. Here, it is found that utilizing the superhydrophobic materials on the end surface of a nozzle combined with the dragging and shearing effects of an airflow, micrometersized droplets can be generated under a quite low ejection/extrusion pressure. This variation of the traditional IJP technique is called pneumatic conveying printing (PCP) and is capable of handling viscous inks. Two PCP prototypes using micropump and micropiezo as the ink extruder, respectively, are homemade to demonstrate the printing performance. For the PCP using micropump inks with viscosities as high as several thousand mPa s can be printed. For the PCP using a micropiezo, the maximum allowed viscosity is about 700 mPa s. Furthermore, the pressure within the pipeline or ink chamber and the shear rate at the orifice during PCP are much smaller than those of the traditional IJP due to the slower ink extrusion rate. Both experiment and simulation are carried out to reveal the mechanisms of the proposed PCP technique.
The Journal of Physical Chemistry C, 2018
Photo-driven water oxidation reaction (WOR) at nanoparticles assembled at polarized liquid-liquid... more Photo-driven water oxidation reaction (WOR) at nanoparticles assembled at polarized liquid-liquid interfaces is a possible realization of the anodic reaction for water splitting at chemically polarized liquid-liquid interfaces. The rational development of photocatalyst for the WOR requires their characterization under appropriate process conditions. A micropipette filled with an aqueous dispersion of nanostructured BiVO 4 as a well-defined photoactive substrate is immersed into an immiscible organic solution containing perchlorate as common anion. Under illumination, hydroxyl radicals (OH •) are generated as adsorbed intermediates of the WOR under chemically controlled polarization. Combining the miniaturized liquid-liquid interface with a scanning electrochemical microscope allowed for application of the surface interrogation mode (SI-SECM) for quantitative assessment of adsorbed photo-generated intermediates. The loading of OH • intermediates per projected area of substrate (Γ = 3.33×10-5 mol m-2) and kinetics of their decay by a bimolecular reaction (k = 0.61×10-5 mol-1 m 2 s-1) were determined with bare BiVO 4 assembled at soft interface electrified by ClO 4 transfer and irradiated by visible-light. This determination was possible without processing BiVO 4 nanostructures to a solid electrode where particle-particle contacts and other structural features strongly modulate the overall outcome.
Current Opinion in Electrochemistry, 2019
The conversion of photon energy to chemical energy and vice versa requires the close arrangement ... more The conversion of photon energy to chemical energy and vice versa requires the close arrangement of absorber/emitters and (electro)chemical reactions sites. This review considers local measurement techniques aiding in the design of efficient oxide systems for the utilization of light as energy source and as efficient detection principle. Artificial photoelectrochemical systems are often build on oxides as they are abundant and have semiconducting properties. However, no single oxide fulfills all requirements for an efficient conversion of sunlight to chemical energy and thus complex oxides are explored. These oxides might be obtained by doping oxides with other metal cations or by combining different oxides for absorbance and catalyzing the desired reaction, mainly water splitting. Due to the enormous amount of possible combinations combinatorial search for new material systems has been pursued and accelerated around the world making use of local photoelectrochemical characterization techniques in the screening step. Local detection schemes based on scanning electrochemical microscopy and scanning electrochemical cell microscopy also provide details about the kinetics for heterogeneous charge transfer and the release of soluble reaction products. During the recent years the scanning probe methods have been complemented by local detection of fluorescent reaction products that are formed by heterogeneous electron transfer reactions from and non-fluorescent precursor molecules. Such detection is possible with single molecule sensitivity and spatial resolution exceeding the diffraction limit (superresolution). Such approaches enabled the discovery of population within ensembles of metal oxide nanoparticles that are distinguished by the location and reactivity of their reaction sites. Optical techniques for measuring Faradaic currents hold great promise for the measurement of very low currents beyond the study of photoelectrochemistry of metal oxides.
Chemical Communications, 2016
A nanostructured BiVO4photocatalyst assembled at a chemically polarized liquid–liquid interface g... more A nanostructured BiVO4photocatalyst assembled at a chemically polarized liquid–liquid interface generates an efficient amount of O2with a [Co(bpy)3]3+scavenger in the organic phase.
CHINESE JOURNAL OF ANALYTICAL CHEMISTRY (CHINESE VERSION), 2010
In this work, a novel electrochemical sensor was fabricated for determination of amoxicillin in b... more In this work, a novel electrochemical sensor was fabricated for determination of amoxicillin in bovine milk samples by decoration of carboxylated multi-walled carbon nanotubes (MWCNTs) with gold nanoparticles (AuNPs) using ethylenediamine (en) as a cross linker (AuNPs/en-MWCNTs). The constructed nanocomposite was homogenized in dimethylformamide and drop casted on screen printed electrode. Field emission scanning electron microscopy (FESEM), energy dispersive X-Ray (EDX), X-Ray diffraction (XRD) and cyclic voltammetry were used to characterize the synthesized nanocomposites. The results show that the synthesized nanocomposites induced a remarkable synergetic effect for the oxidation of amoxicillin. Effect of some parameters, including pH, buffer, scan rate, accumulation potential, accumulation time and amount of casted nanocomposites, on the sensitivity of fabricated sensor were optimized. Under the optimum conditions, there was two linear calibration ranges from 0.2-10 µM and 10-30 µM with equations of I pa (µA) = 2.88C (µM) + 1.2017; r = 0.9939 and I pa (µA) = 0.88C (µM) + 22.97; r = 0.9973, respectively. The limit of detection (LOD) and limit of quantitation (LOQ) were calculated as 0.015 µM and 0.149 µM, respectively. The fabricated electrochemical sensor was successfully applied for determination of Amoxicillin in bovine milk samples and all results compared with high performance liquid chromatography (HPLC) standard method.
Chemistry – A European Journal, 2020
Abstract Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen... more Abstract Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane‐based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2O2, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.
Chemistry – A European Journal (Chemistry—A European Journal), 2020
Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species ... more Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane-based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2O2, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase.
The Journal of Physical Chemistry C, Nov 3, 2017
Hyperbranched nanostructured bismuth vanadate at a chemically polarized water/organic interface i... more Hyperbranched nanostructured bismuth vanadate at a chemically polarized water/organic interface is applied for efficient visible light-driven catalytic oxidation of water in the presence of [Co(bpy) 3 ](PF 6) 3 as an organic soluble electron acceptor. The photocurrent response originating from the transfer of photo-excited electrons in BiVO 4 to [Co(bpy) 3 ] 3+ is measured by scanning electrochemical microscopy. Inspired by biological photosynthesis, the current research aims at converting sunlight to chemical fuels by driving energetically uphill chemical reactions yielding energy-rich compounds. Conceptually this represents an approach for solving the energy challenge with minimal environmental impact. 1–4 Liquid/liquid (L/L) interfaces, or, more precisely, interfaces between two immiscible electrolyte solutions (ITIES), have been proposed as simple models mimicking important functions of biomembranes at which the process of photosynthesis proceeds in green plants. The analogy extends to charge carrier separation by two interacting photocenters (equivalent to a z-scheme) and catalyst regeneration at interfaces. 5 ITIES can be polarized either externally using a potentiostat or chemically by changing the composition or concentration of supporting electrolytes in the organic or aqueous phase. The applied galvanic potential difference across the interface could control the efficiency and pathway of interfacial processes involving charged reactants. 6–8 Hence, the design of efficient artificial photosynthesis systems based on charge transfer at ITIES has recently received significant attention. 9–11 Such systems utilize sunlight to split water into molecular oxygen O 2 and hydrogen H 2 (as renewable solar fuels). 11 The water oxidation reaction (WOR), a multi-electron multi-proton transfer, is energy demanding and considered as the most challenging step in water splitting. It requires suitable catalytic conditions for reasonable rates and/or overpotentials. 12 Bismuth vanadate (BiVO 4) is one of the most interesting visible-light-driven photocatalysts for water oxidation, because it has a suitable position of the valence band (VB) edge at ca. 2.4 eV vs. RHE, a sufficiently narrow bandgap for visible light absorption, is stable, abundant and of low cost. However, it suffers from poor charge transport properties causing excessive electron–hole recombination. 13–17 Furthermore, the hole transfer kinetics for WOR is sluggish. 14 One direction for further improvement is size and shape control in order to facilitate the collection and separation of electron–hole pairs at the semiconductor/ solution interfaces. 14 Our approach herein is the use of hyperbranched BiVO 4 at a chemically polarized ITIES 18 for enhancing the rate of photo-catalytic WOR (Fig. 1). The nanoscale branches minimize the charge carrier diffusion length to the interface where they are converted before recombining. This is further supported by [Co(bpy) 3 ](PF 6) 3 as an electron-acceptor in the organic phase. By efficient relaying of the photo-excited electrons from BiVO 4 to the electron acceptor the electron/hole pair separation is facilitated after photoexcitation in BiVO 4. This function is analogous to that of the electron transport chain between photo-systems I and II. 1 Interestingly, the driving force for electron transfer to [Co(bpy) 3 ] 3+ can be controlled easily by changing the polarization of the ITIES, which then clearly influences the efficiency of electron transfer from water to photogenerated holes (yielding O 2). In the present work, the interfacial photo-induced electron transfer (ET) reaction is studied by means of scanning electro-chemical microscopy (SECM), which has quickly become an important tool for probing rapid processes at ITIES, including ET, 19–22 ion transfer, 23–26 and molecular transfer 27 with high sensitivity. SECM is used here for recording the scavenging of photoelectrons by reduction of [Co(bpy) 3 ] 3+ at the BiVO 4 /butyro-nitrile interface. The SECM microelectrode (ME) oxidizes the resulting [Co(bpy) 3 ] 2+. Finally, WOR by photo-generated holes of BiVO 4 at the chemically polarized ITIES is followed by online detection of O 2 while the cell is irradiated using visible light (l 4 420 nm).
Talanta, 2014
Electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequen... more Electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequently layer-by-layer preparation of nickel hydroxide nanoparticle-reduced graphene oxide nanosheets (Ni(OH)2-RGO) on a graphene oxide (GO) film pre-cast on a glassy carbon electrode surface. The surface morphology and nature of the nano-hybrid film (Ni(OH)2-RGO) was thoroughly characterized by scanning electron and atomic force microscopy, spectroscopy and electrochemical techniques. The modified electrode appeared as an effective electro-catalytic model for analysis of rifampicin (RIF) by using linear sweep voltammetry (LSV). The prepared modified electrode exhibited a distinctly higher activity for electro-oxidation of RIF than either GO, RGO nanosheets or Ni(OH)2 nanoparticles. Enhancement of peak currents is ascribed to the fast heterogeneous electron transfer kinetics that arise from the synergistic coupling between the excellent properties of RGO nanosheets (such as high density of edge plane sites, subtle electronic characteristics and attractive π-π interaction) and unique properties of metal nanoparticles. Under the optimized analysis conditions, the modified electrode showed two oxidation processes for rifampicin at potentials about 0.08 V (peak I) and 0.69 V (peak II) in buffer solution of pH 7.0 with a wide linear dynamic range of 0.006-10.0 µmol L(-1) and 0.04-10 µmol L(-1) with a detection limit of 4.16 nmol L(-1) and 2.34 nmol L(-1) considering peaks I and II as an analytical signal, respectively. The results proved the efficacy of the fabricated modified electrode for simple, low cost and highly sensitive medicine sensor well suited for the accurate determinations of trace amounts of rifampicin in the pharmaceutical and clinical preparations.
Journal of Electroanalytical Chemistry, 2014
Herein, we present the large scale fabrication of carbon nanotubes (CNT) electrodes supported on ... more Herein, we present the large scale fabrication of carbon nanotubes (CNT) electrodes supported on flexible polymeric sheets by subsequent multilayer inkjet printing of a silver layer for electrical connection, CNT layers as active electrode material and an insulation layer to define a stand-alone CNT active electrode area with high accuracy. Optical and electrochemical characterization using several redox mediators demonstrates the reproducibility of the electrode surfaces and their functionality even with a single inkjet printed CNT layer. These electrodes are targeted to the clinical sector for the determination of the antioxidant power (AOP) of biologically relevant fluids by pseudo-titration voltammetry. As a proof-ofconcept, the AOP of ascorbic acid solutions and biological samples such as erythrocyte concentrates (ECs) from different blood donors were determined demonstrating the potential use of the presented CNT sensors on ECs for blood transfusion purposes and the clinical sector.
Graphene oxide (GO) in water was reduced heterogeneously by decamethylferrocene (DMFc) or ferroce... more Graphene oxide (GO) in water was reduced heterogeneously by decamethylferrocene (DMFc) or ferrocene (Fc) in 1,2-dichloroethane (DCE), which could then act as a catalyst for an interfacial oxygen reduction reaction (ORR) and production of hydrogen peroxide (H 2 O 2 ). The reduced graphene oxide (RGO) produced at the liquid/liquid interface was characterized by using electron microscopy, spectroscopy (Raman, infrared, and electron energy loss), and electrochemical techniques.
Electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequen... more Electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequently layer-by-layer preparation of nickel hydroxide nanoparticle-reduced graphene oxide nanosheets (Ni (OH) 2 -RGO) on a graphene oxide (GO) film pre-cast on a glassy carbon electrode surface. The surface morphology and nature of the nano-hybrid film (Ni(OH) 2 -RGO) was thoroughly characterized by scanning electron and atomic force microscopy, spectroscopy and electrochemical techniques. The modified electrode appeared as an effective electro-catalytic model for analysis of rifampicin (RIF) by using linear sweep voltammetry (LSV). The prepared modified electrode exhibited a distinctly higher activity for electro-oxidation of RIF than either GO, RGO nanosheets or Ni(OH) 2 nanoparticles. Enhancement of peak currents is ascribed to the fast heterogeneous electron transfer kinetics that arise from the synergistic coupling between the excellent properties of RGO nanosheets (such as high density of edge plane sites, subtle electronic characteristics and attractive π-π interaction) and unique properties of metal nanoparticles. Under the optimized analysis conditions, the modified electrode showed two oxidation processes for rifampicin at potentials about 0.08 V (peak I) and 0.69 V (peak II) in buffer solution of pH 7.0 with a wide linear dynamic range of 0.006-10.0 mmol L À 1 and 0.04-10 mmol L À 1 with a detection limit of 4.16 nmol L À 1 and 2.34 nmol L À 1 considering peaks I and II as an analytical signal, respectively. The results proved the efficacy of the fabricated modified electrode for simple, low cost and highly sensitive medicine sensor well suited for the accurate determinations of trace amounts of rifampicin in the pharmaceutical and clinical preparations.
A simple electrodeposition method is employed to construct a thin film modifier of palladium-gold... more A simple electrodeposition method is employed to construct a thin film modifier of palladium-gold nanoparticles (Pd-AuNPs) decorated multi-walled carbon nanotube (MWCNT) on the surface of glassy carbon electrode (GCE). Morphology and property of Pd-AuNPs-MWCNT have been examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Electrochemical performance of Pd-AuNPs-MWCNT/GCE for detection of ceftazidime (CFZ) has been investigated by cyclic voltammetry (CV). This nanostructured film modified electrode effectively exhibited enhanced properties for detection of ceftazidime (CFZ). The effects of various experimental variables such as, the amount of casted MWCNT, time and potential of deposition of metal nanoparticles and the pH of the buffered solution on the electrode response are optimized. The proposed electrode showed a linear dynamic range of 0.05-50 μM and the detection limit of 1 nM for the CFZ. The modified electrode successfully supports the sensitive detection of trace amounts of the CFZ in pharmaceutical and clinical preparations.
Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled... more Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 mM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.
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Papers by Shokoufeh Rastgar