Electron Transfer Behavior Research Articles

Electrochemical detection of hydrogen peroxide based on silver nanoparticles via amplified electron transfer process

A simple electrochemical sensor platform for hydrogen peroxide (H2O2) using silver nanoparticles (Ag NPs) entrenched in silicate matrix (APS(SG)) is reported. The redox molecules such as potassium ferricyanide ([Fe(CN)6]3−), methyl viologen (MV2+) and ruthenium hexamine ([Ru(NH3)6]3+) were utilized to investigate the electron transfer behavior of the APS(SG)–Ag NPs. The glassy carbon (GC) electrode modified with amine-functionalized silicate sol–gel matrix (GC/APS(SG)) exhibited a complete suppression of the electrochemical response toward MV2+ and [Ru(NH3)6]3+. However, GC/APS(SG) electrode displayed a twofold increase in the peak currents and fast electron transfer kinetics toward [Fe(CN)6]3− in comparison with GC electrode, suggesting that GC/APS(SG) electrode demonstrated an excellent anion exchange property. The GC electrode modified with APS(SG)–Ag NPs (GC/APS(SG)–Ag NPs) showed an improved electron transfer kinetics when neither positive nor negative charge of the electroactive species in the electrolyte. The GC/APS(SG)–Ag NP electrode was effectively further applied for the electrocatalytic and sensor applications toward H2O2. The present sensor exhibited the reduction of H2O2 at less negative potential and showed the experimental low detection limit of 25.0 µM with the sensitivity of 0.042 µA/µM. In addition, the developed APS(SG)–Ag NP-based amperometric sensor presented fast response, good stability and reproducibility.

Voltage-Gated Nanoparticle Transport and Collisions in Attoliter-Volume Nanopore Electrode Arrays.

Single nanoparticle analysis can reveal how particle-to-particle heterogeneity affects ensemble properties derived from traditional bulk measurements. High-bandwidth, low noise electrochemical measurements are needed to examine the fast heterogeneous electron-transfer behavior of single nanoparticles with sufficient fidelity to resolve the behavior of individual nanoparticles. Herein, nanopore electrode arrays (NEAs) are fabricated in which each pore supports two vertically spaced, individually addressable electrodes. The top ring electrode serves as a particle gate to control the transport of silver nanoparticles (AgNPs) within individual attoliter volume NEAs nanopores, as shown by redox collisions of AgNPs collisions at the bottom disk electrode. The AgNP-nanoporeis system has wide-ranging technological applications as well as fundamental interest, since the transport of AgNPs within the NEA mimics the transport of ions through cell membranes via voltage-gated ion channels. A voltage threshold is observed above which AgNPs are able to access the bottom electrode of the NEAs, i.e., a minimum potential at the gate electrode is required to switch between few and many observed collision events on the collector electrode. It is further shown that this threshold voltage is strongly dependent on the applied voltage at both electrodes as well as the size of AgNPs, as shown both experimentally and through finite-element modeling. Overall, this study provides a precise method of monitoring nanoparticle transport and in situ redox reactions within nanoconfined spaces at the single particle level.

Quantum mechanical investigation of optoelectronic properties of gold nanoparticle attached titanium dioxide nanorods for device applications

This article reports gold nanoparticle (Au-NP) induced absorption enhancement in hydrothermally synthesized titanium dioxide nanorods (TiO2-NRs) with a possibility of the deposition of hybrid nanostructures on the transparent substrates. The localized surface plasmon resonance (LSPR) and hot electron transfer behaviour of Au-NPs attached to the TiO2-NRs has been correlated to their photocatalytic response. The photocurrent enhancement observed in amperometric studies has been explained on the basis of excess electron density in the conduction band of TiO2 due to hot electron transfer from the attached Au-NPs (size in the range of 3 to 44 nm). The quantum mechanical calculation of the electron transmission probability from the resonant Au-NP to the conduction band of TiO2-NR has been presented with respect to the wavelength of the incident spectrum. Further, the role of Au-NP size dependent electron work function has been correlated to the electron transmission probability. This study provides a quantum mechanical explanation to the better response of Au-NPs/TiO2-NRs system for photo-catalytic device applications.

Strong Electronic Coupling of Molecular Sites to Graphitic Electrodes via Pyrazine Conjugation.

Glassy carbon electrodes were functionalized with redox-active moieties by condensation of o-phenylenediamine derivatives with o-quinone sites native to graphitic carbon surfaces. Electrochemical and spectroscopic investigations establish that these graphite-conjugated catalysts (GCCs) exhibit strong electronic coupling to the electrode, leading to electron transfer (ET) behavior that diverges fundamentally from that of solution-phase or surface-tethered analogues. We find that (1) ET is not observed between the electrode and a redox-active GCC moiety regardless of applied potential. (2) ET is observed at GCCs only if the interfacial reaction is ion-coupled. (3) Even when ET is observed, the oxidation state of a transition metal GCC site remains unchanged. From these observations, we construct a mechanistic model for GCC sites in which ET behavior is identical to that of catalytically active metal surfaces rather than to that of molecules in solution. These results suggest that GCCs provide a versatile platform for bridging molecular and heterogeneous electrocatalysis.

The correlation between surface defects and the behavior of hydrogen adsorption over ZnO under UV light irradiation

A photo-assisted gas sensing response can identify the electron transfer behavior of adsorbed H2 and its oxidation over ZnO.

Graphdiyne with Enhanced Ability for Electron Transfer

As a new member of the carbon allotrope family, graphdiynes (GDs) consist of both sp- and sp(2)-hybridized carbon atoms, possessing unique pi-conjugated carbon skeletons and expanded 18C-hexagonal pores in two dimensions. In contrast with the zero band gap graphene (GR), GD is a semiconductor with a direct band gap of 1.22 eV calculated according to the density functional theory (DFT) using the HSE06 method; this makes it a potential semiconductor material that can supplant silicon in the integrated circuit industry. Moreover, owing to the presence of diacetylenic linkages between its hexagonal carbon rings, GD shows electron-deficient properties, which lead to its electron-accepting tendency. Graphdiynes exhibit unusual semiconducting properties with excellent charge mobilities and electron transport properties that are associated with its distinct topological and electronic structures. Graphdiynes play the role of not only electron-acceptors that efficiently collect the electrons from other materials but also electron-donors that inject electrons into other systems, thus exhibiting excellent electron-transfer enhancement characteristics. The unique electron-transfer enhancement property of GDs inspired us to summarize the interactions between GDs and other materials including metal oxides, metal nano-particles, and organic molecules. In this review paper, we first introduce the TiO2/GD nanocomposite, because the linking of GDs and titania nanoparticles (P25) through the Ti-O-C bond sets an important precedent for exploring the electron-transfer behaviors involving GDs and the metal oxide. These results indicate that the GDs can act as acceptors of the photogenerated electrons in the TiO2/GD system, effectively suppressing charge recombination and resulting in excellent photocatalytic properties. Nevertheless, the GDs in CdSe quantum dots (QDs)/GD composites are able to collect photogenerated holes from the QDs and perform as promising hole-transfer materials in the photoelectrochemical cell for water splitting. As a result, the interactions between GDs and various metal compounds should be explored to deeply understand the electron-transfer properties of GDs. Furthermore, GDs can be also used as electron donors to reduce PdCl42- to Pd nanoparticles that can subsequently be used for the electroless deposition of highly dispersed Pd nanoparticles. Based on electrostatic potential surface analysis over the Pt-2/GD, GDs can attract the electron cloud from the Pt nanoparticles and produce a positive polarization of the metal atom surface. However, due to its large pi-conjugated system, GD can also collect and transfer electrons from the electrode under a bias voltage, making it a new type of electrocatalyst material, especially for single-atom catalysts. The interactions between GDs and metal particles/clusters/atoms have attracted the broad attention of the rapidly developing field of single-atom catalysis. Finally, research on the interactions between GDs and organic molecules, especially biomolecules, is still in its infancy and requires development. In summary, we overview the recent research progress on GD and its enhanced ability for electron transfer in this review paper, including metal oxides/GD, metal nano-particles/GD, polymers/GD, and organic molecules/GD, from both experimental and theoretical perspectives, and emphasize the interactions and electron-transfer enhancement properties.

Bio-electrocatalytic reduction of dissolved oxygen by whole blood chemically modified electrode and its application

Studies related to interaction of whole blood with dissolved oxygen with a new analytical method is a continued research interest in the interdisciplinary areas of biomedical, biochemistry and analytical chemistry. There has been significant number of reports for spectroscopic and electrochemical investigation for the interaction of heme/hemoglobin with dissolved oxygen. Indeed, there is no direct study relating to electron-transfer behaviour of whole blood and oxygen reduction reaction. Complex nature of the blood and difficulty in transferring the electron from the buried hemoglobin in the blood cell are the limitations for the observation. Herein, we report, a human whole blood modified electrode system using graphitized mesoporous carbon and Nafion as a matrix for direct-electron-transfer reaction with dissolved oxygen in physiological solution. The blood modified electrode exhibits a specific redox peak at an apparent standard electrode potential, E°′=−0.38V vs Ag/AgCl corresponding to the electron-transfer reaction of hemoglobin-Fe(III)/Fe(II) redox system and shows a mediated oxygen reduction reaction similar to a commercial Hb modified electrode response. Using the new bio-analytical system, interaction between the blood and dissolved oxygen was studied in terms of oxygen reduction reaction (ORR). Cyclic voltammetry, rotating disc electrode and flow injection analysis coupled with a dual electrode system, wherein, blood and MnO2 modified electrode systems are used for signals corresponding to the oxygen reduction and H2O2 oxidation reactions, kinetics and mechanism. As an extension to practical applicability, quantification of dissolved oxygen using the blood modified electrode was demonstrated with result comparable to that of a commercial dissolved oxygen measurement kit.

Molecular electrochemistry of multi-redox functionalized 5-membered heterocycles

Summary Recent developments in the electron transfer behavior of multi-redox functionalized 5-membered heterocycles are discussed on the basis of (spectro)electrochemistry. Where appropriate, potential applications are presented.

Biofunctionalized graphene oxide wrapped carbon nanotubes enabled microfluidic immunochip for bacterial cells detection

A sensitive and selective microfluidic immunochip was fabricated for detection of Salmonella typhimurium (S. typhimurium) bacterial cells. In this sensor, graphene oxide (GO) nano sheets wrapped carboxylated multiwalled carbon nanotubes (cMWCNTs) composite acted as a transducer material. The colloidal solution of GO-cMWCNTs composite was selectively deposited onto patterned indium tin oxide (ITO) electrode and sealed with polydimethylsiloxane (PDMS) micro channels. The S. typhimurium antibodies (StAb) were in situ biofunctionalized followed by EDC-NHS covalent chemistry via amidation reaction. The presence of abundant functional groups at the GO-cMWCNTs composite improved the loading of antibodies (StAb) against S. typhimurium leading to improved biosensing characteristics. Wrapping of cMWCNTs with GO resulted in superior electron transfer behavior enhancing the sensitivity (162.47 μA/CFU−1/mLcm−2) almost two folds as compared to that based on GO (89.16 μA/CFU−1/mLcm−2) sheets for bacterial cells detection. Besides this, GO wrapped cMWCNTs integrated microfluidics biosensor offered low detection limit as 0.376 CFU/mL and negligible interference due to presence of Escherichia coli (E. coli (O157:H7).

Insights into the Mechanism of Anodic N-N Bond Formation by Dehydrogenative Coupling.

The electrochemical synthesis of pyrazolidine-3,5-diones and benzoxazoles by N-N bond formation and C,O linkage, respectively, represents an easy access to medicinally relevant structures. Electrochemistry as a key technology ensures a safe and sustainable approach. We gained insights in the mechanism of these reactions by combining cyclovoltammetric and synthetic studies. The electron-transfer behavior of anilides and dianilides was studied and led to the following conclusion: The N-N bond formation involves a diradical as intermediate, whereas the benzoxazole formation is based on a cationic mechanism. Besides these studies, we developed a synthetic route to mixed dianilides as starting materials for the N-N coupling. The compatibility with valuable functionalities like triflates and mesylates for follow-up reactions as well as the comparison of different electrochemical set-ups also enhanced the applicability of this method.

Anti-IL8/AuNPs-rGO/ITO as an Immunosensing Platform for Noninvasive Electrochemical Detection of Oral Cancer.

An efficient electrochemical transducer matrix for biosensing devices requires specific characteristics, such as fast electron transfer, stability, high surface area, biocompatibility, and presence of specific functional groups, to facilitate biomolecule attachment. We demonstrate the fabrication of an electrochemical immunosensor based on a highly stable gold nanoparticles-reduced graphene oxide (AuNPs-rGO) composite material as a transducer matrix for label-free and noninvasive detection of salivary oral cancer biomarker interleukin-8 (IL8). The synergy between rGO and AuNPs allowed the immunosensor to exhibit fast response and high sensitivity due to the improved electron transfer behavior of the composite. The immunosensor shows very fast detection (9 min) of IL8 and high sensitivity with an experimental linear dynamic range of 500 fg mL-1 to 4 ng mL-1 and a detection limit of 72.73 ± 0.18 pg mL-1. The fabricated immunosensor exhibits excellent specificity toward the detection of IL8 in human saliva samples. Furthermore, the reusability and stability up to 3 months of the immunosensor demonstrates the commercial potential of this nanoplatform for the detection of other biomarkers of clinical relevance.

Hybrid organic-inorganic coatings via electron transfer behaviour

A novel method to functionalize the surface of inorganic coating by growing organic coating has been investigated based on microstructural interpretation, electrochemical assessment, and quantum chemical analysis. For this purpose, inorganic coating with magnesium aluminate, magnesium oxide, and titanium dioxide was prepared on magnesium alloy via plasma electrolytic oxidation (PEO), and, then, subsequent dip-coating method was used to tailor organic coating using diethyl-5-hydroxyisophthalate (DEIP) as organic molecules. The incorporation of TiO2 particles worked as a sealing agent to block the micro-defects which resulted mainly from the intense plasma sparks during PEO. In addition, such incorporation played an important role in enhancing the adhesion between inorganic and organic coatings. The use of DEIP as organic corrosion inhibitor resulted in a significant decrease in porosity of inorganic coating. Quantum chemical calculation was used to clarify the corrosion inhibition mechanism which was activated by introduction of DEIP. Thus, the electrochemical analysis based on potentiodynamic polarization and impedance spectroscopy tests in 3.5 wt% NaCl solution suggested that corrosion resistance of magnesium alloy sample was enhanced significantly due to a synergistic effect arising from the hybrid inorganic and organic coatings. This phenomenon was explained in relation to electron transfer behaviour between inorganic and organic coatings.

A novel colorimetric fluorescence sensor for Fe3+ based on quinoline Schiff base.

A novel fluorescent sensor bearing a quinoline and an anisidine moiety has been developed for highly selective detection of Fe3+ , which shows photo-induced electron transfer (PET) behavior induced by Fe3+ . Binding of Fe3+ to the sensor induced the electron of C=N group transfer from quinoline to iron, the result exhibits fluorescent enhancement. With the features of easy synthesis, simple structural skeleton and excellent sensing ability, the newly synthesized chemosensor also applied as a highly selective fluorescent probe in complex samples containing various competitive metal ions. The probe could fulfill various needs in biological and environmental fields.

Redox behaviour and surface-confinement of electro active species of ginger extract on graphitized mesoporous carbon surface and its copper complex for [formula omitted] sensing

Probing electron transfer behaviour of natural products and trapping of its intermediate species is a challenging research task in the cross-disciplinary area of phytochemistry and electrochemistry. Ginger is a concoction of zingiberene, shogaol and gingerol (responsible for flavour and pungency) which breaks down to zingerone (less pungent) upon drying or cooking. Several reports in the literature deal with the anti-inflammatory and therapeutic uses of ginger, but very scant reports are available on the electrochemical feature of ginger chemicals. Owing to the complex nature, selective recognition of a redox active compound in a phytochemical is a difficult task. Herein, we report an electrochemical study of redox properties of ginger juice on a graphitized mesoporous carbon modified glassy carbon electrode surface by cyclic voltammetry technique (CV) in pH 2 KCl–HCl solution. CV of the modified electrode in presence of dilute ginger solution showed a distinct surface-confined redox peak at E1∕2, 490±20 mV vs Ag/AgCl with peak-to-peak separation and surface-excess values of 60±2 mV and 20.66×10−9molcm−2 respectively. Physico-chemical characterizations of ginger extract modified electrode by Raman, UV–Vis, FT-IR and TEM reveal electrochemical transformation of 2-methoxyphenol derivatives of ginger compounds such as shogaol and gingerol to respective 1,2-dihydroxy benzene derivatives of gingerol and further anchoring as a surface-confined redox system on the GMC surface via π-π interaction. Ginger based redox system was tuned for complex formation with Cu2+ ion and further to sense electro-catalytic activity towards hydrogen peroxide in neutral pH solution.

Fused-Pentagon-Configuration-Dependent Electron Transfer of Monotitanium-Encapsulated Fullerenes.

We introduce monotitanium-based endohedral metallofullerenes (EMFs) using density functional theory calculations. Isomeric C64 fullerenes are initially employed as hosts, and Ti@C64 species show novel features on the electronic structures. Energetically, the preference of titanium residing on triple-fused-pentagon subunits is proposed in theory. More importantly, different from current knowledge on mono-EMFs, electron transfer between titanium and carbon cages is not unified but is essentially dependent on the pentagon distribution of the binding sites, giving rise to variations of the cationic titanium of Ti@C64. Such selective electron-transfer character is extended to the study of the encapsulation of other neighboring metal atoms (i.e., calcium and scandium). Because of their different capabilities to accept d electrons, fullerene cages with distinct fused-pentagon motifs show selective metal encapsulation characters. In addition, some other fullerenes (C44-C48 and C82) are selected as hosts to study the electron-transfer behavior of titanium in smaller fullerenes and larger systems without pentagon adjacency.

Photoinduced Electron Transfer in Asymmetrical Perylene Diimide: Understanding the Photophysical Processes of Light-Absorbing Nonfullerene Acceptors

In bulk-heterojunction-based organic photovoltaics, strong light-absorbing ability is one of the most important advantages of nonfullerene acceptors prior to fullerene derivatives. Herein, a series of electron-donating units was asymmetrically connected at the imide positions of perylene diimide (PDI), which is a classic-electron acceptor building block. The photoinduced electron-transfer behaviors were compared in different substitutions by steady/time-resolved spectroscopy and theoretical simulation. The electron-donating ability as well as the donor–acceptor distance has a significant impact on the photoinduced electron transition from electron-donating units to the PDI core. Because of the process of charge transfer at excited states, a fast nonradiative deactivation is observed for the PDIs with relatively strong electron substituent. These results would help us to understand the electron-transfer processes from donor to acceptor in the case of the excited electron-acceptor molecule.

Electrospun polyaniline/polyvinyl alcohol/multiwalled carbon nanotubes nanofibers as promising bioanode material for biofuel cells

The polyaniline/polyvinyl alcohol/multiwalled carbon nanotubes (PANI/PVA/MWCNTs) composite nanofibers were synthesized using electrospinning technique. Nanofibres morphology was characterized by using scanning electron microscopy (SEM). The electrospun PANI/PVA/MWCNTs nanofibres with average diameter of about 60–100nm exhibited smooth surface at higher magnifications of ×25000. The PANI/PVA/MWCNTs nanofibres modified electrode showed good electron transfer behavior because of the excellent properties of carbon nanotubes and the three dimensional and porous structures of electrospun nanofibres. The enzyme glucose oxidase (GOx) covalently immobilized with PANI/PVA/MWCNTs nanofibres exhibited good electrocatalytic activity towards oxidation of glucose through redox active as well as biocompatible mediator ferritin (FRT). The maximum current density using this nanostructured bioanode was 7.5mAcm−2 at 100mVs−1 vs Ag/AgCl in a 20mM glucose solution. The heterogeneous electron transfer rate constant (Ks) was found to be 3.09s−1. The results indicated that these electrospun PANI/PVA/MWCNTs nanofibres have potential to be used in BFC device as anode.

Facile synthesis of water soluble fluorescent metal (Pt, Au, Ag and Cu) quantum clusters for the selective detection of Fe3+ions as both fluorescent and colorimetric probes

A facile and green synthetic route is developed to prepare water soluble, green-fluorescent Pt, Au, Ag and Cu quantum clusters (QCs), employing innoxious L-histidine as a capping agent. These metal QCs give out emissions at 455–495 nm, with maximum excitation wavelengths ranging between 350 and 401 nm. Interestingly, these histidine-stabilized metal quantum clusters also possess non-linear optical properties like two-photon luminescence, which is detected when they are exposed to a femtosecond laser at 812 nm. Luminescence quantum yields of Pt (2.93%), Au (13.10%), Ag (6.97%) and Cu (8.29%) clusters are found to be distinctly different, and lifetime measurement results suggest that the emissions of metal clusters (4.59–7.39 ns) stem from singlet transitions among different electron energy levels rather than metal–ligand electron transfer behaviors. The Pt, Au, Ag and Cu quantum clusters have average sizes of 1.3–1.9 nm, and are mainly composed of 11, 9, 4 and 7 metal atoms, respectively, according to the electrospray ionization mass spectrometry results. Moreover, the as-prepared metal clusters are sensitive to aqueous ferric ions, both as highly selective fluorescent and colorimetric probes in a low and wide concentration range, and are promising in many biological applications.

Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior.

Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture.

A Combined Theoretical-Experimental Study of Energy Storage Behavior of Reduced Graphene Oxide/Manganese Oxide Supercapacitor

Miniaturized electrochemical capacitors, such as micro-supercapacitors, have emerged as a new class of micro-power sources. However, they have limited uses in micro-energy storage because of their low volumetric energy densities. Here, compact structured Birnessite (MnO2)/reduced graphene oxide (RGO) hybrid films (Fig.1) consisting of multi-valent Mn ions were prepared via a two-step fabrication process involving a simple chemical redox reaction and post-thermal annealing to form a multi-layer structured film. With this versatile method, GO sheets can act as either a growth template for the highly capacitive MnO2 nanosheets or as a mechanical support for the production of compact hybrid films. Enhanced electrochemical characterization of the MnO2/RGO hybrid film revealed a remarkable ultrahigh volumetric capacitance (493 F/cm3 at 10 mV/s), ultrahigh energy and power density (13.3 mWh/cm3 at 2.5 A/cm3 and 22.6 W/cm3 at 58 A/cm3, respectively) and a semi-permanent cycle life (97% capacitance retention) in an aqueous electrolyte system. We also elucidated operating mechanisms of MnO2/RGO capacitor using state-of-the-art density-functional theory calculations with MnO2 nanoparticle/RGO sheet models. Various materials properties of MnO2/RGO systems including stoichiometric deviation, defect energetics, electron transfer, and kinetic behavior of cations and their contributions to their capacitance have been explored in atomic level. Figure 1