Oxidation Peak Potential Research Articles

Graphene and carbon quantum dots electrochemistry

Abstract Graphene and carbon quantum (QDs) dots exhibit interesting and well-defined properties owing to their quantum confinement. In this work, graphene QDs (G-QDs) and carbon QDs of size ~ 6 nm and ~ 2 nm, respectively, were prepared and their potential uses in electrochemistry and electrochemical sensing were subsequently investigated. It was discovered that the C-QDs surface displayed a faster electron transfer rate compared to the G-QDs following analyses with the ferro/ferricyanide redox probe. Studies were also carried out with redox biomarkers such as uric acid (UA) and ascorbic acid (AA), and it was found that while the C-QDs displayed electrocatalytic properties toward the oxidation of both UA and AA, the G-QDs seemed to only have an impact on AA, from the decrease in the oxidation peak potential. This work provides direct electrochemical comparison of the two latest frontiers of carbon nanomaterials and opens the way for their electrochemical sensing applications.

Electrochemical and Computational Chemistry Study of Mn(β-diketonato)3 complexes

Nine different Mn(β-diketonato)3 complexes, with β-diketonato=dipivaloylmethanato, acetylacetonato, benzoylacetonato, dibenzoylmethanato, trifluoroacetylacetonato, trifluorothenoylacetonato, trifluorofuroylacetonato, trifluorobenzoylacetonato and hexafluoroacetylacetonato, were synthesized. The effect of the various substituents on the β-diketonato backbone of these complexes, on the ease of oxidation and reduction of the central metal in the nine different Mn(β-diketonato)3 complexes, was studied by means of electrochemistry. It was found that, when adding aromatic substituents to the backbone of the β-diketonato ligands of the complexes, the reduced/oxidized species were stabilized. It was also found that, when adding more electron withdrawing groups to the backbone of the β-diketonato ligands of the complexes, that Mn(β-diketonato)3 complex was more easily reduced at a higher potential. Good linear relationships and trends were obtained between the mean value of peak oxidation and reduction potential of the MnIII/MnII redox couple, and various electronic parameters and DFT calculated energies.

A Differential Pulse Voltammetric Sensor for Determination of Glutathione in Real Samples Using a Trichloro(terpyridine)ruthenium(III)/Multiwall Carbon Nanotubes Modified Paste Electrode

A trichloro(terpyridine)ruthenium(III) modified-multiwall carbon nanotubes paste electrode (TChPRuMWCNTPE) was fabricated and used as an electrocatalyst for the oxidation of glutathione (GSH). The effects of variables, such as pH and modifier percentage, were optimized using cyclic voltammetric method. The modified electrode shows a very efficient electrocatalytic activity for the anodic oxidation of GSH in the presence of 0.1 mol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> phosphate buffer solution (pH = 8.0). The oxidation peak potential of the GSH at a surface of TChPRu-MWCNTPE is appeared at 270 mV that is ~330 mV lower than the oxidation peak potential at the surface of a traditional carbon paste electrode in the same condition. The kinetic parameters, such as electron transfer coefficient, rate constant for the chemical reaction between GSH and the redox site in TChPRu-MWCNTPE, and apparent diffusion coefficient (D), was determined in an aqueous buffered solution. The electrocatalytic currents increase linearly with the GSH concentration over the concentration range of 0.6-56.8 μ mol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The detection limit for GSH was found to be 0.3 μ mol L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . In addition, the theoretical calculations were performed to determine the Gibbs free energy changes of the conversion of trichloro(terpyridine)ruthenium(II)(TChPRu') to TChPRu in the acidic and basic media, separately. Finally, this method was examined as a simple and precise electrochemical sensor for determination of GSH in the real samples such as hemolyzed erythrocyte and urine.

Simultaneous Determination of Ascorbic Acid, L-Dopa, Uric Acid, Insulin, and Acetylsalicylic Acid on Reactive Blue 19 and Multi-Wall Carbon Nanotube Modified Glassy Carbon Electrode

A trifunctional electrochemical sensor was fabricated for simultaneous determination of ascorbic acid (AA), levodopa (LD), and insulin. This was done by modifying a glassy carbon electrode (GCE) with multi-walled carbon nanotubes and reactive blue 19 (RB-MWCNT-GCE). Cyclic voltammetry was used to investigate the redox properties of this modified electrode. The electro-catalytic activity of the modified electrode was studied for the oxidation of AA, LD, and insulin. By differential pulse voltammetry (DPV), the detection limits of AA, LD, and insulin were estimated to be 0.45 µmol L -1, 0.37 µmol L-1, and 0.25 µmol L-1, respectively. In DPV measurements, the RB-MWCNT-GCE could separate the oxidation peak potentials of AA, LD, uric acid (UA), insulin, and acetylsalicylic acid (ASA) in a mixture. The practical utility of this modified electrode was demonstrated by detecting AA, LD, UA, insulin, and ASA in real samples.

An electrochemical and computational study for discrimination of D- and L-cystine by reduced graphene oxide/β-cyclodextrin.

Here, we report a novel enantioselective electrochemical biosensor for the discrimination of cystine enantiomers (d- and l-cystine) using a chiral interface for the specific recognition of d- and l-cystine. The biosensor is based on reduced graphene oxide modified by β-cyclodextrin (rGO/β-CD) at the GCE surface. During the preparation of rGO/β-CD/GCE, the modified electrode surfaces were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The electrochemical behaviours of the d- and l-cystine were investigated using the rGO/β-CD/GCE by CV and compared to bare GCE. A clear separation between the oxidation peak potentials of d- and l-cystine was observed at 1.32 and 1.42 V, respectively. The electrochemical discrimination performance of the fabricated chiral sensor was also examined by differential pulse voltammetry (DPV) in a mixed solution of d- and l-cystine. In addition, the DPV technique was used for the determination of d- and l-cystine at low concentration values in the range of 1.0-10.0 μM. To investigate the amperometric response of rGO/β-CD/GCE towards d- and l-cystine, the chronoamperometry technique was used in the concentration range of 10.0-100.0 μM. The interactions of the enantiomers with rGO/β-CD were modelled by molecular docking using AutoDock Vina, and the interaction energies were predicted to be -4.8 and -5.3 kcal mol(-1) for d- and l-cystine, respectively. The corresponding values of binding constants were calculated to be 3.32 × 10(3) and 7.71 × 10(3) M(-1), respectively. The experimental and molecular docking results indicate that the rGO/β-CD/GCE has a different affinity for each enantiomer.

Improved electro-oxidation of triclosan at nano-zinc oxide-multiwalled carbon nanotube modified glassy carbon electrode

An electrochemical sensor for oxidation of triclosan at a nano-zinc oxide-multiwalled carbon nanotube (nZnO–MWCNT) composite modified glassy carbon (GC) electrode was examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry and square wave voltammetry (SWV) in a pH 7.0 phosphate buffer. By combining the benefits of nZnO–MWCNT composite and GC electrode, the resulting modified electrode exhibited outstanding electrocatalytic behavior towards oxidation of triclosan by giving higher currents and lower oxidation peak potential compared to the bare GC electrode, nZnO and MWCNT modified electrodes. The effects of various parameters on the voltammetric response of triclosan were investigated. Under optimized conditions, the resulting sensor offered an excellent response for triclosan in the concentration range from 1.5μgL−1 to 2.0mgL−1 with detection limit of 1.3μgL−1 and a coefficient of determination (R2) of 0.9931. The diffusion coefficient of triclosan was determined to be 1.65×10−6cm2s−1. The electrochemical sensor showed satisfactory stability, selectivity and reproducibility when stored under room conditions.

Graphene nanosheets as a sensing platform for amplified electrochemical measurement of quercetin and uric acid in biological fluids

A simple and selective electrochemical method was investigated for the simultaneous determination of quercetin (Qu) and uric acid (UA) in aqueous media (citrate buffer solution, pH 4.0) on a glassy carbon electrode modified with graphene nanosheets as a sensing platform (GNSs/GCE). Cyclic voltammetry, transmission electron microscopy, and Fourier transform infrared spectroscopy were employed to characterize the nanostructure of the sensor. Separation of the oxidation peak potentials for Qu and UA was about 160 mV, and the anodic currents for the oxidation of both Qu and UA are greatly increased at GNSs/GCE, which makes it suitable for simultaneous determination of these compounds. The detection limits were 0.0011 and 0.0137 μmol/L for Qu and UA, respectively. The method was applied to the determination of Qu and UA in human blood serum and urine samples.

Effect of surface charge and electrode material on the size-dependent oxidation of surface-attached metal nanoparticles.

Here we report on the size-dependent oxidation of Au nanoparticles (NPs) electrodeposited directly on indium tin oxide-coated glass (glass/ITO) electrodes as compared to those chemically synthesized and electrostatically or drop-cast deposited onto aminopropyltriethoxysilane (APTES)-modified, mercaptopropyltrimethoxysilane (MPTMS)-modified, or unmodified glass/ITO electrodes. The peak oxidation potential (Ep) of 54 nm diameter Au NPs shifts by as much as 155 mV negative when deposited electrostatically on the highly positively charged glass/ITO/APTES surface and oxidized at low pH as compared to their oxidation on more neutral glass/ITO or glass/ITO/MPTMS surfaces at all pH's and on glass/ITO/APTES at neutral pH. Electrodeposited Au NPs on glass/ITO of similar size also oxidize at more positive potentials due to the neutral electrode surface charge. Ag NPs show a similar charge dependence on their Ep. Interestingly, the Ep value of Au and Ag NPs smaller than about 10 nm in diameter is independent of surface charge. The Ep of 9 nm diameter citrate-capped Ag NPs attached to Au, Pt, glassy carbon (GC), and glass/ITO electrodes electrostatically through short amine-terminated organic linkers depends on the electrode material, following the order (vs Ag/AgCl) of Au (384 ± 7 mV) ≈ Pt (373 ± 12 mV) > GC (351 ± 2 mV) > glass/ITO (339 ± 1 mV). The underlying electrode material affects the Ag NP Ep even though the NPs are not directly interacting with it. In addition to size, the electrode material and its surface charge have a strong influence on the oxidation potential of surface-confined metallic nanostructures.

Electrochemical synthesis of mixed-valence manganese/copper hybrid composite using graphene oxide and multi-walled carbon nanotubes for nonenzymatic glucose sensor

Electrochemical synthesis of mixed-valence manganese/copper hybrid composite has been successfully performed using graphene oxide (GO) and multi-walled carbon nanotubes (MWCNT) as a conductive and steric hybrid nanotemplate. The MnCu/MWCNT/GO hybrid composite shows compact and nanoporous structure due to high conductivity and high specific surface of the MWCNT/GO nanotemplate. XRD result indicates a mixed-valence hybrid composite including copper manganese oxide (CuMn2O4), tenorite (CuO), and hausmannite (Mn3O4). It is electroactive, pH-dependent, and stable in the electrochemical system. It shows eletrocatalytic activity to glucose oxidation with high current response and low overpotential by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). Particularly, DPV shows lower oxidation peak potential (Epa=−0.05V) due to suitable control of pulse parameters. CV, LSV, and DPV response of MnCu/MWCNT/GO shows linear correlation between current response and glucose concentration estimated with sensitivity of 49.1, 58.6, and 59.3μAmM−1cm−2, respectively. It shows linear concentration range of 1–32mM with a detection limit of 1×10−6M (S/N≧3). Coimmobilization and activity of manganese/copper hybrid composite can be effectively enhanced by MWCNT/GO. The MnCu/MWCNT/GO sensor shows high recovery and low coefficient of variation in bovine serum albumin samples for nonenzymatic glucose sensor.

Simultaneous electrochemical determination of hydroquinone, catechol and resorcinol at Nafion/multi-walled carbon nanotubes/carbon dots/multi-walled carbon nanotubes modified glassy carbon electrode

In this work, an excellent electrochemical sensor based on Nafion/multi-walled carbon nanotubes/carbon dots/multi-walled carbon nanotubes (Nafion/MWCNTs/CDs/MWCNTs) for simultaneous determination of hydroquinone (HQ), catechol (CC) and resorcinol (RS) in 0.1M phosphate buffer solutions (PBS, pH=7.0) was found. The functioned MWCNTs, which contained amido bond, were combined to CDs via the electrostatic interaction to build the Nafion/MWCNTs/CDs/MWCNTs modified electrode. As we know, MWCNTs have large specific surface area and CDs have electrical conductivity, which were benefited to build the composite modified electrode. The three dihydroxybenzene isomers could well separate from each other at the scan rate of 100mVs−1 with a potential difference of 119mV and 419mV for the oxidation peak potentials of HQ–CC and CC–RS, respectively. Differential pulse voltammetry (DPV) was used for the simultaneous determination of HQ, CC and RS in their ternary mixture. The peak current obtained was linearly dependent on the HQ, CC and RS concentrations in the range of 1.0 to 200.0μM, 4.0 to 200.0μM and 3.0 to 400.0μM and the detection limits for HQ, CC and RS were 0.07μM, 0.06μM and 0.15μM (S/N=3), respectively. The modified electrode was applied to detect the tap water, well water and river water and the recoveries of tap water, well water and river water samples were 100.3–109.8% for HQ, 96.0–105.8% for CC and 83.4–101.6% for RS, respectively.

Liquid phase determination of isuprel in pharmaceutical and biological samples using a nanostructure modified carbon paste electrode

The electrochemical behavior of isuprel (ISP) on the ionic liquid of 1,3-dipropylimidazolium bromide NiO nanoparticle (NiO/NPs) modified carbon paste electrode (IL/NiO/NPs/CPE) was studied in this paper and further used for ISP detection. ISP showed a diffusion oxidation process on the IL/NiO/NPs/CPE with the oxidation peak potential located at 0.62V (vs. Ag/AgCl/KClsat) in a pH5.0. Compared with that on the traditional carbon paste electrode, small shift of the oxidation peak potentials appeared but with a great increment of the oxidation peak current on the IL/NiO/NPs/CPE, which was due to the presence of ionic liquid and NiO/NPs in the modified electrode. The diffusion coefficient (D) was also determined using electrochemical approaches. The linear response range and detection limit were found to be 0.4–500μmolL−1 and 0.1μmolL−1, respectively. Other physiological species did not interfere in the determination of ISP at the surface of the proposed sensor in the optimum condition. The proposed sensor was successfully applied for the determination of ISP in real samples.

Simultaneous determination of epinephrine, acetaminophen, and tryptophan using Fe2O3(0.5)/SnO2(0.5) nanocomposite sensor

A nanocomposite of iron(III) oxide and tin(IV) oxide, Fe2O3(0.5)/SnO2(0.5), was prepared by a solid-phase reaction in an alkaline medium. The nanocomposite was characterized by X-ray diffraction, field-emission scanning electron microscopy, and Fourier transform infrared spectroscopy. A fast-response sensor was prepared by electrochemical deposition of the nanocomposite on a glassy carbon electrode. The prepared sensor has an excellent electrocatalytic activity toward the oxidation of epinephrine (EP), acetaminophen (AC), and tryptophan (Trp), therefore, this sensor was used for simultaneous determination of the above drugs. The separation of the oxidation peak potentials for EP–AC and AC–Trp were about 160 and 280 mV, respectively. The calibration curves obtained for EP, AC, and Trp were in the ranges of 0.6–270.0 µmol L−1, 4.5–876.0 µmol L−1, and 0.6–70.0 µmol L−1, respectively. The detection limits (S/N = 3) were 0.07, 0.2, and 0.1 µmol L−1 for EP, AC, and Trp, respectively. Finally, the sensor was used for determination of EP, AC, and Trp in pharmaceutical and biological samples.

Simultaneous determination of norepinephrine, acetaminophen and tyrosine by differential pulse voltammetry using Au-nanoparticles/poly(2-amino-2-hydroxymethyl-propane-1,3-diol) film modified glassy carbon electrode

A novel Au-nanoparticles/poly-(2-amino-2-hydroxymethyl-propane-1,3-diol) film modified glassy carbon electrode (AuNPs/poly(trisamine)/GCE) was constructed for the simultaneous determination of norepinephrine (NE), acetaminophen (AC) and l-tyrosine (Tyr) by differential pulse voltammetry. Electrochemical impedance spectroscopy and scanning electron microscopy indicate that the trisamine film was successfully polymerized on the surface of GCE and the film efficiently decreased the charge transfer resistance value of electrode and improved the electron transfer kinetic between analytes and electrode. The separation of the oxidation peak potentials for NE–AC and AC–Tyr were about 160mV and 240mV, respectively. The calibration curves for NE, AC and Tyr were obtained in the range of 1.3–230.1μmolL−1, 1.90–188.0μmolL−1, and 3.9–61.8μmolL−1, respectively. The detection limits (S/N=3) were 0.07μmolL−1, 0.1μmolL−1 and 0.9μmolL−1, for NE, AC and Tyr, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation reaction of NE at AuNPs/poly(trisamine)/GCE were calculated as 1.55 (±0.2)×10−6cm2s−1 and 2.28 (±0.17)×103mol−1Ls−1, respectively. Finally, AuNPs/poly(trisamine)/GCE was satisfactorily used for the determination of NE, AC, and Tyr in pharmaceutical and biological samples.

Electrodeposition of dendritic Pd nanoarchitectures on n-GaN(0001): nucleation and electrocatalysis for direct formic acid fuel cells

Dendritic Pd nanoarchitectures were electrochemically deposited on single-crystal n-GaN(0001) by cyclic voltammetry and employed as anode electrocatalyst for direct formic acid fuel cells. The Pd deposition on n-GaN(0001) was found to commence at 0.2V vs. Ag/AgCl without underpotential deposition process and follow the typical instantaneous nucleation in large overpotential region. High-resolution transmission electron microscope images revealed that numerous small branches were formed around the trunk of dendritic structures and grew along the <111> directions. The as-obtained dendritic Pd nanoarchitectures showed good catalytic performance for formic acid and the oxidation peak potential appeared at 0.45V vs. Ag/AgCl. The maximum current density and mass activity were 19.7mAcm−1 and 904mAmg−1, respectively, for the dendritic Pd nanocrystals obtained by cycling the potentials from -0.25 to 1.0V for 5 times.

Enhanced catalytic performance of Pd catalyst for formic acid electrooxidation in ionic liquid aqueous solution

A protic ionic liquid (IL), n-butylammonium nitrate (N4NO3), is prepared and employed as the electrolyte for formic acid electrooxidation reaction (FAOR) on Pd catalysts. The oxidation peak potential of FAOR in the IL solution shows about a 200 mV negative shift as compared with those in traditional H2SO4/HClO4 electrolytes, suggesting that FAOR can be more easily carried out on Pd catalysts in IL media. The catalytic properties of Pd toward FAOR are not only dependent on the concentration of IL, as a consequence of the varied electronic conductivity of the IL solution, but also on the high potential limit of the cyclic voltammograms. When the Pd catalyst is cycled up to 1.0 V (vs. SCE), which induces a significant oxidation of Pd, it shows ca. 4.0 times higher activity than that not subjected to the Pd oxidation (up to 0.6 V). The Pd oxides, which are more easily formed in IL solution than in traditional H2SO4/HClO4 electrolytes, may play a crucial role in increasing the catalytic activities of Pd toward FAOR. Our work would shed new light on the mechanism of FAOR and highlight the potential applications of IL as green and environment-friendly electrolytes in fuel cells and other technologies.

A voltammetric biosensor based on ionic liquid/NiO nanoparticle modified carbon paste electrode for the determination of nicotinamide adenine dinucleotide (NADH)

Herein we report a NiO/nanoparticles (NiO/NPs) modified carbon ionic liquid paste electrode (IL/NiO/NPs/CPE) was fabricated and used to investigate the electrochemical behavior of NADH in aqueous solution. The proposed sensor was prepared by mixing hydrophilic ionic liquid 1-methyl-3-butylimidazolium bromide, NiO/NPs, graphite powder and liquid paraffin together. The oxidation peak potential of NADH at the surface of the ionic liquid NiO/NPs carbon paste electrode appeared at 635mV, which was about 70mV lower than the oxidation peak potential at the surface of traditional carbon CPE under similar conditions. On other hand, the oxidation peak current was increased to about four times at the surface of IL/NiO/NPs/CPE compared to CPE. The linear response range and detection limit were found to be 0.03–900μmolL−1 and 0.009μmolL−1, respectively. IL/NiO/NPs/CPE was successfully applied for the determination of NADH in real samples such as water, serum and urine. The results showed that the proposed method is highly selective, sensitive with a fast response for NADH analysis.

Voltammetric Studies of Propranolol and Hydrochlorothiazide Oxidation in Standard and Synthetic Biological Fluids Using a Nitrogen-Containing Tetrahedral Amorphous Carbon (ta-C:N) Electrode

The electrochemical detection of two pharmaceuticals, propranolol (PROP) and hydrochlorothiazide (HTZ), was studied using a nitrogen-containing tetrahedral amorphous carbon (ta-C:N) electrode. Measurements were also made using a boron-doped diamond (BDD) electrode, for comparison. The ta-C:N electrode functioned well for the simultaneous determination of PROP and HTZ in artificial urine and serum by square-wave voltammetry, both of which were detected at high positive potentials. The PROP (ca. 1.2V) and HTZ (ca. 1.4V) oxidation peak potentials were separated by about 200mV. The respective analytical response curves presented good linearity in the investigated concentration range from 0.9 to 9.8μmolL−1 for PROP and from 3.0 to 9.8μmolL−1 for HTZ with calculated limits of detection (S/N=3) of 0.75μmolL−1 (∼194ng/mL) for PROP and 2.50μmolL−1 (∼744ng/mL) for HTZ. Essentially, the lowest concentration measured voltammetrically was the LOD. The results indicate that the ta-C:N electrode could be an excellent new carbon material for electrochemically-active analytes requiring high potentials for detection.

Simultaneous electrochemical determination of catechol and hydroquinone based on graphene–TiO2 nanocomposite modified glassy carbon electrode

In this work, graphene and titanium dioxide nanoparticles nanocomposite modified glass carbon electrode (GR–TiO2/GCE) was developed to serve as a sensor for simultaneous determination of catechol (CC) and hydroquinone (HQ). The GR–TiO2 nanocomposite was characterized by using scanning electron microscopy and electrochemical impedance microscopy. The application of GR–TiO2 nanocomposite in simultaneous determination of CC and HQ was investigated by cyclic voltammetry and differential pulse voltammetry. The GR–TiO2 nanocomposites modified electrode displays excellent electrochemical catalytic activities toward CC and HQ, which could be attributed to high electrical conductivity and larger surface area of GR–TiO2 nanocomposites. The oxidation peak currents of CC and HQ were linear over the range of 0.5–100μM with the detection limits of 0.087μM for CC and 0.082μM for HQ, respectively. In addition, the modified sensor shows excellent anti-interference from resorcinol, phenol and nitrobenzol due to their different oxidation peak potentials. The proposed sensor was successfully applied in the simultaneous determination of CC and HQ in tap and lake water samples with satisfied results.

2-Nitrophenol reduction promoted by S. putrefaciens 200 and biogenic ferrous iron: The role of different size-fractions of dissolved organic matter

The reduction of nitroaromatic compounds (listed as a priority pollutant) in natural subsurface environments typically coexists with dissimilatory reduction of iron oxides effected by dissolved organic matter (DOM). Investigating the impact of the DOM that influences those reduction processes is crucial for understanding and predicting the geochemical fate of these environmental species. This study investigated the impact of different molecular weight DOM fractions (DMWDs) on the 2-nitrophenol (2-NP) reduction by S. putrefaciens 200 (SP200) and α-Fe2O3 with lactate (excluding electron donor interference). Kinetic measurements demonstrated that 2-NP reduction rates were affected by the redox reactivity of active species under DMWDs (denoted as L-DOM, M-DOM, and H-DOM). The enhanced reduction rates are consistent with the negative shifts in peak oxidation potential values, the increases in HA-like/FA-like values, aromaticity index values and electron transfer capacity values. L-DOM acted mainly as ligands to complex Fe(II), whereas the significant role of H-DOM in reductive reactions should be acting as an electron shuttle, transferring electrons from SP200 to Fe(III) and 2-NP and from biogenic Fe(II) to 2-NP, further accelerating the 2-NP reductions. Those observations provide valuable insights into the role of DOM in the biogeochemical redox processes and the remediation of contaminated soil in a natural environment.

The study of adenine and guanine electrochemical oxidation using electrodes modified with graphene-platinum nanoparticles composites

Composite materials based on graphene and platinum nanoparticles (Gr-Pt-2 and Gr-Pt-3) were synthesized over two catalysts (Ptx/MgO, where x=2 or 3wt.%) using radio-frequency catalytic chemical vapor deposition (RF-CCVD), with methane as carbon source. After morphological (TEM/HRTEM) and structural characterization (XRD, XPS, FTIR and UV-Vis) they were used to modify two gold electrodes and subsequently employed for the investigation of adenine and guanine electrochemical oxidation. For the Au/Gr-Pt-2 electrode, the oxidation peak potential of adenine was observed at +1.19V vs. Ag/AgCl, while, for Au/Gr-Pt-3 electrode, this was negatively shifted to +1.09V vs. Ag/AgCl. In addition, the oxidation current densities were approximately 2.7×10−4 and 6.9×10−4 A·cm−2 (for Au/Gr-Pt-2 and Au/Gr-Pt-3, respectively) demonstrating that the Gr-Pt-3 composite had a better electro-catalytic activity towards the oxidation of adenine. A similar behavior was observed for guanine oxidation. The excellent electro-catalytic properties of the Gr-Pt-3 sample were correlated with the fact that the composite material had a higher amount of platinum nanoparticles which were not fully covered by graphene layers (about 50%). In addition, it has a larger surface area (335 m2·g−1) compared with that of the Gr-Pt-2 sample (271 m2·g−1), which also greatly improved the electron kinetics.