Multi-walled Carbon Nanotube Electrodes Research Articles

A new strategy for the determination of dinobuton fungicide by square wave stripping voltammetry on the multi-walled carbon nanotube electrode

Dinobuton is a fungicide with a dinitrophenol group pesticide, and its electrochemical behavior was investigated by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) on a multi-walled carbon nanotube paste electrode (MWCNTPE). First of all, optimum parameters such as pH, step potential, frequency, puls amplitude, deposition time and, deposition potential were specified by using SWSV on the MWCNTPE. In the negative potential scans, two cathodic peaks appeared at nearly −480 mV and –760 mV due to the nitro groups on the molecule and the second sharp one appeared at −760 mV (versus Ag/AgCl) was used for analytical purposes. The linear working range was found to be within 3.74–25.8 μM on the MWCNTPE by SWSV in pH 7.0 Britton Robinson (BR) buffer solution. The limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.73 μM and 2.43 μM, respectively. The interference study was conducted in the presence of some pesticides such as triasulfuron, azinphos-methyl, bromoxynil-octanoate, dialifos, fipronil, vinclozolin, iprodione, procymidone, and some selected metal ions withal. Furthermore, the proposed method was also applied to apple juice, tap water, and grape juice, and percent recoveries (%) were detected as 105.9 ± 4.3; 98.3 ± 0.9; 103.7 ± 2.5% with relative standard deviations of 4.0, 1.0, and 2.4%, respectively. On the other hand, percent relative errors were calculated as 5.90, 1.65, and 3.74%, respectively. High recoveries and low relative standard deviations indicate that the applicability of the proposed method in both matrix and real samples is satisfying.

Ionic liquid-modified multi-walled carbon nanotube paste electrode for cadmium and lead ion determinations

The detection of trace heavy metal ions is important in monitoring water quality, a vital freshwater source. This study presents the preparation of a multi-walled carbon nanotube (MWCNTs) paste electrode using a pasting mixture of 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([Bmim][PF6] IL) and paraffin oil for the determination of Cd2+ and Pb2+. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy were applied to characterize the paste composites. The electrochemical behavior of the fabricated electrodes was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The [Bmim][PF6]-MWCNTs electrode showed enhanced sensitivity for Cd2+ and Pb2+ detections over linear sweep anodic stripping voltammetry (LSASV) performances. Experimental results showed that the MWCNTs-IL-1 electrode using a pasting mixture of 10 μL of [Bmim][PF6] and 190 μL of paraffin oil was the most suitable for Cd2+ and Pb2+ determinations. The LSASV conditions for Cd2+ and Pb2+ analysis at the MWCNTs-IL-1 electrode were optimized, including the deposition potential, deposition time, and pH of the working solution. The stripping peak currents were linearly correlated with the concentration ranges of Cd2+ (1–35 μg/L) and Pb2+ (1–90 μg/L) for both individual and simultaneous determinations. The MWCNTs-IL-1 electrode exhibited high repeatability, reproducibility, and stability over a 30-day storage period. The real applicability of the MWCNTs-IL-1 electrode was demonstrated by successful determinations of Cd2+ and Pb2+ concentrations in tap water and surface water samples, which agreed with the results obtained by inductively coupled plasma mass spectrometry.

Optimising Electrical Interfacing between the Trimeric Copper Nitrite Reductase and Carbon Nanotubes.

The immobilization of copper-containing nitrite reductase (NiR) from Alcaligenes faecalis on functionalised multi-walled carbon nanotube (MWCNT) electrodes is reported. It is demonstrated that this immobilization is mainly driven by hydrophobic interactions, promoted by the modification of MWCNTs with adamantyl groups. Direct electrochemistry shows high bioelectrochemical reduction of nitrite at the redox potential of NiR with high current density of 1.41 mA cm-2 . Furthermore, the desymmetrization of the trimer upon immobilization induces an independent electrocatalytic behavior for each of the three enzyme subunits, corroborated by an electron-tunneling distance dependence.

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes.

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.

The Coupling of Dihydroxybenzene Derivatives to MWCNT and Electrochemical NADH Oxidation

3,4 and 2,5- dihydroxybenzene compounds were separately and covalently coupled to the multiwalled carbon nanotube (MWCNT) deposited on the surface of glassy carbon electrode through electrochemical reduction of diazonium compound of benzylamine bearing Boc protecting group (tert-butyloxycarbonyl). Following the removal of the Boc group, an amide bond was formed between the amine-terminated surface and the acyl group of the dihydroxybenzene derivatives. The electrochemical properties of dihydroxybenzene-modified MWCNT and the influence of the sweep rate on the voltammogram were elucidated by cyclic voltammetry (CV). Electron transfer kinetics of modified MWCNT by dihydroxybenzene derivatives was also studied using Laviron’s theory. As evidenced by an improvement in the anodic peak current and a negative shift in the overpotential of NADH oxidation when compared to the bare MWCNT, 3,4 and 2,5- dihydroxybenzene modified MWCNT electrodes were shown to possess catalytic activity toward NADH oxidation.

Nickel Oxy-Hydroxy/Multi-Wall Carbon Nanotubes Film Coupled with a 3D-Printed Device as a Nonenzymatic Glucose Sensor.

A rapid and simple method for the amperometric determination of glucose using a nanocomposite film of nickel oxyhydroxide and multi-walled carbon nanotube (MWCNTs) was evaluated. The NiHCF)/MWCNT electrode film was fabricated using the liquid-liquid interface method, and it was used as a precursor for the electrochemical synthesis of nickel oxy-hydroxy (Ni(OH)2/NiOOH/MWCNT). The interaction between nickel oxy-hydroxy and the MWCNTs provided a film that is stable over the electrode surface, with high surface area and excellent conductivity. The nanocomposite presented an excellent electrocatalytic activity for the oxidation of glucose in an alkaline medium. The sensitivity of the sensor was found to be 0.0561 μA μmol L-1, and a linear range from 0.1 to 150 μmol L-1 was obtained, with a good limit of detection (0.030 μmol L-1). The electrode exhibits a fast response (150 injections h-1) and a sensitive catalytic performance, which may be due to the high conductivity of MWCNT and the increased active surface area of the electrode. Additionally, a minimal difference in the slopes for ascending (0.0561 µA µmol L-1) and descending (0.0531 µA µmol L-1) was observed. Moreover, the sensor was applied to the detection of glucose in artificial plasma blood samples, achieving values of 89 to 98% of recovery.

LiNO3-poly(vinyl alcohol) polymer electrolytes and its applications in electrochemical capacitors with extended operating temperatures

An ion-conducting neutral pH polymer electrolyte based on LiNO3 and poly(vinyl alcohol) (PVA) was developed for solid electrochemical double layer capacitors (EDLCs). Structural characterizations of LiNO3-PVA electrolytes revealed amorphous structure with well-hydrated ions. The polymer electrolytes are functional over a wide range of temperatures even at −40 °C. Although increasing the concentration of ions can improve the ionic conductivity at and above ambient, it imposes adverse effects at lower temperatures likely due to the freezing of water surrounding the hygroscopic nitrate ions. The optimal electrolyte with relatively high ionic conductivity (ca. 40 mS cm−1 at ambient) and good temperature performance was applied for solid EDLC devices with multi-walled carbon nanotube electrodes. The solid EDLC showed comparable performance to its liquid baseline with excellent rate capability and wide voltage window of 1.6 V. It outperformed the liquid counterpart with lower leakage current and retained capacitive behaviour at −40 °C.

Electrochemical sensor of multiwalled carbon nanotube electrode modified by 1-phenyl-3-methyl-4-orthofluoro benzoyl-5-pyrazolone for sensing dopamine

ABSTRACT. This work explicates a simple, rapid, and sensitive method for the electrochemical detection of dopamine (DOP) utilising 1-phenyl-3-methyl-4-orthofluorobenzoyl-5-pyrazolone (HPMoFBP)/multiwalled carbon nanotube (MWCNT) carbon paste electrode (CPE). The electrochemical behaviour of DOP was performed through cyclic voltammetry and square wave voltammetry. HPMoFBP/MWCNT showed a higher current at the lower potential for the oxidation of DOP compared to bare MWCNT. The sensor's improved electrocatalytic activity was observed to detect in a 1.0 x 10-1 M phosphate buffer saline (PBS) solution at pH 8.0. A good linear regression analysis was observed between electrical response and the concentration of DOP in the range of 1 to 1000 µM. Under optimized experimental conditions, 1.0 x 10-7 M has been determined as the limit of detection (LOD). The sensor has expressed considerable sensitivity towards DOP detection without interference and is successfully used to determine DOP in dopamine hydrochloride injection.
 
 KEY WORDS: Electrochemical sensor, Dopamine, Pyrazolone, MWCNT, Voltammetry
 Bull. Chem. Soc. Ethiop. 2023, 37(4), 845-857. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i4.4

Atomic Layer Deposition of Ultrathin Al2O3 Layer on Carbon Nanotube Anodes for Potassium Ion Batteries with High Initial Coulombic Efficiency and Electrochemical Performance

AbstractPotassium ion batteries (PIBs) have emerged as one of the most attractive alternatives to lithium‐ion batteries (LIBs) to satisfy the burgeoning energy demand. The continuous growth of solid electrolyte interphase (SEI) and consumption of potassium resources cause poor initial Coulombic efficiency (ICE), unstable cycling performance, and even safety issues. Herein, the fabrication of an artificial SEI of an ultrathin Al2O3 layer by atomic layer deposition (ALD) on a multi‐walled carbon nanotubes (MWCNTs) anode for high‐performance PIBs is reported. The SEI resistance and the charge transfer resistance in the MWCNTs electrode are significantly reduced according to electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration (GITT) measurements. The MWCNT electrode with a 2‐nm Al2O3 layer exhibits a much higher ICE of up to 85.9% than that of the uncoated one (20.8 %). It also maintains a remarkably high reversible capacity of 284 mA h g−1 at 100 mA g−1 after 100 cycles. In particular, the anode delivers superior rate capability of 558, 303, 251, 203, and 154 mAh g−1 at a current density of 50, 100, 200, 400, and 800 mA g−1, respectively. This work offers an effective approach for fabricating PIBs with high ICE and electrochemical performance.

Solid-state electrical double layer capacitor using Li-salt incorporated ionic liquid based gel polymer electrolyte and gelled multi-walled carbon nanotubes electrodes

The present investigation is focused on the solid-state supercapacitors which are fabricated with ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMPTFSI) modified multiwalled carbon nanotube (MWCNT) electrodes and ionic liquid incorporated gel polymer electrolyte (ILGPE). Furthermore, the incorporation of the Li-salt lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in ILGPE has been done and the effect of the Li-salt on the performance of supercapacitorsis investigated. On the addition of Li-salt, a wider electrochemical window of ∼ 3 V is found at room temperature. The impact of the Li-salt in the gel polymer electrolyte and comparative performance with the EDLCshave been studied byusing electrochemical impedance spectroscopy, cyclic voltammetric, and galvanostatic charge–discharge studies. It is found that bucky gelled MWCNT electrodes provide specific capacitance of ∼ 57 F/g with Li-salt incorporated ILGPE, which is higher as compared to ILGPE without Li-salt, showing the value of 51 F/g which as also reflect in CV profiles.

Electrochemical characterization of nitrocoumarin-modified nanostructured electrode platforms: New precursors for the electrocatalysis of NADH

All synthesized nitrocoumarins, 3-acetyl-6-nitrocoumarin 6-Coum, 3-(3-nitrocinnamoyl)-coumarin 3-CinCoum, 3-(4-nitrocinnamoyl)-coumarin 4-CinCoum, and 3-(4-nitrocinnamoyl)-6-nitrocoumarin 4-Cin-6-Coum, were used to generate novel nanostructured multiwalled carbon nanotube (MWCNT) electrode platforms that were electrochemically activatable to generate the redox pair ArNHOH/ArNO. This redox pair is capable of acting as a mediator in electrocatalysis of NADH oxidation.Nitrocoumarin-modified nanostructured electrode platforms were prepared using both drop casting and buckypaper (BP) methods for comparative purposes, and they showed no differences in their electrochemical responses.It was observed that the compound most easily reduced was 4-Cin-6-Coum. The reduction occurred first at the 4-nitrocinnamoyl group due to the withdrawing electron effect exerted by the cinnamoyl carbonyl group.The heterogeneous transfer rate constant, kh, was calculated for all of the redox mediators, and they decreased in the order 4-CinCoum> 3-CinCoum> 6-Coum> 4-Cin-6-Coum (II). On the other hand, we observed no significant differences for retention of the redox pairs ArNHOH/ArNO from the nitrocoumarin precursor compounds on the electrode, and the retention values ranged from 79.6 to 91.6% after one hour of working with the nanostructured electrodes.With this electrocatalytic response, it is possible to develop an amperometric sensor for the determination of NADH that includes nanostructured platforms with nitrocoumarins. We obtained LODs of 2.95 µM and 3.43 µM for 6-Coum and 4-Cin-6-Coum (II), respectively.

A multi-responsive self-healing and air-stable ionogel for a vertically integrated device comprised of flexible supercapacitor and strain sensor

We report on the synthesis of multi-responsive self-healing and air-stable ionogel for fabrication of integrated devices of supercapacitor and strain sensor. The ionogel is based on hydrophilic ionic liquid, 1-ethyl-3-methylimidazolium ethyl sulfate and poly(acrylic acid), crosslinked by N, N’-bis(acryloyl)cystamine-coated gold nanoparticles (AuNP@BACAs). The self-healing of the synthesized ionogel can be triggered by thermal heating or irradiation of near-infrared (NIR) laser light, via the reformation of hydrogen bonds and Au-thiolate interactions. Optically healing with NIR laser can be activated due to the introduction of AuNP@BACAs and the healing rate is faster than that by thermal heating. Using the synthesized ionogel electrolyte and multi-walled carbon nanotube electrodes, a high-performance flexible supercapacitor is fabricated with an areal capacitance of 20.4 mF cm−2, perfect capacitance recovery after repetitive self-healing cycles, and air stability over 30 days in ambient air conditions without encapsulation. Furthermore, the strain sensor fabricated using the same ionogel exhibits the self-healing performance of recovering the gauge factor of 0.85 regardless of the healing method. With the vertically integrated device consisting of flexible supercapacitor and strain sensor attached onto the skin, body-motions are successfully detected using the energy stored by the supercapacitor. These results suggest the high application potential of our fabricated electronic devices based on the single self-healable ionogel to wearable electronics with durability and longevity.

Analytical eco-scale determination of vortioxetine using advanced electrochemical platform for screen-printed disposable multiwalled carbon nanotube electrode in the presence of an anionic surfactant

A disposable screen-printed electrode, modified by multiwalled carbon nanotubes, was created as a sensor for the measurement of vortioxetine hydrobromide as an inexpensive quick and convenient method.

Functionalizing Carbon Nanotubes with Bis(2,9-dialkyl-1,10-phenanthroline)copper(II) Complexes for the Oxygen Reduction Reaction.

A new ligand, namely, 2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline, as well as new bis(2,9-dialkyl-1,10-phenanthroline)copper(II) complexes were designed, which were immobilized on multiwalled carbon nanotube (MWCNT) electrodes. These complexes show a high tendency of autoreduction into their copper(I) form according to electrochemical and EPR experiments. These complexes exhibit strong interactions with MWCNT sidewalls either with or without anchor functions such as the pyrene moiety. The pyrene-modified derivative can be electropolymerized on glassy carbon and MWCNT electrodes to form a poly-[bis(2-(5-(pyren-1-yl)pentyl)-9-methyl-1,10-phenanthroline)copper(II)] metallopolymer film. Furthermore, these MWCNT-supported bis(2,9-dialkyl-1,10-phenanthroline)copper complexes demonstrate a low overpotential for a 4H+/4e- oxygen reduction reaction at pH 5 with an onset potential of 0.86 V versus RHE. Integration of these functionalized MWCNTs at gas-diffusion electrodes of H2/air fuel cells led to a high open-circuit voltage of 0.84 V and a maximum current density of 1.77 mW cm-2 using a Pt/C anode.

Fabrication of a Free-Standing MWCNT Electrode by Electric Field Force for an Ultra-Sensitive MicroRNA-21 Nano-Genosensor.

Abnormal expression of microRNA-21 (miR-21) is considered to be closely associated with the pathogenesis of colorectal cancer. However, great challenges do exist for the development of ultra-sensitive biosensors to detect the abnormal expression of miR-21 due to the low concentration in serum (fm level) at the early stage of colorectal cancer. Therefore, electric field force is used to rotate and rearrange random multi-walled carbon nanotubes (MWCNTs) at the microscale to improve the active sites of the electrode in this study. The free-standing MWCNTs are densely and high-orderly embedded into the bare electrode along the direction of the electric field. Compared to the bare electrode, the peak-current response of the free-standing MWCNT electrode improves by 150times in cyclic voltammetric measurement. A nano-genosensor based on the free-standing MWCNT electrode is developed for measuring miR-21. The nano-genosensor for miR-21 shows an ultra-high sensitivity of 48.24 µA µm-1 , a wide linear range from 0.01 × 10-15 to 100 × 10-12 m, and a low detection limit of 1.2 × 10-18 m. The present nano-genosensor shows superior performance for miR-21 in human serum samples and demonstrates a potential application for the diagnosis of early stage colorectal cancer.

Freestanding niobium pentoxide-decorated multiwalled carbon nanotube electrode: Charge storage mechanism in sodium-ion pseudocapacitor and battery

This study investigated flexible, freestanding niobium pentoxide (Nb2O5) decorated multiwalled carbon nanotube (MWCNT) electrode material in a sodium-ion pseudocapacitor and its respective energy storage mechanism. Sodium is an abundant element in the Earth's crust, with attractive sustainability and low-cost appeal for the scientific community and energy markets such as electric vehicles and renewable energies. Combined with niobium pentoxide and carbon nanotubes, sodium ions can perform ultra-fast intercalation into niobium pentoxide and electrostatic adsorption onto carbon high surface areas. Niobium pentoxide particles were investigated using X-ray diffraction via Rietveld refinement, a powerful technique to study crystalline materials' electronic and structural properties that directly influence Na+-ion diffusion. The niobium pentoxide-decorated MWCNT electrode material was investigated within a symmetric supercapacitor (SIC) and as an anode for sodium-ion batteries (SIBs). A finite-length transmission line was used to model the impedance behavior of the solid and liquid phases that comprised the material/solution interface. This numerical modelling allowed investigators to infer the presence of MWCNT as a nanostructured matrix since Nb2O5 dispersive nanoparticles increased the overall pseudopacacitance by 63.2% for Nb2O5/MWCNT compared to MWCNT nanostructured electrodes. Electrochemical findings revealed a maximum capacitance of 192 F g−1 for the SIC full cell, with capacitance retention of 96% after 10,000 cycles. In addition, the SIC delivered outstanding power density from 98.7 to 24,671 W kg−1 and high energy density from 5.4 to 2.7 W h kg−1. In an SIB half-cell configuration, the electrode delivered a reversible sodium-ion storage capacity of ~163 mA h g−1, with a retention capacity of ~68 mA h g−1 after 100 cycles at 25 mA g−1. These systems bridge the gap between supercapacitors and batteries by employing the best properties of them both.

Investigation on performance of adding manganese dioxide into graphene oxide electrode film

ABSTRACT In this paper, the preparation of electroactive polymers artificial muscle electrode membrane with graphene oxide and manganese dioxide as the main research material to explore the performance of electrode membrane. Using sodium alginate as matrix, manganese dioxide with different mass ratios was compounded with graphene oxide and sodium alginate aqueous solution to prepare electrode films. The effects of manganese dioxide on the morphology and electrochemical properties of electrode films were discussed. From the test results, it can be seen that the scanning electron microscopy results show that the manganese dioxide layer is uniformly compounded on graphene oxide. With the increase of manganese dioxide/graphene oxide mass ratio, the specific capacitance of the electrode film gradually increases and the impedance increases. With the increase of driving voltage, the deflection displacement gradually increases and then shows a downward trend. When the mass ratio of manganese dioxide/graphene oxide is 0.1(# 2), the maximum deflection displacement is 14.1 mm, which is 2.76 times of the minimum deflection displacement of the sample (# 1). The specific capacitance of the electrode film was increased by 1.57 times to 15.62 F · g−1. Finally, the performance difference of graphene oxide electrode film and multi-walled carbon nanotube electrode film on EAP artificial muscle was explored.

Fabrication and Seamless Integration of Insensitive-Bending Fully Printed All-in-One Fabric-Based Supercapacitors Based on Cost-Effective MWCNT Electrodes.

All-in-one supercapacitors are considered to be promising due to their advantages of flexibility and structure stability. However, the sophisticated and precise manufacturing processes and difficulty of series/parallel integration hinder their application and development. Herein, cost-effective all-in-one fabric-based supercapacitors (all-in-one FSCs) are fabricated by utilizing the facile screen-printing technique and multiwalled carbon nanotube (MWCNT) electrodes. The MWCNT electrodes are constructed on the gel-electrolyte-soaked fabric that simultaneously serves as separator and electrode substrates. The as-prepared all-in-one FSC exhibits better capacitive behavior and rate capability and lower internal resistance than traditional sandwiched fabric-based supercapacitors (sandwiched FSCs). Moreover, due to the simplified structure and interface interaction, the all-in-one FSC shows excellent flexibility and stability even under dynamic bending cycles with a relatively high strain rate of 20% s-1. This work also demonstrates the seamless series/parallel integration scheme of all-in-one supercapacitors by designing the screen-printing patterns instead of using metal wires. The proposed fabrication process and series/parallel integration scheme definitely improve the portability of integrated supercapacitors and potentially contribute to the large-scale production and application on wearable electronics.

Plasma-functionalized multi-walled carbon nanotubes directly grown on stainless steel meshes as supercapacitor electrodes

Multi-walled carbon nanotubes (MWCNTs) directly grown on a stainless steel mesh were functionalized using a fast, solvent-free radiofrequency (RF) plasma technique. Two different gas mixtures of Ar/C2H6/O2 and Ar/C2H6/N2 were used to add oxygen- and nitrogen-containing functional groups to the surface of MWCNTs. The binder-free forest-like MWCNTs before and after functionalization were tested as supercapacitor electrodes. The structural and electrochemical characteristics of the electrodes were evaluated. The RF power (10–30 W) and functionalization time (1–20 min) were optimized to achieve the highest capacitance. Both nitrogen- and oxygen-functionalized MWCNTs showed improved capacitive behavior due to the presence of the functional groups on the MWCNT surface. The highest capacitance was obtained for the MWCNT electrode functionalized with the RF plasma employing the Ar/C2H6/O2 gas mixture at 20 W for 15 min, reaching the specific capacitance of 37.3 ± 1.1 mF cm−2 (196.3 ± 5.8 F g−1).

Nitrobenzoic acid-functionalized gold nanoparticles: DET promoter of multicopper oxidases and electrocatalyst for NAD-dependent glucose dehydrogenase

We report the synthesis of coated gold nanoparticles with nitrobenzoic moieties (AuNPs-TNB). They displayed small and narrow size distribution (2 nm) as shown by TEM imaging. These functionalized AuNPs-TNB were physically adsorbed on multi-walled carbon nanotubes (MWCNTs) electrodes. Their stable adsorption was monitored by electrochemical methods. The stability of the activated hydroxylamine layer was enhanced compared to the adsorption of the dinitro precursor onto the CNTs layer. Unactivated AuNPs-TNB enhanced the oxygen reduction reaction catalyzed by multicopper oxidases through increased aromatic and electrostatic interactions with limiting current densities higher than 500 µA cm−2. Next, the electrocatalytic properties of the active form toward the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) with low overpotential was shown at near neutral pH. Associated with a NAD-dependent glucose dehydrogenase, the bioelectrodes were assessed for glucose electrooxidation. A complete glucose/O2 enzymatic fuel cell was developed based on unactived and activated AuNPs as cathodic DET promoter and anodic electrocatalyst respectively. The nanostructured assembly exhibited efficient glucose oxidation with current densities of 450 µA cm−2 in high glucose concentration and O2 saturated conditions. In concentration close to those found in physiological fluids (0.04 to 4.00 mmol L−1), the enzymatic biofuel cell displayed a linear range for glucose concentration and a low limit of detection (2.5 ± 0.9 µmol L−1).