Anodic Peak Potentials Research Articles

Cholesteryl Phenolipids as Potential Biomembrane Antioxidants

The lipophilization of polyphenols (phenolipids) may increase their affinity for membranes, leading to better antioxidant protection. Cholesteryl esters of caffeic, dihydrocaffeic, homoprotocatechuic and protocatechuic acids were synthetized in a one-step procedure with good to excellent yields of ~50–95%. After evaluation of their radical scavenging capacity by the DPPH method and establishing the anodic peak potential by cyclic voltammetry, their antioxidant capacity against AAPH-induced oxidative stress in soybean PC liposomes was determined. Their interaction with the liposomal membrane was studied with the aid of three fluorescence probes located at different depths in the membrane. The cholesteryl esters showed a better or similar radical scavenging capacity to that of α-tocopherol and a lower anodic peak potential than the corresponding parental phenolic acids. Cholesteryl esters were able to protect liposomes to a similar or greater extent than α-tocopherol. However, despite their antiradical capacity and being able to penetrate and orientate in the membrane in a parallel position to phospholipids, the antioxidant efficiency of cholesteryl esters was deeply dependent on the phenolipid polyphenolic moiety structure. When incorporated during liposome preparation, cholesteryl protocatechuate and caffeate showed more than double the activity of α-tocopherol. Thus, cholesteryl phenolipids may protect biomembranes against oxidative stress to a greater extent than α-tocopherol.

Comprehensive investigation of zinc and tin-based metal oxides for advanced electrochemical detection of organophosphate pesticides

Different metal oxide (MO) nanomaterials, such as ZnO, SnO2, and nanocomposites of ZnO:SnO2 with various ratios of (1:9), (2:8), and (3:7) were prepared and coated on glassy carbon electrode (GCE). These MOs were tested as sensing material for organophosphate (OP) pesticides detection. Among all MOs, ZnO:SnO2 (1:9) coated GCE increases redox peak current at different buffer solutions with varying pH compared to bare GCE. Moreover, among these pH values, ZnO:SnO2 (1:9) coated GCE significantly enhanced the redox peak at pH 6.2, emphasizing optimal electrochemical conditions for the given pesticides. The morphological, elemental composition, metal ions-functional group interation, and crystallinity of different MO nanocomposites were examined using field-emission scanning electron microscopy (FESEM), fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectrum (EDX), and X-ray diffraction (XRD), respectively. The modified GCE with ZnO:SnO2 (1:9) showed an excellent performance during the electrochemial sensing of the diazinon (DiZn) pesticide. Therefore, detailed study was carried out for the sensing of DiZn. Furthermore, the electrochemical behavior of the ZnO:SnO2 (1:9) coated GCE was evaluated using cyclic voltammetry (CV) with 0.5 mL (5 mM) potassium ferrocyanide, resulting in a pronounced increase in anodic and cathodic peak potentials (Epa = 0.423 V, Epc = 0.1945 V) and currents (Ipa = 9.867 × 10-5 mA, Ipc = -7.993 × 10-5 mA). In addition, electrochemical impedance spectroscopy (EIS) demonstrated a reduction in charge transfer resistance for the coated ZnO:SnO2 (1:9) GCE. Differential pulse voltammetry (DPV) further showed a linear relationship between current and pesticide concentration, with a high correlation coefficient (R2 = 0.996), low limit of detection (LOD = 0.0133 mM) and low limit of quantification (LOQ = 0.0405 mM). Real samples, including tap and seawater, were analyzed to validate the method’s applicability. Additionally, chronoamperometry with a step potential of 1.2 V indicated high sensitivity for DiZn detection, with a sensitivity of 0.23 mA mM−1 cm−2. Finally, the stability of the ZnO:SnO2 (1:9) coated GCE was confirmed through recyclability tests over three cycles using CV and DPV techniques, ensuring its robustness for practical applications in pesticide detection.

Monitoring the Solid-Electrolyte Interphase Formation in Bis(fluorosulfonyl)Amide Ionic Liquid Electrolyte Using a Redox Probe Method

The solid-electrolyte interphase (SEI) has been considered to be formed on the negative electrode surface by reductive decomposition of electrolyte components. In the case of the electrolytes containing lithium ions, the SEI can be regarded as the Li+ conductor that enables the negative electrode reactions and prevents the further decomposition of the electrolytes. The structure of the SEI is often explained by the mosaic model, in which the SEI is a composite of several different inorganic and organic domains [1]. On the other hand, we have proposed the formation of the gelled SEI in bis(fluorosulfonyl)amide (FSA–) ionic liquid electrolytes containing a high concentration of LiFSA [2,3]. Furthermore, we have reported that the SEI formation can be detected by monitoring the redox reaction of ferrocene (Fc) and ferrocenium (Fc+) [4,5]. In the present study, the time-dependent transition of the SEI formed on a Pt electrode was investigated by the redox probe method in BMPFSA (BMP+ = 1-butyl-1-methylpyrrolidinium) containing LiFSA.The formation of SEI by holding a Pt electrode at a negative potential was confirmed by a shift in the anodic peak potential of the cyclic voltammogram for Fc+/Fc couple in LiFSA/BMPFSA. The anodic peak disappeared when the electrode was held at the negative potential for a few hours, indicating the formation of a thick SEI. However, the anodic peak was observed again after keeping the electrode at the open circuit potential for a few hours, indicating the disappearance of the SEI. These results suggest that the SEI is formed by dissolution and/or dispersion of the decomposed products, which form at the electrode surface and diffuse into the electrolyte. Thus, the SEI formed at the potential is considered to exist as a metastable phase in the balance between the formation and diffusion of the decomposition products. This work was partly supported by GteX Program Japan Grant Number JPMJGX23S0.[1] E. Peled, D. Golodnitsky, and G. Ardel, J. Electrochem. Soc., 144, L208 (1997).[2] R. Furuya, T. Hara, T. Fukunaga, K. Kawakami, N. Serizawa, and Y. Katayama, J. Electrochem. Soc., 168, 100516 (2021).[3] N. Serizawa, R. Yamashita, and Y. Katayama, J. Phys. Chem. C, 127, 10434 (2023).[4] S. Kato, N. Serizawa, and Y. Katayama, J. Electrochem. Soc., 169, 076509 (2022).[5] S. Kato, N. Serizawa, and Y. Katayama, J. Electrochem. Soc., 170, 056504 (2023).

Ultrasensitive composite electrochemical sensor with printed wrinkled CNTs nanostructure for simultaneous detection

Combining biomimetic and 3D printing has created new opportunities for the manufacture of electrochemical sensors. Dopamine (DA) and Uric acid (UA) are common body electroactive substances, and their detection is important for diagnosing metabolic diseases. Metal electrochemical sensors have limitations in sensitivity and selectivity due to their smooth 2D structures, which make it challenging to capture comprehensive electrochemical information. Here, inspired by taste buds, an ultrasensitive CNT-Pt composite electrochemical sensor, including a printed biomimetic wrinkled CNTs film, was prepared for simultaneous detection of DA and UA. Nanoscale Pt electrode was prepared by UV-LIGA process and the wrinkled CNTs nanofilm was fabricated by thermally assisted electrohydrodynamic jet (E-Jet) printing. CNT lines of 3∼58 μm, droplets of 4 μm and 2D array structures have been printed. The enhanced sensing mechanism of wrinkled CNTs nanofilm was analyzed theoretically. The nanoscale wrinkled morphology (nanofolds∼50 nm) and hydrophilicity (CÃ20°) of printed wrinkled CNTs nanofilm were analyzed. The anodic peak potential for UA was observed to range from 0.429 V to 0.489 V for the conventional Pt electrochemical sensor, whereas it ranged from 0.205 V to 0.276 V for the CNT-Pt composite electrochemical sensor. The detection performance of CNT-Pt composite electrochemical sensor was improved by ∼40 % contrast with Pt electrochemical sensor. The prepared composite electrochemical sensor can effectively recognize DA, UA and AA. From analysis, the peak value of AA was not obvious, the peak values of DA and UA were 0.096 V and 0.265 V. The composite electrochemical sensor successfully eliminated the detection interference caused by AA in detecting DA and UA. The nanoscale composite electrochemical sensor and its hybrid manufacturing method provide great potential for electrochemical testing applications.

Ni(II) and Pd(II) complexes of a new redox-active pentadentate azo-appended 2-aminophenol ligand: Pd(II)-assisted intraligand cyclization forms a phenoxazinyl ring.

Square planar complexes of Ni(II) and Pd(II) of a new redox-active pentadentate azo-appended 2-aminophenol ligand (H4L = N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'-diamino-ortho-azobenzene) in three accessible redox levels [amidophenolate(2-), semiquinonate(1-) π radical, and quinone(0)] were synthesized. The coordinated HL(3-) ligand provides four donor sites [two N(iminophenolates), an N'(azo), and an O(phenolate)], while the phenolic OH group remains free in the three complexes. Cyclic voltammetry on complex [Ni(L)] 1 and its corresponding Pd(II) analogue [Pd(L)] 2 in CH2Cl2 displayed three redox responses (two oxidative at E1/2 = 0.06 V and Epa (anodic peak potential) = 0.80 V and one reductive at -0.77 V for 1 and at E1/2 = 0.08 V and Epa = 0.85 V and at -0.74 V for 2vs. Fc+/Fc). The chemical oxidation of 1 with AgSbF6 afforded [Ni(L)]SbF6·2CH2Cl2 (3·2CH2Cl2). Complex [Pd(L*)] 4, which is coordinated by a phenoxazinyl derivative of L(4-), was obtained via intraligand cyclization in the parent complex 2 under basic oxidizing conditions. The molecular structures of 1, 2, 3·2CH2Cl2 and 4 were elucidated through X-ray crystallography at 100 K. Characterization using 1H NMR, X-band EPR, and UV-VIS-NIR spectroscopy established that the complexes have [NiII{(LISQ)˙2-}] 1, [PdII{(LISQ)˙2-}] 2, [NiII{(LIBQ)-}]SbF6/1+SbF6-(3), and [PdII{(L*AP)˙2-}] 4 electronic states. Complexes 1, 2, and 4 possess paramagnetic St (total spin) = 1/2 ground-state, whereas 3 is diamagnetic (St = 0). Density functional theory (DFT) electronic structural calculations at the B3LYP level rationalized the observed experimental results. Time-dependent (TD)-DFT calculations allowed us to identify the nature of the observed absorption spectra.

Reliable Information about Electrochemical Potentials from Cyclic Voltammograms That Look “Messy”

The importance of voltammetry for characterizing electronic properties of molecular species and (nano)materials cannot be overstated. Among the most broadly used electroanalytical techniques, cyclic voltammetry (CV) offers an incomparably facile means for estimating standard electrochemical potentials, E (0), which are essential for analysis of charge transfer, energy conversion and photocatalysis [Phys. Chem. Chem. Phys. 2020, 22, 21583-21629]. Redox irreversibility, liquid-junction potentials, and uncertainties about the microenvironment on the surfaces of polarized working electrodes present key challenges for the validity of CV analysis [Curr. Opin. Electrochem. 2022, 31, 100862]. As an average of anodic and cathodic peak potentials extracted from cyclic voltammograms, half-wave potentials, E (1/2), serve as a good approximation for E (0). This approximation is acceptable for results from voltammograms exhibiting even partial chemical reversibility [J. Electrochem. Soc. 2019, 166, H3175-H3187]. Conversely, cyclic voltammograms lacking an anodic or cathodic peak die to irreversible reduction or oxidation, respectively, render estimating E (1/2) impossible. In fact, irreversibility of electrochemical oxidation and reduction is more or less the rule rather than the exception. Statistical analysis of a series of voltammograms allows us to demonstrate that the potentials at the inflection points at the rise of the cathodic and anodic waves represent a good approximation of E (1/2) for reduction and oxidation, respectively [J. Electrochem. Soc. 2019, 166, H3175-H3187]. The use of inflection potentials significantly broadens the applicability of CV for extracting meaningful results from voltammograms showing irreversible behavior. It allows us to investigate in parallel a series of electron-rich and electron-deficient polycyclic aromatic species not only with similar structures, but also with similar spin-density distributions of their radical ions, regardless their stability and reversible redox behavior in different solution media. Reformulating the Rehm-Weller equation for CT thermodynamic analysis, offers a means for eliminating the effects of liquid-junction potentials while studying electron donor-acceptor pairs [Proc. Natl. Acad. Sci. USA 2021, 118, e2026462118]. Employing this approach to donors and acceptors with similar structures reveals patterns correlated with the microenvironment at the surfaces of polarized working electrodes. Global-fit analysis of the dependence of CV-extracted reduction potentials on the concentration of the supporting electrolyte for different solvents yields information about the liquid-junction potentials in the electrochemical cell and about the polarity of the microenvironment of the redox species at the electrode surface [J. Phys. Chem. B 2023, 127, 1443-1458]. These outcomes offer a key foundation not only for improved voltammetric estimates of standard electrochemical potentials of redox species, but also for the polarity dependence of these potentials, permitting their broad applicability to systems in widely different media.

Electrodeposition of Ti in Molten Alkali Metal Fluoride–Chloride Mixtures: Comparative Study of Li, Na, K, and Cs Systems

1. IntroductionTitanium (Ti) is a metal with excellent properties such as high corrosion resistance and biocompatibility. However, it is still not widely used due to its high production cost and poor workability. If Ti films can be plated on a variety of substrates, the excellent surface properties of Ti can be imparted, and it is expected to be applied in a wider range of fields.We have previously studied Ti electrodeposition using KF–KCl [1-3] and LiF–LiCl [4,5] melts and reported that smooth Ti films were obtained. Here, fluoride–chloride melts containing a single cation, such as KF–KCl and LiF–LiCl, were used so that differences due to cations could be compared. As a result, we have already reported that the electrodeposition potential of Ti differs significantly between the K- and Li-based systems [4]. Therefore, in this study, we investigated the electrodeposition of Ti and the electrochemical behavior of Ti(III) ions in the CsF-CsCl and NaF-NaCl melts. This allowed us to systematically compare the effects of cations on titanium electrodeposition for the Li-, Na-, K-, and Cs-based systems.2. ExperimentalThe experiments were conducted in eutectic CsF–CsCl and NaF–NaCl melts in an Ar glove box. A2TiF6 (A = Cs, Na) and sponge Ti were added to the melts and Ti(IV) ions were converted to Ti(III) ions by comproportionation reaction. Ni plate, Mo and Au flag electrodes were used as the working electrodes. The counter and reference electrodes were Ti rods. The potential of the reference electrode was calibrated by A+/A (A = Cs, Na) potential measured at a Mo electrode. The electrochemical behavior of Ti(III) was studied by cyclic voltammetry. Samples prepared by galvanostatic electrolysis of Ni plate substrates were analyzed by X-ray diffraction (XRD) after washing with distilled water.3. Result and DiscussionFigure 1 (a) shows cyclic voltammograms measured at a Mo flag electrode in the negative potential region in molten CsF–CsCl at 823 K. After the addition of Ti(III) ions, cathodic currents around 0.3 V were larger than those before the addition, and a current shoulder was observed at 0.3 V. Furthermore, a sample prepared by galvanostatic electrolysis at a cathodic current density of 25 mA cm−2 was confirmed to be Ti metal by XRD. Considering that the potential during the electrodeposition was around 0.3 V, the cathodic currents around 0.3 V in the CV were confirmed to beTi(III) + 3e− → Ti(0).Figure 1 (b) shows cyclic voltammograms measured at a Au flag electrode in the positive potential region in molten CsF–CsCl containing Ti(III) ions at 823 K. A pair of redox currents were observed around 1.7 V. The number of electrons transferred was 0.86 which was calculated from the difference in the cathodic and anodic peak potentials. This result indicates that the redox reaction around 1.7 V isTi(IV) + e− ⇄ Ti(III).Here, the formal potential of Ti(IV)/Ti(III) was calculated to be 1.63 V from the average values of the cathodic and anodic peak potentials.We compared the obtained potentials of Ti(III)/Ti(0) and Ti(IV)/Ti(III) to those previously reported in KF–KCl and LiF–LiCl melts [2,4]. Figure 2 shows the comparison of the Ti(III)/Ti(0) and Ti(IV)/Ti(III) potentials in CsF–CsCl, KF–KCl, and LiF–LiCl melts. All potentials were calibrated using F2/F− potential for comparison because Ti(III) ions exist as fluoro-complexes in the melts. Both Ti(III)/Ti(0) and Ti(IV)/Ti(III) potentials were negative in the order of Li-, K-, Cs-based systems. Such potential differences are explained by the interactions of alkaline cations (A+) and fluoride ions (F−); smaller cations interact more strongly with F−, resulting in reduced stability of Ti fluoro-complexes. At the meeting, we will compare and discuss all the results, including those obtained with NaF-NaCl melts.AcknowledgmentA part of this work was supported by JSPS KAKENHI Grant Number 22K14507. A part of this study was conducted as a collaboration with Sumitomo Electric Industries, Ltd.

Electrochemical platform based on molecularly imprinted polymer with zinc oxide nanoparticles and multiwalled carbon nanotubes modified screen-printed carbon electrode for amaranth determination.

Anovel electrochemical platform for amaranth determination has been developed using a rapid, easy, inexpensive, and portable molecularly imprinted polymer technique. The MIP platform was fabricated by electropolymerizing melamine as monomer in the presence of amaranth as template on the surface of ZnO-MWCNT/SPCE. Then, amaranth was completely eluted, leaving imprinted cavities in the polymeric film that could effectively recognize amaranth in solution. The electrochemical platform based on a molecularly imprinted polymelamine was analyzed by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Under optimum conditions, the developed MIP/ZnO-MWCNT/SPCE platform can be properly used for amaranth determination, with high sensitivity of 96.2 µA µM cm-2, two linear concentration ranges (0.01 to 1µM and 1 to 1000µM) and a low limit of detection of 0.003µM. The anodic peak potential of amaranth was found to be 0.73V. Additionally, the polymelamine MIP films specifically recognize amaranth molecules, making it possible to detect amaranth in a complex solution with high selectivity, excellent repeatability, reproducibility, and stability. The MIP/ZnO-MWCNT modified screen-printed carbon electrode was successfully applied to determine amaranth in pharmaceutical and water samples, with recovery values ranging from 99.7 to 102% and RSD% values less than 3.2%.

Solid-Electrolyte Interphase Formation in Amide-Type Ionic Liquids in the Presence of Different Metal Cations

The formation of solid-electrolyte interphase (SEI) on a glassy carbon (GC) electrode in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Li+, Na+, K+, and Ni2+ was investigated using the redox reaction of ferrocene (Fc). The anodic peak potential (E pa) for the oxidation of Fc changed after holding the electrode at –1.4 to –1.5 V vs Ag|Ag(I) in BMPFSA in the presence of the alkali metal ions. The decomposition of FSA– was confirmed by X-ray photoelectron spectroscopy (XPS) on a GC electrode held at –1.5 V vs Ag|Ag(I) for 6 h in BMPFSA containing the alkali metal ions. The change in E pa may also suggest the formation of homogeneous SEI in the FSA–-type ionic liquid. Moreover, E pa changed after holding the electrode at the potential more negative than –0.9 V vs Ag|Ag(I) in 50 mM Ni(TFSA)2/BMPTFSA while the decomposition of TFSA– was not confirmed by XPS on the electrode held at –1.1 V vs Ag|Ag(I) for 6 h, suggesting the bonds except C-F (e.g., S-C) were dissociated to form the SEI. Since the deposition potential of Ni in BMPTFSA was more negative than the SEI formation potential, the deposition of Ni may be inhibited by the SEI.

Simultaneous voltammetric determination of 7-methyl-guanine and 5-methyl-cytosine using a cathodically pre-treated boron-doped diamond electrode

Given the importance of identifying the presence of biomarkers of human diseases in DNA samples, the main objective of this work was to investigate, for the first time, the electro-catalytic oxidation of 7-methyl-guanine (7-mGua) and 5-methyl-cytosine (5-mCyt) on a boron doped diamond electrode pre-treated cathodically (red-BDDE), using differential pulse voltammetry (DPV) and cyclic voltammetry (CV). The anodic peak potentials of 7-mGua and 5-mCyt by DPV were at E = 1.04 V and E = 1.37 V at pH = 4.5, indicating excellent peak separation of approximately 330 mV between species. Using DPV, experimental conditions such as supporting electrolyte, pH and influence of interferents were also investigated to develop a sensitive and selective method for individual and simultaneous quantification of these biomarkers. The analytical curves for the simultaneous quantification of 7-mGua and 5-mCyt in the acid medium (pH = 4.5) were: concentration range of 0.50–5.00 μmol L−1 (r = 0.999), detection limit of 0.27 μmol L−1 for 7-mGua; from 3.00 to 25.00 μmol L−1 (r = 0.998), with a detection limit of 1.69 μmol L−1 for 5-mCyt. A new DP voltammetric method for the simultaneous detection and quantification of biomarkers 7-mGua and 5-mCyt using a red-BDDE is proposed.

Analysis of the bioactive components in Swietenia macrophylla leaves for their antibacterial and antioxidant capabilities

In this study, the extraction of bioactive compounds from Swietenia macrophylla leaves resulted in 50 % (v/v) acetone being the best solvent for extraction of gallic acid, total phenolic compounds, hydrolyzable tannins, and flavonoid content with maximum values of 58.769 μg/mL; 38.153 mgGAE/gdw; 10.586 mg/mL and 64.172 rutin/gdw respectively. FTIR studies indicated the presence of various compounds that have antimicrobial and antibacterial properties. Further, the study of antimicrobial activity showed that the sample acted against Gram-positive bacteria, but not Gram-negative bacteria. On conducting cyclic voltammetry and differential pulse voltammetry, CV showed an anodic peak at 0.2 V with a maximum peak current was at 212 μM; whereas DPV showed various anodic peak potentials at −0.05 V, 0.13 V, 0.23 V, and 0.65 V. TLC was used to qualitatively assess the presence of various bioactive compounds in the plant sample. This study produces bioactive chemicals that are antibacterial and antioxidant.

Effect of Current Density on Preparation and Properties of TF/β-PbO2 in MSA Media.

The lead-based alloy and DSA anodes have drawbacks, such as poor corrosion resistance, easy peeling of coating, low electrocatalytic activity, and environmental pollution in electrode preparation processes. In this study, titanium foam/β-PbO2 (TF/β-PbO2) was prepared by electrodeposition in methanesulfonic acid (MSA) media. The current efficiency and the deposition rate were 89.7% and 5.36 v/(μm·min-1) at the best current density of 80 mA·cm-2, respectively. The TF/β-PbO2 was characterized by electrochemical tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The cyclic voltammetry (CV) test shows that the anodic peak potential of the optimum TF/β-PbO2 was as low as 2.135 V and anodic voltammetry charge was up to the maximum value of 3.564 × 10-2 C. The linear sweep voltammetry (LSV) test indicates that exchange current density of the optimum TF/β-PbO2 reached the maximum value of 8.284 × 10-6 A·cm-2. CV and LSV tests indicate that the optimum TF/β-PbO2 had a high electrocatalytic activity. Electrochemical impedance spectroscopy test Tafel polarization curves show that the optimum TF/β-PbO2 had better corrosion resistance. The XRD test shows that the crystal was mainly β-PbO2 of the optimum TF/β-PbO2 surface and the current density affected the preferential growth of the crystal surface of PbO2. SEM tests show that grains of the optimum TF/β-PbO2 coating prepared were tightly bound and uniform in size.

3D printed electrodes design and voltammetric response

The limiting aspects in the voltammetric response of 3D printed electrodes is thoroughly investigated with numerical simulations and new 3D printed electrode designs. Severe diffusion limitations, resulting from a recessed electrode geometry, is found in a commonly used 3D printed electrode and electrochemical cell design, impeding the investigation of electron transfer kinetics at these electrodes by classical methods, such as Nicholson's, widely used on this and similarly mass transport-limited designs. A new 3D printed electrode design, an inlaid disk (non-recessed) geometry, is used to investigate the voltammetric response of printed electrodes in bulk solution, i.e., without mass transport limitations. At this condition, it is clear that the voltammetric response is limited by contact resistance, arising from the printed material low electrical conductivity. Gold modified electrodes, deliberately designed with different contact resistances, highlight the resistive behavior, with quasi-reversible voltammetric profiles. This contrasts with the common assumption of a voltammetric response limited by finite electron kinetics. Electron transfer rate constants (k0) and transfer coefficients (α) for electrodes with and without surface modifications are calculated from experimental data using a modified Butler-Volmer equation, incorporating ohmic losses. The reported k0 and α values are independent of electrode geometry or printing parameters, unlike the observable rate constant usually reported for 3D printed electrodes. By accounting for contact resistance and finite electron transfer kinetics, cathodic and anodic peak potentials and currents of voltammograms recorded with 3D printed electrodes are predicted before printing, allowing electrode designs to be optimized in the virtual space.

A voltammetric sensor for bisphenol A using gold nanochains and carbon nanotubes

Gold nanochains (AuNCs) were prepared, and this novel material was combined with carboxylated multi-walled carbon nanotubes (cMWCNTs) to be a nanocomposite for the first time. The transmission electron microscopy (TEM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and UV-Vis spectra were used to characterize the successful preparation of AuNCs and AuNC-cMWCNT composite. Based on this hybrid material, a voltammetric sensor of bisphenol A (BPA) was established. The proposed sensor displayed excellent performance for the measurement of BPA by obvious decreased anodic peak potential and enlarged peak current. Using the optimized conditions, BPA was detected using linear sweep voltammetry, and the linear range showed as wide as 0.5 μM to 2000 μM with the detection limit estimated to be 12 nM (S/N = 3). The as-proposed sensor also exhibited satisfactory performance in determining BPA of actual plastic samples.

Porous Nickel Electrode for Highly Sensitive Non-Enzyme Electrochemical Glucose Detection

Porous metals have great potential for applications in non-enzyme glucose detection because they have a high surface area and therefore improved the sensitivity of detection and the accuracy of measurement. An LCS/DHBT porous nickel with both macropores (710–1000 μm) and microscale pores (1–25 μm) has been produced by combining the Lost Carbonate Sintering (LCS) and Dynamic Hydrogen Bubble Template (DHBT) processes. Its behavior for glucose measurement has been studied by cyclic voltammetry and compared with a nickel plate and the LCS porous nickel substrate. The as-fabricated porous nickel has an electroactive surface area 18% higher than the LCS porous nickel. The anodic peak current density of the LCS/DHBT electrode in an electrolyte of 0.1 M KOH containing 0.5 mM glucose at scan rates in the range of 25–300 mV/s are in the range of 3.43–13.94 mA/cm2, which is approximately 2 and 10 times those of the plate and LCS electrodes. Increasing the scan rate results in a higher current density and a larger anodic peak potential shift. Current density increases with glucose concentration in several linear segments. The sensitivity and limit of detection of LCS/DHBT nickel electrode in the glucose measurement are 5775 μA/cm2mM and 0.66–2.91 μΜ, respectively. It shows excellent performance for glucose measurement due to its porous nanostructure and its highly effective surface area.

Comparison of carbon paste and boron-doped diamond electrodes for determination of cefepime in pharmaceutical dosage forms and biological samples

The electrochemical analysis of cefepime, a fourth-generation cephalosporin, was investigated in the direction of oxidation using a carbon paste (CP) electrode and a boron-doped diamond (BDD) electrode. The optimum paste composition was determined as 25 % mineral oil-75 % graphite powder for the CP electrode. The effects of different pHs and scan rates on the anodic peak potential and peak current of cefepime were investigated. Scan rate studies were carried out in the range of 5–200 mV s −1 (vs. Ag/AgCl). It was found that the CP electrode had an adsorption-controlled process and the BDD electrode had a diffusion-controlled process under some adsorption effect. The linear ranges of cefepime obtained for the CP electrode were determined as 0.08–10 μM (correlation coefficient; r = 0.998) for differential pulse stripping voltammetry with a detection limit of 3.73 nM and 0.4–10 μM ( r = 0.998) for square wave stripping voltammetry with a detection limit of 22.1 nM. For the BDD electrode, cefepime gave a linear range of 0.04–10 μM ( r = 0.999) for differential pulse voltammetry with a detection limit of 1.58 nM and 0.4–60 μM ( r = 0.998) for square wave voltammetry with a detection limit 11.0 nM. The precision of the proposed methods was examined by repeatability studies and presented by relative standard deviation (RSD) values below 1.76 %. Quantitative analysis of cefepime from pharmaceutical dosage forms and human serum samples using the developed methods was performed for both electrodes without any separation or filtering pretreatment. Recoveries were between 99.41 and 102.07 % for pharmaceutical dosage forms and between 99.79 and 100.50 % for human serum samples, with RSD ranging from 0.70 % to 0.98 %. • Sensitive detection of cefepime helps to increase the effectiveness of treatment. • Side effects in the treatment can be reduced by the determination of cefepime. • Oxidative determination of cefepime can be done using non-toxic solid electrodes. • Carbon paste and boron doped diamond electrodes offer advantages over each other. • Voltammetric methods enable determination from serum samples without pretreatment.

Irreversible oxidation of hydroxide ion in the light of negative capacitance by fast scan voltammetry

Intermediates associated with dioxygen generation by anodic decomposition of water were detected at a thin wire platinum electrode by fast scan cyclic voltammetry. Hydroxide ion was oxidized through the diffusion-controlled one-electron transfer reaction to immediately yield hydrogen peroxide, which was detected as adsorbed species on the electrode. The anodic peak potential was almost independent of the scan rates in spite of distinctive following chemical reactions. The anodic peak current at fast scans was observed to be smaller than the diffusion-controlled one. The lower deviation failed to be explained in terms of the heterogeneous electrode kinetics. It was ascribed to the negatively capacitive current which was caused by dipoles of hydroxide ion and the counter cation. The capacitance values were invariant to the concentrations of hydroxide ion. The invariance was explained in terms of destruction of dipoles by agitation of hydroxyl radicals.

Novel and Highly Sensitive Electrochemical Sensor for the Determination of Oxytetracycline Based on Fluorine-Doped Activated Carbon and Hydrophobic Deep Eutectic Solvents.

Residues of oxytetracycline (OTC), a veterinary antibiotic and growth promoter, can be present in animal-derived foods; their consumption is harmful to human health and their presence must therefore be detected and regulated. However, the maximum residue limit is low, and consequently highly sensitive and accurate detectors are required to detect the residues. In this study, a novel highly sensitive electrochemical sensor for the detection of OTC was developed using a screen-printed electrode modified with fluorine-doped activated carbon (F-AC/SPE) combined with a novel deep eutectic solvent (DES). The modification of activated carbon by doping with fluorine atoms (F-AC) enhanced the adsorption and electrical activity of the activated carbon. The novel hydrophobic DES was prepared from tetrabutylammonium bromide (TBABr) and a fatty acid (malonic acid) using a green synthesis method. The addition of the DES increased the electrochemical response of F-AC for OTC detection; furthermore, it induced preconcentration of OTC, which increased its detectability. The electrostatic interactions between DES and OTC as well as the adsorption of OTC on the surface of the modified electrode through H-bonding and π-π interactions helped in OTC detection, which was quantified based on the decrease in the anodic peak potential (E pa = 0.3 V) of AC. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Under optimum conditions, the calibration plot of OTC exhibited a linear response in the range 5-1500 μg L-1, with a detection limit of 1.74 μg L-1. The fabricated electrochemical sensor was successfully applied to determine the OTC in shrimp pond and shrimp samples with recoveries of 83.8-100.5% and 93.3-104.5%, respectively. In addition to the high sensitivity of OTC detection, the proposed electrochemical sensor is simple, cost-effective, and environmentally friendly.

Determination of the Formation Potential of Solid-Electrolyte Interphase in Some Amide-Type Ionic Liquids Containing Metal Salts

Amide-type ionic liquids (ILs) have been investigated as the electrolyte for secondary batteries because they have such favorable properties as non-flammability, low-volatility, and the electrochemical stability.1,2 However, the ILs have been reported to decompose cathodically at the potentials more positive than the deposition potential of Li and form solid-electrolyte interphase (SEI) on the electrode.3 Although the formation of the SEI is favorable for lithium secondary batteries, the SEI may hinder the electrode reactions of the active materials when the ILs are used as the electrolytes for redox flow batteries. In the present study, the formation potentials of the SEI in two amide-type ILs, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing metal salts were investigated in the presence of a redox species.BMPBr was prepared by the reaction of 1-methylpyrrolidine and 1-bromobutane in acetonitrile. BMPFSA was obtained by the interaction of BMPBr with LiFSA in distilled water. BMPFSA was dried under vacuum at 80 °C for 48 hours before use. BMPTFSA and the metal salts were used as supplied. The water content in BMPFSA and BMPTFSA was less than 10 ppm. The electrochemical measurement was carried out with a three-electrode cell in an argon-filled globe box. A Pt disk and wire were used as a working and counter electrode, respectively. Ag wire immersed in BMPFSA or BMPTFSA containing 0.10 M AgCF3SO3 was used as a reference electrode, which is denoted by Ag|Ag(I).The anodic peak potentials in the cyclic voltammograms in the ILs containing the redox species were almost constant after holding the potentials more positive than the cathodic decomposition potentials. On the other hand, the anodic peak potentials changed by holding the potential at the negative potential region in the presence of the metal species, suggesting that the potential of the SEI formation can be determined more sensitively by monitoring the redox reaction.

Mesoporogen free synthesis of CuO/TiO2 heterojunction for ultra-trace detection of catechol in water samples

Creating mesoporous architecture on the surface of metal oxides without using pore creating agent is significant interest in electrochemical sensors because these materials act as an efficient electron transfer process between the electrode interface and the analytes. Recent advances in mesoporous titanium dioxide (TiO2)-based materials have acquired extraordinary opportunities because of their interconnected porous structure could act as a host for doping with various transition metals or heteroatoms to form a new type of heterojunction. Herein, a simple method is developed to synthesize mesoporous copper oxide (CuO) decorated on TiO2 nanostructures in which homogenous shaped CuO nanocrystals act as dopants decorated on the mesoporous structure of TiO2, resulting in p-n heterojunction nanocomposite. The TiO2 particles exhibit a mesoporous structure with a pore volume of about 0.117 cm3/g is capable to load CuO nanocrystals on the surface. As a result, large pore volume 0.304 cm³/g is obtained for CuO–TiO2 heterojunction nanocomposite with the loading of uniform-shaped CuO nanocrystals on the mesoporous TiO2. The resulting CuO–TiO2 nanocomposite on modified glassy carbon (GC) electrode exhibits good electrochemical performance for oxidation of catechol with the observation of strong enhancement in the anodic peak potential at +0.36 V. The decrease in the overpotential for the oxidation of catechol when compared to TiO2/GC is attributed to the presence of CuO nanocrystals providing a large surface area, resulting in wide linear range 10 nM to 0.57 μM. Moreover, the resultant modified electrode exhibited good sensitivity, selectivity and reproducibility and the sensor could able to determine the presence of catechol in real samples such as lake and river water. Therefore, the obtained CuO–TiO2 nanocomposite on the modified GC delivered good electrochemical sensing performance and which could be able to perform a promising strategy for designing various metal oxide doped nanocomposites for various photochemical and electrocatalytic applications.