Reduction Peak Research Articles

Complexation effect between Pb2+ and carbendazim in natural waters: An electroanalytical study

• The interaction between the metal ion Pb 2+ and the pesticide CBZ affects the analysis of the pesticide in aqueous solution. • Natural compounds in water decrease the sensitivity of the method in the pesticide analysis. • Pb 2+ contributes to the increase in the intensity of the oxidation peak current of CBZ. • IES study confirms the formation of the complex in solution. The use of pesticides has been increased to obtain higher agricultural yields, prevent the proliferation of harmful organisms and ensure durability in food storage. The inappropriate use of these substances present risks to the environment and human health, and in the presence of metal ions can interact, forming complexes with different properties. Thus, in this work, the interaction between the metal ion Pb 2+ and carbendazim was evaluated by electrochemical techniques using a glassy carbon electrode. The metal ion Pb 2+ showed a reduction peak at −0.570 V, and, in systematic studies in the presence of CBZ, this peak shifted to a more negative potential, indicating the complex formation. The K f value founded for the complex formed was 4.5 × 10 16 , and the estimated proportion metal:pesticide was 1:3.7, using the data collected from these experiments. On the other hand, CBZ showed an oxidation peak at 0.989 V and a reduction peak at 0.919 V, with the characteristic of a quasi -reversible process. A shift of the oxidation peak to less positive potentials was observed when in the presence of the metallic ion. Furthermore, experiments on the analysis of carbendazim in the presence of Pb 2+ were performed in aqueous solutions and natural water, indicating that the metal ion affects the electrochemical signal of the pesticide. The electrochemical impedance spectroscopy results showed that Pb 2+ ions do not interfere in the electrochemical double layer during oxidation of carbendazim, indicating that the interaction between the metallic ion and the pesticide occurs in solution. The analyses performed using samples of natural water showed an increase in charge transfer resistance without alteration of the electrical double layer or significant changes in the oxidation potential of the pesticide. The results showed that the electroanalytical method is feasible for the analysis of CBZ in the presence of Pb 2+ and analysis of the influence of the metal on the electrochemical response of the pesticide, with low sample preparation.

Cation effect on the electrochemical reduction of polyoxometalates in room temperature ionic liquids

Polyoxometalates (POMs) are compounds that undergo multiple successive one-electron redox transitions, making them convenient model reactants to study ion solvation effects. Room temperature ionic liquids (RTILs) are solvents made entirely of ions, and are expected to have interactions with the highly negatively charged POM reduction products. In this work, 12 RTILs with a range of different anions ([FSI]−=bis(fluorosulfonyl)imide, [TFSI]−=bis(trifluoromethylsulfonyl)imide, [BETI]−=bis(pentafluoroethylsulfonyl)imide, [BF4]−, [PF6]−) and cations (imidazolium, pyrrolidinium, sulfonium, ammonium, phosphonium) were employed as solvents to study the kinetics and thermodynamics of [S2W18O62]4− reduction, to shed light on solvation effects and ion-pairing effects caused by different RTIL structures. Up to six reversible reduction processes (producing highly negatively charged [S2W18O62]10−) were observed. For the RTILs that showed multiple processes, a clear trend in both the thermodynamics (inferred from the reduction peak potentials) and kinetics (inferred from the peak-to-peak separation) was observed, in the order: imidazolium < sulfonium ≈ ammonium < pyrrolidinium < phosphonium, supporting strong interactions of the negatively charged POM reduction products with the cation. Two related POMs, [P2W18O62]6− and [PW12O40]3−, were also studied in the optimum RTIL found for [S2W18O62]4− ([C2mim][FSI]=1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide), revealing fast kinetics and asymmetric peaks for [PW12O40]3−. This work demonstrates the importance of understanding the solvation effects of RTIL ions for highly charged electrogenerated products, allowing tuning of the RTIL structure to achieve the optimum kinetics and thermodynamics for an electrochemical process.

VOLTAMMETRIC DETERMINATION OF 1,4-NAPHTHOQUINONE DERIVATIVES

In this work, we have studied the physicochemical behaviors of oxidation-reduction of 2,3-dichloro-1,4-naphthoquinone (NQ) and 2-chloro-3-((4-hydroxyphenyl) amino)-1,4-naphthoquinone (NQ1) synthesized on the basis of NQ, on impregnated graphite electrode. The nature of the electrochemical processes was determined and the mechanism of oxidation-reduction of substances was assumed. The operating conditions for the voltammetric determination of compounds on an impregnated graphite electrode were selected, such as the supporting electrolyte – 0.1 M NaClO4 solution in 96% ethanol (pH=2 for NQ, pH=10 for NQ1), V=100 mV·s-1, as well as the potential and time of accumulation (Eacc +1 V; tacc 50 s for NQ and Eacc -1 V; tacc 30 s for NQ1). It is shown that the pH of the supporting electrolyte has a high influence on NQ and NQ1 analytical signal. For NQ, the current reaches its maximum value at pH = 2. For NQ1, the opposite effect of pH on the current intensity is observed: the maximum current value is reached at pH = 12. The linear dependence of the reduction peak current at a potential of 0.12 V on the concentration of NQ is observed in the range 2·10-5 – 8·10-4 mol·l-1 with the regression equation I=3.14C - 0.35 (R2=0.9992). For NQ1, the linear range of the calibration curve of the electro oxidation current at a potential of -0.58 V on the concentration is maintained in the range 1·10-6 – 8·10-4 mol·l-1 with regression equation I=45.74C +0.37 (R2=0.9992). The detection limit (LOD) for NQ, calculated according to the 3S criterion, is 7.2·10-6 mol·l-1, for NQ1 8·10-7 mol·l-1. The accuracy of the method of analyzed compounds quantitative determination in the substance was checked by the "spiked test" method.

Study of the Anodic Dissolution Solutions of Single Crystals of Molybdenum Diselenide (MoSe2) in KOH Media

This work is a contribution to the study of semiconductor materials that are used in semiconductor electrolyte junctions for the conversion of light energy into electrical energy. The study was carried out in KOH medium on single crystals of molybdenum diselenide obtained by physical vapor transport and previously characterized by different analysis techniques (SEM, XRD, etc.). A preliminary study on standard molybdate ion solutions was first carried out in order to establish the potential domain of molybdate ions. Cyclic anodic redissolution voltammetry was used for the analysis of standard solutions and MoSe2 dissolving solutions obtained by anodic attack at fixed potential. The results obtained show a reduction peak towards -0.812V indicating the deposit during the pre-electrolysis. A first oxidation peak at around -0.740V and a secondary peak at around -0.429V corresponding to the oxidation of the deposit during redissolution. Analysis of the results shows that MoSe2 is not stable in KOH media.

Elaboration of a novel nanosensor using nanoparticles of α-Fe2O3 magnetic cores for the detection of metronidazole drug. Urine human and tap water

Metronidazole (MTZ) is a widely used antibiotic to treat infections caused by anaerobic bacteria, protozoa, and bacteroids such as trichromonosis and vaginosis. In this study, we present a simple strategy for constructing an electroanalysis platform for metronidazole in real samples. We prepared a modified carbon paste with α-Fe2O3 magnetic core nanoparticles to construct an α-Fe2O3@CPE electrochemical sensor. The surface morphology and composition of the sensor were evaluated using several methods, such as X-ray diffraction and scanning electron microscope. The average size of the α-Fe2O3 magnetic core nanoparticles was around 34.30 ​nm. Cyclic voltammetry, electrochemical impedance spectroscopy and chrono-coulometry were performed for the understanding of the electron transfer behavior on the electrocatalytic surface of α-Fe2O3@CPE and the unmodified electrode CPE. The resulting sensor demonstrates a very good shift of the Metronidazole reduction peak to a more positive potential (−0.57v vs Ag/AgCl) compared to the unmodified CPE electrode (−0.71v .vs Ag/AgCl). The Metronidazole peak reduction current Ipc varies linearly with metronidazole concentration in the range of 10-4 ​M to 0.8x10-6 ​M with a limit of detection and limit of quantification of 2.852x10-7 ​M and 9.509x10-7 ​M respectively. Exceeding the detection limits of several existing analytical methods. The proposed procedure has been successfully demonstrated on pharmaceutical tablets and real tap water and urine samples.

Polyaniline grafted mesoporous zinc sulfide nanoparticles for hydrogen evolution reaction

Numerous efforts have been directed to fabricate the cost-effective structure for hydrogen evolution reaction (HER). However, it is still a challenging task for clean energy. Herein, mesoporous zinc sulfide nanoparticles with various contents of polyaniline have been synthesized using the solvothermal process. Morphological and structural analysis has been carried out in detail for HER activity in KOH electrolyte at pH 10.20 and 13.55. The hybrid of zinc sulfide and Polyaniline (ZnS-90 mg), exhibits a lower specific surface area of 5.54 m2 g-1 and a greater mesoporous size of 10.10 nm as compared to individual polyaniline nanofibers (75.13 m2 g-1 and 6.02 nm) and zinc sulfide nanoparticles (80.90 m2 g-1 and 6.81 nm) due to interface, which creates the unique characteristics as compared to PANI-Nbs and ZnS-NPs. Hybrid ZnS-90 mg, synergistically, exhibits the greater electrical conductivity of 17.90 × 10−4 Scm−1 and reveals the lower over potential of 168 mV with an onset potential of 41 mV at pH 13.55, and an over potential of 345 mV with an onset potential of 69 mV at pH 10.20 of 1 M KOH for HER activity at the state of art current density of 10 mAcm−2. Hybrid ZnS-90 mg also shows the smaller Tafel slope of 234 mVdec−1 with the greater turnover frequency of 5.22 ms-1 at pH 13.55, recommending the better HER activity. A symmetric system consisting of Hybrid ZnS-90 mg reveals the two reduction peaks, where the over potential has been measured as 524 mV at the current density of 2.76 mAcm−2 and 947 mV at the current density of 10 mAcm−2 at pH 13.55. The symmetric system exhibits a good Tafel slope of 26 mVdec−1 and suggests it is the suitable and cost-effective electrode structure for HER to produce clean hydrogen energy.

SELEKSI SEL BAKTERI DARI MINYAK BUMI SEBAGAI MOLEKUL PENGENAL DALAM BIOSENSOR BENZENA

Benzene is one of the harmful compounds which can affect both healthcare and environmental quality. Conventionally the effort of detecting this compound still requires several sample pre-treatments, contributing to a long analysis time and sophisticated instrumentation. Therefore, this study was aimed to determine the potency of bacteria as the bioreceptor for detecting benzene electrochemically. The bacteria isolate was immobilized on the working electrode surface. Four bacteria isolates from the petroleum sample were evaluated. The results showed that isolate II produced high oxidation and reduction peak currents as much as 150 µA and -490 µA respectively. The selected bacteria showed characteristics to Pseudomonas sp. physiologically. Since the bacteria can degrade benzene, thus hypothetically it can produce benzene dioxygenase. Through the catechol formation, 3 mM benzene produced 108.7 µA after 11.4 s from the starting scan. This result suggested that the excreted enzyme from the selected bacteria could react with benzene enzymatically.

Depolarization of Cu electrodeposition in the presence of Ag: A cyclic-voltammetry study

Cyclic voltammetry profiles of Cu-Ag acidic sulfate deposition baths at Cu, Cu-Ag, Au or Ru substrates have been systematically studied, revealing the existence of an early Cu reduction peak before the bulk Cu deposition peak. The Cu deposit thickness produced by this early Cu reduction peak is estimated to decrease with scan rate and increase with the [Ag+] concentration in the electrolyte. The early Cu reduction peak generates Cu deposits thicker than 3 nm for the Cu-Ag electrolyte with 2 mM Ag(I). Electrochemical quartz crystal microbalance (EQCM) and CV reveal that the early Cu reduction peak is associated with a Cu(II)/Cu(0) reaction at 65% Coulombic efficiency, slightly smaller than that of the main Cu(II)/Cu(0) reduction peak (∼78%). Directly observing the linear regions in the polarization curves produced by CV, the early Cu reduction peak is estimated to show a Tafel slope ∼30 mV/dec. We hypothesize that the early Cu reduction peak is caused by the catalytic effect of Ag in the substrate or in the initial deposit on the intermediate reduction step of Cu(II)/Cu(I), leading to a shift of the rate determining step of Cu(II)/Cu(0) reduction.

Electrodeposition of Indium from an Ionic Liquid Investigated by In Situ Electrochemical XPS

The electrochemical behavior and electrodeposition of indium in an electrolyte composed of 0.1 mol/L InCl3 in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) on a gold electrode were investigated. The cyclic voltammogram revealed several reduction and oxidation peaks, indicating a complex electrochemical behavior. In the cathodic regime, with the formation of an In-Au alloy, the reduction of In(III) to In(I) and of In(I) to In(0) takes place. In situ electrochemical X-ray photoelectron spectroscopy (XPS) was employed to investigate the reduction process by monitoring the oxidation states of the components during the cathodic polarization of 0.1 mol/L InCl3/[Py1,4]TFSI on a gold working electrode under ultra-high vacuum (UHV) conditions. The core electron binding energies of the IL components (C 1s, O 1s, F 1s, N 1s, and S 2p) shift almost linearly to more negative values as a function of the applied cell voltage. At −2.0 V versus Pt-quasi reference, In(I) was identified as the intermediate species during the reduction process. In the anodic regime, a strong increase in the pressure in the XPS chamber was recorded at a cell voltage of more than −0.5 V versus Pt quasi reference, which indicated, in addition to the oxidation reactions of In species, that the oxidation of Cl− occurs. Ex situ XPS and XRD results revealed the formation of metallic In and of an In-Au alloy.

Novel fluoride selective voltammetric sensing method by amino phenylboronic acid-zirconium oxide nanoparticles modified gold electrode

A novel fluoride selective voltammetric method has been developed by using the 3-amino phenylboronic acid (APBA)-zirconium oxide (ZrO2) nanoparticles modified gold (APBA-ZrO2-NPs/Au) electrode for sensitive detection of F− at trace levels in water and toothpaste. A co-precipitation approach was applied to synthesize ZrO2 nanoparticles (ZrO2-NPs) using Salvadora oleoides leaves extract and characterized by UV–Visible spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-Ray Diffraction (XRD) for morphological and structural analysis. The APBA-ZrO2-NPs/Au electrode was fabricated by coated of ZrO2-NPs on the surface of Au electrode by drop costing method followed by electrochemical polymerization of APBA. The reduction response of peak current of potassium ferricyanide was achieved by the interaction of the phenylboronic acid with F−to produce the boronate anions. Thus, the method was optimized in detailed for successive electrochemical detection of F−. Two linear relations were observed in reduction peak current and logarithm of F− concentration in the range of 1.0 × 10–9 – 3.0 × 10–4 M and 3.0 × 10–4 – 1.0 × 10–2M, respectively. The limits of detection (LOD) and limit of quantification (LOQ) were calculated as 3.0 × 10–10 and 1.0 × 10–9 M, respectively. Interference of other competing anions, including chloride, bromide, iodide, acetate, sulphate, carbonate, and nitrate, was also investigated. Furthermore, the developed APBA-ZrO2-NPs/Au was employed to the fast detection, wide range of response, and high selectivity of F− in water and toothpaste samples.

Electrocatalytic oxidation of sorbitol on PdxAuy/C bimetallic nanocatalysts

In the present work, the sorbitol electro-oxidation reaction (SOR) was studied in alkaline medium employing bimetallic catalysts of palladium and gold (PdxAuy/C). The activity for SOR was mainly correlated to bimetallic interactions, because the catalysts presented similar characteristics like morphology, average particle sizes (∼10 nm), and metallic mass contents (∼20 wt%). The bimetallic interactions induced changes like shifts in the lattice parameters, as well in Pd binding energies (up to −0.25 eV) and into the reduction peak of Pd oxides during the electrochemical characterization. Pd40Au60/C and Pd60Au40/C presented the best activities at 3 M KOH achieving onset potentials of −0.43 V vs. NHE and current densities of 128 and 209 mA mg−1 at a fixed potential of 0.1 V, respectively. Pd60Au40/C presented almost 3.5-fold more current density than Pd/C, and 10-fold more than Au/C at the same conditions. These materials also displayed superior stability, maintaining their maximum current densities after 1000 cycles in 0.5 M sorbitol + 3 M KOH. The SOR by-products were determined by HPLC and GC/MS, revealing that these catalysts break sorbitol C–C bonds by attacking intermediate carbons (C3 and C4) and/or by subsequent removal of chain-end carbons. Among the detected by-products, value-added molecules like glycerol, ethylene glycol, formic acid, and γ-butyrolactone were found. In summary, the stability and activity of Pd-based materials make them suitable for the oxidation of sorbitol as a promising alcohol for fuel cell technology.

SWCNT/ZnO nanocomposite decorated with carbon dots for photoresponsive supercapacitor applications

In this work, we report the fabrication of an optically responsive hybrid supercapacitor. The hybrid electrode material for the supercapacitor was synthesized by attaching carbon dots (CDs) on the SWCNT/ZnO nanocomposites. The optical properties of CDs and ZnO have been explored by operating the supercapacitor under illuminated conditions (UV light). It was observed that the areal capacitance of the fabricated supercapacitor got enhanced by ∼ 41.38% at 50 mV/s scan rate under UV light. The photo-charging and galvanostatic discharging of the device were also examined. The maximum photo-charged areal capacitance value was calculated to be 1.53 mF/cm2 at a current density of 1.25 μA/cm2, whereas the values of areal energy density and areal power density at this current density value were 19.85×10-3 μWh/cm2, and 0.0953 μW/cm2, respectively. The working mechanism of the supercapacitive system has also been explored. It is observed that the overall capacitance of the hybrid electrode is a combination of both electric double layer capacitance (EDLC) and pseudocapacitance. The EDLC and pseudocapacitance contributions were confirmed by using the Dunn method, and the values of the individual capacitance contributions are 69.35 and 30.65% for EDLC and pseudocapacitance, respectively. Further, it was observed that the pseudocapacitance phenomenon was dominated by the diffusion of the ions in the electrode material. The diffusivity of the electrolytic ions was calculated to be 0.13 and 0.14 mm2/s for the oxidation peaks, whereas 1 and 0.07 mm2/s for the reduction peaks, respectively. Moreover, the reaction mechanism of the system has also been explored, and the occurrence of intercalation of K+ ions in the defects of ZnO has been confirmed with justified explanations.

Oxidation of capsaicin in acetonitrile in dry and wet conditions

• Water greatly affects the formal potential of capsaicin oxidation. • Two anodic processes were observed for capsaicin under dried conditions. • The second anodic processes shifted negatively with increasing water content. • Different numbers of electrons transferred under CV and CPE conditions. • Two to four electrons were transferred during the electrolysis of capsaicin. An electrochemical study of the phenol capsaicin (CAPH), the active ingredient in chilli pepper, was performed in dried and wet acetonitrile on a glassy carbon electrode. Under dried conditions, two oxidation peaks at ca. 0.7 vs. (Fc/Fc + )/V (labelled E 1 ) and 1.0 vs. (Fc/Fc + )/V (labelled E 2 ) and two reduction peaks at ca . 0.1 and −0.5 vs. (Fc/Fc + )/V when the scan direction was reversed were observed. Rotating disk electrode experiments indicated that the two oxidation processes occur by same number of electrons and it is proposed they occur in two one-electron steps. As water was added to the acetonitrile, hydrogen bonding interactions between the water and the phenolic groups led to the E 1 and E 2 potentials shifting progressively more negatively. The shift in E 2 as water was added was greater than the shift in E 1 , so that after the addition of approximately 0.2 M H 2 O, only one voltammetric wave was observed (labelled as E 1 ′) corresponding to a two-electron oxidation, that continued to shift more negatively as more water was added. Under very wet conditions ([H 2 O] > 1 M), only one chemically irreversible oxidation peak was observed ( E 1 ′) at ca . > 0.5 vs. (Fc/Fc + )/V with one reduction peak at ca . −0.1 vs. (Fc/Fc + )/V upon reversal of the scan direction. Controlled-potential electrolysis under wet conditions indicated a total of two-electrons per molecule were transferred with the overall mechanism interpreted as a −2e – /−H + oxidation, followed by a hydrolysis reaction and loss of a methoxy group to form a 1,2-benzoquinone moiety.

Simple Electrochemical Chloramphenicol Assay at a Disposable Pencil Graphite Electrode by Square Wave Voltammetry and Linear Sweep Voltammetry

Chloramphenicol (CAP) is a widely used, broad spectrum antibiotic that contains a nitrobenzene moiety with a possible poisonous feature. Thus, the development of low cost, simple, and rapid analytical methods for the reliable CAP quantification is necessary. Starting from the nitro group electroactivity, the cyclic voltammetric properties of CAP were investigated at the common commercially available, disposable pencil graphite electrode (PGE). The effect of the electrode material, the electrolyte pH and the potential scan rate were investigated. At 2H type PGE, the CAP cyclic voltammograms presented an anodic and two cathodic diffusion controlled, pH-dependent peaks, each involving the exchange of two electrons and two protons. Based on CAP main reduction peak at PGE in pH 5.00 Britton Robinson buffer, a square wave voltammetric (SWV) method was developed for its quantification from 2.50 × 10−6 to 7.50 × 10−4 mol L−1 with a limit of detection (LoD) of 1.39 × 10−6 mol L−1. Moreover, the anodic peak was also employed for the first time for a CAP linear sweep voltammetric (LSV) assay (2.50 × 10−6 to 1.00 × 10−3 mol L−1; LoD 6.09 × 10−7 mol L−1 CAP). Both voltammetric methods using the cost-effective PGE were applied for the determination of CAP in pharmaceuticals, obtaining recoveries of 100.9 ± 1.4% (relative standard deviation of 3.54%) for SWV and 100.7 ± 1.4% (relative standard deviation of 3.55%) for LSV.

Effect of annealing and oxygen partial pressure on the RF sputtered WO3 thin films for electrochromic applications

the electrochromic thin layer of Tungsten trioxide (WO3) was RF sputtered on FTO (fluorine-doped tin oxide) slide. In a reactive Ar + O2 gas environment with varying oxygen partial pressures, the deposition continued. The samples were air annealed at 400 °C for 2 h after being deposited at room temperature. SEM, XRD, UV–Visible spectrometer, and electrochemical analyzer characterization methods were employed to analyze the surface, structural morphology, optical, and electrochromic behaviour of the deposited material after annealing. The Optical Bandgap and Transmittance were found to be of a higher value for air annealed samples than RT deposited samples because RT deposited samples are amorphous whereas air annealed samples exhibit crystalline nature with Oxidation, reduction peak currents variation with respect to the temperature.

Reaction mechanism and kinetics of ferrotitanium preparation by aluminothermic reduction of CaTiO3

A ferrotitanium alloy production process by aluminothermic reduction and using perovskite as materials was studied in laboratory. The thermodynamics of the Al-CaO, Al-CaO-CaTiO3, Al-CaO-Fe-CaTiO3 system was calculated and the reduction process of CaTiO3 to prepare ferrotitanium was investigated. The Freeman-Carroll method was used to analyze the kinetics of aluminothermic reduction process. The results show that ferrotitanium alloys can be produced by aluminothermic reduction using perovskite as material. In the reduction process, the reduction reaction of TiO2 in CaTiO3 by aluminum proceeds at 1000–1100 ℃, and the formation temperature of ferrotitanium alloy is between 1400 ℃ and 1500 ℃. CaO not only acts as a slag-forming agent in the reaction process, but also participates in the reduction reaction process. The apparent activation energy and the reaction order at the reduction peak decrease with the increasing of heating rate which indicates that the reaction is easier with the increase of heating rate.

Rapid Voltammetric Screening Method for the Assessment of Bioflavonoid Content Using the Disposable Bare Pencil Graphite Electrode

Hesperidin (HESP) is a plant bioflavonoid found in various nutritional and medicinal products. Many of its multiple health benefits rely on the compound’s antioxidant ability, which is due to the presence of oxidizable hydroxyl groups in its structure. Therefore, the present study aimed to investigate the electrochemical behavior of HESP at a cheap, disposable pencil graphite electrode (PGE) in order to develop rapid and simple voltammetric methods for its quantification. Cyclic voltammetric investigations emphasized a complex electrochemical behavior of HESP. The influence of the electrode material, solution stability, supporting electrolyte pH, and nature were examined. HESP main irreversible, diffusion-controlled oxidation signal obtained at H type PGE in Britton Robinson buffer pH 1.81 was exploited for the development of a differential pulse voltammetry (DPV) quantitative analysis method. The quasi-reversible, adsorption-controlled reduction peak was used for HESP quantification by differential pulse adsorptive stripping voltammetry (DPAdSV). The linear ranges of DPV and DPAdSV were 1.00 × 10−7–1.20 × 10−5 and 5.00 × 10−8–1.00 × 10−6 mol/L with detection limits of 8.58 × 10−8 and 1.90 × 10−8 mol/L HESP, respectively. The DPV method was applied for the assessment of dietary supplements bioflavonoid content, expressed as mg HESP.

Electrochemical studies on the interfaces of freshwater biofilm/oxide film of alloy steels

The present research focused on the interaction between oxide films of different alloys in presence of freshwater biofilm. The electrochemical behavior of freshwater biofilm/oxide films of alloys were investigated using the open circuit potential measurements, cathodic polarization, electrochemical impedance spectroscopy, and cyclic voltammetry studies. The cyclic voltammetry studies shows that biofilm on the 316L SS was entirely different from other alloys due to their oxidation peak and reduction peak which identified at +0.24 V and 0 V vs SCE respectively. The present study revealed that the nature of oxide films was responsible for the electrochemical behavior of biofilms on the alloy steels.

Aerobic biocathodes with potential regulation for ammonia oxidation with concomitant cathodic oxygen reduction and their microbial communities

Aerobic biocathodes are effective construct for the simultaneous nitrification and denitrification, but the disturbance of cathodic oxygen reduction on ammonia oxidation and denitrification remains unclear. In this study, we revealed the oxygen reduction peak at −0.4 V (versus silver/silver chloride) by cyclic voltammetry analysis at a cathode without a biofilm. The reduction peak, however, showed a right shift from −0.4 to −0.3 V for the biocathode, indicating that the aerobic biocathode could simultaneously perform traditional nitrification and cathode oxygen reduction. Therefore, different electrode potentials ranging from −0.5 to −0.1 V were designed for regulating the ammonia oxidation rate, and the results showed that the highest oxidation rate reached 3.08 mg/h/L at a potential of −0.2 V under a low-aeration rate of 5 mL/min. High-throughput sequencing showed that Nitrosomonas and Rhodococcus were the dominant nitrogen removal genera in the biocathode, and the abundance of Devosia was related to the interactions between the aeration rate and the electrode potential. Furthermore, the amoC and hao genes responded to aeration and electrode potential regulation, and −0.2 V was more suitable for promoting the denitrification process under low-aeration conditions. Therefore, these findings provided new insights on cathodic potential control for ammonia oxidation and nitrogen removal as well as for the regulation of microbial communities.

Electrochemical Sensor for the Detection of 1-Hydroxypyrene Based on Composites of PAMAM-Regulated Chromium-Centered Metal-Organic Framework Nanoparticles and Graphene Oxide.

A nanocomposite was formed by combining graphene oxide (GO) with chromium-centered metal–organic framework (Cr-MOF) nanoparticles regulated by the dendrimer polyamidoamine (PAMAM). PAMAM can successfully regulate the synthesis of Cr-MOF; in doing so, the size of Cr-MOF is reduced, its original morphology is maintained, and it has good crystallinity. A simple ultrasonication method was used to make the Cr-MOF/GO hybrid nanocomposite. Various characterization methods confirmed the successful synthesis of PAMAM/Cr-MOF/GO nanocomposites. The PAMAM/Cr-MOF/ERGO modified electrode could be used with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) to study the electrochemical behaviors of 1-hydroxypyrene (1-OHPyr). The results indicated that the constructed PAMAM/Cr-MOF/ERGO electrochemical sensor had a significantly enhanced electrocatalytic effect on the electrochemical reduction of 1-OHPyr compared with the sensors with no PAMAM and the ERGO sensor, which could be ascribed to the synergetic effect from the high porosity of Cr-MOF and the high conductivity of ERGO, as well as the further electron transport action of the nanocomposite. Under the optimal conditions, the reduction peak current and concentration of 1-OHPyr showed a good linear relationship in the range of 0.1–1.0 and 1.0–6.0 μM, and the detection limit of 1-OHPyr was calculated to be 0.075 μM. Moreover, the PAMAM/Cr-MOF/ERGO electrochemical sensor constructed in this paper can be expected to provide some instructions for the construction of electrochemical sensing platforms and wider potential applications.