Volt-amperometric Technique Research Articles

Enhanced visible-light-driven peroxymonosulfate activation for antibiotic mineralization using electrosynthesized nanostructured bismuth oxyiodides thin films

The search for non-specific catalysts capable of removing a wide range of organic contaminants remains a key challenge given their increasing presence in aquatic environments. In this ongoing exploration, this work proposes the use of bismuth oxyiodides as activators of ecological oxidative radicals, wherein raw substances like peroxymonosulfate (PMS) gain prominence due to the valuable efficiency of the radicals they can generate. For BiOI, serving as a precursor to the photocatalysts, the effect of the electroactive solution components on its electrochemical preparation was analyzed using the voltamperometric technique. The compositional and structural characterization confirmed successful formation. Deposit annealing treatments result in new species such as Bi7O9I3 at 250ºC and, primarily, Bi5O7I at 420 or 520ºC—species that also exhibit visible light absorption, paving the way for their use under sunlight. Initially, a single tetracycline (TC) solution was employed to test the degradation and mineralization capability of the prepared films, assessing the impact of the solution's pH, the presence of PMS, light irradiation, and annealing temperature. The annealing temperature increases the catalytic effect. It is noteworthy that for all bismuth iodide films, the highest catalytic activity was observed when combining PMS and visible light irradiation, showcasing a synergistic improvement. This trend holds for multipollutant solutions as well. In a crucial role for the material's application, the results demonstrate that annealing temperatures below 450ºC promote films that reasonably maintain their activity and chemical stability after continuous reuse.

Electrodeposition of strictly alpha,alpha’-polythiophene chains on oxidizable metals in acidic concentrated aqueous media

Electropolymerization of thiophene was performed in aqueous acidic media on various substrates, namely, titanium, nickel and SS steel. The films were successfully elaborated using voltamperometric, chronopotentiometric and chronoamperometric techniques. It was shown that concentrated acids increase the solubility of the monomer, lower its oxidation potential and inhibit the dissolution of the working electrode. Furthermore, the electrosynthesized polythiophene (PT) films are homogeneous and present similar properties to those obtained in organic media. On the other hand, analyses by X-ray photoelectron and infrared spectroscopies indicate the higher oxidation state of the polymers and the contribution of the supporting electrolyte in the doping process. In addition, IR spectra have demonstrated the strictly a, a’ linked polythiophene chains and an estimated degree of polymerization (DP) of about 40. Finally, scanning electron microscopy (SEM) has been used to characterize the morphology of the obtained coating. In this context, the nature of the films depends closely on the type of the electrode, the electrosynthesized mode and the electrolytic medium.

Complex Activity and Sensor Potential toward Metal Ions in Environmental Water Samples of N-Phthalimide Azo-Azomethine Dyes.

Herein, the spectral and electrochemical characterizations of three different substituted N-phthalimide azo-azomethine (NAA) dyes (L) containing an o-hydroxy group and their NAA-M(II) chelates [M(II): Cu, Ni, Co, Pb] were reported by using UV–Vis and fluorescence spectroscopy and potentiometric and voltamperometric techniques. The pK value of the dyes as well as the stoichiometry and stability of the NAA-metal chelates were studied, and the stoichiometry was found to be mostly 1:2 (ML2) with high complex stability constant values. The sensor activity of N-phthalimide azo-azomethine derivatives toward pH and metal ions has been also investigated and tested for indicator application in acid–base analysis and detection of Cu(II) ions in real samples of surface river water using voltamperometric detection. The results showed that one of the ligands possesses the highest electrochemical response upon binding to copper ions and could be successfully used in the analysis of copper in water at a concentration range of the analyte from 3.7 × 10−7 to 5.0 × 10−6 mol L−1, with analytical characteristics of the method being Sr = 1.5%, LOD = 3.58 µg L−1 and LOQ =11.9 µg L−1

SnO2/SnSe2 Heterostructures for NO2 and H2 Sensing

SnO2/SnSe2 Heterostructures for NO2 and H2 Sensing

Enhanced lithium ionic conductivity of lithium perchlorate in the metal-organic framework matrix

Nanocomposite solid electrolytes were prepared by impregnation of LiClO4 into pores of the metal-organic framework Cr3[C6H4(COO)2]3F (MIL-101(Cr)), and their conductivity was investigated. At temperatures 25–150 °C and relative humidity of 50%, the composites easily absorb water with formation liquid phase in the pores and have conductivity values typical for water solutions. Conductivity decreases with diminishing the humidity; however, complete dehydration may be achieved only after prolonged heating in vacuum at 180 °C. The concentration dependence of conductivity of dehydrated samples goes through the maximum at nearly 6 mol% of MIL-101(Cr) and reaches 3 × 10−3 S/cm at 160 °C; the activation energy decreases in the nanocomposites. Using the volt-amperometric technique on the sample with two nickel electrodes, the electrochemical decomposition voltage value was found to be nearly 3.5 V at 160 °C. It suggests that the ionic conductivity is caused by lithium cations rather than protons or electrons.

SnO2/SnSe2 Heterostructures for NO2 and H2 Sensing

Among layered semiconductors, tin diselenide (SnSe2) deserves particular attention thanks to its high intrinsic electron mobility (462.6 cm2 V-1 s-1 at T = 300 K) and ultralow thermal conductivity (3.82 W m-1 K-1). So far, some applications of SnSe2 have been proposed in several fields regarding superconductivity, Li- and Na- ion batteries, photodetection, photocatalysis, saturable absorbers for eye-safe lasers and thermoelectricity.In this work we report the gas sensing performances of nanostructured SnSe2 thin film as NO2 (400-800 ppb range) and H2 (10-50 ppm range), operating at low temperature (75-150°C).DFT calculations carried out on SnSe2 demonstrate that, while the stoichiometric single crystal is chemically inert even in air, the non-stoichiometric sample (SnSe2-x , with x~0.3) assumes a sub-nanometric SnO2 surface oxide layer, when it is exposed to ambient atmosphere. Remarkably, from theoretical results, it turns out that this self-assembled SnO2/SnSe2-x heterostructure is suitable to be particularly efficient in gas sensing.Given such theoretical evidences, we performed gas sensing measurements to prove the suitability of the SnO2/SnSe2 heterostructure for gas sensing applications. SnSe2 crystals have been ground to obtain SnSe2 powder and gas sensing measurements have been performed using a volt-amperometric technique. SnSe2 thin films have been prepared by drop casting 10μl of ground powder suspended in Ethanol in the concentration of 1 mg/ml on Si3N4 substrates provided with 30 μm-spaced Pt interdigitated electrodes on the front side and a Pt resistor acting as a heater on the back side.Prior to gas sensing, powderized sample has been characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), as shown in Figure 1a and 1b. While the XPS measurements on the bulk crystal do not show the presence of any oxide, XPS on powder, shown in Figure 1a, reveals the presence of a huge amount of SnO2 on the surface, meaning the occurrence of a spontaneous oxidation process. Nevertheless, regarding the nature of surface layer, XRD spectrum in Figure 1b shows complete merging with crystalline SnSe2 according to ICDS card 98-004-9240 and no evidence of crystalline phase of SnO2.Regarding experimental gas sensing response of the SnO2/SnSe2 heterostructure, Figure 1c shows the gas response to increasing concentrations of oxidizing NO2 gas in the range 400-800 ppb in the operating temperature (OT) range 75-150°C, utilizing dry air as carrier gas.As can be observed, the material reveals a decrease of the Base line resistance (BLR i.e. the resistance in dry air) with increasing the OT, confirming its semiconducting behaviour. Moreover, it responds as an n-type semiconductor, with increasing its resistance under the exposure to oxidizing gases, according to the well-known behaviour of SnO2 [1]. Both panels show a good response to sub-ppm NO2 concentrations. In particular, Relative Response is 3.63 for 75°C OT while it is 1.08 when OT is 150°C. Even if temperature reduces somehow the ratio Rg/Ra in case of NO2 sensing, thermal activation confirms the advantages in terms of kinetics and adsorption/desorption times which are shorter increasing the operating temperature. This evidence, together with the encouraging results obtained at 75°C, can open future perspective regarding the light activation of the sensor, combining low temperature and opportune light-associated energies. These results are supported by the evidences coming out from theoretical calculation, giving SnO2/SnSe2 a potential material to be employed as low temperature gas sensor.Moreover, SnO2/SnSe2 heterostructure has been tested as hydrogen gas sensor exposing the material to increasing concentrations of reducing H2 gas in the range 10-50 ppm. According to theoretical calculations, in the case of H2, adsorption provides smaller changes in electronic structure and charge densities and, therefore, sensitivity to H2 is smaller compared to the case of NO2, as shown in Figure 1d. However, the low detection limit for hydrogen in this work is found to be 10 ppm which is a good result compared to the existing literature.To the best of our knowledge, this work reports for the first time the issues related to spontaneous oxidation of SnSe2 [2,3] and the lowest sensitivity of the SnO2/SnSe2 heterostructure to both NO2 and H2 gases, suggesting the possibility to further investigate the performances of this material as gas sensor. 1. Barsan, N.; Weimar, U. Conduction model of metal oxide gas sensors. J. Electroceramics 2001, 7, 143–167; DOI:10.1023/A:1014405811371.2. Pawar, M.; Kadam, S.; Late, D.J. High-Performance Sensing Behavior Using Electronic Ink of 2D SnSe2 Nanosheets. ChemistrySelect 2017, 2, 4068–4075; DOI:10.1002/slct.201700261.3. Camargo Moreira, Ó.L.; Cheng, W.-Y.; Fuh, H.-R.; Chien, W.-C.; Yan, W.; Fei, H.; Xu, H.; Zhang, D.; Chen, Y.; Zhao, Y.; et al. High Selectivity Gas Sensing and Charge Transfer of SnSe 2 . ACS Sensors 2019, 4, 2546–2552; DOI:10.1021/acssensors.9b01461. Figure 1

Electrochemical and genomic analysis of novel electroactive isolates obtained via potentiostatic enrichment from tropical sediment

Abstract Enrichment of electrochemically-active microorganisms (EAM) to date has mostly relied on microbial fuel cells fed with wastewater. This study aims to enrich novel EAM by exposing tropical sediment, not frequently reported in the literature, to sustained anodic potentials. Voltamperometric techniques and electrochemical impedance spectroscopy, performed over a wide range of potentials, characterise extracellular electron transfer (EET) over time. Applied potential is found to affect biofilm electrochemical signature. Geobacter metallireducens is heavily enriched on the electrodes, as determined by metagenomic and metatranscriptomic analysis, in the first report of the species in a lactate-fed system. Two novel isolates are grown in pure culture from the enrichment, identified by 16S rRNA gene sequencing as Aeromonas and Enterobacter, respectively. The names proposed are Aeromonas sp. CL-1 and Enterobacter sp. EA-1. Both isolates are capable of EET on carbon felt and screen-printed carbon electrodes without the addition of exogenous redox mediators. Enterobacter sp. EA-1 can also perform mediated electron transfer using the soluble redox mediator 2-hydroxy-1,4-naphthoquinone (HNQ). Both isolates are able to use acetate and lactate as electron donors. This work outlines a comprehensive methodology for characterising novel EAM from unconventional inocula.

Transport number and current–voltage of a cation exchange membrane equilibrated in aqueous and organic solutions

A physical-chemistry study of a Nafion 117 membrane is undertaken and a correlation between the transport number and current–voltage data of this cation exchange membrane is established. The current–voltage characteristics of the membrane are obtained with the voltamperometric technique, by means of two feed platinised titanium electrodes and two measuring silver–silver chloride electrodes. Previous measurements show that the membrane presents low electrical resistance and weak permselectivity towards the proton in the presence of other metallic cations. However, its chemical modification with the conducting polymer highly improves the proton conduction and gives better selectivity towards the monovalent cation (Na+) against the divalent cation (Zn2+). The effects of the co-ion (anion), charge, solvent and chemical modification are made in evidence by the current–voltage curves. As a result of its pre-concentration near the anionic layer, the divalent cation increases the value of the limiting current density. Besides, the presence of an organic solvent inside the polymeric matrix of the membrane decreases the limiting current density. Different graphical methods are applied to deduce the limiting current density and the derivative method is found to be more reliable.

A Monolithic Continuous-Flow Microanalyzer with Amperometric Detection Based on the Green Tape Technology

The development of micro total analysis systems (muTAS) has become a growing research field. Devices that include not only the fluidics and the detection system but also the associated electronics are reported scarcely in the literature because of the complexity and the cost involved for their monolithic integration. Frequently, dedicated devices aimed at solving specific analytical problems are needed. In these cases, low-volume production processes are a better alternative to mass production technologies such as silicon and glass. In this work, the design, fabrication, and evaluation of a continuous-flow amperometric microanalyzer based on the green tape technology is presented. The device includes the microfluidics, a complete amperometric detection system, and the associated electronics. The operational lifetime of the working electrode constitutes a major weak point in electrochemical detection systems, especially when it is integrated in monolithic analytical devices. To increase the overall system reliability and its versatility, it was integrated following an exchangeable configuration. Using this approach, working electrodes can be readily exchanged, according to the analyte to be determined or when their surfaces become passivated or poisoned. Furthermore, the electronics of the system allow applying different voltamperometric techniques and provide four operational working ranges (125, 12.5, 1.25, and 0.375 microA) to do precise determinations at different levels of current intensity.

Accommodation study via a sensorless measurement technique

We present the results of an experimental analysis aimed at further characterizing the accommodation phenomenon. The measurements are done on commercial ferrite cores by the use of a volt-amperometric measurement technique. Accommodation of minor cycles positioned along the major ascending (descending) branch as well as of minor loops defined through more complex trajectories is considered. A description of the measurement results is reported and obtained data are discussed.

Functionalized single-wall carbon nanotube-based gas sensor

In this paper – which was first presented at the 5th IEEE Conference on Sensors in Daegu, Republic of Korea, October 2006 – an improvement of the gas-sensing properties of the single-wall carbon nanotube (SWNT) by functionalizing its surface is reported upon. SWNTs were functionalized with sodium dodecyl sulphate (SDS), which improved the gas-sensing properties of the SWNTs. Solutions of SWNTs were deposited on the alumina substrate prepatterned with Pt contacts and heater to form the sensors. The morphology of the SWNT films were characterized by atomic force microscope (AFM) and transmission electron microscope (TEM) imaging, and their gas-sensing properties were studied using a voltamperometric technique. The sensors' sensitivity was tested in the presence of O3 (70–350 ppb), NO2 (0.1–5 ppm), CO (500 ppm), and NH3 (5 ppm) diluted in humid air (50 per cent relative humidity (RH)). The working temperature was varied in the range 20 °C–70 °C. The sensors showed an appreciable response to low concentrations of 70 ppb of ozone and 100 ppb of NO2, while showing virtually no response to CO and NH3.

Influence of iron addition on ethanol and CO sensing properties of tin oxide prepared with the RGTO technique

Effects of iron introduction in RGTO prepared tin oxide gas sensors are presented. The films were deposited by sputtering from a tin target with the introduction of an adjustable number or iron inset. Iron content was varied in the range 0–7%. The thin films are investigated by the volt-amperometric technique for electrical and gas-sensing properties. The layers are capable of sensing CO and ethanol, no evidence of surface poisoning is detected, and recovery of the resistance is complete. The response of the sensors is stable and reproducible at all operating temperatures tested (200–500 °C) during 3 months of operation.

Nanostructured mixed oxides compounds for gas sensing applications

We present some recent trends about research on gas sensors based on semiconducting thin films based on Ti, W, and Mo mixed oxides. The structural, electrical and gas-sensing properties of these films, deposited by rf reactive sputtering from composite targets of W–Mo, Ti–W and Ti–Mo at different abundance, were investigated through electron microscopy and volt-amperometric techniques. All of these layers showed sensing capability toward CO, NO 2 or ethanol. The thin films obtained were able to detect CO, NO 2, and ethanol below the concentration limit for environmental-monitoring and breath-analysis application.

High-frequency magnetoimpedance relaxation in melt-spun Co-based ribbons

The large changes of the impedance in soft magnetic alloys submitted to an external magnetic field caused a renewed interest due to perspective application in magnetic sensors. Magnetic relaxation effects are intrinsic properties of amorphous materials and may be detrimental to applications. In this work, the magnetoimpedance relaxation has been studied in melt-spun Co 68.25Fe 4.5Si 12.25B 15 ribbons in a wide range of frequency (500 kHz–6 GHz). The low-frequency measurements have been performed using the classical volt-amperometric technique. In the high-frequency region, the magnetoimpedance relaxations have been studied measuring the reflection parameter S 11 of a coaxial line containing the magnetic sample by means of a vectorial network analyzer.

Front-side micromachined porous silicon nitrogen dioxide gas sensor

In this paper a new C-MOS compatible fabrication process is presented for a nitrogen dioxide porous silicon (PS) sensor. Electrically insulated PS sensing layers and even free-standing PS membranes have been obtained by front side electrochemical micromachining, reducing in this way electrical leakage towards the crystalline substrate. The electrical behavior of the device in a controlled environment was measured by means of a volt–amperometric technique at constant bias. A huge variation of the current was detected at RT for NO 2 concentrations as low as 200 ppb (Δ G/ G=111). The interference of humidity, ethanol, methanol, CO and ozone is also discussed.

CO and NO 2 response of tin oxide silicon doped thin films

Research trends of gas sensors based on silicon doped tin oxide semiconducting thin films are presented. The films, deposited by DC and RF sputtering from targets of Sn and Si, are investigated by the volt-amperometric technique for electrical and gas-sensing properties. The layers are capable of sensing CO and NO 2, no evidence of surface poisoning is detected, and recovery of the resistance is complete. The response of the sensors is stable and reproducible at all operating temperatures tested (200–500°C). The layers are capable of detecting concentrations as low as 15 ppm of CO and 200 ppb of NO 2 with a response time of approximately 2–5 min.

Ti–W–O sputtered thin film as n- or p-type gas sensors

We present some recent trends about research on gas sensors based on semiconducting thin films together with a discussion on the development of novel nanostructured materials such as TiO, TiO 2, and WO 3 in single phase or as mixed oxides. The films, deposited by RF reactive sputtering from a composite target of W and Ti at two different abundances, are investigated through scanning and transmission electron microscopy (SEM and TEM) techniques for structural characterisation and by volt-amperometric technique for electrical and gas-sensing properties. All of the layers were capable to sense NO 2, no effect of poisoning of the surface was recorded, and recovery of the resistance was complete. A concentration as low as 0.5 ppm was detected with a relative change in the resistance Δ R/ R about 1400% and as short a response time as 2 min. A detection limit lower than 100 ppb of NO 2 is expected.

Mo-W-O thin films for CO sensing

AbstractThe Mo-W-O thin films were deposited by RF reactive sputtering from composite target of W and Mo (20:80 weight ratio). Structural characterisation was carried out by X-ray diffraction spectroscopy and the composition of the film was obtained by Rutherford backscattering analysis. The layers were investigated by volt-amperometric technique for electrical and gas-sensing properties. The films were capable of sensing CO. No effect of poisoning of the surface was recorded and recovery of the resistance was complete. A concentration of CO as low as 15 ppm produced a relative variation in the conductance of 390% with response and recovery times of about 2 minutes at a working temperature of 200°C.

Characterization of the oxygen electrode reaction on stabilized zirconia at temperatures below 550 K

Abstract Electrochemical characterization of the oxygen electrode reaction using stabilized zirco nia electrolyte and bismuth ruthenium oxide electrodes has been carried out at temperatures as low as 420 K. The influence of chemical treatment has been studied by means of microstructural studies, potentiometric measurements, impedance spectroscopy and voltamperometric techniques.

Microstructure and electrical properties of an α-hematite ceramic humidity sensor

α-Hematite porous ceramic material has been investigated as a humidity sensitive material, responding in the 0–95% relative humidity (r.h.) range. α-Hematite powders, with controlled microporosity, were obtained through the topotactic decomposition reaction of α-goethite and sintered at 50 °C steps in the 850–1100 °C range. SEM, TEM and Hg intrusion porosimetry techniques were employed in the microstructural characterization of the sintered compacts. The electrical response was investigated by means of the volt-amperometric technique, at 300 frequency Hz and 1 V pp signal generator, in the 0–95% r.h. range. The use of different types of electrode configurations showed that the electrical response was largely affected by their geometry. The humidity sensitivity and the response time were also found to be influenced by the microstructure, i.e. by the sintering temperature. All the results are highly reproducible.