Supporting Electrolyte Solution Research Articles

Development of a Miniature Sensor for Point-of-Care Determination of Mercury

Mercury is toxic to human health. In developing countries, artisanal and small scale gold mining (ASGM) entails mixing elemental mercury with crushed sediments to amalgamate gold. The mercury is then burned off, making it inhalable during the process. More than 15 million people -men, women, and children- in Central and South America, Africa and Asia are involved in ASGM. ASGM is responsible for ~40% of elemental mercury emitted into the environment. Mercury can cause mild to severe neurologic toxicity and even death. The US federal Biological Exposure Index (BEI) is currently set at 50 ppb (μg/L) for urine. Blood mercury may include both organic and inorganic forms and must be speciated to quantify the inorganic form. The half-life in blood is 70 days after acute exposure. The half-life of elemental mercury in the urine is ~7 days and requires a spot urine (single, one-time specimen). The current gold standard analytical methods for elemental mercury quantification are AAS and ICP-MS, which are costly and time consuming, and not readily available in countries where testing is needed. Electrochemical point-of-care (POC) sensors can reduce costs and time and could help expedite effective treatment.Our POC system relies on the Square Wave Anodic Stripping Voltammetry (SWASV) electrochemical approach. It is performed on disposable miniature three-electrode sensors (gold WE, gold CE and Ag/AgCl RE). The light weight, small and low-cost miniature USB potentiostat was used for the measurements. The sensor interface with the potentiostat included a vibration motor to provide sample agitation. Each experiment used a single 10 µL droplet of sample. We measured mercury in urine because it is non-invasive measurement, with a simpler organic matrix and no necessary preparation steps. During this work, fresh urine samples were stored in a -20 °C freezer.First, the SWASV conditions were optimized in buffer solution to demonstrate the feasibility of Hg detection on miniature sensors. Then, the validity of the POC system was confirmed by analysis with human urine. Nature and ionic strength of the supporting electrolyte (0.1 M HCl), pH (0.6), deposition potential (0 V), deposition time (900 s), parameters of the square wave scan (amplitude 10 mV, increment 4 mV, scan rate 600 mV/s, period 6 ms), intensity of the motor vibration (3.5 V) and dilution of the urine samples (dilution factor = 4) were perfectioned. A cleaning step in between measurements was introduced to overcome the forming of amalgam of Hg and Au. The cleaning step reduced the standard deviation of measurements, removing all Hg from the surface. Nature, conditions, and duration of it were investigated (chronoamperometry at +1.3 V for 120 s in 0.01 M HCl). After optimization, the limits of quantitation were 15 ppb Hg and 5 ppb Hg respectively in 0.1 M HCl and urine (linear ranges are respectively 15 ppb – 200 ppb Hg and 5 ppb – 20 ppb Hg). Urine broadened the shape of the peak: peak area was the best indicator of Hg concentration in urine. The vibration motor enhanced the sensitivity of the system by allowing all metal ions to enter in contact with the electrode surface and participate to the experiment. The lowest limits of detection were 3.14 ppb Hg in peak height measurements in supporting electrolyte solution (sensitivity 80.2 nA/ppb) and 3.79 ppb Hg in area measurements in urine solutions (15.16 ppb Hg considering a dilution factor 4x for urine; sensitivity 14.795 nW/ppb). The validity of the point-of-care system was confirmed by performing standard addition analysis of unknown Hg concentrations in urine, reaching 85 % accuracy (number of samples n=5).This POC system for mercury detection in urine could offer rapid help for individuals in the field, far from big laboratories. We succeeded in detecting trace concentrations of mercury on miniature sensors, reaching LOQ and LOD below the BEI intervention threshold in urine samples. This is a key innovation: at the moment lab-on-a-chip devices for mercury detection in urine do not exist. Future steps will focus on validation with a large number of samples from Hg-exposed population.

Voltammetric quantification of a nonsteroidal anti-inflammatory agent diflunisal based on the enhancement effect of cationic surfactant on boron-doped diamond electrode

The present work describes a simple, fast, and inexpensive voltammetric method for diflunisal measurement using a non-modified boron-doped diamond (BDD) electrode. The oxidation of the agent was irreversible and presented a diffusion‐controlled process. The sensitivity of the square wave voltammetric measurements were significantly improved when the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was present in the supporting electrolyte solution. Using square-wave mode, a linear response was obtained for diflunisal quantification in 0.1 mol L-1 phosphate buffer solution (pH 2.5) solution containing 5×10-5 mol L-1 CTAB at +1.07 V (vs. Ag/AgCl) (after 30 s accumulation under open-circuit conditions). Linearity was found for 0.05 to 2.0 μg mL-1 (2.0×10-7-8.0×10-6 mol L-1) with a detection limit 0.013 μg mL-1 (5.2×10-8 mol L-1). The developed approach could be used for the quantification of diflunisal in pharmaceutical formulations.

Cost‐effective and Facile Production of a Phosphorus‐doped Graphite Electrode for the Electrochemical Determination of Pyridoxine

AbstractIn this study; a sensitive, selective, and simple electrochemical sensor was developed to determine low concentration pyridoxine (Py) using a phosphorus‐doped pencil graphite electrode (P‐doped/PGE). Electrode modification was implemented using the chronoamperometry method at +2.0 V constant potential and 100 seconds in 0.1 mol L−1 H3PO4 supporting electrolyte solution. The characterization processes of the P‐doped/PGE were carried out using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), X‐ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDX), and atomic force microscope (AFM) methods. In the concentration study, using the differential pulse voltammetry (DPV) method, a linear calibration plot was acquired in the concentration range of 0.5 to 300 μmol L−1 Py. The limit of quantification (LOQ) and limit of detection (LOD) of the developed method were calculated as 0.219 μmol L−1 and 0.0656 μmol L−1, respectively. Detection of Py has been successfully performed on the P‐doped/PGE in the beverage samples. As a result, the method developed has been shown to have fast, low cost, and simple for the sensitive and selective detection of Py as an effective electrode.

A novel carbon nanosphere-based sensor used for herbicide detection

Bentazon (BTZ) is a post-emergence herbicide widely applied in different cultures. It is characterized by low adsorption and high solubility in water, which facilitates its penetration and contamination of aquatic environments. Human exposure to BTZ is responsible for numerous toxic effects and, therefore, it is of great importance to develop simple and efficient analytical methods capable of accurately detecting the presence of this herbicide in environmental samples. The present paper reports the development and application of a glassy carbon electrode modified with carbon nanosphere-based cross-linked chitosan film for the voltammetric determination of BTZ herbicide. The incorporation of cetyltrimethylammonium bromide surfactant into the supporting electrolyte solution helped enhance the voltammetric signal and the sensor repeatability. The use of chitosan film crosslinked with epicholorohydrin contributed toward improving the properties of the carbon nanospheres, including the electron transfer rate. A set of assays were conducted aiming optimizing the experimental parameters related to the supporting electrolyte composition (pH and surfactant concentration) and the square-wave voltammetry technique. Under optimized conditions and based on the application of the method proposed in the study, a linear concentration range of 1.99 to 65.4 μ mol L −1 was obtained, with limit of detection of 1.4 μ mol L −1 and sensitivity of 6.22 A mol −1 L cm −2 . The modified electrode presented good intra- (2.8%, n = 10 ) and inter-day (1.4%, n = 5 ) repeatability and high selectivity for bentazon. The optimized electroanalytical technique was successfully applied for the quantification of bentazon in environmental water samples (recoveries close to 100%). • Nanostructuring a glassy carbon surface for herbicide sensing purposes is reported. • A robust modified electrode is designed by immobilizing carbon nanospheres within a cross-linked chitosan film. • Adsorptive effects from bentazon oxidation products are reduced by applying cetyltrimethylammonium bromide. • The optimized voltammetric sensor was successfully applied for bentazon determination at environmental water samples.

Simple and rapid voltammetric method for the detection of the synthetic adulterant fluoxetine in weight loss products

In the global obesity pandemic, the demand for healthy products that provide weight loss is increasing. However, undeclared adulterants are commonly added to increase their performance and the development of rapid methods for detecting these compounds is fundamentally important. In this work, it was demonstrated that an electrochemical technique (square wave voltammetry) using boron-doped diamond (BDD) as the working electrode can be used for rapid screening and quantification of the doping substance fluoxetine (FLU) in samples like thermogenic supplements, compounded drugs, and weight loss herbal medicines. Fast screening of FLU is possible after easy sample dilution in a supporting electrolyte solution (0.1 mol L-1 H2SO4). In addition to the simplicity and low cost of the proposed method, adequate analytical characteristics in terms of limits of detection (0.1 mg L-1), linear range (1 to 50 mg L-1; r = 0.993), and recovery values (104 ± 6 %) were obtained. These results suggest that the method has great potential as a simple and fast screening test to detect FLU in natural products for anti-obesity therapy.

Electrochemical Synthesis of Conducting Polyporphyrin Films based on 5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin

A hydroxy-substituted tetraphenylporphyrin was oxidatively electropolymerized from its solutions in ethanol by cyclic voltammetry. The electropolymerization process is investigated using cyclic voltammetry, absorption spectroscopy, and electrochemical quartz crystal microbalance. The results of IR and electronic absorption spectroscopy studies show that, in deposition from ethanol, the polymerization occurs via the O−H group of the phenyl substituent, which results in the formation of C−O−C bonds. The mechanism of polyporphyrin formation is similar to polymerization of simple organic compounds. The deposited polyporphyrin film (thickness of 80 nm) has a smooth surface. Using the Mott−Schottky approach, it was establish that the films have hole conductivity (i.e., they are a p-type semiconductor). The flat band potential of the poly-5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin is 0.33 V. The film is further oxidized in a supporting electrolyte solution by applying positive potentials, with anions of the supporting electrolyte incorporating into the polyporphyrin.

Voltammetric determination of natamycin using a cathodically pretreated boron-doped diamond electrode in the presence of sodium dodecyl sulfate

The work describes a new electrochemical method of assaying natamycin in pharmaceutical preparations and food products. The proposed procedure involves the use of cathodic-conditioned boron-doped diamond electrode (BDD) and sensitive electrochemical techniques. Well-defined oxidation peaks of natamycin, but no reduction peaks, were obtained in cyclic voltammetry. The sensitivity of the obtained measurements was significantly improved when a surfactant, sodium dodecyl sulfate (SDS), was present in the supporting electrolyte solution. The method of square-wave voltammetry was used to determine the linear relationship between the current and natamycin concentration. The linear relationship was obtained in the concentration range from 9.75 × 10−8 to 1.16 × 10−6 mol·L−1. In optimum conditions, i.e., 0.05 mol·L−1 H2SO4 containing 5.07 × 10−4 mol·L−1 SDS at the potential of 0.81 V (vs. SCE), the limit of detection was 3.1 × 10−8 mol·L−1. The method has good precision, which is proved by low relative standard deviation (approx. 1%). The obtained values of recovery prove the accuracy of the proposed procedure. The developed procedure was successfully tested for the assay of natamycin in single-ingredient and multi-ingredient pharmaceutical preparations and in wine samples.

Electrochemical Behavior of m-Nitrosulfonic Acid of Benzene in Aqueous Solutions of Different Composition

The electrochemical behavior of m-nitrosulphonic acid of benzene was studied by polarography, voltammetry at glassy carbon electrode, electrolysis at the controlled potential, and electrolysis in galvanostatic mode. A distinguishing feature of the m-nitrosulphonic acid of benzene electroreduction, as compared with that of aromatic nitro-compounds, both on mercury dropping electrode and glassy carbon electrode, is shown to be a strong dependence of parameters and shape of the polarization curve on the supporting electrolyte solution composition and рН in neutral and alkaline solutions. The two waves observed are bound to the reduction of undissociated m-nitrosulphonic acid of benzene molecule and its anion; the reduction intermediately product is hydroxylaminesulphonic acid of benzene. The wave of its further reduction to m-aminosulfonic acid of benzene is camouflaged by the supporting-electrolyte discharge. Ammoniac-buffered solutions can be recommended for preparative electrosynthesis of m-aminosulfonic acid of benzene because its yield in the electrolysis at nickel cathode in galvanostatic mode in these solutions is as high as 92.8%, with current efficiency of 82.0%.

Voltammetric determination and electrochemical behavior of vanillin based on 1H-1,2,4-triazole-3-thiol polymer film modified gold electrode

Poly(1H-1,2,4-triazole-3-thiol) (poly(T3T)) conductive film was coated successfully on the gold electrode (Au). The electrochemical behavior of vanillin (VAN) was studied on the 1H-1,2,4-triazole-3-thiol-Au (T3T-Au) electrode. The determination of VAN was performed on the T3T-Au electrode using a differential pulse voltammetry (DPV) technique. In order to detect the concentration of VAN, suitable supporting electrolyte solution and pH value were determined. At pH 3 in HClO4 solution, the anodic peak current of VAN obtained with the T3T-Au electrode is 4.3 times greater than the bare Au electrode. The response oxidation peak current and concentration of VAN showed a good linear relationship in the range of 0.1–11.3 µM. The limit of detection was found as 0.04 µM. Besides, the reproducibility, repeatability, stability, and interference measurements were also assayed. This sensor was applied successfully for the detection of VAN in synthetic samples and various food samples.

Experimental design on determination of Sn(II) by the modified carbon paste electrode with Fe(II)-exchanged clinoptilolite nanoparticles

In the present study, clinoptilolite nanoparticles (CN) were prepared in a planetary ball-mill instrument and ion exchanged in Fe(II) solution. The resulted Fe(II)–CN material was then used as an effective modifier to modify carbon paste electrode (CPE). When the resulted Fe(II)–CN-CPE electrode was immersed in HCl supporting electrolyte, Fe(II) cations were located at the electrode-solution interface via an ion exchange process with protons which were present in the supporting electrolyte solution. Next, Fe(II) cations could be immediately oxidized to Fe(III) at the electrode surface by scanning the potential toward more positive values in order to create an anodic peak current. When Sn(II) cations were added into the supporting electrolyte solution, they could immediately react with the produced Fe(III) cations as well. This reaction provided more Fe(II) cations at the electrode-solution interface, causing a significant increase in the peak current of the electro-oxidation of Fe(II) cations. Hence, this electrocatalytic current was utilized for the voltammetric determination of Sn(II) in aqueous solution. In addition, the experimental design by response surface methodology was applied to study the interaction effects between the influencing variables. Further, the best voltammetric response was obtained by performing the voltammetric measurement based on the run (with conditions of pH 2, ν = 100 mV s−1, modifier% = 10%, and CFe = 0.7 mol L−1). Finally, the Fe(II)–CN-CPE electrode showed a linear response in the concentration range of 10–400 μmol L−1 Sn(II) with a detection limit (DL) of 0.1 μmol L−1.

Enhancement of Voltammetric Signals Using a Graphene Oxide Modified Carbon Electrode for Electrochemical Paper-Based Analytical Devices

This work presents an enhancement of the voltammetric signal on an electrochemical paper-based analytical device (ePAD) using a graphene oxide (GO) modified carbon electrode. The ePAD is fabricated using a screen printing technique for fabrication of the hydrophobic area and three electrode strips. The graphene film was directly prepared on ePAD by dropping 2 µL of GO dispersed in water onto the working electrode surface and leaving it to dry at room temperature. The electrochemical reduction process of GO was carried out by applying a constant voltage of -1.20 V (vs. Ag/AgCl electrode strip) in 0.1 M KCl for 800 s. The GO-modified carbon working electrode on ePAD was readily obtained and ready to use after removing KCl solution. We tested the enhancement of the voltammetric signal on ePAD with a 6 mM [Fe(CN)6]4–/3– redox couple in 0.1 M KCl supporting electrolyte solution. Our results obtained from cyclic voltammograms showed that the unmodified working electrode and the GO-modified working electrode on ePAD provided similar anodic and cathodic peaks. Due to accelerated electron transfer process, it was found that the GO-modified working electrode on ePAD provided approximately a 2-fold increase in voltammetric signals when compared to the unmodified working electrode on ePAD. The reproducibility (inter-day precision) of the voltammetric signal measurement using a GO-modified working electrode on ePAD was acceptable. The relative standard deviation (RSD) was 5-8%. Therefore, the GO-modified carbon working electrode on ePAD offers an effective approach to enhance the signal and sensitivity for chemical analysis.

Effects of atom substitutions and dissolved carbonate species on monazite electrophoretic mobility

In this study, the atom substitutions that commonly affect the monazite lattice were considered as potential factors affecting the monazite electrophoretic mobility. The influence of light rare earth elements (LREE) substitutions and the presence of thorium, calcium, and silicate within the monazite crystal lattice was also examined using a natural monazite and synthetic cerium, lanthanum and neodymium monazite materials. Electrophoretic mobility measurements performed after treatment in an electrolyte solution equilibrated with air outline that LREE substitutions and other substitutions observed in the tested natural monazite did not affect the mineral surface properties.Conversely, the electrophoretic mobility of the synthetic monazites was found to be significantly affected by the amount of dissolved carbonate species present in the aqueous media. More precisely, carbonate species were found to decrease the electrophoretic mobility of monazite. Unlike tests performed with a solution equilibrated with air, the electrophoretic mobility of monazite treated in a CO2 depleted electrolyte solution, under controlled atmosphere, were found erratic. This highlights the difficulty in obtaining reliable electrophoretic mobility data when the carbonate content in the supporting electrolyte solutions is not controlled.

Selective and Highly Sensitive Voltammetric Determination of Citalopram with Glassy Carbon Electrode

This work proposes a simple and very sensitive method for electrochemical determination of citalopram by differential pulse voltammetry (DPV) using glassy carbon electrode. The cyclic voltammetry measurements proved that citalopram undergoes irreversible, adsorption-controlled, two-electron oxidation process, accompanied by the release of two protons. The influence of different measurement conditions, such as type and pH of supporting electrolyte solution, as well as DPV parameters was investigated. The glassy carbon electrode (GCE) exhibits fast linear response toward citalopram oxidation in concentration ranges of 0.05–10 μmol L−1 and 10–115 μmol L−1 with detection limit (LOD) of 0.036 μmol L−1. The proposed method provides low detection limit, high accuracy and precision with good selectivity in comparison to previously reported methods. The applicability of developed method was tested by determination of citalopram in pharmaceuticals and spiked tap, river and waste water samples.

Differential pulse polarographic investigation of micafungin and anidulafungin using a dropping mercury electrode.

The electrochemical behavior of the echinocandin antifungals anidulafungin (AF) and micafungin (MF) has been investigated by differential pulse polarography (DPP). The measurements were carried out in a supporting electrolyte solution consisting of Britton-Robinson buffer and methanol at various substance concentrations and pH values. An amperometric cell with a three electrode system consisting of a dropping mercury electrode (DME) as working electrode, an auxiliary platinum electrode and an Ag/AgCl reference electrode was used in all experiments. AF was electrochemically reduced at potentials between -1.3 and -1.5 V. MF showed a first reduction peak (a) between -1.0 and -1.4 V and a second peak (b) between -1.5 and -1.8 V. A strong pH-dependence was observed, with optimal results at pH 2.0-3.0 for the AF peak, pH 2.0 for the MF peak (a) and pH 5.0 for the MF peak (b). A linear correlation between the concentration and the peak current has been demonstrated for all reduction peaks. MF peak (a) showed a similar behavior to the AF peak regarding shape, peak current and pH-dependence. Therefore, it can be assumed that both reductions are based on the same mechanism, a two-step reduction of the N-acyl group.

A comprehensive study on the kinetic aspects and experimental design for the voltammetric response of a Sn(IV)-clinoptilolite carbon paste electrode towards Hg(II)

The Sn(IV) ion exchanged clinoptilolite nanoparticles (Sn(IV)-CNP) were used as a modifier for the modification of carbon paste electrode (CPE). When the modified electrode was immersed in HCl supporting electrolyte, Sn(IV) cations can locate at the Sn(IV)-CNP-CPE electrode surface via an ion exchange process with protons of the supporting electrolyte. These electroactive cations underwent a redox process at the electrode surface. Increased peak current of Sn(IV) reduction by adding Hg(II) analyte into the supporting electrolyte solution was used for the voltammetric determination of Hg(II). Focus of the work was on study of the interaction effects between the influencing variables in square wave voltammetric response of the modified electrode in the presence of Hg(II) cations by designing the experiments (via response surface methodology: RSM) and study of some kinetic aspects of the process in linear sweep voltammetry and chronoamperometry. The optimal run in RSM was obtained in: Csn(IV) in ion exchange solution: 0.37 mol L−1, modifier%: 22.45, amplitude: 60 mV and step potential: 2.9 mV. The response current of the modified electrode was proportion to Hg(II) concentration in the range of 0.1–10 μM (DL: 0.05 μM) in square wave voltammetry and in the range of 0.1–10 μM (DL: 0.01 μM) in chronoamperometry. Using the Tafel plots, the values of α and Ko were determined for the modified electrode as 0.298, 1.91 × 10−3 s−1 and 0.311, 6.62 × 10−3 s−1 in the absence and presence of Hg(II) cations, respectively.

The effect of the supporting electrolyte on the voltammetric determination of the veterinary drug nitroxinil

In this work, a new approach for the determination of the veterinary drug nitroxinil is presented, and its electrochemical behavior is investigated as well as voltammetric determination based on its oxidation signal is proposed. A glassy carbon electrode (GCE) was used as an electrochemical sensor for the determination of this compound, and a square–wave voltammetric (SWV) technique with the optimized parameters was applied for the quantification of nitroxinil. The effect of the supporting electrolytes, such as Britton–Robinson buffer solution (BRBS), citrate buffer solutions (CBS), and hydrochloric acid–potassium chloride buffer solutions (HCl–KClBS), on the SWV determinations of nitroxinil was investigated, and the experiments showed that the supporting electrolyte has a significant effect on the nitroxinil determination. The highest analytical SWV response of nitroxinil was obtained in acidic medium of the investigated supporting electrolytes, i.e. in the BRBS at pH 2.0, the CBS at pH 2.0, and the HCl–KClBS at pH 1.8. The corresponding current at ca. +1.3 V vs. Ag/AgCl/3 mol L−1 KCl reference electrode increased linearly with the concentration of nitroxinil within two linear dynamic ranges (LDR) in each supporting electrolyte solution. The lowest limit of detection (LOD) and quantification (LOQ) for nitroxinil were achieved in the BRBS at pH 2.0 (LOD = 0.28 μmol L−1 and LOQ = 0.93 μmol L−1). In addition, the analytical parameters obtained from calibration curves indicated the best sensitivity in the BRBS at pH 2.0 (0.124 μA L μmol−1). Cyclic voltammetric (CV) experiments showed that the electrode reaction of nitroxinil is irreversible (oxidation peak at ca. +1.3 V) and diffusion–controlled in each supporting electrolyte solution.

Wax-printed paper-based device for direct electrochemical detection of 3-nitrotyrosine

An overview of the last trends in lab-on-chip technology highlights the continuous development of biosensing approaches in terms of simplicity, low-cost, and quick response, with a higher sensitivity and selectivity. In this context, electrochemical sensors arrived to overcome the need to develop small, accurate, portable and compact sensing devices, compatible with routine use in loco analysis, especially in point-of-care (POC) assessment.Herein, we have presented the first paper-based electrochemical sensor towards the detection of 3-nitrotyrosine (3-NT), a relevant oxidative stress biomarker. This innovative sensor was designed by, first, modifying paper to become a hydrophobic support and, second applying carbon and silver conductive inks to generate a three electrode-system on a small spot. An intensive voltammetric investigation of the paper-based screen-printed electrodes (SPEs), including the study of different redox-probes, scan-rate values, probe concentrations and supporting electrolyte solutions, confirmed their suitable and reliable electrochemical performance. Square wave voltammetry (SWV) was employed to assess the sensitivity of the proposed sensor at various concentrations of 3-NT, ranging from 500 nM to 1 mM, enabling a low detection limit (LOD) of 49.2 nM. The interference of co-existing species was also tested and good selectivity against 3-NT was accomplished. Overall, this flexible paper-based platform constitutes a promising sensor material towards a quick, sensitive, cost-effective, sustainable and reproducible detection of 3-NT biomarker.

(Invited) Plasmon-Induced Photocurrent Generation for Exploring the Near-Field Ofstrongly Coupled Plasmonic Systems

[Introduction] Metallic nanostructures which show localized surface plasmon resonances (LSPRs) have received considerable attention as a light harvesting optical antenna for light-energy conversion systems such as solar cells as well as artificial photosynthesis [1,2]. To construct efficient light harvesting optical antennae, an optimization of structural design is one of the most important research topics in plasmon-induced light energy conversions. Coupled plasmonic systems such as nanogap heptamer, dolmen, metal-insulator-metal nanostructures, and so on is promising as a photoelectrode design because of their strong near-field enhancement and wide wavelength responsibility. In this study, a coupled plasmonic system based on a waveguide-LSPR coupling system is employed to investigate whether the photocurrent response extends over a wide wavelength range and is promoted by near-field enhancement in the plasmon-induced photocurrent generation using gold nanostructured titanium dioxide (TiO2) photoelectrodes. Near-field spectrum and photocurrent action spectrum are compared to elucidate the effect of near-field enhancement on the photocurrent generation. [Experimental] TiO2 photoelectrodes supporting periodic gold nanogratings (AuNGs) with different pitch sizes were fabricated by a deposition of TiO2 on a glass substrate with a thickness of 250 nm using an atomic layer deposition (ALD) reactor, and subsequent electron beam lithography and lift-off processes. A conventional photoelectrochemical measurement was performed. The AuNGs/TiO2 photoelectrode, a platinum wire and a saturated calomel electrode (SCE) were employed as working, counter and reference electrodes, respectively. An aqueous Ar-gas-bubbled KClO4 (0.1 mol/dm3) solution was used as a supporting electrolyte solution. A plasmon-induced water oxidation as a half reaction of water splitting was explored [3]. [Results and Discussion] Figure 1(a) shows a scanning microscope (SEM) image of AuNGs/TiO2 photoelectrode with a pitch size of 300 nm. Extinction spectra of the AuNGs/TiO2 photoelectrode with a different pitch size are shown in Fig. 1(b). There is only one peak corresponding to the LSPR mode of periodic Au-NGs with 200 nm and 225 nm pitch sizes. Starting with a pitch size of 250 nm, three peaks can be observed, and the peaks show a spectral shift with increasing the pitch size. The two outer peaks can be assigned as coupled modes (P+ and P-) deriving from the symmetric waveguide mode Ew and LSPR mode Ep as shown in the illustration of the waveguide-LSPR coupling system (Fig. 1(c)). The center peak can be considered as a coupling mode between the asymmetric waveguide mode and the waveguide-LSPR coupling system. Internal quantum efficiency (IQE) spectra and simulated near-field spectra of the AuNGs/TiO2 photoelectrodes with 300 nm and 350 nm pitch sizes are shown in Fig. 2. The near-field intensity in the spectra was calculated by monitoring at the interface between the AuNGs and the TiO2 film by the electromagnetic simulations using a finite-difference time-domain (FDTD) method. It was clearly elucidated that IQE spectrum has successfully reproduced the near-field spectrum under the coupling conditions. This indicates that the photocurrent response extended over a wide wavelength range utilizing the coupled plasmonic systems and near-field enhancement effects promoted the plasmon-induced water oxidation because IQE values increased responding to the near-field spectra [4]. References Ueno, K., Oshikiri, T., Sun, Q., Shi, X., Misawa, H. Chem. Rev., DOI: 10.1021/acs.chemrev.7b00235.Ueno, K., Oshikiri, T., H. Misawa, ChemPhysChem, 2016, 17, 199−215.Nishijima, Y., Ueno, K., Yokota, Y., Murakoshi, K., Misawa, H. J. Phys. Chem. Lett. 2010, 1, 2031−2036.Guo, J., Ueno, K., Shi, X., Oshikiri, T., Misawa, H. et al., J. Phys. Chem. C 2017, 121, 21627−21633. Figure 1

(Invited) Fabrication and Operation Under the Same Conditions: Oxygen Reduction on Cathodically Deposited Manganese Oxide

We present the data on the oxygen reduction (ORR) and oxygen evolution (OER) in an alkaline solution for manganese oxide electrocatalysts fabricated by means of cathodic electrocrystallization. The catalysts are deposited from a permanganate alkaline bath, and later operate in the same 1 M NaOH medium. The effect of the deposition potential is addressed. The goal of the study is to obtain carbon-free oxide electrocatalysts with satisfactory activitiy and stability. A qualitative difference of the electrochemical behavior is observed for oxides deposited at low (potentials above ~0.75 V RHE, region 1) and at higher overvoltage (potentials below ~0.75 V (RHE) region 2). Current efficiency is close to 40% in region 1, and increases up to 60% in region 2. All the samples consist of delta-MnO2 (birnessite), but their microstructure is essentially different for electrodeposition from regions 1 and 2. For the deposits fabricated in region 2 the birnessite structure is slightly distorted, while for the deposits prepared in region 1 a complete disordering along the layer stacking direction is observed. The voltammograms of oxides in supporting electrolyte solution undergo fast evolution under potential cycling, accompanied by a decrease of the total charge. Stabilized voltammograms for the samples fabricated in region 2 are featureless and demonstrate a pronounced Ohmic contribution, while for the samples deposited in region 1 a reversible redox behavior is observed, with broad current peaks and formal potential of ~ 0.85 V RHE. The total charge is proportional to the oxide loading in the interval under study (~ 10 – 90 mkg/cm2). Both types of samples do not exhibit reductive degradation at potentials above 0.7 V (RHE). ORR activities are estimated from the rotating disc electrode data in an O2-saturated solution. For oxides fabricated in region 1 the kinetic currents at 0.85 V RHE approach 40-50 A/g (for intermediate loadings), making them promising binder-free ORR catalysts. The ORR activity of oxides electrodeposited at higher overvoltages is an order of magnitude lower corroborating the influence of structure on the electrocatalytic activity. Even though the OER activities of electrodeposited oxides at 1.63 V RHE do not exceed 3 A/g, their remarkable stabilities both in the ORR and in the OER potential interval allows one to hope that these materials may be of interest as a component of hybrid bi-functional catalytic compositions together with other oxides more active in the OER. The authors are grateful to Yu.A. Velikodnyi and A.Ye. Baranchikov for their help with structural characterization of the samples. The work is supported by EraNetRus program, project (#270 NANO-Morf).

The coverage control and electric desorption kinetics of polypyridyl ruthenium dye molecule fixed on the interface of nanoporous TiO2

This paper conducted researches on electric desorption kinetics, desorption mechanism and quantitative desorption of the adsorbed polypyridyl ruthenium based dye on the surface of nanoporous TiO2 film under negative potential. Change external negative potential to obtain the relationship between dye desorption amount of sensitized-TiO2 film and potential. After the negative potential exceeds about −0.5 V, amount of dye left on the surface of TiO2 film decreases rapidly. According to the pseudo-first-order kinetic equation, dye desorption rate kd under potential of −0.6 V is 6.92 × 10−3 s−1. Research the relationship between the amount of desorbed dye and the potential duration, ionic concentration in supporting electrolyte solution as well as film thickness. It implies that the amount of adsorbed dye can be accurately controlled. Based on the measurement and analysis of the adsorption property of desorbed dye through UV–Visible absorption spectroscopy, there is no change of number of absorption peaks of the desorbed dye or no occurrence of new peak, while the absorption peak position of the desorbed dye shows a blue shift. Cyclic voltammetry is used to research the TiO2/dye/electrolyte interface and TiO2/electrolyte interface, and analyze the influence of dye desorption on the cyclic voltammetric response. Two possible dye desorption mechanisms are provided: one is the fracture of ester bond between dye and TiO2 under negative potential; another is the electrostatic repulsion desorption mechanism. Work in this paper is of theoretical guiding significance for compounding new dyes, defining assembly mechanism of dye, enhancing the stability of solar cell, and improving solar cell efficiency.