Hemin-adsorbed carbon felt for sensitive and rapid flow-amperometric detection of dissolved oxygen

Participation in Negative Capacitance of Diffusion-Controlled Voltammograms of Hemin

Hemin in dimethyl sulfoxide solution has exhibited voltammograms controlled by diffusion at glassy carbon electrodes for slow scan rates, although it is adsorbed slightly. In contrast, voltammograms for high scan rates, v > 1 V s^-1, were governed by some kinds of kinetics judging from the scan rate dependence of peaks. The kinetics is close to that of a ferrocenyl derivative, in which the currents include the capacitive component with negative values. The capacitive one can be identified with the proportionality to the scan rates. The variation of the peak currents with v yielded -200 μF cm^-2. This negative value, being associated with the charge transfer reaction, makes cyclic voltammograms deviated downward from the diffusion-controlled behavior, resembling an irreversible reaction of the Butler-Volmer kinetics. Double layer capacitances are generally formed so that the applied electric field may be relaxed. The reduction of hemin forms a dipole coupled with a cation of the salt. The dipole orients from the electrode to the bulk, whereas the solvent dipoles orients in the opposite direction. Therefore, the capacitance is observed negatively. The capacitance determined by ac impedance took also negative values when the applied dc potential was only in the potential domain for the charge transfer. These complications can be avoided in electrocatalysis by use of such slow voltammetry as scan rates of 0.1 V s^-1 and ac frequency of 0.2 Hz.

Enhancement of simultaneous batik wastewater treatment and electricity generation in photocatalytic fuel cell

The objective of this study was to investigate several operating parameters, such as open circuit, different external resistance, pH, supporting electrolyte, and presence of aeration that might enhance the degradation rate as well as electricity generation of batik wastewater in solar photocatalytic fuel cell (PFC). The optimum degradation of batik wastewater was at pH 9 with external resistor 250 Ω. It was observed that open circuit of PFC showed only 17.2 ± 7.5% of removal efficiency, meanwhile the degradation rate of batik wastewater was enhanced to 31.9 ± 15.0% for closed circuit with external resistor 250 Ω. The decolorization of batik wastewater in the absence of photocatalyst due to the absorption of light irradiation by dye molecules and this process was known as photolysis. The degradation of batik wastewater increased as the external resistor value decreased. In addition, the degradation rate of batik wastewater also increased at pH 9 which was 74.4 ± 34.9% and at pH 3, its degradation rate was reduced to 19.4 ± 8.7%. The presence of aeration and sodium chloride as supporting electrolyte in batik wastewater also affected its degradation and electricity generation. The maximum absorbance of wavelength (λ_max) of batik wastewater at 535 nm and chemical oxygen demand gradually decreased as increased in irradiation time; however, batik wastewater required prolonged irradiation time to fully degrade and mineralize in PFC system.

Hemin-Modified SnO2/Metglas Electrodes for the Simultaneous Electrochemical and Magnetoelastic Sensing of H2O2

In this work, we present a simple and efficient method for the preparation of hemin-modified SnO2 films on Metglas ribbon substrates for the development of a sensitive magneto-electrochemical sensor for the determination of H2O2. The SnO2 films were prepared at low temperatures, using a simple hydrothermal method, compatible with the Metglas surface. The SnO2 film layer was fully characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), photoluminescence (PL) and Fourier Transform-Infrared spectroscopy (FT-IR). The properties of the films enable a high hemin loading to be achieved in a stable and functional way. The Hemin/SnO2-Metglas system was simultaneously used as a working electrode (WE) for cyclic voltammetry (CV) measurements and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The CV scans reveal direct reduction and oxidation of the immobilized hemin, as well as good electrocatalytic response for the reduction of H2O2. In addition, the magnetoelastic resonance (MR) technique allows the detection of any mass change during the electroreduction of H2O2 by the immobilized hemin on the Metglas surface. The experimental results revealed a mass increase on the sensor during the redox reaction, which was calculated to be 767 ng/μM. This behavior was not detected during the control experiment, where only the NaH2PO4 solution was present. The following results also showed a sensitive electrochemical sensor response linearly proportional to the concentration of H2O2 in the range 1 × 10−6–72 × 10−6 M, with a correlation coefficient of 0.987 and detection limit of 1.6 × 10−7 M. Moreover, the Hemin/SnO2-Metglas displayed a rapid response (30 s) to H2O2 and exhibits good stability, reproducibility and selectivity.

Reactive Black 5 as electron donor and/or electron acceptor in dual chamber of solar photocatalytic fuel cell

The role of azo dye Reactive Black 5 (RB5) as an electron donor and/or electron acceptor could be distinguished in dual chamber of photocatalytic fuel cell (PFC). The introduction of RB5 in anode chamber increased the voltage generation in the system since degradation of RB5 might produce electrons which also would transfer through external circuit to the cathode chamber. The removal efficiency of RB5 with open and closed circuit was 8.5% and 13.6%, respectively and removal efficiency for open circuit was low due to the fact that recombination of electron-hole pairs might happen in anode chamber since without connection to the cathode, electron cannot be transferred. The degradation of RB5 in cathode chamber with absence of oxygen showed that electrons from anode chamber was accepted by dye molecules to break its azo bond. The presence of oxygen in cathode chamber would improve the oxygen reduction rate which occurred at Platinum-loaded carbon (Pt/C) cathode electrode. The V_oc, J_sc and P_max for different condition of ultrapure water at cathode chamber also affected their fill factor. The transportation of protons to cathode chamber through Nafion membrane could decrease the pH of ultrapure water in cathode chamber and undergo hydrogen evolution reaction in the absence of oxygen which then increased degradation rate of RB5 as well as its electricity generation.

Application of pyrite and chalcopyrite as sensor electrode for amperometric detection and measurement of hydrogen peroxide

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium.

Influence of supporting electrolyte in electricity generation and degradation of organic pollutants in photocatalytic fuel cell

This study investigated the effect of different supporting electrolyte (Na2SO4, MgSO4, NaCl) in degradation of Reactive Black 5 (RB5) and generation of electricity. Zinc oxide (ZnO) was immobilized onto carbon felt acted as photoanode, while Pt-coated carbon paper as photocathode was placed in a single chamber photocatalytic fuel cell, which then irradiated by UV lamp for 24 h. The degradation and mineralization of RB5 with 0.1 M NaCl rapidly decreased after 24-h irradiation time, followed by MgSO4, Na2SO4 and without electrolyte. The voltage outputs for Na2SO4, MgSO4 and NaCl were 908, 628 and 523 mV, respectively, after 24-h irradiation time; meanwhile, their short-circuit current density, J SC, was 1.3, 1.2 and 1.05 mA cm(-2), respectively. The power densities for Na2SO4, MgSO4 and NaCl were 0.335, 0.256 and 0.245 mW cm(-2), respectively. On the other hand, for without supporting electrolyte, the voltage output and short-circuit current density was 271.6 mV and 0.055 mA cm(-2), respectively. The supporting electrolyte NaCl showed greater performance in degradation of RB5 and generation of electricity due to the formation of superoxide radical anions which enhance the degradation of dye. The mineralization of RB5 with different supporting electrolyte was measured through spectrum analysis and reduction in COD concentration.

Carbon Felt-Based Bioelectrocatalytic Flow-Through Detectors: 2,6-Dichlorophenol Indophenol and Peroxidase Coadsorbed Carbon-Felt for Flow-Amperometric Determination of Hydrogen Peroxide

2,6-dichlorophenol indophenol (DCIP) and horseradish peroxidase (HRP) were coadsorbed on a porous carbon felt (CF) from their mixed aqueous solution under ultrasound irradiation for 5 min. The resulting DCIP and HRP-coadsorbed CF (DCIP/HRP-CF) showed an excellent bioelectrocatalytic activity for the reduction of H₂O₂. The coadsorption of DCIP together with HRP was essential to obtain larger bioelectrocatalytic current to H₂O₂. The DCIP/HRP-CF was successfully used as a working electrode unit of a bioelectrocatalytic flow-through detector for highly sensitive and continuous amperometric determination of H₂O₂. Under the optimized operational conditions (i.e., applied potential, +0.2 V versus Ag/AgCl; carrier pH 5.0, and carrier flow rate, 1.9 mL/min), the cathodic peak current of H₂O₂ linearly increased over the concentration range from 0.1 to 30 μM (the sensitivity, 0.88 μA/μM (slope of linear part); the limit of detection, 0.1 μM (S/N = 3) current noise level, 30 nA) with a sample through-put of ca. 40–90 samples/h.