Flow-through Electrolytic Cell Research Articles

Synergistic nitrate removal: Coupling electrocatalysis and chemical reduction for exceptional nitrogen selectivity

Nitrate pollution in natural water bodies poses a severe threat to human health and the environment. Developing efficient and environmentally friendly nitrate removal methods has become a global need. Electrochemical techniques offer a cost-effective strategy for nitrate remediation; however, the complexity of the reaction and the formation of multiple by-products make the selective production of harmless nitrogen a challenging task. This study proposes a novel two-step strategy to achieve high efficiency and selectivity in converting nitrate into nitrogen. First, a membrane electrode consisting of silver nanowires (Ag NWs) is used to electrochemically reduce nitrate to nitrite through a direct electron transfer pathway. Whether in a static electrolytic cell or a flow cell, the process has very high nitrite selectivity and Faraday efficiencies, with Faraday efficiency up to 98.40 % and selectivity up to 99.90 % at −1.0 V vs Ag/AgCl. Subsequently, the nitrite is converted into nitrogen through a specific reaction with sulfamic acid with near 100 % conversion and selectivity. By coupling these two reactions, the selectivity for converting nitrate to nitrogen can reach more than 99 %. In addition, the membrane electrode can be readily used in a flow-through electrolytic cell to treat nitrates at a maximum rate of 150 L h−1 m−2. When operated at 50 L h−1 m−2, the membrane electrode demonstrates relatively stable performance for 100 h, reducing nitrates at 1.61 mM to below 0.81 mM (50 ppm), as recommended by the World Health Organization for drinking water. This novel synergistic approach not only enhances nitrogen selectivity but also simplifies the process of electrocatalytic nitrate reduction, making it a promising method for nitrate removal.

Layered Double Hydroxide-Modified Electrodes for Gaseous Acetaldehyde Degradation at the Solid-Gas Interphase

Electrochemical application has been considered a promising technology in environmental remediation. However, the development of hydrocarbon ligand-free mediators for long-term operation still deserves further assessments. In this study, three different combinations (NiAl, CoAl, NiCo) of layered double hydroxide (LDH) electrodes were prepared using in situ and ex situ methods. These LDH electrodes were applied as solid electrocatalysts for gaseous acetaldehyde degradation using a membrane-divided flow-through electrolytic cell. In cyclic voltammetry analysis, the in situ prepared LDH-electrodes had high peak currents in high-valent redox couples (Ni3+/2+Al3+, Co3+/2+Al3+, and Ni3+/2+Co3+/2+) compared to low-valent redox couples (Ni2+/1+Al3+, Co2+/1+Al3+, and Ni2+/1+Co2+/1+). Due to the higher active surface area, the overall redox peak current was higher in the in situ prepared LDH electrode than the ex situ LDH electrode. During electrocatalytic degradation of acetaldehyde, the LDH electrodes containing cobalt ions had a higher mediated catalysis activity than the LDH containing nickel ions (NiAl-LDH). The Co3+ ions placed in the layered hydroxide synergistically mediate the electrons to degrade acetaldehyde at the solid-gas interface sustainably.

Electrochemically Simulated Oxidative Metabolization Pattern of Neurokinin-1 Antagonist Aprepitant

Considering the scarcity of data regarding the electrochemical behavior of neurokinin-1 (NK1) antagonists, the electrochemical oxidation pathways of one of the class representatives, aprepitant, were investigated. The development of drugs capable of blocking NK1 receptors brought into light several new potential therapeutic applications, therefore the elucidation of their oxidative metabolic pathway aiding in completing the picture of the observed pharmacological activity is desired. For the simulation of the human microsomal oxidation of aprepitant, a mechanistic study in an EC/MS setup using a thin-layer flow-through electrolytic cell based on a boron-doped diamond working electrode on the range of 0–2500 mV vs Pd/H2 was performed. Potential isomers of electrochemically generated species, previously unknown oxidative products and collision induced ionic fragments were identified by LC-MS analysis and confirmed by MS2 fragmentation, establishing a correlation pattern between the formerly reported in vivo and in vitro metabolites and the electrochemically generated ones.

Structural effects on electrosorptive behavior of aromatic organic acids from aqueous solutions onto activated carbon cloth electrode of a flow-through electrolytic cell

A flow-through electrolytic cell, constructed specially for electrosorption processes, was connected to a UV–Vis spectrophotometer to examine the electrosorptive behaviors of benzoic acid (BA), phthalic acid (PA) and nicotinic acid (NA) from aqueous 0.01M Na2SO4 solutions onto activated carbon cloth (ACC) electrode. Effect of pH on electrosorptive behavior of BA was determined. Competitive electrosorption from binary mixtures of BA and NA was carried out. In situ regeneration of ACC was examined by reversing the polarization direction upon which electrodesorption of 95% of electrosorbed NA was achieved. Kinetic data of both open circuit adsorption and electrosorption were found to obey successfully to pseudo-first-order law and rate constants were determined. Appreciable increase in the removal rate of aromatic organic acids was achieved by electrosorption compared to open circuit adsorption. Rate constants for electrosorption at +600mV polarization were found to decrease in the order of NA>PA>BA.

Electrosorption based waste water treatment system using activated carbon cloth electrode: Electrosorption of benzoic acid from a flow-through electrolytic cell

An electrosorption based waste water treatment system including specially constructed flow-through electrolytic cell was designed. Electrosorptive removal of benzoic acid (BA) from dilute aqueous solutions in 0.01M Na2SO4 onto activated carbon cloth (ACC) electrode was carried out with this system. Kinetics of both adsorption and electrosorption were followed by an online UV–Vis spectrophotometric analysis method. The data were successfully treated according to pseudo-first-order law and rate constants were determined. Appreciable increase, compared to open circuit adsorption, was obtained in the removal rate of BA by electrosorption. Effects of operating parameters such as applied potential and volumetric flow rate on electrosorption were examined. Optimum conditions for the process were found to be 30mLmin−1 for flow rate and +600mV for polarization. The capacity of ACC under these conditions for electrosorption of BA was found as 180 (mgg−1) upon four successive electrosorption steps. An in-situ regeneration procedure applied at this saturation point caused 155 (mgg−1) of electrosorbed BA to electrodesorb upon −900mV polarization, corresponding to about 86% regeneration of ACC.

Electrochemical oxidation of benzoic acid in water over boron-doped diamond electrodes: Statistical analysis of key operating parameters, kinetic modeling, reaction by-products and ecotoxicity

The electrochemical oxidation of benzoic acid over boron-doped diamond electrodes was studied. Experiments were conducted in a flow-through electrolytic cell at current intensities ranging from 11 to 24 A, an electrolyte concentration of 0.05 M and initial substrate concentrations ranging from 16 to 185 mg L −1. Liquid chromatography (LC) coupled to diode array detector was employed to follow benzoic acid concentration profiles, while chemical oxygen demand and dissolved organic carbon (DOC) analyses were carried out to assess the extent of mineralization. In preliminary experiments, the effect of different electrolytes (NaNO 3, NaCl or Na 2SO 4) and the initial pH of the solution (10 or 3.8) was evaluated. The effects of operating parameters such as applied current intensity, electrolysis time and initial benzoic acid concentration on the degradation and mineralization efficiency were investigated with the application of factorial design methodology and simple linear models describing and predicting adequately the removal of the substrate and DOC were developed. The initial substrate concentration and the treatment time constitute important parameters with regard to the efficiency of the process. Benzoic acid conversion proceeds through the hydroxylation of the aromatic ring as evidenced by the formation of several hydroxylated derivatives identified by LC coupled to mass spectroscopy (LC/MS-MS). Of these, monohydroxybenzoic acids appear to be quite stable to electrochemical oxidation. Toxicity tests with marine bacteria V. fischeri showed that, at the conditions in question, degradation by-products are consistently more toxic than the parent compound even after deep oxidation.

H2S(g) Removal Using a Modified, Low-pH Liquid Redox Sulfur Recovery (LRSR) Process with Electrochemical Regeneration of the Fe Catalyst Couple

A modified pH 1.0 liquid redox sulfur recovery (LRSR) process, based on reactive absorption of H(2)S((g)) in an acidic (pH 1.0) iron solution ([Fe(III)] = 9-8 g L(-1), [Fe(II)] = 1-2 g L(-1)) and electrochemical regeneration of the Fe(III)/Fe(II) catalyst couple, is introduced. Fe(II) was oxidized in a flow-through electrolytic cell by Cl(2(aq)) formed on a Ti/RuO(2) anode. pH 1.0 was applied to retard the potential precipitation of predominantly jarosite group Fe(III) species. At pH 1.0, the presence of chloride ions at [Cl(-)] = 30 g L(-1) allows for both efficient (indirect) electrochemical oxidation of Fe(II) and efficient H(2)S((g)) reactive absorption. The latter observation was hypothesized to be associated with higher concentrations of Fe(III)-Cl complexes that are more highly reactive toward H(2)S((aq)) than are free Fe(III) ions and Fe-SO(4) complexes that otherwise dominate pH 1.0 Fe(III) solutions in the absence of a significant Cl(-) concentration. At the described operational conditions the rate of Fe(II) oxidation in the experimental system was 0.793 kg Fe h(-1) per m(2) anode surface area, at a current efficiency of 58%. Electricity cost within the electrochemical step was approximated at $0.9 per kg H(2)S((g)) removed.

Electrodeposition of copper and lead on palm shell activated carbon in a flow-through electrolytic cell

Palm shell is an abundant solid waste generated from the palm oil industry in Malaysia. Activated carbon obtained from palm shells has good electrochemical properties and may be used as a working electrode material to remove ions of heavy metals from industrial wastewaters. Results are presented on the electrodeposition of copper and lead ions onto palm shell activated carbon electrodes in terms of current efficiency (%). The study was carried out in a continuous packed-bed electrochemical cell. The effects of applied current, solution flow rate, pH of the feed, and presence of complexing agents namely malonic and boric acids on the overall current efficiency were investigated. The results showed that the current efficiency increases with an increase of the flow rate. The application of more negative current to the electrolytic cell resulted in the decrease of current efficiency values. Presence of malonic acid resulted in a relative increase of the current efficiency compared to the single metal system for both pH 3 and 5. The presence of boric acid also resulted in a similar overall increase of the current efficiency. The concentration of the solution leaving the cell strongly depended on the current values applied as well as the solution flow rate; for copper it varied between 0–20 mg/L, and for lead it was between 0–5 mg/L from an inlet value of 50 mg/L for both ions.

Electrochemical treatment of textile dyes and dyehouse effluents

The electrochemical oxidation of textile effluents over a titanium–tantalum–platinum–iridium anode was investigated. Batch experiments were conducted in a flow-through electrolytic cell with internal recirculation at current intensities of 5, 10, 14 and 20 A, NaCl concentrations of 0.5, 1, 2 and 4% and recirculation rates of 0.81 and 0.65 L/s using a highly colored, synthetic effluent containing 16 textile dyes at a total concentration of 361 mg/L and chemical oxygen demand (COD) of 281 mg/L. Moreover, an actual dyehouse effluent containing residual dyes as well as various inorganic and organic compounds with a COD of 404 mg/L was tested. In most cases, quantitative effluent decolorization was achieved after 10–15 min of treatment and this required low energy consumption; conversely, the extent of mineralization varied between 30 and 90% after 180 min depending on the operating conditions and the type of effluent. In general, treatment performance improved with increasing current intensity and salinity and decreasing solution pH. However, the use of electrolytes not containing chloride (e.g. FeSO 4 or Na 2SO 4) suppressed degradation. Although the acute toxicity of the actual effluent to marine bacteria Vibrio fischeri was weak, it increased sharply following treatment, thus suggesting the formation of persistent toxic by-products.

Electrochemical oxidation of olive oil mill wastewaters

The electrochemical oxidation of olive oil mill wastewaters over a titanium–tantalum–platinum–iridium anode was investigated. Batch experiments were conducted in a flow-through electrolytic cell with internal recycle at voltage of 5, 7 and 9 V, NaCl concentrations of 1%, 2% and 4%, recirculation rates of 0.4 and 0.62 L/s and initial chemical oxygen demand (COD) concentrations of 1475, 3060, 5180 and 6545 mg/L. The conversion of total phenols and COD as well as the extent of decolorization generally increased with increasing voltage, salinity and recirculation rate and decreasing initial concentration. In most cases, nearly complete degradation of phenols and decolorization were achieved at short treatment times up to 60 min; this was accompanied by a relatively low COD removal that never exceeded 40% even after prolonged (up to 240 min) times. The consumption of energy per unit mass of COD removed after 120 min of treatment was found to be a strong function of the operating conditions and was generally low at high initial concentrations and/or reduced salinity. The acute toxicity to marine bacteria Vibrio fischeri decreased slightly during the early stages of the reaction and this was attributed to the removal of phenols. However, as the reaction proceeded toxicity increased due to the formation of organochlorinated by-products as confirmed by GC/MS analysis. The toxicity to Daphnia magna increased sharply at short treatment times and remained quite high even after prolonged oxidation.

The efficiency of the electrochemical generation of volatile hydrides studied by radiometry and atomic absorption spectrometry

Efficiencies of electrochemical generation (EcHG) of SeH 2, AsH 3 and SbH 3 in a thin layer flow-through electrolytic cell with lead as wire as the cathode were studied by atomic absorption spectrometry (AAS) and, in the case of SeH 2, by radiometry employing the radiotracer 75Se. The influence of relevant experimental parameters was investigated. The parameters studied were: electrolytic current; catholyte type (HCl, H 2SO 4), flow rate and concentration; the age of the lead cathode; analyte concentration and carrier gas flow rate. The influence of the most critical experimental parameters, i.e. electrolytic current and catholyte flow rate, on the fraction of analyte lost to the waste was determined by (wet chemical) hydride generation AAS and checked by graphite furnace AAS. These results indicate that EcHG efficiency for Se, As and Sb, respectively, in the electrolytic cell with the wire Pb cathode must be lower than 90%, 57% and 92%. The 75Se radiotracer was employed to determine SeH 2 generation efficiency and to track ways in which analyte can be lost in the course of EcHG. The tracer experiments proved that the EcHG efficiency for selenium (72±2%) is lower than that estimated from analyte fraction lost to the waste – by the analyte fraction retained at all surfaces. Possible ways of improving the efficiency of EcHG are suggested.

Flow-injection chemiluminescence detecting sulfite with in situ electrogenerated Mn 3+ as the oxidant

By designing a novel flow-through electrolytic cell, the Mn 3+ was firstly in situ generated electrochemically on the near surface of the platinum electrode by constant current oxidizing MnSO 4 in H 2SO 4 medium. It was then found that this Mn 3+ could oxidize sulfite, which was injected into the electrolytic cell, to produce the strong chemiluminescence (CL) emission signal. Based on this observation, a novel CL method for sulfite is developed in this paper. Under the optimum conditions developed, the CL emission intensity was linear with sulfite concentration in the range 3.0×1.0 −7 to 1.0×10 −4 mol/l ( r=0.9998). The detection limit was 8.0×10 −8 mol/l original concentration. The method was successfully used for the determination of SO 2 in the air sample.

Flow Injection Chemiluminescence Determination of Captopril with In Situ Electrogenerated Mn3+ as the Oxidant

By designing a novel flow-through electrolytic cell, a new flow-injection electrogenerated chemiluminescence method for the determination of captopril is described. It is based on the direct chemiluminescence oxidation of captopril by nascent Mn3+ which was in situ electrogenerated on the near surface of the platinum flake electrode by electrochemical oxidizing MnSO4 in sulfuric acid medium. The proposed procedure has a linear application range of 3.0×10−7–1.0×10−4 mol/L for captopril (r=0.9998) and with a detection limit of 8.0×10−8 mol/L original concentration. Designing of the flow-through electrolytic cell as well as some experimental conditions for the determination of captopril are optimized and the possible reaction mechanism is also discussed. The method was successfully used for the determination of captopril in a pharmaceutical preparation.

Flow-injection chemiluminescence determination of tetracyclines with in situ electrogenerated bromine as the oxidant

By designing a novel flow-through electrolytic cell (FEC), bromine was produced near to the surface of the platinum electrode by electrochemical oxidation of acidic KBr. The fast and weak chemiluminescence signal produced by the chemical reaction of the electrogenerated bromine with H 2O 2 was greatly enhanced by tetracyclines Based on these observations, a new, sensitive and simple electrogenerated chemiluminescence (ECL) method for the determination of tetracyclines was developed. Under the optimum experimental conditions, the calibration graphs are linear over the range 3.0×10 −8 to 5.0×10 −5 g ml −1 for tetracycline, 2.0×10 −7 to 2.4×10 −5 g ml −1 for oxytetracycline and 1.0×10 −7 to 5.0×10 −5 g ml −1 for chlortetracycline. The limits of detection ( S/ N=3) are 1.0×10 −8 g ml −1 for tetracycline, 7.0×10 −8 g ml −1 for oxytetracycline and 1.5×10 −7 g ml −1 for chlortetracycline. For the determination 5.0×10 −7 g ml −1 tetracycline, the relative standard deviation was <5%. The proposed method was used to determine tetracyclines in pharmaceutical formulations.

Flow Injection Chemiluminescence Determination of Hydrogen Peroxide with in-Situ Electrogenerated Br2 as the Oxidant

ABSTRACT By designing a novel flow-through electrolytic cell, Br2, an unstable and toxic reagent, can be produced in-situ on the near region of a platinum electrode surface by constant current oxidizing KBr in H2SO4 medium. At the same time, it was found that a strong CL signal was produced when the basic H2O2 solution was injected into the electrolytic cell. Based on this observation, a simple, rapid and selective ECL method for the determination of H2O2 was proposed. Factors affecting the determination of H2O2, including the chemical and flow-injection parameters as well as the design of flow-through electrolytic cell, were investigated, and the possible ECL reaction mechanism was also discussed. Under the optimum conditions, the ECL emission intensity was linear with H2O2 concentration in the range of 1.0x10−6 − 4.0x10−3 mol/L and with 3.5x10−7 mol/L detection limit.

Determination of nickel using electrochemical reduction and carbonyl generation with in situ trapping electrothermal atomic absorption spectrometry†

A method is described for the determination of nickel at sub-ng g–1 concentration levels. Electrochemical reduction of nickel in a flow-through electrolytic cell is followed by the generation and transfer of volatile Ni(CO)4 to a graphite furnace where it is decomposed and trapped. Nickel is atomised and determined by atomic absorption spectrometry. The system has an overall efficiency of about 70% and gives a detection limit of 87 ng l–1, based on a 1.0 ml sample volume. Limitations of the method are described; changes of the working electrode surface are shown to have a major influence on the reliability and sensitivity of the method. A method based on the chemical reduction of nickel using NaBH4 was used for comparison. The methods were validated by the determination of nickel in a water reference material.

On-Line Elimination of Electroactive Interferents for Flow-Type Electrochemical Biosensor System

Abstract A flow-through electrolytic cell (electrochemical filter; ECF) was newly designed for the elimination of electroactive interferents with electrochemical biosensors. The ECF has been combined with a glucose oxidase monolayer electrode in a flow injection analysis (FIA) setup. The addition of ferricyanide to the carrier buffer drastically increased the elimination efficiency for L-ascorbic acid and the biosensor output. Glucose content in soft drinks has been determined without any pretreatment.

On-line electrolytic dissolution of alloys in flow-injection analysis. Part 3. Multi-elemental analysis of stainless steels by inductively coupled plasma atomic emission spectrometry

The simultaneous determination of chromium, nickel, manganese, silicon and iron in stainless steels was achieved by inductively coupled plasma atomic emission spectrometry (ICP-AES) after on-line electrodissolution using an improved flow-through electrolytic cell. The solution containing the electrodissolved ions was impelled by an air carrier stream in a flow-injection manifold towards a mixing-dilution chamber. From this chamber, the diluted and homogenized solution was aspirated and nebulized into the ICP torch. A quantification procedure is proposed for direct solid analysis without the use of certified reference materials. Under the proposed electrolysis conditions, up to 60 solid samples can be analysed per hour. Results obtained for alloying elements in austenitic and ferritic stainless steels were in good agreement with the certified values.