Ali Özcan

Electrochemical Treatment of the Antibiotic Sulfachloropyridazine: Kinetics, Reaction Pathways, and Toxicity Evolution

The electro-Fenton treatment of sulfachloropyridazine (SCP), a model for sulfonamide antibiotics that are widespread in waters, was performed using cells with a carbon-felt cathode and Pt or boron-doped diamond (BDD) anode, aiming to present an integral assessment of the kinetics, electrodegradation byproducts, and toxicity evolution. H(2)O(2) electrogeneration in the presence of Fe(2+) yielded (•)OH in the solution bulk, which acted concomitantly with (•)OH adsorbed at the anode (BDD((•)OH)) to promote the oxidative degradation of SCP (k(abs,SCP) = (1.58 ± 0.02) × 10(9) M(-1) s(-1)) and its byproducts. A detailed scheme for the complete mineralization was elucidated. On the basis of the action of (•)OH onto four different SCP sites, the pathways leading to total decontamination includes fifteen cyclic byproducts identified by HPLC and GC-MS, five aliphatic carboxylic acids, and a mixture of Cl(-), SO(4)(2-), NH(4)(+), and NO(3)(-) that accounted for 90-100% of initial Cl, S, and N. The time course of byproducts was satisfactorily correlated with the toxicity profiles determined from inhibition of Vibrio fischeri luminescence. 3-Amino-6-chloropyridazine and p-benzoquinone were responsible for the increased toxicity during the first stages. Independent electrolyses revealed that their toxicity trends were close to those of SCP. The formation of the carboxylic acids involved a sharp toxicity decrease, thus ensuring overall detoxification.

Removal of Acid Orange 7 from water by electrochemically generated Fenton's reagent.

The removal of azo dye Acid Orange 7 (AO7) from water was investigated by the electro-Fenton technology using electrogenerated hydroxyl radicals (OH) which leads to the oxidative degradation of AO7 up to its complete mineralization. H(2)O(2) and Fe (II) ions are electrogenerated in a catalytic way at the carbon-felt cathode. AO7 decay kinetics and evolution of its oxidation intermediates were monitored by high-performance liquid chromatography. The absolute rate constant of AO7 hydroxylation reaction has been determined as (1.20+/-0.17)x10(10)M(-1)s(-1). The optimal current value for the degradation of AO7 was found as 300 mA. AO7 degradation rate was found to decrease by increase in Fe(3+) concentration beyond 0.1mM. Mineralization of AO7 aqueous solutions was followed by total organic carbon (TOC) measurements and found to be 92%. Based on TOC evolution and identification of aromatic intermediates, short-chain carboxylic acids and inorganic ions released during treatment, a plausible mineralization pathway was proposed.

Propham mineralization in aqueous medium by anodic oxidation using boron-doped diamond anode : Influence of experimental parameters on degradation kinetics and mineralization efficiency

This study aims the removal of a carbamate herbicide, propham, from aqueous solution by direct electrochemical advanced oxidation process using a boron-doped diamond (BDD) anode. This electrode produces large quantities of hydroxyl radicals from oxidation of water, which leads to the oxidative degradation of propham up to its total mineralization. Effect of operational parameters such as current, temperature, pH and supporting electrolyte on the degradation and mineralization rate was studied. The applied current and temperature exert a prominent effect on the total organic carbon (TOC) removal rate of the solutions. The mineralization of propham can be performed at any pH value between 3 and 11 without any loss in oxidation efficiency. The propham decay and its overall mineralization reaction follows a pseudo-first-order kinetics. The apparent rate constant value of propham oxidation was determined as 4.8 x 10(-4)s(-1) at 100 mA and 35 degrees C in the presence of 50mM Na(2)SO(4) in acidic media (pH: 3). A general mineralization sequence was proposed considering the identified oxidation intermediates.

A novel approach for the selective determination of tryptophan in blood serum in the presence of tyrosine based on the electrochemical reduction of oxidation product of tryptophan formed in situ on graphite electrode.

In this study, a novel method was proposed for the selective determination of tryptophan (TRP) in blood serum in the presence of tyrosine. This method is based on the electrochemical reduction of 2-amino-3-(5-oxo-3,5-dihydro-2H-indol-3-yl)-propionic acid (5-O-3,5DH-TRP) formed by the oxidation of TRP on the electrochemically treated pencil graphite (ETPG) electrode surface at a suitable potential value. The parameters affecting the TRP determination were deeply investigated. The optimal pH value was determined as 3. The highest reduction current intensity was obtained at the accumulation potential and time values of +0.95 V and 120 s, respectively. The reduction peak current values of 5-O-3,5DH-TRP versus TRP concentration at the ETPG electrode showed linearity in the range from 0.5 μM to 50.0 μM (R(2)=0.9962) with a detection limit of 0.05 μM (S/N=3). The reduction peak intensity of 5-O-3,5DH-TRP on the ETPG electrode showed no significant change in the presence of different interfering substances. The analytical application of the proposed novel method was successfully tested by using human blood serum samples.

Preparation of selective and sensitive electrochemically treated pencil graphite electrodes for the determination of uric acid in urine and blood serum

In this study, the preparation of electrochemically treated pencil graphite (ETPG) electrodes in the mixture of lithium perchlorate and sodium carbonate solutions was investigated for the first time in the literature. The prepared ETPG electrodes showed high selectivity and sensitivity for uric acid (UA) oxidation over ascorbic acid and dopamine. Differential pulse voltammetry (DPV) was used as electrochemical method. The parameters affecting the UA oxidation were investigated. The optimal pH for UA oxidation was determined as 2. The adsorption of UA on ETPG surface reached saturation in 180s. The oxidation peak current values versus UA concentration at the ETPG electrode showed linearity in the range from 0.05 microM to 10.0 microM (R(2)=0.9962) with a detection limit of 1.5 nM (S/N=3). The oxidation peak of UA on the ETPG electrode did not show any significant change in the presence of certain interferents except bovine serum albumin. The prepared electrodes showed good fabrication reproducibility. The analytical applications of the prepared electrodes were tested by using human urine and blood serum samples. The recovery results of different amounts of UA in urine were varied between 98.6% and 106.4% implying no matrix effect. It was observed that the standard addition method was more satisfactory in the case of blood serum samples.

Removal of propham from water by using electro-Fenton technology: kinetics and mechanism.

The removal of a carbamate herbicide, propham, from aqueous solution has been carried out by the electro-Fenton process. Hydroxyl radical, a strong oxidizing agent, was generated catalytically and used for the oxidation of propham aqueous solutions. The degradation kinetics of propham evidenced a pseudo-first order degradation. The absolute rate constant of second order reaction kinetics between propham and ()OH was determined as (2.2+/-0.10)x10(9)m(-1)s(-1). The mineralization of propham was followed by the organic carbon (TOC) removal. The optimal Fe(3+) concentration was found as 0.5mM at 300 mA. The 94% of initial TOC of 0.25 mM propham solution was removed in 8h at the optimal conditions by using the cathode area to solution volume ratio of 3.33 d m(-1). The maximum mineralization current efficiency values were obtained at 60 mA in the presence of 0.5mM Fe(3+). During the electro-Fenton treatment, several degradation products were formed. These intermediates were identified by using high performance liquid chromatography, liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry and ion chromatography analysis. The identified by-products allowed proposing a pathway for the propham mineralization.

A novel approach for the determination of paracetamol based on the reduction of N-acetyl-p-benzoquinoneimine formed on the electrochemically treated pencil graphite electrode.

A novel approach was proposed for the simple and rapid electrochemical determination of paracetamol (PC) in the presence of uric acid in body fluids. The voltammetric determination of PC is based on the electrochemical reduction of N-acetyl-p-benzoquinoneimine formed simultaneously on the electrochemically treated pencil graphite (ETPG) electrode during the measurement. ETPG electrodes were prepared by the potential cycling between -0.3V and +2.0V in 0.1M H(3)PO(4) solution. The electrochemical performance of the ETPG electrode was evaluated by adsorptive transfer stripping differential pulse voltammetry (ATSDPV). The resulting sensor showed good performance for the determination of PC in human blood serum samples with a linear range of 0.05-2.5 μM and a highly reproducible response (RSD of 3.1%). The calculated detection limit was 2.5 nM (S/N=3). The proposed method does not require any sample pretreatment, prevents the interference of uric acid and allows the determination of PC directly in blood serum samples.

Complete removal of the insecticide azinphos-methyl from water by the electro-Fenton method – A kinetic and mechanistic study

The removal of organophosphorous insecticide azinphos-methyl (AZPM) from water has been investigated by the electro-Fenton method which produces hydroxyl radicals electro-catalytically. The reaction between these radicals and AZPM has led to the oxidation of AZPM up to carbon dioxide and inorganic ions indicating its complete removal from water. The oxidation kinetics was fitted to pseudo-first order reaction and absolute rate constant of the second order reaction kinetic was determined as (6.82 ± 0.18) × 10(9) M(-1) s(-1) by using competitive kinetics method. The oxidation of AZPM by hydroxyl radicals leads to the formation of different intermediates species; such as aromatic derivatives, short-chain carboxylic acids and inorganic ions as end products. The identification and quantification of these intermediates were deeply investigated by HPLC, GC-MS and ion chromatography analyses. Based on the identified intermediates, a general oxidation mechanism was proposed. Mineralization ability of the process was also tested by using aqueous AZPM solutions and its commercial formulation, Gusathion M WP 25 (GMWP25). Mineralization efficiency was followed by the chemical oxygen demand (COD) analysis of treated solutions. The overall mineralization of synthetic AZPM solution and that of commercial formulation at the end of treatment highlights the outstanding mineralization power of the electro-Fenton process.

Electro-Fenton treatment of aqueous Clopyralid solutions

The removal of Clopyralid (CLPYD) from aqueous solutions was performed by the electro-Fenton process in which hydroxyl radicals are produced electrocatalytically and used to degrade the persistent organic pollutants. The decay kinetics well fitted to pseudo-first order reaction and absolute rate constant of the oxidation reaction of CLPYD was determined as (4.4 ± 0.2) × 108 M–1 s–1. The oxidation intermediates of CLPYD were identified by HPLC and IC analysis. Based on these intermediates, a general oxidation mechanism was proposed in acid medium. Mineralisation ability of the system was followed by the chemical oxygen demand (COD) analysis. The obtained results showed that the CLPYD aqueous solutions were efficiently mineralised during the electro-Fenton treatment.

Development of a disposable and low-cost electrochemical sensor for dopamine detection based on poly(pyrrole-3-carboxylic acid)-modified electrochemically over-oxidized pencil graphite electrode

In this study, preparation of a single-use electrochemical sensor for the selective and sensitive determination of dopamine (DOP) was investigated by electrochemical polymerization of pyrrole-3-carboxylic acid on electrochemically over-oxidized pencil graphite electrode (p(P3CA)/EOPGE). Cyclic voltammetry measurements of Fe(CN)64-/3- indicated that the electrochemically over-oxidized PGE (EOPGE) showed superior electron transfer characteristics according to bare PGE. The ionized carboxyl groups found in the structure of poly(pyrrole-3-carboxylic acid) (p(P3CA)) showed high affinity towards positively charged DOP. The combination of the advantages of EOPGE and p(P3CA) in p(P3CA)/EOPGE led to a synergistic effect on the electrochemical oxidation of DOP. The effects of experimental variables on the voltammetric performance of the p(P3CA)/EOPGE were examined by preparing the electrodes at different conditions. The p(P3CA)/EOPGE showed high selectivity towards DOP by discriminating its oxidation potential from the common interfering substances such as ascorbic and uric acids. The p(P3CA)/EOPGE showed linear responses in the electrochemical oxidation of DOP between the concentration values of 0.025µM and 7.5µM. Detection limit was determined as 0.0025µM according to signal to noise ratio (S/N: 3). Analytical application of p(P3CA)/EOPGE was successfully tested in the determination of DOP in blood serum and pharmaceutical samples.