Christos Comninellis

Electrocatalysis in the electrochemical conversion/combustion of organic pollutants for waste water treatment

The electrochemical oxidation (or combustion) of organics with simultaneous oxygen evolution has been investigated using different electrode material (Pt, Ti/IrO2, Ti/SnO2). A simplified mechanism for the electrochemical oxidation or combustion of organics is presented according to which selective oxidation occurs with oxide anodes (MOx) forming the so-called higher oxide MOx+1 and combustion occurs with electrodes at the surface of which OH radicals are accumulated. Detection of OH radicals formed by water discharge at different anodes using N,N-dimethyl-p-nitrosoaniline (RNO) as a spin trap and preparative electrolysis confirm the proposed mechanism.

Electrochemistry for the environment

Basic Principles of the Electrochemical Mineralization of Organic Pollutants for Wastewater Treatment.- Importance of Electrode Material in the Electrochemical Treatment of Wastewater Containing Organic Pollutants.- Techniques of Electrode Fabrication.- Modeling of Electrochemical Process for the Treatment of Wastewater Containing Organic Pollutants.- Green Electroorganic Synthesis Using BDD Electrodes.- Domestic and Industrial Water Disinfection Using Boron-Doped Diamond Electrodes.- Drinking Water Disinfection by In-line Electrolysis: Product and Inorganic By-Product Formation.- Case Studies in the Electrochemical Treatment of Wastewater Containing Organic Pollutants Using BDD.- The Persulfate Process for the Mediated Oxidation of Organic Pollutants.- Electrocoagulation in Water Treatment.- Electroflotation.- Electroreduction of Halogenated Organic Compounds.- Principles and Applications of Solid Polymer Electrolyte Reactors for Electrochemical Hydrodehalogenation of Organic Pollutants.- Preparation, Analysis and Behaviors of Ti-Based SnO2 Electrode and the Function of Rare-Earth Doping in Aqueous Wastes Treatment.- Wet Electrolytic Oxidation of Organics and Application for Sludge Treatment.- Environmental Photo(electro)catalysis: Fundamental Principles and Applied Catalysts.- Solar Disinfection of Water by TiO2 Photoassisted Processes: Physicochemical, Biological, and Engineering Aspects.- Fabrication of Photoelectrode Materials.- Use of Both Anode and Cathode Reactions in Wastewater Treatment.

Oxidation of carboxylic acids at boron-doped diamond electrodes for wastewater treatment

Thin boron-doped diamond films have been prepared by HF CVD (hot filament chemical vapour deposition technique) on conductive p-Si substrate (Si/Diamond). The morphology of these Si/diamond electrodes has been investigated by SEM and Raman spectroscopy. The electrochemical behaviour of the Si/diamond electrodes in 1 M H2SO4 and in 1 M H2SO4 + carboxylic acids has been investigated by cyclic voltammetry. Finally, the electrochemical oxidation of some simple carboxylic acids (acetic, formic, oxalic) has been investigated by bulk electrolysis. These acids can be oxidized at Si/diamond anodes to CO2, in the potential region of water and/or the supporting electrolyte decomposition, with high current efficiency.

Oxidation of organics by intermediates of water discharge on IrO2 and synthetic diamond anodes

IrO2 and boron-doped diamond electrodes were tested by preparative electrolysis of simple model compds. in acid medium. In oxidn. reactions of more complex mechanism than simple electron transfer, these electrodes are active only at potentials of simultaneous oxygen evolution. At IrO2 electrodes, the reaction is mediated by chemisorbed oxygen, probably forming IrO3-type active sites, and yield highly selective oxidn. products at low overpotentials and with moderate current efficiency. At diamond electrodes, mediation at high overpotentials is due to physisorbed OH radicals leading to complete combustion of the org. compd. with high current efficiency. [on SciFinder (R)]

Electrochemical detoxification of a 1,4-benzoquinone solution in wastewater treatment

The electro-oxidn. of 1,4-benzoquinone in water soln. was investigated. The benzoquinone concn., intermediate products, dissolved org. C (DOC), COD, and toxicity of the oxidized soln. was monitored during oxidn. with Ti/IrO2 and Ti/SnO2 anodes (in the following text: IrO2 and SnO2 anodes). It was found that the most important parameter is the nature of the anode. With the IrO2 anode, primary oxidn. was attained, i.e. benzene ring rupture occurred, resulting in an accumulation of carboxylic acids formation as final non-toxic products. With the SnO2 anode, carboxylic acids are formed in a much faster reaction and then oxidized, giving only CO2 as the final product. Detoxification of benzoquinone soln. using both electrodes was detd. in the course of the reaction by the Microtox test, activated sludge respirometric test, and were also predicted using a developed formula. Calcd. av. toxicity, knowing the chem. compn. of the oxidized soln., DOC, and individual EC50 of the components were in agreement with obsd. values. The biodegradability of compds. in the soln. at the end of electrolysis with the IrO2 anode was demonstrated. [on SciFinder (R)]

Electrochemical oxidation of 4-chlorophenol for wastewater treatment: Definition of normalized current efficiency (Φ)

The electrochem. behavior of PbO2 and synthetic B-doped diamond thin film electrodes (BDDs) was studied in acid media contg. 4-chlorophenol (4-CP) by bulk electrolysis under different exptl. conditions. To quantify the electrochem. activity of a given electrode, for the electrochem. oxidn. of org. compds. (4-CP), the current efficiency of the anodic oxidn. was normalized taking into consideration mass-transport limitations. The normalized current efficiency (j) was defined as the ratio between the current efficiency of the investigated anode to the current efficiency of an ideal anode which has a very fast oxidn. rate, resulting in a complete combustion of orgs. to CO2. The results showed that even if the complete combustion of 4-CP was achieved at both PbO2 and BDD anodes, the latter give higher j. The difference in reactivity of the electrogenerated hydroxyl radicals on the anode surface, is proposed to explain the high j values obtained using B-doped diamond anodes. [on SciFinder (R)]

Electrochemical Behavior of Synthetic Diamond Thin Film Electrodes

The inertness and unique electrochem. properties of diamond present great potential for a variety of applications in aggressive environments. Preliminary results showed the widest known electrochem. window before water decompn., allowing new possibilities for both anodic and cathodic reactions. Studies of the oxidn. of org. compds. was performed with alcs. such as isopropanol, phenol and org. acids. Cyclic voltammetry demonstrates no activity in the potential range where water is stable. In the potential region of oxygen evolution, the org. compds. are mainly oxidized to CO2. No deactivation or redn. in the thickness of the electrode was obsd. No fouling of the diamond surface was detected. Also, no hydrodynamic effects were obsd. Concd. (1 M) and dild. (3 * 10-4 M) cyanide solns. were oxidized on diamond electrodes both in the presence and in the absence of chloride ions. The results show a direct oxidn. with a current efficiency of .apprx.40% for concd. solns. At low cyanide concns., the current efficiency is strongly increased by the presence of Cl-. Electrochem. redn. of cadmium and copper was carried out on diamond electrodes. Nonadherent deposits were obtained on diamond cathodes. [on SciFinder (R)]

Electron Transfer Kinetics on Boron-Doped Diamond Part I: Influence of Anodic Treatment

Boron-doped diamond electrodes, both as-grown and polarized anodically under different conditions, were prepared in order to study the chemical and electrochemical changes of diamond and clarify the role played by the surface-state density. Many different treatments were employed: as-grown (BDDag), mildly polarized (BDDmild), strongly polarized in perchloric acid (BDDsevererpar;, and strongly polarized in a sulphuric acid-acetic acid mixture (BDDAcOHrpar;. Charge transfer processes at the electrode surface were studied by cyclic voltammetry. Simple electron transfer processes such as the outer-sphere redox system ferri/ferrocyanide (FeIII/II;(CN)6rpar; and complex charge transfer reactions such as the inner-sphere 1,4-benzoquinone/hydroquinone (Q/H2Q) redox reaction were chosen to test the electrochemical properties of the electrodes. The properties of the diamond electrodes were found to undergo strong modification as a function of surface treatment. The active surface area and the reaction rate constants decreased significantly upon anodic polarization. Important drops in the charge carrier concentration on the surface and in true surface area led to hindrance of electron transfer at the electrode.

Boron doped diamond electrodes for nitrate elimination in concentrated wastewater

Electrochem. and phys. properties of polycryst. B-doped diamond electrodes with a metallic conduction grown by MPCVD and HFCVD were studied with the goal to use them as cathodes, for the electrochem. redn. of nitrate in neutral solns. All electrodes contain a mean B concn. [B] >3 * 1020/cm3 and show a significant redn. of nitrate. However, the higher efficiency is obtained for the electrode having the highest [B] (1.5 * 1021/cm3) and the lowest concn. of parasitic phases. The anal. of the Raman spectrum proved to be a valuable tool to probe these characteristics. Quant. anal. of the solns. showed that the relative concns. of the nitrogenous species formed during the redn. of nitrates at -2 V do not depend on the B doping level. [on SciFinder (R)]

Basic principles of the electrochemical mineralization of organic pollutants for wastewater treatment

The electrochemical mineralization of organic pollutants is a new technology for treatment of dilute wastewater (COD < 5 g∕L). In this method, utilizing the electrical energy, a complete oxidation of pollutants can be achieved on high oxidation power anodes. An ideal anode for this type of treatment is a boron-doped diamond electrode (BDD) characterized by a high reactivity toward organics oxidation. In the present work, both thermodynamic and kinetic aspects of organics mineralization are discussed. The proposed theoretical kinetic model of organics mineralization on BDD anodes is in excellent agreement with the experimental results. In addition, the economical aspect of electrochemical organics mineralization is reported.