Alexandros Katsaounis

Electrochemical enhancement of solar photocatalysis: degradation of endocrine disruptor bisphenol-A on Ti/TiO2 films.

The photoelectrocatalytic oxidation over immobilized Ti/TiO(2) films in the presence of simulated solar light was investigated for the degradation of bisphenol-A (BPA) in water. The catalyst, consisting of 75:25 anatase:rutile, was prepared by a sol-gel method and characterized by cyclic voltammetry, X-ray diffraction and scanning electron microscopy. Experiments were conducted to assess the effect of applied current (0.02-0.32 mA/cm(2)), TiO(2) loading (1.3-9.2 mg), BPA concentration (120-820 μg/L), initial solution pH (1 and 7.5) and the aqueous matrix (pure water and treated effluent) on BPA photoelectrocatalytic degradation which was monitored by high performance liquid chromatography equipped with a fluorescence detector. The reaction was favored at anodic currents up to 0.04 mA/cm(2) and lower substrate concentrations, but it was hindered by the presence of residual organic matter and radical scavengers (e.g. bicarbonates) in treated effluents. Moreover, a pseudo-first order kinetic model could fit the experimental data well with the apparent reaction constant taking values between 2.9 and 32.4 10(-3)/min. The degradation of BPA by pure photocatalysis or electrochemical oxidation alone was also studied leading to partial substrate removal. In all cases, the contribution of applied potential to photocatalytic degradation was synergistic with the photocatalytic efficiency increasing between 24% and 97% possibly due to a more efficient separation and utilization of the photogenerated charge carriers. The effect of photoelectrocatalysis on the ecotoxic and estrogenic properties of BPA was also evaluated measuring the bioluminescence inhibition of Vibrio fischeri and performing the yeast estrogen screening assay, respectively.

Anodic oxidation of textile dyehouse effluents on boron-doped diamond electrode

The electrochemical oxidation of textile effluents over a boron-doped diamond anode was investigated in the present study. Experiments were conducted with a multi-component synthetic solution containing seventeen dyes and other auxiliary inorganics, as well as an actual effluent from a textile dyeing process. The effect of varying operating parameters, such as current density (4-50 mA/cm2), electrolyte concentration (0.1-0.5 M HClO4), initial solution pH (1-12.3) and temperature (22-43 °C), on process efficiency was investigated following changes in total organic carbon (TOC), chemical oxygen demand (COD) and color. Complete decolorization accompanied by significant mineralization (up to 85% depending on the conditions) could be achieved after 180 min of treatment. Performance was improved at higher electrolyte concentrations and lower pH values, while the effect of temperature was marginal. Energy consumption per unit mass of COD removed was favored at lower current densities, since energy was unnecessarily wasted to side reactions at higher densities.

Electrochemical oxidation of model compounds and olive mill wastewater over DSA electrodes: 1. The case of Ti/IrO2 anode

The electrochemical oxidation of olive mill wastewater (OMW) and model compounds over a Ti/IrO(2) anode was studied by means of cyclic voltammetry and bulk electrolysis. Experiments were conducted at 1300 mg/L initial COD, 0-1.23V vs SHE and 1.4-1.54V vs SHE potential windows, 50 mA/cm(2) current density, 0-25 mM NaCl, 60-80 degrees C temperature and acidic conditions. The reactivity of model compounds decreases in the order phenol approximately p-coumaric acid>cinnamic acid>caffeic acid. Partial and total oxidation reactions occur with the overall rate following zero-order kinetics with respect to COD and increasing with temperature. Oxidation of OMW at 43 Ah/L, 80 degrees C and in the presence of 5mM NaCl leads to complete color and phenols removal, elimination of ecotoxicity but moderate (30%) COD reduction. Similar performance can be achieved at 6 Ah/L in the presence of 15 mM NaCl. In the absence of salt, the respective color and phenols removal (at 6 Ah/L) is less than 10%. Excessive salinity (25 mM), although does not change color, phenols and COD removal, has an adverse effect on ecotoxicity.

Electrochemical oxidation of stabilized landfill leachate on DSA electrodes

The electrochemical oxidation of stabilized landfill leachate with 2960 mg L(-1) chemical oxygen demand (COD) over a Ti/IrO(2)-RuO(2) anode was investigated in the presence of HClO(4) as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80°C), current density (8, 16 and 32 mA cm(-2)), initial effluents pH (0.25, 3, 5 and 6), HClO(4) concentration (0.25 and 1M) and the addition of NaCl (20 and 100mM) or Na(2)SO(4) (20mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluents pH and the addition of salts. Treatment for 240 min at 32 mA cm(-2) current density, 80°C and the pH adjusted from its inherent value of 0.25 (i.e. after the addition of HClO(4)) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35 kWh kg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWh kg(-1) COD removed.

Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO2 in alkaline media.

Reprint of: Electrochemical oxidation of stabilized landfill leachate on DSA electrodes ☆

The electrochemical oxidation of stabilized landfill leachate with 2960 mgL(-1) chemical oxygen demand (COD) over a Ti/IrO2-RuO2 anode was investigated in the presence of HClO4 as the supporting electrolyte. Emphasis was given on the effect of electrolysis time (up to 240 min) and temperature (30, 60 and 80 °C), current density (8, 16 and 32 mAcm(-2)), initial effluents pH (0.25, 3, 5 and 6), HClO4 concentration (0.25 and 1M) and the addition of NaCl (20 and 100 mM) or Na2SO4 (20 mM) as source of extra electrogenerated oxidants on performance; the latter was evaluated regarding COD, total carbon (TC), total phenols (TPh) and color removal. Moreover, the anode was studied by scanning electron microscopy and cyclic voltammetry. The main parameters affecting the process were the effluents pH and the addition of salts. Treatment for 240 min at 32 mAcm(-2) current density, 80 °C and the pH adjusted from its inherent value of 0.25 (i.e., after the addition of HClO4) to 3 yielded 90% COD, 65% TC and complete color and TPh removal at an electricity consumption of 35kWhkg(-1) COD removed. Comparable performance (i.e. 75% COD reduction) could be achieved without pH adjustment but with the addition of 100mM NaCl consuming 20 kWhkg(-1) COD removed.

Photoelectrocatalytic disinfection of water and wastewater: Performance evaluation by qPCR and culture techniques

Photoelectrocatalytic oxidation (PEC) was evaluated as a disinfection technique using water and secondary treated wastewater spiked with Escherichia coli and Enterococcus faecalis. PEC experiments were carried out using a TiO(2)/Ti-film anode and a zirconium cathode under simulated solar radiation. Bacterial inactivation was monitored by culture and quantitative polymerase chain reaction (qPCR). Inactivation rates were enhanced when the duration of the treatment was prolonged and when the bacterial density and the complexity of the water matrix were decreased. E. coli cells were reduced by approximately 6 orders of magnitude after 15 min of PEC treatment in water at 2V of applied potential and an initial concentration of 10(7) CFU/mL; pure photocatalysis (PC) led to about 5 log reduction, while electrochemical oxidation alone resulted in negligible inactivation. The superiority of PEC relative to PC can be attributed to a more efficient separation of the photogenerated charge carriers. Regarding disinfection in mixed bacterial suspensions, E. coli was more susceptible than E. faecalis at a potential of 2V. The complex composition of wastewater affected disinfection efficiency, yielding lower inactivation rates compared to water treatment. qPCR yielded lower inactivation rates at longer treatment times than culture techniques, presumably due to the fact that the latter do not take into account the viable but not culturable state of microorganisms.

Preface to the Special Issue

This special issue of Topics in Catalysis is dedicated to Professor Constantinos (Costas) G. Vayenas on the occasion of his 65th birthday and in recognition of his outstanding contributions to the field of heterogeneous catalysis and electrochemistry, in particular in electrocatalysis, promotion and metal-support interactions. The manuscripts were submitted in response to direct invitations from the guest editors, and consist of contributions from well-known scientists in the above fields. All the manuscripts followed the peer-review process of the Journal. The guest editors are grateful to the authors for their excellent work. Costas Vayenas studied Chemical Engineering at the National Technical University of Athens (NTU, 1968–1973) and received his PhD from the University of Rochester in NY, USA in 1976. He then taught as Assistant Professor at Yale University (1976–1977) and as Assistant and Associate Professor at the Massachusetts Institute of Technology (LIS, 1977–1982). Since 1982 he is Professor of Chemical Engineering at the University of Patras. He has also been Visiting Professor at Yale, EPFL (Lausanne) and the University of Lyon. His research focuses in the areas of Catalysis, Electrochemistry and mathematical modeling of physicochemical phenomena. He has coauthored 250 refereed publications in International Journals, four of them in the journals Science and Nature. He has received several international Awards which include the Outstanding Achievement Award of the High Temperature Materials Division of the Electrochemical Society (ECS) in 1996, the Wason Medal for Materials Research of the American Concrete Institute in 1992, the Chemistry Award of the Academy of Athens in 1992, and the Outstanding Faculty Award of the Chemical Engineering Department at MIT in 1979 and 1981. Together with his coworkers at MIT and at the University of Patras he has discovered the phenomenon of the Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA effect) which is also known in the literature as the phenomenon of the Electrochemical Promotion of Catalysis (EPOC). In 2005 he was elected Fellow of the International Society of Electrochemistry (ISE), being chronologically the 14th scientist to receive this honor. He is Editor of the well known Electrochemistry book series Modern Aspects of Electrochemistry and has coauthored three books published by Springer and Marcel Dekker. He has supervised 40 PhD Theses and 12 of these PhD students have become Professors in Greek but also non-Greek (USA, China) Universities and Research Centers. In 2010 he was elected & S. Bebelis simeon@chemeng.upatras.gr