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The continuous ozonation of benzalkonium chloride (BAC) and nickel oxide nanoparticles (NiO-NPs) has been performed in a synthetic water matrix and in a sewage treatment plant influent. This study aims to assess ozonation as pre-treatment of an activated sludge process, with emphasis on the toxicity of treated water. BAC was completely removed in synthetic matrix independently of the presence of NiO-NPs, although the ozone dose was influenced by NPs co-occurrence. The extent of mineralization was limited and a number of intermediate transformation products (TPs) appeared, twelve of which could be identified. The degradation pathway was shown to initiate both on the hydrophobic (alkyl chain) and hydrophilic (benzyl and ammonium moiety) region of the surfactant. The reactions on the hydrophilic region were affected by the presence of NiO-NPs as a consequence of the adsorption of BAC onto NP surface via the aromatic group. Water matrix strongly influenced BAC depletion. The aquatic toxicity of treated mixtures was assessed using a biotest battery composed of single species (the bacteria Vibrio fischeri and Pseudomonas putida and the protozoan Tetrahymena thermophila), as well as a whole biological community assay using activated sludge. Although, BAC showed considerable aquatic toxicity in all bioassays, ozonation decreased the toxic effects of treated water samples at ozone dosages below those required for total BAC depletion. Further treatment would not be justified, neither for a significant increase in BAC abatement nor concerning the toxicity of treated wastewater, which increased as a result of nickel leaching from the NPs.

Rh modified Au(111-25 nm) electrodes, prepared by electron beam evaporation and galvanostatic deposition, were employed to study adsorption and electro-oxidation of CO on Rh in 0.1 M sulfuric acid solution by in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). The results of ATR-SEIRAS experiments were compared with those obtained by infrared reflection absorption spectroscopy on three low-index Rh single crystal surfaces. The Rh film deposited on Au(111-25 nm) electrode consists of 3D clusters forming a highly stepped [n(111) × (111)]-like surface with narrow (111) terraces. When CO was dosed at the hydrogen adsorption potential region, CO adsorbed in both atop (COL) and bridge (COB) configurations, as well as coadsorbed water species, were detected on the Rh film electrode. A partial interconversion of spectroscopic bands due to the CO displacement from bridge to atop sites was found during the anodic potential scan, revealing that there is a potential-dependent preference of CO adsorption sites on Rh surfaces. Our data indicate that CO oxidation on Rh electrode surface in acidic media involves coadsorbed water and follows the nucleation and growth model of a Langmuir-Hinshelwood type reaction. The work was supported by the Research Center Jülich, the University of Bern, Swiss National Science Foundation (200020_144471, 200021-124643), the Spanish Ministerio de Economía y Competitividad (project CTQ2013-44083-P) and University of Alicante. QX acknowledges fellowships of the Research Center Jülich; IP acknowledges support by COST Action TD 1002; and AK acknowledges the financial support by CTI Swiss Competence Centers for Energy Research (SCCER Heat and Electricity Storage).

Palladium deposition on Pt(1 1 0) electrodes was studied. Differently from Pt(1 1 1) and Pt(1 0 0), first and further layers cannot be distinguished in this case only through the voltammetric behavior of hydrogen and anion adsorption. The potential of zero total charge (pztc) was determined as a function of the amount of deposited Pd using CO charge displacement experiments and voltammetric curves. The variation of the voltammetric charge due to hydrogen and anion adsorption has been followed during Pd deposition. The voltammetric charge between 0.06 and 0.4 V first decreases to a minimum, then increases and finally becomes stable, suggesting that the surface is finally covered with a Pd multilayer. The pztc and CO oxidation charge show similar behavior. CO oxidation, NO reduction and Cu UPD were used as probes to monitor Pd coverage. The potential of CO oxidation increases with Pd coverage while the potential of NO reduction decreases. Using the information obtained from Cu UDP and FTIR experiments it has been possible to determine when the first Pd single layer was completed and when a second (further) layer(s) starts to grow.

Ministerio de Educacion y Ciencia of Spain[CTQ2010-16271]; China Scholarship Council; NSFC[20833005]

In this work we report on the occurrence of at least two different redox pairs on the cell surface of the electrogenic bacteria Geobacter sulfurreducens adsorbed on gold that are expressed in response to the polarization potential. As previously reported on graphite (Environ. Sci. Technol. 42 (2008) 2445) a typical low potential redox pair is found centered at around − 0.06 V when cells are polarized for a few hours at 0.2 V, while a new pair centered at around 0.38 V is expressed upon polarization at 0.6 V. Reversible changes in the IR band pattern of whole cells where obtained by Attenuated Total Reflection-Surface Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) upon potential cycling around both redox pairs. Changes clearly resemble the electrochemical turnover of oxidized/reduced states in c-type cytochromes, thus evidencing the nature of the involved molecules. The expression of external cytochromes in response to the potential of the electron acceptor suggests the existence of alternative pathways of electron transport with different energy yield, though it remains to be demonstrated. Fil: Busalmen, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Universidad de Alicante; España Fil: Esteve-Nuñez, Abraham. Centro de Astrobiología; España Fil: Berná, Antonio. Universidad de Alicante; España Fil: Feliu, Juan Miguel. Universidad de Alicante; España

In the present work the electrooxidation of methanol, 2-propanol and different mixtures of both alcohols has been studied on the three platinum basal planes in three different electrolytes (H 2 SO 4 , HClO 4 and NaOH). The results indicate that, like in the case of both individual alcohols, the electrooxidation of the mixture is a structure sensitive reaction and that Pt(1 1 1) leads to higher current densities for some mixture compositions as compared to what could be expected from the contribution of the individual compounds. The effect of the methanol concentration in the mixture points out that 2-propanol is the main reacting fuel at the Pt(1 1 1) surface. Interestingly, the addition of methanol clearly has a positive effect on 2-propanol oxidation. For a specific mixture composition, while results from cyclic voltammetry indicate a modest twofold increase in current density, chronoamperometric results after 10 min experiment show a nearly 200 times higher current density. IR experiments have been performed to gain information about the enhancement mechanism. Nevertheless, we have found that both methanol and 2-propanol seem to follow the same mechanism as they follow in the absence of the other alcohol, and therefore the enhancement could be probably related to a competitive adsorption for the active surface sites.

The variation of electrode nature and surface structure (the use of stepped single crystal faces with controlled width of (1 1 1) terraces and monoatomic steps of (1 0 0) or (1 1 0) orientation) allows to determine peculiarities of co-adsorption of acetonitrile molecules, hydrogen adatoms and (bi)sulfate anions. It has been shown that first of all acetonitrile blocks adsorption sites at the steps. Anion adsorption at terraces of stepped platinum surfaces in 0.5 M H2SO4 solution with additions of acetonitrile depends on terrace width and the step orientation. This demonstrates the important role of structural factors in competitive adsorption processes. The decrease in adsorption of hydrogen and anions on narrow terraces is substantially due to the influence of acetonitrile molecules placed at the steps or nearby sites. At E < 1.0 V, electrochemical conversion of acetonitrile has not been detected at single crystal Pt surfaces. However, acetonitrile oxidation might proceed on polycrystalline platinum followed by product desorption. On Au(1 1 1) surface acetonitrile adsorption is considerably weaker than that on platinum electrodes.

Conventional electrochemical methods have been applied to study the oxidation of a possible alternative fuel for a direct oxidation fuel cell. The electrooxidation of dimethoxymethane (DMM) was investigated on the three low index planes, (1 0 0), (1 1 0) and (1 1 1) of platinum single crystals and compared with its oxidation on a platinum polycrystalline electrode. Among platinum electrodes, electroreactivity of DMM observed is Pt(1 1 1) > Pt(1 0 0) > Pt(1 1 0) ∼ Pt poly. Hydrogen adsorption is limited by the presence of DMM, except for Pt(1 1 1) plane. In situ IR experiments show the presence of bands of COads with all electrodes except Pt(1 1 1). This work shows that the mechanism of DMM electrooxidation is structure sensitive. A path takes place on Pt(1 0 0) and Pt(1 1 0) which is favourable to the formation of COads. Another path proceeds on Pt(1 1 1), where COads is not present and reaction does not occur at low potential. Results indicate that peak intensities are higher in perchloric acid than in sulphuric acid. So DMM adsorption is dependent on the specific adsorption of the anions. In situ IR reflectance spectroscopy identified some intermediates and reaction products of DMM adsorption and electrooxidation on Pt electrodes: COL (linearly bonded) and COB (bridge bonded), adsorbed CHO and CH3O species, methanol and CO2. The electrochemical and spectroelectrochemical experiments suggest a complex mechanism of DMM electrooxidation.

Acetate adsorption at gold electrodes is studied in perchloric acid solutions by cyclic voltammetry and in-situ infrared spectroscopy. External reflection measurements, performed with gold single crystal electrodes, are combined with Surface Enhanced Infrared Reflection Absorption Spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) carried out with sputtered gold thin-film electrodes. Theoretical harmonic IR frequencies of acetate species adsorbed with different geometries on Au clusters with (1 1 1), (1 0 0) and (1 1 0) orientations have been obtained from B3LYP/LANL2DZ, 6–31 + G* calculations. The theoretical and experimental results confirm that, irrespective of the surface crystallographic orientation, bonding of acetate to the surface involves the two oxygen atoms of the carboxylate group, with the OCO plane perpendicular to the metal surface. DFT calculations reveal also that the total charge of the metal cluster–acetate supermolecule has small effect on the vibrational frequencies of adsorbed acetate species. Both the external and the internal reflection measurements show the co-adsorption of acetate and perchlorate anions. Step-scan measurements carried out with the gold thin-film electrodes have allowed the monitoring of the time-dependent behaviour of perchlorate, acetate and water bands in potential step experiments. Acetate adsorption under those conditions is shown to involve perchlorate desorption and to follow a Langmuir-type kinetics. The step-scan spectra also show the rise and decay of transient water structures with parallel time-dependent shifts of the background intensity in the infrared spectra.

The adsorption of hydroxyl on Pt(111) single crystal electrodes from aqueous acidic solutions is carefully reinvestigated. The effect of small additions (10−8–10−5 M) of chloride and bisulphate anions on the OH adsorption region in perchloric acid solution has been studied. Two regions can be differentiated in the voltammetric profile, that behave differently after the addition of the foreign anion. The initial broad adsorption process is unaffected until the highest concentration is attained. However, the sharper peak at higher potentials is affected even at the lower anion concentration. Since mass transport limitations allow to discard the anion adsorption as the main process giving this peak, we propose that the two processes are due to the dissociative adsorption of two different kinds of water, that are affected by the anion in a different way. From this idea, a new model, based on the Frumkin adsorption isotherm, is proposed, which gives an excellent fit of the experimental results. Keywords: Pt(111), Single crystal electrodes, Hydroxyl adsorption, Anion adsorption, Frumkin isotherm

The formation of submonolayers of palladium on well-defined Pt(1 0 0) electrodes is described. It has been found that the adsorption of NO at open circuit and its further reductive stripping enable the possibility to prepare Pt(1 0 0) electrodes fully covered by the first palladium layer, without contributions coming from palladium in the subsequent layers. This method enables a better characterization of the palladium islands formed in the submonolayer range. The CO displacement method points out that hydrogen and anion adsorption play a role in the charge transfer processes involved in the voltammetric profile. The analysis of the charge-potential curves is used to determine the values of the potentials of zero total charge (pztc) of the different adelectrodes. The pztc diminishes almost linearly with palladium coverage, this shift being related to increasing anion adsorption at low potentials. Adsorbed palladium does not electrocatalyze the oxidation of adsorbed CO.

Oxalic acid adsorption has been studied at platinum single crystal electrodes belonging to the [011] zone. Cyclic voltammetry and charge displacement experiments have been combined with in situ external reflection infrared experiments and results compared with those previously reported for the Pt(1 1 1) and Pt(1 0 0) electrodes. The spectroscopic data confirm the potential dependent behaviour of oxalic acid adsorption derived from the electrochemical experiments. At the same time, the infrared spectra show distinct CO stretching bands for adsorbates on (1 0 0) and (1 1 1) terraces. As previously concluded for Pt(1 0 0) and Pt(1 1 1) electrodes, oxalate and bioxalate anions are adsorbed, respectively, at the (1 0 0) and (1 1 1) terraces for potentials above 0.30 V. Oxalate and bioxalate anions adsorb at edge and step sites at potentials lower than at terrace sites. For Pt(2n−1,1,1) = Pt(S)[n(1 0 0) × (1 1 1)], bands are observed at potentials higher than 0.20 V that can be assigned to oxalate anions adsorbed at (1 0 0) edge sites and bioxalate adsorbed at (1 1 1) step sites. In the case of Pt(n+1,n−1,n−1) = Pt(S)[n(1 1 1) × (1 0 0)] electrodes, bands for oxalate anions adsorbed at the (1 0 0) step sites appears at potentials lower than bands for bioxalate adsorption at the (1 1 1) terrace sites. For all the stepped surfaces, adsorbed CO is slowly formed at the step sites in the hydrogen adsorption region. The extent of this process can be minimised during the collection of the infrared spectra by taking the reference spectrum at 0.20 V.

Oxalic acid adsorption and oxidation processes have been studied at platinum single crystal electrodes with basal orientations. Cyclic voltammetry and charge displacement experiments have been combined with in situ external reflection infrared experiments for the study of oxalic acid adsorption at potentials below 0.70 V. Whereas reversible anion-like adsorption is observed for Pt(100) and Pt(111) electrodes, oxalic acid is reduced at Pt(110) leading to the formation of an irreversibly bonded adsorbate which has been identified as adsorbed CO from the infrared spectra. Spectroscopic data confirm the potential dependent behaviour of oxalic acid adsorption on Pt(111) and Pt(100) electrodes derived from electrochemical data. At the same time, the infrared spectra show distinct C–O stretching bands for adsorbates on Pt(100) and P(111). In acidic solutions (pH = 1), for which oxalic acid and bioxalate anions predominate as solution species, oxalate anions are adsorbed at the Pt(100) electrode surface whereas bioxalate anions seem to be the adsorbed species at Pt(111). In neutral solutions, oxalate anions are adsorbed on both Pt(111) and Pt(100) surfaces. No intermediates coming from oxalic acid other than adsorbed CO for Pt(110) and adsorbed (bi)oxalate anions for Pt(111) and Pt(100) are detected during the oxidation of oxalic acid. Adsorbate bands are observed between 1400 and 1600 cm −1 for the Pt(111) electrode for potentials between 0.85 and 1.0 V. These bands are related to adsorbed carbonate anions formed in the presence of carbon dioxide molecules generated from oxalic acid oxidation.