Maria Rachele Guascito

A new amperometric nanostructured sensor for the analytical determination of hydrogen peroxide

A new amperometric, nanostructured sensor for the analytical determination of hydrogen peroxide is proposed. This sensor was constructed by immobilizing silver nanoparticles in a polyvinyl alcohol (PVA) film on a platinum electrode, which was performed by direct drop-casting silver nanoparticles that were capped in a PVA colloidal suspension. UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy were used to give a complete characterization of the nanostructured film. Cyclic voltammetry experiments yielded evidence that silver nanoparticles facilitate hydrogen peroxide reduction, showing excellent catalytic activity. Moreover, the cronoamperometric response of modified sensors was dependent on nanoparticle lifetime. Experiments were performed, using freshly prepared solutions, after 4 and 8 days. Results concerning the quantitative analysis of hydrogen peroxide, in terms of detection limit, linear range, sensitivity and standard deviation (STD), are discussed for each tested sensor type. Utilization of two different linear ranges (40 microM to 6mM and 1.25 microM to 1.0mM) enabled the assessment of concentration intervals having up to three orders of magnitude. Moreover, the electrode made using a 4-day-old solution showed the maximal sensitivity of 128 nA microM(-1)(4090 nA microM(-1)cm(-2)), yielding a limit of detection of 1 microuM and STD of 2.5 microAmM(-1). All of these analytical parameters make the constructed sensors suitable for peroxide determination in aqueous solution.

Anodic electrodeposition of conducting cobalt oxyhydroxide films on a gold surface. XPS study and electrochemical behaviour in neutral and alkaline solution

A novel chemically modified electrode prepared by anodic electrodeposition of cobalt (III) film on the gold electrode substrate (Au-Co) was characterised by cyclic voltammetry and XPS techniques in both neutral and alkaline medium. Cobalt oxyhydroxide film was deposited by cycling the potential between 0.0 and 1.1 V versus SCE in 0.1 M sodium acetate solutions containing 10 mM CoCl2. The electrocatalytic properties of the Au-Co electrode were investigated in alkaline medium using glucose as a model compound. A comparative XPS study of bare gold, bare cobalt and Au-Co electrodes after electrochemical treatment in neutral and alkaline solutions has been carried out. A detailed XPS analysis of the Au4f7/2, Co2p3/2, O1s and C1s regions was performed to check the chemical composition of the Au-Co electrode upon electrochemical treatments. Film deposition is attributed to growth of conducting and compact CoOOH oxyhydroxide with significant insertion of carbonyl groups within the electrodeposited layer. The prolonged electrochemical treatment in alkaline medium produces a good stabilization of the CoIII oxyhydroxide film, with a dominant O1s feature at about 532.4 eV of BE corresponding to a non-stoichiometric surface oxygen. The absence of CoO species proves good conducting properties of the cobalt film and the absence of any passivation effects on the catalytic performance.

Source apportionment of size-segregated atmospheric particles based on the major water-soluble components in Lecce (Italy).

Atmospheric aerosols have potential effects on human health, on the radiation balance, on climate, and on visibility. The understanding of these effects requires detailed knowledge of aerosol composition and size distributions and of how the different sources contribute to particles of different sizes. In this work, aerosol samples were collected using a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI). Measurements were taken between February and October 2011 in an urban background site near Lecce (Apulia region, southeast of Italy). Samples were analysed to evaluate the concentrations of water-soluble ions (SO4(2-), NO3(-), NH4(+), Cl(-), Na(+), K(+), Mg(2+) and Ca(2+)) and of water-soluble organic and inorganic carbon. The aerosols were characterised by two modes, an accumulation mode having a mass median diameter (MMD) of 0.35 ± 0.02 μm, representing 51 ± 4% of the aerosols and a coarse mode (MMD=4.5 ± 0.4 μm), representing 49 ± 4% of the aerosols. The data were used to estimate the losses in the impactor by comparison with a low-volume sampler. The average loss in the MOUDI-collected aerosol was 19 ± 2%, and the largest loss was observed for NO3(-) (35 ± 10%). Significant losses were observed for Ca(2+) (16 ± 5%), SO4(2-) (19 ± 5%) and K(+) (10 ± 4%), whereas the losses for Na(+) and Mg(2+) were negligible. Size-segregated source apportionment was performed using Positive Matrix Factorization (PMF), which was applied separately to the coarse (size interval 1-18 μm) and accumulation (size interval 0.056-1 μm) modes. The PMF model was able to reasonably reconstruct the concentration in each size-range. The uncertainties in the source apportionment due to impactor losses were evaluated. In the accumulation mode, it was not possible to distinguish the traffic contribution from other combustion sources. In the coarse mode, it was not possible to efficiently separate nitrate from the contribution of crustal/resuspension origin.

A novel nonenzymatic amperometric hydrogen peroxide sensor based on CuO@Cu2O nanowires embedded into poly(vinyl alcohol).

A new, very simple, rapid and inexpensive nonenzymatic amperometric sensor for hydrogen peroxide (H2O2) detection is proposed. It is based on the immobilization of cupric/cuprous oxide core shell nanowires (CuO@Cu2O-NWs) in a poly(vinyl alcohol) (PVA) matrix directly drop casted on a glassy carbon electrode surface to make a CuO@Cu2O core shell like NWs PVA embedded (CuO@Cu2O-NWs/PVA) sensor. CuO nanowires with mean diameters of 120-170nm and length in the range 2-5μm were grown by a simple catalyst-free thermal oxidation process based on resistive heating of pure copper wires at ambient conditions. The oxidation process of the copper wire surface led to the formation of a three layered structure: a thick Cu2O bottom layer, a CuO thin intermediate layer and CuO nanowires. CuO nanowires were carefully scratched from Cu2O layer with a sharp knife, dispersed into ethanol and sonicated. Then, the NWs were embedded in PVA matrix. The morphological and spectroscopic characterization of synthesized CuO-NWs and CuO@Cu2O-NWs/PVA were performed by transmission electron microscopy (TEM), selected area diffraction pattern (SAD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. Moreover a complete electrochemical characterization of these new CuO@Cu2O-NWs/PVA modified glassy carbon electrodes was performed by Cyclic Voltammetry (CV) and Cronoamperometry (CA) in phosphate buffer (pH=7; I=0.2) to investigate the sensing properties of this material against H2O2. The electrochemical performances of proposed sensors as high sensitivity, fast response, reproducibility and selectivity make them suitable for the quantitative determination of hydrogen peroxide substrate in batch analysis.

Electrochemical preparation of a composite gold–cobalt electrode and its electrocatalytic activity in alkaline medium

Abstract A chemically modified electrode composed of cobalt(III) oxyhydroxide film dispersed on the gold substrate (AuCo) was characterised by cyclic voltammetry. Electrochemical deposition of the cobalt film was accomplished by cycling the potential between 0.0 V and 1.1 V (vs. saturated calomel electrode (SCE)) in 0.1 M acetate solution (at pH 7.3) containing 10 mM CoCl 2 . The effects of several experimental parameters (pH, applied potentials, etc.) on the film formation and growth were evaluated. The electrochemical behaviour of the AuCo composite electrode was investigated in alkaline medium. The film appears uniform and compact and shows good electrical conductivity and electrochemical activity towards the oxidation of several scarcely electroactive organic molecules. The concomitant presence on the electrode surface of both active catalysts leads to a wide range of potential applications where a significant electrochemical activity towards the electrooxidation of several classes of organic compounds is observed.

Conducting polymer electrodes modified by metallic species for electrocatalytic purposes—spectroscopic and microscopic characterization

Abstract Poly-3-methylthiophene (PMT) electrodes, modified by the dispersion of copper-containing particles in which copper is in the Cu(I) oxidation state, were prepared by an all-electrochemical procedure. Cu(I) deposition was achieved by applying a potential pulse program. The microscopic characterization of the deposit was performed by scanning electron microscopy/energy dispersive X-ray analysis (SEM-EDX), and showed a correlation between the pulse width and the amount and size of the deposited particles. The Cu(I), the major copper species for pulse width ⩽500 ms, was shown by X-ray photoelectron spectroscopy (XPS) analysis to be present as Cu 2 O and/or CuCl. Some preliminary results on the electrocatalytic properties of these modified electrodes in the oxidation of polyhydroxy compounds (e.g., glucose, tartaric acid, xylose, ribose, fructose, galactose, mannose) are reported.

Low-potential sensitive H2O2 detection based on composite micro tubular Te adsorbed on platinum electrode

In this work a new original amperometric sensor for H(2)O(2) detection based on a Pt electrode modified with Te-microtubes was developed. Te-microtubes, synthesized by the simple thermal evaporation of Te powder, have a tubular structure with a hexagonal cross-section and are open ended. Modified electrode was prepared by direct drop casting of the mixture of Te-microtubes dispersed in ethanol on Pt surface. The spectroscopic characterization of synthesized Te-microtubes and Pt/Te-microtubes modified electrodes was performed by scanning electron microscopy (SEM), energy-dispersive X-rays microanalysis (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). Moreover a complete electrochemical characterization of the new composite material Pt/Te-microtubes was performed by cyclic voltammetry (CV) and cronoamperometry (CA) in phosphate buffer solution (PBS) at pH 7. Electrochemical experiments showed that the presence of Te-microtubes on modified electrode was responsible for an increment of both cathodic and anodic currents in presence of H(2)O(2) with respect to bare Pt. Specifically, data collected from amperometric experiments at -150 mV vs. SCE in batch and -200 mV vs. SCE in flow injection analysis (FIA) experiments show a remarkable increment of the cathodic current. The electrochemical performances of tested sensors make them suitable for the quantitative determination of H(2)O(2) substrate both in batch and in FIA.

Analysis by X-ray photoelectron spectroscopy of ruthenium stabilised polynuclear hexacyanometallate film electrodes

Abstract The role and effects of ruthenium on the electrochemical stabilisation of some metal-hexacyanometallate film electrodes was investigated by X-ray photoelectron spectroscopy (XPS). The following inorganic films were studied, cobalt(II)-hexacyanoferrate(II/III) (CoHCFe), nickel(II)-hexacyanoferrate(II/III) (NiHCFe), and iron(II/III)-hexacyanorutenate(II/III) (FeHCRu), and their corresponding ruthenium stabilised ones, Ru-CoHCFe, Ru-NiHCFe and Ru-FeHCRu. A mass increase of CoHCFe, NiHCFe, and FeHCRu, during continuous redox cycles (75–90 times) in a millimolar solution of RuCl3, was monitored by an electrochemical quartz crystal microbalance. Detailed XPS analysis of C 1s, O 1s, Fe 2p, Ni 2p, Co 2p, and Ru 3d peaks has allowed a comprehensive description of changes that occurred. The results obtained demonstrate that the insertion of ruthenium oxo species (e.g., Ru2O63+) was effective for the increase in lifetimes and for the electrocatalytic properties of ruthenium-modified metal-hexacyanometallate film electrodes. Three possible models of stabilisation are discussed.

Te oxide nanowires as advanced materials for amperometric nonenzymatic hydrogen peroxide sensing.

A new nonenzymatic platinum Te oxide nanowires modified electrode (Pt/TeO2-NWs) for amperometric detection of hydrogen peroxide (H2O2) is proposed. The modified electrode has been developed by direct drop casting, with TeO2 nanowires (TeO2-NWs), synthesized by thermal evaporation of Te(0) in an oxygen atmosphere. The morphological and spectroscopic characterization of the TeO2-NWs as synthesized on Pt foil was performed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. XPS and XRD analyses are especially involved to gain information on the chemical environment of TeO2-NWs in contact with Pt surface. Moreover electrochemical characterization of these new modified Pt/TeO2-NWs modified electrodes was performed by Cyclic Voltammetry (CV) and Cronoamperometry (CA) in phosphate buffer (pH=7; I=0.2) to investigate the sensing properties of this material against H2O2. The proposed sensor exhibits a wide linear and dynamic range from 2 µM to 16 mM (R(2)=0.9998) and the detection limit is estimated to be 0.6 µM (S/N=3). Moreover, this sensor shows a rapid amperometric response time of less than 5s and possessed good reproducibility. These results indicate that Pt/TeO2-NWs composite is suitable to be used as material for sensing applications.

QCM sensors for aqueous phenols based on active layers constituted by tetrapyrrolic macrocycle Langmuir films

Three different metalated tetrapyrrolic macrocycles have been transferred by Langmuir-Blodgett technique directly onto piezoelectric quartz crystal covered with gold electrodes of a commercial quartz crystal microbalance instrument in order to perform a flow injection analysis. All floating films at the air-water interface have been analyzed by registration of Langmuir curves and by UV-vis reflection spectroscopy and brewster angle microscopy. The sensing performances of the modified gold electrodes were investigated by monitoring the frequency variation induced by the presence of several toxic phenols. The explored concentrations ranged around 10-3 M and the corresponding frequency variations ranged between 10 and 200 Hz. All responses observed were fast, reproducible and reversible; moreover, the active layers are stable over long periods of utilization. The observation that interferences from fulvic acid are absolutely negligible is also noteworthy. The responses are not selective for each singular phenol derivative; notwithstanding this, to the best of our knowledge, this contribution represents one of the first examples of sensing layers for the monitoring of the total content of phenols.