Christian Durante

Metal-support interaction in platinum and palladium nanoparticles loaded on nitrogen-doped mesoporous carbon for oxygen reduction reaction.

Mesoporous carbons are highly porous materials, which show large surface area, chemical inertness and electrochemical performances superior to traditional carbon material. In this study, we report the preparation of nitrogen-doped and undoped mesoporous carbons by an optimized hard template procedure employing silica as template, sucrose and ammonia as carbon and nitrogen source, respectively. Surface area measurements assert a value of 900 and 600 m(2) g(-1) for the best doped and undoped samples, respectively. Such supports were then thoroughly characterized by surface science and electron microscopy tools. Afterward, they were decorated with Pt and Pd nanoparticles, and it was found that the presence of nitrogen defects plays a significant role in improving the metal particles dimension and dispersion. In fact, when doped supports are used, the resulting metal nanoparticles are smaller (2-4 nm) and less prone to aggregation. Photoemission measurements give evidence of a binding energy shift, which is consistent with the presence of an electronic interaction between nitrogen atoms and the metal nanoparticles, especially in the case of Pd. The catalytic properties of electrodes decorated with such catalyst/support systems were investigated by linear sweep voltammetry and by rotating disk electrode measurements, revealing excellent stability and good activity toward oxygen reduction reaction (ORR). In particular, although Pd nanoparticles always result in lower activity than Pt ones, both Pt and Pd electrodes based on the N-doped supports show an increased activity toward ORR with respect to the undoped ones. At the same mass loading, the Tafel slope and the stability test of the Pt@N-doped electrocatalysts indicate superior performances to that of a commercial Pt@C catalysts (30 wt % Pt on Vulcan XC-72, Johnson Matthey).

Advanced oxidation processes coupled with electrocoagulation for the exhaustive abatement of Cr-EDTA

Using Cr-EDTA as a model system, a two-step method has been investigated for the abatement of persistent chromium complexes in water. The treatment consists of an oxidative decomposition of the organic ligands by means of ozonization or electrochemical oxidation at a boron doped diamond (BDD) electrode, followed by removal of the metal via electrochemical coagulation. In the designed synthetic waste, EDTA has been used both as a chelating agent and as a mimic of the organic content of a typical wastewater provided by a purification leather plant. A crucial point evaluated is the influence of the oxidative pretreatment on the chemical modification of the synthetic waste and hence on the electrocoagulation efficacy. Because of the great stability of Cr complexes, such as Cr-EDTA, the classical coagulation methods, based on ligand exchange between Cr(III) and Fe(II) or Fe(III), are ineffective toward Cr abatement in the presence of organic substances. On the contrary, when advanced oxidation processes (AOPs), such as ozonization or electrooxidation at a BDD anode are applied in series with electrocoagulation (EC), complete abatement of the recalcitrant Cr fraction can be achieved. ECs have been carried out by using Fe sacrificial anodes, with alternating polarization and complete Cr abatement (over 99%) has been obtained with modest charge consumption. It has been found that Cr(III) is first oxidized to Cr(VI) in the AOP preceding EC. Then, during EC, Cr(VI) is mainly reduced back to Cr(III) by electrogenerated Fe(II). Thus, Cr is mainly eliminated as Cr(III). However, a small fraction of Cr(VI) goes with the precipitate as confirmed by XPS analysis of the sludge.

Multiple doping of graphene oxide foams and quantum dots: new switchable systems for oxygen reduction and water remediation

Single- and multi-boron, nitrogen, sulphur doped graphene oxide quantum dots and three-dimensional foams are synthesized by a simple and environmentally friendly electrochemical method. The electrochemical activity of these materials in the oxygen reduction reaction is investigated by cyclic voltammetry and rotating disk electrode measurements. The experimental data demonstrate that the reaction selectivity is controlled by the oxidation degree of the materials: as-prepared graphene oxide quantum dots, which present highly oxidized functional groups, follow a two-electron reduction pathway and produce hydrogen peroxide, whereas after a reduction treatment by NaBH4, the same materials favour a four-electron reduction of oxygen to water. The high selectivity and high efficiency of the graphene oxide quantum dots for the production of hydrogen peroxide can be efficiently used for water remediation applications (phenol decomposition).

Growth and optical properties of silver nanostructures obtained on connected anodic aluminum oxide templates

Ag nanostructures are grown by AC electrodeposition on anodic alumina oxide (AAO) connected membranes acting as templates. Depending on the thickness of the template and on the voltage applied during the growth process, different Ag nanostructures with different optical properties are obtained. When AAO membranes about 1 μm thick are used, the Ag nanostructures consist in Ag nanorods, at the bottom of the pores, and Ag nanotubes departing from the nanorods and filling the pores almost for the whole length. When AAO membranes about 3 μm thick are used, the nanostructures are Ag spheroids, at the bottom of the pores, and Ag nanowires that do not reach the upper part of the alumina pores. The samples are characterized by angle resolved x-ray photoelectron spectroscopy, scanning electron microscopy and UV-vis and Raman spectroscopies. A simple NaOH etching procedure, followed by sonication in ethanol, allows one to obtain an exposed ordered array of Ag nanorods, suitable for surface-enhanced Raman spectroscopy, while in the other case (3 μm thick AAO membranes) the sample can be used in localized surface plasmon resonance sensing.

One step forward to a scalable synthesis of platinum–yttrium alloy nanoparticles on mesoporous carbon for the oxygen reduction reaction

In this paper, we report the synthesis and characterization of nanoparticles (NPs) of a PtxY alloy supported on a commercial mesoporous carbon (MC). The NPs were prepared following a solid state synthesis in a quartz tubular furnace under H2 flow. The influence of Pt precursors on the NP shape and alloy formation was investigated together with the temperature and reaction time. The best synthesis afforded the obtainment of small spherical PtxY NPs (4 nm diameter) on the surface and inside pores of a MC with a maximum of alloy content of 41% with respect to the whole Pt loading. The electrochemical properties of PtxY NPs were investigated with special attention to their catalytic properties. The results in ORR studies showed that the catalyst containing the highest amount of PtxY alloy exhibits higher catalytic activity expressed in terms of mass and specific activity and comparable stability, after accelerated degradation tests, for oxygen reduction as compared to a standard Pt/C catalyst.

Electrochemical deposition of silica sol–gel films on stainless steel: preliminary analysis of key variables

The sol–gel electrodeposition of coatings on conductive substrates has been presented the first time in 1999, and since then, a significant number of papers have been published, mainly devoted to explore the possibilities of application. However, a clear and complete picture of the fundamental aspects and of the role of the many parameters involved is still lacking. In this work, which is intended to be a preliminary approach to a systematic study, the effect of potential and time on the coating thickness was studied, trying to analyze the different factors that make experimentation difficult, looking for possible solutions and putting the basis for a more complete and analytic investigation. Simple tetraethyl orthosilicate-based acidic solutions were used to coat planar stainless steel samples. Different starting solutions were tested, varying the amount of precursor, water and hydrochloric acid. The role of working temperature, oxygen concentration and the presence of potassium nitrate until saturation was tested. Morphology, thickness, cyclic voltammetry and chronoamperometry were used to characterize the coatings and to monitor the current in function of potential and time. The thickness was found to increase with both the concentration of the solution and the HCl/TEOS ratio. Temperature was found to be an important factor, but also the amount of oxygen and electrolyte (KNO3) in solution seems to influence the thickness of coatings.Graphical Abstract

Physico-Chemical, Electrochemical and Structural Insights Into Poly(3,4-ethylenedioxythiophene) Grafted from Molecularly Engineered Multi-Walled Carbon Nanotube Surfaces

Composites of multi-walled carbon nanotubes (MWCNTs) and poly(3,4-ethylenedioxythiophene) (PEDOT) are attracting the attention of material scientists since more than a decade as potential next-generation optoelectronic materials for their peculiar features, arising from the combination of the intrinsic electrical, thermal and morphological properties of the two components. They are indeed a promising platform for the development of low-cost, portable and environmentally friendly electronic devices such as supercapacitors, sensors and actuators. Here a novel synthetic strategy for their preparation is envisaged, exploiting the possibility to covalently functionalize the external surface of MWCNTs with tailored molecular units, starting from which the growth of the conjugated polymer can be induced oxidatively. The approach demonstrates its value in being able to effectively promote the formation of PEDOT chains in direct contact with the surface of MWCNTs, differently from what results when the monomer is polymerized in the presence of the pristine carbon nanomaterial. In addition, significant differences are found in the physico-chemical properties and electrochemical behavior when MWCNT-PEDOT covalent composites are studied in comparison to a non-covalent analogue, here illustrated in detail. These evidences constitute a starting point for the future development of novel more finely tuned functional materials based on MWCNT-PEDOT composites, featuring the required optoelectronic properties to precisely target the desired application.

Exhaustive depletion of recalcitrant chromium fractions in a real wastewater

This paper reports investigations on electrochemical removal of Cr(III) from a real wastewater sample from a 4x10(4)m(3)d(-1) purification plant located in the leather district of Arzignano (Italy). A crucial point evaluated is the relation between Cr(III) abatement and the reduction of total organic carbon and chemical oxygen demand. Here we present the results of different abatement approaches including advanced oxidation processes (AOPs) and electrocoagulation applied separately or in series. Neither of these methods show satisfactory results when applied alone. In particular, AOPs are completely inefficient owing to the formation of Cr(VI), which is more soluble than Cr(III). Almost total depletion (99.7%) of the recalcitrant fraction of Cr(III) is successfully achieved by combining ozonization and electrocoagulation processes. The results are consistent with the abatement of Cr in its hexavalent form by fast precipitation as NH(4)Fe(CrO(4))(2).

SiO2–TiO2 multilayer via electrochemical deposition: characterization of reflection and refractive index

AbstractThe deposition of silica and titania films by electro-assisted technique, with the objective to obtain a multilayer structure, was studied. Tetraethyl orthosilicate/methyl triethoxysilane (TEOS/MTES) mixture and titanium(IV) isopropoxide (TTIP) were used as precursors. The films were deposited on both bare stainless steel and indium tin oxide (ITO) substrates and a total thickness of about 550 nm was obtained for the four-layer structure. No heat treatment was performed before optical characterizations.Optical characterization was performed by ellipsometry on the single layers and on the multilayer coatings. The refractive index of silica and titania single layer, deposited on different substrates by electro-assisted technique and conventional dip coating, was measured in order to elucidate the influence of the substrates and deposition technique on the densification of the coatings. Moreover, the reflectance of the multilayer structure was also measured to demonstrate the possible use of the multilayer systems as Bragg reflector. HighlightsSiO2–TiO2 multilayer deposition via electrochemistry without heat treatment.Characterization of refractive index of SiO2 and TiO2 single layers on different substrates.Thin films intercalation of low and high refractive index was obtained.A multilayer system as Bragg reflector was developed.

Bioadsorbent Hura Crepitans for the removal of phenol from solution

The use of Hura crepitans (sandbox tree) seed as a biomass adsorbent was studied for the removal of phenol from aqueous solutions before extraction (HC) and after extraction (EHC) with hexane and methanol. The surface chemistry of HC and EHC was characterized by using the Boehm titration and pH drift while the removal of phenol from solution was monitored by using high performance liquid chromatography (HPLC). Decrease in the pH of solutions led to a significant increase in the adsorption capacity of HC and EHC. The linear regression of the experimental data showed that the Freundlich model fitted well with the values of adsorption capacity equal to 121 mmol/g for HC and 85 mmol/g for EHC, and the pseudo-second order kinetic model best described the adsorption process for HC and EHC. The experimental data indicated that the seed of Hura crepitans could be effectively used as an adsorbent for the removal of phenol from aqueous solutions.