New Sustainable Multilayered Membranes Based on ZrVTi for Hydrogen Purification.

Some metals belonging to groups IV and V show a high permeability to hydrogen and have been studied as possible alternatives to palladium in membranes for hydrogen purification/separation in order to increase their sustainability and decrease their costs. However, to date, very few alloys among those metals have been investigated, and no membrane studies based on 4-5 element alloys with low or zero Pd content and quasi-amorphous structure have been reported so far. In this work, new membranes based on ZrVTi- and ZrVTiPd alloys were tested for the first time for this application. The unprecedented deposition of micrometric-based multilayers was performed via high-power impulse magnetron sputtering onto porous alumina substrates. Dense Pd/ZrxVyTizPdw/Pd multilayers were obtained. The composition of the alloys, morphology and structure, hydrogen permeance, selectivity, and resistance to embrittlement were tested and analyzed depending on the deposition conditions, and the membrane with the enhanced performance was tuned. The environmental impact of these membranes was also investigated to ascertain the sustainability of these alloys relative to more common Pd77Ag23 and V93Pd7 thin-film membranes using a life cycle assessment analysis. The results showed that the partial substitution of Pd can efficiently lead to a decrease in the environmental impacts of the membranes.

Tuning PEDOT:Tos Thermoelectric Properties Through Nanoparticle Inclusion.

Thermoelectric application of conjugated polymers has recently become a subject of scientific interest. This is due to the peculiar features of these organic materials, such as low cost, safety, abundance of atomic components, and easy processing, which make them an interesting alternative to inorganic materials commonly used for this application in the room temperature range, i.e., tellurides derivatives, such as Bi2Te3 and Sb2Te3. Two are the main drawbacks of organic materials employment: the first is their poor thermoelectrical performance, which is still low in comparison with inorganic benchmark, the second is the scarcity of stable and easy-to-dope n-type polymers. In order to address the first issue, we tried to obtain a further and crucial efficiency improvement, developing a nanocomposite embedding inorganic nanoparticles in a matrix of conjugated polymer. A hybrid film of poly(3,4-ethylenedioxithiophene):Tosylate (PEDOT:Tos) and Mn3O4 nanoparticles have been achieved through a novel strategy, involving nanoparticle functionalization and in situ polymerization. The purpose is to enable energy filtering thanks to the presence of the NPs so as to extend this beneficial effect already been observed in inorganic semiconductor to polymers. Our study indicates a new path to obtain PEDOT-based nanocomposite and enlightens the peculiar behaviour of this hybrid material.

Nanostructured Tetrahedrite Synthesis for Thermoelectric Applications.

Nowadays, a big challenge in the thermoelectric field is the identification of efficient thermoelectric materials but inexpensive, easy to synthesize, and comprised of Earth-abundant elements. On this basis, tetrahedrite mineral family (Cu(12−x)Tr(x)Sb4S13 where Tr = Cu, Mn, Fe, Co, Ni, Zn) seems to be an attractive p-Type Pb-free thermoelectric material, showing a relatively high conversion efficiency. In this work, a solvothermal synthesis method was developed for undoped tetrahedrite Cu12Sb4S13 and the introduction of Zn and Ni as substituents of copper was also tested. The influence of the stoichiometry and the synthesis conditions on the tetrahedrite phase content and density of the samples were investigated by X-ray diffraction (with profile Rietveld refinements) and scanning electron microscope (equipped with energy dispersive X-ray spectroscopy). Preliminary sintering test were performed by Open Die Pressing.

Tuning the thermal diffusivity of silver based nanofluids by controlling nanoparticle aggregation.

With the aim of preparing stable nanofluids for heat exchange applications and to study the effect of surfactant on the aggregation of nanoparticles and thermal diffusivity, stable silver colloids were synthesized in water by a green method, reducing AgNO3 with fructose in the presence of poly-vinylpyrollidone (PVP) of various molecular weights. A silver nanopowder was precipitated from the colloids and re-dispersed at 4 vol% in deionized water. The Ag colloids were characterized by UV-visible spectroscopy, combined dynamic light scattering and ζ-potential measurements, and laser flash thermal diffusivity. The Ag nanopowders were characterized by scanning electron microscopy and thermal gravimetric analysis. It was found that the molecular weight of PVP strongly affects the ζ-potential and the aggregation of nanoparticles, thereby affecting the thermal diffusivity of the obtained colloids. In particular, it was observed that on increasing the molecular weight of PVP the absolute value of the ζ-potential is reduced, leading to increased aggregation of nanoparticles. A clear relation was identified between thermal diffusivity and aggregation, showing higher thermal diffusivity for nanofluids having higher aggregation. A maximum improvement of thermal diffusivity by about 12% was found for nanofluids prepared with PVP having higher molecular weight.

An electrochemical gas sensor based on paper supported room temperature ionic liquids.

A sensitive and fast-responding membrane-free amperometric gas sensor is described, consisting of a small filter paper foil soaked with a room temperature ionic liquid (RTIL), upon which three electrodes are screen printed with carbon ink, using a suitable mask. It takes advantage of the high electrical conductivity and negligible vapour pressure of RTILs as well as their easy immobilization into a porous and inexpensive supporting material such as paper. Moreover, thanks to a careful control of the preparation procedure, a very close contact between the RTIL and electrode material can be achieved so as to allow gaseous analytes to undergo charge transfer just as soon as they reach the three-phase sites where the electrode material, paper supported RTIL and gas phase meet. Thus, the adverse effect on recorded currents of slow steps such as analyte diffusion and dissolution in a solvent is avoided. To evaluate the performance of this device, it was used as a wall-jet amperometric detector for flow injection analysis of 1-butanethiol vapours, adopted as the model gaseous analyte, present in headspace samples in equilibrium with aqueous solutions at controlled concentrations. With this purpose, the RTIL soaked paper electrochemical detector (RTIL-PED) was assembled by using 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide as the wicking RTIL and printing the working electrode with carbon ink doped with cobalt(II) phthalocyanine, to profit from its ability to electrocatalyze thiol oxidation. The results obtained were quite satisfactory (detection limit: 0.5 µM; dynamic range: 2-200 µM, both referring to solution concentrations; correlation coefficient: 0.998; repeatability: ±7% RSD; long-term stability: 9%), thus suggesting the possible use of this device for manifold applications.

Cathodoluminescence evaluation of oxygen vacancy population in nanostructured titania thin films for photocatalytic applications.

Room-temperature results of cathodoluminescence (CL) spectroscopy investigations are presented for nanostructured titanium dioxide (anatase) thin films (500 nm thick) deposited via RF magnetron sputtering on high-purity silica substrates. The collected CL bands of the anatase thin films, as deposited and after different annealing cycles, showed a broad morphology consisting of three Voigtian bands located at 500, 550, and 610 nm that were partially overlapping. The overall CL emission increased with increasing temperature and time of the annealing cycle as a consequence of the increased crystallinity of the thin film. A clear trend was found for the oxygen-vacancy-related band (located at 610 nm), whose relative intensity decreased, as compared with the as-grown sample, after annealing in air; the higher the annealing temperature, the lower the relative intensity. We evaluated the photoactivity of the nanostructured thin film samples by measuring their photocatalytic activity in aqueous solution toward the degradation of phenol. A relationship between the decrease in oxygen vacancy concentration as a consequence of the annealing and the increase in the photoactivity was highlighted.