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A comparison of the ethanol sensing properties of α-iron oxide nanostructures prepared via the sol–gel and electrospinning techniques

Haematite (α-Fe2O3) nanostructures were synthesized via a Pechini sol-gel method (PSG) and an electrospinning (ES) technique. Their texture and morphology were investigated by scanning and transmission electron microscopy. α-Fe2O3 nanoparticles were obtained by the PSG method, whereas fibrous structures consisting of interconnected particles were synthesized through the ES technique. The crystallinity of the α-Fe2O3 nanostructures was also studied by means of x-ray diffraction and Raman spectroscopy. Gas-sensing devices were fabricated by printing the synthesized samples on ceramic substrates provided with interdigitated Pt electrodes. The sensors were tested towards low concentrations of ethanol in air in the temperature range (200-400 °C). The results show that the α-Fe2O3 nanostructures exhibit somewhat different gas-sensing properties and, interestingly, their sensing behaviour is strongly temperature-dependent. The availability of active sites for oxygen chemisorption and the diffusion of the analyte gas within the sensing layer structure are hypothesized to be the key factors responsible for the different sensing behaviour observed.

Oxygen-sensing properties of electrospun CNTs/PVAc/TiO2 composites

Multi-walled-carbon-nanotubes/polyvinylacetate/titanium oxide (MWCNTs/PVAc/TiO2) composite fibers with different MWCNT loadings were prepared using the electrospinning technique. The addition of cetyl trimethyl ammonium bromide (CTAB) as a surfactant agent to promote the dispersion of the MWCNTs was also evaluated. The morphological and microstructural properties of as-spun and annealed samples in air at 600°C were examined using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and x-ray diffraction (XRD). The sensing characteristics of the synthesized TiO2-based nanostructures were evaluated for oxygen monitoring at moderate temperatures. The effects of the MWCNT loading, the addition of the surfactant and the composition of the TiO2 crystalline phases were investigated and discussed.

Polyaniline nanofibers: Towards pure electrospun PANI

Nanofibers of conducting polymers, as polyaniline (PANI), have received a great deal of attention by the scientific community for their potential applications (electronic, magnetic, biomedical, optical fields). Recently the electrospinning has emerged as a promising technique to produce wires and fibers of polymers with diameters ranging from 10 nm to 10μm. PANI has poor processability by electrospinning due to its poor solubility in common solvents, but it is possible to spun polyaniline nanofibers adding another polymer to the organic solutions. The presence of an insulator copolymer decreases the fibers/wires conductivity. In this work we report the preparation of highly pure polyaniline fibers by electrospinning process. PANI powder has been characterized by FT-IR, UV-VIS, and X-Ray diffraction. The spun sample obtained have been characterized by SEM to evaluate the wire morphology and complex impedance spectroscopy (EIS) in order to measure the electrical conductivity. We observed that, reducing the amount of PEO in the PANI/PEO blend organic solution, the fiber sizes decreased from 421nm for higher content of PEO (PANI: PEO= 1: 1, w/w) to 230 nm (PANI: PEO= 1: 0.1, w/w). The way to collect the fiber has been also investigated. Using a rotanting collector we observed a stretching effect on the fibers which promotes a narrow distribution of fibers dimension with respect to the fibers obtained with static collector.Nanofibers of conducting polymers, as polyaniline (PANI), have received a great deal of attention by the scientific community for their potential applications (electronic, magnetic, biomedical, optical fields). Recently the electrospinning has emerged as a promising technique to produce wires and fibers of polymers with diameters ranging from 10 nm to 10μm. PANI has poor processability by electrospinning due to its poor solubility in common solvents, but it is possible to spun polyaniline nanofibers adding another polymer to the organic solutions. The presence of an insulator copolymer decreases the fibers/wires conductivity. In this work we report the preparation of highly pure polyaniline fibers by electrospinning process. PANI powder has been characterized by FT-IR, UV-VIS, and X-Ray diffraction. The spun sample obtained have been characterized by SEM to evaluate the wire morphology and complex impedance spectroscopy (EIS) in order to measure the electrical conductivity. We observed that, reducing t...

Electrospinning fabrication of polyvinyl alcohol and polyvinyl pyrrolidone/Sm(NO3)3-Sm2O3 composites nanofibers:

Polyvinyl pyrrolidone and polyvinyl alcohol thickeners and Sm(NO3)3 have been directly processed by electrospinning method to obtain composite nanofibers. Scanning electron microscopy micrographs indicated that the surface of the prepared composite fibers was smooth. X-ray diffraction analysis revealed that the composite nanofibers were amorphous in structure. Sm2O3 nanoparticles and nanofibers were fabricated by calcination of the composite fibers.

The behaviour of the framework aluminium during ITQ-2 formation from MCM-22(P)

The aim of this paper is to systematically investigate the formation mechanisms of ITQ-2 from different MCM-22(P) materials. Particular attention has been devoted to understand how each delamination step influences the final materials ITQ-2. In order to characterize the intermediate products of the delamination steps, various types of analysis have been carried out: XRD, 27 Al-NMR, 29 Si-NMR, DSC-TG and chemical analysis. It has been confirmed that the delamination process is favoured by the decreasing aluminium concentration of parent materials. The investigation carried out has shown that aluminium always remains in tetrahedral coordination, because it is protected, during the delamination process, by the organic cation used in the MCM-22(P) synthesis.

Binders alternative to Portland cement and waste management for sustainable construction—part 1:

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Rheological Influence of Synthetic Zeolite on Cement Pastes

Self Compacting Concrete (SCC) is characterized by specific and particular mechanical properties, often due to the addition of components, able to modify the paste rheology. Concrete properties are strongly affected by characteristics of the fresh cement paste that is the continuous phase dispersing larger aggregates. Therefore, aiming to characterize mechanical properties of final concrete is relevant to know rheological properties of the base cement paste. In this work cement pastes for SCC were prepared by using, as additive, synthetic zeolite 5A in different amounts and they were analyzed by small amplitude oscillations. Experimental results have shown a relationship between dynamic moduli and zeolite content, identifying a proper level of zeolite addition. Moreover samples containing traditional fine additives, such as silica fume and limestone, were prepared and experimental data were compared to those obtained by using zeolite. It was found that zeolite seems to give better properties to cement pas...

Direct synthesis of zeolites self-bonded pellets for biocatalyst immobilization

In this work, the preparation, by direct synthesis, of Silicalite-1 self-bonded pellets as supports for immobilization of lipase enzyme is presented. The Silicalite-1 pellets have been prepared in view of the results obtained from the lipase enzyme adsorption on the most suitable supports in powder form. The different pellet preparation procedures strongly influence the final properties of the product. The main synthesis parameter that leads to pellets having high performance, especially regarding the crystal cohesion in aqueous system, is the alkalinity of the synthesis mixture. All possible attachment sites of the support surface of the self-bonded pellets prepared without a binding agent are available to the enzyme. The amount of the enzyme retained on the pellet surface (275 mg/g) is comparable to the amount adsorbed on the powder Silicalite-1 support.

Preparation of mesoporous silica using low cost green reactants

Abstract The synthesis and characterization of mesoporous silicate obtained by utilizing commercial reactants are reported. Materials were prepared at two temperatures (25°C and 100°C) using, together with sodium silicate, two different surfactants normally commercialized in the detergency market. This choice has been made for two main reasons: the very low cost of the organic molecule and their biodegradable characteristics, which allows a soft environmental impact. The synthesis procedures have been optimized making them suitable for a large scale production. In general obtained samples exhibit very high pore volumes and specific surface areas. The same synthesis system produces porous solids with different pore diameters depending on synthesis temperature. The nitrogen isotherm pattern varies from Type I typical of microporous solids to Type IV typical of mesoporous solids if the same synthesis system is runned at 25°C or 100°C. The effect of temperature seems to be determinining for the interactions between surfactant polar heads and silicate surface. The degree of extension of surfactant molecole conformation determines the pore diameters of resulting materials.

In situ dynamic light scattering and synchrotron X-ray powder diffraction study of the early stages of zeolite growth

The synthesis of zeolite LTA from a clear solution of nominal composition 8.6 Na 2 O−0.18Al 2 O 3 −SiO 2 −150H 2 O was investigated using a combination of techniques (Dynamic Light Scattering, DLS, and X-ray Powder diffraction, XRPD, in situ experiments performed at the BM8 beam line of the ESRF facility in Grenoble, France) to obtain information on the early stages of the nucleation process. The experiments were performed at temperatures ranging between 60 and 100°C. The DLS data clearly show at all temperatures the rapid development of an amorphous phase which consistently precedes the appearance of the LTA crystals. The observation of the amorphous precursor, the delayed formation of the crystalline zeolite, and the analysis of the kinetic parameters of the process indicate that the nucleation process of zeolite LTA from clear solution is heterogeneous and occurs at the interface between the solution and the amorphous precursor.