Surface modification of activated carbon fabric with ozone. Part 2: Thermal analysis with TGA-FTIR and DTA

Two samples of activated carbon fabrics (ACF) with very high surface area (>1300 to >1800 m²/g) fully ozonized in the part 1 of this study were analyzed by thermogravimetric analysis (TGA) coupled both with differential thermal analysis (DTA) and FT-IR spectroscopy (TGA-FTIR). The adsorbed water and the amount of oxygenated functional groups were determined. The ozonized ACF shows an exothermal decomposition at about 181–189°C which may be due at least in part to the decomposition of ozonide and/or peroxide groups. The TGA-FTIR has revealed that the main products released from the thermal decomposition are CO₂ followed by CO. Formic acid was detected only in correspondence to the exothermal transition at 181°C and was taken as a proof of the decomposition of secondary ozonides.     

Optical properties of hybrid T3Pyr/SiO2/3C-SiC nanowires

A new class of nanostructured hybrid materials is developed by direct grafting of a model thiophene-based organic dye on the surface of 3C-SiC/SiO₂ core/shell nanowires. TEM-EDX analysis reveals that the carbon distribution is more spread than it would be, considering only the SiC core size, suggesting a main contribution from C of the oligothiophene framework. Further, the sulfur signal found along the treated wires is not detected in the as-grown samples. In addition, the fluorescent spectra are similar for the functionalized nanostructures and T3Pyr in solution, confirming homogeneous molecule grafting on the nanowire surface. Chemical and luminescence characterizations confirm a homogeneous functionalization of the nanowires. In particular, the fluorophore retains its optical properties after functionalization.     

Application of chemical and physical agents in model systems to controlling phenoloxidase enzymes

Several chemical and physical anti-browning agents are studied in different model systems in which caffeic acid (as substrate) and laccase from Trametes versicolor (LAC) and polyphenoloxidase from sunflower seeds (PPO) (as enzymes) are used to emulate the browning reaction. Temperature and low electric current were the tested physical agents, while acetic acid, sodium acetate, sodium chloride and, finally, sodium bisulfite were the chemical agents. Sunflower PPO was observed to be less heat sensitive than LAC that was fully inactivated after 1 and 3 min of exposure to 100 and 80 °C, respectively. Conversely, PPO required more than 3 min at 100 °C to be fully inactivated, and it still showed a significant activity (ca. 17%) after an exposure to 80 °C for 15 min. Both LAC and PPO were found to be active at frozen (−18 °C) and cool (+4 °C) temperature, and their activities were strengthened at 40 and 60 °C. As concerning chemical agents, inhibitory power of acetic acid on LAC was observed to be very weak. In the sodium acetate solution at the concentrations of 0.5, 1.0, 2.0 and 4.0%, LAC residual activity was equal to 81.5, 63.9, 61.1 and 35.2%, respectively. PPO is shown to be more sensitive to the NaCl than LAC and indifferent to the presence of NaHSO₃. A 28% residual activity of LAC was found in the solution with 200 mg L⁻¹ NaHSO₃. Finally, LAC activity was decreased to 72.3, 60.0, 16.7 and 8.4% after a low electric current (LEC) treatment of 30 s and 1, 3 and 6 min, respectively. Conversely, PPO activity was not affected under these conditions.     

Glass-Ceramic Materials for Guided-Wave Optics

Glass-ceramics (GCs) are multiphase micro- or nano-crystalline materials produced by the controlled nucleation and crystallization of an amorphous glass through a proper heating or chemical process. Most optical applications require transparency, and this usually implies that the crystalline phase be made of nanocrystals. Transparent GCs are able to combine the advantages of all their components, glasses, and crystals. Incorporation of semiconducting, ferroelectrical, and nonlinear optical phases in glass matrices can produce very promising materials for different applications. A very important role is played by nanocrystals which are activated by luminescent species, as rare earth ions. The presence of the crystalline environment around a rare earth ion allows high absorption and emission across sections, and reduction in the nonradiative relaxations thanks to the lower phonon cut-off energy. Such materials may lead to real advances in optical amplifiers, up-conversion fibers, solid-state lasers, medical sensors, and several other devices, especially if combined with a guided-wave configuration, which allows high energy densities and efficient delivery of the transmitted optical beams. The present review article covers the properties and current state of transparent glass-ceramics for guided-wave devices, including the discussion of the preparation methods and of their spectral and luminescent properties.     

Towards controlled cationic polymer growth from inorganic oxide defects: Directing the mechanism of polystyrene grafting from γ-irradiated silica

Most studies on surface-initiated controlled polymerizations for the synthesis of polymeric covalent organic-inorganic hybrid materials focus on chemical methods requiring specific modifications of the inorganic substrate. Few mechanistically-aware approaches have been undertaken towards exploiting the reactivity of defects induced by physical techniques such as ionizing radiations or UV–Vis light. Within this framework, we take grafted polymerization of styrene from γ-irradiated silica as a mechanistic testing ground where para- and diamagnetic silica defects are present, and polymerization proceeds through both radical and cationic mechanisms, resulting in a bimodal molecular weight distribution. We show that these mechanistic intricacies can be sorted out by resorting to the chemical arsenal developed in the last decades for controlled polymerizations. Specifically, we obtained a silica-polystyrene grafted material by cationic grafting from at 30 °C, a unimodal molecular weight distribution, and a relatively high molecular weight (Mn = 7.4 kDa) with a PDI of 1.68.     

Revisitation of Formaldehyde Aniline Condensation. VII. 1,3,5-Triarylhexahydro-sym-triazines and 1,3,5,7-Tetraaryl-1,3,5,7-tetrazocines from Aromatic Amines and Paraformaldehyde

A product study of the reaction between a number of aromatic amines substituted with widely different groups and paraformaldehyde in inert solvents was performed and found to yield 1,3,5-triaryl-1,3,5-hexahydrotriazines, 1,3,5,7-tetraaryl-1,3,5,7-tetrazocines and formaminals. It was not possible to correlate the product outcomes with the actual structure of the amine substrate. The X-ray diffraction structural determination of 1,3,5-tri-(t-butylphenyl)-( 1b ) and 1,3,5-tri-(m-fluorophenyl)-1,3,5-hexahydrotriazine ( 1c ) showed the diaxial arrangement of the N-substituents.     

Revisitation of Formaldehyde Aniline Condensation. I High Yield Synthesis of 1,3,5-Triphenylhexahydro-symtriazine and its X-Ray Crystal Structure Determination

A rapid and efficient preparation of 1,3,5-triphenylhexahydro-sym-triazine ( 10 ) using paraformaldehyde is reported. The trimeric nature of the compound and its structure in solid state, where a biaxial chair conformation is favoured, are conclusively shown by X-ray diffraction analysis. A recent report on a preparation of 1,3-diphenyl-1,3-diazetidine is invalidated.     

Elevated-Temperature-Delayed Failure of Alumina Reinforced with 20 vol% Silicon Carbide Whiskers

Alumina composites reinforced with 20 vol% SiC whiskers were exposed to applied stresses in four-point flexure at temperatures of 1000°, 1100°, and 1200°C in air for periods of up to 14 weeks. At 1000° and 1100°C, an "apparent" fatigue limit was established at stresses of ∼ 75% of the fast fracture strength. However, after long-term (>6 weeks) tests at 1100°C, some evidence of crack generation as a result of creep cavitation was detected. At 1200°C applied stresses as low as 38% of the 1200°C fracture strength were sufficient to promote creep deformation and accompanying cavitation and crack generation and growth resulting in failures in times of <250 h.     

Preparation and Use of a Boron Nitride Precursor as Binder for the Densification of Boron Nitride

A precursor of boron nitride was prepared through the partial condensation of 2,4,6-trichloroborazine and bis-(trimethylsilyl)acetylene. This reaction was conducted at 100°C and is catalyzed by AlCl₃. The condensation product pyrolyzed at 800°C, producing trimethylsilyl chloride as a volatile product and a boron nitride rich residue containing 54 wt% of the initial weight. Mixtures of the precursor and commercial boron nitride were made and hot-pressed at 800°C and 27.6 MPa. A maximum density of 1.84 g/cm³ is reached at a loading corresponding to the deposition of 13 wt% residue derived from the precursor. Examination by analytical electron microscopy, including X-ray energy dispersive spectroscopy and electron energy loss spectroscopy analyses, revealed the location of material derived from the precursor in BN-binder composites through the presence of residual aluminum, silicon, and carbon. Crystallization of boron nitride from the precursor appears to have taken place, as deduced from the morphology of the phases observed and association with residual elements present in the binder.     

Cloud-assisted body area networks: state-of-the-art and future challenges

Body area networks (BANs) are emerging as enabling technology for many human-centered application domains such as health-care, sport, fitness, wellness, ergonomics, emergency, safety, security, and sociality. A BAN, which basically consists of wireless wearable sensor nodes usually coordinated by a static or mobile device, is mainly exploited to monitor single assisted livings. Data generated by a BAN can be processed in real-time by the BAN coordinator and/or transmitted to a server-side for online/offline processing and long-term storing. A network of BANs worn by a community of people produces large amount of contextual data that require a scalable and efficient approach for elaboration and storage. Cloud computing can provide a flexible storage and processing infrastructure to perform both online and offline analysis of body sensor data streams. In this paper, we motivate the introduction of Cloud-assisted BANs along with the main challenges that need to be addressed for their development and management. The current state-of-the-art is overviewed and framed according to the main requirements for effective Cloud-assisted BAN architectures. Finally, relevant open research issues in terms of efficiency, scalability, security, interoperability, prototyping, dynamic deployment and management, are discussed.