1,721,034 research outputs found
TGA coupled with FTIR gas analysis to quantify the vinyl alcohol unit content in ethylene-vinyl alcohol copolymer
No full textThermo-gravimetric analysis coupled to time/temperature-resolved FTIR spectroscopy of evolved gases was used to measure the vinyl alcohol units content in EVOH copolymer. Pure homopolymers were used as references. The quantitative analysis here proposed is based on the calculation of integral profiles relative to FTIR signals of water molecules evolved during the thermal degradation (pyrolysis) of vinyl alcohol units
Evolution of host/guest interactions with heating in a palygorskite/methyl red (Maya Red) hybrid composite
No full textAn exceptionally stable hybrid material, fit for possible use as an innovative, cheap and ecologic pigment in the Cultural Heritage and Materials Science fields, can be obtained by grinding and heating palygorskite clay with the methyl red dye (2 wt%).
Due to its multiple analogies with the famed Maya Blue pigment (an ancestor of modern hybrid materials formed by indigo incorporation in palygorskite/sepiolite clay minerals), such a red/purple adduct can be considered an analogous Maya Red composite.
As per its renowned blue predecessor, the chemical and photo-thermal stability observed for this red equivalent is achieved through methyl red diffusion and bonding within the palygorskite tunnels, which occurs after heating or evacuation of a properly ground clay/dye mixture. Specific interactions form inside the host pores between the clay framework and dye reactive groups, contributing to ensure the composite stabilization at different temperatures.
An innovative, in-line coupled TGA-FTIR-GC-MS, synchrotron XRPD and molecular mechanics approach was performed on both pristine palygorskite and the related composite with methyl red with the aim to monitor the development of the interactions formed between the host and the guest while progressively heating. Such a study evidenced that several kinds of bonds can exist and differently affect this complex stability, each characterized by a specific binding energy and subjected to a dynamic but reversible evolution as a function of the magnitude of the heating treatment.
Weak to moderate temperatures (120-300°C) trigger zeolitic H2O loss and methyl red diffusion but do not imply release of Mg-coordinated OH2, which acts as H-bond donor to the dye carboxyl group. More severe heating (300-490°C) causes a two-step structural OH2 loss and triggers a ligand-displacement mechanism which favors straight interactions between octahedral Mg and the dye COOH acceptor atoms (i.e. oxygen).
Reversibility and shift between these different host/guest interactions severely affect the dehydration/rehydration process of the host framework, compared to the pristine clay. Several interrelated phenomena mutually interact in a sort of positive feedback: guest incorporation inside the tunnels prevents structural folding typical of pure palygorskite and modifies the release of both zeolitic H2O and structural OH2, consequently influencing both the nature and the strength of the host/guest interactions. Such a situation is further complicated by the different polymorphs of palygorskite (monoclinic and orthorhombic) showing peculiar and distinct behaviors, which concern both their affinity to form specific bonds with the encapsulated dye and the release of structural OH2 while heating.
Sheltering granted by incorporation in the host pores dramatically enhances methyl red thermal stability, whose degradation is likely to occur at temperatures sensibly higher than those decaying the isolated dye
Evolution and Reversibility of Host/Guest Interactions with Temperature Changes in a Methyl Red@Palygorskite Polyfunctional Hybrid Nanocomposite
Full text linkPalygorskite is a microporous clay mineral with several important applications, including use as dye nano-scaffold, due to its ability to incorporate apt guest molecules and form exceptionally stable composites. Such a property covers widespread fields of interest, from pottery pigments to light harvesting. In all these applications, the stability of these composites at progressively increasing temperatures is an important parameter to determine their condition of usage. This work investigates the nature and strength of the stabilizing host/guest interactions at the basis of the exceptional stability of the methyl red@palygorskite composite system, which undergo a dynamic but reversible evolution depending on the level of heating. A multi-technique analytical protocol involving synchrotron X-ray powder diffraction (S-XRPD) and thermogravimetric analysis (TGA) coupled with infrared spectroscopy (FT-IR) and gas chromatography (GC-MS) was followed, which allowed to sharply identify the species evolved during heating. Moderate temperatures (140°-300°C) cause stabilization of H-bonds between the structural H2O and the carboxyl group of the dye, whereas higher ones (> 300°C) trigger formation of direct COOH/octahedral Mg bonds favoured by dehydration. Cooling below 300°C implies gradual reversibility of the observed trend due to rehydration from environmental moisture; additional heating (> 400°C), conversely, causes methyl red decomposition, fragmentation and further expulsion from the host tunnels ( 500°C). The encapsulated dye in zwitterionic, trans and/or protonated form affects the hosting system properties, preventing structural folding and strongly modifying the mechanism of water release for both structural and zeolitic H2O. Experimental results were interpreted also with the help of structural models obtained by molecular mechanics simulations, offering atomistic insights on the mechanisms at the basis of the observed phenomena
Gallic acid grafting modulates the oxidative potential of ferrimagnetic bioactive glass-ceramic SC-45
Full text linkEffects of particle size on properties and thermal inertization of bottom ashes (MSW of Turin’s incinerator)
Full text linkThe aim of this study is twofold: (i) characterization of the bottom ashes from the Incinerator plant of the city of Turin (northern Italy), in terms of their chemical/phase compositions and capacity to release heavy metals in leachates, as a function of particle size; (ii) investigation of thermal treatments’ efficacy to promote inertization of the same bottom ashes, exploring time-temperature ranges with t ≤ 6 h and T ≤ 1000 °C. Special attention is paid to macro-sampling techniques in order to have samples that are representative of the average bottom ashes production. Micro-XRF, ICP-OES, SEM-EDS, Ion Chromatography and X-ray powder diffraction were used to investigate bottom ashes and leachates. Bottom ashes are mainly constituted by an amorphous phase, ∼66–97 wt%, regardless of particle size; the remaining phases are quartz, calcite, Fe-oxides, melilite and other minor crystalline materials. The amorphous phase exhibits a relevant dependence on particle size, and undergoes dissolution in water up to 20 wt%, thus being the most important component in affecting chemical species release. The smaller the bottom ashes’ particle size, the more the heavy metals (major species: Zn, Cu, Ti, Pb) and calcium contents increase, whereas silicon’s decreases. Electrolytic current observations in combination with phase/chemical composition and metals release as a function of particle size, suggest that bottom ashes partition into two classes, i.e. ≥1 and <1 mm, for inertization purposes. Thermal treatments exhibit partial efficacy to curb heavy metals mobility: whilst they reduce Cu release, they lead to a inverse effect in the case of Cr
Surface reactivity of amphibole asbestos. A comparison between two tremolite samples with different surface area
Full text linkSurface reactivity of a fibrous tremolite sample from Castelluccio Superiore (Italy) was investigated by means of free radical generation following incubation in H2O2solution buffered at pH 7.4, for several time points, ranging from 1 day to 1 month. Results obtained were compared with those of another fibrous tremolite sample (from Maryland, USA), with much smaller surface area. Structural, morphological, and chemical alterations induced on tremolite by incubation were investigated by HR-TEM/EDS. The generation of HO•and COO-•radicals following reaction of tremolite with H2O2or formate ion was investigated by spin trapping/EPR spectroscopy. The dissolution process and surface modification were slower for the Maryland sample, with lowest surface area. Surface modification indicated the occurrence of either low- or high-coordinated Fe centres on the surface, as well as the evolution of their nuclearity. In turn, iron centres determine the reactivity of the fibre surface and the yield of HO•and COO-•radical species. The evolution of radical reactivity over time was proved to be largely dependent on surface area, with the highest radical yield occurring for low-area tremolite incubated over long times. The experimental results obtained in this study as well as the comparison with previous studies further confirm that surface reactivity of mineral fibres and inorganic particles is not dependent on Fetotcontent per se, but is likely due to surface properties and occurrence of specific iron sites
Bioactive glass coupling with natural polyphenols: Surface modification, bioactivity and anti-oxidant ability
No full textMechanical properties and surface reactivity in relationship to toxicity of new Ti-Cu based hard metals
No full textSurface functionalization of bioactive materials with polyphenols for bone contact applications
No full textPolyphenols as smart molecules for the surface functionalization of bioactive materials in bone contact applications
No full text- …
