1,720,989 research outputs found
Photodegradation of linseed oil by Cd.ZnS Nanocrystal Solid Solutions (NCSSs): effect of structure and composition
No full textThermal analysis of MgFe-Cl Layered doubled hydroxide (LDH) directly synthetized and produced “via memory effect”
No full textLayered doubled hydroxides (LDHs) are known to be an interesting class of 2D layered materials, with a wide range of possible composition and a flexible structure suitable for topochemical reactions. Thus, LDHs have been applying in different fields, such as catalysis, energy storage and all the applications in which a high exchange capability (of both cations and anions) is required. For remediation purpose, a MgFe-Cl LDH [(Mg0.662+Fe0.333+(OH)2]0.33+(Cl0.33-)0.33- (MFC in the following) could be a promising candidate to capture the toxic CrO42− from water, in exchange with the Cl− in an efficient way. The synthesis of this compound might seem simple, consisting of a coprecipitation reaction, and actually, it is strongly affected by the environmental carbon dioxide able to replace the Cl− with the more stable CO32−. To avoid this problem, LDHs could be also prepared with a rehydration of their calcinated oxide (memory effect). In this work were prepared two samples of MFC: one via coprecipitation (MFC-1 in the following) and one via “memory effect” (MFC-mem in the following). Both the compounds were characterized by means of X-ray powder diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and differential thermal analysis-thermogravimetry (DTA-TG) coupled with evolved gas analysis. The results demonstrated that the synthesis of pure MFC is very difficult, and only a minimum contamination of carbon dioxide led to the formation of the carbonate LDH in a massive way. It was also demonstrated that Mg-Fe LDHs in the presence of carbonate could catalyse the formation of the formic acid (HCOOH) at low temperature (< 300 °C)
Cd.ZnS paint films degradation: effect of pigment’s properties and environmental conditions
No full textCd.ZnS photocatalytic activity in paintings: effect of structure, composition and particle size
No full textStructural properties of defective (CH3NH3)2Cu(Cl1-xBrx)4 compounds
No full textThe crystal structures of (CH3NH3)2Cu(Cl1-xBrx)4 compounds have been investigated by means of synchrotron powder X-ray diffraction and pair distribution function analysis at room temperature. As a result, new insights are gained about the structural properties of these compounds, suggesting a monoclinic symmetry (space group No. 14: P21/c - C_{2h}^{5}) induced by the co-operative orbital ordering produced by the Jahn-Teller distortion characterizing the 3d9 Cu2+ ion. In contrast to previous studies, a significant amount of vacancies is found at halogen positions, a feature that can be likely ascribed to the synthesis technique adopted in the present study. Br atoms preferentially occupy axial positions, likely on account of reduced steric hindrance at these sites
Gli dei nel cristallo: studio del blu egizio, mappatura di superficie e rilievo tridimensionale del sarcofago del sacerdote Pasherienaset
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Structure Dynamics and Vibronic Coupling in AECuSi4O10 (AE: Ca, Sr, Ba) Compounds
No full textAlkaline earth copper silicate-based pigments are compounds of interest from a historical point of view, thanks to their interesting near-infrared (NIR) photoemission. It is well recognized that the emission originates from the Cu2+ d-d transitions inside the chromophore group [CuO4]6-; however, the optical properties are slightly different, probably related to a variation in the local structure. Here, we report detailed X-ray powder diffraction and pair distribution function analysis of AECuSi4O10 (AE = Ca2+, Sr2+, Ba2+) silicates. Remarkably, our investigation shows that all of these compounds are characterized by a complex structural dynamic involving the [SiO4]4- tetrahedral framework embedding the [CuO4]6- chromophore group. This structure dynamics induces a vibronic coupling, allowing the d-d transitions responsible for the characteristic color of the compounds as well as a strong vibronic broadening of the electronic states. As a consequence, the absorption and emission spectra in the visible and NIR range are influenced by the alkaline earth metal and are characterized by broad bands and display the Stokes shift typically observed in vibronic systems
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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