Abstract
Octahedral molecular sieves (OMS) are built of transition metal-oxygen octahedra that delimit sub-nanoscale cavities. Compared to other microporous solids, OMS exhibit larger versatility in ...properties, provided by various redox states and magnetic behaviors of transition metals. Hence, OMS offer opportunities in electrochemical energy harnessing devices, including batteries, electrochemical capacitors and electrochromic systems, provided two conditions are met: fast exchange of ions in the micropores and stability upon exchange. Here we unveil a novel OMS hexagonal polymorph of tungsten oxide called
h’-WO
3
, built of (WO
6
)
6
tunnel cavities.
h’-WO
3
is prepared by a one-step soft chemistry aqueous route leading to the hydrogen bronze
h’-H
0.07
WO
3
. Gentle heating results in
h’-WO
3
with framework retention. The material exhibits an unusual combination of 1-dimensional crystal structure and 2-dimensional nanostructure that enhances and fastens proton (de)insertion for stable electrochromic devices. This discovery paves the way to a new family of mixed valence functional materials with tunable behaviors.
Leonardo da Vinci (1452-1519) is a key artistic and scientific figure of the Renaissance. He is renowned for his science of art, taking advantage of his acute observations of nature to achieve ...striking pictorial results. This study describes the analysis of an exceptional sample from one of Leonardo's final masterpieces: The Virgin and Child with St. Anne (Musée du Louvre, Paris, France). The sample was analyzed at the microscale by synchrotron-based hyperspectral photoluminescence imaging and high-angular X-ray diffraction. The results demonstrate Leonardo's use of two subtypes of lead white pigment, thus revealing how he must have possessed a precise knowledge of his materials; carefully selecting them according to the aesthetical results he aimed at achieving in each painting. This work provides insights on how Leonardo obtained these grades of pigment and proposes new clues regarding the optical and/or working properties he may have tried to achieve.
A new variety of alumina with micron-sized crystallization was obtained in mixture with other phases (a Si-doped transition alumina, α-Al2O3 and small amounts of mullite) by firing an Al2O3:SiO2 ...(12:1) gel at 1200 °C, beyond the domain of existence of the heretofore known transition aluminas. The so-called ω-Al2O3 transforms very slowly into α-Al2O3, even at such temperatures. According to X-ray diffraction /Rietveld analysis, the ordered orthorhombic (space group P21212) crystal structure corresponds to a 1 × 1.5 × 1 superstructure of the cubic spinel cell, with a 50 % deficiency in the occupancy of the octahedral sites in 1/3rd of the (010) layers. Though many arguments are in favor of a pure - or almost pure - form of alumina, no evidence can be given of the absence of silicon.
The 3-layer sequence of new ω-Al2O3 results from the insertion of a cation-deficient octahedra layer into the usual spinel array. Display omitted
•A new variety of micron-sized alumina.•Long-time metastability up to 1200 °C.•A novel form of fully ordered cation-deficient spinel structure.
The European Synchrotron Radiation Facility (ESRF) has recently commissioned the new Extremely Brilliant Source (EBS). The gain in brightness as well as the continuous development of beamline ...instruments boosts the beamline performances, in particular in terms of accelerated data acquisition. This has motivated the development of new access modes as an alternative to standard proposals for access to beamtime, in particular via the "block allocation group" (BAG) mode. Here, we present the recently implemented "historical materials BAG": a community proposal giving to 10 European institutes the opportunity for guaranteed beamtime at two X-ray powder diffraction (XRPD) beamlines-ID13, for 2D high lateral resolution XRPD mapping, and ID22 for high angular resolution XRPD bulk analyses-with a particular focus on applications to cultural heritage. The capabilities offered by these instruments, the specific hardware and software developments to facilitate and speed-up data acquisition and data processing are detailed, and the first results from this new access are illustrated with recent applications to pigments, paintings, ceramics and wood.
Catalysts enriched in Zinc ferrite (ZFO) were synthesized using coprecipitation and hydrothermal methods. Mixtures of crystalline nanoparticles (ZFO and α-Fe2O3, several allotropic varieties of FeO) ...were characterized by various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM, SEM), N2 sorption, UV-visible spectrophotometry (UV-Vis) and X-ray photoelectron spectroscopy (XPS). After detailed characterizations, the catalytic performance of the solids (1 g/L) in the degradation of amoxicillin (AMX) (10 mg/L) as an antibiotic pollutant in water was evaluated. In addition, we used air as the oxygen source and adjusted the pH to 5.0. Consequently, the catalysts obtained via the hydrothermal method HT-ZFO had a high activity (100% of AMX removal in less than 100 min when an LED (75 W) light was used) compared to a similar mixture of oxides with graphene HT-ZFO-GO (a longer time of 150 min) that was necessary for the complete degradation of AMX. Impregnation with an aqueous solution containing 80 mg of GO obtained using Hummer’s method, reduced into RGO by an ultrasound treatment, enhances the initial reaction rate but is associated with a prolonged time for complete AMX removal (10 ppm in water) that we attribute to its spontaneous corrosion.
This study is the first systematic survey of a large corpus of zinc white (ZnO) artists’ materials. Zinc white is a white pigment developed within the wave of 19th-century technological developments ...in the paint industry. The composition, particle morphology and size, and luminescence of 49 zinc white samples from artists’ materials were characterized, including three references of known synthesis methods (indirect and direct) and synthesized by the authors (ZnO nanosmoke). The corpus included historical and modern zinc white pigment powders and paint materials from the leading European and American color manufacturers. The study aims to characterize and evaluate the variability of the properties of zinc white and its paint formulations. The reference materials presented properties in agreement with the literature: indirect ZnO exhibited submicron prismoidal blue-luminescent particles of higher purity than direct ZnO, which had larger acicular green-luminescent particles. ZnO nanosmoke presented acicular (tetrapod-like) blue/green-luminescent nanoparticles. Composition, particle morphology, size, and documentary sources suggested a production via the indirect method for the analyzed corpus. However, the luminescence behavior was more complex to interpret. The fundamental emission of ZnO was not always detected, even in pure ZnO powders. Three trends were identified: smaller ZnO particles for the most recent samples; green luminescence connected to larger particle size; fewer trace elements, and of the same type (i.e., lead, sulfur) for historical materials. Another interesting finding was the detection of hydrozincite in some powders, likely a degradation product of ZnO. In terms of methodology, cathodoluminescence proved a valuable tool for pigment identification. The study provides a database of zinc white references for pigment and artwork analysis.
Since its discovery in 1959 as a transient nanocrystalline product of the thermal transformation of aluminum‐rich clays, the so‐called Al–Si spinel has been the object of numerous studies aimed at ...determining its composition. In this work, samples obtained from fired kaolinite‐ and halloysite‐containing clays were analyzed using X‐ray diffraction, leading to conclude in a single cubic (space group Fd‐3m) form, with an unvarying size of crystallites of 5 nm and a constant cell volume, typical of a transition alumina form. Trial‐and‐error Rietveld fitting procedure revealed a crystal structure consisting in an oxygen close packing and a disordered cation sublattice that differs from the known forms of spinel alumina. Rietveld quantitative phase analysis based on this model was successfully implemented on a series of fired halloysite clays, giving a first quantitative insight on the transformations in the 980–1260°C range.
The resolution of the crystal structure of the “cubic Al–Si spinel” allows the first quantitative Rietveld analysis of the thermal transformation of kaolinite
Three major corpora of architectural glazed bricks from Ancient Mesopotamia dating to the Neo-Assyrian (Aššur and Khorsabad sites) and the Neo-Babylonian (Babylon site) Periods have been submitted to ...an in-depth comparative study of the orange–yellow and black glazes. Distinct hues in the orange–yellow range were observed according to the archaeological site. They appear to have been well mastered by the glassmakers, consisting in the ex situ preparation of the antique lead antimonate pigment and its mixing with transparent soda-lime glass frit or with the glass-forming components. The intentional addition of hematite or of Cu2+ colouring ions in a controlled amount is suggested in two cases. SEM-EDX and Raman analysis of the lead antimonate pigments have pointed out different chemical substitutions in their pyrochlore structure, mainly Fe3+ in the Sb5+ site and Ca2+ in the Pb2+ site, the proportion of which being correlated to the pigment shade (from pale yellow to orange–red). Part of these substitutions arises from the chemical reaction of the pigment with the hematite and glass melt during firing. Regarding the black glazes, an unexpected colouring technique involving copper sulphide nanoparticles together with the chromophore Fe3+-S2− is highlighted for Khorsabad (8th century BC) and for Babylon (6th century BC). For Aššur blacks, the study reveals a change in their colouring technique between the 9th and 8th centuries BC, from a colouration with Mn oxides to an enigmatic one that could also have involved copper sulphide nanoparticles.
The structural properties, X-ray-excited radioluminescence and thermally stimulated luminescence (TSL) of Ca9Ln(PO4)7 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were investigated. ...(La–Nd) occupied mainly the largest M3 site, whereas the smallest lanthanides (Yb, Lu) adopted the smallest octahedral M5 site. The intermediate-sized ions (Sm–Tm) occupied the medium-sized sites M1 and M2. Only the Ln3+ ions with the highest Ln3+/4+ ionization energy (Ln=Pr, Nd, Tb, Dy) were able to trap holes and become luminescent centers for thermally stimulated Ln3+ 4f–4f emission. For low Ln3+/4+ ionization potential (Ln=La, Gd, Yb, Lu), no hole trapping at Ln3+ was possible and Mn2+ impurities at the M5 sites were the effective hole traps and luminescent centers for thermally stimulated Mn2+ 3d–3d red emission. Very broad TSL peaks were attributed to thermally assisted detrapping of electrons from positive traps, possibly Ln3+ at Ca2+ sites, tunneling back towards the hole trap/luminescent center. Ca9Ln(PO4)7 compounds doped with Ln=Tb or Lu were found to be efficient X-ray-excited long-lasting phosphorescence materials, emitting in the green and in the red, respectively.
PDF
