Ester Mateo

ZIF-8 micromembranes for gas separation prepared on laser-perforated brass supports

ZIF-8 is an imidazolate-based metal–organic framework (MOF). ZIF-8 micromembranes of 20–32 μm diameter are prepared by synthesizing the MOF on Nd:YAG laser-perforated 75 μm thick brass sheets (63/37 Cu/Zn). The laser irradiation activates the brass support, promoting ZIF-8 growth. A thick and continuous ZIF-8 membrane is crystallized on the laser irradiation outlet side of the support, while the inlet side and the inner surface of the microperforations are also coated with ZIF-8 intergrowth crystals. Laser perforated brass supports are not only cheap, flexible, strong, and easy to handle and to process as membrane materials; they are also chemically compatible with the ZIF-8 composition because of the shared Zn element. The ZIF-8 membranes obtained are characterized by XRD, SEM, EDX, TGA and N2 sorption analysis. Furthermore, the membranes are applied to the separation of equimolar H2–CH4, He–CH4, CO2–CH4 and O2–N2 mixtures confirming the expected molecular sieving effect due to the MOF microporosity.

Insight into the synthesis and characterization of zeolite millimeter-sized crystals

The effect of time, composition and structure-directing agents on the synthesis of silicalite-1 and octadecasil zeolite millimeter-sized crystals has been studied. Crystals up to about 3 mm size range were obtained and special attention was paid to their aspect ratio, thermal behavior, monocrystallinity and textural properties by means of electronic and optical microscopy, powder and single-crystal X-ray diffraction (XRD), thermogravimetry and Ar adsorption. For the silicalite-1 crystals obtained after 34 days of hydrothermal synthesis, more than one thousand specimens from two repeated batches were measured along a, b and c axes. Reproducibility was thus assessed simultaneously with a statistical analysis to obtain cumulative and differential distributions of crystal dimensions. Single-crystal XRD evidenced a high degree of monocrystallinity, while thermal analyses suggested that crystals with sizes above 125 μm have serious difficulties in activation, giving rise to high external specific surface area values upon Ar adsorption.

Laser control of zeolite nucleation.

Precursor solutions for the synthesis of zeolites are irradiated by means of a Nd-YAG laser. These solutions are subsequently submitted to a hydrothermal treatment and the results analyzed by X-ray diffraction and electron microscopy. Laser irradiation promotes the formation of silica nanoparticles that nucleate into zeolite (silicalite-1), following a hydrothermal treatment. The average crystal size (in the 0.6-3.6 μm range) of the zeolite exponentially decreases as a function of laser irradiation time. In addition, a longer irradiation time results in a narrower crystal size distribution.

A model for the diagenetic formation of sandstone-hosted copper deposits in Tertiary sedimentary rocks, Aragón (NE Spain): S/C ratios and sulphur isotope systematics

Abstract Numerous small, noneconomic copper deposits are associated with syntectonic sandstones of Tertiary age (Campodarbe and Uncastillo Formations) in the South Pyrenean foreland basin (SPFB). Sulphides, native metal, and their oxidation products occur within elongate lenses in fluvial sandstones and conglomerates. In all cases, the geometry of the ore is highly consistent with the primary depositional and biogenic structures of the host sandstones. Copper ores replace wood debris and diagenetic pyrite or, more frequently, appear as intergranular cement replacing previous diagenetic calcite cement. Sulphide sulphur and organic carbon distribution shows that pyrite-rich sandstones are the copper ore precursor, and that mineralizing processes provoked the depletion of both reduced S and organic C as a consequence of interaction with an oxidized Cu-bearing fluid. On the other hand, low δ34S values are consistent with bacteriogenic derivation of sulphur after Pyrenean evaporites. Petrographic studies, sulphide sulphur and organic carbon concentrations, and δ34S values suggest that Cu-rich fluids were introduced into reduced sediments during diagenesis. Mineralizing processes took place in two different periods: the first one related to the filling of the Jaca Basin during erosion of the Pyrenean basement and the second one related to the emplacement of a thrust ramp which initiated the erosion of the previously formed cupriferous sandstones.

X-ray photoelectron spectroscopy characterization of natural chromite from Mercedita Mine (Eastern Cuba): quantification of the Fe3+/Fe2+ ratio

The quantitative estimation of the Fe 3+ /Fe 2+ ratio has a crucial interest to know the upper-mantle oxidation state. The relative proportions of Fe 3+ and Fe 2+ are usually estimated from electron microprobe analysis (EPMA) assuming chromite stoichiometry. In order to test a new technique to estimate the Fe 3+ /Fe 2+ ratio and to avoid EPMA systematic errors, X-ray photoelectron spectroscopy (XPS) has been used to determine the Fe 3+ /Fe 2+ ratio in four chromite samples from Cuba and the results compared with those obtained by EPMA. Due to the high surface sensitivity of XPS the samples were etched by removing the outermost layers by bombarding with an Ar + ion gun. Therefore, the surface, as well as 8, 16 and 24 nm in-depth levels, were analyzed, revealing that the spectra change significantly with depth. Thus, from the surface down to 24 nm deep, Fe 3+ concentrations decrease from values up to 10 at.% to values below the detection limit of XPS (0.1 at.%). By contrast, a systematic Fe 3+ detection (between 1.32 and 4.04 at.%) was observed by EPMA. Consequently, XPS allows us to calculate ferric iron contents, a key datum for the calculation of the real structural formula of chromite. XPS can therefore be considered a useful tool in evaluating mantle oxidation state.

Activation of giant silicalite-1 monocrystals combining rapid thermal processing and ozone calcination

A rapid thermal processing (RTP) technique combined with ozone/oxygen calcination was applied to activate and heal the structure of a 1.1 mm2 section of a silicalite-1 giant monocrystal. Crystallinity was monitored by single crystal X-ray diffraction and high sensitive thermogravimetry (TGA) was performed to prove the complete removal of the structure directing agent.