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1.
DRIFTS study of surface reactivity to NO2 by zinc nanoparticle aggregates and zinc hollow nanofibers
Zinc nanostructures synthesized with different morphologies from the same evaporation/condensation technique are studied with concern to surface reactivity to NO2 by Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS). Synthesis of nanopowders is obtained, according to previous work, by gas flow thermal evaporation at 540 °C of bulk Zn grains. Two types of Zn powders are obtained and studied in experiments. The first one is collected on the cold walls of the reactor as a deposit produced by thermophoretic effect. It is constituted by grains (∼10 μm) originated by the stratification of smaller aggregates (∼200 nm) and isolated primary particles (∼50 nm) born in the gas flow. The second type of powder is grown from the condensation of Zn chemical vapors within the expansion orifice of the quartz reactor after relatively long time (∼1 h) deposition process. It is constituted mainly by hollow Zn nanofibers with external and internal diameter about 100 and 60 nm. Preliminary characterization of the two types of powders is made by SEM, TEM, XRD. Thereafter, the two types of samples are studied by DRIFTS at variable temperature (VT). Comparison is made between the home-synthesized nanopowders with respect to commercial Zn standard dust. The Zn hollow nanofibers when exposed to NO2 are found to exhibit dramatic reactivity, which is not observed at all either in the case of clustered aggregate zinc or of commercial Zn dust powders. Results indicate that, at increasing temperature from RT to 300 °C, the hollow nanofibers surface reacts distinctively with adsorbant gas NO2, with contemporary formation of a progressively growing narrow absorption band at 2500 cm−1 and contemporary depression of a doublet (∼1600-1628 cm−1) band. In order to justify this striking spectral feature, we propose the occurring of a possible polymerization process at nanofibers surface where most probably as a consequence of pre-treatment and exposure to gas NO2 a very thin film of ZnO is formed. The possible role of huge specific surface of hollow nanofibers as inferred by preliminary SEM, TEM, XRD studies is discussed. 相似文献
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Computerized analytical instruments of late 70's and 80's are facing rapid technological obsolescence, although they are often retaining good analytical performances. Responsibility is to be attributed to the fast advance in computer technology, which is leaving little or no back-compatibility with old standards and data formats. Rejuvenation may be reached by simple hardware and software modifications, to allow data exchange with modern PC's and LIMS. Two typical case histories for spectrometric instrumentation of late 70's are then presented and discussed in a general fashion. 相似文献
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Fatema Bakro Malgorzata Jedryczka Katarzyna Wielgusz Barbara Sgorbini Raffaella Inchingolo Vladimiro Cardenia 《Journal of separation science》2020,43(14):2817-2826
Hemp (Cannabis sativa L.) has become widely used in several sectors due to the presence of various bioactive compounds such as terpenes and cannabidiol. In general, terpenes and cannabidiol content is determined separately, which is time consuming. Thus, a fast gas chromatography with flame ionization detection method was validated for simultaneous determination of both terpenes and cannabidiol in hemp. The method enabled a rapid detection of 29 different terpenes and cannabidiol within a total analysis time of 16 min, with satisfactory sensitivity (limit of detection = 0.03–0.27 µg/mL, limit of quantitation = 0.10–0.89 µg/mL). The inter‐ and intraday precision (RSD) was <7.82 and <3.59%, respectively. Recoveries at two spiked concentration levels (low, 3.15 µg/mL; high, 20.0 µg/mL) were determined on both apical leaves (78.55–101.52%) and inflorescences (77.52–107.10%). The reproducibility (RSD) was <5.94 and <5.51% in apical leaves and inflorescences, respectively. The proposed and validated method is highly sensitive, robust, fast, and accurate for determination of the main terpenes and cannabidiol in hemp and could be routinely used for quality control. 相似文献
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Barbaro P Bianchini C Giambastiani G Oberhauser W Bonzi LM Rossi F Dal Santo V 《Dalton transactions (Cambridge, England : 2003)》2004,(12):1783-1784
New systems based on cationic chiral phosphine-rhodium complexes anchored to a commercial cation-exchange gel-type resin showed high efficiency and easy recycling in the asymmetric hydrogenation of prochiral olefins. 相似文献
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