Zdeněk Bastl

Laser photolysis of liquid benzene and hexafluorobenzene: Graphitic and polymeric carbon formation at ambient temperature

Abstract ArF laser-induced liquid-phase photolysis of benzene and hexafluorobenzene afford similar products which are polyaromatic hydrocarbons or fluorocarbons with the preponderance of biphenyl or decafluorobiphenyl, graphite, and polymeric H-containing or F-containing carbon. The remarkable feature is that the graphite formation occurs at ambient temperature of the irradiated liquids; photolytic graphitization modes must therefore be different from those occurring in thermally-induced graphitization at temperatures above 2500 °C.

Hoveyda-Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15.

Summary A commercially available Hoveyda–Grubbs type catalyst (RC303 Zhannan Pharma) was immobilized on mesoporous molecular sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and solvent used (the lowest leaching was found for ring-closing metathesis of 1,7-octadiene in cyclohexane – 0.04% of catalyst Ru content). Results of XPS, UV–vis and NMR spectroscopy showed that at least 76% of the Ru content was bound to the support surface non-covalently and could be removed from the catalyst by washing with THF.

Spectroscopic study of the surface oxidation of mechanically activated sulphides

Surfaces of chalcopyrite CuFeS2, sphalerite ZnS, pyrite FeS2 and galena PbS modified by mechanical activation have been studied by means of infrared (IR) spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray photoelectron spectroscopy (XPS). The different oxidation species were identified on mechanically disordered surfaces of the minerals. The mechanochemical surface oxidation increases with the time of mechanical activation. The sulphides under study are partially covered with oxidised sulphates and carbonate species. They are distinguished by an affinity to the formation of surface compounds. According to the affinity of sulphides for mechanochemical S2−→S6+ surface oxidation the decreasing rate was observed in the following order: FeS2>PbS>CuFeS2>ZnS. The ratio between bivalent and hexavalent form of sulphur depends on the degree of mechanochemical surface oxidation of the sample under study.

Very low rate constants of bimolecular CO adsorption on anionic gold clusters: Implications for catalytic activity

Absolute bimolecular rate constants for radiative stabilization of CO on gold cluster anions are measured by Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry, employing a sequence of reaction gas pulses to acquire sufficient product intensities of these exceedingly inefficient reactions. While some of the observed reactivity patterns seem to be in agreement with the jellium model if CO is viewed as a two electron donor, it cannot provide an explanation for some other observations, for instance for the secondary reactions of Au10− and Au11−. Interesting cooperative effects are observed in conjunction with O2, which is present as a trace component of the reaction gas. No evidence is found for catalytic CO2 formation on the clusters.

Si/C phases from the IR laser-induced decomposition of silacyclobutane and 1,3-disilacyclobutane

CO 2 laser-induced infrared multiphoton decomposition (IRMPD) and SF 6 photosensitized decomposition (LPD) of silacyclobutane (SCB) and 1,3-disilacyclobutane (DSCB) in the gas phase results in the very efficient deposition of Si/C/H and SiC materials, and it is inferred that the process is dominated by formation of transient silene ; silene rearrangement to methylsilylene ; silene and methylsilylene dehydrogenation ; and polymerization of SiCH n (n < 4) species. The deposits are sensitive to oxygen. Decomposition and SiC formation are favoured with IRMPD experiments conducted with high-energy fluxes. The laser technique is promising for low-temperature chemical vapour deposition of amorphous SiC.

Pt0 in alkali faujasites. 1. Preparation by thermal decomposition of [Pt(NH3)4]2+ in vacuum

Pt2+ autoreduction during the thermal vacuum decomposition of [Pt(NH3)4]2+Me+ faujasites as well as the reaction of CO+NO were studied in dependence on the zeolite composition (effect of different alkali ions Me+: Li, Na, K, Cs, and zeolite Si/Al ratio: X and Y zeolites). Infrared spectroscopy was employed to characterize the surface species during the decomposition of the tetraamine complex. Gases evolved in this process were identified by mass spectrometry (which was also used in the CO+NO reaction), t.p.r., XPS and TEM assisted in the examination of the metal/zeolite system. It was found that at least four ammonia complexes are formed during the vacuum decomposition of [Pt(NH3)4]2+ and that two of them are more abundant in Y zeolites. Ammonia is evolved from the zeolites in two temperature regions. In the low temperature interval, the higher electropositivity and size of the alkali cations facilitate the disruption of Pt2+-N bonds in the same way in both X and Y zeolites. In the high temperature region, where the autoreduction of Pt2+ is dominant, the cations affect temperature of the NH3 release to a lesser extent. However, the amount of gases evolved from Y zeolites in this temperature region is higher compared with that from X zeolites, which corresponds with a higher fraction of more thermally stable Pt ammonia complexes found in Y zeolites. Under our experimental conditions, about 20–30% of Pt2+ does not undergo autoreduction. Pt clusters are formed inside the zeolite cavities with a size of 1–4 nm. No effect of the faujasite matrix (Si/Al ratio, nature of alkali cations) on the extent of the autoreduction or on the Pt0 size and location is observed in contrast to the reaction of CO+NO, which is substantially accelerated by the increasing electropositivity, diameter, and number (X > Y) of alkali cations.

Laser-induced aerosol particle formation from a gaseous mixture of trimethyl(2-propynyloxy)silane and acrolein

Abstract Upon exposure to N2 laser light, a gaseous mixture of trimethyl(2-propynyloxy)silane (TMPSi) and acrolein (AC) produced sedimentary spherical aerosol particles with a mean diameter of ≈ 0.5 μm. The IR spectrum of the sedimentary aerosol particles showed bands characteristic of polyacrolein, and XPS showed two Si 2p bands assignable to elemental silicon and silicon bonded in an organosilicon polymer, indicating that TMPSi was incorporated into the parent aerosol particles of polyacrolein, and cleavage of Si-C and Si-O bonds took place in the aerosol particles. The nucleation process of the aerosol particles was investigated by measuring He-Ne laser light intensity scattered by the aerosol particles as formed under irradiation with N2 laser light.

Chemical vapour deposition of polycarbosilanes via ArF laser-induced photolysis of sila-, 1-methyl-1-sila- and 1,3-disila-cyclobutanes

Laser-induced photolysis of the title silacycles in the gas phase is dominated by cleavage of the four-membered ring and results in deposition of polycarbosilanes formed by polymerization of assumed transient silenes and silylenes. The polycarbosilane films are reactive towards oxygen.

Nanobubble-assisted formation of carbon nanostructures on basal plane highly ordered pyrolytic graphite exposed to aqueous media.

Ambient gas nanobubbles of size approximately 10(1)-10(2) nm occupying the hydrophobic surface of basal plane highly ordered pyrolytic graphite (HOPG) immersed in aqueous media at room temperature cause exfoliation of the top graphene layers, as revealed by both in situ and ex situ atomic force microscope (AFM) imaging. The formation of nanoparticles composed mostly from graphene-based nanoscrolls, nanohorn-like and onion-like nanostructures was resolved by high resolution transmission electron microscopy (TEM) and examined by diffraction and x-ray photoelectron spectroscopy (XPS) analyses. The diameter of nanostructures varied from about 5 nm for single-layered scrolls to tens of nanometres for multishells. Raman spectroscopy confirmed the structural rearrangement of the HOPG basal plane after the above-mentioned treatment. The implications for nanobubble interfacial forces are discussed.

IR laser-induced reactive ablation of silicon monoxide in hydrogen and water atmosphere

TEA CO2 laser induced ablation of solid amorphous silicon monoxide in H2 and H2O atmosphere results in deposition of hydrogenated SiOx films, which reveals that ablated silicon monoxide fragments are reactive towards H2 and H2O. The films analyzed by FTIR and XP spectroscopy are revealed as rich in H, composed of Si0 and several SixOyHz configurations and containing both Si–OH and Si–H bonds. The films produced in H2O have (Si)H mostly bonded in the (O3)Si–H unit and those produced in H2 have H attached to Si which is bonded to 1–3 oxygen atoms.