Szilvia Klébert

Guest escape and uptake in nonporous crystals of a gold(I) macrocycle

The nonporous gold(I) diphosphine complex [Au(2)(cis-dppe)(2)](NO(3))(2) [1, cis-dppe = cis-1,2-bis(diphenylphosphino)ethylene] is robust enough to trap guests, but at the same time, it is flexible enough to allow guest release without destruction of its crystal lattice. This nonporous gold(I) compound 1 is also efficient at capturing and releasing carbon dioxide in a controlled manner.

Acetone alkylation with ethanol over multifunctional catalysts by a borrowing hydrogen strategy

Step by step alkylation of acetone (A) with ethanol (E) in a ratio of 1:2 was investigated. A fixed bed flow-through reactor system was used at a total pressure of 21 bar and in the temperature range of 150–350 °C in inert He or a reducing H2 medium. Following the hydrogen borrowing methodology, two types of catalysts were prepared; using neutral activated carbon (AC) and alkaline hydrotalcite (HT) supports, namely 5 wt% Pd/AC in the presence of alkaline additives (10, 20 and 30 wt% KOH or 20% K3PO4); 9 wt% Cu/HT and 5 wt% Pd/HT. The catalysts were activated in a H2 flow at 350 °C. Different yields of mono- or dialkylated ketones were observed. In a hydrogen medium over the same catalyst systems the ketone products could be reduced to alcohols. In this study the Pd/HT catalyst seems to be the most promising for fuel production based on biomass fermentation.

Spark plasma sintering of Si3N4/multilayer graphene composites

Abstract Mulitlayer graphene reinforced silicon nitride composites were prepared by spark plasma sintering to investigate the effect of the graphene addition on mechanical properties. The composites contained multilayer graphene (MLG) in various (0, 1, 3 and 5 wt%) content. Significantly higher fracture toughness of 8.0 MPa m1/2 was obtained at 1% MLG content, however, on further increasing the graphene content the toughness did not increase, but dropped to the value of the monolithic silicon nitride. The maximum hardness of 18.8 MPa was also obtained at 1% MLG, while at higher MLG contents it gradually decreased. Graphical Abstract

Decomposition of Chlorobenzene by Thermal Plasma Processing

Decomposition of chlorobenzene as a model molecule of aromatic chlorinated compounds was studied in radiofrequency thermal plasma both in neutral and oxidative conditions. Optical emission spectroscopy was applied for the evaluation of the plasma excitation and molecular rotational-vibrational temperature. Atomic (C, H, O) and molecular (CH, OH, C2) radicals were identified, while the morphology of the formed soot was characterized by electron microscopy. Organic compounds adsorbed on the surface of the soot after plasma processing were comprised of various polycyclic aromatic hydrocarbons (PAH) and chlorinated PAH molecules. Their amount was greatly affected by experimental conditions, especially the oxygen content and plate power. The higher input power reduced the ring number of the PAH molecules. Addition of oxygen significantly reduced the amount of both PAHs chlorinated PAH molecules but enhanced the formation of polychlorinated benzene compounds.

Optical emission spectra analysis of thermal plasma treatment of poly(vinyl chloride)

Abstract Decomposition of poly(vinyl chloride) (PVC) was investigated in radiofrequency thermal plasma in neutral, oxidative and reductive conditions. Optical emission spectroscopy (OES) was applied for the characterization of the plasma column. OES was used to identify active plasma components such as excited atoms, ions, radicals and molecules. The spectra were dominated by molecular C2, CN, OH, and CH bands, and atomic H, Ar, C, Cl and O lines. Emission intensities of main species were monitored versus various experimental parameters. The rotational-vibrational temperatures determined from different bimolecular species were considered in the range of 2000–6400 K. Solid soot samples were collected and purified to investigate the possibility of graphene formation as a by-product of the decomposition process. Graphical Abstract

Acetic acid hydroconversion over mono-and bimetallic indium doped catalysts supported on alumina and silicas of various textures

Abstract Consecutive hydroconversion of acetic acid (AA) to ethanol was compared over monometallic and novel bimetallic (containing In as guest metal) catalysts on alumina and silica supports (inter alia highly ordered SBA-15) of different porosity and pore structure. The transformation was studied in a fixed bed, flow-through reactor in the temperature range of 220–380°C using hydrogen flow at 21 bar total pressure. AA hydroconversion activity of Cu and Pt catalysts and the yield of selectively produced alcohol were increased drastically by applying SBA-15 as highly ordered, mesoporous silica support instead of alumina. The most active nickel catalysts do not allow the selective addition of hydrogen to carbon-oxygen bonds independently of supports producing mainly CH4; however, indium doping can completely eliminate the hydrodecarbonylation activity as found in earlier studies. The textural properties of studied silica supports of various textures such as SBA-15, CAB-O-SIL, and Grace Sylobead have a profound impact on the catalytic performance of Ni and Ni2In particles. Graphical Abstract

Direct immobilization of manganese chelates on silica nanospheres for MRI applications

The development of tissue specific magnetic resonance imaging (MRI) contrast agents (CAs) is very desirable to achieve high contrast ratio combined with excellent anatomical details. To this end, we introduce a highly effective manganese(II) containing silica material, with the aim to shorten the longitudinal (T1) relaxation time. The microporous silica nanospheres (MSNSs) with enlarged porosity and specific surface area were prepared by a surfactant assisted aqueous method. Subsequently, the surface silanol groups were amino-functionalized, reacted with diethylenetriaminepentaacetic (DTPA) dianhydride and finally deposited with Mn2+. After comprehensive characterization, the MRI properties of functionalized MSNSs were investigated. The resulting nanospheres demonstrated substantial contrast enhancement during the in vitro MRI investigations, which was also evidenced by significant contrast enhancement on T1-weighted MR images in vivo. Moreover, in vitro cytotoxicity assay of functionalized MSNSs on hepatocyte mono- and hepatocyte-Kuppfer cell co-cultures showed no significant decrease in cell viability. Our findings confirmed our hypothesis, that Mn2+-chelating MSNSs are appropriate candidates for liver-specific T1-weighted MRI CAs with high relaxivities (r1=7.18mM-1s-1).

Enhancing the accessibility of starch size and cellulose to enzymes in raw cotton woven fabric by air-plasma pretreatment

In this paper, raw cotton fabric was pretreated with non-thermal atmospheric air-plasma and the accessibility of the surface polymers of the fibers and yarns that act as respective substrates for the enzymes was evaluated. Results proved that plasma slightly destroyed and oxidized the starch size on the surface of warp yarns and partially removed the thin and perfectly hydrophobic waxy coverage of the fibers in weft yarns, creating deep “pits” with a depth of 215 nm. This latter process contributed to the exposure of cellulose and pectin located under the waxy outer layer of the elementary fibers in the weft yarns, and significantly increased the surface roughness of the fibers (from Rq of 25 to 67 nm for the raw and 180 s plasma-treated samples, respectively). Amount of the reducing sugars released during the amylase and cellulase digestion of the plasma-treated fabrics confirmed that air-plasma significantly increased the accessibility of the starch and cellulose, respectively, to the enzymes and resulted in an enhanced solubilization of both polymers. Since the plasma-treated substrates displayed significantly faster enzyme reactions, the time of enzymatic treatments can be sharply reduced.

Thermal Plasma Decomposition of Tetrachloroethylene

Tetrachloroethylene (C2Cl4) has been used widely as a solvent and dry cleaning agent, but was later specified as possible human carcinogen. As a result, its safe treatment became a priority. In this paper, we report on its decomposition in an atmospheric radiofrequency thermal plasma reactor. Main components of the exhaust gases were determined by Fourier transform infrared spectroscopy. We found that complete decomposition can be achieved in either oxidative or reductive conditions but not in neutral one. The solid soot product was characterised by transmission electron microscopy and specific surface area measurement. Organic compounds adsorbed on the surface of the soot were extracted by toluene and comprised, based on gas chromatography mass spectrometry, of various perchlorinated aliphatic (for example hexachlorocyclopentadiene) and aromatic compounds (like hexachlorobenzene, octachloronaphthalene or octachloroacenaphthylene). Several nitrogen containing molecules were also identified whose presence are rare during thermal plasma treatments. Further investigation of the extract by mass spectrometry revealed various higher molar mass chlorinated carbon clusters and two types of fullerenes (C60 and C70).

Unexpected Sequential NH3/H2O Solid/Gas Phase Ligand Exchange and Quasi-Intramolecular Self-Protonation Yield [NH4Cu(OH)MoO4], a Photocatalyst Misidentified before as (NH4)2Cu(MoO4)2

[NH4Cu(OH)MoO4] as active photocatalyst in the decomposition of Congo Red when irradiated by UV or visible light has been prepared in an unusual ammonia/water ligand exchange reaction of [tetraamminecopper(II)] molybdate, [Cu(NH3)4]MoO4. [Cu(NH3)4]MoO4 was subjected to moisture of open air at room temperature. Light blue orthorhombic [Cu(NH3)(H2O)3]MoO4 was formed in 2 days as a result of an unexpected solid/gas phase ammonia-water ligand exchange reaction. This complex does not lose its last ammonia ligand on further standing in open air; however, a slow quasi-intramolecular (self)-protonation reaction takes place in 2-4 weeks, producing a yellowish-green microcrystalline material, which has been identified as a new compound, [NH4Cu(OH)MoO4], ( a = 10,5306 Å, b = 6.0871 Å, c = 8.0148 Å, β = 64,153°, C2, Z = 4). Mechanisms are proposed for both the sequential ligand exchange and the self-protonation reactions supported by ab initio quantum-chemical calculations and deuteration experiments as well. The [Cu(NH3)(H2O)3]MoO4 intermediate transforms into NH4Cu(OH)(H2O)2MoO4, which loses two waters and yields [NH4Cu(OH)MoO4]. Upon heating, both [Cu(NH3)4]MoO4 and [Cu(NH3)(H2O)3]MoO4 decompose, losing three NH3 and three H2O ligands, respectively, and stable [Cu(NH3)MoO4] is formed from both. The latter can partially be hydrated in boiling water into [NH4Cu(OH)MoO4. This compound can also be prepared in pure form by boiling the saturated aqueous solution of [Cu(NH3)4]MoO4. All properties of [NH4Cu(OH)MoO4] match those of the active photocatalyst described earlier in the literature under the formulas (NH4)2[Cu(MoO4)2] and (NH4)2Cu4(NH3)3Mo5O20.