Hydrodechlorination of CCl4 over carbon-supported palladium–gold catalysts prepared by the reverse “water-in-oil” microemulsion method

Two series of carbon-supported Pd–Au catalysts were prepared by the reverse “water-in-oil, W/O” method, characterized by various techniques and investigated in the reaction of tetrachloromethane with hydrogen at 423 K. The synthesized nanoparticles were reasonably monodispersed having an average diameter of 4–6 nm (Pd/C and Pd–Au/C) and 9 nm (Au/C). Monometallic palladium catalysts quickly deactivated during the hydrodehalogenation of CCl₄. Palladium–gold catalysts with molar ratio Pd:Au = 90:10 and 85:15 were stable and much more active than the monometallic palladium and Au-richer Pd–Au catalysts. The selectivity toward chlorine-free hydrocarbons (especially for C₂₊ hydrocarbons) was increased upon introducing small amounts of gold to palladium. Simultaneously, for the most active Pd–Au catalysts, the selectivity for undesired dimers C₂H_xCl_y, which are considered as coke precursors, was much lower than for monometallic Pd catalysts. Reasons for synergistic effects are discussed. During CCl₄ hydrodechlorination the Pd/C and Pd–Au/C catalysts were subjected to bulk carbiding.     

Adsorption of dimethyl methylphosphonate and trimethyl phosphate on calcium oxide: an ab initio study

Ab initio study of the adsorption of dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) on three types of models simulating the calcium oxide surface (non-hydroxylated Ca₄O₄, completely hydroxylated Ca₄O₄(OH)₂H₂, and partially hydroxylated Ca₄O₄(OH)H) was performed. The target molecule and the surface hydroxyl groups were optimized while the CaO fragment was kept frozen. The intermolecular interactions were investigated applying Bader’s Atoms in Molecules theory. The maps of electrostatic potential of the studied adsorption systems were also produced. The interaction energies of studied adsorption systems corrected by the basis set superposition error were obtained. The most energetically favorable adsorption of DMMP and TMP was found at the configuration where the oxygen atoms of the P=O and methoxy groups point toward the Ca cation of the surface. The P atom points toward the O atom of the surface and forms a P–O chemical bond. This configuration was revealed for the non-hydroxylated and partially hydroxylated CaO-DMMP and CaO-TMP systems. The presence and number of surface hydroxyl groups on the CaO models play a key role in the adsorption of the studied compounds. DMMP and TMP were found to be much less stable on the completely hydroxylated CaO surface where they are adsorbed only via weak electrostatic interactions and H-bonding to the surface oxygen atoms and hydroxyl groups. TMP was found to be slightly more stable on this type of surface than DMMP. The difference in stability is even larger if one compares this TMP system with the complex of tabun adsorbed on completely hydroxylated CaO surface model (Michalkova et al. Chem Phys Lett 438:72, 2007).

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K _i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K _i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K _i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.     

Effects of a non-ionic surfactant,Tween 20, on adsorption/desorption of saccharification enzymes onto/from lignocelluloses and saccharification rate

In this work, we examined the role of a non-ionic surfactant, Tween 20, on enzymatic hydrolysis of lignocelluloses. Delignified lignocelluloses (pine wood chip) were used as model substrates. Effects of Tween 20 on adsorption/desorption onto/from lignocelluloses with and without hydrolysis were evaluated respectively. Tween 20 lowered the non-biospecific adsorption of β-glucosidase and enhanced the bio-specific adsorption of cellulase. Tween 20 did not affect the liquid phase reaction (cellobiose hydrolysis). However, for the solid surface reaction (cellulose hydrolysis), cellulose conversion for 72 hrs was increased 9–21% and 1–8.5% for samples with high lignin contents (PI) and low lignin contents (PIII) by injection of Tween 20 (0.024–0.24 mM), respectively. Moreover, Tween 20 increased the cellulose conversion rate substantially. It is suggested that the increase of cellulase amount adsorbed due to the increase of effective cellulose surface by Tween 20 contribute to the enhancement of cellulose conversion.     

Equilibrium and kinetic studies on the adsorption of VB_(12) onto CMK-3

The adsorption of VB12 onto CMK-3 was studied as a function of temperature and initial VB12 concentration. The highest VB12 adsorption capacity was determined as 353.4 mg/g at 40℃. Adsorption data were well described by the Langmuir model, although they could be modelled by the Freundlich equation. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second-oider kinetic model provided the best correlation of the experimental data compared to the pseudo-nrsi-order model.     

The study of thermal,microstructural and magnetic properties of manganese–zinc ferrite prepared by co-precipitation method using different precipitants

Mn–Zn ferrite was prepared from the solution after acid leaching of spent batteries by co-precipitation method using ammonia oxalate, sodium carbonate and sodium hydroxide as precipitating agents. The co-precipitation process was performed at temperature of over 50 °C by continuous magnetic stirring. The precipitates were pre-sintered at 850 °C in air. Dilatometric study has revealed that lowest shrinkage (only 5.6%) showed a material obtained from an oxalate precipitant. After pressing and high-temperature sintering at 1325 °C, it showed both insufficient density and the presence of pores, which contribute to the deterioration in the magnetic properties of the ferrites: the low magnetic permeability value and high magnetic losses. Ferrite prepared from hydroxide and carbonate precipitant showed a much higher shrinkage, sintered density and much higher magnetic permeability compared with the ferrite prepared from oxalate precursor.     

γ-Ray-induced grafting of DMAEMA and AAc onto PP by two step method

Binary graft copolymerization of thermosensitive 2-(dimethylamino) ethyl methacrylate (DMAEMA) and pH sensitive acrylic acid (AAc) monomers onto polypropylene (PP) films was carried out by a two step method using a ⁶⁰Co gamma radiation source. The PP film was initially modified by grafting of DMAEMA through a direct method. The DMAEMA-g-PP film obtained was then subjected to radiation grafting of AAc by the pre-irradiation method to give (DMAEMA-g-PP)-g-AAc. The optimal conditions, such as reaction time, reaction temperature, monomer concentration, and dose were studied. The grafted samples were verified by the FTIR-ATR spectroscopy and swelling; thermal properties were analyzed by DSC and TGA.     

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

A series of lithium complexes were prepared from 2(N-piperazinyl-N'-methyl)-2-methylene-4-R'-6-R-phenols ([ONN](RR')) and characterized through elemental analysis, (1)H and (13)C{(1)H} NMR spectroscopy, and X-ray crystallography. Treatment of the ligands with n-butyllithium afforded {Li[ONN](RR')}(3) [R = Me, R' = (t)Bu, (1); R = R' = (t)Bu (2); R = R' = (t)Am, (3), (t)Am = C(CH(3))(2)CH(2)CH(3)], with trimetallic structures in the solid-state as shown by single-crystal X-ray diffraction. The reactivity of these complexes in the ring-opening polymerization of ε-caprolactone (ε-CL), as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, was studied. Rates of polymerization were first order with respect to both monomer and lithium concentrations, and activation energies for the reactions were determined. MALDI-TOF MS analysis revealed that transesterification had occurred during the polymerization.     

Synthesis and characterization of lead oxide nano-powders by sol–gel method

Our goal in this research was to obtain lead oxide nano-powders by sol–gel method. In this method, lead oxide nano-powders were synthesized through the reaction of citric acid (C₆H₇O₈·H₂O) solution and lead acetate [Pb(C₂H₃O₂)₂] solution as stabilizer and precursor, respectively. The effect of different parameters including calcination temperature, (molar ratio of citric acid to lead acetate) and drying conditions were investigated. The prepared lead oxide nano-powders were characterized by FT-IR spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The prepared PbO samples consist of the particles in the range of 50–120 nm or the thick plate like structures with thickness of 53 nm depending on the drying conditions.     

The removal and kinetic study of Mn,Fe, Ni and Cu ions from wastewater onto activated carbon from coconut shells

Activated carbon from coconut shells (ACCS) was synthesised and used for the removal of metal ions (manganese, iron, nickel and copper) from aqueous solutions. Two different adsorption models were used for analysing the data. Adsorption capacities were determined: copper ions exhibited the greatest adsorption on activated carbon obtained from coconut shells because of their size and pH conditions. Adsorption capacity varied as a function of the pH. Adsorption isotherms from aqueous solutions of heavy metals on ACCS were determined and were found to be consistent with Langmuir’s adsorption model. Adsorbent quantity and immersion enthalpy were studied. The results were compared with other adsorbents used in a prior study.     

Synthesis and characterization of nanocrystalline tin oxide by sol–gel method

Nanocrystalline SnO₂ particles have been synthesized by a sol–gel method from the very simple starting material granulated tin. The synthesis leads a sol–gel process when citric acid is introduced in the solution obtained by dissolving granulated tin in HNO₃. Citric acid has a great effect on stabilizing the precursor solution, and slows down the hydrolysis and condensation processes. The obtained SnO₂ particles range from 2.8 to 5.1 nm in size and 289–143 m² g⁻¹ in specific surface area when the gel is heat treated at different temperatures. The particles show a lattice expansion with the reduction in particle size. With the absence of citric acid, the precursor hydrolyzes and condenses in an uncontrollable manner and the obtained SnO₂ nanocrystallites are comparatively larger in size and broader in size distribution. The nanocrystallites have been characterized by means of TG-DSC, FT-IR, XRD, BET and TEM.     

Structure and magnetic properties of manganese–zinc-ferrites prepared by spray pyrolysis method

A spray pyrolysis of a water solution of iron, manganese and iron nitrates is applied to prepare Zn_0.5Mn_0.5Fe₂O₄ single-phase ferrite with a spinel-type structure. The samples are characterized by means of differential scanning calorimetry, scanning and transmission electron microscopy, X-ray diffraction, infrared and ⁵⁷Fe Mössbauer spectroscopy. The mass magnetization σ and the magnetic susceptibility 1/χ of the ferrites are measured as a function of temperature over the range of 78–728 K. The obtained sample contains nanoparticles with an average diameter d ∼7 nm possessing Mn_xZn_yFe_3−(x+y)O₄ spinel-type structure with a uniform distribution of manganese and zinc atoms over the ferrite lattice. The Curie temperature is determined to be 375 ÷ 380 K.     

Radiation grafting of N,N′-dimethylacrylamide and 2-hydroxyethylmethacrylate onto polypropylene films by one step method

The work presented herein reports on polypropylene films grafted with N,N′-dimethylacrylamide and 2-hydroxyethylmethacrylate. The grafted films were obtained by an oxidative pre-irradiation method in one step using a gamma source of ⁶⁰Co. The optimal conditions such as reaction time, monomer concentrations and radiation doses were investigated. Characterization of the grafted polymers was carried out through FTIR-ATR, TGA, DSC, and swelling. Grafts onto polymeric films between 10 and 850% were obtained at doses from 20 to 150 kGy and a dose rate of 8.3 kGy/h.     

Investigation of structural,morphological, optical,and magnetic properties of Sm-doped LaFeO3 nanopowders prepared by sol–gel method

Journal of Sol-Gel Science and Technology - Pure orthorhombic phase of La1?xSmxFeO3 (x?=?0, 0.1, 0.2, and 0.3) nanoparticles can be obtained by sol–gel method after...