FTIR spectroscopic evidence of formation of geminal dinitrogen species during the low-temperature N2 adsorption on NaY zeolites

Adsorption of N₂ on NaY zeolites at 85 K and equilibrium pressures higher than 1 kPa results in the formation of geminal dinitrogen complexes characterized by an IR band at 2333.5 cm⁻¹ (2255.4 cm⁻¹ after adsorption of ¹⁵N₂). With decreasing equilibrium pressure the complexes tend to loose one N₂ ligand, thus forming linear species characterized by an IR band at 2336.8 cm⁻¹ (2258.7 cm⁻¹ after adsorption of ¹⁵N₂). All species disappear completely after evacuation. Co-adsorption of N₂ and CO revealed that the dinitrogen complexes are formed on Na⁺ cations. The changes in the concentrations of the linear and geminal N₂ species with the changes in the equilibrium pressure are excellently described by equations of adsorption isotherms proposed earlier for mono- and di-carbonyls. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of the branching theory in approximation of viscosity of the thermoset: Phenol-formaldehyde resin and boron oxide

The kinetics of step polycondensation is described on the basis of the classical branching theory. A simple method is proposed for calculation of the average longest length (L) of the linear chain in a crosslinked molecule under arbitrary functionalities of original monomers. A viscosity of the system is represented as a product of a structure factor by a friction factor. The latter was taken as the Arrhenius exponent. The structure factor was chosen in the form of a power function of L. The method has been used for the approximation of the viscosity of phenol-formaldehyde resin in the course of curing by boron oxide. An activation energy of 11.8 kcal/mol was found by the method of a best matching of the structure factor for the different viscosity kinetic isotherms in the scale of a reduced time of the reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 319–328, 1997     

One-step spray pyrolysis synthesized CuO-carbon composite combined with carboxymethyl cellulose binder as anode for lithium-ion batteries

Copper oxide-carbon composite with hollow sphere structure has been synthesized by a one-step spray pyrolysis method and tested as anode material for lithium-ion batteries. Different analytical methods, including X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric analysis, and systematic electrochemical tests were performed. The results demonstrate that the CuO-carbon composite in conjunction with carboxymethyl cellulose (CMC) binder has an excellent electrochemical performance, with a capacity of 577 mAh g(-1) up to 100 cycles. The usage of the water soluble binder, CMC, not only obviously improves the electrochemical performance, but also makes the electrode fabrication process much easier and more environmentally friendly.     

Giant magnetocaloric effect driven by structural transitions

Magnetic cooling could be a radically different energy solution substituting conventional vapour compression refrigeration in the future. For the largest cooling effects of most potential refrigerants we need to fully exploit the different degrees of freedom such as magnetism and crystal structure. We report now for Heusler-type Ni–Mn–In–(Co) magnetic shape-memory alloys, the adiabatic temperature change ΔT(ad) = ?3.6 to ?6.2?K under a moderate field of 2?T. Here it is the structural transition that plays the dominant role towards the net cooling effect. A phenomenological model is established that reveals the parameters essential for such a large ΔT(ad). We also demonstrate that obstacles to the application of Heusler alloys, namely the usually large hysteresis and limited operating temperature window, can be overcome by using the multi-response to different external stimuli and/or fine-tuning the lattice parameters, and by stacking a series of alloys with tailored magnetostructural transitions.     

Metal-graphene interaction studied via atomic resolution scanning transmission electron microscopy

Distributions and atomic sites of transition metals and gold on suspended graphene were investigated via high-resolution scanning transmission electron microscopy, especially using atomic resolution high angle dark field imaging. All metals, albeit as singular atoms or atom aggregates, reside in the omni-present hydrocarbon surface contamination; they do not form continuous films, but clusters or nanocrystals. No interaction was found between Au atoms and clean single-layer graphene surfaces, i.e., no Au atoms are retained on such surfaces. Au and also Fe atoms do, however, bond to clean few-layer graphene surfaces, where they assume T and B sites, respectively. Cr atoms were found to interact more strongly with clean monolayer graphene, they are possibly incorporated at graphene lattice imperfections and have been observed to catalyze dissociation of C-C bonds. This behavior might explain the observed high frequency of Cr-cluster nucleation, and the usefulness as wetting layer, for depositing electrical contacts on graphene.     

3D Printing to Increase the Flexibility of the Chemical Synthesis of Biologically Active Molecules: Design of On-Demand Gas Generation Reactors

The development of new drugs is accelerated by rapid access to functionalized and D-labeled molecules with improved activity and pharmacokinetic profiles. Diverse synthetic procedures often involve the usage of gaseous reagents, which can be a difficult task due to the requirement of a dedicated laboratory setup. Here, we developed a special reactor for the on-demand production of gases actively utilized in organic synthesis (C₂H₂, H₂, C₂D₂, D₂, and CO₂) that completely eliminates the need for high-pressure equipment and allows for integrating gas generation into advanced laboratory practice. The reactor was developed by computer-aided design and manufactured using a conventional 3D printer with polypropylene and nylon filled with carbon fibers as materials. The implementation of the reactor was demonstrated in representative reactions with acetylene, such as atom-economic nucleophilic addition (conversions of 19–99%) and nickel-catalyzed S-functionalization (yields 74–99%). One of the most important advantages of the reactor is the ability to generate deuterated acetylene (C₂D₂) and deuterium gas (D₂), which was used for highly significant, atom-economic and cost-efficient deuterium labeling of S,O-vinyl derivatives (yield 68–94%). Successful examples of their use in organic synthesis are provided to synthesize building blocks of heteroatom-functionalized and D-labeled biologically active organic molecules.     

Legislative aspects of radiation hazards from both gamma emitters and radon exhalation of concrete containing coal fly ash

Utilization of coal fly ash in concrete construction has clear environmental, technological and economical advantages. At the same time, fly ash is known to have enhanced concentrations of Naturally Occurring Radioactive Materials (NORM). Legislative issues related to the utilization of coal fly ash in concrete construction are analyzed. Different approaches implemented in standards regulating gamma radiation and radon emanation of concrete and other building materials are reviewed. Although radon exhalation rate of concrete containing coal fly ash can be sometimes slightly higher than that of the reference concrete, radon emanation coefficient is usually lower. In view of this, the standards regulating radioactivity of building materials, but not addressing radon emanation properly could be detrimental to the utilization of fly ash in concrete. At the same time, the evaluation of the excess dose caused by building materials for the radon pathway is complicated, and much more research work is required to justify the assumptions of the physical models in the future standards.