Synthesis and Degradation of Hexamethylene Triperoxide Diamine (HMTD)

The synthesis and decomposition of hexamethylene triperoxide diamine (HMTD) were studied. Mechanisms were proposed based on isotopic labeling and mass spectral interpretation of both condensed phase products and head‐space products. Formation of HMTD from hexamine appeared to proceed from dissociated hexamine as evident from scrambling of the ¹⁵N label when synthesis was carried out with equal molar labeled/unlabeled hexamine. Decomposition of HMTD was considered with additives and in the presence and absence of moisture. In addition to mass spectral interpretation, density functional theory (DFT) was used to calculate energy differences of transition states and the entropies of intermediates along different possible decomposition pathways. HMTD is destabilized by water and citric acid making purification following initial synthesis essential in order to avoid unanticipated violent reaction.     

Properties of ZnO coatings obtained by mechanoactivated oxidation

In this work a new method based on the mechanoactivated oxidation has been applied for obtaining thin nanostructured transparent ZnO coatings on glass. Zn has been transferred onto a glass substrate at room temperature using a quickly rotating steel wire brush. Afterwards by subsequent annealing it is modified into a transparent ZnO coating. The temperature range in which formation of the needle-like (whiskers) structure and transition to the fine-grained structure occurs has been determined. The interrelation between physical properties and the change of microstructure of the ZnO coatings has been shown.     

The time-resolved luminescence characteristics of Ce and Ce/Pr doped YAG ceramics obtained by high pressure technique

Transparent Ce and Ce/Pr doped YAG ceramics were prepared under high pressures (up to 8 GPa) and relative low temperature (450 °C). Grain size of the ceramics is less than 50 nm. However unknown defects or disorders strains on grain boundaries caused the additional absorption in these ceramics. The luminescence intensity, spectra and the decay time dependence on pressure applied during ceramic preparation were studied. Concentration of some intrinsic point defect was reduced under the high pressure applied for sintering process.It is shown that formation time of the excited state of Ce luminescence depends on the pressure applied during ceramic sintering.     

Raman and infrared fingerprint spectroscopy of peroxide-based explosives

A comparative study of the vibrational spectroscopy of peroxide-based explosives is presented. Triacetone triperoxide (TATP) and hexamethyl-enetriperoxide-diamine (HMTD), now commonly used by terrorists, are examined as well as other peroxide-ring structures: DADP (diacetone diperoxide); TPTP [3,3,6,6,9,9-Hexaethyl-1,2,4,5,7,8-hexaoxo-nonane (tripentanone triperoxide)]; DCypDp {6,7,13,14-Tetraoxadispiro [4.2.4.2]tetradecane (dicyclopentanone diperoxide)}; TCypDp {6,7,15,16,22,23-Hexaoxatrispiro[4.2.4.2.4.2] henicosane (tricyclopentanone triperoxide)}; DCyhDp {7,8,15,16-tetraoxadispiro [5.2.5.2] hexadecane (dicyclohexanone diperoxide)}; and TCyhTp {7,8,14,15,21,22-hexaoxatrispiro [5.2.5.2.5.2] tetracosane (tricyclohexanone triperoxide)}. Both Raman and infrared (IR) spectra were measured and compared to theoretical calculations. The calculated spectra were obtained by calculation of the harmonic frequencies of the studied compounds, at the density functional theory (DFT) B3LYP/cc-pVDZ level of theory, and by the use of scaling factors. It is found that the vibrational features related to the peroxide bonds are strongly mixed. As a result, the spectrum is congested and highly sensitive to minor changes in the molecule.     

Excitonic luminescence in ZnO nanopowders and ceramics

Fast photoluminescence spectra in the spectral region of 3.1–3.45 eV in ZnO and ZnO:Al ceramics were studied at 14 and 300 K. Ceramics with grains smaller than 100 nm were sintered from nanopowders by high pressure (8 GPa) and low temperature (350 °C). Ceramics with grain sizes 1–5 μm were sintered at 1400 °C. It is shown that excitonic luminescence spectra depend on the ceramics grain size, post preparing annealing and doping. The excitonic luminescence decay time was faster than 2 ns and the afterglow at 30 ns was 0.05%.     

Catalytic Oxidation of Thiol Compounds by Novel Fuel Cell-inspired Co-Porphyrin and Co-Imidazole Catalysts

The catalytic performance of pyrolyzed carbon-supported cobalt-nitrogen donor (CoN₄) catalysts for the oxidation of thiol compounds by dioxygen in aqueous solution was studied. This paper continues our previous line of research, which was inspired by the electrocatalytic reduction of oxygen on pyrolyzed carbon-supported cobalt-porphyrins and related tetra-coordinated nitrogen donor-transition metal complexes (MeN₄, where Me stands for a transition metal atom). Both pyrolyzed carbon-supported Co-imidazole and Co-porphyrin exhibited fast catalytic oxidation of the different thiols. The rate of oxidation of different thiols on the pyrolyzed CoN₄ catalysts was compared to the homogeneous rate of oxidation using 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin Co(II) tetrasodium salt as catalyst. Based on the cobalt content, the heterogeneous catalysts always outperformed the homogeneous one, and at times even exhibited 4,100-fold better catalysis. The dependence of the catalytic rate of oxidation on the preparation temperature was investigated, showing an optimal catalysis at ˜650 °C for the cobalt-imidazole catalyst. The decrease in catalytic performance after heat treatment at elevated temperature was attributed to the formation of cobalt metal acting as a generator of carbon nanotubes.     

Polymer-Immobilized Photosensitizers for Continuous Eradication of Bacteria

The photosensitizers Rose Bengal (RB) and methylene blue (MB), when immobilized in polystyrene, were found to exhibit high antibacterial activity in a continuous regime. The photosensitizers were immobilized by dissolution in chloroform, together with polystyrene, with further evaporation of the solvent, yielding thin polymeric films. Shallow reservoirs, bottom-covered with these films, were used for constructing continuous-flow photoreactors for the eradication of Gram-positive Staphylococcus aureus, Gram-negative Escherichia coli and wastewater bacteria under illumination with visible white light using a luminescent lamp at a 1.8 mW·cm⁻² fluence rate. The bacterial concentration decreased by two to five orders of magnitude in separate reactors with either immobilized RB or MB, as well as in three reactors connected in series, which contained one of the photosensitizers. Bacterial eradication reached more than five orders of magnitude in two reactors connected in series, where the first reactor contained immobilized RB and the second contained immobilized MB.     

Ring expansion and isomerization in methyl indene and methylene indene radicals. Quantum chemical and transition-state theory calculations

Ring expansion and isomerization in 1- and 2-methylene indene radicals and isomerizations among the three isomers of methyl indene were studied by the Becke three-parameter hybrid method with Lee-Yang-Parr correlation functional approximation (B3LYP). Structure, energy, and frequency calculations were carried out with the Dunning correlation consistent polarized doubleζ, (cc-pVDZ) basis set. In contrast to methyl cyclopentadiene, transition states for ring expansion starting from the molecule methyl indene could not be located. The potential energy surfaces for ring expansion in methylene indene radicals consist of several intermediates and transition states and involve two principal pathways. One pathway is associated with cleavage of the five-membered ring adjacent to the methylene group and formation of a six-membered ring. In the second pathway, the transition states of the first stage consist of a newly-formed three-membered ring fused to the original cyclopentadiene ring. In all cases, the reaction pathways leading to ring expansion include an intermediate that, via an additional transition state, produces an α- or (β-hydronaphthalene radical. The latter, by a fast H-atom ejection, forms naphthalene. The structure, energetics, and additional parameters on the potential energy surfaces are shown. Several transition states and intermediates are common to both ring expansion and isomerization, so that there are competing parallel pathways that determine the final distribution among the isomerization and ring expansion products. Potential energy surfaces for interisomerization among the various isomers of methyl indene were calculated, and several reaction pathways were suggested.