Radiation-induced copolymerisation of trioxane with penta-acetyl-glucose

Copolymerisation of trioxane (TOX) with penta-acetyl-glucose (PAG) in the solid state was investigated by gamma radiation. Effects of radiation doses, PAG concentration, and related parameters were studied and compared with that of the homopolymerisation of TOX. The yield of copolymer was lower than homopolymer and only a fraction of the PAG taken entered into the polymer. Chemical properties of the copolymer were determined; after amine treatment the copolymer showed good thermal stability. The kinetics of homopolymerisation were similar to those of TOX-homopolymerisation.     

Photocatalytic activity of SrTiO3 codoped with nitrogen and lanthanum under visible light illumination

Yellow SrTiO3 powders codoped with nitrogen and lanthanum (STO:N,La) were studied as visible light photocatalysts. The crystal phase of STO:N,La exhibited a pure perovskite phase, and O and Sr sites atoms were substitutionally doped with N and La atoms, respectively. The first principle calculation of STO:N,La indicated that the edge of the N(2p) band is situated above the valence band, which consisted of O(2p) orbitals, and the La orbitals did not exist in the band gap of SrTiO3. STO:N,La exhibited a higher oxidation activity of gaseous 2-propanol under vis illumination than SrTiO3 doped only with nitrogen (STO:N). The high activity of STO:N,La was due to the decrease in the oxygen vacancies, which acted as electron-hole recombination centers, because codoping with La3+ and N3- ions maintained the charge balance. The optimum doping density of N and La for visible light activity was 0.5%, and STO:N,La(0.5%) had an activity under UV illumination similar to pure SrTiO3.     

Cationic ring‐opening copolymerization behavior of trioxane and seven‐membered cyclic carbonate

Cationic ring‐opening copolymerization behavior of trioxane (TOX) and a seven‐membered cyclic carbonate, 1,3‐dioxepan‐2‐one (7CC) is described. When TOX and 7CC were cationically copolymerized under various feed ratios using trifluoromethane sulfonic acid (TfOH) as an initiator in nitrobenzene at 30 °C, 7CC was consumed faster than TOX and the decarboxylation was accompanied to afford the corresponding polyacetal–polycarbonate type copolymers containing poly(oxytetramethylene) units. The copolymer composition could be controlled by the feed ratio of 7CC, whose increase resulted in the high copolymer composition of the 7CC unit. The solubility of the copolymers increased as the increase of the 7CC content. Thermogravimetric, size‐exclusion chromatographic, and X‐ray analyses of the copolymers suggest that the sequences of the copolymer chains consist of the segments containing the units originated from 7CC and those with TOX unit‐rich compositions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 733–739, 2008     

Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

An unequivocal1H NMR structural assignment of TOX8 and TOX9, the two most abundant toxaphene congeners in marine mammals

The structure of the two most abundant toxaphene congeners has unequivocally been established by 500 MHz¹H NMR spectroscopy as 2-endo,3-exo,5-endo, 6-exo,8,8,9,10,10-nonachlorobornane (TOX9) and as 2-endo,3-exo,5-endo,6-exo,8,8,10,10-octachlorobornane (TOX8). Semiempirical calculations (AM1 and PM3-MNDO) were carried out for both structures. The distance information found by nuclear Overhauser enhancement (NOE) for the protons is in agreement with the energy minimized AM1 and PM3-MNDO structures. For these definitively established NMR data for TOX8 and TOX9, together with literature data for other toxaphene isolates, a set of rules has been derived for¹H chemical shifts in polychlorinated bornane structures. A set of rules is also proposed for assigning systematical nomenclature to NMR-derived polychloro bornane structures.     

Hydrogenation and Ammoniation of SrTiO3 for an Enhanced Visible-light Photocatalysis

Hydrogenation and ammoniation of SrTiO₃ (STO), a normal ultraviolet photocatalyst, were performed by annealing STO〈100〉in H₂:N₂=5%:95% and NH₃, respectively, at various tem-peratures T. It was found that hydrogenation at T≥900 oC remarkably enhanced the UV photocatalytic ability of STO, but the visible-light photocatalysis was still unavailable, while ammoniation at T≥800 oC introduced the N doping, resulting in visible-light photocat-alytic activity. Furthermore, when a hydrogenated STO was subjected to ammoniation, the visible-light photocatalytic ability was nearly the same as that of the ammoniated one; but the hydrogenation of an ammoniated one significantly enhanced visible-light photocatalysis, indicating a synergetic effect of hydrogenation and ammoniation. Discussions and identifi-cations have been made to analyze these results.     

Effect of quenching time and quenching agent dose on total organic halogen measurement

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all the halogenated organic disinfection byproducts (DBPs) in a water sample. TOX measurement involves concentration of halogenated organic DBPs by adsorption onto activated carbon. Prior to activated carbon adsorption, quenching the chlorine residual in a water sample is an indispensable step to eliminate the positive interference resulting from continued chlorination with organic compounds adsorbed on the activated carbon surface or with the activated carbon surface itself. Arsenite is generally applied as the quenching agent. In this study, the arsenite quenching agent dose that was 100% of the stoichiometric amount of the chlorine residual in a water sample was demonstrated to be most appropriate. In practice, to ensure complete reduction of chlorine residual, slight overdose of arsenite is often recommended, but this was found to cause negative interferences in the TOX measurement due to two reasons. First, the competitive adsorption existed between halogenated organic DBPs and the excessive arsenite on the activated carbon. This competitive adsorption effect was pronounced within a quenching time of 15?min. After 15?min of quenching, a large fraction of arsenite might have reacted with some easily-reduced halogenated DBPs to become arsenate, which is partially ionized at pH 2 and less likely adsorbed on the activated carbon. In this case, more halogenated organic DBPs could be adsorbed on the activated carbon, resulting in the measured TOX concentrations to be much closer to the actual one contained in the sample. Second, excessive arsenite might lead to reduction or decomposition of halogenated organic DBPs with a prolonged quenching time (>60?min). Thus, to avoid the negative interferences, the appropriate quenching time should be 15–60?min.     

An unequivocal1H NMR structural assignment of TOX8 and TOX9, the two most abundant toxaphene congeners in marine mammals

The structure of the two most abundant toxaphene congeners has unequivocally been established by 500 MHz¹H NMR spectroscopy as 2-endo,3-exo,5-endo, 6-exo,8,8,9,10,10-nonachlorobornane (TOX9) and as 2-endo,3-exo,5-endo,6-exo,8,8,10,10-octachlorobornane (TOX8). Semiempirical calculations (AM1 and PM3-MNDO) were carried out for both structures. The distance information found by nuclear Overhauser enhancement (NOE) for the protons is in agreement with the energy minimized AM1 and PM3-MNDO structures. For these definitively established NMR data for TOX8 and TOX9, together with literature data for other toxaphene isolates, a set of rules has been derived for¹H chemical shifts in polychlorinated bornane structures. A set of rules is also proposed for assigning systematical nomenclature to NMR-derived polychloro bornane structures.     

Chemical modification of neodymium high cis-1,4 polybutadiene with styreneoxide

The polymerization of 1,3-butadiene (BD) was carried out in the presence of a catalyst composed of neodymium 2-ethylhexanoate, triisobutyl aluminum, diisobutyl aluminum hydride (DIBAH), ethylaluminum sesquichloride and acetylacetone. The molecular weight of the BR could be controlled with DIBAH. The reactive polymer was then chemically modified with styreneoxide (STO). The STO content of BR increased with the decrease in the molecular weight of the BR. This polymer was modified by the STO at the chain terminal end. The physical properties of the vulcanizates with the modified BR were measured. The abrasion resistance and the tensile strength were found to be improved.     

Determination of TOCl, TOBr and TOI in drinking water by pyrolysis and off-line ion chromatography

The objective of this research was to determine the optimum total organic halogen (TOX) protocol for use with ion chromatographic (IC) detection to analyze total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI) in drinking water simultaneously. Two commercial analyzers (one using a pure O₂ carrier and one using O₂/CO₂ mixture) and three commercially available activated carbons (two coconut-based and one bituminous coal-based) were examined in this study. Results showed that the pyrolytic analyzer using pure O₂ and off-line IC combined with a standard TOX carbon (coconut-based) achieved the most complete recovery of TOCl, TOBr and TOI for both model compounds and real samples. There was no obvious difference between the two analyzers when used in microcoulometric detection mode. The TOX method is moderately sensitive to nitrate rinse volume. The monohaloacetic acids were partly washed out during sample preparation. This problem was solved by a modified nitrate rinsing solution.     

Fundamental considerations on the mechanism of copolymerization of trioxane and ethylene oxide initiated with boron trifluoride dibutyl etherate

A comprehensive mechanistic scheme that accounts for the unique experimental features of the copolymerization of bulk trioxane (TOX) with 2% (wt/wt) ethylene oxide (EO) was developed. The formation of the primary initiating species is shown as the diffusion-limited reaction of trace water with boron triflouride dibutyletherate [BF₃O(Bu)₂] to form a Bronsted acid. This acid complexes principally with the more basic EO and partly with the less basic TOX. The acid-complexed TOX depolymerizes to formaldehyde which can react with acid-complexed EO in an insertion reaction to form an acid-complexed dioxolane. Further insertion of formaldehyde yields an acid-complexed trioxepane. This sequence is generalized into a propagation scheme that involves propagation by expansion and ring opening. Displacement of complexed dioxolane and trioxepane can occur in the event that the more basic EO attacks the oxonium-active site at the reactive position outside the oxonium ring. These displacement reactions account for the observation of formation of dioxolane and trioxepane. The polymerization of formaldehyde is not considered significant until all EO has been consumed. During the latter stages of polymerization, cyclic oxonium-active sites are transformed into oxocarbenium sites that are stabilized by complexation with the polymer chain. This complexation is the origin of the phenomena of transacetalization and hydride transfer.     

Clarification by TEM and SIMS of abnormal Ti depth distribution in chemical solution-deposited SrTiO3/La0.5Sr0.5CoO3

A chemical solution-deposited multilayer system of SrTiO3 ("STO")/La0.5Sr0.5CoO3 ("LSCO") on a platinized wafer with a layer sequence Pt/TiO2/SiO2/Si(bulk) has been investigated by dynamic SIMS (secondary ion mass spectroscopy) and TEM (transmission electron microscopy); element determination was performed with EELS (electron energy-loss spectroscopy). The STO layer is intended to serve as a dielectric layer for a microelectronic capacitor; the conducting LSCO layer is a buffer layer intended to eliminate fatigue effects which usually occur at the STO/Pt interface. The SIMS depth profiles obtained for the main components revealed intense diffusion processes which must have occurred during the deposition/crystallization processes. Ti is found to diffuse from the (insulating) STO layer into the conductive LSCO layer where a region of constant concentration is observable. TEM-EELS experiments showed that these Ti plateaus are caused by precipitates approximately 20-80 nm in diameter.     

Electrical properties of the YSZ/STO/YSZ-STO superlattice electrolyte film at low temperatures

This study is focused on characterization of the low temperature properties of the YSZ/STO/YSZ superlattice film deposited onto unilateral polished SrTiO₃ (STO) monocrystalline substrates using pulsed laser deposition (PLD). The phase composition, structure, surface morphology and electrical properties of the oxygen ion conducting electrolyte YSZ/STO/YSZ multilayers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The minimum conductivity activation energy of YSZ/STO/YSZ is 0.76 eV at 300–500°C. The YSZ/STO/YSZ superlattice film shows an enhancement in conductivity by three orders of magnitude compared to bulk YSZ at a temperature of 300°C.     

Ab initioSCF MO calculations on the reactions of hydroxyl radical with imidazole and monoprotonated imidazole

The addition reactions of hydroxyl radical with imidazole and its protonated form to yield radical adducts have been investigated by ab initio SCF MO methods using STO -3G and 4-31G basis sets. Analogous radical species are of importance in radiation damage to biological systems. Of the possible radical products, the calculations indicate that the allylic species are generally favored energetically over the nonallylic forms. On an energetic basis, the results show that the allylic adducts formed by addition at the C2 and C5 positions are about equally favorable. Although the C5 species is generally identified as the experimentally observed product in aqueous media for both protonated and unprotonated imidazole, some experimental evidence exists indicating the presence of other forms. Our results suggest that this other form is the C2 adduct. The calculations also point to the protonated form of imidazole being less reactive than imidazole, which is in accord with experimental observations.     

Activating Inert,Nonprecious Perovskites with Iridium Dopants for Efficient Oxygen Evolution Reaction under Acidic Conditions

Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium‐containing strontium titanates (Ir‐STO) as active and stable, low‐iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir‐STO contains 57 wt % less iridium relative to the benchmark catalyst IrO₂, but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium‐based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.     

SO4−2/SnO2–catalyzed cyclocondensation for the synthesis of fully functionalized pyridines

An efficient and promising synthetic approach to assemble skeletons of multifunctionalized pyridine derivatives in presence of recyclable heterogeneous sulfated tin oxide (STO) catalyst has been evolved. The STO catalyst was used as a promoter for the cyclocondensation process in ethanol at 70°C. Overall performance of this catalyst was attributed to the cooperative contribution of its Lewis and Brønsted-Lowry acidic sites. Nanosized STO catalyst was synthesized by using sol-gel process and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), ¹H-NMR, and scanning electron microscopy (SEM). This catalyst tolerates most of the substrates, and protocol shows precious capabilities consist of high yields, operational simplicity, less reaction time, and eco-friendly conditions. The newly synthesized heterogeneous catalyst was easily separated and reused. All the reactions are carried out for subsequent cycles without significant loss of catalytic activity and with good proficiency.     

Influence of solution pH and reaction atmosphere on the morphology of SrTiO<Subscript>3</Subscript> nanocubes synthesized by thermohydrolysis

The influence of synthetic conditions on the shape and size of SrTiO₃ (STO) nanocubes was studied. These were synthesized in aqueous solution using Sr(OH)₂ as the Sr²⁺ source and titanium(IV) bis(ammonium lactate)dihydroxide (TALH) as the Ti^IV source in the presence of oleic acid and hydrazine. A large excess of OH^? at a pH of the precursor solution higher than 12 is necessary for the formation of STO nanocubes without the need for any calcination. Performing the synthesis in a N₂ atmosphere additionally prevents the formation of SrCO₃ impurity, leading to the creation of uniformly sized STO nanocubes in a reproducible manner. Such size-regulated STO nanocubes are found to align over a large area.