Effect of nano-SiO2 films on the evolution of proton-irradiated free radicals in Kapton

The free radical behaviors were investigated on the 170 keV proton-irradiated nano-SiO₂ deposited polyimide, using electron paramagnetic resonance (EPR) measurement. The results indicate that, compared with the case of nude polyimide, the population of free radicals is much higher and increase faster with the irradiation fluence and the nona-SiO₂ film thickness, but the g value of irradiated free radicals keeps at a constant of 2.0025. Theoretical analysis demonstrates that large quantities of the free radicals could be formed in the interface region, thus, the film coverage and thickness show significant influence on the population of the radicals in the interface. Due to the distribution heterogeneity of the free radical, the free radical evolution during the post-storage follows a sum of two exponential modes. The interface characteristic takes great effects during the evolution process. The mechanisms of the free radical formation and evolution are discussed detailedly in this paper.     

Heterogeneous nucleation for synthesis of sub-20 nm ZnO nanopods and their application to optical humidity sensing

We present a novel method for colloidal synthesis of one-dimensional ZnO nanopods by heterogeneous nucleation on zero-dimensional ZnO nanoparticle ‘seeds’. Ultra-small ZnO nanopods, multi-legged structures with sub-20 nm individual leg diameters, can be synthesized by hydrolysis of a Zn2+ precursor growth solution in presence of ∼4 nm ZnO seeds under hydrothermal conditions via microwave-assisted heating in as little as 20 min of reaction time. One-dimensional ZnO nanorods are initially generated in the reaction mixture by heterogeneous nucleation and growth along the [0001] direction of the ZnO crystal. Growth of one-dimensional nanorods subsequently yields to an ‘attachment’ and size-focusing phase where individual nanorods fuse together to form multi-legged nanopods having diameters ∼15 nm. ZnO nanopods exhibit broad orange-red defect-related photoluminescence in addition to a near-band edge emission at 373 nm when excited above the band-gap at 350 nm. The defect-related photoluminescence of the ZnO nanopods has been applied towards reversible optical humidity sensing at room temperature. The sensors demonstrated a linear response between 22% and 70% relative humidity with a 0.4% increase in optical intensity per % change in relative humidity. Due to their ultra-small dimensions, ZnO nanopods exhibit a large dynamic range and enhanced sensitivity to changes in ambient humidity, thus showcasing their ability as a platform for optical environmental sensing.     

The use of optical microscopy to follow the degradation of isotactic polypropylene (iPP) subjected to natural and accelerated ageing

Microscopy and mechanical properties are commonly used to follow the changes in morphology and mechanical resistance, respectively, of materials before and after any type of treatment. In this work, we used light microscopy (LM), scanning electron microscopy (SEM) and measurement of the mechanical properties to assess the natural ageing of samples of isotactic polypropylene (iPP) in Campinas and after exposure to Weather-Ometer type accelerated ageing equipment. The results obtained for the mechanical properties and by light microscopy (LM) allowed us to identify the ageing time based on the amount of radiation, for a 50% loss of elongation at break. The results were similar for samples subjected to the two types of ageing processes. Although a simple technique, LM was considered efficient when compared with SEM and the measurement of mechanical properties.     

A comparative study on thermal and catalytic degradation of polybutylene terephthalate

A comparative study on the thermal and catalytic degradation of polybutylene terephthalate (PBT) at atmospheric pressure was conducted. The weight loss of PBT under thermal degradation was significantly influenced by the temperature between 360 °C and 380 °C, but little affected by the PBT particle size. Four groups of catalysts include metal chloride, metal oxide, metal acetate, and metal copper powder were used to test PBT degradation activity. Copper (II) chloride is the most active one for increasing the percentage PBT weight loss more than 100% in comparison with the result of thermal degradation at a temperature of 360 °C for 30 min. PBT and catalyst mixtures can be prepared by impregnation and physical method, the former resulted in a better PBT degradation. The percentage PBT weight loss in the presence of CuCl₂ increased steadily between 320 °C and 380 °C which was different from the results of thermal degradation. The time for obtaining a same percentage PBT weight loss reduced effectively when compared to the catalytic to thermal degradation. The weight ratio of CuCl₂/PBT was tested between 0 and 0.2 and the optimal ratio was 0.1. The gaseous product distribution analyzed by GC/MS for PBT thermal and catalytic degradation revealed almost the same and the major products were ethane, carbon monoxide, carbon dioxide, 1-butene, 2-butene, 1,3-butadiene, and butadiene dimmer. But the relative abundance of major products was changed, especially for 1,3-butadiene increased dramatically, and a new chlorocompound was produced in catalytic degradation. In condensed liquid product, both the number and the molar mass of components were more and greater than that of in gaseous product and 4-heptylacetophenone was the most abundance product. In PBT catalytic degradation, 4-heptylacetophenone and some products were decreased and some even disappeared completely while the abundance of benzoic acid increased and three new products were generated.     

Hydrosilylation vs. [2 + 2]-cycloaddition: A theoretical study with iron and ruthenium complexes

Recently an exciting new mechanism of hydrosilylation had been found in experiments with the ruthenium-silylene complex [Cp^∗(i-Pr₃P)Ru(H)₂Si(H)Ph · OEt₂][B(C₆F₅)₄] by Glaser and Tilley. The mechanism of the hydrosilylation and possible alternative pathways are investigated with quantum chemical methods utilizing the B3LYP method, a double zeta pseudopotential basis set for iron and ruthenium and the 6-31G^∗ basis set for all other elements. Starting from the model complex [Cp(H₃P)Ru(H)₂Si(H)Ph]⁺ the coordination of ethene at the silicon atom leads preferably to the hydrosilylation of a terminal Si-H-bond. The analysis of the electron density distribution of the catalytic active complex shows surprising bond features between Ru and Si. The Ru-Si bond is bridged by two hydrogen atoms.The [2 + 2]-cycloaddition of the alkene to the Ru-Si-bond, which would be a reasonable alternative reaction pathway, was not observed. It is necessary to make drastic changes in the ligand environment of the transition metal-silicone complex to observe cycloaddition reactions. With complexes of the type (OC)₄MSi(H)Ph (M = Ru, Fe) the cycloaddition could be a serious alternative to the hydrosilylation.     

Isothermal vapor–liquid equilibrium at 303.15 K and excess molar volumes at 298.15 K for the ternary system of propyl vinyl ether + 1-propanol + 2,2,4-trimethyl-pentane and its binary sub-systems

Isothermal vapor–liquid equilibrium data determined by the static method at 303.15 K are reported for the binary systems propyl vinyl ether + 1-propanol, 1-propanol + 2,2,4-trimethylpentane and propyl vinyl ether + 2,2,4-trimethylpentane and also for the ternary system propyl vinyl ether + 1-propanol + 2,2,4-trimethyl-pentane. Additionally, new excess volume data are reported for the same systems at 298.15 K. The experimental binary and ternary vapor–liquid equilibrium data were correlated with different G^E models and excess molar volume data were correlated with the Redlich–Kister equation for the binary systems and the Cibulka equation for the ternary system, respectively.     

Volumetric properties of the ternary system ethanol + chloroform + benzene at temperature range (288.15–313.15) K: Experimental data,correlation and prediction by cubic EOS

Densities ρ of the ternary system (ethanol + chloroform + benzene) and binaries (ethanol + chloroform) and (chloroform + benzene), have been measured at six temperatures (288.15, 293.15, 298.15, 303.15, 308.15, 313.15) K and pressure 101.33 kPa with an Anton Paar DMA 5000 digital vibrating tube densimeter. Excess molar volumes V^E were calculated from these densities data and fitted by the polynomial Redlich–Kister (for binary data) and Nagata and Tamura (for ternary data) equations. Radojkovi? et al. equation was used for the prediction of the V^E of ternary data. The obtained results have been explained in terms of different effects between molecules of present species, taking into consideration influence of temperature on them.     

Kinetic study of the degradation of forskolin in aqueous systems by stability-indicating HPLC method and identification of its degradation products

The degradation kinetics of forskolin in aqueous solution was investigated qualitatively and quantitatively. Two degradation products were isolated and identified as isoforskolin and forskolin D by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and nuclear magnetic resonance (NMR) spectroscopy. A stability-indicating high-performance liquid chromatography (HPLC) method was developed and validated for the quantification of forskolin and its degradation products. Chromatographic separation was performed on a Luna C₁₈ column with acetonitrile–water (65:35, v/v) as the mobile phase. The flow rate was kept at 1 mL/min, and the detection wavelength was 210 nm. The kinetic study of forskolin was carried out in aqueous solutions of pH 1.5–8.5 at 37, 50, 65, and 80°C. The degradation rate of forskolin increases with increasing temperature. Forskolin is relatively stable in the pH range 3.5–6.5, but its stability decreases when the pH is outside this range. In the pH range 6.5–8.5, the forskolin degradation follows pseudo-first-order kinetics. Based on the structural identification and quantitative analysis of the degradation products, a possible pathway for forskolin degradation is proposed. Forskolin can be converted to isoforskolin rapidly, and both forskolin and isoforskolin can further decompose to forskolin D.     

聚α烯烃光催化降解的机理研究

采用光催化微反应器对铜箔表面附着的聚α烯烃进行了光催化降解处理, 利用X射线光电子能谱(XPS)、 电子自旋共振谱(ESR)和傅里叶变换红外光谱(FTIR)等对光催化降解前后聚α烯烃的元素化学状态、 自由基和官能团进行了检测, 并探讨了光催化降解机理. 结果表明, 聚α烯烃光催化降解过程中发生了含氧基团的引入和CO₂脱附; 参加降解反应的自由基主要为羟基自由基·OH, 降解过程中—OH逐渐增多、 C—H键逐渐减少; 聚α烯烃光催化降解过程中, ·OH进攻聚α烯烃是从取代反应开始的, 首先取代的是末端的氢原子, 然后是末端羟基向醛基和羧基的转变, 最后是碳链断裂形成小分子有机物, 这一过程持续进行, 最终生成CO₂和H₂O等无机物.     

Structural and optical properties of Ga2O3:In films deposited on MgO (1 0 0) substrates by MOCVD

Ga₂O₃:In films with different indium (In) content x [x=In/(Ga+In) atomic ratio] have been deposited on MgO (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). Structural analyses revealed that the film deposited with actual In content (x′) of 0.09 was an epitaxial film and the films with x′=0.18 and 0.37 had mixed-phase structures of monoclinic Ga₂O₃ and bixbyite In₂O₃. The absolute average transmittance of the obtained films in the visible region exceeded 95%, and the band gap was in the range of 4.74-4.87 eV. Photoluminescence (PL) measurements were performed at room temperature, in which the visible luminescences were strong and could be seen by the naked eye. The strong emissions in the visible light region were proposed to originate from the gallium vacancies, oxygen deficiencies and other defects in these films.     

A comparative study of the optical properties of TbRhGe and DyRhGe

In this paper, experimental and theoretical optical properties of TbRhGe and DyRhGe have been reported and compared. Our measurements by the ellipsometric method in the wavelength range 0.22–15 μm revealed significant differences in energy positions of the interband peaks in the spectral functions of these ternary compounds. The electronic structure of TbRhGe and DyRhGe calculated within the LSDA + U method was used to obtain theoretical optical conductivity, which is in good agreement with the experimental one. Further analysis allowed us to track changes in interband transitions related to the rare-earth 4f and rhodium 4d states, which are responsible for the observed differences in optical properties of TbRhGe and DyRhGe compounds.     

First-principles study of the electronic and magnetic properties of oxygen-deficient rutile TiO2(1 1 0) surface

Based on first-principles electronic structure calculations we find that the bridging oxygen vacancies on the (1 1 0) surface is more favorable and may be responsible for the unexpected ferromagnetism in undoped rutile TiO₂. Our results show that the ferromagnetism largely originates from the d orbitals of low-charge-state Ti ions converted from Ti⁴⁺ ions induced by the surface oxygen vacancies. The second-nearest neighbors of these ions (fivefold coordinated Ti) also contribute to the total magnetic moments. The spins induced by the local oxygen vacancies form a ferromagnetic arrangement.     

Synthesis,structure, optical and magnetic properties of [CrL(X)3], {L = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine; X = Cl,N3, NCS}

Three complexes of composition [CrL(X)₃], where L = 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine and X = Cl⁻, N₃⁻, NCS⁻ are synthesized. They are characterized by IR, UV–Vis, fluorescence, EPR spectroscopic, and X-ray crystallographic studies. Structural studies reveal that the Cr(III) ion is coordinated by three N atoms of L in a meridional fashion. The three anions occupy the other three coordination sites completing the mer-N₃Cl₃ (1) and mer-N₃N₃ (2 and 3), distorted octahedral geometry. The Cr–N2 has a shorter length than the Cr–N1 and Cr–N3 distances and the order Cr–N(NCS⁻) < Cr–N(N₃⁻) < Cr–Cl is observed. They exhibit some of the d–d transitions in the visible and intra-ligand transitions in the UV regions. The lowest energy d–d transition follows the trend [CrLCl₃] < [CrL(N₃)₃] < [CrL(NCS)₃] consistent with the spectrochemical series. In DMF, they exhibit fluorescence having π → π^∗ character. All the complexes show a rhombic splitting as well as zero-field splitting (zfs) in X-band EPR spectra at 77 K.     

Pressurized Hot Water Extraction of anthocyanins from red onion: A study on extraction and degradation rates

Pressurized Hot Water Extraction (PHWE) is a quick, efficient and environmentally friendly technique for extractions. However, when using PHWE to extract thermally unstable analytes, extraction and degradation effects occur at the same time, and thereby compete. At first, the extraction effect dominates, but degradation effects soon take over. In this paper, extraction and degradation rates of anthocyanins from red onion were studied with experiments in a static batch reactor at 110 °C. A total extraction curve was calculated with data from the actual extraction and degradation curves, showing that more anthocyanins, 21-36% depending on the species, could be extracted if no degradation occurred, but then longer extraction times would be required than those needed to reach the peak level in the apparent extraction curves. The results give information about the different kinetic processes competing during an extraction procedure.     

Dioxouranium(VI)-carboxylate complexes: A calorimetric and potentiometric investigation of interaction with oxalate at infinite dilution and in NaCl aqueous solution at I = 1.0 mol L and T = 25 °C

In this paper we investigated the interactions between dioxouranium(VI) and oxalate using (H⁺-glass electrode) potentiometry and titration calorimetry. Potentiometric measurements were carried out in NaCl aqueous solutions and at T = 25 °C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants) at low ionic strength values (I ≤ 0.090 mol L⁻¹, without supporting electrolyte) and at I = 1.0 mol L⁻¹; different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the binary mononuclear species UO₂(ox)⁰, UO₂(ox)₂²⁻, UO₂(ox)₃⁴⁻ widely reported in literature, the ternary hydroxyl mononuclear species UO₂(ox)OH⁻, UO₂(ox)(OH)₂²⁻, UO₂(ox)₂OH³⁻, UO₂(ox)₃OH⁵⁻, the protonated ternary mononuclear species UO₂(ox)₃H³⁻ and the binuclear species (UO₂)₂(ox)₅⁶⁻.Calorimetric measurements were carried out following similar procedures and in the same experimental conditions as employed for the potentiometric measurements at I = 1.0 mol L⁻¹ in NaCl. The stability of UO₂²⁺-oxalate²⁻ complexes is fairly high and their main contribution to stability is entropic in nature. Some linear empirical relationships were found which make it possible to calculate (i) the contribution of a single bond: and ; (ii) chelate stabilisation per ring: and and (iii) the mean stability of negatively charged Na⁺-ion pair complexes: log^TK = (0.46 ± 0.02)·|z| (z = charge of complex species), ΔG° = −(2.60 ± 0.1)·|z| kJ mol⁻¹ and TΔS° = 2.5 ± 0.5 kJ mol⁻¹. Both potentiometric and calorimetric results provide evidence of the penta-coordination of the species UO₂(ox)₃⁴⁻. SIT parameters were calculated from the data at I = 0 and I = 1.02 mol kg⁻¹. Comparisons are made with literature data. An insoluble dioxouranium(VI) ternary complex was synthesised (at I = 1.0 mol L⁻¹ in NaCl) and characterised by thermoanalysis and elemental analysis.     

A comprehensive two-dimensional normal-phase × reversed-phase liquid chromatography based on the modification of mobile phases

A comprehensive orthogonal two-dimensional liquid chromatography (2D-LC) based on the modification of mobile phases was developed with a sample loop–valve interface. To improve the compatibility of mobile phases and analysis speed, some special solvents were chosen as the mobile phases, and the column temperature was elevated to decrease the viscosity of mobile phases of reversed-phase liquid chromatography (RPLC). Based on this principle, the first dimension was normal-phase liquid chromatography (NPLC) with a SiO₂ column, and the second dimension was reversed-phase liquid chromatography containing two tandem C18 columns. 1,4-Dioxane was used in the NPLC mobile phase, and isopropyl alcohol was employed in the RPLC mobile phase. Moreover, the elevated column temperature enabled the reduction of the backpressure and using tandem C18 columns to improve the resolving power in RPLC. The new comprehensive 2D-LC system and applied strategy offered a novel idea for construction of 2D-LC system. A traditional Chinese medicine, Zhengtian pill, was used as the test sample to evaluate the constructed 2D-LC system. 876 peaks were detected, and the peak capacity reached 1740.     

The effect of AlBr<Subscript>3</Subscript> additive on the thermal degradation of PMMA A study using TG-DTA-DTG,IR and PY-GC-MS techniques

The thermal behavior of poly(methyl methacrylate) (PMMA) was studied in the presence of AlBr₃ using TG-DTA-DTG, IR and Py-GC-MS techniques. Degradation products were identified. It was found that PMMA started degrading at a lower temperature due to the generation of free radicals (Br^•), being the product of decomposition of AlBr₃. Despite early destabilization of the system, stabilization zone was also highlighted. Flammability test was conducted to check the affectivity of AlBr₃. Degradation mechanism has been proposed. Pyrolysis of the system (PMMA–AlBr₃) was also monitored by heating it at different temperatures.     

Enhanced visible photocatalytic degradation of diclofen over N-doped TiO2 assisted with H2O2: A kinetic and pathway study

Increasing discharge and inadequate removal of pharmaceutical compounds pose significant concerns over global aquatic systems and human health. The accomplishment of affordable and safe water requires a stringent elimination of these micropollutants. This study evaluated the performance of Visible/N-doped TiO₂ and Visible/N-doped TiO₂/H₂O₂ processes using a submerged photocatalytic membrane reactor (SMPR) with suspended N-doped TiO₂ to address the removal of diclofenac (DCF). The kinetic and pathway of photodegradation of DCF were of particular interest in this study. The initial DCF concentrations upon the experiments were also examined using a wide range of 5–50 mg/L and 20–100 mg L⁻¹ for Vis/N-doped TiO₂, and Vis/N-doped TiO₂/H₂O₂ process, respectively. The results indicated that higher initial concentration reduces the efficiency of the process, but one with H₂O₂ demonstrated an enhanced performance. The experimental data were found to fit well a pseudo-first-order kinetic model. Our findings demonstrated the analogous pathways of DCF for both processes. The Vis/N-doped TiO₂/H₂O₂ process tends to hasten the degradation rate as evidenced by the disappearance of some DCF byproducts at a similar irradiation period as compared to the other. The study provided useful information of the degradation rate and the potential formation of DCF intermediates upon the hybrid photocatalytic systems, therefore being of importance for scaling-up as well as evaluating potential detoxification of DCF upon the novel photocatalytic system.     

利用电子自旋共振(ESR)技术研究啤酒原辅料自由基及其对麦汁自由基的影响

利用电子自旋共振(ESR)技术研究了啤酒生产原辅料固有自由基含量,发现麦芽自由基量最多,大麦其次,大米中未测到;且自由基存在于皮壳中.全麦麦汁和30%大米辅料麦液都含有羟基自由基和FR1.随糖化进行,羟基自由基上升,FR1下降;但全麦麦汁羟基出现较早,且糖化终了含量较高.     

Probing the effects of π–π stacking on the controlled radical polymerization of styrene and fluorinated styrene

The addition of the π–π stacking agent octafluorotoluene (OFT) resulted in up to a 50% reduction in monomer conversion after 24 h for atom transfer radical polymerization (ATRP) reactions of styrene, when performed at 85 °C with 1 eq of OFT compared with styrene in the initial reaction mixture. Monitoring the progress showed that the ATRP of styrene in the presence of either OFT or hexafluorobenzene (HFB) maintained a linear relationship between monomer conversion and number average molecular weights, while showing a first order rate dependence on monomer. The effects of π–π stacking on the K_ATRP could be overcome by using adjusting the redox activity of the metal‐ligand complex while maintaining reaction temperatures of 85 °C. Further experiments showed that nitroxide‐mediated polymerizations of St were affected to an identical extent by the presence of the π–π stacking agent HFB. The ATRP of pentafluorostyrene (PFSt) in the presence of π–π stackers benzene or toluene showed an increase in monomer conversion compared with reactions in their absence, consistent with M_n π–π stacking increasing the stability of the active radical. Interactions between the π–π stacking agents OFT and HFB and the aromatic groups in the ATRP of St or PFSt were verified by ¹H NMR analysis. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012