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1.
Production of hydroxyl radical (OH) is of significant concern in engineered and natural environment. A simple in situ method was developed to measure OH formation in UV/H2O2, UV/Fe(III), and UV/NO3? systems using trapping of OH by benzoic acid (BA) and measuring fluorescence signals from hydroxylated products of BA. Method development included characterization of OH trapping mechanism and measurement of quantum yields (ΦOH) for OH. The distribution of OHBA isomers was in the order of o-OHBA > p-OHBA > m-OHBA, although it changed with the H2O2 concentration and light intensity. This supports that OH attacks dominantly on the benzene rings. The quantum yields for OH formation in the UV/H2O2 process were 1.02 and 0.59 at 254 and 313 nm, which were in good agreement with the literature values, confirming that the method is suitable for the measurement of OH production from UV/H2O2 processes. Using the continuous flow method developed, quantum yields for OH in UV/H2O2, UV/Fe(III), and UV/NO3? systems were measured varying the initial concentration of OH precursors. The ΦOH values increased with increasing concentrations of H2O2, Fe(III), and NO3? and approached constant values as the concentration increased. The ΦOH values were 0.009 for H2O2 at 365 nm, showing that OH production is not negligible at such high wavelength. The ΦOH values during the photolysis of Fe(OH)2+ (pH 3.0) and Fe(OH)2+ (pH 6.0) at 254 nm were 0.34 and 0.037, respectively. The ΦOH values for NO3? approached a constant value of 0.045 at 254 nm at the initial concentration of 10 mM.  相似文献   

2.
It is important to determine reaction kinetics of the hydroxyl radical (OH) with various water pollutants for understanding advanced oxidation processes (AOPs). Hence, a simple competition kinetics in a continuous flow system was employed to determine the second-order rate constants of OH with 14 organic and inorganic solutes selected in this study. In this method, p-nitrosodimethylaniline (PNDA) was specifically employed as a well-known reference probe for OH, which gave a competitive relationship between the PNDA and each solute over OH radicals. PNDA decay with OH radicals obeyed reaction kinetics in a first-order as long as the initial concentrations of H2O2 and PNDA were less than 30 μM and 2 μM, respectively. The second-order rate constants of OH radical with 14 solutes obtained in this study were found to be consistent with literature values using pulse radiolysis method.  相似文献   

3.
The work deals with the preparation of dense SiC based ceramics with high electrical conductivity. SiC samples with different content of conductive TiNbSiCO based phase were hot pressed at 1820 °C for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of 50 wt% TiNbC (molar ratio of Ti/NbC is 1:1.8) and 50 wt% eutectic composition of Y2O3SiO2. Composite with 30% of conductive TiNbSiCO phase showed the highest electrical conductivity 28.4 S mm?1, while the good mechanical properties of SiC matrix were preserved (fracture toughness KIC = 5.4 MPa m1/2 and Vickers hardness 17.8 GPa).The obtained results show that the developed additive system is suitable for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.  相似文献   

4.
Dense TiC–SiC nanocomposite ceramics were prepared by infiltration of porous TiC scaffolds with a SiOC sol, followed by spark plasma sintering (SPS). The porous nano TiC scaffold was first synthesized by direct carbothermal reduction of a monolithic TiOC precursor obtained from a controlled sol–gel process. The TiC scaffold was infiltrated with a SiOC sol and then the sample was aged in a container for 48 h at 80 °C to convert the sol into gel. After this, the sample was heated at 550 °C to remove the organic components and then 1350 °C to convert the SiOC gel to SiC by carbothermal reduction reaction. The cycle of the infiltration and carbothermal reduction was repeated several times to obtain relatively dense TiC–SiC composite samples. Dense TiC–SiC composite with a uniform nano-sized grain microstructure was obtained by spark plasma sintering at 1800 °C for 5 min under 40 MPa uniaxial pressure. Compared with conventional powder mixing methods, the sol–gel infiltration approach has shown distinct advantages of achieving dense TiC–SiC composites with uniform nano-sized grain structures.  相似文献   

5.
The photoassisted degradation (HPLC-UV absorption), dehalogenation (HPLC-IC) and mineralization (TOC decay) of the flame retardants tetrabromobisphenol-A (TBBPA) and tetrachlorobisphenol-A (TCBPA) were examined in UV-irradiated alkaline aqueous TiO2 dispersions (pH 12), and for comparison the parent bisphenol-A (BPA, an endocrine disruptor) in pH 4–12 aqueous media to assess which factor impact most on the photodegradative process. Complete degradation (2.7–2.8 × 10−2 min−1) and dehalogenation (1.8 × 10−2 min−1) of TBBPA and TCBPA occurred within 2 h of UV irradiation, whereas only 45–60% mineralization (2.3–2.7 × 10−3 min−1) was complete within 5 h for the flame retardants at pH 12 and ca. 80% for the parent BPA. Factors examined in the pH range 4–12 that impact the degradation of BPA were the point of zero charge of TiO2 particles (pHpzc; electrophoretic method), particle or aggregate sizes of TiO2 (light scattering), and the relative number of OH radicals (as DMPO–OH adducts; ESR spectroscopy) produced in the UV-irradiated dispersion. Dynamics of BPA degradation (2.0–2.4 × 10−2 min−1) were pH-independent and independent of particle/aggregate size, but did correlate with the number of OH radicals, at least at pHs 4 to 8–9, after which the rates decreased somewhat at pH > 9 with decreasing adsorption owing to Coulombic repulsive forces between the very negative TiO2 surface and the anionic forms of BPA (pKas ca. 9.6–11.3), even though the number of OH radicals continued to increase at the higher pHs.  相似文献   

6.
The synthesis and characterisation of a novel [(η2-dppf)(η5-C5H5)Ru(CC)-1,4-(C6H4)PPh2–Au–CC-bipy({[Ti](μ-σ,π-CCSiMe3)2}Cu)]PF6 (dppf = 1,1′-bis(diphenylphosphino)ferrocene) is reported in which five different transition metals (Fe–Ru–Au–Cu–Ti) are linked by carbon-rich organic bridging units.  相似文献   

7.
Herein, we describe the synthesis and crystal structure of mononuclear CuII and ZnII complexes containing the new pentadentate H2L ligand (H2L = N-(methyl)-N-(2-pyridylmethyl)-N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-1,3-propanediamine. The [CuII(L)] and [ZnII(L)] complexes and their one-electron oxidized [CuII]+ ([1]+) and [ZnII]+ ([2]+) compounds exhibit electrochemical and spectroscopic (UV–Vis and EPR) features with relevant insight into the oxidizing half-reaction of the metalloenzyme galactose oxidase.  相似文献   

8.
The ligand precursors 2-(R3PN)CH2Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl2(CHPh)(Py)2(H2IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl2(CHPh)(PyCH2(NPR3))(H2IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.  相似文献   

9.
One new dinuclear multioxomolybdenum(VI) complex containing long MoO bands with imidazole, [Mo2O6(imi)4] (1) (imi = imidazole), has been prepared and characterized, and the geometric structure, electronic structure and spectroscopic properties, investigated experimentally and theoretically. The rarely observed long MoO bonds in 1 (ca. 0.15 Å longer than documents previously) are analysed by orbital structure analysis. The electronic origins of the optical transitions are also mainly related to the MoO groups with ligand-to-metal charge transfer (LMCT) nature (Pterminal-oxo  dMo).  相似文献   

10.
《Dyes and Pigments》2006,68(1):1-10
To improve hydrophilicity and photoactivity of the new type of therapeutic agent, hypocrellin, a novel long-wavelength ethanolamino-substituted hypocrellin B (EAHB) was synthesized and its molecular structure was characterized by IR, NMR, MS, and UV–vis spectrometers, and EAHB had strong absorption at the phototherapeutic window (600–900 nm). Illumination of deoxygenated DMSO solution containing EAHB generated a strong electron paramagnetic resonance (EPR) signal, which was assigned to the semiquinone anion radical of EAHB (EAHB). Absorption measurements displayed that the absorptive bands at 632 and 565 nm (shoulder) arose from the semiquinone anion radical (EAHB) and the absorptive bands at 519 and 450 nm (shoulder) belonged to hydroquinone (EAHBH2), which were formed via the decay of EAHB in water-contained solution. Superoxide anion radical (O2) was produced via electron transfer from EAHB (the precursor) to ground state oxygen. The presence of NADH, a bio-electron donor, significantly enhanced production of EAHB and O2. Singlet oxygen O2 (1Δg) could be produced via energy transfer from triplet EAHB to ground state oxygen molecules. The quantum yield of O2 (1Δg) and the relative quantum yield of O2 of EAHB were 0.15 and 0.76, respectively, with the parent compound hypocrellin B (HB) as the standard. It was inferred that Type I pathway was possibly a major photodynamic mechanism of EAHB. The study on photobiological action of EAHB on MGC803 cancer cells revealed that EAHB kept the same good phototoxic ability as HB but reduced 4 times cytotoxicity than HB, and also its photopotentiation factor increased 4-folds.  相似文献   

11.
Two coordination polymers based on a flexible desymmetric ligand precursor H2L have been synthesized, that is, [Ni(L)(dpe)3/2] H2O (1), [Ni2(H2O)(L)2(bpp)2] H2O (2), [H2L = 4,4′-(phenylazanediyl)dibenzoic acid, dpe = 1,2-di(pyridin-4-yl)ethane, bpp = 1,3-di(pyridin-4-yl)propane]. These complexes were characterized by elemental analysis, IR spectroscopy, X-ray single-crystal and power diffraction. In addition, the second nonlinear optical properties of 2 were measured.  相似文献   

12.
A novel chemical bond transformation from BN to BC was observed in BCN films synthesized using pulsed laser deposition (PLD). BCN film prepared by using green laser (λ=532 nm) induced two IR absorption at 1370 and 800 cm−1. This film was dominated by amorphous carbon phase and sp2 hybridized BN bonds. BCN film deposited using an ultraviolet (UV) laser (λ=266 nm ) induced an addition infrared (IR) absorption at 1250 cm−1. As we deposit BCN film by deep-UV laser (λ=213 nm), the absorption at 1370 and 800 cm−1 disappeared while the absorption at 1250 cm−1 remained. According to X-ray photoelectron spectroscopy (XPS), BC bonds with a carbon rich composition were formed. The formation of BC bonds in BCN films was also sensitive to deposition gas pressure and substrate temperature. Reactive carbon and boron species were needed to enable BC bonds that hybridized the carbon and the BN phases. A low substrate temperature was required to avoid competition with sp2 hybridized pure BN and pure carbon bonds.  相似文献   

13.
To explain the nitrogen low rate in CVD CNx layers, and their amorphisation, a release of gaseous species containing N was proposed. Previous modelling studies based on local density functional theory use pyrite type CN2 as starting model to assess the release of molecular nitrogen. This model is completed here to investigate another mechanism of release of cyanogen as another gaseous species. The theoretical pyrite-like C2N wherein C and N atoms form dumbbells in octahedral sites of a carbon face-centred sub-lattice is proposed as likely to model it. It demonstrates a good compressibility (B0 = 272 GPa) and a mechanical instability, which supports both release of atoms and the amorphisation of layers. However, the variation of interatomic distances under strain leads to propose the formation of a radical species CN. This is enforced by the consideration of the chemical bonding and its evolution in the model with the ECOV and ELF functions. The release of nitrogen in molecular cyanogen is consequently substituted by a mechanism which implies a CN radical species, which is likely to recombinate at the CVD layers surfaces.  相似文献   

14.
A series of UV curable EA-Si hybrid coatings were prepared by a simple approach combining radical and cationic photopolymerization, with epoxy acrylate (EA) as monomer, γ-glycidoxypropyltrimethoxysilane (GPTMS) as inorganic precursor, benzophenone (BP) as free radical photo initiator and a diaryliodonium salt DPIHFP as cationic photo initiator. The chemical structures of EA-Si hybrid coatings were characterized by Fourier transform infrared (FTIR), Raman spectroscopy and X-ray diffraction (XRD). The thermal and optical properties of hybrid coatings were investigated by thermal gravimetric analysis (TGA) and UV–vis transmission spectroscopy, respectively. The results indicated that cross-linked network structure of SiOSi formed in the hybrid coatings, which led to the decrease in crystallinity and of EA-Si hybrid coating. The final conversion of CC bonds was also decreased because of the addition of GPTMS. The thermal stability of EA-Si hybrid coatings was enhanced in the second decomposition stage (300–400 °C) because of the existence of organic–inorganic cross-linked network structures. The transparency of coatings at around 346 nm tended to increase with increasing concentration of inorganic precursor GPTMS.  相似文献   

15.
Copper containing methacrylic polymers were prepared by the polymerization of a copper methacrylate complex (Cu[CH2C(CH3)COO](COD), where COD = 1,5-cyclooctadiene) with different methylmethacrylate and methacrylic acid compositions. These polymers were found to be soluble in many organic solvents including THF and chloroform. Copper nano-networks or aggregated nanoparticles were obtained when a THF solution of the polymers was reduced using an aqueous sodium borohydride solution. When a thin film of the polymers coated on a silicon wafer was irradiated with an electron beam, nanoparticles were produced on the irradiated area, while the non-irradiated areas could be washed away with a weak base developer, such as a tetramethylammoniumhydroxyde (TMAH) aqueous solution, to produce a copper pattern through an electron beam lithography process.  相似文献   

16.
A processable poly[(n-propylamino/methylamino)borazine] (PPAB) has been pyrolyzed in Ar to study its thermal decomposition behavior. The structural evolution and chemical composition change during pyrolysis were characterized by chemical analysis, thermal gravimetry–mass spectrometry (TG–MS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the polymer-to-ceramic transition of PPAB involved two steps. Below 400 °C, the gas species were mainly methane and methylamine, while from 400 to 900 °C those were methane and n-propylamine. The PPAB displayed a ceramic yield of 52 wt% at 1000 °C and the pyrolyzed product was amorphous boron nitride (BN) with a small quantity of carbon impurity, in presence as CC and CN bonds. Moreover, for the pyrolyzed product, further heat treatment resulted in the occurrence of a transformation from amorphous to turbostratic.  相似文献   

17.
This work summarizes the results related to the influence of the starting composition and of microstructure on properties degradation, due to oxidation and corrosion, relatively to the following structural ceramics: Si3N4TiN, Si3N4MoSi2, AlNSiCMoSi2, AlNSiC.The effects of: (i) long-term oxidation in air (100 h), in the temperature range 600–1500 °C and (ii) of long-term corrosion (400 h) in acid or basic aqueous solution at RT, 40 and 70 °C, on the electrical resistivity and mechanical strength of the composites are analysed and compared. The degradation of the properties are related to the characteristics of the surface and sub-surface damage after oxidation and corrosion treatments.  相似文献   

18.
Controlled grafting of well-defined cationic poly[(ar-vinylbenzyl)trimethylammonium chloride] [poly(VBTAC)] brushes on a hydrogen-terminated silicon substrate (SiH) was performed via surface-initiated RAFT polymerization. The azo-initiator was immobilized on the SiH surface via a three step process involving (i) coupling of the t-butyloxycarbonyl (t-BOC) protected allylamine to the SiH surface under UV irradiation, (ii) conversion of the t-BOC protected allylamine groups into the free amine groups by trifluoroacetic acid, and (iii) the amide reaction of allylamine with the 4,4′-azobis(4-cyanopentanoyl chloride) initiator. The living polymerization produced silicon substrate coated with well-defined cationic poly(VBTAC) with a target molecular weight and a grafting density as high as 0.93 chains/nm2.  相似文献   

19.
A liquid hyperbranched polycarbosilane (LHBPCS) with stoichiometric C/Si ratio but without unsaturated groups was synthesized. Different from traditional thermal crosslinking, ultraviolet (UV) irradiation crosslinking was taken. The molecular weight, the consumption of SiH group and ceramic yield of LHBPCS showed an increase trend with increasing the UV irradiation time. After 30 min of UV irradiation, 71.8 wt% ceramic yield was obtained. In addition, extra divinyldimethylsilane was added into LHBPCS. Under UV irradiation, both the SiH group and vinyl group of divinyldimethylsilane were consumed. But the reaction extend of vinyl group was much faster than that of SiH group. Compared with pure LHBPCS, the mixture of LHBPCS and 5 wt% divinyldimethylsilane gave a higher ceramic yield of 79 wt% after 30 min of UV irradiation. By heating the crosslinked LHBPCS to 1000 °C, a near stoichiometric SiC ceramic was got. It exhibited excellent thermal stability at 1400 °C in air.  相似文献   

20.
Subcritical water extraction (SWE) of phenolic compounds from pomegranate seed residues (PSR) was performed. Total phenolic content (TPC) and antioxidant capacities of the extracts obtained at different temperatures were determined, and the individual antioxidant capacities were evaluated by coupling high performance liquid chromatography with ABTS radical reaction system (HPLC–ABTS+). The results showed that the optimum extraction time was 30 min, solid to water ratio was 1:40, and the highest TPC was obtained at 220 °C. The effect of extraction temperature on TPC was significant (p < 0.05), and TPC ranged from 651.7 to 4854.7 (mg/100 g DW) between 100 °C and 220 °C. HPLC–ABTS+ profiles revealed that nine compounds had antioxidant activity. Furthermore, the formation of Maillard reaction products during SWE was investigated, and the content of 5-hydroxymethylfurfural (5-HMF) was determined. The comparative study indicated that SWE was a promising technique for preparation of PSR phenolics.  相似文献   

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