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1.
Kangle Lv Jiaguo Yu Kejian Deng Mei Li 《Journal of Physics and Chemistry of Solids》2010,71(4):519-6235
To study the relationship between the phase structures of TiO2 and the photoinduced hydroxyl radicals (OH), TiO2 nanocrystallines were synthesized by a hydrolysis-precipitate method using tetrabutylorthotitanate (TBOT) as precursor, and then calcined at 450, 600, 700, 800 and 900 °C for 2 h, respectively. The calcined samples were characterized by X-ray diffraction and N2 sorption. The formation rate of OH on the surface of UV-illuminated TiO2 was detected by the photoluminescence (PL) technique using terephthalic acid as a probe molecule. The results show that with increasing calcined temperatures, the amorphous (Am) TiO2 precursor begins to turn into anatase (A) at 450 °C and rutile (R) phase appears at 600 °C, which is completely turned into the rutile phase at 900 °C. The BET specific surface areas of the catalyst decrease as the calcined temperatures increase. TiO2 sample calcined at 600 °C, with a mixed phase of anatase and rutile, shows the highestOH formation rate, and the order of the OH formation rate is as follows: A+R>A>R>Am. Phase structures of TiO2 play a more important role than specific surface areas in the OH formation rate. Two phase structure of anatase and rutile with a proper ratio is beneficial to the OH formation due to decrease of the combination rate of photo-generated electrons and holes. Our experimental result implies that the mixed phase of anatase and rutile can markedly enhance the photocatalytic activity of TiO2. 相似文献
2.
Kevin Summers 《Surface science》2007,601(6):1443-1455
The surface reactions of 2-iodopropane ((CH3)2CHI) on gallium-rich GaAs(1 0 0)-(4 × 1), was studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). CH3CHICH3 adsorbs molecularly at 120 K but dissociates below room temperature to form chemisorbed 2-propyl ((CH3)2CH) and iodide (I) species. Thermal activation causes desorption of the molecular species at 240 K, and this occurs in competition with the further reactions of the (CH3)2CH and I chemisorbed species. Self-coupling of the (CH3)2CH results in the formation of 2,3-dimethylbutane ((CH3)2CH-CH(CH3)2) at 290 K. β-Hydride elimination in (CH3)2CH yields gaseous propene (CH3CHCH2) at 550 K while reductive elimination reactions of (CH3)2CH with surface hydrogen yields propane (CH3CH2CH3) at 560 K. Recombinative desorption of the adsorbed hydrogen as H2 also occurs at 560 K. We observe that the activation barrier to carbon-carbon bond formation with 2-propyls on GaAs(1 0 0) is much lower than that in our previous investigations involving ethyl and 1,1,1-trifluoroethyl species where the β-elimination process was more facile. The difference in the surface chemistry in the case of 2-propyl species is attributable to its rigid structure resulting from the bonding to the surface via the second carbon atom, which causes the methyl groups to be further away from the surface than in the case of linear ethyl and 1,1,1-trifluoroethyl species. The β-hydride and reductive elimination processes in the adsorbed 2-propyl species thus occurs at higher temperatures, and a consequence of this is that GaI desorption, which is expected to occur in the temperature range 550-560 K becomes suppressed, and the chemisorbed iodine leaves the surface as atomic iodine. 相似文献
3.
Water-soluble l-cysteine capped Mn-doped ZnS@Si quantum-dots (QDs), a kind of sensitizer, were synthesized. It was found that this sensitizer could enhance chemiluminescence (CL) signals emitted from interaction of NaClO with H2O2 in basic medium. The CL mechanism was studied experimentally by singlet oxygen (1O2) quenching method, UV-vis spectra, X-ray photoelectron spectra, transmission electron microscopy studies and ESR spin-trapping spectra. The results demonstrated that the CL enhancement of NaClO-H2O2 originate from the catalysis of the sensitizer, which catalyzed the decomposition of H2O2, producing reactive intermediates hydroxyl radical (OH) and superoxide anion (O2−). Then the resulting OH reacted with O2− to form 1O2 and oxygen excimer species (1O2)2?, which rapidly returned to its ground state by passing its energy to the sensitizer through an electron-transfer process. Finally, the sensitizer being in excited state, returned to the ground state through enhanced CL-emission. 相似文献
4.
Bianca Montanari Sidney J.L. Ribeiro Gaël Poirier Máximo S. Li 《Applied Surface Science》2008,254(17):5552-5556
Thin films were prepared using glass precursors obtained in the ternary system NaPO3BaF2WO3 and the binary system NaPO3WO3 with high concentrations of WO3 (above 40% molar). Vitreous samples have been used as a target to prepare thin films. Such films were deposited using the electron beam evaporation method onto soda-lime glass substrates. Several structural characterizations were performed by Raman spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES) at the tungsten LI and LIII absorption edges. XANES investigations showed that tungsten atoms are only sixfold coordinated (octahedral WO6) and that these films are free of tungstate tetrahedral units (WO4). In addition, Raman spectroscopy allowed identifying a break in the linear phosphate chains as the amount of WO3 increases and the formation of POW bonds in the films network indicating the intermediary behavior of WO6 octahedra in the film network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed identifying the presence of WO− and WO terminal bonds and a progressive apparition of WOW bridging bonds for the most WO3 concentrated samples (above 40% molar) attributed to the formation of WO6 clusters. 相似文献
5.
R. Navamathavan 《Applied Surface Science》2007,253(21):8788-8793
Low dielectric constant SiOC(H) films are deposited on p-type Si(100) substrates by plasma enhanced chemical vapor deposition (PECVD) using methyltriethoxysilane (MTES, C7H18O3Si) and oxygen gas as precursors. The SiOC(H) films are deposited at room temperature, 100, 200, 300 and 400 °C and then annealed at 100, 200, 300 and 400 °C temperatures for 30 min in vacuum. The influence of deposition temperature and annealing on SiOC(H) films are investigated. Film thickness and refractive index are measured by field emission scanning electron microscopy and ellipsometry, respectively. Chemical bonding characteristics of as-deposited and annealed films are investigated by Fourier transform infrared (FTIR) spectroscopy in the absorbance mode. As more carbon atoms are incorporated into the SiOC(H) films, both film density and refractive index are decreased due to nano pore structure of the film. In the SiOC(H) film, CH3 group as an end group is introduced into OSiO network, thereby reducing the density to decrease the dielectric constant thereof. The dielectric constant of SiOC(H) film is evaluated by C-V measurements using metal-insulator-semiconductor (MIS), Al/SiOC(H)/p-Si structure and it is found to be as low as 2.2 for annealed samples deposited at 400 °C. 相似文献
6.
Nanoplate γ-Bi2MoO6 is prepared by hydrothermal method. Using this material as photocatalyst, rhodamine B and methylene blue were efficiently degraded under visible light irradiation. The degradation kinetics, total organic carbon changes, and electron spin resonance detection of active oxygen species were investigated to clarify the degradation process. The experimental results indicated that the target dyes could be facilely bleached and mineralized. The formation of active oxygen species of OH and O2− is detected, and they are proposed to be responsible for the degradation of the target dyes. The γ-Bi2MoO6 catalyst is very stable and can be reused. 相似文献
7.
Gamma irradiated [(CH3)4N]InCl4 and [(CH3)4N]2CdCl4 single crystals were investigated by electron paramagnetic resonance at ambient temperature, and it has been found that both compounds indicate the existence of (CH3)3N+ radicals. The g factors were found to be isotropic, and the hyperfine constant for H atoms was measured as 2.86 mT and is isotropic for this radical in these substances. The hyperfine coupling constant of the N nucleus with the hole in (CH3)3N+ in [(CH3)4N]InCl4 was found to be anisotropic with the Azz=2.92, Ayy=1.62 and Axx=1.40 mT. From these, it has been revealed that the C3v-axis of (CH3)3N+ radical performs rotational or jumping reorientational motions around a fixed axis, in addition to the rotations of protons in CH3 groups and the rotational motions of CH3 groups around the C3v-axis of the radical. The g, and the hyperfine coupling factors of the N nucleus were isotropic in (CH3)3N+ in [(CH3)4N]2CdCl4. This indicates the motional behaviour of the radical in this compound is as in a liquid. This isotropic behaviour of the hyperfine coupling constants was found to be same until the attainable lowest temperature of 113 K in our laboratory. 相似文献
8.
D.K. Havey 《Journal of Molecular Spectroscopy》2004,228(1):152-159
This work investigates the vibrational spectroscopy of a series of organic acids, CH3(CH2)nCOOH (n = 1-5), previously unobserved in the IR and near-IR (2000-15 000 cm−1). The work obtains frequencies and relative intensities for all OH and CH stretching transitions. Comparison of the frequencies and intensities of CH and OH stretching transitions reveal interesting trends in acid chain length that are discussed. Literature values for acetic acid (CH3COOH) and formic acid (HCOOH) are used to gain a broader understanding for the spectroscopy of the organic acids CH3(CH2)nCOOH. The observation of several combination bands involving the CH and OH stretching vibrations and possible rotational isomer and hot band transitions are reported. 相似文献
9.
G.S. Grubbs II A. King W.C. Bailey S.A. Cooke 《Journal of Molecular Spectroscopy》2010,263(2):127-134
A potential energy scan of chlorodifluoroacetyl chloride, CF2ClC(O)Cl, at the MP2/6-311+G(d) level of theory predicts stable gauche and trans conformers, with Egauche<Etrans. Ab initio calculations were made of approximate equilibrium structures of these and, on these structures, calculations were made of 35Cl and 37Cl nuclear quadrupole coupling constant tensors. Coupling constants here predicted, as well as rotational constants and molecular dipole moments, are applied to aid analyses of experimental microwave spectra. Chirped pulse Fourier transform microwave spectroscopy has been used to rapidly record the rotational spectra of four isotopologues of the title molecule, CClF2C(O)Cl, namely 35Cl35Cl, 35Cl37Cl, 37Cl35Cl, and 37Cl37Cl. Only the gauche conformer was observed under the experimental conditions. For the four isotopologues a total of 464, 219, 197, and 77 transitions have been recorded, respectively. With the exception of the 37Cl37Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made. 相似文献
10.
Ying Wu 《Applied Surface Science》2006,252(14):5220-5226
Nanosized TiNiO catalysts prepared by a modified sol-gel method have been investigated in the oxidative dehydrogenation of propane (ODP) to propene. At 300 °C the yield to propene of 12.1% was obtained on 9.1 wt.% TiNiO catalyst with the selectivity of 43%. The continued variety of lattice parameter and variation of chemical value of nickel and titanium ion on the surface indicates that there are strong interactions of TiO2 and NiO. The decreased low temperature oxygen desorption and the weaker reducibility seems to be responsible for the decreased activity and enhanced selectivity of propane oxidative dehydrogenation over TiNiO catalysts. 相似文献
11.
Porous silicon (PS) was passivated by silica film using a sol-gel method; the photoluminescence (PL) properties were significantly improved; namely, PL intensity and stability increased and PL peak shifted to shorter wavelength. Scanning electron microscope (SEM) and Fourier transformed infrared spectroscope (FTIR) results indicated that silica passivation produced a compact film on the PS surface and modified the surface state of PS. The number of stable surface bonds (HSiO3, HSiSiO2 and H2SiO2) increased due to the oxidation of SiH back-bonds during the gelation process, and thus the PL intensity and stability were improved. Moreover, the blue-shift of PL peak was determined due to the increase in the ratio of SiO/SiH. 相似文献
12.
Xugeng Guo 《Journal of Molecular Spectroscopy》2009,256(2):242-246
Geometries and stabilities of the linear aluminum-bearing carbon chains AlC2nH (n = 1-5) in their ground states have been explored by the DFT-B3LYP and RCCSD(T) methods. Structures of the X1Σ+ and 11Π electronic states have also been optimized by the CASSCF approach. The studies indicate that these species have single-triple bond alternate pattern, AlCCCC?CCH, and the electronic excitation from X1Σ+ to 11Π leads to the shortening of the AlC bonds. The vertical excitation energies of the 11Π ← X1Σ+ and 21Π ← X1Σ+ transitions for AlC2nH (n = 1-5) have been investigated by the CASPT2, EOM-CCSD, and TD-B3LYP levels of theory with the cc-pVTZ basis set, respectively. CASPT2-predicted 11Π ← X1Σ+ transition energies are 3.57, 3.44, 3.33, 3.26, and 3.21 eV, respectively. For AlC2H, our estimate agrees very well with the experimental value of 3.57 eV. In addition, the AlC bond dissociation energies and the exponential-decay curves for these vertical excitation energies are also discussed. 相似文献
13.
Xiuqin Chen 《Applied Surface Science》2008,254(20):6693-6696
Fabrication of PF-codoped TiO2 nanotubes was carried out using a one-step electrochemical anodization process by tailoring the composition of the electrolyte with the aim of PF-codoping to extend the optical absorption of TiO2 to the visible-light region. The as-prepared PF-codoped TiO2 nanotubes were characterized by SEM, XPS, and UV-vis diffuse reflectance absorption spectra (DRS). The results showed that the tube diameter of the nanotubes was approximately 100 nm and the tube length was approximately 510 nm. The phosphorus and fluorine were successfully doped into TiO2 nanotubes, as evidenced by XPS. Moreover, the PF-codoped samples displayed remarkably strong visible-light response. 相似文献
14.
A theoretical study of the H2O and O2 adsorption on an illuminated TiO2 anatase surface is presented. The electronic structure and the spin distribution were examined by employing the DFT formalism and the BHandHLYP functional. The adsorbates geometries were fully optimized, including the cluster relaxation. Our results show the dissociative adsorption of the H2O molecule on the photoactivated TiO2 (0 0 1) surface. This reaction produces one hydroxyl group with radical character (OH) and an unpaired electron localized in the 5c-Ti atom. In case of the O2 molecule, the non-dissociative chemisorption was obtained. This molecule shows one unpaired electron and a negative charge. In these sense, the adsorbed O2 acts as a superoxide species (O2−). 相似文献
15.
The visible-light photocatalytic behavior of two different N-doped TiO2 correlated with their physicochemical properties was investigated. The results show that N-TiO2-1, prepared by a novel TiO2 with unique defect structure, is more active in visible-light photocatalytic oxidation of C3H6 than N-TiO2-2, prepared by standard P25-TiO2 (Degussa). The specific rate constant of the former is ca. 5 times that of the latter. One model of photoactive center (Vo-NO-Ti) in anatase phase responsible for the visible-light photocatalytic activity is proposed. The higher the Vo-NO-Ti concentration is, the better the visible-light photocatalytic activity is. 相似文献
16.
Chemisorption of 1,1-dichloroethene (Cl2CCH2) to a Si(1 1 1)-7 × 7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds.The results confirm the identity of covalently bonded 1-chlorovinyl (-CClCH2) and vinylidene (CCH2) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C-Cl bond while about two-thirds of the adsorbates break two C-Cl bonds. We do not, however, find evidence for isomerization of CCH2 to di-bonded vinylene (-CHCH-). 相似文献
17.
Two novel ternary rare earth complexes LnL5L′(ClO4)32H2O (Ln=Eu(III), Tb(III); L=bis(benzoylmethyl) sulfoxide, L′=phen) were synthesized and characterized by elemental analysis, coordination titration analysis, molar conductivity, IR, TG-DSC,1H NMR and UV spectra. The fluorescence spectra illustrated that both the Eu(III) and Tb(III) ternary complexes displayed strong characteristic metal-centered fluorescence in solid state. After the introduction of the second ligand phen group, the relative emission intensities and fluorescence lifetimes of the ternary complex EuL5L′(ClO4)32H2O (L=C6H5COCH2SOCH2COC6H5, L′=phen) enhanced more obviously than that of the binary complex EuL5(ClO4)33H2O. This indicated that the presence of both organic ligands bis(benzoylmethyl) sulfoxide and the second ligand phen could sensitize fluorescence intensities of Eu(III) ions, and the introduction of phen group was resulted in the enhancement of the fluorescence properties of the Eu(III) ternary rare earth complexes. The phosphorescence spectra are also discussed. 相似文献
18.
19.
The wide use of high intensity ultrasound (HIU) in modern medicine raises the question of bio-safety. It has been shown that the effect of HIU in biological media may have similarity to the effects of ionizing radiation. Exposure of biological media to HIU field may lead to cavitation phenomenon followed by formation of free radicals such as hydroxyl radical (OH) and the super-oxide ion (O2-). These are highly reactive species that may cause harmful effects and induce oxidative stress. In the present study we employed electron spin resonance (ESR) spectroscopy together with spin traps to quantify the dynamics of hydroxyl radical formation during exposure to HIU field in the presence of different amounts of six antioxidants. Thus, the efficiency of water-soluble antioxidants, namely Allicin, Melatonin, Deoxyribose, Trolox, Nuphlutine and Hermidin, to suppress accumulation of OH radicals was examined. The results show that among the six, Trolox and Allicin reduce hydroxyl concentration with the highest efficiency. 相似文献
20.
Poly(ethylene terephthalate) (PET) films were treated with CF4 plasma immersion. The samples were processed at different RF powers and treatment time. The surface modification of PET films was evaluated by water contact angle (CA), X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Decrease in contact angle of both sides of PET films was observed under mild treatment conditions. However, as raising treatment power and/or time, the change in contact angle between the two sides of PET films was different. The relatively hydrophobic and hydrophilic surfaces were being in situ formed on the two sides of PET films, respectively. And the extreme values of water contact angle reached 108.63 and 7.56°, respectively. XPS analyses revealed that there was a substantial incorporation of fluorine and/or oxygen atoms in both side surfaces. The relative chemical composition of the C (ls) spectra's showed the incorporation of non-polar fluorine-based functionalities (i.e. CFCFn, CF2 or CF3 groups) and polar oxygen-based functionalities (i.e. COOH or OH groups) in the surfaces. Correlation between the plasma parameters and the surface modification of PET films is also discussed. 相似文献