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1.
The enthalpies of solution of 1,4-dioxane in {(1  x)F + xH2O}, {(1  x)NMF + xH2O}, and {(1  x)DMF + xH2O} have been measured within the whole mole fraction range at T = 298.15 K. Based on the obtained data, the effect of substituting methyl groups at the nitrogen atom in formamide on the preferential solvation of 1,4-dioxane has been analyzed. A simple model has been proposed to describe the influence of structural and energetic properties of the mixed solvent on the energetic effect of hydrophobic hydration and preferential solvation of 1,4-dioxane by the components of the examined mixture.  相似文献   

2.
Excess enthalpies and excess heat capacities of { x 2-butanone  +  (1   x)1,4-dioxane}, and { x cyclohexanone, or 2-butanone, or 1,4-dioxane  +  (1   x)1,2-dimethoxyethane} were measured atT =  298.15 K. Excess enthalpies were negative for { x 2-butanone  +  (1   x)1,2-dimethoxyethane}, and negative with a small positive part in the region ofx >  0.8 for { x cyclohexanone  +  (1   x)1,2-dimethoxyethane}, whereas excess enthalpies of { x 2-butanone  +  (1   x)1,4-dioxane} were positive as for { x cyclohexanone  +  (1   x)1,4-dioxane} previously reported. Excess enthalpies of {x 1,4-dioxane  +  (1   x)1,2-dimethoxyethane} were positive. The results were compared with the systems reported earlier. Excess heat capacities are positive for { x 2-butanone  +  (1   x)1,2-dimethoxyethane} and { x cyclohexanone  +  (1   x)1,2-dimethoxyethane}, and negative for { x 2-butanone  +  (1   x)1,4-dioxane} and { x 1,4-dioxane  +  (1   x)1,2-dimethoxyethane}. The last mixture shows a W-shaped curve of excess heat capacity.  相似文献   

3.
Cu and N-doped TiO2 photocatalysts were synthesized from titanium (IV) isopropoxide via a microwave-assisted sol-gel method. The synthesized materials were characterized by X-ray diffraction, UV-vis diffuse reflectance, photoluminescence (PL) spectroscopy, SEM, TEM, FT-IR, Raman spectroscopy, photocurrent measurement technique, and nitrogen adsorption–desorption isotherms. Raman spectra and XRD showed an anatase phase structure. The SEM and TEM images revealed the formation of an almost spheroid mono disperse TiO2 with particle sizes in the range of 9-17 nm. Analysis of N2 isotherm measurements showed that all investigated TiO2 samples have mesoporous structures with high surface areas. The optical absorption edge for the doped TiO2 was significantly shifted to the visible light region. The photocurrent and photocatalytic activity of pure and doped TiO2 were evaluated with the degradation of methyl orange (MO) and methylene blue (MB) solution under both UV and visible light illumination. The doped TiO2 nanoparticles exhibit higher catalytic activity under each of visible light and UV irradiation in contrast to pure TiO2. The photocatalytic activity and photocurrent ability of TiO2 have been enhanced by doping of the titania in the following order: (Cu, N) - codoped TiO2 > N-doped TiO2 > Cu-doped TiO2 > TiO2. COD result for (Cu, N)-codoped TiO2 reveals ∼92% mineralization of the MO dye on six h of visible light irradiation.  相似文献   

4.
Combustion of wheat straw incorporating TiO2, CuO and MnO2 was investigated by means of thermal analysis carried out at 20 °C/min in the temperature range from 50 °C to 900 °C. Combustion characteristic indexes had been put forward to describe wheat straw combustion characteristics. All the results showed that the catalysis of the catalysts to the wheat straw combustion had been embodied in facilitation of the volatile matters release from wheat straw, which reduced the temperature of the maximum combustion rate, and the relative active sequence of catalysts to the ignition characteristic could be improved remarkably. The catalysis of different catalysts to the Devolatilization Index could be described as follows: MnO2 > TiO2 > CuO, and the relative active sequence of catalysts to the Combustion Characteristic Index could be described as follows: CuO > TiO2 > MnO2.  相似文献   

5.
The results from electrooptical absorption measurements (EOAM) on the ground and excited Franck–Condon state dipole moments of Prodan and Laurdan in 1,4-dioxane and cyclohexane are presented. The ground and excited Franck–Condon state electric dipole moments as well as the respective transition moment of both probes are parallel. The electric dipole moments of Prodan and Laurdan in the ground state in cyclohexane and 1,4-dioxane have values within the range (15.7–16.5) × 10−30 C m. On optical excitation the dipole moments increase by (42.1–49.5) × 10−30 C m. The obtained results are compared with the values of the dipole moments of Prodan and Laurdan determined by other methods.  相似文献   

6.
7.
In this work, the performance of integrated photocatalytic and biological treatment was studied for the degradation of 4-chlorophenol (MCP) present in wastewaters. Photocatalysis was used as a pre-treatment to biological degradation. Pollutant removal efficiency was quantified using MCP removal and total organic carbon (TOC) removal. Both photocatalytic as well as biological treatments were carried out in batch reactors, using TiO2 as the photocatalyst. The inoculum for biological experiments was obtained from paper mill effluent treatment plant and was developed through a process of selection and acclimatization. Effect of TiO2 concentration on the photocatalytic degradation of MCP was studied along with the effect of the duration of photochemical oxidation and glucose concentrations (0 g/L, 1 g/L and 2 g/L) on the biodegradation of MCP. Integrated biological and photochemical degradation was found to be more effective in treating MCP, especially at higher concentrations (400 mg/L). An initial MCP concentration of 400 mg/L required 96 h for complete mineralization when treated with the process combination, whereas the treatment went on up to 264 h when biodegradation alone was employed.  相似文献   

8.
《Fluid Phase Equilibria》2006,245(2):158-167
Employing a previously derived model to describe intra-diffusion coefficients in liquid mixtures based on molecular simulations of spherical Lennard–Jones particles [T. Merzliak, A. Pfennig, Mol. Simul. 30 (7) (2004) 459–468], an improved set of coefficients was obtained from optimized molecular dynamics simulations. In these simulations, the thermodynamic states were planned with the help of optimal experimental design, which allows to reduce the number of simulations necessary for significant determination of the coefficients by roughly a decade. The model was then applied to the real liquid mixtures toluene + cyclohexane, toluene + 1,4-dioxane, n-hexane + toluene, 1,4-dioxane + cyclohexane and cyclohexane + n-hexane, which have molecular properties that correspond to the model assumptions. Experimental intra-diffusion coefficients for the mixtures toluene + cyclohexane, toluene + 1,4-dioxane, n-hexane + toluene and 1,4-dioxane + cyclohexane were determined with nuclear magnetic resonance (NMR) techniques in this work. Even without additional parameters for the mixture the proposed model can describe the diffusion coefficients with an average accuracy of 5%. Allowing a deviation from Lorentz–Berthelot mixing rules leads generally only to slight improvement.  相似文献   

9.
A novel (μ3-oxo)tetraruthenium cluster (2) was synthesized in an isolated yield of 73% by the reaction of a zerovalent ruthenium complex, Ru(η6-cot)(η2-dmfm)2 (1) [cot = 1,3,5-cyclooctatriene, dmfm = dimethyl fumarate], with water under reflux in 1,4-dioxane for 6 h. The structure and the X-ray characterization of this novel complex 2 as well as a possible formation mechanism of 2 are disclosed.  相似文献   

10.
WO3 nanoparticles were synthesized by the precipitation method varying the time employed in the formation of their precursor in aqueous media and the calcination temperature. The WO3 crystallization process and morphology of the synthesized samples were followed by the XRD, TEM and SEM techniques. The effects of the calcination temperature on the surface area and optical properties of the WO3 nanoparticles were also investigated. Nanoparticles with morphologies such as square and rectangular plates and ovoid forms were observed for the different experimental conditions. WO3 nanoparticles with different morphologies were tested for the photocatalytic degradation of organic dyes. In general, the photocatalysts showed a capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > congo red (CR). The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (93%, within 75 h) only for IC. This value was even better than the one concerning the P-25 Degussa reference.  相似文献   

11.
The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 and 18-crown-6 in {(1 ? x)AN + xH2O} have been measured over the whole mole fraction range at T = 298.15 K. Based on the results obtained, the effects of base–acid properties of mixed solvent and the number of –CH2CH2– groups in cyclic ethers molecules on the solution enthalpy of cyclic ethers in {(1 ? x)AN + xH2O} have been analyzed.  相似文献   

12.
La/Ti mixed oxides with weight ratios of 1:9, 2:8, 3:7, and 4:6 were prepared by sol–gel method. The photocatalytic activity of La/Ti oxides was evaluated based on the pCBA photodecomposition. The catalyst samples were characterized by XRD, TEM, DRS, BET, and photoluminescence (PL) spectra. Particles of the La/Ti-mixed oxides showed the diameter of about 7 nm. We found that 30% doping of lanthanum ions on the TiO2 powders induced the highest pCBA (4-chlorobenzonic acid) photodecomposition in these experimental conditions. The order of its photoactivity was as following: 30 > 20 > 0 > 10 > 40 wt%, which was the same for PL tendency. Also, PL spectra intensity increased with calcination temperature from 500 to 600 °C, then decreased at 700 °C. Phtotcatalytic activity followed the trend of the PL spectra intensity. The modification of TiO2 surface by lanthanum ion made it possible to enhance the photoactivity by retarding the recombination of photoexcited electron/hole pairs, in the result of the higher photoactivity in the stronger PL intensity.  相似文献   

13.
Characteristics of 2.45-GHz microwave radiation were examined on two second generation nitrogen-doped TiO2 nanomaterials prepared by annealing Degussa P-25 TiO2 and Ishihara ST-01 TiO2 at 400 °C and 500 °C, respectively, in air in the presence of urea, and for comparison on the undoped pristine samples. Band gaps of all four samples were determined by diffuse reflectance spectroscopy. Both the sizes and the BET specific surface areas of the TiO2 particles were determined, together with dielectric constants and dielectric loss factors. Nitrogen doping caused the size to increase and surface area to decrease. Temperature–time profiles showed that the heating efficiency of the N-doped specimens by the microwaves was greater, particularly significant for the N-doped P25 sample, but rather small for the N-ST01 sample. The effect of microwaves on the surface optical phonons of the samples, with and without UV–vis irradiation, was examined by an in situ Raman spectroscopic technique; for the undoped P-25 and nitrogen-doped N-P25 TiO2 systems the effect was negligible. By contrast, microwave irradiation of Ishihara ST-01 and nitrogen-doped N-ST01 TiO2 samples showed significant changes in the 144-cm?1 optical phonons. Results infer a microwave thermal effect on the Ishihara ST-01 and N-ST01 specimens, whereas for the Degussa P-25 samples the microwaves also imparted a specific effect as the microwaves influenced the N-dopant sites in contrast to the ST-01 systems where the dopant sites were unaffected as evidenced by temperature–time profiles. The microwave-/photo-assisted degradation of 4-chlorophenol under various conditions of UV–vis irradiation and conventional heating, as opposed to microwave heating, confirms the specific microwave effect for the P-25 systems.  相似文献   

14.
《Solid State Sciences》2007,9(10):944-949
A Bi-based oxychloride Na0.5Bi1.5O2Cl with a layered structure as a novel efficient photocatalyst was studied in the present paper. The powder was synthesized by a solid state reaction method. It was characterized by X-ray diffraction, scanning electron microscope and UV–vis diffuse reflectance spectrum. Degradation of methyl orange was used to evaluate the photocatalytic activity. The as-synthesized Na0.5Bi1.5O2Cl has a smaller optical band gap of 3.04 eV than BiOCl (Eg = 3.44 eV). It possesses a fair visible-light-response ability. The UV-induced photocatalytic activity follows the decreasing order of BiOCl > Na0.5Bi1.5O2Cl > TiO2, different from the order of Na0.5Bi1.5O2Cl > TiO2 > BiOCl under visible light irradiation. The dispersion of Pt over Na0.5Bi1.5O2Cl leads to an obvious increase in the photocatalytic performance. The internal electric fields between [Na0.5Bi1.5O2] and [Cl] slabs favor the efficient separation of photostimulated electron–hole pairs.  相似文献   

15.
The photocatalytic degradation of paraquat (1,1-dimethyl-4,4′-bipyridylium dichloride) aqueous solutions in the presence of polycrystalline TiO2 Degussa P25 irradiated by near-UV light was investigated. The substrate and total organic carbon concentrations were monitored by UV spectroscopy and TOC measurements, respectively: the complete photocatalytic mineralization of paraquat (20 ppm) was achieved after ca. 3 h of irradiation by using 0.4 g l−1 of catalyst amount at natural pH (ca 5.8). On the contrary no significant photodegradation of paraquat was observed in the absence of TiO2 under similar experimental conditions. To evaluate the genotoxicity of paraquat and its intermediates produced during heterogeneous photocatalytic treatment, in vitro tests such as Ames test, with and without rat liver microsomal fractions (S9 mix), and micronucleus test, were used. Results obtained with Salmonella typhimurium (strain TA100) showed that paraquat and photocatalytic products were unable to induce gene mutations when photocatalysis was used in the presence of the optimum amount of TiO2, i.e. 0.4 g l−1, whereas an increase of revertants his+ per plate was observed after 300 min irradiation in the presence of very low amount of TiO2 (0.04 g l−1). The negative results from micronucleus test suggest that mutagenic, but non-clastogenic, late intermediates of paraquat photo-oxidation were formed when the photocatalytic runs of paraquat degradation were carried out by using 0.04 g l−1 of photocatalyst.  相似文献   

16.
The measurement of excess enthalpies, HE, at T=298.15 K and densities at temperatures between 283.15 K and 313.15 K are reported for the (2-methoxyethanol + 1,4-dioxane) and (1,2-dimethoxyethane + benzene) systems. The values of HE and the excess volumes, VE, are positive, and the temperature dependence of VE is quite small for (2-methoxyethanol + 1,4-dioxane). The (1,2-dimethoxyethane + benzene) system shows a negative HE and sigmoid curves in VE, which change sign from positive to negative with an increase in 1,2-dimethoxyethane. The temperature dependence of VE for this system is negative.  相似文献   

17.
We report the electrochemical performance of carbon-coated TiO2 nanobarbed fibers (TiO2@C NBFs) as anode material for lithium-ion batteries. The TiO2@C NBFs are composed of TiO2 nanorods grown on TiO2 nanofibers as a core, coated with a carbon shell. These nanostructures form a conductive network showing high capacity and C-rate performance due to fast lithium-ion diffusion and effective electron transfer. The TiO2@C NBFs show a specific reversible capacity of approximately 170 mAh g 1 after 200 cycles at a 0.5 A g 1 current density, and exhibit a discharge rate capability of 4 A g 1 while retaining a capacity of about 70 mAh g 1. The uniformly coated amorphous carbon layer plays an important role to improve the electrical conductivity during the lithiation–delithiation process.  相似文献   

18.
Cu-deposited TiO2 films were prepared by photoreduction of Cu(II) in the presence of sodium formate. With the initial Cu(II) concentrations more than 100 mg L?1, induction periods were observed before the transmittance decreased. Scanning electron microscopy indicated that Cu particles of 2.6 ± 0.5 μm were deposited isolatedly with much open space in the induction periods. The films prepared by changing the irradiation time within the induction periods showed a higher photocatalytic activity than a pure TiO2 for the degradation of methylene blue under the reaction condition without purging air.  相似文献   

19.
The present work describes the development of a new strategy to photoelectrochemical detection of L-Dopa at low potential based on oxygen reduction on TiO2 sensitized with iron phthalocyanine (FePc/TiO2). The FePc/TiO2 composite shows a photocurrent 10-fold higher than that of pure TiO2 nanoparticles and it was 4-fold higher than that of FePc exploiting visible light. The band gaps of pure TiO2 nanoparticles, FePc and FePc/TiO2, calculated according to the Kubelka–Munk equation, were 3.22 eV, 3.11 eV and 2.82 eV, respectively. The FePc/TiO2 composite showed a low charge transfer resistance in comparison to the photoelectrode modified with FePc or TiO2. Under optimized conditions, the photoelectrochemical sensor shows a linear response range from 20 up to 190 μmol L 1 with a sensitivity of 31.8 μA L mmol 1 and limit of detection of 1.5 μmol L 1 for the detection of L-Dopa.  相似文献   

20.
Titanium dioxide (i.e. TiO2) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO2 nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO2 as Ti4+ is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO2 nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti4+ from 6 μg mL?1 aqueous suspensions prepared from 10 μg mL?1 suspension of different forms of TiO2, including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL?1, and the limit of quantification (LOQ) was 0.20 ng mL?1. Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO2 of 1.8 and 1.6 ng mL?1 for the wastewater samples, respectively, and 317.4 ng mg?1 dry weights for the biosolids. The reactions between persulfate ions and TiO2 were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.  相似文献   

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