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1.
The effects of critical factors such as Henry’s Law constant, atmospheric OH rate constant, initial concentration, H2O2, FeSO4 and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1 mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H2O2 under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H2O2 under sonication. 0.1 mM of fumaric acid suppresses H2O2 formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO4) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.  相似文献   

2.
The degradation of a reactive azo dye, Direct Red 81 (DR81), by Fenton process and in conjunction with sonolysis (SonoFenton) was studied. The synergistic effect of Fenton process and sonolysis enhanced the degradation of Direct Red 81 in aqueous solutions and the reaction followed the mechanism of hydroxyl radical (HO) oxidation. The influence of the initial substrate concentration, pH and catalyst loading on the rate of decolorisation were studied. The dye decolorisation followed apparent first order kinetics. The optimum conditions for decolorisation were pH = 3.0, [Fe2+] = 0.2 g/l, [H2O2] = 5.1 × 10−3 mol/l and ultrasonic frequency = 120 kHz, 60 W. These conditions yielded 99% decolorisation of DR81 within 75 min. The sonolytic degradation products of DR81 were identified using Electrospray Ionization-Mass Spectrometry (ESI-MS). The presence of CO32−, HCO3, Cl, NO3, and SO42− ions in the dye solution did not have a considerable effect on the decolorisation efficiency. This study demonstrates that Fenton and SonoFenton methods can effectively decolorize DR81 dye in waste water. The dye concentration used in this study is higher compared to earlier studies illustrating the effective mineralization by the SonoFenton process. The mechanism of dye degradation is also proposed.  相似文献   

3.
4.
In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700 kHz) for an acoustic power of 14 W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H2O2 were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H2O2 and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation.  相似文献   

5.
The degradation and mineralization of orange-G (OG) in aqueous solutions by means of ultrasound irradiation at a frequency of 213 kHz and its combination with a heterogeneous photocatalyst (TiO2) were investigated. The effects of various operational parameters such as, the concentration of the dye and solution pH on the degradation efficiency were studied. The degradation of the dye followed first-order like kinetics under the conditions examined. The sonolytic degradation of OG was relatively higher at pH 5.8 than that at pH 12. However, an alkaline pH was favoured for the photocatalytic degradation of OG using TiO2. Total organic carbon (TOC) measurements were also carried out in order to evaluate the mineralization efficiency of OG using sonolysis, photocatalysis and sonophotocatalysis. The hybrid technique of sonophotocatalytic degradation was compared with the individual techniques of photocatalysis and sonolysis. A simple additive effect was observed during the sonophotocatalytic oxidation of OG using TiO2 indicating that the combined treatment offers no synergistic enhancement. TOC results also support the additive effect in the dual treatment process.  相似文献   

6.
The present study has investigated the degradation of thiamethoxam using ultrasound cavitation (US) operated at a frequency of 20 kHz and its combination with intensifying additives viz. hydrogen peroxide, Fenton and photo-Fenton reagent. At the outset, the performance of US (20 kHz) has been maximised by the optimization of process parameters. Highest rate of degradation of thiamethoxam was observed at the optimum ultrasonic power density of 0.22 W/mL, thiamethoxam concentration of 10 ppm and the pH of 2. The established optimum values of operating parameters were used further in case of combined treatment approaches. The effect of concentration of H2O2 on the rate of degradation of thiamethoxam in the case of US + H2O2 process has confirmed the existence of optimum concentration of H2O2 with the ratio of thiamethoxam: H2O2 as 1:10. US + Fenton process indicated the optimal molar ratio of FeSO4·7H2O:H2O2 as 1:15. The combined processes of US + H2O2, US + Fenton and US + photo-Fenton have resulted in the extent of degradation of 20.47 ± 0.61%, 34.41 ± 1.03% and 85.17 ± 2.56% respectively after 45 min. of operation. These combined processes lead to the synergistic index of 2.04 ± 0.06, 2.26 ± 0.07 and 2.42 ± 0.07 in case of US + H2O2, US + Fenton and US + photo-Fenton processes respectively over only US/stirring treatment with the additive. Additionally, the extent of mineralization and the energy efficiency of individual and combined processes have been compared. US + photo-Fenton process has been found to be the best strategy for effective degradation of thiamethoxam with a significant intensification benefit. The by-products formed during the ultrasonic degradation of thiamethoxam have been identified by using LC-MS/MS analysis.  相似文献   

7.
In this study, TiO2−xNx/TiO2 double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO2 film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO2 film thickness, the optical transmittance of TiO2−xNx/TiO2 film was compared with TiO2 thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.  相似文献   

8.
The magnetocaloric properties of melt-spun Gd-B alloys were examined with the aim to explore their potential application as magnetic refrigerants near room temperature. A series of Gd100−xBx (x=0, 5, 10, 15, and 20 at%) alloys were prepared by melt spinning. With the decrease in Gd/B ratio, Curie temperature (TC) remains constant at ∼293 K, and saturation magnetization, at 275 K, decreases from ∼100 to ∼78 emu/g. Negligible magnetic hysteresis was observed in these alloys. The peak value of magnetic entropy change, (−ΔSM)max, decreased from ∼9.9 J/kg K (0-5 T) and ∼5.5 J/kg K (0-2 T) for melt-spun Gd to ∼7.7 J/kg K (0-5 T) and ∼4.0 J/kg K (0-2 T), respectively for melt-spun Gd85B15 and Gd80B20 alloys. Similarly, the refrigeration capacity (q) decreased monotonously from ∼430 J/kg (0-5 T) for melt-spun Gd to ∼330 J/kg (0-5 T) for melt-spun Gd80B20 alloy. The near room temperature magnetocaloric properties of melt-spun Gd100−xBx (0≤x≤20) alloys were found to be comparable to few first-order transition based magnetic refrigerants.  相似文献   

9.
This paper constitutes an experimental and numerical study, using uncertainty analysis of the most important parameters, to evaluate the mechanism for the combustion of CO + H2 mixtures at high pressures in the range 15-50 bar and temperatures from 950 to 1100 K. Experiments were performed in a rapid compression machine. Autoignition delays were measured for stoichiometric compositions of CO + H2 containing between 0 and 80% CO in the total fuel mixture. The experimental results showed an unequivocal monotonic increase as the proportion of CO in the mixture was raised. Comparisons were made also with the measured ignition delays in mixtures of H2 with increasing dilution by N2, corresponding to the proportions of CO present. These times also increased monotonically, albeit with a greater sensitivity to the extent of dilution than those measured in the CO + H2 mixtures. By contrast, numerical simulations for the same mixtures, based on a kinetic model derived by Davis et al. displayed a qualitative discrepancy as there was virtually no sensitivity of the ignition delay to the changing ratio of CO + H2, certainly up to 80% replacement. No exceptions to this trend were found, despite tests being made using seven other kinetic models for CO + H2 combustion. Global uncertainty analyses were then applied to the Davis et al. model in order to trace the origins of this discrepancy. The analyses took into account the uncertainties in all rate parameters in the model, which is a pre-requisite for evaluation against ignition delay data. It is shown that the reaction rate constant recommended by Baulch et al. for the HO2 + CO reaction, at T ∼ 1000 K, could be up to a factor of 10 too high and that lowering this rate corrected the qualitative anomaly between experiment and numerical prediction.  相似文献   

10.
In the present work, degradation of 2,4-dinitrophenol (DNP), a persistent organic contaminant with high toxicity and very low biodegradability has been investigated using combination of hydrodynamic cavitation (HC) and chemical/advanced oxidation. The cavitating conditions have been generated using orifice plate as a cavitating device. Initially, the optimization of basic operating parameters have been done by performing experiments over varying inlet pressure (over the range of 3–6 bar), temperature (30 °C, 35 °C and 40 °C) and solution pH (over the range of 3–11). Subsequently, combined treatment strategies have been investigated for process intensification of the degradation process. The effect of HC combined with chemical oxidation processes such as hydrogen peroxide (HC/H2O2), ferrous activated persulfate (HC/Na2S2O8/FeSO4) and HC coupled with advanced oxidation processes such as conventional Fenton (HC/FeSO4/H2O2), advanced Fenton (HC/Fe/H2O2) and Fenton-like process (HC/CuO/H2O2) on the extent of degradation of DNP have also been investigated at optimized conditions of pH 4, temperature of 35 °C and inlet pressure of 4 bar. Kinetic study revealed that degradation of DNP fitted first order kinetics for all the approaches under investigation. Complete degradation with maximum rate of DNP degradation has been observed for the combined HC/Fenton process. The energy consumption analysis for hydrodynamic cavitation based process has been done on the basis of cavitational yield. Degradation intermediates have also been identified and quantified in the current work. The synergistic index calculated for all the combined processes indicates HC/Fenton process is more feasible than the combination of HC with other Fenton like processes.  相似文献   

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