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1.
A lost of culturability of bacteria Escherichia coli K12 was observed after exposition to a solar simulator (UV–vis) in a laboratory batch photoreactor. The bacterial inactivation reactions have been carried out using titanium dioxide (TiO 2) P25 Degussa and FeCl 3 as catalysts. At the starting of the treatment, the suspensions were at their “natural” pH. An increase in the efficiency in the water disinfection was obtained when some advanced oxidation processes such as UV–vis/TiO 2, UV–vis/TiO 2/H 2O 2, UV–vis/Fe 3+/H 2O 2, UV–vis/H 2O 2 were applied. The presence of H 2O 2 accelerates the rate of disinfection via TiO 2. The addition of Fe 3+ (0.3 mg/l) to photocatalytic system decreases the time required for total disinfection (<1 CFU/ml), for TiO 2 concentrations ranging between 0.05 and 0.5 g/l. At TiO 2 concentrations higher than 0.5 g/l the addition of Fe 3+ does not significantly increase the disinfection rate. The systems: Fenton (H 2O 2/Fe 3+/dark), H 2O 2/dark, H 2O 2/TiO 2/dark showed low disinfection rate. The effective disinfection time (EDT 24) was reached after 60 and 30 min of illumination for the Fe 3+ and TiO 2 photoassisted systems, respectively. EDT 24 was not reached for the system in the absence of catalyst (UV–vis). The effect on the bacterial inactivation of different mixture of chemical substance added to natural water was studied. 相似文献
2.
The use of hydrogen peroxide (H 2O 2) for improved photocatalytic degradation of phenol in aqueous suspension of commercial TiO 2 powders (Degussa P-25) was investigated. Photodegradation was compared using direct photolysis (UV alone), H 2O 2/UV, TiO 2/UV, and H 2O 2/TiO 2/UV processes in a batch reactor with high-pressure mercury lamp irradiation. The effects of operating parameters such as catalyst dosage, light intensity, pH of the solution, the initial phenol, and H 2O 2 concentrations on photodegradation process were examined. It was shown that photodegradation using H 2O 2/TiO 2/UV process was much more effective than using either H 2O 2/UV or TiO 2/UV process. The effect of the initial phenol concentration on TOC removal was also studied, demonstrating that more than 8 h was required to completely mineralize phenol into water and carbon dioxide. For all the four oxidation processes studied, photodegradation followed the first-order kinetics. The apparent rate constants with 400-W UV ranged from 5.0 × 10 −4 min −1 by direct photolysis to 1.4 × 10 −2 min −1 using H 2O 2/TiO 2/UV process. The role of H 2O 2 on such enhanced photodegradation of phenol in aqueous solution was finally discussed. 相似文献
3.
Field disinfection of water in a large solar compound parabolic collector (CPC) photoreactor (35–70 l) was conducted at 35 °C by different photocatalytic processes: sunlight/TiO 2, sunlight/TiO 2/Fe 3+, sunlight/Fe 3+/H 2O 2 and compared to the control experiment of direct sunlight alone. Experiments were carried out using a CPC and natural water spiked with E. coli K 12. Under these conditions, total disinfection by bare sunlight irradiation was not reached after 5 h of treatment; and bacterial recovery was observed during the subsequent 24 h in the dark. The addition of TiO2, TiO2/Fe3+ or Fe3+/H2O2 to the water accelerates the bactericidal action of sunlight, leading to total disinfection by solar-photocatalysis. No bacterial regrowth was observed during 24 h after stopping sunlight exposure. For some samples, the decrease of bacteria continues in the dark. A “residual disinfection effect” was observed for these samples before reaching the total inactivation. The effective disinfection time (EDT24), defined as the treatment time required to prevent any bacterial regrowth during the subsequent 24 h in the dark, after stopping the phototreatment, was reached in the presence but not in the absence of different photocatalytic systems. EDT24 was 2 h 30 min, 2 h and 1 h 30 min for sunlight/TiO2, sunlight/TiO2/Fe3+ and sunlight/Fe3+/H2O2 systems, respectively. The post irradiation events observed when the phototreated water is poured into an optimal growth medium are also discussed. 相似文献
4.
Decolorization of reactive brilliant red X-3B was studied by using an Fe–Ce oxide hydrate as the heterogeneous catalyst in the presence of H 2O 2 and UV. The decolorization rate was in the order of UV–Fe–Ce–H 2O 2 > UV–Fe 3+–H 2O 2 > UV–H 2O 2 > UV–Fe–Ce ≥ Fe–Ce–H 2O 2 > Fe–Ce. Under the conditions of 34 mg l −1 H 2O 2, 0.500 g l −1 Fe–Ce, 36 W UV and pH 3.0, 100 mg l −1 X-3B could be decolorized at efficiency of more than 99% within 30 min. The maximum dissolved Fe during the reaction was 1 mg l −1. From the fact that the decolorization rate of the UV–Fe–Ce–H 2O 2 system was significantly higher than that of the UV–Fe 3+–H 2O 2 system at Fe 3+ = 1 mg l −1, it is clear that the Fe–Ce functioned mainly as an efficient heterogeneous catalyst. UV–vis, its second derivative spectra, and ion chromatography (IC) were employed to investigate the degradation pathway. Fast degradation after adsorption of X-3B is the dominant mechanism in the heterogeneous catalytic oxidation system. The first degradation step is the breaking down of azo and CN bonds, resulting in the formation of the aniline- and phenol-like compounds. Then, the breaking down of the triazine structure occurred together with the transformation of naphthalene rings to multi-substituted benzene, and the cutting off of sulphonic groups from the naphthalene rings. The last step includes further decomposition of the aniline structure and partial mineralization of X-3B. 相似文献
5.
The photodegradation of phenol was investigated in the presence of TiO 2 (anatase) as photocatalyst in near-UV-irradiated aqueous unbuffered suspensions. The distribution of degradation products and a reduction in total organic carbon are reported, focusing on the influence of charge-trapping species (O 2, Ag + and H 2O 2). In the presence of dissolved O 2, the degradation proceeds predominantly via OH , where hydroxylated aromatics were detected: catechol, hydroquinone and 1,2,4-trihydroxybenzene; in the presence of Ag +, the direct hole oxidation dominates, with p-benzoquinone as the only identified transient product; in the presence of H 2O 2, both OH and direct oxidation by positive holes contribute to the degradation of phenol. Besides the identified compounds, the formation of presumed ring-opening products occurs simultaneously. In contrast with the general view, it is pointed out that the appearance of aliphatic products in the early stage of the oxidation process is not unambiguous proof of the participation of direct hole oxidation in the degradation mechanism. 相似文献
6.
Ta 3N 5 was synthesized by nitridation of Ta 2O 5 under NH 3 flow at 700 °C. The catalyst was pure Ta 3N 5 according to X-ray diffraction (XRD), and was about 5 nm in size with a BET specific surface area 52.8 m 2/g. When Ta 3N 5 was added to Fe 3+/H 2O 2 solution (known as Fenton-like system), most Fe 3+ were adsorbed on the Ta 3N 5 surface and could not react with H 2O 2 in the dark, which is different from the general Fenton reaction. Under visible light irradiation, adsorbed Fe 3+ ions were reduced to Fe 2+ rapidly and Fe 2+ were reoxidized by H 2O 2 on the Ta 3N 5 surface, thus a fast Fe 3+/Fe 2+ cycling was established. Kinetics and ESR measurements supported this mechanism. The Ta 3N 5/Fe 3+/H 2O 2 system could efficiently decompose H 2O 2 to generate hydroxyl radicals driven by visible light, which could accelerate significantly the degradation of organic molecules such as N, N-dimethylaniline (DMA), and 2,4-dichlorophenol (DCP). A mechanism was proposed for iron cycling on the basis of experimental results. 相似文献
7.
Oxidative reactions of phenol and chlorobenzene with electrogenerated Fenton's reagent, Fe 2+ + H 2O 2, were investigated. The electrogeneration of H 2O 2 and the regeneration of Fe 2+ were performed at a graphite cathode. Results are compared for conventional vs. electrogenerated Fenton's reagent. It was found that the conversion of chlorobenzene was substantially greater by the electrochemical method than the conventional system. The rates of H 2O 2 generation were dependent on solution pH; electrogeneration was favored at low pH, while the opposite was the case for the hydroxylation of the organics. The hydroxylation products of phenol with electrogenerated Fenton's reagent included hydroquinone, catechol and resorcinol. For chlorobenzene, a hydroxylated product (p-chlorophenol) and a dehalogenated product (phenol) were obtained. The rates of phenol and chlorobenzene hydroxylation were dependent on pH, and concentrations of F 2+ and H 2O 2. Results indicated that the electrochemical system provided an efficient way to regenerate Fe 2+ 相似文献
8.
The effects of charge-trapping species on the kinetics of phenol decomposition were studied in near-UV-irradiated aqueous TiO 2 (anatase) suspensions in a batch photoreactor. The influence of catalyst loading, initial phenol concentration, dissolved O 2 concentration, Ag + content and H 2O 2 concentration on the rate of phenol degradation is reported. The observed heterogeneous degradation of phenol followed apparently zero-order kinetics up to ca. 70% conversion. The Langmuir–Hinshelwood kinetic model successfully described the influence of the initial phenol concentration and dissolved O 2 concentration on the rate of heterogeneous photooxidation of phenol. The data obtained by applying the Langmuir–Hinshelwood treatment are consistent with the available kinetic parameters. The results of the experiments in the presence of Ag + indicated that the phototransformation of phenol can proceed via direct electron transfer, neither dissolved O 2 nor its reduction forms playing a significant role in the degradation mechanism. 相似文献
9.
Alachlor, atrazine and diuron dissolved in water at 50, 25 and 30 mg/L, respectively were photodegraded by Fe 2+/H 2O 2, Fe 3+/H 2O 2, TiO 2 and TiO 2/Na 2S 2O 8 treatments driven by solar energy at pilot-plant scale using a compound parabolic collector (CPC) photoreactor. All the advanced oxidation processes (AOPs) employed mainly compared the TOC mineralisation rate to evaluate treatment effectiveness. Parent compound disappearance, anion release and oxidant consumption are discussed as a function of treatment time. The use of Fe 2+ or Fe 3+ showed no influence on the reaction rate under illumination and the reaction using 10 or 55 mg/L of iron was quite similar. TiO 2/Na 2S 2O 8 showed a quicker reaction rate than TiO 2 and a similar rate compared to photo-Fenton. The main difference found was between TiO 2/Na 2S 2O 8 and photo-Fenton, detected during atrazine degradation, where pesticide transformation into cyanuric acid was confirmed only for TiO 2/Na 2S 2O 8. 相似文献
10.
The catalytic photodegradation of phenol and 4-chlorophenol with white and UV light over TiO 2, BaTi 4O 9 and Hollandite catalysts has been studied in our laboratories. BaTi 4O 9 and Hollandite catalysts were prepared by solid state reaction at 900°C and 1200°C, respectively. All the catalysts were characterized by different techniques such as surface area measurements by the BET method, atomic absorption spectroscopy and XRD. Photodegradation reaction experiments were monitored by HPLC analysis. The reaction intermediates: hydroquinone and 1,4-benzoquinone were identified by GC–MS analysis. The photocatalytic activities of these catalysts in the degradation of phenol and 4-chlorophenol were evaluated in comparison with titanium oxide. Experimental results showed that BaTi 4O 9 and Hollandite catalysts exhibit small photocatalytic activity as compared with TiO 2. 相似文献
11.
We have investigated the catalytic behavior of Pt encapsulated TiO 2 nanotubes for the water gas shift reaction as well as the hydrogenation of CO. Pt–TiO 2 nanotube catalysts were prepared by employing fine fiber shaped crystals of [Pt(NH 3) 4](HCO 3) 2 complex as a structure determining template material. The turnover frequencies (TOF) of these nanotube catalysts were more than one order of magnitude larger than conventional impregnation Pt/TiO 2 catalysts, and the selectivity for methanol in CO–H 2 reaction was extraordinary high compared to the impregnation catalysts. The XPS and XRD analyses of the nanotubes revealed characteristic electronic state of reduced TiO 2 (Ti 3+ in rutile structure) with zerovalent Pt even after the calcination at 773 K. In WGS reaction, electron rich Ti 3+ on the nanotube wall may play an important role to activate water molecules for the oxidation of CO. In CO–H 2 reaction, similar promotion effect of Ti 3+ species may be operating for selective methanol formation by supplying active OH(a). 相似文献
12.
The new photocatalysts based on commercially available titanium dioxide powders: Tytanpol A11 (Police, Poland), pure anatase and P-25 (Degussa, Germany) containing about 20% rutile were modified by carbon via ethanol carbonisation. Titanium dioxides were heated at different temperature from 150 to 400 °C for 1 h in an atmosphere of ethanol vapour. The photocatalytic activity of carbon-modified TiO 2 was studied by oxidation of phenol in water under UV and artificial solar light irradiation. With increasing of carbon content in TiO 2 photocatalysts the activity for phenol decomposition under UV light was decreasing but that under visible light was stable. Turbidity of the slurry solution decreased with increasing of carbon content for all prepared photocatalysts because of the change of their surface character from hydrophilic to hydrophobic. 相似文献
13.
Ag-based catalysts supported on various metal oxides, Al 2O 3, TiO 2, and TiO 2–Al 2O 3, were prepared by the sol–gel method. The effect of SO 2 on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO 2–Al 2O 3 in comparison to Ag/Al 2O 3 and Ag/TiO 2, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO 2–Al 2O 3. NO 3− rather than NO 2− or NO x reacted with the carboxylate species to form CN or NCO. NO 2 was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO 2–Al 2O 3. More amount of formate (HCOO −) and CN were generated on the Ag/TiO 2–Al 2O 3 catalyst than the Ag/Al 2O 3 catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO 2 oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO 2–Al 2O 3 system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO 2 toleration to the Ag/Al 2O 3 catalyst. 相似文献
14.
TM/TiO 2/SiO 2 photocatalysts were prepared by the photodeposition method using transition metal salts (TM=Fe 3+, Co 2+, Ni 2+ and Cu 2+) as precursors and the surface bond-conjugated TiO 2/SiO 2 as supporter in N 2 atmosphere, and were characterized by XRD, XPS, UV-Vis diffuse reflection and zeta-potential. Their photocatalytic activities were evaluated using reactive brilliant red K-2G (K-2G) and cationic blue X-GRL (CBX) showing different adsorption behavior on the oxides. Fe, Cu supported TiO 2/SiO 2 can efficiently extend the light absorption to the visible region. XPS analysis verified that the introduction of transition metal lead to the changes of the electronic environmental of Ti cations and the zeta-potential of oxides. As a result, K-2G has higher adsorption on the modified TiO 2/SiO 2 than that on the baked one, while the adsorption of CBX has a little change on the both oxides. At the same time, for the photodegradation of K-2G, Fe 3+, Co 2+, Ni 2+-modified catalysts show that their photoactivities are 3.3–2.2 times higher than the bare one. On the contrast, all transition-metal-supported catalysts have no significant activity improvement except that Fe/TiO 2/SiO 2 shows 1.68 times higher activity for the photodegradation of CBX. The results indicate that the photoactivity could be increased in photodegradation of dyes by changing the performances of adsorption to dyes and absorption to light of photocatalyst. 相似文献
15.
采用实验方法研究了低成本环境友好型添加剂抗坏血酸(AA)对Fe 2+/H 2O 2体系氧化NO气体及其对体系内H 2O 2分解的影响,分析了AA对体系氧化NO能力及H 2O 2分解的影响机制。研究结果表明:AA通过加速Fe 3+向Fe 2+的转化而促进Fe 2+/H 2O 2体系对NO的氧化。[AA] 0:[Fe 2+] 0对体系氧化NO的能力及H 2O 2的分解具有重要影响。综合考虑NO氧化脱除量及H 2O 2消耗量,合理的[AA] 0:[Fe 2+] 0为1/3~1/2。AA的分次添加方式可大幅度提升体系氧化NO气体的能力。研究结果可望为发展基于H 2O 2为氧化剂的烟气NO绿色氧化技术提供理论基础。 相似文献
16.
Cu 2O/TiO 2, Bi 2O 3/TiO 2 and ZnMn 2O 4/TiO 2 heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UV–vis spectroscopy analysis showed that the junctions-based Cu 2O, Bi 2O 3 and ZnMn 2O 4 are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000 nm). This fact was confirmed in the case of Cu 2O/TiO 2 and Bi 2O 3/TiO 2 by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UV–vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed. 相似文献
17.
The application of metal ion-implantation method has been made to improve the electronic properties of the TiO 2 photocatalyst to realize the utilization of visible light. The photocatalytic properties of these unique TiO 2 photocatalysts for the purification of water have been investigated. By the metal ion-implantation method, metal ions (Fe +, Mn +, V +, etc.) are accelerated enough to have the high kinetic energy (150 keV) and can be implanted into the bulk of TiO 2. TiO 2 photocatalysts which can absorb visible light and work as a photocatalyst efficiently under visible light irradiation were successfully prepared using this advanced technique. The UV-Vis absorption spectra of these metal ion-implanted TiO 2 photocatalysts were found to shift toward visible light regions depending on the amount and the kind of metal ions implanted. They were found to exhibit an effective photocatalytic reactivity for the liquid-phase degradation of 2-propanol diluted in water at 295 K under visible light (λ>450 nm) irradiation. The investigation using XAFS analysis suggested that the substitution of Ti ions in TiO 2 lattice with implanted metal ions is important to modify TiO 2 to be able to adsorb visible light. 相似文献
18.
The effect of the TiO 2–Al 2O 3 mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO 2 into the support, and particularly over rich- and pure-TiO 2-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO 2. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO 2 content and large differences are observed between the catalysts supported on pure Al 2O 3 and pure TiO 2. In contrast, in the case of the thiophene test, the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al 2O 3-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al 2O 3- and pure TiO 2-based catalysts is relatively small and dependent on the H 2 pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H 2 partial pressure on the thiophene HDS, and on the effect of H 2S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking. 相似文献
19.
Heterogeneous photocatalysis (HP) using UV/TiO 2, photo-Fenton (PF) reaction using UV/Fe/H 2O 2 and the combination UV/TiO 2/Fe/H 2O 2 (HP–PF) were tested as processes to degrade oxalic acid (Ox) at relatively high concentrations (0.032 M). PF reactions were generally more efficient than HP including the reaction in the absence of H 2O 2. Oppositely to previous results (e.g., with EDTA), HP–PF combinations did not result, in the case of oxalate, better techniques for degradation than systems in the absence of TiO 2. The kinetic behavior was not unique and two parameters were taken to evaluate the efficiency of each system: initial rates ( R0) and time to 95% of total mineralization (TOC 95). Addition of hydrogen peroxide improves the initial HP reaction rate and reduces TOC 95. Addition of Fe 3+ also affects the reaction parameters but the effect of H 2O 2 seems to be higher, at least under the present conditions. When both H 2O 2 and iron were added simultaneously, the efficiency was higher. The optimal H 2O 2:Ox:Fe molar ratio was established and the results indicated that, at a fixed iron concentration, H 2O 2 increased R0 until a limit beyond which it did not cause any effect. No intermediates were formed in the reaction, oxalate being degraded directly to CO 2. Analogies and differences with the EDTA system are presented. 相似文献
20.
TiO 2-mounted activated carbon was prepared through hydrolytic precipitation of TiO 2 from teraisopropyl orthotitanate and following heat treatment at 650–900 °C for 1 h under a flow of nitrogen. The removal of phenol from its aqueous solution under UV irradiation was measured on TiO 2-mounted activated carbons thus prepared. Although BET surface area of TiO 2-mounted activated carbons decreased drastically in comparison with the original activated carbon, the efficiency of phenol removal under UV irradiation was high. The sample heated at 900 °C, which consisted mainly of rutile phase, showed the highest total removal of phenol. Efficiency of phenol degradation is reduced because of phenol adsorption on the catalyst. 相似文献
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