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1.
The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C 14H 14N 3SO 3Na) and orange II (C 16H 11N 2SO 4Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO 2 irradiated by sunlight. Compound parabolic collectors, installed at the “Plataforma Solar de Almería” (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H 2O 2, S 2O 82−) and some ions (Cl −, SO 42−) on the process was also studied. 相似文献
2.
UV/TiO 2/H 2O 2, UV/TiO 2 and UV/H 2O 2 were compared as pre-treatment processes for the detoxification of mixtures of 4-chlorophenol (4CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP) and pentachlorophenol (PCP) prior to their biological treatment. When each chlorophenol was initially supplied at 50 mg l −1, UV/TiO 2/H 2O 2 treatment supported the highest pollutant removal, COD removal, and dechlorination efficiencies followed by UV/TiO 2 and UV/H 2O 2. The remaining toxicity to Lipedium sativum was similar after all pre-treatments. Chlorophenol photodegradation was always well described by a first order model kinetic ( r2 > 0.94) and the shortest 4CP, DCP, TCP and PCP half-lives of 8.7, 7.1, 4.5 and 3.3 h, respectively, were achieved during UV/TiO 2/H 2O 2 treatment. No pollutant removal was observed in the controls conducted with H 2O 2 or TiO 2 only. Inoculation of all the photochemically pre-treated mixtures with activated sludge microflora was followed by complete removal of the remaining pollutants. Combined UV/TiO 2/H 2O 2-biological supported the highest detoxification, dechlorination (99%) and COD removal (88%) efficiencies. Similar results were achieved when each chlorophenol was supplied at 100 mg l −1. COD and Cl mass balances indicated UV, UV/H 2O 2, and UV/TiO 2 treatments lead to the formation of recalcitrant photoproducts, some of which were chlorinated. 相似文献
3.
Fe-doped TiO 2 was prepared by the calcination of Fe xTiS 2 ( x = 0, 0.002, 0.005, 0.008, 0.01) and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible diffuse reflectance spectra. All the Fe-doped TiO 2 were composed of an anatase crystal form and showed red shifts to a longer wavelength. The activity of the Fe-doped TiO 2 for the degradation of phenol was investigated by varying the iron content during UV (365 nm) and visible light (405 nm and 436 nm) irradiation. The degradation rate depended on the Fe content and the Fe-doped TiO 2 was responsive to the visible light as well as the elevated activity toward UV light. The molar ratio of 0.005 was the optimum for both the UV and visible light irradiations. The result was discussed on the basis of the balance of the excited electron–hole trap by the doped Fe 3+ and their charge recombination on the doped Fe 3+ level. The Fe-doped TiO 2 ( x = 0.005) was more active than P25 TiO 2 under solar light irradiation. The suspended Fe-doped TiO 2 spontaneously precipitated once the stirring of the reaction mixture was terminated. 相似文献
4.
The photocatalytic inactivation (PCI) of Escherichia coli (Gram-negative) and Bacillus subtilis (Gram-positive) was performed using polyoxometalate (POM) as a homogeneous photocatalyst and compared with that of heterogeneous TiO 2 photocatalyst. Aqueous suspensions of the microorganisms (10 7–10 8 cfu ml −1) and POM (or TiO 2) were irradiated with black light lamps. The POM-PCI was faster than (or comparable to) TiO 2-PCI under the experimental conditions employed in this study. The relative efficiency of POM-PCI was species-dependent. Among three POMs (H 3PW 12O 40, H 3PMo 12O 40, and H 4SiW 12O 40) tested in this study, the inactivation of E. coli was fastest with H 4SiW 12O 40 while that of B. subtilis was the most efficient with H 3PW 12O 40. Although the biocidal action of TiO 2 photocatalyst has been commonly ascribed to the role of photogenerated reactive oxygen species such as hydroxyl radicals and superoxides, the cell death mechanism with POM seems to be different from TiO 2-PCI. While TiO 2 caused the cell membrane disruption, POM did not induce the cell lysis. When methanol was added to the POM solution, not only the PCI of E. coli was enhanced (contrary to the case of TiO 2-PCI) but also the dark inactivation was observed. This was ascribed to the in situ production of formaldehyde from the oxidation of methanol. The interesting biocidal property of POM photocatalyst might be utilized as a potential disinfectant technology. 相似文献
5.
The degradation of a common textile dye, Reactive-brilliant red X-3B, by several advanced oxidation technologies was studied in an air-saturated aqueous solution. The dye was resistant to the UV illumination (wavelength λ 320 nm), but was decolorized when one of Fe 3+, H 2O 2 and TiO 2 components was present. The decolorization rate was observed to be quite different for each system, and the relative order evaluated under comparable conditions followed the order of Fe 2+–H 2O 2–UV Fe 2+–H 2O 2 > Fe 3+–H 2O 2–UV > Fe 3+–H 2O 2 > Fe 3+–TiO 2–UV > TiO 2–UV > Fe 3+–UV > TiO 2–visible light ( λ 450 nm) > H 2O 2–UV > Fe 2+–UV. The mechanism for each process is discussed, and linked together for understanding the observed differences in reactivity. 相似文献
6.
Lanthanum-doped anatase TiO 2 thin films on glass prepared via a sol–gel process have been shown to have much higher photocatalytic activity for the degradation of gaseous benzene than pure anatase TiO 2 thin film. The photodecomposition of benzene on both types of TiO 2 films follows the first-order kinetics while the CO 2 and CO formation followed the zero-order kinetics. GC/MS identification of the intermediates produced during the photodegradation of benzene revealed that doping lanthanum into TiO 2 thin film favors a cleavage of benzene ring. An optimal lanthanum amount with respect to photocatalytic activity was about 2.5 wt% (La 2O 3/TiO 2). 相似文献
7.
Fourteen sediment samples with different content of Fe 2O 3 were collected from the lower reaches of the Liao River in China. The photodegradation of lindane on the surfaces of these sediments was investigated to observe the effects of Fe 2O 3 and other photoinducable substances, such as TiO 2 and organic substances, on photodegradation of lindane. A partial least-squares (PLS) analysis model was developed to find out the statistical relationship between the photodegradation and the contents of these photoinducable substances. It was concluded from the PLS analysis that inorganic carbon and organic carbon have negative effects, whereas Fe 2O 3 and TiO 2 accelerate the photodegradation of lindane in the sediment samples when 365 nm UV light was used as light source. In all cases of the experiments, the photodegradation of lindane in the sediment samples were fitted for pseudo-first-order kinetics. 相似文献
8.
The synthesis of TiO 2 and Fe–TiO 2 by sol–gel method is demonstrated and characterized. The characterization of TiO 2 and Fe–TiO 2 is performed with instruments, including TGA/DTA, FTIR, UV–Vis, N 2 adsorption and SEM. Dichloromethane is used for the photocatalytic activity test. From the results of dichloromethane photocatalyitc degradation, the calcined temperature of TiO 2 and the presence of water vapor influence the photocatalytic activity. The optimum doping amount of iron ions is 0.005 mol%, and this can enhance the photocatalytic activity, while too great an amount will make the iron ions become recombination centers for the electron–hole pairs and reduce the photocatalytic activity. UV–Vis diffuse reflectance spectra of Fe–TiO 2 show an increase in absorbency in the visible light region with the increase in iron ions doping concentration The intermediate of dichloromethane photodegradation includes CHCl 3, CCl 4, CH 2Cl 2 and COCl 2. The presence of iron ions may reduce the adsorption of Cl element on the surface of the photocatalyst. 相似文献
9.
This paper studies the nitration and hydroxylation of benzene in the presence of nitrite/nitrous acid in aqueous solution, both in the dark upon addition of hydrogen peroxide and under 360 nm irradiation. In both cases the detected transformation intermediates were phenol (P), nitrobenzene (NB), 2-nitrophenol (2NP) and 4-nitrophenol (4NP). P and NB directly form from benzene, and the initial formation rate of P is at least an order of magnitude higher than that of NB. In our experiments nitrophenols arise from P nitration, as can be inferred by their time evolution and isomer ratio (2NP:4NP=60:40, 3NP below detection limit). Nitrophenols may also form upon hydroxylation of NB, but in a different ratio (2NP:3NP:4NP=45:30:25). The detection of 3NP is thus a marker for the hydroxylation of NB, since this isomer is not formed in P nitration processes. The formation rates of P and NB increase with decreasing pH, both in the presence of HNO 2 + H 2O 2 in the dark (which produce HOONO) and in the presence of NO 2−/HNO 2 under irradiation. In the former case the pH dependence reflects the formation rate of HOONO. In the case of the irradiation experiments the pH effect can be accounted for by the higher molar absorbivity and photolysis quantum yield of nitrous acid when compared with nitrite. Interestingly, benzene does not react with HNO 2 alone in the dark. An important feature of benzene nitration in the presence of NO 2−/HNO 2 under irradiation is that the process is not inhibited by the addition of hydroxyl scavengers, differently from the case of phenol nitration. This finding indicates that nitrite irradiation might lead to the nitration of certain aromatic compounds in natural waters even in the presence of natural hydroxyl scavenging agents, which are usually thought to limit the environmental role of many photochemical processes. 相似文献
10.
TiO 2 powder-containing paper composites, called TiO 2 paper, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO 2 paper has a porous structure originating from the layered pulp fiber network, with TiO 2 powders scattered on the fiber matrix. Under UV irradiation, the TiO 2 paper decomposed gaseous acetaldehyde more effectively than powdery TiO 2 and a pulp/TiO 2 mixture not in paper form. Scanning electron microscopy and mercury intrusion analysis revealed that the TiO 2 paper had characteristic unique voids ca. 10 μm in diameter, which might have contributed to the improved photocatalytic performance. TiO 2 paper composites having different void structures were prepared by using beaten pulp fibers with different degrees of freeness and/or ceramic fibers. The photodecomposition efficiency was affected by the void structure of the photocatalyst paper, and the initial degradation rate of acetaldehyde increased with an increase in the total pore volume of TiO 2 paper. The paper voids presumably provided suitable conditions for TiO 2 catalysis, resulting in higher photocatalytic performance by TiO 2 paper than by TiO 2 powder and a pulp/TiO 2 mixture not in paper form. 相似文献
11.
Arsenic oxidation (As(III) to As(V)) and As(V) removal from water were assessed by using TiO 2 immobilized in PET (polyethylene terephthalate) bottles in the presence of natural sunlight and iron salts. The effect of many parameters was sequentially studied: TiO 2 concentration of the coating solution, Fe(II) concentration, pH, solar irradiation time; dissolved organic carbon concentration. The final conditions (TiO 2 concentration of the coating solution: 10%; Fe(II): 7.0 mg l −1; solar exposure time: 120 min) were applied to natural water samples spiked with 500 μg l −1 As(III) in order to verify the influence of natural water matrix. After treatment, As(III) and total As concentrations were lower than the limit of quantitation (2 μg l −1) of the voltammetric method used, showing a removal over 99%, and giving evidence that As(III) was effectively oxidized to As(V). The results obtained demonstrated that TiO 2 can be easily immobilized on a PET surface in order to perform As(III) oxidation in water and that this TiO 2 immobilization, combined with coprecipitation of arsenic on Fe(III) hydroxides(oxides) could be an efficient way for inorganic arsenic removal from groundwaters. 相似文献
12.
To sufficiently utilize chemically active species and enhance the degradation rate and removal efficiency of toxic and biorefractory organic pollutant para-chlorophenol ( para-CP), the introductions of iron metal ions (Fe 2+/Fe 3+) into either pulsed discharge plasma (PDP) process or the PDP process with TiO 2 photo-catalyst were tentatively performed. The experimental results showed that under the same experimental condition, the degradation rate and removal efficiency of para-CP were greatly enhanced by the introduction of iron ions (Fe 2+/Fe 3+) into the PDP process. Moreover, when iron ions and TiO 2 were added together in the PDP process, the degradation rate and removal energy of para-CP further improved. The possible mechanism was discussed that the obvious promoting effects were attributed to ferrous ions via plasma induced Fenton-like reactions by UV light irradiation excited and hydrogen peroxide formed in pulsed electrical discharge, resulting in a larger amount of hydroxyl radicals produced from the residual hydrogen peroxide. In addition, the regeneration of ferric ions to ferrous ions facilitates the progress of plasma induced Fenton-like reactions by photo-catalytic reduction of UV light, photo-catalytic reduction on TiO 2 surface and electron transfer of quinone intermediates, i.e. 1,4-hydroquinone and 1,4-benzoquinone. 相似文献
13.
The photocatalytic degradation of dimethyl phthalate (DMP) in aqueous TiO 2 suspension under UV illumination has been investigated using oxygen (O 2) and ferrate (Fe(VI)) as electron acceptors. The experiments demonstrated that Fe(VI) was a more effective electron acceptor than O 2 for scavenging the conduction band electrons from the surface of the catalyst. Some major intermediate products from DMP degradation were identified by HPLC and GC/MS analyses. The analytical results identified dimethyl 3-hydroxyphthalate and dimethyl 2-hydroxyphthalate as the two main intermediate products from the DMP degradation in the TiO 2–UV–O 2 system, while in contrast phthalic acid was found to be the main intermediate product in the TiO 2–UV–Fe(VI) system. These findings indicate that DMP degradation in the TiO 2–UV–O 2 and TiO 2–UV–Fe(VI) systems followed different reaction pathways. An electron spin resonance analysis confirmed that hydroxyl radicals existed in the TiO 2–UV–O 2 reaction system and an unknown radical species (most likely an iron–oxo species) is suspected to exist in the TiO 2–UV–Fe(VI) reaction system. Two pathway schemes of DMP degradation in the TiO 2–UV–O 2 and TiO 2–UV–Fe(VI) reaction systems are proposed. It is believed that the radicals formed in the TiO 2–UV–O 2 reaction system preferably attack the aromatic ring of the DMP, while in contrast the radicals formed in the TiO 2–UV–Fe(VI) reaction systems attack the alkyl chain of DMP. 相似文献
14.
A novel paper-based material containing titanium dioxide (TiO 2) photocatalyst was successfully prepared by a papermaking technique with the internal addition of inorganic fibers on which TiO 2 particles were supported. Photodegradation performance of acetaldehyde gas, an indoor pollutant, and the durability of the TiO 2-containing papers were investigated under UV irradiation. Ceramic fiber suspension and polydiallyldimethylammonium chloride as a cationic flocculant were mixed, followed by the addition of TiO 2 suspension and anionic polyacrylamide. Subsequently, the inorganic mixture was poured into a pulp suspension, and TiO 2 handsheets then prepared by a papermaking method. The tensile strength of TiO 2-containing paper without a ceramic carrier decreased by more than 30% after 240-h UV irradiation (2 mW/cm 2), although the strength of the TiO 2 sheet with ceramic fibers remained reasonably stable. The efficiency of acetaldehyde decomposition by the TiO 2 paper containing an inorganic carrier was nearly equal to that of the carrier-free TiO 2 paper. Scanning electron microscopic observation suggested that most TiO 2 particles were predominantly supported on the inorganic fiber matrix, and were mostly out of contact with organic pulp fibers. The TiO 2 paper with an inorganic carrier demonstrated both excellent photocatalytic performance and durability, which before had been mutually incompatible for organic materials containing TiO 2 photocatalyst. The two-stage mixing procedure for TiO 2 sheet-making is promising for the simple manufacture of high performance paper with photocatalytic ability. 相似文献
15.
The combined electrochemical oxidation-solar-light/immobilized TiO 2 film process was conducted to degrade an azo dye, Reactive Black 5 (RB5). The toxicity was also monitored by the Vibrio fischeri light inhibition test. The electrochemical oxidation rapidly decolorized RB5 (55, 110 μM) with a supporting electrolyte of 2 g l −1 NaCl at current density 277 A m −2 and pH 4. However, TOC mineralization and A 310 removal were low. Additionally, the treated solution showed high biotoxicity. RB5 at 110 μM significantly retarded the de-colorization efficiency by using the solar-light/immobilized TiO 2 film process. The combined electrochemical oxidation-solar-light/immobilized TiO 2 process effectively increased the removal of color, A 310, and TOC. The toxicity was also significantly reduced after 3 h of solar irradiation. The results indicated that the low-cost combined process is a potential technique for rapid treatment of RB5. 相似文献
16.
Catalytic activity of V, Mn, Ni, Cu, Zn, Mo, Zr and Ce oxides over an -alumina support was evaluated for cyclohexane oxidation under oxygen deficient conditions in order to understand the relation between carbon deposition and catalytic activity/selectivity. Carbon formation over the catalysts during the oxidation reaction was measured by means of Fourier transformed infrared spectroscopy (FTIR). Catalysts Mn/Al 2O 3 and Ce/Al 2O 3, which are selective for deep oxidation of cyclohexane, possessed relatively carbon free surfaces. The catalysts with relatively high carbon deposition (V, Ni, Cu, Zn, Mo and Zr) produced CO in addition to CO 2. Traces of formaldehyde were produced over the catalysts Mo and V. 相似文献
17.
In this study, the rates of degradation of organic compounds by several AOPs (H 2O 2/UV, Fe(III)/UV, Fe(III)/H 2O 2/UV, Fe(II)/H 2O 2 and Fe(III)/H 2O 2) have been compared. Experiments were carried out at pH ≈ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 run). The data obtained with atrazine ([Atrazine] o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H 2O 2/UV. Photo-Fenton process (Fe(III)/H 2O 2/UV) was found to be more efficient than H 2O 2/UV and Fe(II)/H 2O 2 for the mineralization of acetone ([Acetone] o = 1 mM). 相似文献
18.
The photocatalytic removal of humic acid (HA) using TiO 2 under UVA irradiation was examined by monitoring changes in the UV 254 absorbance, dissolved organic carbon (DOC) concentration, apparent molecular weight distribution, and trihalomethane formation potentials (THMFPs) over treatment time. A resin fractionation technique in which the samples were fractionated into four components: very hydrophobic acids (VHA), slightly hydrophobic acids, hydrophilic charged (CHA) and hydrophilic neutral (NEU) was also employed to elucidate the changes in the chemical nature of the HA components during treatment. The UVA/TiO 2 process was found to be effective in removing more than 80% DOC and 90% UV 254 absorbance. The THMFPs of samples were decreased to below 20 μg l −1 after treatments, which demonstrate the potential to meet increasingly stringent regulatory level of trihalomethanes in water. Resin fractionation analysis showed that the VHA fraction was decreased considerably as a result of photocatalytic treatments, forming CHA intermediates which were further degraded with increased irradiation time. The NEU fraction, which comprised of non-UV-absorbing low molecular weight compounds, was found to be the most persistent component. 相似文献
19.
Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide (UV/H 2O 2. The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with UV/H2O2. The decreases were dependent on the time of irradiation (UV dose) as well as on the H2O2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and UV/H2O2-treated waters, respectively. No mutagenic activity was generated by the UV irradiation or the UV/H2O2 treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step. 相似文献
20.
An experiment was carried out to decompose chlorinated dioxins (PCDDs, PCDFs) Chlorobenzenes, NOx and odourous compounds (H 2S, CH 4S, C 2H 6S 2, C 8H 8, C 2H 6S, C 2H 4O, NH 3) simultaneously using a catalyst in the MSW incineration plant. The experiments were conducted at temperatures from 200°C to 400°C and from 3000h −1 to 6000h −1 at space velocity. A catalyst containing V 2O 5 and WO 3 on the basis of TiO 2 is used, an oxidizing catalyst of the honeycomb type. The average decomposition efficiencis were 95%, 98%, 92% for PCDDs(48CDDs), PCDFs(48CDFs) and Chlorobenzenes(36CLBs) at a reaction temperature of 350°C and a space velocity of 3000h −1, more than 90% for NOx at a reactiont temperature of 300°C and more than 80% for odourous compounds at the reaction temperature of 300°C and a space velocity of 6000h −1. All those compounds were decomposed successfully with increasing contact time and surface. The rate-determing step was the chemical reaction of catalyst surface. 相似文献
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