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1.
The effects of four metals (Ag, Au, Pt, and Cu) doped on TiO 2 on the photocatalysis of pentachlorophenol (PCP) were investigated. The results of this study indicated that all four metals-doped TiO 2 catalysts were able to enhance the efficiency of PCP photocatalysis with an optimum metallic content of 0.1 wt%. For the metal-doped TiO 2 samples (Au, Pt, and Cu), the patterns of light absorption were significantly extended toward visible light spectra in the wavelengths between 400 and 800 nm. The photocatalysis of PCP was pH dependent with the maximum degradation rate achieved in the solution at pH 3. The formation of chloride ion corresponded with the concentration of PCP degraded which confirmed that dechlorination was the major pathway of PCP photocatalysis. The overall toxicities of PCP samples were reduced with the extension of light exposure using the microtox test. The results of PCP photocatalysis are also discussed based on the characteristics of metal/TiO 2 including X-ray differential (XRD) patterns, Brunquer Emmett Teller (BET) specific area analysis, and Ultra Violet (UV)-Vis absorption spectra. 相似文献
2.
TiO 2-supported activated carbon felts (TiO 2–ACFTs) were prepared by dip coating of felts composed of activated carbon fibers (ACFs) with either polyester fibers (PS-A20) and/or a polyethylene pulp (PE-W15) in a TiO 2 aqueous suspension followed by calcination at 250 °C for 1 h. The as-prepared TiO 2–ACFTs with 29–35 wt.% TiO 2 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N 2 adsorption. The TiO 2–ACFT(PS-A20) samples with 0 and 29 wt.% TiO 2 were microporous with specific surface areas ( S BET) of 996 and 738 m 2/g, respectively, whereas the TiO 2–ACFT(PE-W15) samples with 0 and 35 wt.% TiO 2 were mesoporous with S BET of 826 and 586 m 2/g, respectively. Adsorption and photocatalytic activity of the as-prepared samples were evaluated by measuring adsorption in the dark and photodegradation of gaseous acetaldehyde (AcH) and methylene blue (MB) in aqueous solution under UV light. The TiO 2 loading caused a considerable decrease in the S BET and MB adsorption capacity along with an increase in MB photodegradation and AcH mineralization. Lemna minor was chosen as a representative aquatic plant for ecotoxicity tests measuring detoxification of water obtained from the MB photodegradation reaction with the TiO 2–ACFT samples under UV light. 相似文献
3.
Background, aim and scope Photocatalytic oxidation using UV irradiation of TiO 2 has been studied extensively and has many potential industrial applications, including the degradation of recalcitrant contaminants
in water and wastewater treatment. A limiting factor in the oxidation process is the recombination of conduction band electrons
(e
−
cb) with electron holes (h vb+) on the irradiated TiO 2 surface; thus, in aqueous conditions, the presence of an effective electron scavenger will be beneficial to the efficiency
of the oxidation process. Ferrate (FeO 42−) has received much recent attention as a water treatment chemical since it behaves simultaneously as an oxidant and coagulant.
The combination of ferrate [Fe(VI)] with UV/TiO 2 photocatalysis offers an oxidation synergism arising from the Fe(VI) scavenging of e
−
cb and the corresponding beneficial formation of Fe(V) from the Fe(VI) reduction. This paper reviews recent studies concerning
the photocatalytic oxidation of problematic pollutants with and without ferrate. 相似文献
4.
This study reports the synthesis and characterization of composite nitrogen and fluorine co-doped titanium dioxide (NF-TiO 2) for the removal of contaminants of concern in wastewater under visible and solar light. Monodisperse anatase TiO 2 nanoparticles of different sizes and Evonik P25 were assembled to immobilized NF-TiO 2 by direct incorporation into the sol–gel or by the layer-by-layer technique. The composite films were characterized with X-ray diffraction, high-resolution transmission electron microscopy, environmental scanning electron microscopy, and porosimetry analysis. The photocatalytic degradation of atrazine, carbamazepine, and caffeine was evaluated in a synthetic water solution and in an effluent from a hybrid biological concentrator reactor (BCR). Minor aggregation and improved distribution of monodisperse titania particles was obtained with NF-TiO 2-monodisperse (10 and 50 nm) from the layer-by-layer technique than with NF-TiO 2?+?monodisperse TiO 2 (300 nm) directly incorporated into the sol. The photocatalysts synthesized with the layer-by-layer method achieved significantly higher degradation rates in contrast with NF-TiO 2-monodisperse titania (300 nm) and slightly faster values when compared with NF-TiO 2-P25. Using NF-TiO 2 layer-by-layer with monodisperse TiO 2 (50 nm) under solar light irradiation, the respective degradation rates in synthetic water and BCR effluent were 14.6 and 9.5?×?10 ?3?min ?1 for caffeine, 12.5 and 9.0?×?10 ?3?min ?1 for carbamazepine, and 10.9 and 5.8?×?10 ?3?min ?1 for atrazine. These results suggest that the layer-by-layer technique is a promising method for the synthesis of composite TiO 2-based films compared to the direct addition of nanoparticles into the sol. 相似文献
5.
The combined effects of titanium dioxide (TiO 2) nanoparticles and humic acid (HA) on the bioaccumulation of cadmium (Cd) in Zebrafish were investigated. Experimental data on the equilibrium Cd bioaccumulation suggest that only the dissolved Cd effectively contributed to Cd bioaccumulation in HA solutions whereas both the dissolved and TiO 2 associated Cd were accumulated in TiO 2 or the mixture of HA and TiO 2 solutions, due likely to the additional intestine uptake of the TiO 2-bound Cd. The equilibrium Cd bioaccumulation in the mixed system was comparable to that in the corresponding HA solutions, and significantly lower than that in the corresponding TiO 2 solutions ( n = 3, p < 0.05). The presence of either HA or TiO 2 (5-20 mg L −1) in water slightly increased the uptake rate constants of Cd bioaccumulation whereas combining HA and TiO 2 reduced the uptake rate constants. 相似文献
6.
1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (or p,p′-DDT) is one of the most persistent pesticides. It is resistant to breakdown in nature and cause the water contamination problem. In this work, a major objective was to demonstrate the application of N-doped TiO 2 in degradation and mineralization of the p,p′-DDT under UV and visible light in aqueous solution. The N-doped TiO 2 nanopowders were prepared by a simple modified sol–gel procedure using diethanolamine (DEA) as a nitrogen source. The catalyst characteristics were investigated using XRD, SEM, TEM, and XPS. The adsorption and photocatalytic oxidation of p,p′-DDT using the synthesized N-doped TiO 2 under UV and visible light were conducted in a batch photocatalytic experiment. The kinetics and p,p′-DDT degradation performance of the N-doped TiO 2 were evaluated. Results show that the N-doped TiO 2 can degrade p,p′-DDT effectively under both UV and visible lights. The rate constant of the p,p′-DDT degradation under UV light was only 0.0121 min ?1, whereas the rate constant of the p,p′-DDT degradation under visible light was 0.1282 min ?1. Under visible light, the 100% degradation of p,p′-DDT were obtained from N-doped TiO 2 catalyst. The reaction rate of p,p′-DDT degradation using N-doped TiO 2 under visible light was sixfold higher than that under UV light. According to Langmuir-Hinshelwood model, the adsorption equilibrium constant (K) for the N-doped TiO 2 under visible light was 0.03078 L mg ?1, and the apparent reaction rate constant (k) was 1.3941 mg L ?1-min. Major intermediates detected during the p,p′-DDT degradation were p,p′-DDE, o,p′-DDE, p,p′-DDD and p,p′-DDD. Results from this work can be applied further for the breakdown of p,p′-DDT molecule in the real contaminated water using this technology. 相似文献
7.
Photocatalytic degradation of bisphenol A (BPA) in waters and wastewaters in the presence of titanium dioxide (TiO 2) was performed under different conditions. Suspensions of the TiO 2 were used to compare the degradation efficiency of BPA (20 mg L ?1) in batch and compound parabolic collector (CPC) reactors. A TiO 2 catalyst supported on glass spheres was prepared (sol–gel method) and used in a CPC solar pilot plant for the photodegradation of BPA (100 μg L ?1). The influence of OH·, O 2 ·?, and h + on the BPA degradation were evaluated. The radicals OH· and O 2 ·? were proved to be the main species involved on BPA photodegradation. Total organic carbon (TOC) and carboxylic acids were determined to evaluate the BPA mineralization during the photodegradation process. Some toxicological effects of BPA and its photoproducts on Eisenia andrei earthworms were evaluated. The results show that the optimal concentration of suspended TiO 2 to degrade BPA in batch or CPC reactors was 0.1 g L ?1. According to biological tests, the BPA LC 50 in 24 h for E. andrei was of 1.7?×?10 ?2 mg cm ?2. The photocatalytic degradation of BPA mediated by TiO 2 supported on glass spheres suffered strong influence of the water matrix. On real municipal wastewater treatment plant (MWWTP) secondary effluent, 30 % of BPA remains in solution; nevertheless, the method has the enormous advantage since it eliminates the need of catalyst removal step, reducing the cost of treatment. 相似文献
8.
The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO 2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO 2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO 2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO 2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir–Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm ? 1 and 0.984 ppm min ? 1, respectively. In this work, we also compared the reactivity between the commercial TiO 2 Degussa P-25 and a rutile TiO 2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO 2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO 2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO 2. 相似文献
9.
This study investigates the mechanism of photosensitization and the recombination of excited electron–hole pairs affected by depositing platinum (Pt) on the surface of titanium dioxide (TiO 2). A new catalyst of Pt–TiO 2 was prepared by a photoreduction process. Being model reactions, the photocatalytic oxidation of methylene blue (MB) and methyl orange (MO) in aqueous solutions using the Pt–TiO 2 catalyst was carried out under either UV or visible light irradiation. The experimental results indicate that an optimal content of 0.75%Pt–TiO 2 achieves the best photocatalytic performance of MB and MO degradation and that the Pt–TiO 2 catalyst can be sensitized by visible light. The interaction of Pt and TiO 2 was investigated by means of UV–Vis absorption spectra, photoluminescence emission spectra, and X-ray photoelectron emission spectroscopy. The Pt 0, Pt 2+ and Pt 4+ species existing on the surface of Pt–TiO 2, and the Ti 3+ species existing in its lattice may form a defect energy level. The Pt impurities, including Pt, Pt(OH) 2, and PtO 2, and the defect energy level absorb visible light more efficiently in comparison with the pure TiO 2 and hinder the recombination rate of excited electron–hole pairs. 相似文献
10.
The influences of HCO 3 ?, Cl ?, and other components on the UV/TiO 2 degradation of the antineoplastic agents ifosfamide (IFO) and cyclophosphamide (CP) were studied in this work. The results indicated that the presence of HCO 3 ?, Cl ?, NO 3 ?, and SO 4 2? in water bodies resulted in lower degradation efficiencies. The half-lives of IFO and CP were 1.2 and 1.1 min and increased 2.3–7.3 and 3.2–6.3 times, respectively, in the presence of the four anions (initial compound concentration = 100 μg/L, TiO 2 loading =100 mg/L, anion concentration = 1000 mg/L, and pH = 8). Although the presence of HCO 3 ? in the UV/TiO 2/HCO 3 ? system resulted in a lower degradation rate and less byproduct formation for IFO and CP, two newly identified byproducts, P11 (M.W. = 197) and P12 (M.W. = 101), were formed and detected, suggesting that additional pathways occurred during the reaction of ?CO 3 ? in the system. The results also showed that ?CO 3 ? likely induces a preferred ketonization pathway. Besides the inorganic anions HCO 3 ?, Cl ?, NO 3 ?, and SO 4 2?, the existence of dissolved organic matter in the water has a significant effect and inhibits CP degradation. Toxicity tests showed that higher toxicity occurred in the presence of HCO 3 ? or Cl ? during UV/TiO 2 treatment and within 6 h of reaction time, implying that the effects of these two anions should not be ignored when photocatalytic treatment is applied to treat real wastewater. 相似文献
11.
This study synthesized multiwall carbon nanotube (MWNT)–titania (TiO 2) composites and examined their characteristics and photocatalytic performance for the cleaning of gas-phase benzene, toluene, ethyl benzene, and o-xylene (BTEX) under simulated indoor conditions. Optical and spectral surveys of the as-synthesized composite confirmed that the TiO 2 nanoparticles were bound intimately to the MWNT networks. The photocatalytic performance was evaluated using an annular-type reactor inner-coated with MWNT–TiO 2 or Degussa P25 TiO 2. The composite revealed gas removal ability superior to that of stand-alone TiO 2. This composite was also less affected by humidity during toluene decomposition compared to the previous result obtained from a stand-alone TiO 2. Unlike another previous result obtained from the TiO 2, the performance of the composite was not affected by changes in input concentration (IC) within a simulated indoor air quality range (0.1–1.0 ppm) but it decreased significantly when the IC was increased to 5 and 10 ppm. As the flow rate was decreased from 4.0 to 1.0 L min ?1, the average efficiency for the target compounds increased to 95% or ~100%. The MWNT–TiO 2 composite could be applied effectively to the decomposition for BTEX under certain simulated indoor conditions. Implications: Unlike water applications, there are few reports of gas-phase applications of multiwall carbon nanotubes (MWCNT)–TiO 2 composites. This study found that MWCNT–TiO 2 composites showed performance in the removal of toxic gaseous aromatic superior to that of stand-alone TiO 2. In addition, the pollutant degradation efficiency of the composite was less affected by humidity than for a stand-alone TiO 2 unit within a simulated indoor relative humidity range. Moreover, unlike the TiO 2 unit, the composite's performance was not affected by variations in the input concentrations within the simulated indoor air quality (IAQ) range. In addition, the decomposition efficiencies increased to 100% with decreasing flow rate. 相似文献
12.
In this work, hexadecyltrimethylammonium-bromide (HTAB)-modified polythiophene (PTh)/TiO2 nanocomposite (HTAB/PTh/TiO2) was applied to remove uranyl ions (UO22+). FT-IR, XRD, ζ potential, TGA, SEM, and XPS were utilized to obtain the chemical and physical properties of HTAB/PTh/TiO2. The effects of HTAB content, preparation temperature, and adsorption conditions on UO22+ removal were investigated comprehensively. And the UO22+ adsorption process on HTAB/PTh/TiO2 was fitted to the Sips model with a saturated adsorption capacity of 234.74 mg/g, which was 6 times over TiO2. The results suggested that the surfactant of HTAB can significantly improve the adsorption ability of TiO2 for UO22+ ions. This work provides a strategy of surfactant modification for enhancing the separation and recovery ability of adsorbent toward UO22+ in the radioactive wastewater. 相似文献
13.
The impact of suspended particles on the bioavailability of pollutants has long been a controversial topic. In this study, adsorption of pentachlorophenol (PCP) onto a natural suspended particulate matter (SPM) and multi-walled carbon nanotubes (MWCNTs) was studied. Facilitated transports of PCP into carp by SPM and MWCNTs were evaluated by bioaccumulation tests exposing carp ( Carassius auratus red var.) to PCP-contaminated water in the presence of SPM and MWCNTs, respectively. Desorption of PCP on SPM and MWCNTs in simulated digested fluids was also investigated. The results demonstrate that MWCNTs ( K F?=?7.99?×?10 4) had a significantly stronger adsorption capacity for PCP than the SPM ( K F?=?19.0). The presence of SPM and MWCNTs both improved PCP accumulation in the carp during the 21 days of exposure, and the 21 days PCP concentration in the carp was enhanced by 25.9 and 12.8 % than that without particles, respectively. The enhancement in bioaccumulation by MWCNTs was less than that by the SPM. Considerably more PCP was accumulated in the viscera of the fish (BCF?=?519495 for SPM and 148955 for MWCNTs), and the difference in PCP concentrations between different tissues became greater with particles. PCP desorption in the simulated digestive fluids was faster than that in the background solution. Compared to MWCNTs-bound PCP, more SPM-bound PCP was desorbed, and K F of desorption for SPM was at least 4 orders of magnitude higher than that for MWCNTs, which can explain the greater enhancement in bioaccumulation in the presence of SPM. Particle-bound pollutants might pose more risk than pollutants alone. 相似文献
14.
A previously proposed technology incorporating TiO 2 into common household fluorescent lighting was further tested for its Hg 0 removal capability in a simulated flue-gas system. The flue gas is simulated by the addition of O 2, SO 2, HCl, NO, H 2O, and Hg 0, which are frequently found in combustion facilities such as waste incinerators and coal-fired power plants. In the O 2 + N 2 + Hg 0 environment, a Hg 0 removal efficiency (η Hg) greater than 95% was achieved. Despite the tendency for η Hg to decrease with increasing SO 2 and HCl, no significant drop was observed at the tested level (SO 2: 5–300 ppm v, HCl: 30–120 ppm v). In terms of NO and moisture, a significant negative effect on η Hg was observed for both factors. NO eliminated the OH radical on the TiO 2 surface, whereas water vapor caused either the occupation of active sites available to Hg 0 or the reduction of Hg 0 by free electron. However, the negative effect of NO was minimized (η Hg > 90%) by increasing the residence time in the photochemical reactor. The moisture effect can be avoided by installing a water trap before the flue gas enters the Hg 0 removal system. Implications: This paper reports a novel technology for a removal of gas-phase elemental mercury (Hg 0) from a simulated flue gas using TiO 2-coated glass beads under a low-cost, easily maintainable household fluorescent light instead of ultraviolet (UV) light. In this study, the effects of individual chemical species (O 2, SO 2, HCl, NO, and water vapor) on the performance of the proposed technology for Hg 0 removal are investigated. The result suggests that the proposed technology can be highly effective, even in real combustion environments such as waste incinerators and coal-fired power plants. 相似文献
15.
The study is aimed at evaluating the potential of immobilized TiO 2-based zeolite composite for solar-driven photocatalytic water treatment. In that purpose, TiO 2-iron-exchanged zeolite (FeZ) composite was prepared using commercial Aeroxide TiO 2 P25 and iron-exchanged zeolite of ZSM5 type, FeZ. The activity of TiO 2-FeZ, immobilized on glass support, was evaluated under solar irradiation for removal of diclofenac (DCF) in water. TiO 2-FeZ immobilized in a form of thin film was characterized for its morphology, structure, and composition using scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX). Diffuse reflectance spectroscopy (DRS) was used to determine potential changes in band gaps of prepared TiO 2-FeZ in comparison to pure TiO 2. The influence of pH, concentration of hydrogen peroxide, FeZ wt% within the composite, and photocatalyst dosage on DCF removal and conversion efficiency by solar/TiO 2-FeZ/H 2O 2 process was investigated. TiO 2-FeZ demonstrated higher photocatalytic activity than pure TiO 2 under solar irradiation in acidic conditions and presence of H 2O 2. 相似文献
16.
The simultaneous photocatalytic removal of nitrate from aqueous environment in presence of organic hole scavenger using TiO 2 has long been explored. However, the use of unmodified TiO 2 in such reaction resulted in non-performance or release of significant amount of undesirable reaction products in the process, a problem that triggered surface modification of TiO 2 for enhanced photocatalytic performance. Previous studies focused on decreasing rate of charge carrier recombination and absorption of light in the visible region. Yet, increasing active sites and adsorption capacity by combining TiO 2 with a high surface area adsorbent such as activated carbon (AC) remains unexploited. This study reports the potential of such modification in simultaneous removal of nitrates and oxalic acid in aqueous environment. The adsorptive behaviour of nitrate and oxalic acid on TiO 2 and TiO 2/AC composites were studied. The Langmuir adsorption coefficient for nitrate was four times greater than that of oxalic acid. However, the amount of oxalic acid adsorbed was about 10 times greater than the amount of nitrate taken up. Despite this advantage, the materials did not appear to produce more active photocatalysts for the simultaneous degradation of nitrate and oxalic acid. The photocatalytic activity of TiO 2 and its carbon-based composites was improved by combination with Cu 2O particles. Consequently, 2.5 Cu 2O/TiO 2 exhibited the maximum photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, while selectivity stood at 45.7, 12.4 and 41.9% for NH 4+, NO 2? and N 2, respectively. For the carbon based, 2.5 Cu 2O/TiO 2-20AC showed removal of 12.7% nitrate and 80.3% oxalic acid and achieved 21.6, 0 and 78.4% selectivity for NH 4+, NO 2? and N 2, respectively. Using the optimal AC loading (20 wt%) resulted in significant decrease in the selectivity for NH 4+ with no formation of NO 2?, which unveils that selectivity for N 2 and low/no selectivity for undesirable products can be manipulated by controlling the rate of consumption of oxalic acid. In contract, no nitrate reduction was observed with Cu 2O promoted TiO 2-T and its TiO 2-(T)-20AC, which may be connected to amorphous nature of TiO 2-T and perhaps served as charge carrier trapping sites that impeded activity. 相似文献
17.
This study has been undertaken to investigate the relationship between Pd oxidation states on TiO 2 photocatalysts and their photocatalytic oxidation behaviors of NO. Three types of Pd-modified TiO 2 with different Pd oxidation states were prepared by wet impregnation method, neutralization method and photodeposition method, respectively. And these Pd-modified photocatalysts were characterized by X-ray diffraction analysis, X-ray photoelectron spectrum analysis (XPS), UV–Vis diffuse reflectance spectra and temperature programmed desorption (TPD). It was found from XPS results that the dominant oxidation states of Pd on these Pd-modified TiO 2 catalysts were Pd 2+, PdO, and Pd 0, respectively. NO-TPD results showed that the NO adsorption capacity was improved greatly by the modification of Pd 2+ ions. The activity tests showed that Pd-modified TiO 2 by a wet impregnation method increased photocatalytic activity compared to pure TiO 2 (Degussa P25). It was concluded that Pd 2+ ions on as-prepared TiO 2 catalysts provided key contributions to the improvement of photocatalytic activity. However, Pd 0 and PdO deposits on TiO 2 almost had no positive effect on NO oxidation. The mechanism of photocatalytic oxidation of NO in gas phase over Pd-modified TiO 2 was also proposed. 相似文献
18.
Degradation of perfluorooctanoic acid (PFOA) is of great importance due to its global distribution, persistence and toxicity to bioorganisms. In present study, a composite TiO 2 with multiple wall carbon nano-tubes (MWCNTs) was synthesized using sol-gel method and it was used as photocatalyst to degrade PFOA in water. The prepared composite catalyst displayed significant absorption in UV to visible light region. The loading content of TiO 2 on MWCNTs could be adjusted by changing the ratio of precursor to MWCNTs. Due to the combined effect of the adsorption ability and e − transport capacity of MWCNT, the composites displayed much higher photocatalytic ability to PFOA as compared to pure TiO 2 under UV irradiation. The photocatalyst prepared with 10:1 of tetrabutyl titanate/MWCNT was the most effective. With the optimal dosage at 1.6 g L −1, almost 100% of PFOA was degraded in acid medium after irradiation for 8 h. It was proposed that PFOA were mainly degraded by stepwise losing a moiety of CF 2. 相似文献
19.
ABSTRACT The kinetics of pentachlorophenol (PCP) ozonation in terms of the gaseous O 3 and dissolved PCP concentrations has been investigated. When the O 3 concentration in the gas phase was in the range of 10 to 40 g O 3/m 3, the O 3 dissolved for a short time period was proportional to the gaseous O 3 concentration. In this range, the ozonation reaction was first order for each reactant and the overall reaction was second order. At 25 °C, in an aqueous solution, the reaction rate constant was estimated to be 10.048 L/mol-sec. The reaction rate was much greater than the mass-transfer rate, indicating that the reaction of O 3 and PCP was an interface reaction on the surface of gaseous O 3 bubbles. The final product of the PCP ozonation was oxalic acid, with the carbon yield of the reaction being 59.4%. The ozonation of PCP in the aqueous solution was not a radical reaction but a direct reaction between O 3 and PCP molecules under the conditions investigated in this study, since O 3 has a high selectivity toward PCP. The reaction rate increased with the reaction temperature up to 35 °C but decreased at temperatures greater than 35 °C due to the decreased solubility of O 3. The addition of H 2O 2 did not increase the reaction rate significantly. 相似文献
20.
This paper demonstrated the relative bactericidal activity of photoirradiated (6W-UV Torch, λ?>?340 nm and intensity?=?0.64 mW/cm 2) P25–TiO 2 nanoparticles, nanorods, and nanotubes for the killing of Gram-negative bacterium Agrobacterium tumefaciens LBA4404 for the first time. TiO 2 nanorod (anatase) with length of 70–100 nm and diameter of 10–12 nm, and TiO 2 nanotube with length of 90–110 nm and diameter of 9–11 nm were prepared from P-25 Degussa TiO 2 (size, 30–50 nm) by hydrothermal method and compared their biocidal activity both in aqueous slurry and thin films. The mode of bacterial cell decomposition was analyzed through transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR), and K + ion leakage. The antimicrobial activity of photoirradiated TiO 2 of different shapes was found to be in the order P25–TiO 2?>?nanorod?>?nanotube which is reverse to their specific surface area as 54?<?79?<?176 m 2 g ?1, evidencing that the highest activity of P25–TiO 2 nanoparticles is not due to surface area as their crystal structure and surface morphology are entirely different. TiO 2 thin films always exhibited less photoactivity as compared to its aqueous suspension under similar conditions of cell viability test. The changes in the bacterial surface morphology by UV-irradiated P25–TiO 2 nanoparticles was examined by TEM, oxidative degradation of cell components such as proteins, carbohydrates, phospholipids, nucleic acids by FT-IR spectral analysis, and K + ion leakage (2.5 ppm as compared to 0.4 ppm for control culture) as a measure of loss in cell membrane permeability. 相似文献
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