The photodegradation of Acid blue 74 in aqueous solution employing a H2O2/ultraviolet system in a photochemical reactor was investigated. The kinetics of decolorization were studied by application of a kinetic model. The results show that the reaction of decolorization followed pseudo-first order kinetics. We demonstrate that there is an optimum H2O2 concentration, at which the rate of the decolorization reaction is maximum. Irradiation at 253.7 nm of the dye solution in the presence of H2O2 results in complete discoloration after ten minutes of treatment. 相似文献
The NO/H2/O2 reaction was studied under oxidizing conditions in the 100-400 °C range over 0.1 wt% Pt supported on various metal oxides such as MgO, CeO2, SiO2, La2O3, CaO, Y2O3 and TiO2. The Pt/MgO and Pt/CeO2 catalysts showed good catalytic behaviours. Here, we find that the Pt/Mg-Ce-O catalyst, prepared from MgO and CeO2 by the sol-gel method, is a very active and selective catalyst towards N2 formation in the whole 100–400 °C range. This catalyst appears to be the most active, selective and stable one ever reported in the literature for the NO/H2/O2 reaction, even in the presence of 5%v H2O or 20 ppmv of SO2 in the feed stream.Selected article from the Regional Symposium on Chemistry and Environment, Krusevac, Serbia, June 2003, organised by Dr. Branimir Jovancicevic. 相似文献
We have discovered that HNO3 and related species are released from the TiO2 surface into air in the TiO2 photocatalytic oxidation of NO2 (1 ppm) under continuous UV light illumination (1 mW cm−2) by dehumidifying the outlet gas of the reaction and analyzing the recovered condensate liquid by ion chromatography. The
origin of the HNO3 recovered in the dehumidifier could not be explained by a simple desorption of HNO3 overproduced on the TiO2 surface. The produced HNO3 must be activated on the TiO2 surface and causing the unidentified reaction. 相似文献
Chromium oxide and manganese oxide promoted ZrO2-CeO2 catalysts were prepared by a homogeneous precipitation method for the selective catalytic reduction of NOx with NH3. A series of characterization including X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM), Brunauer–Emmett–Teller (BET) surface area analysis, H2 temperatureprogrammed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the influence of the physicochemical properties on NH3-SCR activity. Cr-Zr-Ce and Mn-Zr-Ce catalysts are much more active than ZrO2-CeO2 binary oxide for the low temperature NH3-SCR, mainly because of the high specific surface area, more surface oxygen species, improved reducibility derived from synergistic effect among different elements. Mn-Zr-Ce catalyst exhibited high tolerance to SO2 and H2O. Cr-Zr-Ce mixed oxide exhibited>80% NOx conversion at a wide temperature window of 100°C–300°C. In situ DRIFT studies showed that the addition of Cr is beneficial to the formation of Bronsted acid sites and prevents the formation of stable nitrate species because of the presence of Cr6 +. The present mixed oxide can be a candidate for the low temperature abatement of NOx.
The transformation of the fungicide carbendazim (methyl-2 benzimidazole carbamate) induced by hydroxyl radical generated by
the UV photolysis of H2O2 has been studied in dilute aqueous solution. The efficient reaction of hydroxyl radicals with carbendazim led to the rapid
degradation of carbendazim. The study of reaction kinetics yielded a second order rate constant of 2.2±0.3 109 M−1 s−1 for HO· radicals with carbendazim. This value is in agreement with a high reactivity of HO· radicals with carbendazim. Most degradation products were identified by high performance liquid chromatography mass spectrometry
(HPLC-MS). In the presence of hydrogenocarbonate and carbonate ions, hydroxyl radicals were quenched and in turn carbonate
radicals CO3·− were formed. Carbonate radicals are indeed known to react efficiently with compounds containing electron-rich sites such
as nitrogen or sulfur atoms. The use of a kinetic modelling software gave evidence for the occurrence of such reactions with
carbendazim. The second order rate constant of carbonate radical with carbendazim was equal to 6±2 106 M−1 s−1.
Electronic Publication 相似文献
Photocatalytic oxidation using semiconductors is one of the advanced oxidation processes for degradation of organic pollutants in water and air. TiO2 is an excellent photocatalyst that can mineralize a large range of organic pollutants such as pesticides and dyes. The main challenge is to improve the efficiency of the TiO2 photocatalyst and to extend TiO2 light absorption spectra to the visible region. A potential solution is to couple TiO2 with a narrow band gap semiconductor possessing a higher conduction band such as bismuth oxide. Therefore, here we prepared Bi2O3/TiO2 heterojunctions by the impregnation method with different Bi/Ti ratio. The prepared composites have been characterized by UV–Vis diffused reflectance spectra and X-ray diffraction. The photocatalytic activity of the heterojunction has been determined from the degradation of orange II under visible and UV light. Results show that Bi2O3/TiO2 heterojunctions are more effective than pure TiO2-anatase under UV-A irradiation, with an optimum for the Bi/Ti ratio of 5 %, for the photocatalytic degradation of Orange II. However, the photocatalytic activity under irradiation at λ higher than 420 nm is not much improved. Under UV–visible radiation, the two semiconductors are activated. We propose a mechanism explaining why our products are more effective under UV–visible irradiation. In this case the charge separation is enhanced because a part of photogenerated electrons from the conduction band of TiO2 will go to the conduction band of bismuth oxide. In this composite, titanium dioxide is the main photocatalyst, while bismuth oxide acts as adsorbent photosensitizer under visible light. 相似文献
N2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalysts, Pt/BaO/Al2O3, Pt/Pd mechanical mixing catalyst (Pt/BaO/Al2O3 + Pd/Al2O3) and Pt-Pd co-impregnation catalyst (Pt-Pd/BaO/Al2O3) were prepared by incipient wetness impregnation method. These catalysts were first evaluated in NSR activity tests using H2/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about N2O formation mechanism. Compared with Pt/BaO/Al2O3, (Pt/BaO/ Al2O3 + Pd/Al2O3) produced less N2O and more NH3 during NOx storage and reduction process, while an opposite trend was found over (Pt-Pd/BaO/Al2O3 + Al2O3). Temperature programmed reactions of NO with H2/CO results showed that Pd/Al2O3 component in (Pt/BaO/Al2O3 + Pd/Al2O3) played an important role in NO reduction to NH3, and the formed NH3 could reduce NOx to N2 leading to a decrease in N2O formation. Most of N2O formed over (Pt-Pd/BaO/Al2O3 + Al2O3) was originated from Pd/BaO/Al2O3 component. H2-TPR results indicated Pd-Ba interaction resulted in more difficultto- reduce PdOx species over Pd/BaO/Al2O3, which inhibits the NO dissociation and thus drives the selectivity to N2O in NO reduction.
Porous carbon material facilitates the reaction SO2 + O2 + H2O → H2SO4 in coal-burned flue gas for sulfur resources recovery at mild conditions. It draws a long-term mystery on its heterogeneous catalysis due to the complicated synergic effect between its microstructure and chemical components. To decouple the effects of geometric structure from chemical components, classical molecular dynamics method was used to investigate the static and dynamic characteristics of the reactants (H2O, SO2 and O2) in the confined space truncated by double-layer graphene (DLG). Strong adsorption of SO2 and O2 by the DLG was observed, which results in the filling of the solute molecules into the interior of the DLG and the depletion of H2O. This effect mainly results from the different affinity of the DLG to the species and can be tuned by the separation of the two graphene layers. Such dimension dependence of the static and dynamic properties like distribution profile, molecular cluster, hydrogen bond and diffusion coefficient were also studied. The conclusions drawn in this work could be helpful to the further understanding of the underlying reaction mechanism of desulfurization process in porous carbon materials and other applications of carbon-based catalysts.
The photocatalytic degradation of a sulfonylurea herbicide, cinosulfuron, has been studied in TiO2 aqueous suspensions. A first order kinetic law was found. The influence of the initial concentration of cinosulfuron and
of the initial radiant flux on the kinetics were evaluated. The identification of the intermediate products was based on high
performance liquid chromatography coupled with mass spectrometry analyses (HPLC-MS). The mineralization of cinosulfuron was
traced using ion chromatography and total organic carbon (TOC) measurements. These results indicate that the photocatalytic
degradation of cinosulfuron leads to CO2, NO3− and SO42− as final products, and in addition cyanuric acid (C3H3O3N3), confirming previous results on triazinic ring-containing compounds.
Electronic Publication 相似文献
Reductive dechlorination of chlorobenzene by Fe/ZrO2 in supercritical water was investigated. The effects of the operation conditions were studied. The dechlorination of chlorobenzene obeyed pseudo-first-order kinetics models. In supercritical water, the rate constant increases more rapidly with temperature than those in subcritical water. The results showed that the rate-determining step of dechlorination in subcritical water is diffusion; whereas the rate-determining of dechlorination in supercritical water is chemical reaction. The reaction mechanism in subcritical water might involve with an ionic mechanism; whereas the reaction mechanism in supercritical water might involve with a homolytic reaction. 相似文献
In this work, Er3+:YAlO3/TiO2 composite was synthesized by a ultrasonic dispersion and liquid boil method. The Er3+:YAlO3/TiO2 composite and pure TiO2 powder were characterized by XRD. The degradation of different organic dyes was used to evaluate the photocatalytic activity of the Er3+:YAlO3/TiO2 composite. It is found that the photocatalytic activity of Er3+:YAlO3/TiO2 composite is much higher than that for the similar system with only TiO2. Moreover, this Er3+:YAlO3/TiO2 composite provides a new way to take advantage of TiO2 in sewage treatment aspects using solar light. 相似文献
Although the flow dynamics of pure liquid drops in other liquids has been well researched, little attention has been paid to the impacts of impurities. Hence, most of research is not directly applicable to the real world. To address this gap, we conducted numerical experiments simulating the rise of pure and contaminated drops. It was selected to study liquid CO2 drops contaminated with SO2 under high pressure because such mixtures mimic potential scenarios in which drops may leak from carbon capture and storage (CCS) facilities or pipelines. First, numerical simulation experiments were performed to validate our method by comparing our results with previous research on pure drops. Second, the validated numerical approach was applied to simulations of contaminated drops to investigate how contaminants affect rising drops. The results show that the SO2 contamination caused changes in deformation, breakup phenomena, rising velocities, surrounding flow fields and drag coefficients. Most importantly, the contamination resulted in the formation of smaller “child drops”; such breakup is not observed in pure CO2 drops. The formation of child drops in turn affects the streamlines, patterns and areas of wakes behind the contaminated drops. The addition of contaminants also enhances the dissolution rate, which is affected by the contaminant concentration and by the flow dynamics of the rising drop. Our results would improve understanding the rise of impure CO2 drops, such as drops potentially leaked by future CCS operations. 相似文献
Bi2WO6 was synthesized with a hydrothermal method at different pHs and used for the degradation of tetracycline (TC) in water. The mesoporous Bi2WO6 prepared at pH 1 (BWO-1) displayed the highest adsorption and degradation capacity to TC due to its large surface area and more efficient capacity to separate photogenerated electrons and holes. 97% of TC at 20 mg·L?1 was removed by BWO-1 at 0.5 g·L?1 after 120 min irradiation under simulated solar light. Only 31% of the total organic carbon (TOC) was removed after 360 min irradiation although the TC removal reached 100%, suggesting that TC was mainly transformed to intermediate products rather than completely mineralized. The intermediates were identified by high-performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS) and possible photodegradation pathways were proposed. 相似文献
A pot experiment was conducted to examine the influence of potassium (K) fertilizer (K2SO4) application on the phytoavailability and speciation distribution of cadmium (Cd) and lead (Pb) in soil. Spring wheat (Triticum aestivum L.) was selected as the test plant. There were seven treatments including single and combined contamination of Cd and Pb.
CdCl2·2.5 H2O and Pb(NO3)2 were added to the soil at the following dosages: Cd + Pb = 0.00 + 0.00, 5.00 + 0.00, 25.0 + 0.00, 0.00 + 500, 0.00 + 1000,
5.00 + 500 and 25.0 + 1000 mg kg−1, denoted by CK, T1, T2, T3, T4, T5 and T6, respectively. The K fertilizer had five levels: 0.00, 50.0, 100, 200 and 400 mg
K2O kg−1 soil, denoted by K0, K1, K2, K3 and K4, respectively. The results showed that the K fertilizer promoted the dry weight (DW)
of wheat in all treatments and alleviated the contamination by Cd and Pb. The application of K2SO4 reduced the uptake of Cd in different parts including roots, haulms and grains of wheat; the optimum dosage was the K2 level.
K supply resulted in a significant (P < 0.05) decrease in the soluble plus exchangeable (SE) fraction of Cd and there was a negative correlation (not significant,
P > 0.05) between the levels of K and the SE fraction of Cd in soil. The application of the K fertilizer could obviously restrain
the uptake of Pb by wheat and there were significant (P < 0.05) negative correlations between the concentrations of Pb in grains and the levels of K in soil. K supply resulted in
a decrease in the SE fraction of Pb (except the K1 level) from the K0 to K4 levels. At the same time, the application of the
K fertilizer induced a significant (P < 0.05) decrease in the weakly specifically adsorbed (WSA) fraction of Pb and a significant (P < 0.05) increase in the bound to Fe–Mn oxides (OX) fraction of Pb. At different K levels, the concentration of Pb in the
roots, haulms and grains had a positive correlation with the SE (not significant, P > 0.05) and WSA (significant, P < 0.05) fractions of Pb in the soil. All the K application levels in this experiment reduced the phytoavailability of Cd
and Pb. Thus, it is feasible to apply K fertilizer (K2SO4) to alleviate contamination by Cd and/or Pb in soil. Moreover, the level of K application should be considered to obtain
an optimal effect with the minimum dosage. 相似文献
Fine particulate matter (PM2.5) levels, carbon dioxide (CO2) levels and particle-number concentrations (PNC) were monitored in train carriages on seven routes of the mass transit railway in Hong Kong between March and May 2014, using real-time monitoring instruments. The 8-h average PM2.5 levels in carriages on the seven routes ranged from 24.1 to 49.8 µg/m3, higher than levels in Finland and similar to those in New York, and in most cases exceeding the standard set by the World Health Organisation (25 µg/m3). The CO2 concentration ranged from 714 to 1801 ppm on four of the routes, generally exceeding indoor air quality guidelines (1000 ppm over 8 h) and reaching levels as high as those in Beijing. PNC ranged from 1506 to 11,570 particles/cm3, lower than readings in Sydney and higher than readings in Taipei. Correlation analysis indicated that the number of passengers in a given carriage did not affect the PM2.5 concentration or PNC in the carriage. However, a significant positive correlation (p < 0.001, R2 = 0.834) was observed between passenger numbers and CO2 levels, with each passenger contributing approximately 7.7–9.8 ppm of CO2. The real-time measurements of PM2.5 and PNC varied considerably, rising when carriage doors opened on arrival at a station and when passengers inside the carriage were more active. This suggests that air pollutants outside the train and passenger movements may contribute to PM2.5 levels and PNC. Assessment of the risk associated with PM2.5 exposure revealed that children are most severely affected by PM2.5 pollution, followed in order by juveniles, adults and the elderly. In addition, females were found to be more vulnerable to PM2.5 pollution than males (p < 0.001), and different subway lines were associated with different levels of risk. 相似文献
A solution of atrazine in a TiO2 suspension, an endocrine disruptor in natural water, was tentatively treated by microwave-assisted photocatalytic technique. The effects of mannitol, oxygen, humic acid, and hydrogen dioxide on the photodegradation rate were explored. The results could be deduced as follows: the photocatalytic degradation of atrazine fits the pseudo-first-order kinetic well with k = 0.0328 s?1, and ·OH was identified as the dominant reactant. Photodegradation of atrazine was hindered in the presence of humic acid, and the retardation effect increased as the concentration of humic acid increased. H2O2 displayed a significant negative influence on atrazine photocatalysis efficiency. Based on intermediates identified with gas chromatography-mass spectrometry (GC-MS) and Liquid chromatography-mass spectrometry (LC-MS/MS) techniques, the main degradation routes of atrazine are proposed. 相似文献
In this study, FeVO4 was prepared and used as Fenton-like catalyst to degrade orange G (OG) dye. The removal of OG in an aqueous solution containing 0.5 g·L–1 FeVO4 and 15 mmol·L–1 hydrogen peroxide at pH 7.0 reached 93.2%. Similar rates were achieved at pH 5.7 (k = 0.0471 min–1), pH 7.0 (k = 0.0438 min–1), and pH 7.7 (k = 0.0434 min–1). The FeVO4 catalyst successfully overcomes the problem faced in the heterogeneous Fenton process, i.e., the narrow working pH range. The data for the removal of OG in FeVO4 systems containing H2O2 conform to the Langmuir–Hinshelwood model (R2 = 0.9988), indicating that adsorption and surface reaction are the two basic mechanisms for OG removal in the FeVO4–H2O2 system. Furthermore, the irradiation of FeVO4 by visible light significantly increases the degradation rate of OG, which is attributed to the enhanced rates of the iron cycles and vanadium cycles.
Radon (222Rn) and carbon dioxide were monitored simultaneously in soil air under a cool-temperate deciduous stand on the campus of Hokkaido
University, Sapporo, Japan. Both 222Rn and CO2 concentrations in soil air varied with atmospheric (soil) temperature in three seasons, except for winter when the temperature
in soil air remained constant at 2–3°C at depth of 80 cm. In winter, the gaseous components were influenced by low-pressure
region passing through the observation site when the ground surface was covered with snow of ~1 m thickness. Carbon isotopic
analyses of CO2 suggested that CO2 in soil air may result from mixing of atmospheric air and soil components of different origins, i.e. CO2 from contemporary soil organic matter and old carbon from deeper source, to varying degrees, depending on seasonal meteorological
and thus biological conditions. 相似文献
Agricultural soils are an important source of greenhouse gases (GHG). Biochar application to such soils has the potential of mitigating global anthropogenic GHG emissions. Under irrigation, the topsoils in arid regions experience repeated drying and wetting during the crop growing season. Biochar incorporation into these soils would change the soil microbial environment and hence affect GHG emissions. Little information, however, is available regarding the effect of biochar addition on carbon dioxide (CO2) and nitrous oxide (N2O) emissions from agricultural soils undergoing repeated drying and wetting. Here, we report the results of a 49-day aerobic incubation experiment, incorporating biochar into an anthropogenic alluvial soil in an arid region of Xinjiang Province, China, and measuring CO2 and N2O emissions. Under both drying–wetting and constantly moist conditions, biochar amendment significantly increased cumulative CO2 emission. At the same time, there was a significant reduction (up to ~20 %) in cumulative N2O emission, indicating that the addition of biochar to irrigated agricultural soils may effectively slow down global warming in arid regions of China. 相似文献
Semiconductor photocatalysis is a solution to issues of environmental pollution and energy shortage because photocatalysis can use solar energy to degrade pollutants. The photocatalytic activity can be improved by using composites of ZnO and other semiconductors. Here, composites of ZnO and polymeric graphite-like C3N4 (g-C3N4) with high photocatalytic activities were prepared by microwave synthesis. Products were characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible and Fourier transform infrared spectroscopy. The photocatalytic degradation of Rhodamine B was tested under irradiation from a Xe lamp. Results show that adding graphite-like C3N4 promotes the photocatalytic activity of ZnO. Composites with 1.0 wt% g-C3N4 showed the best photodegradation efficiency, and the reaction average energy was approximately 33.71 kJ mol?1. 相似文献