In this work, two technologies are studied for the removal of phenol from aqueous solution: dynamic adsorption onto activated carbon and photocatalysis. Almond shell activated carbon (ASAC) was used as adsorbent and catalytic support in the phenol degradation process. The prepared catalyst by deposition of anatase TiO2 on the surface of activated carbon was characterized by scanning electron microscopy, sorption of nitrogen, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, and pHZPC point of zero charge. In the continuous adsorption experiments, the effects of flow rate, bed height, and solution temperature on the breakthrough curves have been studied. The breakthrough curves were favorably described by the Yoon–Nelson model. The photocatalytic degradation of phenol has been investigated at room temperature using TiO2-coated activated carbon as photocatalyst (TiO2/ASAC). The degradation reaction was optimized with respect to the phenol concentration and catalyst amount. The kinetics of disappearance of the organic pollutant followed an apparent first-order rate. The findings demonstrated the applicability of ASAC for the adsorptive and catalytic treatment of phenol. 相似文献
In this study, the TiO2 photocatalytic decomposition process of aqueous phenol was investigated. The intermediate products generated in the elementary reaction steps in the mineralization process were experimentally identified as hydroquinone, catechol and hydroxyhydroquinone. The concentration variations of these intermediate products with time passage were traced by high performance liquid chromatograph. The pathways of the decomposition process were given. Based on Langmuir isothermal theory and Langmuir-Hinshelwood mechanism, the multi-compounds competition kinetic model was established. In this model, the observed time-dependent concentrations of phenol and the intermediate products were simulated. 相似文献
Textile industry wastes raise a great concern due to their strong coloration and toxicity. The objective of the present work was to characterize the degradation and mineralization of textile effluents by advanced oxidative processes using either TiO2 or TiO2/H2O2 and to monitor the toxicity of the products formed during 6-h irradiation in relation to that of the in natura effluent. The results demonstrated that the TiO2/H2O2 association was more efficient in the mineralization of textile effluents than TiO2, with high mineralized ion concentrations (NH4+, NO3?, and SO42?) and significantly decreased organic matter ratios (represented by the chemical oxygen demand and total organic carbon). The toxicity of the degradation products after 4-h irradiation to Artemia salina L. was not significant (below 10 %). However, the TiO2/H2O2 association produced more toxicity under irradiation than the TiO2 system, which was attributed to the increased presence of oxidants in the first group. Comparatively, the photogenerated products of both TiO2 and the TiO2/H2O2 association were less toxic than the in natura effluent. 相似文献
In this paper, magnetic carbon nanotube (M-CNT) was synthesized. The photocatalytic dye degradation ability of M-CNT in the presence of hydrogen peroxide (H2O2) from colored wastewater was studied. Manganese ferrite (MnFe2O4) was synthesized in the presence of multiwalled carbon nanotube. Direct Red 23 (DR23), Direct Red 31 (DR31), and Direct Red 81 (DR81) were used as anionic dyes. The characteristics of M-CNT were investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The photocatalytic dye degradation using M-CNT was studied by UV–vis spectrophotometer and ion chromatography (IC). The effects of M-CNT dosage, initial dye concentration, and salt on the degradation of dye were evaluated. Formate, acetate, and oxalate anions were detected as dominant aliphatic intermediates. Inorganic anions (nitrate and sulfate anions) were detected and quantified as the mineralization products of dyes during the degradation process. The results indicated that the M-CNT could be used as a magnetic catalyst to degrade anionic dyes from colored wastewater. 相似文献
Titanium dioxide is the most important photocatalysts used for purifying applications. If a TiO2- containing material is left outdoors as a form of flat panels, it is activated by sunlight to remove harmful NOx gases during
the day. The photocatalytic efficiency of a TiO2-treated mortar for removal of NOx was investigated in the frame of this work. For this purpose a fully equipped monitoring
system was designed at a pilot site. This system allows the in situ evaluation of the de-polluting properties of a photocatalytic
material by taking into account the climatologic phenomena in street canyons, accurate measurements of pollution level and
full registration of meteorological data The pilot site involved three artificial canyon streets, a pollution source, continuous
NOx measurements inside the canyons and the source as well as background and meteorological measurements. Significant differences
on the NOx concentration level were observed between the TiO2 treated and the reference canyon. NOx values in TiO2 canyon were 36.7 to 82.0% lower than the ones observed in the reference one. Data arising from this study could be used to
assess the impact of the photocatalytic material on the purification of the urban environment. 相似文献
Thin-film technique is becoming an industry standard for the preparation of TiO2-based photocatalyst for organic destruction. The catalyst provides several advantages over the conventional powder TiO2 in the treatment of wastewater and groundwater. In this study, a continuous stir flow reactor model is developed capable of describing the photocatalytic process. The model incorporates the following fundamental mechanisms: adsorption, diffusion, liquid-film transfer, UV attenuation, and photocatalytic reaction. All of the simulation results indicate that there exists a highly nonlinear relation between each of these parameters and the destruction rate. Various incident light intensities also are incorporated to simulate the energy efficiency. The simulations illustrate that the photocatalytic model can be used to elucidate the effect of process variables. It is also possible to “custom-design” a catalyst for the treatment of a particular waste stream. 相似文献
The degradation of some organophosphorus pesticides (OPPs) in the presence of metal ions was studied by 31P-NMR spectroscopy. Both 31P-NMR and gas chromatography/mass spectroscopy results were used in order to determine the nature of metabolites formed after degradation. The degraded organophosphorus pesticide were investigated for chlorpyrifos and phoxim in the presence of several metal ions including Hg2+, Cu2+, Cd2+, Ni2+, Pb2+, and Ag+. 31P-NMR results indicated Ag+ and Hg2+ ion promoted degradation of OPPs and other metal ions formed complex with OPPs and cannot degrade OPPs. We found that the degradation of chlorpyrifos and phoxim with Ag+ or Hg2+ led to the formation of O,O-diethyl-O-methyl phosphorothionate, (C2H5O)2(CH3O)PS, at metal ion/pesticide mole ratios ≤1.0 and completely decomposed at a higher mole ratio of 10. Finally, the method was successfully applied to the degradation study of a number of technical and formulated pesticides in the presence of Ag+ ion at a metal ion/pesticide mole ratio of 10. 相似文献
Modelled and measured indicator species ratios of O3/NOz, O3/NOy, H2O2/HNO3, HCNO/NOy for the Lower Fraser Valley were compared with VOC-NOx-O3 sensitivity threshold values reported in previous studies. Modelled region - specific indicator ratio thresholds derived from 50% NOx and 50% VOC reduction scenarios are provided. They show strongest agreement with the H2O2/HNO3 ratio values found elsewhere. A clear transition region for the LFV from VOC to NOx sensitivity could not be identified, but there is evidence that O3 concentrations in the western valley, dominated by metropolitan Vancouver, are VOC sensitive, and the more rural eastern valley O3 concentrations exhibit greater NOx sensitivity. The UAM-V Process Analysis utility was used to identify physical and chemical mechanisms which contributed to O3 formation and destruction and indicate the key importance of entrainment from elevated layers generated by the highly complex meteorological conditions in determining near surface O3 concentrations. 相似文献
Aquatic stability and impact of titanium dioxide nanoparticles (TiO2 NPs, 10–30 nm) were investigated using Artemia salina. Acute exposure was conducted on nauplii (larvae) and adults in seawater in a concentration range from 10 to 100 mg/L TiO2 NPs for 24 and 96 h. Rapid aggregation occurred in all suspensions of TiO2 NPs to form micrometer size particles. Yet, both nauplii and adults accumulated the aggregates significantly. Average TiO2 content in nauplii ranged from 0.47 to 3.19 and from 1.29 to 4.43 mg/g in 24 and 96 h, respectively. Accumulation in adults was higher ranging from 2.30 to 4.19 and from 4.38 to 6.20 mg/g in 24 and 96 h, respectively. Phase contrast microscopy images revealed that Artemia were unable to excrete the particles. Thus, the TiO2 aggregates filled inside the guts. No significant mortality or toxicity occurred within 24 h at any dose. Lipid peroxidation levels characterized with malondialdehyde concentrations were not statistically different from those of the controls (p?>?0.05). These results suggested that suspensions of the TiO2 NPs were nontoxic to Artemia, most likely due to the formation of benign TiO2 aggregates in water. In contrast, both mortality and lipid peroxidation increased in extended exposure to 96 h. Highest mortality occurred in 100 mg/L TiO2 NP suspensions; 18 % for nauplii and 14 % for adults (LC50?>?100 mg/L). These effects were attributed to the particle loading inside the guts leading to oxidative stress as a result of impaired food uptake for a long period of time. 相似文献
The aim of this study is to examine the relative contribution of the outdoor concentration, the ventilation rate, the geometric characteristics of the indoor environment (i.e., extent of indoor surfaces and indoor volume), the deposition, and chemical reactions to the indoor air quality of the office microenvironment. For this case study, the NO, NO2, and O3 concentrations indoors and outdoors and TVOCs and CO2 concentrations indoors were measured in an office microenvironment in Athens, Greece, that was ventilated both naturally and mechanically. The calculated ventilation and loss rates and the measured outdoor concentrations of NO, NO2, and O3 were set as input to Multi-chamber Indoor Air Quality Model in order to study the temporal variation of the indoor NO, NO2, and O3 concentrations. Results showed that when the ventilation rate and outdoor concentration are high, the relative contribution of the transport process contributes significantly, while the chemical process depends on the contemporary interplay between the indoor O3, NO, and NO2 concentrations and lighting levels. The significance of each process was further examined by performing sensitivity tests, and it was found that the most important parameters were the deposition velocities, the UV infiltration rates (which determines the indoor chemical reaction rates), the ventilation rates, and the filtration (when a mechanical ventilation system is used). The effect of the hydrocarbon chemistry was not significant. 相似文献
A bioassay for rhizosphere-applied phytotoxicants was developed and evaluated with a broad range of chemicals. Test substances were applied to the rhizosphere of whole, intact bush bean plants (Phaseolus vulgaris L. cv. Bush Blue Lake 290) grown in a solid support medium and the resultant ethylene production was measured to detect the presence of phytotoxic materials. The beans were encapsulated in plastic bags for 2 hr following treatment and then incubated for 24 hr in the dark. Ethylene and ethane accumulating within the bags were quantified via gas-solid chromatography. The application of various concentrations of inorganic and organic chemicals induced various responses. No single equation adequately described the dose-response curves; therefore, a critical value (a statistically significant increase in stress ethylene) was computed for each test substance. A phytotoxic-response threshold for each test substance was defined as the test-substance concentration that caused ethylene production to exceed its respective critical-value concentration. Based on threshold concentrations determined by analysis of stress ethylene production, the relative phytotoxicity rankings of the inorganic test substances were: CdCl2>CuCl2>Pb(C2H3O2)2>LiCl, while those of the organic test substances were 2,4-D esters>paraquat dichloride>1-butanol>2-propanone>2-propanol. Both stress ethylene and ethane production were nonresponsive to hydrogen-ion concentration (measured before application) over a broad pH range. However, significant ethane production was detected at pH 2 and stress ethylene was produced at pH 1. The measurement of stress-induced ethylene provides a rapid and simple means to determine the relative phytoxicity of rhizosphere-applied substances. 相似文献
Seventeen fog events were sampled in Baton Rouge, Louisiana during 2002–2004 as part of characterizing wet deposition by fogwater
in the heavily industrialized corridor along the Louisiana Gulf Coast in the United States. These samples were analyzed for
chemical characteristics such as pH, conductivity, total organic and inorganic carbon, total metals and the principal ion
concentrations. The dominant ionic species in all samples were NH4+, NO3−, Cl− and SO42−. The pH of the fogwater sampled had a mean value of 6.7 with two cases of acidic pH of 4.7. Rainwater and fogwater pH were
similar in this region. The acidity of fogwater was a result of NO3− but partly offset by high NH4+. The measured gaseous SO2 accounted for a small percentage of the observed sulfate concentration, indicating additional gas-to-particle conversion
of SO2 to sulfate in fogwater. The gaseous NOx accounted for most of the dissolved nitrate and nitrite concentration in fogwater. The high chloride concentration was attributable
to the degradation of chlorinated organics in the atmosphere. The metal composition was traced directly to soil-derived aerosol
precursors in the air. The major metals observed in fogwater were Na, K, Ca, Fe, Al, Mg and Zn. Of these Na, K, Ca and Mg
were predominant with mean concentrations > 100 μM. Al, Fe and Zn were present in the samples, at mean concentrations < 100
μM. Small concentrations of Mn (7.8 μM), Cu (2 μM), Pb (0.07 μM) and As (0.32 μM) were also observed in the fogwaters, and
these were shown to result from particulates (PM2.5) in the atmosphere. The contribution to both ions and metals from the marine sources in the Louisiana Gulf Coast was minimal.
The concentrations of all principal ionic species and metals in fogwater were 1–2 orders of magnitude larger than in rainwater.
Several linear alkane organic compounds were observed in the fogwater, representing the contributions from petroleum products
at concentrations far exceeding their aqueous solubility. A pesticide (atrazine) was also observed in fogwater, representing
the contribution from the agricultural activities nearby. 相似文献
Fenton oxidation was compared with Fenton oxidation coupled with ultrasonication (Fenton?+?US) for sludge dewatering. Different Fenton reagent (H2O2, Fe2+) concentrations, pH, and reaction times were studied in different systems on the basis of the specific resistance to filtration (SRF) and capillary suction time (CST). It was found that Fenton?+?US can significantly reduce Fe2+ and H2O2 dosages and reaction times. After ultrasonication of the system at pH 3, with an ultrasonic frequency of 25 kHz and a sound energy density of 100 W/L, the Fe2+, H2O2 dosage, and reaction time were reduced by 66.7, 75.0, and 75.0 %, respectively, when compared with Fenton oxidation at the same dewaterability of sludge. The microstructure of sludge and hydroxyl radical (·OH) density in Fenton oxidation and Fenton?+?US was further examined. Fenton?+?US produced more?·?OH in a sludge system than did individual Fenton oxidation. The concentration of?·?OH in Fenton?+?US fell from 79.2 to 6 mg/L over 3.5 h, while the concentration of?·?OH in Fenton oxidation fell from 59.6 to 1 mg/L over 2 h, thus destroying the microstructure of sludge more effectively. Sludge treated using Fenton?+?US for 30 min showed a much thinner and looser microstructure. 相似文献
The objective of this study is to analyze the concentrations of SO2, NO2, and O3 measured by a Differential Optical Absorption Spectroscopy (DOAS) system that was operating at the campus of Technological Education Institute of Piraeus during 2008 and 2009 warm periods (July to September) in relation to the prevailing meteorological conditions. The DOAS system was operating in a particularly polluted area of the West part of Attica basin on a continuous basis, measuring the concentration levels of the main pollutants (O3, NO2, and SO2) as well as aromatic hydrocarbon substances (benzene, toluene, and xylene). According to the analysis, the SO2 concentration levels at this measuring site are rather high and this may be attributed to the characteristics of this measuring site. Proximity of roadways and local circulation are just some of the factors that can affect the concentration levels of monitoring of pollutant concentrations such as NO2 and surface ozone. The results provide evidence for the occurrence of an atmospheric phenomenon that produces higher ozone concentrations during weekends despite lower concentrations of ozone precursors. This phenomenon is known as the weekend effect. 相似文献
Seedlings of two full-sib families of loblolly pine expressing different degrees of sensitivity to O3 were exposed to 0.05 ppm O3, 0.10 ppm NO2, and/or 0.14 ppm SO2 for 6 hr/day for 28 consecutive days. The treatments were O3, NO2, SO2 (each used alone), O3+SO2, O3+NO2, and O3+NO2+SO2. Significant growth suppressions were noted with the relatively sensitive family in all but the the NO2 alone treatments. The O3+SO2 treatment had a more significant effect than O3 alone, but adding NO2 had an inconsistent effect. Significant growth suppressions were noted for the relatively non-sensitive family only in the O3+SO2 and O3+SO2+NO2 combination treatments. Adding NO2 to O3+SO2 had a slightly stimulatory effect. The relatively sensitive pine family suffered a 30% height growth suppression versus a 14% height growth suppression for the relatively insensitive family when exposed to the 3 pollutant combination. Symptoms were noted on less than 4% of the foliage in the most severe treatments. The pollutant concentrations used in this study were below the National Ambient Air Quality Standards (NAAQS) for each pollutant. 相似文献
Ozone and a Fe2+/TiO2-based catalyst were examined in the degradation of a synthetic solution of benzene toluene and xylene (BTX) in an advanced oxidation process (AOP). The catalyst beads were made from the slurry waste of aluminum production process, by inserting the TiO2 content and subsequent calcination. The reduction of the BTX concentration load was monitored by the reduction of chemical oxygen demand (COD) and BTX concentration. Different levels were used on factors: pH, time of treatment, initial concentration of BTX, and percentage of TiO2. The process was conducted in a bubble column reactor with the insertion of catalyst beads. A response surface methodology technique (CCD) was used to build a model based on COD reduction results. The model was optimized using the normal-boundary intersection (NBI) algorithm to maximize COD reduction and minimize the variance attributed to the process. Optimization led to COD reductions of 80% in 2 h of experiment. Correlation analysis of coefficient models from experimental data R2adj was 0.9966, showing a good fit of model data. In the optimized conditions, the possible increase of the biodegradability ratio of the BTX solution, through the biochemical oxygen demand (BOD) and COD, was also analyzed. Under pre-treatment conditions, the BOD/COD ratio was 0.13. After the treatment, it increased to 0.56.
Towards the aim of improving the air quality in the urban environment via the application of innovative TiO2 based photocatalytic coverings, a field campaign took place within the frame of the EU PICADA project () to asses the expected depollution efficiency of such materials under realistic conditions. Furthermore, extensive numerical
modeling was performed via the application of the RANS CFD code for microscale applications MIMO, in an effort to asses the
sensitivity of the developing flow field and the corresponding dispersion mechanism and hence of the depollution efficiency
of the PICADA products on a wide range of factors, with most notably the length of the street canyon, the thermal exchange
between the heated street canyon walls and the air and the approaching wind direction. For the needs of the PICADA project
a new, simple module had to be implemented into MIMO to be able to model the removal of NOx from a street canyon whose walls have been treated with a photocatalytic product. The model simulations results presented
in this paper, show that MIMO is indeed capable of predicting the effectiveness of the photocatalytic products in question.
At the same time, they reveal a strong dependence of the developing flow and concentration fields inside the field site street
canyon configuration on most of the aforementioned factors with most notably the direction of the approaching wind.