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1.
Laboratory and field filtration experiments were conducted to study the effectiveness of As(V) removal for five types of adsorbent media. The media included activated alumina (AA), modified activated alumina (MAA), granular ferric hydroxide (GFH), granular ferric oxide (GFO), and granular titanium dioxide (TiO 2). In laboratory batch and column experiments, the synthetic challenge water was used to evaluate the effectiveness for five adsorbents. The results of the batch experiments showed that the As(V) adsorption decreased as follows at pH 6.5: TiO 2 > GFO > GFH > MAA > AA. At pH 8.5, however, As(V) removal decreased in the following order: GFO = TiO 2 > GFH > MAA > AA. In column experiments, at pH 6.5, the adsorbed As(V) for adsorbents followed the order: TiO 2 > GFO > GFH, whereas at pH 8.5 the order became: GFO = TiO 2 > GFH when the challenge water containing 50 μg/L of As(V) was used. Field filtration experiments were carried out in parallel at a wellhead in New Jersey. Before the effluent arsenic concentration increased to 10 μg/L, approximately 58,000 and 41,500 bed volumes of groundwater containing an average of 47 μg/L of As(V) were treated by the filter system packed with GFO and TiO 2, respectively. The As(V) adsorption decreased in the following sequence: GFO > TiO 2 > GFH > MAA > AA. Filtration results demonstrated that GFO and TiO 2 adsorbents could be used as media in small community filtration systems for As(V) removal. 相似文献
2.
In this study, we report the effects of pH and divalent cations on the adsorption of arsenate (As(V)) by titanium dioxide
(TiO 2) nanoparticles. The extent of As(V) adsorption on TiO 2 decreased with increasing pH due to the decrease of positively charged binding sites on the TiO 2 surface. The Langmuir maximum uptake capacity at pH 4 is about three times higher than that at pH 7. Here we show that the
relatively low As(V) uptake at circumneutral pH could be substantially enhanced by the addition of common divalent cations
such as magnesium and calcium. At a concentration of approximately 7 mM, magnesium and calcium increased the extent of As(V)
adsorption from 2.1 to 6.5 and 7.7 mg As(V)/g TiO 2, respectively. 相似文献
3.
We studied the removal of nitrogen oxides pollutants via TiO 2 Degussa P25 powder by photocatalysis. Parameters such as mass of catalyst, geometric irradiated surface, catalyst morphology, and thermal treatment were tested to explain the photocatalytic concentration decrease of nitrogen oxides. According to our working conditions, the conversion rates increased until an optimal value of the TiO 2 weight, 35% of NO concentration and around 20% of NOx, was decomposed by the photocatalysis. The NOx removal increased proportionally with the irradiated geometric surface. The structural transformation of anatase to rutile performed by thermal treatment involved the decrease of the photocatalytic activity. 相似文献
4.
作为一种新兴的纳米材料,羟基多壁碳纳米管(OH-MWCNTs)可能与其他污染物在水环境中共存,并进一步影响它们的毒性、输移和归趋。因此,评价碳纳米管存在下砷的毒性变化需要得到更多的关注。该试验探索了在不同pH值条件下,OH-MWCNTs诱导砷(As(III)和As(V))对水生生物大型蚤的毒性变化的潜在机制。发现了H 2AsO 3-和H 2AsO 4-是对大型蚤毒性最大的As(III)和As(V)。比较As(III)和As(V)的结果,发现pH值是影响砷毒性最重要的因素。此外,OH-MWCNTs影响砷对大型蚤毒性的结果表明,OH-MWCNTs的存在可以提高砷的毒性。通过吸附实验进一步研究了砷与OH-MWCNTs的相互作用。OH-MWCNTs 对As(V)吸附容量高于As(III)。总而言之, OH-MWCNTs对某些形态砷的吸附是解释砷毒性增强的可靠证据。
精选自Xinghao Wang, Ruijuan Qu, Ahmed A. Allam, Jamaan Ajarem, Zhongbo Wei, Zuoyao Wang. Impact of carbon nanotubes on the toxicity of inorganic arsenic [As(III) and As(V)] to Daphnia magna: the role of the certain arsenic species. Environmental Toxicology and Chemistry: Volume 35, Issue 7, pages 1852–1859, July 2016.
DOI: 10.1002/etc.3340
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3340/full 相似文献
5.
The results of a study of photocatalytic degradation of phenol using aqueous oxygenated TiO 2 (anatase) suspensions in a batch Pyrex photoreactor are reported. The influence on the photodegradation rate of various parameters as pH, phenol and TiO 2 content, oxygen partial pressure, anions present in the dispersions was investigated. A complete oxidation of phenol was observed. Intermediate compounds, catechol and quinone, were detected. It was observed that the photodegradation also proceeded with sunlight radiation. A mechanistic and kinetic model, which accounts for the results obtained, is given. Likely reasons for inactivity of the rutile modification for this reaction are also given. 相似文献
6.
Titanium dioxide is coated on the surface of MCM-41 wafer through the plasma enhanced chemical vapor deposition (PECVD) method using titanium isopropoxide (TTIP) as a precursor. Annealing temperature is a key factor affecting crystal phase of titanium dioxide. It will transform an amorphous structure to a polycrystalline structure by increasing temperature. The optimum anatase phase of TiO 2 which can acquire the best methanol conversion under UV-light irradiation is obtained under an annealing temperature of 700°C for 2 h, substrate temperature of 500°C, 70 mL·min ?1 of oxygen flow rate, and 100W of plasma power. In addition, the films are composed of an anatase-rutile mixed phase, and the ratio of anatase to rutile varies with substrate temperature and oxygen flow rate. The particle sizes of titanium dioxide are between 30.3 nm and 59.9 nm by the calculation of Scherrer equation. Under the reaction conditions of 116.8 mg·L -1 methanol, 2.9 mg·L ?1 moisture, and 75°C of reaction temperature, the best conversion of methanol with UV-light is 48.2% by using the anatase-rutile (91.3/8.7) mixed phase TiO 2 in a batch reactor for 60 min. While under fluorescent light irradiation, the best photoactivity appears by using the anatase-rutile (55.4/44.6) mixed phase TiO 2 with a conversion of 40.0%. 相似文献
7.
The aim of the plesent investigation was to study the effect of SiO 2 addition on the thermal deactivation of V 2O 5/WO 3/TiO 2 catalysts used for NOx pollution abatement. The results suggest that the degradation of the catalytic properties is strongly correlated to the structural ageing which is, in turn, mainly related to the anatase–rutile phase transformation and to the WO 3 phase segregation. The addition of SiO 2 strongly influences the temperature at which these phenomena occur. In fact, it was found that the introduction of this oxide stabilizes the material, retarding the collapse of surface area, and increases the temperature of the anatase to rutile phase transition. 相似文献
8.
A southern Italian area that is characterized by large outcrops of rocks that are rich in titanium oxide (TiO2) phases were investigated to determine the mineralogical risk induced by the natural dispersion of TiO2 minerals. Rock, sediment and surface water samples were collected to determine the physicochemical and mineralogical factors (i.e., size distribution, morphology and alteration) indicative of potential TiO2 toxicity. X-ray diffraction data suggested that titanium oxides were present as rutile and anatase. Scanning electron microscopy images showed elongated TiO2 morphologies; fibres were found as either isolated or embedded/enclosed in flake-like phyllosilicates. The concentration of fibres in stream water ranged from 1.7 to 4.6 million fibres per litre. The highest fibre amounts in the sediments were in the <8-µm fraction, while single fibres were primarily concentrated in the <2-µm fraction. The results indicate that titanium oxide minerals represent a natural source of environmental risk and that the geomineralogical characterization of rich TiO2 areas is indispensable for understanding their geoavailability, dispersion and distribution. 相似文献
9.
为了探讨超富集植物蜈蚣草在处理高砷地下水方面的可行性,研究了水培条件下砷的浓度、形态和碳酸氢盐(HCO-3)对超富集植物蜈蚣草吸收砷的影响。实验中使用了浓度为0.1~100mg·L-1的As(III)和As(V)溶液。HCO-3处理中,HCO-3浓度范围为0.5~20mmol·L-1,As(III)或As(V)的浓度为5mg·L-1。结果表明,在水培条件下,蜈蚣草具有明显的耐高砷特征。当介质砷含量高达100mg·L-1时,砷的去除率可达到80%,且对As(III)的吸收效率高于As(V)。植物体内砷形态研究表明,蜈蚣草体内2种形态砷的含量与外源砷形态有一定的关系,As(V)处理条件下,植物体中的As(V)比例较As(III)处理高。高浓度的HCO-3(20mmol·L-1)处理对蜈蚣草地上部分生物量没有明显影响,但是抑制了地下部分的生长,并且对砷的吸收表现出明显的抑制作用。 相似文献
10.
大同盆地是典型的高砷地下水分布区。利用从地方性砷中毒严重病区山阴县采集的高砷地下水样品,用稀释培养法实验研究了外加砷源对地下水中微生物数量的影响;同时基于生物学可培养法和16S rDNA序列比对法,选取代表性高砷水样,研究了耐砷菌的种群特征。结果表明,外加砷源对地下水中微生物数量影响显著,高浓度砷会抑制大部分微生物生长,使微生物数量减少;低浓度砷对微生物生长具有一定促进作用。通过多次分离、纯化从3个不同砷含量地下水样中分离到多株砷抗性菌,经鉴定属于主要为 Bacillus、 Pseudomonas、 Paenibacillus、 Aeromonas、 Enterobacter5个属。从RDP(Ribosomal Database Project)分析显示3个水样可培养微生物组成不同,都有生存能力强能够耐低浓度NaAsO 2的Bacillales,优势耐砷菌是γ-proteobacteria,其中 Enterbacter具有耐高浓度NaAsO 2的能力。 相似文献
11.
Biochar derived from food waste was modified with Fe to enhance its adsorption capacity for As(III), which is the most toxic form of As. The synthesis of Fe-impregnated food waste biochar (Fe-FWB) was optimized using response surface methodology (RSM), and the pyrolysis time (1.0, 2.5, and 4.0 h), temperature (300, 450, and 600 °C), and Fe concentration (0.1, 0.3, and 0.5 M) were set as independent variables. The pyrolysis temperature and Fe concentration significantly influenced the As(III) removal, but the effect of pyrolysis time was insignificant. The optimum conditions for the synthesis of Fe-FWB were 1 h and 300 °C with a 0.42-M Fe concentration. Both physical and chemical properties of the optimized Fe-FWB were studied. They were also used for kinetic, equilibrium, thermodynamic, pH, and competing anion studies. Kinetic adsorption experiments demonstrated that the pseudo-second-order model had a superior fit for As(III) adsorption than the pseudo-first-order model. The maximum adsorption capacity derived from the Langmuir model was 119.5 mg/g, which surpassed that of other adsorbents published in the literature. Maximum As(III) adsorption occurred at an elevated pH in the range from 3 to 11 owing to the presence of As(III) as H2AsO3? above a pH of 9.2. A slight reduction in As(III) adsorption was observed in the existence of bicarbonate, hydrogen phosphate, nitrate, and sulfate even at a high concentration of 10 mM. This study demonstrates that aqueous solutions can be treated using Fe-FWB, which is an affordable and readily available resource for As(III) removal. 相似文献
12.
Adsorption of vanadate(V) from aqueous solution onto industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide was investigated.
HCl treated Fe(III)/Cr(III) hydroxide was found to be more efficient for the removal of vanadate(V) compared to untreated
adsorbent. The adsorption follows second-order kinetics. Langmuir and Freundlich isotherms have been studied. The Langmuir
adsorption capacity ( Q
0) of the treated and untreated adsorbents was found to be 11.43 and 4.67 mg g −1, respectively. Thermodynamic parameters showed that the adsorption process was spontaneous and endothermic in the temperature
range 32–60°C. Maximum adsorption was found at system pH 4.0. The adsorption mechanism was predominantly ion exchange. Effect
of other anions such as phosphate, selenite, molybdate, nitrate, chloride, and sulfate on adsorption of vanadium has been
examined. 相似文献
13.
We report a facile approach for preparing mesoporous boron-doped TiO 2 materials by combining the sol?Cgel process with the dehydration of glucose. Specifically a high surface carbon material was formed by dehydration of glucose, then used as template. This material and the TiO 2 dry gel were calcinated to produce porous TiO 2. The as-synthesized boron-doped TiO 2 was in pure anatase crystallite phase with high surface area. X-ray photoelectron spectroscopy (XPS) results showed that boron was incorporated into the anatase TiO 2 lattice to form TiO 2?xB x. The absorption spectra of TiO 2?xB x extended into the visible region to 460?nm. The TiO 2?xB x exhibited much higher photocatalytic activity on phenol degradation than pure TiO 2. It showed that the phenol degradation by-products of TiO 2?xB x were different from that of pure TiO 2. Mechanism of the photocatalytic degradation of phenol at TiO 2?xB x was also proposed. 相似文献
14.
Nanocrystalline TiO 2 films were prepared by magnetron sputtering technique on stainless-steel substrates. The as-deposited TiO 2 thin films were in anatase structure with smooth surface morphology. Decomposition of methyl orange was used to measure the photoelectrocatalytic activity. The degradation rate of methyl orange increased with externally applied potential. To further accelerate the photocatalytic reaction, a novel method was employed by applying an external electric field in the mid-frequency domain. The fastest photocatalytic degradation rate of methyl orange was obtained when the frequency was maintained at 20 kHz with an external anodic bias at 3.0 V. 相似文献
15.
Hydro-electric plasma technology in the presence of TiO 2 catalyst used to treat 2,4-dinitrophenol (2,4-DNP) simulated wastewater is reported. The catalytic activity of TiO 2 prepared by ammonia precipitation was greater than the activity of the TiO 2 prepared by NaOH precipitation. The presence of chloride ions during the preparation process of TiO 2 had a large negative effect on the catalytic activity. The catalytic activity of TiO 2 calcined at 673 K was significantly higher than the activity of the TiO 2 that was calcined at higher and lower temperatures. After being calcined at 673 K, TiO 2 was mainly in the anatase phase and degraded 81% of the 2,4-DNP after 10 min of treatment. 相似文献
16.
Multi-walled carbon nanotubes (MWCNTs)/TiO 2 composite photocatalysts with high photoactivity were prepared by sol-gel process and further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), and UV-vis absorption spectra. Compared to pure TiO 2, the combination of MWCNTs with titania could cause a significant absorption shift toward the visible region. The photocatalytic performances of the MWCNTs/TiO 2 composite catalysts were evaluated for the decomposition of Reactive light yellow K-6G (K-6G) and Mordant black 7 (MB 7) azo dyes solution under solar light irradiation. The results showed that the addition of MWCNTs enhanced the adsorption and photocatalytic activity of TiO 2 for the degradation of azo dyes K-6G and MB 7. The effect of MWCNTs content, catalyst dosage, pH, and initial dye concentration were examined as operational parameters. The kinetics of photocatalytic degradation of two dyes was found to follow a pseudo-first-order rate law. The photocatalyst was used for seven cycles with photocatalytic degradation efficiency still higher than 98%. A plausible mechanism is also proposed and discussed on the basis of experimental results. 相似文献
17.
Fe-Mn binary oxide incorporated into porous diatomite (FMBO-diatomite) was prepared in situ and regenerated in a fixed-bed column for arsenite [As(III)] and arsenate [As(V)] removal. Four consecutive adsorption cycles were operated under the following conditions: Initial arsenic concentration of 0.1 mg·L -1, empty bed contact time of 5 min, and pH 7.0. About 3000, 3300, 3800, and 4500 bed volumes of eligible effluent (arsenic concentration≤0.01 mg·L -1) were obtained in four As(III) adsorption cycles; while about 2000, 2300, 2500, and 3100 bed volumes of eligible effluent were obtained in four As(V) adsorption cycles. The dissection results of FMBO-diatomite fixed-bed exhibited that small amounts of manganese and iron were transferred from the top of the fixed-bed to the bottom of the fixed-bed during As(III) removal process. Compared to the extremely low concentration of iron (<0.01 mg·L -1), the fluctuation concentration of Mn 2+ in effluent of the As(III) removal column was in a range of 0.01–0.08 mg·L -1. The release of manganese suggested that manganese oxides played an important role in As(III) oxidation. Determined with the US EPA toxicity characteristic leaching procedure (TCLP), the leaching risk of As(III) on exhausted FMBO-diatomite was lower than that of As(V). 相似文献
18.
Degradation and toxicity reduction of perfluorooctanoic acid (PFOA) were investigated using TiO 2 adsorption, vacuum ultraviolet (VUV) photolysis, and VUV/TiO 2 photocatalysis in acidic and basic aqueous solutions. Chemical analyses of PFOA and its selected by-products and an acute toxicity assessment using the luminescent bacteria Vibrio fischeri (Microtox®) were conducted during and after the various treatment methods. PFOA was found to be best treated by VUV/TiO 2 at pH 4 with HClO 4, as illustrated by the almost complete degradation of PFOA within 360?min and rapid removal of acute microbial toxicity within 60?min. This difference in the efficiency may be attributed to the strong oxidation effectiveness of the radical species generated in acidic media and the electron scavenger effect of the addition of HClO 4 in VUV/TiO 2 photocatalysis. In addition, the proposed method could effectively decompose other perfluorocarboxylic acid (PFCA) species (C 3–C 7 perfluoroalkyl groups) if the initial intermediates formed were longer-chain species that degraded stepwise into shorter-chain compounds by VUV photolysis and VUV/TiO 2 photocatalysis in acidic and basic aqueous solutions. 相似文献
19.
In this study, the adsorption characteristics of As(III) and As(V) from water and wastewater using polyacrylamide-grafted banana stem with quaternary ammonium functionality (PGBS-AE) were investigated. Infrared spectroscopic, and thermogravimetric analyses were performed to affirm the polymer grafting, functionality, morphology, and thermal stability. Batch experiments were carried out to understand the effect of contact time, concentration, pH, adsorbent dose, and temperature of the solution for the adsorption of As(III) and As(V) onto PGBS-AE. Equilibrium was achieved within 1 h and the optimum pH was found to be 9.0 and 3.0 for As(III) and As(V), respectively. Isotherm studies showed that the Langmuir equation fits best. Maximum adsorption capacities of 50 and 5.5?g?kg ?1 were obtained for As(III) and As(V) at 30°C. The endothermic nature of adsorption was evident as the adsorption efficiency increased with temperature. The thermodynamic parameters were evaluated to explain the feasibility of adsorption and to predict the nature of adsorption. The competence of the adsorbent for practical purposes was also analyzed by treating with a fertilizer industry effluent sample. Studies pertaining to adsorbent regeneration and readsorption of As(III) and As(V) were carried out for four consecutive cycles. 相似文献
20.
Adsorption of arsenic (V) by natural zeolitic tuff, modified with iron (III), was investigated. Also, the iron (III) adsorption
characteristics by natural zeolitic tuff was evaluated. It was determined that iron (III) adsorption by starting zeolitic
tuff was best represented by the Freundlich type of isotherm, having correlation coefficient ( r
2) of 0.990. Arsenic (V) adsorption by iron (III)-modified zeolitic tuff followed a nonlinear type of isotherm. The best fit
of the experimental data was obtained using the Langmuir–Freundlich model ( r
2 = 0.99), with the estimated maximum of arsenic (V) adsorption to iron (III)-modified zeolitic tuff of 1.55 mg/g. 相似文献
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