Electrical conductivity of CNT/polysulfonamide composites

Carbon nanotube/polysulfonamide (CNT/PSA) composite spinning solutions with different CNTs contents were prepared using the physical blending method. The corresponding composite fibers were extruded through a set of wet spinning unit and the composite membranes were prepared using a digital spin-coating technique. The distribution of CNTs in PSA matrix and the crystalline structure of composite fibers were investigated by scanning electron microscope (SEM) and X-ray diffraction, respectively. The influences of CNTs on mechanical properties as well as electrical conductivity of PSA composites were also analyzed. In addition, the general effective media equation was chosen to explain the electrical conductivity behavior of the CNT/PSA composites. The experimental results showed that CNTs with low contents can be distributed evenly in PSA; the crystallization in PSA was promoted at low CNTs contents; the mechanical properties of composites can be improved significantly; and the electrical conductivity of composites increased obviously and the percolation threshold of the blending system was at about 3?wt%.     

不同粉体催化剂对甲基红光催化降解的研究

以钛酸四丁酯为原料,采用溶胶-凝胶法（Sol-Gel）制备纳米级锐钛矿二氧化钛粉末;利用激光粒度仪、AFM、XRD等方法分别对自制纳米TiO2、市售纳米TiO2和工业钛白粉等3种粉体进行表征。以典型的偶氮染料甲基红为目标污染物,测试以上3种粉体对甲基红无水乙醇溶液的降解情况。结果表明,自制产物为锐钛矿型TiO2纳米粉末,其平均粒径约为20nm;当甲基红的质量浓度为20mg／L,3种不同催化剂粉体粉末投加量为0．7g／L时,它们均具有光催化脱色性能。其中加入自制纳米TiO2粉末的甲基红溶液经紫外光照30min后．甲基红脱色率达到98％。     

Fe掺杂改性介孔TiO_2的制备及表征

为解决介孔TiO_2在光催化处理染料废水中可见光利用率低的问题,采用溶胶-凝胶法制备介孔Fe/TiO_2光催化剂.利用扫描电镜(SEM)、X射线衍射仪(XRD)、紫外-可见漫反射吸收光谱(UV-vis DRS)和N2/吸附-脱附等检测手段表征介孔材料的形貌结构和晶型组织;以亚甲基蓝染液(MB)为目标降解物,研究材料的光催化性能.结果表明:复合材料中TiO_2晶粒主要以锐钛矿的形式存在,平均粒径在5~30nm之间;Fe的掺入和NaOH处理提高了材料的比表面积,达到85.03m2/g,其吸收边带红移至687nm,禁带宽度减小到1.80eV.而且NaOH处理后的Fe/TiO_2光催化剂对亚甲基蓝染液的降解率远高于单一光催化剂的.     

Uric acid photo-oxidation assay: in vitro comparison of sunscreening agents

We present a new method to evaluate the photo-oxidative activity of sunscreening agents based on the photodynamic oxidation of uric acid. Uric acid was selected as the oxidant probe for its high reactivity to singlet oxygen and oxygen radicals, high sensitivity of detection using electrochemical (EC) techniques, low light absorptivity and high photochemical stability in the UVA/B region of interest, and stability to autoxidation. The method is demonstrated by the photodynamic oxidation of uric acid on co-irradiation with Rose Bengal, a highly efficient photosensitizing dye for the production of singlet oxygen (1O2). Using this assay we found that the relative photodynamic oxidation rates of UVB-absorbing sunscreens in 80% methanol on irradiation with >290 nm light decreased in the order 2-ethylhexyl 4-dimethylaminobenzoate (DMABA-2EH) > 2-ethylhexyl 4-methoxycinnamate (MCA-2EH) and the experimental sunscreens, 1-(1,1-dimethylethyl)-3-octanoyl-4,4-dimethyl- 1,4,5,6,-tetrahydropyridine (ICI-319) and 1-(2-methylpropyl)-3-propionyl-4,4-dimethyl-1,4,5,6-tetrahydropyridine (ICI-855). The relative photodynamic oxidation rates of UVA-absorbing sunscreens decreased in the order 4-tert-butyl-4'-methoxydibenzoylmethane (BMDBM) and 4-(2-propyl)benzophenone (PB) > 2-hydroxy-4'-methoxy-benzophenone (HMB) and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB). We have confirmed the photodynamic activity of DMABA-2EH for the production of singlet oxygen (1O2) using electron paramagnetic resonance (EPR) spectroscopy and the reagent 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TEMP). We failed to detect the photodynamic production of the oxyradicals, superoxide (O2.-) and hydroxyl radical (HO.) using N-tert-butyl-a-phenylnitrone (PBN) and 5,5-dimethyl-1-pyrrolidine-1-oxide (DMPO) as a result of photochemical interference caused by these spin-trapping reagents. The uric acid photo-oxidation assay was also used to compare the photodynamic reactivity of light-reflective, microfine oxides TiO2, ZnO and ZrO2 suspended in aqueous 80% methanol. All of the microfine oxides (uncoated) showed greater photodynamic reactivity in equimolar dispersion than did any of the organic UVA- and UVB-absorbing sunscreens in homogeneous solution. In this assay the photodynamic oxidation rates for the microfine oxides decreased in the order ZnO > TiO2 (anatase) > ZrO2 > TiO2 (rutile).     

二氧化钛/还原氧化石墨烯复合材料的制备及其光催化降解脱色性能

为比较二氧化钛/ 还原氧化石墨烯(TiO2 / rGO)复合材料和TiO2 的光催化降解脱色性能,以钛酸丁酯为前驱体,采用水热法制备了不同晶型的TiO2 和TiO2 / rGO 复合材料,借助紫外漫反射吸收光谱仪、傅里叶红外光谱仪、拉曼光谱仪、X 射线衍射仪和扫描电子显微镜等对TiO2 及其复合材料进行表征。分析混晶TiO2 和混晶TiO2 / rGO复合材料对活性红3BS 染料废水的降解脱色效果。结果表明：在150 ℃水热12 h,再经过650 ℃煅烧4 h 后,可制得锐钛矿型和金红石型同时存在的混晶TiO2 体系;在碱性条件下,于140 ℃水热72 h,不经过煅烧可制得较为纯净的板钛矿型TiO2;锐钛矿型和金红石型混晶结构TiO2 体系对染料有一定的降解脱色效果,混晶TiO2 / rGO 复合材料降解染料120 min 后,降解脱色率高达99%。     

纳米SnO2/TiO2/MMT制备及其光催化性能

比较不同制备方法制得的复合催化剂,由超临界干燥法制备的光催化剂具有粒径小,分散性好,光催化活性高等特点.以TiCl4为原料,采用溶胶凝胶法结合超临界流体干燥法(SCFD)制备了纳米级SnO2TiO2/MMT(蒙脱土)复合光催化剂.采用XRD和TEM对样品进行了表征.结果表明:TiO2以锐钛矿型形式存在,催化剂粒径在13～20 nm.以活性红X-3B溶液、活性橙K-NG和活性紫X-2R为反应模型,对所得催化剂的催化活性进行了评价,降解率分别达到99.9％、99.6％和99.5％,化剂循环利用时仍具有较高的催化活性.     

Electrochemical carbon nanotube filter oxidative performance as a function of surface chemistry

An electrochemical carbon nanotube filter has been reported to be effective for the removal and electrooxidation of aqueous chemicals and microorganisms. Here, we investigate how carbon nanotube (CNT) chemical surface treatments including calcination to remove amorphous carbon, acid treatment to remove internal residual metal oxide, formation of surficial oxy-functional groups, and addition of Sb-doped SnO(2) particles affect the electrooxidative filter performance. The various CNT samples are characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) and electrochemically evaluated by cyclic voltammetry, open circuit potential versus time analysis, and electrochemical impedance spectroscopy. Voltammetry results indicate that the near CNT surface pH is at least two units lower than the bulk pH. The electrooxidative performance of the various CNT samples is evaluated with 1 mM of methyl orange (MO) in 100 mM sodium sulfate at a flow rate of 1.5 mL min(-1). At both 2 and 3 V, the efficacy of electrochemical filtration is observed to be function of CNT surface chemistry. The samples with the greatest electrooxidation were the calcinated then HCl-treated CNTs, i.e., the CNTs with the most surficial sp(2)-bonded carbon, and the Sb-SnO(2)-coated CNTs, i.e., the CNTs with the most electrocatalytic surface area. At 3 V applied voltage, these CNT samples are able to oxidize 95% of the influent MO within the liquid residence time of <1.2 s. The broader applicability of electrochemical filtration is evaluated by challenging the C-CNT-HCl and C-CNT-HNO(3) networks with various organics including methylene blue, phenol, methanol, and formaldehyde. At 3 V applied voltage, both CNTs are able to degrade a fraction of all the organics with the extent organic degradation dependent on both CNT and organic properties. The C-CNT-HCl network generally had the better oxidative performance than the C-CNT-HNO(3) network with an exception being the positively charged methylene blue. The extent of MO degradation, steady-state current, anode potential, effluent pH, and back pressure are also measured as a function of applied voltage (1-3 V) and CNT surface chemistry. Mass spectrometry of electrochemical CNT filter effluent at 2 and 3 V is utilized to evaluate plausible electrooxidation products. Energy consumption as compared to state-of-the-art electrodes and strategies to tailor the CNT surface for a specific target molecule are discussed.     

Influence of polyethyleneimine graftings of multi-walled carbon nanotubes on their accumulation and elimination by and toxicity to Daphnia magna

Modifications of carbon nanotubes (CNTs) for different applications may change their physicochemical properties such as surface charge. Assessments of the extent to which such modifications influence CNT ecotoxicity, accumulation, and elimination behaviors are needed to understand potential environmental risks these variously modified nanoparticles may pose. We have modified carbon-14 labeled multi-walled carbon nanotubes (MWNTs) with polyethyleneimine (PEI) surface coatings to increase their aqueous stability and to give them positive, negative, or neutral surface charges. Uptake and elimination behaviors of Daphnia magna exposed to PEI-coated and acid-modified MWNTs at concentrations of approximately 25 and 250 μg/L were quantified. PEI surface coatings did not appear to substantially impact nanotube accumulation or elimination rates. Although the PEI-modified nanotubes exhibited enhanced stability in aqueous solutions, they appeared to aggregate in the guts of D. magna in a manner similar to acid-treated nanotubes. The MWNTs were almost entirely eliminated by Daphnia fed algae during a 48 h elimination experiment, whereas elimination without feeding was typically minimal. Finally, PEI coatings increased MWNT toxicities, though this trend corresponded to the size of the PEI coatings, not their surface charges.     

Fabrication of a TiO2-BDD heterojunction and its application as a photocatalyst for the simultaneous oxidation of an azo dye and reduction of Cr(VI)

A TiO2-boron doped diamond (TiO2-BDD) heterojunction was employed as a photocatalyst to simultaneously oxidize an azo dye C.I. reactive yellow 15 (RY15) and reduce hexavalent chromium (Cr(VI)). This heterojunction was fabricated first by depositing a BDD film on a Ti sheet in a hot filament chemical vapor deposition reactor, followed by covering a layer of TiO2 in a metal-organic chemical vapor deposition system. The morphology of this heterojunction was characterized by using a scanning electron microscope (SEM). X-ray diffraction (XRD), Raman spectroscopy, and current-voltage (I-V) measurement were used to characterize its structures. Additionally, the characterization of surface photovoltage showed that the TiO2-BDD heterojunction exhibited a higher photovoltage response and a better ability for charge separation than the photocatalyst of TiO2 directly deposited on a Ti sheet (TiO2-Ti). The photocatalytic experiments revealed that the kinetic constants for the oxidation of RY15 and the reduction of Cr(VI) were, respectively, increased by 85 and 71% when the photocatalyst of TiO2-Ti was replaced by the TiO2-BDD heterojunction. Meanwhile, a significant synergy was confirmed in the simultaneous oxidation of RY15 and reduction of Cr(VI). The enhanced photocatalytic ability of the TiO2-BDD composite could be attributed to the heterojunction. The possible photocatalytic mechanism was also discussed.     

Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis

Here we report the simultaneous Cr(VI) reduction and 4-chlorophenol (4-CP) oxidation in water under visible light (wavelength > 400 nm) using commercial Degussa P25 TiO2. This remarkable observation was attributed to a synergistic effect among TiO2, Cr(VI), and 4-CP. It is well known that TiO2 alone cannot remove either 4-CP or Cr(VI) efficiently under visible light. Moreover, the interaction between Cr(VI) and 4-CP is minimal if not negligible. However, we found that the combination of TiO2, Cr(VI), and 4-CP together can enable efficient Cr(VI) reduction and 4-CP oxidation under visible light. The specific roles of the three ingredients in the synergistic system were studied parametrically. It was found that optimal concentrations of Cr(VI) and TiO2 exist for the Cr(VI) reduction and 4-CP oxidation. Cr(VI) was compared experimentally with other metals such as Cu(ll), Fe(lll), Mn(IV), Ce(IV), and V(V). Among all these metal ions, only Cr(VI) promotes the photocatalytic oxidation of 4-CP. The amount of 4-CP removed was directly related to the initial concentration of Cr(VI). The system was also tested with four other chemicals (aniline, salicylic acid, formic acid, and diethyl phosphoramidate). We found that the same phenomenon occurred for organics containing acid and/or phenolic groups. Cr(VI) was reduced at the same time as the organic chemicals being oxidized during photoreaction under visible light. The synergistic effect was also found with pure anatase TiO2 and rutile TiO2. This study demonstrates a possible economical way for environmental cleanup under visible light.     

Directed synthesis of hierarchical nanostructured TiO2 catalysts and their morphology-dependent photocatalysis for phenol degradation

Nanostructured TiO2 with different hierarchical morphologies were synthesized via a warmly hydrothermal route. The properties of the products were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption, UV-vis spectroscopy, etc. Two of the products, TiO2 1D nanorods (one-dimensional rutile TiO2 nanorods) and TiO2 3D0D microspheres (three-dimensional anatase TiO2 nanoparticle-assembled microspheres) exhibited superior photocatalytic effects on phenol degradation under UV illumination, compared with TiO2 3D1D microspheres (three-dimensional rutile TiO2 nanorods-assembled microspheres). Moreover, TiO2 3D0D was superior to TiO2 1D, as indicated by a 30% higher mineralization of dissolved phenol. Dihydroxybenze, 4,4'-dihydroxybiphenyl, benzoquinone, maleic anhydride, etc. were identified as the degradation intermediates. The excellent catalytic effect was attributed to the structural features of TiO2 1D nanorods and TiO2 3D0D microspheres, that is, a larger amount of surface active sites and a higher band gap energy resulted in more efficient decomposition of organic contaminants.     

Photocatalytic degradation characteristics of different organic compounds at TiO2 nanoporous film electrodes with mixed anatase/ rutile phases

Nanoporous TiO2 film electrodes with a mixed anatase/ rutile phase were prepared by dip-coating TiO2 nanoparticle colloid onto Indium Tin Oxide (ITO) conducting glass substrates and a subsequent calcination process at 700 degrees C for 16 h. The photocatalytic oxidation of a wide range of organic compounds has been studied using the photoelectrochemical method under the conditions that the photohole capturing step controls the overall photocatalytic processes. The characteristics of the mixed anatase/ rutile phase TiO2 film electrodes were compared with pure anatase phase TiO2 film electrodes to identify the key differences between them. The results revealed that different organic compounds, despite their difference in chemical entities, can be stoichiometrically mineralized at the mixed-phase TiO2 electrode under diffusion-controlled conditions, which is in great contrast to the situation at the pure anatase phase TiO2 electrode. The exceptional ability of the mixed-phase TiO2 electrodes for mineralization of organic compounds and their remarkable resistance to the inhibition by aromatic compounds at higher concentration has been explained by the synergetic effect of the rutile and anatase phases. For this type of mixed phase electrodes, upon absorption of UV light, the electron-transfer pathway from anatase phase to rutile phase facilitates the separation of photoelectron and photohole, extending the lifetime of the photoelectron and photohole.     

Selective photocatalytic oxidation of NH3 to N2 on platinized TiO2 in water

Selective photocatalytic oxidation of NH3 to N2 is proposed as a new treatment method for controlling the levels of ammonia in water. The photocatalytic oxidation of ammonia on naked and metallized TiO2 in water saturated with air, nitrogen, or NO2 gas was investigated. While the slow photocatalytic oxidation of NH3 to NO2-/NO3- is the only pathway for decomposition of NH3 on naked TiO2 and Au/TiO2, a new pathway, that of selective oxidation of ammonia to dinitrogen, opens up on Pt/TiO2. The formation of dinitrogen from the oxidation of 15NH3 was confirmed by mass spectrometric detection of 15N2. The photocatalytic conversion of NH3 to N2 greatly increases when the Pt/TiO2 suspension is saturated with NO2 gas, whereas NO2 itself shows little reactivity with naked TiO2 and Au/TiO2. Over 80% of the total nitrogen available in ammonia (0.1 mM) is converted into N2 within 40 min illumination of the N2O-saturated Pt/TiO2 suspension. The ability of N2O to accept the conduction band electrons of Pt/TiO2 was verified by photoelectrochemical measurements. NO2 reductively decomposes to generate OH radicals on Pt/TiO2; the rate of ammonia degradation in the NO2-saturated Pt/TiO2 suspension significantly decreases in the presence of excess tert-butyl alcohol, an OH radical scavenger. The presence of Pt deposits on the TiO2 particles changes the photocatalytic pathway of ammonia conversion by both enhancing OH radical production from NO2 and stabilizing intermediate NHx (x=0, 1, 2) species to facilitate their recombination into N2.     

Improvement in photocatalytic activity of TiO2 under visible irradiation through addition of N-TiO2

This work is focused on improvement in photocatalytic activity of anatase-TiO2 (a-TiO2) photocatalyst under visible-light irradiation by adding nitrogen-doped TiO2 (N-TiO2) for depression of recombination rate between photoexcited electron and hole. The composites (a-TiO2/N-TiO2) were prepared by grinding in ethanol solvent at 200 rpm for 15 min with change in weight ratio of N-TiO2. In addition to the characterizations by X-ray diffraction and X-ray photoelectron spectroscopy, measurements of existing singlet oxygen by chemiluminescens method and photocatalytic activity by using NO(x) decomposition were conducted. The increases in singlet oxygen and photocatalytic activity have been observed and the phenomena are discussed based on the efficient prevention of recombination between photoexcited electron and hole within the prepared composite.     

Photocatalytic oxidation mechanism of As(III) on TiO2: unique role of As(III) as a charge recombinant species

Using TiO(2) photocatalyst, arsenite, As(III), can be rapidly oxidized to arsenate, As(V), which is less toxic and less mobile in the aquatic environment. Therefore, the TiO(2)/UV process can be employed as an efficient pretreatment method for arsenic contaminated water. Since we first reported in 2002 that the superoxide (or hydroperoxyl radical) plays the role of main oxidant of As(III) in the TiO(2)/UV process, there has been much debate over the true identity of the major photooxidant among superoxides, holes, and OH radicals. The key issue is centered on why the much stronger OH radicals cannot oxidize As(III), and it has been proposed that the unique role of As(III) as an external charge recombination center on the UV-excited TiO(2) particle is responsible for this eccentric mechanism. Although the proposed mechanism has been supported by many experimental evidences, doubts on it were not clearly removed. In this study, we provided direct and undisputed evidence to support the role of As(III) in the charge recombination dynamics using time-resolved transient absorption spectroscopy. The presence of As(III) indeed mediated the charge recombination in TiO(2). Under this condition, the role of the OH radical is suppressed because of the null cycle, and the weaker oxidant, superoxide, should prevail. The role of the superoxide has been previously doubted on the basis of the observation that the addition of excess formic acid (hole scavenger that should enhance the production of superoxides) inhibited the photocatalytic oxidation of As(III). However, this study proved that this was due to the photogeneration of reducing radicals (HCO(2)·) that recycle As(V)/As(IV) back to As(III). It was also demonstrated that the 4-chlorophenol/TiO(2) system under visible light that cannot generate neither OH radicals nor valence band holes converted As(III) to As(V) through the superoxide pathway.     

Adsorption of phenolic compounds by carbon nanotubes: role of aromaticity and substitution of hydroxyl groups

With increasing production and application of carbon nanotubes (CNTs), it becomes necessary to understand the interaction between CNTs and aromatic compounds, an important group of organic contaminants and structural components of large organic molecules in biological systems. However, so far few experimental studies have been conducted to systematically investigate the sorption mechanism of polar aromatics to CNTs. Therefore, cyclohexanol, phenol, catechol, pyrogallol, 2-phenylphenol, 1-naphthol, and naphthalene were selected to investigate the role of aromatic structure and -OH substitution in the polar aromatics-CNTs system. Sorption affinity of these compounds by CNTs increased with increasing number of aromatic rings, with an order of cyclohexanol < phenol < 2-phenylphenol < 1-naphthol, and was greatly enhanced by -OH substitution, with an order of phenol (1 -OH) < catechol (2 -OH) < pyrogallol(3-OH). Four possible solute-sorbent interactions, i.e., hydrophobic effect, electrostatic interaction, hydrogen bonding, and pi-pi bonds, were discussed to addressthe underlying mechanism of the enhanced sorption affinity by -OH substitution. It was evident that electron-donating substitution on the aromatic rings strengthened the pi-pi interaction between the aromatics and CNTs and thus the adsorption affinity. These results will advance the understanding of the sorption behavior of CNTs in the environmental systems.     

Potential release pathways, environmental fate, and ecological risks of carbon nanotubes

Carbon nanotubes (CNTs) are currently incorporated into various consumer products, and numerous new applications and products containing CNTs are expected in the future. The potential for negative effects caused by CNT release into the environment is a prominent concern and numerous research projects have investigated possible environmental release pathways, fate, and toxicity. However, this expanding body of literature has not yet been systematically reviewed. Our objective is to critically review this literature to identify emerging trends as well as persistent knowledge gaps on these topics. Specifically, we examine the release of CNTs from polymeric products, removal in wastewater treatment systems, transport through surface and subsurface media, aggregation behaviors, interactions with soil and sediment particles, potential transformations and degradation, and their potential ecotoxicity in soil, sediment, and aquatic ecosystems. One major limitation in the current literature is quantifying CNT masses in relevant media (polymers, tissues, soils, and sediments). Important new directions include developing mechanistic models for CNT release from composites and understanding CNT transport in more complex and environmentally realistic systems such as heteroaggregation with natural colloids and transport of nanoparticles in a range of soils.     

Photocatalytic degradation of pesticide pyridaben. 3. In surfactant/TiO2 aqueous dispersions

The effective TiO2 photocatalytic degradation of pyridaben in an acetronitrile/water dispersion has been investigated in previous work, but could not be achieved in the case of real waters. In this paper, photocatalytic degradation of pyridaben on TiO2 particles under UV light (lambda> 360 nm) illumination in surfactant CTAB (cetyltrimethyl ammonium bromide) aqueous dispersions was studied. 1H NMR was used to determine quantitative information about the adsorption mode of pyridaben in CTAB micelles. The results showed that the upfield 1H shifts were largest for long chain protons of CTAB, indicating that the hydrophobic aromatic rings were primarily located in this region. Adsorption models on TiO2 surface were thus proposed. The reaction rates decreased with the increase of pH value, which can be attributed to the surface charge variations of pyridaben adsorbed onto TiO2 particles. The adsorption isotherms at different pH values confirmed that preadsorption on the surface of TiO2 particles was prerequisite for efficient degradation. Furthermore, an oxidation reagent such as H2O2 was added to the photocatalytic system, which may act as an alternative electron acceptor and result in a notably enhanced rate of pollutant destruction. On the basis of intermediates identified by GC/MS, a degradation pathway was proposed.     

Photocatalytic oxidation of arsenite in TiO2 suspension: kinetics and mechanisms

Arsenite [As(III)] and arsenate [As(V)] are highly toxic aquatic contaminants. Since arsenite is more mobile in natural waters and less efficiently removed in adsorption/coagulation processes than arsenate, the oxidation of arsenite to arsenate is desirable in water treatment. We performed the photocatalytic oxidation of arsenite in aqueous TiO2 suspension and investigated the effects of pH, dissolved oxygen, humic acid (HA), and ferric ions on the kinetics and mechanisms of arsenite oxidation. Arsenite oxidation in UV-illuminated TiO2 suspension was highly efficient in the presence of dissolved oxygen. Homogeneous photooxidation of arsenite in the absence of TiO2 was negligibly slow. Since the addition of excess tert-butyl alcohol (OH radical scavenger) did not reduce the rate of arsenite oxidation, the OH radicals should not be responsible for As(III) oxidation. The addition of HA increased both arsenite oxidation and H2O2 production at pH 3 under illumination, which could be ascribed to the enhanced superoxide generation through sensitization. We propose that the superoxide is the main oxidant of arsenite in the TiO2/UV process. The addition of ferric ions also significantly enhanced the arsenite photooxidation. In this case, the addition of tert-butyl alcohol reduced the arsenite oxidation rate, which implied thatthe OH radical-mediated oxidation path was operative in the presence of ferric ions. Since both Fe3+ and HA that were often found with the arsenic in groundwater were beneficial to the photocatalytic oxidation of arsenite, the TiO2/UV process could be a viable pretreatment method. This can be as simple as exposing the arsenic-polluted water in a TiO2-coated trough to sunlight.     

TiO2/蒙脱土复合光催化材料的制备与结构性能

以钛酸丁酯为原料,采用溶胶-凝胶法制备TiO2光催化材料,研究了水、硝酸用量和反应温度对TiO2性能的影响.以蒙脱土为复合基质制备TiO2/MMT复合材料,采用XRD和FT-IR表征了产物的结构,并考察了该材料对亚甲基蓝的降解行为.结果表明:锐钛矿型TiO2已插层柱化到蒙脱土层间,形成分子级别的TiO2支柱,钛的掺入导致原土层间域内离子性质发生变化,从而使TiO2/MMT复合材料的光降解效率远远高于纯TiO2粉体,并形成吸附-光降解协同作用,在降解40 min后对亚甲基蓝溶液的降解率可达到95%.