Titanium dioxide-mediated heterogeneous photocatalytic degradation of terbufos: parameter study and reaction pathways

The photocatalytic degradation of terbufos in aqueous suspensions was investigated by using titanium dioxide (TiO(2)) as a photocatalyst. About 99% of terbufos was degraded after UV irradiation for 90 min. Factors such as pH of the system, TiO(2) dosage, and presence of anions were found to influence the degradation rate. Photodegradation of terbufos by TiO(2)/UV exhibited pseudo-first-order reaction kinetics, and a reaction quantum yield of 0.289. The electrical energy consumption per order of magnitude for photocatalytic degradation of terbufos was calculated and showed that a moderated efficiency (E(EO)=71 kWh/(m(3)order)) was obtained in TiO(2)/UV process. To obtain a better understanding of the mechanistic details of this TiO(2)-assisted photodegradation of terbufos with UV irradiation, the intermediates of the processes were separated, identified, and characterized by the solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) technique. The probable photodegradation pathways were proposed and discussed.     

射频磁控共溅射制备光催化Ag-TiO2薄膜

采用射频磁控共溅射法制备Ag-TiO2复合薄膜,通过控制Ag靶的溅射时间可调节Ag与TiO2的比例.所制备的Ag-TiO2薄膜为锐钛矿结构.通过紫外光照降解亚甲基蓝溶液和循环伏安法研究Ag-TiO2薄膜光催化及光电化学特性.实验结果表明:掺1.5% Ag的Ag-TiO2薄膜在紫外光照射下能增强亚甲基蓝溶液的降解并得到更大的光生电流.这种光催化的增强主要是由于光生电子-空穴对的复合被抑制的结果.     

Microwave assisted rapid and complete degradation of atrazine using TiO(2) nanotube photocatalyst suspensions

A technology, microwave-assisted photocatalysis on TiO(2) nanotubes, which can be applied to degrade atrazine rapidly and completely, was investigated. TiO(2) nanotubes were prepared, and confirmed by XRD, TEM and ESR. Microwave-assisted photocatalytic degradation of atrazine in aqueous solution was investigated. The result indicates that atrazine is completely degraded in 5min and the mineralization efficiency is 98.5% in 20min, which is obviously more efficient than that by the traditional photocatalytic degradation methods. It may be attributed to the intense UV radiation generated by electrodeless discharge lamps under microwave irradiation, the increased number of OH, additional defect sites on TiO(2) under the irradiation of microwave and larger specific surface area of TiO(2) nanotubes which could adsorb more organic substances to degrade than TiO(2) nanoparticles. Along with the degradation of atrazine, the concentrations of Cl(-) and NO(3)(-) increase gradually. In 20min [Cl(-)] and [NO(3)(-)] are 3, 27.8mg/L, respectively, which are close to their stoichiometric values. The major intermediates of atrazine were identified by HPLC/MS and possible degradation pathways of atrazine in microwave-assisted photocatalysis on TiO(2) nanotubes were proposed.     

Photocatalytic degradation of aqueous propoxur solution using TiO2 and Hbeta zeolite-supported TiO2

Photocatalytic activity of TiO2 and zeolites supported TiO2 were investigated using propoxur as a model pollutant. Hbeta, HY and H-ZSM-5 zeolites were examined as supports for TiO2. Hbeta was chosen as the TiO2 support based on the adsorption capacity of propoxur on these zeolites (Hbeta>HY=H-ZSM-5). TiO2/Hbeta photocatalysts with different wt.% were prepared and characterized by XRD, FT-IR and BET surface area. The progress of photocatalytic degradation of aqueous propoxur solution using TiO2 (Degussa P-25) and TiO2 supported on Hbeta zeolite was monitored using TOC analyzer, HPLC and UV-vis spectrophotometer. The degradation of propoxur was systematically studied by varying the experimental parameters in order to achieve maximum degradation efficiency. The initial rate of degradation with TiO2/Hbeta was higher than with bare TiO2. TOC results revealed that TiO2 requires 600min for complete mineralization of propoxur whereas TiO2/Hbeta requires only 480min. TiO2/Hbeta showed enhanced photodegradation due to its high adsorption capacity on which the pollutant molecules are pooled closely and hence degraded effectively.     

TiO2光催化降解2,4,6-三硝基间苯二酚机理初探

在多相光催化反应体系中,使用所制备的催化剂TiO2,光催化降解2,4,6-三硝基间苯二酚,初步探讨其降解机理.反应过程中,2,4,6-三硝基间苯二酚开环反应迅速发生,目标污染物被降解为小分子有机物直至矿化;目标污染物上的硝基被·OH攻击、脱落,在光催化反应前期生成N-2,当光催化反应完全时,N-2被硝化,目标污染物中的N元素以N-3、 NH 4形式存在.NH 4的存在意味着降解过程同时存在还原反应.     

太阳光下Cr~(3+)掺杂TiO_2复合微粒光催化性能研究

利用酸催化的溶胶一凝胶法成功地合成了一系列不同CP3+掺杂量(x=0.01%～10%)的TiO2复合光催化剂(Cd3+/TiO2).在太阳光条件下,以亚甲基蓝溶液的光催化降解对复合材料的光催化性能进行了表征,并考察了催化剂投加量、Cr3+掺杂量和溶液pH值等因素对光催化降解反应的影响.结果表明,亚甲基蓝溶液在复合微粒上的光催化降解反应遵循Langmuir-Hinshelwood动力学模型,在催化剂投加量为lg/L、Cr3+掺入量为0.3%和pH=7时,Cr3+/TiO2复合微粒光催化活性达最佳,测得表观反应速率常数 K为7.27×10-3 rag(L·min)-1,t1/2为95min,反应4h后亚甲基蓝的降解率可达79%,与纯的TiO2相比较,反应速率提高了2倍,降解率提高了20%.中性或碱性条件下有利于亚甲基蓝溶液的光催化降解.     

Optimized photocatalytic degradation of Alcian Blue 8 GX in the presence of TiO2 suspensions

The photocatalytic degradation of Alcian Blue 8 GX, a cationic copper phthalocyanine dye, has been investigated in aqueous suspensions containing the commercial catalyst TiO(2) P-25. The photodegradation of the organic molecule follows approximately a pseudo-first kinetic order, according to the Langmuir-Hinshelwood model. The effect of catalyst concentration, pH of the initial solution and the H(2)O(2) concentration upon the reaction rate was ascertained. It was shown that the photocatalytic degradation reaction can be mathematically described as a function of parameters such as pH, H(2)O(2) concentration and irradiation time, being modeled by the use of the response surface methodology. Optimized values for oxidizing agent, concentration, pH and UV exposure time for the studied system were determined.     

Surface modification of nanometer size TiO2 with salicylic acid for photocatalytic degradation of 4-nitrophenol

The efficiency of photocatalytic reactions was limited by the wide band-gap of TiO(2) and the high degree of electron-hole recombination inherent in photocatalytic process, as well as by the limited adsorption capability of photocatalysts. In order to increase the overall efficiency, the surface of nanometer size TiO(2) was simply and fast modified by chemical adsorption in saturated solution of salicylic acid. A stable, light yellow surface complex was formed quickly, which has obvious absorption in the region from 320 to 420 nm. Through surface modification, the adsorption efficiency of 4-nitrophenol by TiO(2) was enhanced from 42 to 84%. The photocatalytic efficiency was tested on the degradation of 4-nitrophenol. The influences of catalyst and its dosage, pH value, and 4-nitrophenol concentration on the degradation were investigated. Under such photodegradation conditions as initial pH 4.0, 4-nitrophenol 5 mg l(-1), catalyst 100 mg, and irradiation time 160 min with 160 W high-pressure mercury lamp, the degradation efficiency of 4-nitrophenol by TiO(2) was increased from 39.5 to 79.3% after surface modification, and furthermore, the degradation efficiency could be enhanced to 91.1% if the concentration of 4-nitrophenol was not more than 1 mg l(-1). Compared with the pure TiO(2), surface modification led not only to improve the surface coverage of 4-nitrophenol, but also to increase the light utilization. Both of these factors were crucial for the photocatalytic activity of heterogeneous photocatalysis, especially for photodegradation of aromatic pollutants.     

Effects of mineral tourmaline particles on the photocatalytic activity of TiO2 thin films

Titania composite thin films (T/TiO2) containing tourmaline particles were prepared by a sol-gel method, using alkoxide solutions as precursor. The tourmaline particles and thin films were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and so on. The effects of tourmaline on the photocatalytic activity of TiO2 were measured with methyl orange as an objective photodegradation substance. The results showed that the photocatalytic degradation of methyl orange conformed to the first-order kinetic equation and the composite thin films had better photocatalytic activity due to the cooperation of polarity and the far infrared emission of tourmaline. The T/TiO2 thin films including 0.5 wt% tourmaline exhibited better photocatalytic activity when heat-treated at 250 degrees C for 3 h, than pure TiO2 thin films under the ultraviolet irradiation.     

Photodegradation of 17beta-estradiol in water by UV-vis/Fe(III)/H2O2 system

Photodegradation of 17beta-estradiol (E2) in aqueous solutions by UV-vis/Fe(III)/H(2)O(2) system, namely Photo-Fenton system, was preliminarily investigated under a 250 W metal halide lamp (lambda > or = 313 nm). The influences of initial pH value, initial concentration of H(2)O(2) and E2 on photodegradation efficiency of E2 were discussed and the amount of CO(2) produced by the photodegradation reaction was measured. The results indicates that E2 could be decomposed efficiently in UV-vis/Fe(III)/H(2)O(2) system. Under the condition of 10.0 micromol L(-1) Fe(III), 1000 micromol L(-1) H(2)O(2) and pH 3.0, the degradation efficiency of 18.4 micromol L(-1) E2 reach 75.2% after the irradiation of 160 min. Over the range of pH 3.0-6.0, the higher acidity, the higher the degradation efficiency of E2 and initial reaction rate are. The degradation efficiency of E2 increases with increasing of initial concentration of H(2)O(2) and with decreasing of initial concentration of E2. The E2 mineralization efficiency increases with reaction time but the mineralization efficiency was lower. When the initial concentration of Fe(III) and H(2)O(2) were 10.0 and 1000 micromol L(-1), respectively, the mineralization efficiency of 18.4 micromol L(-1) E2 solution with pH 3.0 was only 21.6% after 160 min irradiation. It is suggested that the mineralization occurred probably only at aromatic ring.     

Degradation of aqueous solutions of camphor by heterogeneous photocatalysis

In this study the photocatalytic degradation of aqueous solutions of camphor was investigated by using TiO2 and ZnO photocatalysts. In the presence of artificial UV-light the highly photosensitive camphor was almost totally degraded after reaction times of 60 min. However, under these conditions the mineralization degree was lower than 25%. In the presence of semiconductors the degradation was complete after a treatment time of about 30 min. Moreover, the mineralization was considerably greater, mainly with the use of TiO2 (> 80% at reaction time of 60 min). Heterogeneous photocatalytic processes applied in the presence of solar radiation show a promising degradation capability. TiO2-based processes afforded mineralization degrees of about 90% after a reaction time of 120 min, when the system was assisted by aeration.     

Oxidation of triclosan by ferrate: reaction kinetics, products identification and toxicity evaluation

The Crystal Violet (CV) dye represented one of the major triphenylmethane dyes used in textile-processing and some other industrial processes. Various metals doped titanium dioxide (TiO(2)) photocatalysts have been studied intensively for the photodegradation of dye in wastewater treatment. In order to understand the mechanistic detail of the metal dosage on the activities enhancement of the TiO(2) based photocatalyst, this study investigated the CV photodegradation reactions under UV light irradiation using a Pt modified TiO(2) photocatalyst. The results showed that Pt-TiO(2) with 5.8% (W/W) Pt dosage yielded optimum photocatalytic activity. Also the effect of pH value on the CV degradation was well assessed for their product distributions. The degradation products and intermediates were separated and characterized by HPLC-ESI-MS and GC-MS techniques. The results indicated that both the N-de-methylation reaction and the oxidative cleavage reaction of conjugated chromophore structure occurred, but with significantly different intermediates distribution implying that Pt doped TiO(2) facilitate different degradation pathways compared to the P25-TiO(2) system.     

Photocatalytic degradation of 2,4-dinitrophenol

Contamination of the food supply from agricultural waste is an increasing concern worldwide. Numerous hazardous chemicals enter the environment from various industrial sources daily. Many of these pollutants, including 2,4-dinitrophenol (2,4-DNP), are water soluble, toxic, and not easily biodegradable. The solar photocatalytic degradation of 2,4-DNP was investigated in a solution of titanium dioxide (TiO(2)) that was prepared to be an optically clear aqueous solution of nanosized particles of TiO(2). In order to achieve optimal efficiency of the photodegradation, the effects of light intensity and pH were conducted. All experiments were carried out in a batch mode. At a pH of 8, maximum removal of 70% of 2,4-DNP was achieved within 7h of irradiation time. The nearly homogeneous solution of 5.8nm TiO(2) particles, size determined by XDS, were very effective in the photocatalytic degradation of 2,4-DNP.     

二氧化钛催化光降解聚对苯二甲酸乙二酯的研究

利用原位聚合法合成PET/TiO2复合材料.通过分析PET/TiO2复合薄膜在紫外光降解过程中的质量和表面形态的变化情况,研究了锐钛矿型二氧化钛对PET光氧化降解性能的影响.结果说明,在试验范围内,在253.9nm的紫外光照射的光降解实验中,锐钛矿型TiO2的含量越高,PET/TiO2复合薄膜的质量损失率就越高;同时,紫外光照射试样288h之后,由SEM照片发现复合材料表面损伤程度也随着TiO2含量的升高而越发严重.这说明,锐钛矿型TiO2对PET的光氧化降解具有催化作用,而且含量越高催化作用就越强.     

Photocatalytic degradation of methylene blue in TiO2 aqueous suspensions using microwave powered electrodeless discharge lamps

Photocatalytic degradation of methylene blue (MB) in TiO(2) aqueous suspensions using microwave (MW) powered electrodeless discharge lamps (EDLs) was studied. MB of initial concentration 100 mg/l was mainly decomposed in the process of photocatalytic degradation using EDLs (PCD/EDLs) after 15 min of irradiation. The corresponding mineralization efficiency was 45%. The influence of factors as EDLs, solution volume and TiO(2) catalyst dosage on the decomposition of MB in the PCD/EDLs process was also investigated. The optimal decomposition efficiency was observed when EDLs-4 (four 10 mm x 50 mm EDLs), solution volume of 50 ml and TiO(2) catalyst dosage of 1-4 g/l were used in the study. The PCD/EDLs process was promising in treating MB polluted water.     

Photocatalytic activity of TiO2 doped with boron and vanadium

Boron (B)- and vanadium (V)-doped TiO(2) photocatalysts were synthesized using modified sol-gel reaction processes and characterized by X-ray diffraction (XRD), Raman spectroscopy and N(2) physisorption (BET). The photocatalytic activities were evaluated by monitoring the degradation of methylene blue (MB). The results showed that the materials possess high surface area. The addition of B favored the transformation of anatase to rutile, while in the presence of V, anatase was the only phase detected. The MB degradation on V-doped TiO(2) was significantly affected by the preparation method. In fact while the presence of V in the bulk did not influence strongly the photoreactivity under visible irradiation, an increase of surface V doping lead to improved photodegradation of MB. The degradation of MB dye indicated that the photocatalytic activities of TiO(2) increased as the boron doping increased, with high conversion efficiency for 9mol% B doping.     

Modeling electrowinning process in an expanded bed electrode

In this paper, the photocatalytic degradation of methamidophos, an organophosphorous pesticide, was investigated in aqueous solution by using TiO(2) as a photocatalyst. The degradation was studied under different conditions such as the amount of the photocatalyst, illumination time, pH of the system, reaction temperature, initial concentration, electron acceptors, metal ions and presence of anions. The results showed that the photocatalytic degradation of methamidophos was strongly influenced by these parameters. The best conditions for the photocatalytic degradation of methamidophos were obtained. The optimum amount of the photocatalyst used is 12.0g/L. The photodegradation efficiency of methamidophos increases with the increase of the illumination time. Alkaline media are favorable for the photocatalytic degradation of methamidophos. The degradation efficiency is enhanced by increasing reaction temperature, and the photodegradation efficiency decreases with the increase in the initial concentration of methamidophos. The photodegradation efficiency of methamidophos is accelerated by adding a small amount of H(2)O(2), K(2)S(2)O(8), KBrO(3), Fe(3+) or Cu(2+). There are no obvious effects on the reactions with the addition of a small amount of Na(+), K(+), Mg(2+), Ca(2+), Zn(2+), Co(2+) and Ni(2+) or adding trace amount of SO(4)(2-), Cl(-), Br(-). The possible roles of the additives on the reactions and the possible mechanisms of effect were also discussed.     

Fabrication characterization and activity of a solar light driven photocatalyst: cerium doped TiO2 magnetic nanofibers

A novel magnetic separable composite photocatalytic nanofiber consisting of TiO2 as the major phase, CeO(2-y) and CoFe2O4 as the dopant phase was prepared by sol-gel method and electrospinning technique, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectrum (UV-vis DRS) and vibrating sample magnetometer (VSM). The photocatalytic activity of the resultant CoFe2O4-TiO2 and CeO(2-y)/CoFe2O4-TiO2 nanofibers was evaluated by photodegradation of methylene blue (MB) in an aqueous solution under xenon lamp (the irradiation spectrum energy distribution is similar to sunlight) irradiation in a photochemical reactor. The results showed that the dopant of Ce could affect the absorbance ability and photo-response range. The sample containing 1.0 wt% CeO(2-y) exhibited the highest degradation with 35% for MB under simulate solar light irradiation. Furthermore, the as-synthesized composite photocatalytic nanofibers could be separated easily by an external magnetic field, thus it might hold potential for application in wastewater treatment.     

Heterogeneous photocatalytic degradation of monochlorobenzene in water

This investigation evaluated the photocatalytic degradation of monochlorobenzene (MCB) in an aqueous TiO(2) suspension. In accordance with the experimental results, the degradation of MCB was a function of the initial substrate concentration, incident light intensity, and TiO(2) dosage. However, the solution pH had insignificant effect on the degradation efficiency. The heterogeneous photocatalytic degradation of MCB followed the Langmuir-Hinshelwood kinetics. The adsorption coefficient of MCB (K) and the observed degradation rate constant (k) were calculated as 13.4 mM(-1) and 0.0054 mM min(-1), respectively. In addition, a 0.255 dependency of the initial degradation rate on the light intensity revealed the considerable adverse effect of e(-)-h(+) pair recombination. Both mineralization and dechlorination occurred during the photocatalytic degradation of MCB. Under the operating condition of initial MCB concentration of 0.1mM, light intensity of 5.68 microEinsteins(-1), TiO(2) dosage of 1.0 g L(-1), and solution pH of 7, about 93.7% of MCB was mineralized after 240 min of irradiation. Nevertheless, 64.3% of the stoichiometric amount of Cl(-) ions was released into the bulk solution. The simulation results derived from the X-ray photoelectron spectroscopy (XPS) analysis was suggested that the interaction between Cl(-) ions and TiO(2) surface tended to lower the released amount of Cl(-) ions.     

Photocatalytic degradation of Congo Red by hydrothermally synthesized nanocrystalline TiO2 and identification of degradation products by LC-MS

Degradation of Congo Red (CR) dye in aqueous solutions was investigated by means of photocatalysis of TiO2 which was hydrothermally synthesized at 200 degrees C in 2 h, in anatase phase with 8 nm crystallite size. Efficiency of TiO2 in photocatalytic degradation under visible irradiation was studied by investigating the effects of amount of TiO2, irradiation time, initial CR concentration and pH. It was found that complete decolorization is achieved within 30 min of irradiation. Effects of nitrate and sulphate ions and humic acid on the degradation were also tested. The results were compared with Degussa P-25 TiO2 at the same degradation conditions. Degradation products were detected using LC-MS technique. The probable pathways for the formation of degradation products were proposed.