Simultaneous decontamination of hexavalent chromium and methyl tert-butyl ether by UV/TiO2 process

Hexavalent chromium and methyl tert-butyl ether (MTBE) are two important environmental pollutants. Simultaneous decontamination of Cr(VI) and MTBE was studied by UV/TiO2 process. The influences of pH and the concentrations of pollutants on the kinetics of the photocatalytic reactions were evaluated. Dark adsorption tests showed that the acidic pH favored the adsorption of Cr(VI) while neutral pH favored the adsorption of MTBE. Under UV irradiation, Cr(VI) reduction was observed in Cr(VI)/TiO2 system, and MTBE oxidation was observed in MTBE/TiO2 system. The system containing Cr(VI) and MTBE by UV/TiO2 process demonstrated the synergistic effect between oxidation of MTBE and reduction of Cr(VI). The results demonstrated that two pollutants Cr(VI) and MTBE could be eliminated simultaneously by UV/TiO2 process. tert-Butyl formate, tert-butyl alcohol and acetone were identified as primary degradation products of MTBE by gas chromatography-mass spectrometry in the degradation of MTBE by UV/TiO2 process.     

Photocatalytic production of hydrogen in single component and mixture systems of electron donors and monitoring adsorption of donors by in situ infrared spectroscopy

The photocatalytic production of hydrogen using aqueous Pt/TiO2 suspension has been investigated in single component and mixture systems of electron donors (pollutants). The reaction systems consisted of oxalic acid, formic acid and formaldehyde, respectively. The adsorption of these donors on TiO2 was also monitored by in situ attenuated total reflection infrared spectroscopy (ATRIR). In the single component systems, the efficiency order of electron donors is as follows: H2C2O4 > HCOOH > HCHO. The order is consistent with the order of adsorption affinity of the electron donors on TiO2 determined by ATRIR, which suggests a link between the strength of surface interaction and the efficiency of photocatalytic hydrogen evolution. In the binary mixture systems, competitive inhibition kinetics is observed. When a donor adsorbed strongly on TiO2 in a state of saturated adsorption in a binary system, the overall rate of the hydrogen evolution is consistent with that of decomposition of the donor, and the system can be treated as a single component system.     

Characteristics of MnO2 catalytic ozonation of sulfosalicylic acid and propionic acid in water

The characteristics of different types of MnO₂ catalytic ozonation of sulfosalicylic acid (SSal) and propionic acid (PPA) have been investigated in this paper. The experimental results show the dependence of catalytic activity of MnO₂ on organic compounds and the pH of solutions, but it is independent on the type of MnO₂. For example, three types of MnO₂ have not any catalytic activity when ozonation of PPA under the condition of this experiment. All MnO₂ catalytic ozonation of SSal at pH=1.0 have a greater total organic carbon removal than ozonation alone has, however, at pH=6.8 and 8.5, catalytic efficiency is not observed. Furthermore, the batch experimental results indicate that there are no direct relationship between the activity of metal oxide catalytic decomposition of ozone and that of its catalytic degradation of organic compounds.     

Enhanced bioaccumulation of cadmium in carp in the presence of titanium dioxide nanoparticles

In this study adsorption of Cd onto TiO2 nanoparticles and natural sediment particles (SP) were studied and the facilitated transports of Cd into carp by TiO2 nanoparticles and SP were assessed by bioaccumulation tests exposing carp (Cyprinus carpio) to Cd contaminated water in the presence of TiO2 and SP respectively. The results show that TiO2 nanoparticles had a significantly stronger adsorption capacity for Cd than SP. The presence of SP did not have significant influence on the accumulation of Cd in carp during the 25 d of exposure. However, the presence of TiO2 nanoparticles greatly enhanced the accumulation of Cd in carp. After 25 d of exposure Cd concentration in carp increased by 146%, and the value was 22.3 and 9.07 microg/g, respectively. And there is a positive correlation between Cd and TiO2 concentration. Considerable Cd and TiO2 accumulated in viscera and gills of the fish.     

Enhancement of photocatalytic oxidation of humic acid in TiO2 suspensions by increasing cation strength

This study aimed at improving the photocatalytic (PC) oxidation of humic acids (HA) in TiO2 suspensions by adding cationic ion such as calcium or magnesium. A set of tests was first conducted in the dark to study the adsorption of HA onto TiO2 in suspensions at different pH and calcium concentrations. The experiment demonstrated that the adsorption of HA onto the TiO2 particles was either pH-dependent or calcium strength-dependent due to electrostatic interaction and calcium ion bridging. The photodegradation of HA in the presence of UV irradiation was investigated as a function of pH and the concentration of calcium and magnesium ions. The results showed that the adsorption behavior between HA and TiO2 played a very important role during the PC oxidation process. The PC oxidation could be enhanced at neutral pH by increasing the cation strength. The kinetics of HA PC degradation in TiO2 suspensions with different initial concentrations was also studied using the Langmuir-Hinshelwood model.     

Photocatalytic oxidation of toxic organohalides with TiO2/UV: the effects of humic substances and organic mixtures

TiO2/UV photocatalytic oxidation of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), 1,2,3-trichlorobenzene and 4-chlorophenol were examined in aqueous solution in the presence of humic substances and organic mixtures to study if the degradation rates were affected. Both commercial and natural humic substances were observed to retard the photodegradation rates, with a greater effect from the natural humic substances. Acetonitrile and isopropanol also caused significant retardation of 4-chlorophenol photodegradation. The overall retardation can be attributed to the combination of light attenuation, inhibition and competition effects. Moreover, the TiO2/UV system favors the decomposition of compounds that have stronger adsorption onto the TiO2 surface. To engineer effective treatment facilities that use the TiO2/UV system for the treatment of toxic substances in wastewater, the methodology must allow for concerns about adventitious species which are present.     

纳米TiO_2光催化降解硝基酚类污染物动力学及机理的研究

采用纳米TiO2(P25)粉末作为催化剂,研究了几种典型硝基取代酚在TiO2/UV悬浮体系下的光催化降解.研究表明,这些化合物的降解过程符合Langmuir-Hinshelwood动力学方程,其表观速率常数(kapp)的大小为:2-氨基-4硝基酚(2-A,4-NP)>4-硝基酚(4-NP)>2-硝基酚(2-NP)>3-硝基酚(3-NP)>2,4-二硝基酚(2,4-DNP)>2,4,6-三硝基酚(2,4,6-TNP),而吸附平衡常数(KL)却与Kapp成反比.苯环上取代基的种类和数日对有机物光催化降解活性有很大的影响,硝基的加入降低了光催化活性,并且kapp与Hammett常数(σ)具有较好的线性关系.     

负载TiO2的活性炭纤维改性电极电吸附除氟

采用溶胶-凝胶法制备TiO2凝胶,将TiO2凝胶涂覆在活性炭纤维表面并进行热处理制备改性电极(TiO2/ACF),利用扫描电子显微镜(SEM)、X射线衍射光谱仪(XRD)、比表面和孔隙度分析仪对负载前后电极的表面特性进行表征,并探讨了其对NaF溶液的电吸附效果。结果表明,电极负载TiO2后表面变得粗糙,比表面积和总孔体积减小,而介孔体积和平均孔径增大。此外,表面的TiO2同时以金红石和锐钛矿的晶型存在。电吸附实验结果显示,加电可以提高吸附容量,而且电压、pH和初始氟离子浓度均对电吸附容量产生影响:电压增大,吸附容量增加,当施加电压为2 V时,电吸附容量为1.03 mg/g,比开路电位时提高40%;pH可以通过影响氟离子在溶液中的存在形态和TiO2/ACF电极表面的羟基基团对电吸附容量产生影响;初始氟离子浓度升高,电极吸附容量增大,但是去除率降低。在处理初始氟离子浓度为4 mg/L的NaF溶液时,在2 V电压、中性pH和12 h的吸附时间下,改性ACF为电极的吸附量为1.32 mg/g。     

MWNTs及MWNTs/TiO_2对水中1,2,3-三氯苯的吸附特性研究

采用批量平衡实验,对比研究了多壁碳纳米管（MWNTs）及多壁碳纳米管/二氧化钛复合材料（MWNTs/TiO2）对水中1,2,3-三氯苯的吸附特性。结果表明,在相同条件下,MWNTs及MWNTs/TiO2对1,2,3-三氯苯（1,2,3-TCB）的最大吸附量分别为71.8 mg/g和3.05 mg/g,pH值在2~11之间变化时,两者的吸附均不受pH值变化的影响。2种吸附剂的吸附过程均符合拟二级动力学方程,但MWNTs/TiO2对1,2,3-TCB的吸附速率常数为0.4159 g/（mg.m in）,约为MWNTs的50倍左右,说明MWNTs/TiO2具有更强的吸附驱动力。1,2,3-TCB在2种吸附剂上的吸附过程均可用Freund lich吸附等温线来描述,其热力学参数吉布斯自由能△G0均为负、标准焓变△H0与熵变△S0均为正表明,MWNTs及MWNTs/TiO2吸附1,2,3-TCB过程为自发吸热反应。与MWNTs相比,MWNTs/TiO2具有可光催化再生的优点,能用于被污染水体的原位修复。     

Photocatalytic degradation of the herbicide erioglaucine in the presence of nanosized titanium dioxide: comparison and modeling of reaction kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm-1 and 0.984 ppm min-1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.     

Fine route for an efficient removal of 2,4-dichlorophenoxyacetic acid (2,4-D) by zeolite-supported TiO2

Zeolites HY, Hbeta and HZSM-5 with different physico-chemical properties were chosen as support for TiO2 to illustrate their adsorption, dispersion and electronic structure in photocatalysis. The extent of TiO2 loading was monitored by XRD and BET surface area measurements. The adsorption capacity of HY zeolite was found to be high and hence chosen for further modification to continue the investigation. Photodegradation kinetics were carried out with 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. The extent of 2,4-D degradation on TiO2/HY loading revealed the importance of adsorption in photocatalysis. Mineralisation studies on all three zeolites with 1 wt.% TiO2 loading demonstrated the good dispersion properties of TiO2/HY. Its photocatalytic activity was found to be excellent with formulated 2,4-D. Comparison of relative photonic efficiencies demonstrated that supported photocatalysts exhibited higher activity than some of the commercial photocatalysts. The high activity of supported TiO2 is due to synergistic effects of improved adsorption of 2,4-D and efficient delocalisation of photogenerated electrons by zeolite support.     

纳米TiO2花式分层微球的合成及其对Pb（Ⅱ）的吸附性能

利用仿生合成的方法,以甘氨酸为模板剂、钛酸正四丁酯作钛源,水热合成一种新型纳米TiO2花式微球,并对其进行了表征。通过考察pH值、温度和Pb（Ⅱ）溶液的初始浓度对吸附效果的影响,研究了TiO2花式微球对水溶液中Pb（Ⅱ）的吸附性能及其吸附动力学特性。结果表明,纳米TiO2花式微球直径约2Ixm,平均孔径约56nm,比表面积约是270．3m。／g;当pH值为4．0时TiO2花式微球对溶液中Pb（Ⅱ）吸附率达到最高,210min时基本达到吸附平衡,20、30和40qE的最大吸附量分别为75．64、76．34和77．52mg／g。吸附过程遵循准二级速率方程,与Langmuir等温式拟合更好。     

亚甲基蓝表面修饰纳米TiO2降解造纸废水动力学

以亚甲基蓝(MB)作为表面修饰剂,采用简单的化学吸附法制备亚甲基蓝表面修饰的纳米TiO2光催化剂(TiO2-MB)。经表面修饰后,TiO2-MB光催化剂波长响应范围红移至可见光区575 nm处。探讨了光催化剂量、光照时间和溶液pH值对TiO2-MB光催化降解造纸废水的影响;研究了纳米TiO2-MB对造纸废水的暗吸附规律和光降解性能。结果表明:纳米TiO2-MB对造纸废水的吸附规律都较好地符合Langmuir和Freundlich吸附等温模型,属于吸热反应;光催化降解动力学符合Langmuir-Hinshelwood动力学模型。在160 W高压汞灯光照80 min,3.0 g/L纳米TiO2-MB光催化降解pH=2.0的造纸废水(COD:2 069.8 mg/L),COD去除率可达94.7%,处理效果远高于避光条件下。光催化剂经8次使用仍具有较高的催化活性。     

Removal of Cr(VI) and humic acid by using TiO2 photocatalysis

The removal efficiencies of Cr(VI) and HA, using a TiO(2)-mediated photocatalytic process, were investigated with variations in the pH, TiO(2) dosage and Cr(VI)/HA ratio. During the photocatalytic reaction, the total removal of Cr(VI) occurred through adsorption onto TiO(2), as well as its reduction to Cr(III). However, oxidation and adsorption were identified as important removal processes for the treatment of HA. Due to the anionic type adsorption onto TiO(2) and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while that of HA increased with increasing pH. The TiO(2) dosage was also an important parameter for the removal of Cr(VI). As the TiO(2) dosage was increased to 2.5 g l(-1), the removal of Cr(VI) was continuously enhanced, but decreased at dosages above 3 g l(-1) due to the increased blockage of the incident UV light used for the photocatalytic reaction. The removal of Cr(VI) was greatly enhanced when the system contained both HA and Cr(VI) compared to Cr(VI) alone. Also, the removal of HA was greatly enhanced when the system contained both HA and Cr(VI) compared to HA alone. The removal of Cr(VI) was continuously enhanced as the HA concentration gradually increased; however, no further increase was observed above 20 mg l(-1) HA due to the increased absorption of the UV light. This result supports that the photocatalytic reaction, with illuminated TiO(2), could be applied to more effectively treat wastewater containing both Cr(VI) and HA than that containing a single species only.     

Effect of adsorbents coated with titanium dioxide on the photocatalytic degradation of propoxur

Photocatalytic oxidation of pesticides in aqueous media irradiated by UV light is a rapidly growing field of research. Therefore, the treatment technology for degradation of propoxur (an insecticide) using titanium dioxide coated on the supports such as activated carbon, zeolite, brick, quartz and glass beads, was performed in this research. Results show that GAC/TiO2 is the best complexing agent for oxidizing propoxur because of its adsorption properities. The others follow the sequence: plain TiO2 > glass beads > zeolite > brick > quartz. The degradation rate of propoxur with plain TiO2 is higher than that with TiO2/GAC complexing agent. But the mineralization rate of propoxur with plain TiO2 is lower than that with TiO2/GAC complexing agent. However, it can be concluded that using GAC as the support can improve the photocatalytic efficiency.     

Synergy of ozonation and photocatalysis to mineralize low concentration 2,4-dichlorophenoxyacetic acid in aqueous solution

Concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) may affect its degradation kinetics in advanced oxidation systems, and combinations of two or more systems can be more effective for its mineralization at low concentration levels. Degradations and mineralizations of 0.045mM 2,4-D using O(3), O(3)/UV, UV/TiO(2) and O(3)/UV/TiO(2) systems were compared, and influence of reaction temperature on the mineralization in O(3)/UV/TiO(2) system was investigated. 2,4-D degradations by O(3), O(3)/UV and UV/TiO(2) systems were similar to the results of earlier investigations with higher 2,4-D concentrations. The degradations and total organic carbon (TOC) removals in the four systems were well described by the first-order reaction kinetics. The degradation and removal were greatly enhanced in O(3)/UV/TiO(2) system, and further enhancements were observed with larger O(3) supplies. The enhancements were attributed to hydroxyl radical (()OH) generation from more than one reaction pathway. The degradation and removal in O(3)/UV/TiO(2) system were very efficient with reaction temperature fixed at 20 degrees C. It was suspected that reaction temperature might have influenced ()OH generation in the system, which needs further attention.     

MWNTs及MWNTs/TiO2对水中1,2,3-三氯苯的吸附特性研究

采用批量平衡实验,对比研究了多壁碳纳米管（MWNTs）及多壁碳纳米管/二氧化钛复合材料（MWNTs/TiO₂）对水中1,2,3-三氯苯的吸附特性。结果表明,在相同条件下,MWNTs及MWNTs/TiO₂对1,2,3-三氯苯（1,2,3-TCB）的最大吸附量分别为71.8 mg/g和3.05 mg/g,pH值在2~11之间变化时,两者的吸附均不受pH值变化的影响。2种吸附剂的吸附过程均符合拟二级动力学方程,但MWNTs/TiO₂对1,2,3-TCB的吸附速率常数为0.4159 g/(mg·min),约为MWNTs的50倍左右,说明MWNTs/TiO₂具有更强的吸附驱动力。1,2,3-TCB在2种吸附剂上的吸附过程均可用Freundlich吸附等温线来描述,其热力学参数吉布斯自由能△G⁰均为负、标准焓变△H⁰与熵变△S⁰均为正表明,MWNTs及MWNTs/TiO₂吸附1,2,3-TCB过程为自发吸热反应。与MWNTs相比,MWNTs/TiO₂具有可光催化再生的优点,能用于被污染水体的原位修复。     

Titanium dioxide mediated photocatalytic degradation of monochlorobenzene in aqueous phase

The reaction sequence for the photocatalytic degradation of monochlorobenzene (MCB) in UV/TiO2 process, including substrate adsorption, degradation, and mineralization, was studied. The theoretical maximum quantity of MCB that could be adsorbed onto TiO2 surface in aqueous phase was 0.18+/-0.04 micromol m(-2) of TiO2. In accordance with the upper limit of the relative surface coverage of MCB molecules to surface hydroxyls of TiO2 was around 2.2%, the water molecules as the major adjacent species near TiO2 surface would compete with MCB molecules. Increasing the initial substrate concentration to an appropriate value or enhancing the affinity between the MCB and the TiO2 surface by adjusting the solution pH would promote the photocatalytic degradation. Experimental results revealed that the neutral medium was beneficial for the degradation of MCB. In comparison, the mineralization was most improved at acidic condition. Generally, 90% of the total organic carbon (TOC) was mineralized after 240 min illumination time in the examined pH range except solution pH 11. The suppressed mineralization of MCB at solution pH 11 was ascribed to the lack of adsorption. A simplified 2-step consecutive kinetic model was used to simulate the mineralization.     

Modification of carbon-coated TiO2 by iron to increase adsorptivity and photoactivity for phenol

Carbon-coated TiO(2) modified by iron, were prepared from TiO(2) of anatase structure and PET modified by FeC(2)O(4). Catalysts were prepared by mixing powders of TiO(2) and modified PET and heating at different temperatures, from 400 to 800 degrees C under flow of Ar gas. High adsorption of phenol was observed on the catalyst heated at 400 degrees C, confirmed by FT-IR analysis. On this catalyst, fast rate of phenol decomposition was achieved by addition of small amount of H(2)O(2) to the reaction mixture. Phenol decomposition proceeded mainly through the direct oxidation of phenol species adsorbed on the catalyst surface due to the photo-Fenton reaction. Iron-modified carbon-coated TiO(2) catalysts heated at 500-800 degrees C showed almost no phenol adsorption or oxidation.     

Removal of arsenic from groundwater by granular titanium dioxide adsorbent

A novel granular titanium dioxide (TiO2) was evaluated for the removal of arsenic from groundwater. Laboratory experiments were carried out to investigate the adsorption capacity of the adsorbent and the effect of anions on arsenic removal. Batch experimental results showed that more arsenate [As(V)] was adsorbed on TiO2 than arsenite [As(III)] in US groundwater at pH 7.0. The adsorption capacities for As(V) and As(III) were 41.4 and 32.4 mgg(-1) TiO2, respectively. However, the adsorbent had a similar adsorption capacity for As(V) and As(III) (approximately 40 mgg(-1)) when simulated Bangladesh groundwater was used. Silica (20 mgl(-1)) and phosphate (5.8 mgl(-1)) had no obvious effect on the removal of As(V) and As(III) by TiO2 at neutral pH. Point-of-entry (POE) filters containing 3 l of the granular adsorbent were tested for the removal of arsenic from groundwater in central New Jersey, USA. Groundwater was continuously passed through the filters at an empty bed contact time (EBCT) of 3 min. Approximately 45,000 bed volumes of groundwater containing an average of 39 microgl(-1) of As(V) was treated by the POE filter before the effluent arsenic concentration increased to 10 microgl(-1). The total treated water volumes per weight of adsorbent were about 60,000 l per 1 kg of adsorbent. The field filtration results demonstrated that the granular TiO2 adsorbent was very effective for the removal of arsenic in groundwater.