Photodegradation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans: direct photolysis and photocatalysis processes

This study employed direct photolysis to treat mixed polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) solutions. The solutions included a synthetic standard 17 2, 3, 7, 8-substituted congeners solution and a practical liquid extracted from the bag filter ash of an electric arc furnace. Additionally, this work utilized a coupled catalyst (ZnO/SnO2) under UV irradiation for photocatalytic degradation of 1, 2, 3, 6, 7, 8-HxCDD and OCDD. The direct photolysis rate of PCDFs was faster than that of PCDDs. The degradation rate of international toxicity equivalency quantity (I-TEQ) for PCDDs and PCDFs in the synthetic standard solution was 1.369 and 1.472 h(-1), respectively, and that in the ash-extracted solution was 0.061 and 0.117 h(-1), respectively. The rate of photocatalytic degradation declined as the number of chlorine atoms increased. No 2, 3, 7, 8-substituted congeners were identified during photocatalytic degradation; additionally, the photolytic rate of the UV/coupled catalyst was higher than that of UV/single catalyst system. Experimental results suggested that the primary degradation pathway for direct photolysis and photocatalysis of PCDD/Fs was the CCl cleavage and CO cleavage, respectively.     

高活性多孔纳米TiO2的制备及协同光催化作用机理的探讨

本文采用新的合成工艺制备了一种多孔纳米TiO2粉体材料,具有很高的光催化活性,在365nm的中压汞灯幅照下,仅17分钟就使甲基橙溶液(50mg/L)的降解率达99.6%以上;实验发现,在光幅照停止后仍然存在降解的暗反应,且前快后慢;首次提出在锐钛矿型TiO2基质中,存在极少量的金红石型TiO2可产生协同光催化降解作用,有利于光催化活性的提高.     

Photocatalytic degradation of Azure and Sudan dyes using nano TiO2

The present study investigates the dependence of photocatalytic rate on molecular structure of the substrate that is degraded. The photocatalytic degradation of Azure (A and B) and Sudan (III and IV) dyes, having similar structure, but different functional groups, were investigated with two catalysts. The photocatalytic activity of solution combustion synthesized TiO(2) (CS TiO(2)) was compared with that of Degussa P-25 for degrading these dyes. The effect of solvents and mixed-solvent system on photodegradation of Sudan III was investigated. The photodegradation rate was found to be higher in solvents with higher polarity. The effect of pH and the presence of metal ions in the form of chloride and nitrate salt, on degradation rate of Azure A was also investigated. The metal ions significantly reduced the photocatalysis rates. A detailed Langmuir-Hinshelwood kinetic model has been developed to explain the effect of metal ions on degradation rate of the substrate. This model elucidates the contribution of holes and electrons towards degradation of the dye.     

A new submerged membrane photocatalysis reactor (SMPR) for fulvic acid removal using a nano-structured photocatalyst

The study focuses on the degradation of fulvic acid by nano-structured TiO2 in a submerged membrane photocatalysis reactor (SMPR). It has been demonstrated that the composite TiO2 photocatalyst could be automatically settled due to its gravity and then be easily separated by MF membrane. In addition, it was more efficient to maintain high flux of membranes than that of commercial TiO2 P25. The paper describes the effects of operational parameters on the photocatalytic degradation of fulvic acid in SMPR. It was found that the photocatalyst at 0.5 g/L and airflow at 0.06 m3/h were the optimal condition for the removal of fulvic acid (FA) and the FA degradation rate was higher at acidic condition than that at alkalinous media. In order to compare the effects of different filtration duration on permeate flux rate of MF, P25 powder and nano-structured TiO2 were employed. According to the experiments, the permeate flux rate of MF is improved and thus the membrane fouling phenomenon is reduced with the addition of nano-structured TiO2 catalyst. Therefore, the submerged membrane photocatalysis reactor can be potentially applied in photocatalytic oxidation process during drinking water treatment.     

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.     

Photocatalytic degradation of Direct Red 23 dye using UV/TiO2: Effect of operational parameters

In this study, the photocatalytic degradation of Direct Red 23 (Scarlet F-4BS) was investigated in UV/TiO2 system. The effect of catalyst loading and pH on the reaction rate was ascertained and optimum conditions for maximum degradation were determined. The results obtained showed that acidic pH is proper for the photocatalytic removal of Direct Red 23. In addition, the effects of several cations (Cu2+, Al3+, Cr3+, and Sn4+) and anions (BiO3(-), SO4(2-), and CN(-)) and C2H5OH were examined in this photocatalytic process. On the order hand, three types of catalysts (Fe2O3, SnO2, and ZnO) were compared with TiO2. After 90 min reaction, the relative decomposition order established was UV/TiO2>UV/SnO2>UV/Fe2O3>UV/ZnO.     

Application of visible-light photocatalysis with nitrogen-doped or unmodified titanium dioxide for control of indoor-level volatile organic compounds

The present study evaluated visible-light photocatalysis, applying an annular reactor coated with unmodified or nitrogen (N)-doped titanium dioxide (TiO(2)), to cleanse gaseous volatile organic compounds (VOCs) at indoor levels. The surface chemistry investigation of N-doped TiO(2) suggested that there was no significant residual of sulfate ions or urea species on the surface of the N-doped TiO(2). Under visible-light irradiation, the photocatalytic technique using N-doped TiO(2) was much superior to that for unmodified TiO(2) for the degradation of VOCs. Moreover, the degradation efficiency by a reactor coated with N-doped TiO(2) was well above 90% for four target compounds (ethyl benzene, o,m,p-xylenes), suggesting that this photocatalytic system can be effectively employed to cleanse these pollutants at indoor air quality (IAQ) levels. The degradation efficiency of all target compounds increased as the stream flow rate (SFR) decreased. For most target compounds, a reactor with a lower hydraulic diameter (HD) exhibited elevated degradation efficiency. The result on humidity effect suggested that the N-doped photocatalyst could be employed effectively to remove four target compounds (ethyl benzene, o,m,p-xylenes) under conditions of less humidified environments, including a typical indoor comfort range (50-60%). Consequently, it is suggested that with appropriate photocatalytic conditions, a visible-light-assisted N-doped photocatalytic system is clearly an important tool for improving IAQ.     

Degradation and mineralization of Direct Blue 71 in a circulating upflow reactor by UV/TiO2 process and employing a new method in kinetic study

Direct Blue 71 (C(40)H(23)N(7)Na(4)O(13)S(4)), an azo dye with a high worldwide consumption and providing toxic effluents, can be highly degraded using TiO(2) catalyst suspension and irradiation with a UV-C lamp in a circulating upflow photo-reactor with no dead zone. An initial concentration of 50 mgL(-1) of dye, within the range of typical concentration in textile wastewaters, was used. The influence of catalyst concentration, pH and temperature were investigated. The results showed that degradation of this dye can be conducted in the both processes of only UV irradiation and UV/TiO(2); but with the aim of mineralization, the later process provides significantly better results. Accordingly, a degradation of more than 97% of dye was achieved by applying the optimal operational parameters with 40 mgL(-1) of catalyst, natural pH and 45 degrees C, during 120 min irradiation. A removal of about 50% of COD could also be obtained at the same time. In kinetic investigations, the effect of catalyst particles' turbidity was taken into account and the rate of degradation of the dye, under mild conditions, was expressed as the sum of the rates of individual photolysis and photocatalysis process branches, with mainly influence of the bulk hydroxyl radicals.     

Sn~(4+)-TiO_2的制备及其光催化降解苯酚的研究

采用硬脂酸法制备出Sn4+-TiO2复合光催化剂,用透射电子显微镜和X光衍射仪对粉体的粒径、物相、形貌和热稳定性进行了表征。样品经500℃焙烧2h后,5%Sn4+-TiO2纳米粉末颗粒细小均匀,形状完整,粉末的平均晶粒度约为14nm。通过粉体对苯酚的降解情况对其光催化活性进行了测试,结果表明,与纯TiO2相比,Sn4+-TiO2的光催化活性有较大提高,当SnO2的掺入量为摩尔比5.0%时催化活性最高。以高压汞灯为光源,苯酚的初始浓度为80mg.L-1、催化剂5%Sn4+-TiO2投加量为1.0g.L-1时,溶液的pH为4,苯酚的光催化降解效果最好。     

复合电沉积制备SnO2/TiO2薄膜及其光电催化性能

为了寻求廉价、高效和稳定的光催化剂,用复合电沉积技术在紫铜片上制备了Sn/TiO2薄膜,经300℃热氧化使之形成SnO2/TiO2复合电极.利用SEM,XRD对薄膜进行了表征,以甲基橙为模型化合物,对复合电极的光催化和光电催化性能进行了测定.研究表明:该薄膜由0.3~1μm的颗粒构成,每个颗粒又由纳米晶粒形成;电极具有多孔结构,膜中的SnO2以两种不同的晶体结构存在;在薄膜质量相等的情况下,SnO2/TiO2薄膜的光催化活性是纯TiO2粒子膜的2.87倍;外加一定偏压下,其催化性能大幅度提高.     

Degradation of 4-chlorophenol in TiO2, WO3, SnO2, TiO2/WO3 and TiO2/SnO2 systems

The present study was undertaken to evaluate the degradation performance of 4-chlorophenol (4-CP) using TiO2/WO3 and TiO2/SnO2 systems. A BET surface area analyzer, UV-vis spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron spectroscopy for chemical analysis (ESCA) were employed to characterize the photocatalyst. The band edge wavelength increased to 475 nm and gap energy decreased to 2.61 eV in the TiO2/WO3 system as compare to the single TiO2. Although the specific surfaces area of TiO2/WO3 decreases due to its larger size as compared to either TiO2 or WO3, the 4-CP degradation efficiency significantly increased as compared to single TiO2 or WO3 system at 435 nm wavelength. The TiO2/WO3 degradation of 4-CP at 369 nm was in fact inhibited. For TiO2/SnO2, the degradation efficiency also suffered at 369 nm, and only slightly increased compared to otherwise hardly 4-CP degraded in single TiO2 or SnO2 system. Since there is a significant accumulation of byproducts, the buildup of these intermediates on the catalyst surface may be responsible for their poor performance.     

离子注入改善纳米二氧化钛薄膜光催化性能

利用直流磁控反应溅射技术在玻璃衬底上制备了透明的纳米TiO2光催化薄膜。利用离子注入技术将Sn离子注入到TiO2表面以提高其光催化活性。用X射线衍射（XRD）、X射线光电子谱（XPS）以及UV－VIS分光光度计对薄膜进行结构与性能表征。Sn离子注入后的薄膜具有更高的光催化活性，这是因为在TiO2和SnO2半导体的复合体系中，电子－空穴对的分离变得更加有效，从而提高了其催化性能。     

Prolonged lifetime and enhanced separation of photogenerated charges of nanosized α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> by coupling SnO<Subscript>2</Subscript> for efficient visible-light photocatalysis to convert CO<Subscript>2</Subscript> and degrade acetaldehyde

To develop efficient visible-light photocatalysis on α-Fe2O3,it is highly desirable to promote visible-light-excited high-energy-level electron transfer to a proper energy platform thermodynamically.Herein,based on the transient-state surface photovoltage responses and the atmosphere-controlled steady-state surface photovoltage spectra,it is demonstrated that the lifetime and separation of photogenerated charges of nanosized α-Fe2O3 are increased after coupling a proper amount of nanocrystalline SnO2.This naturally leads to greatly improved photocatalytic activities for CO2 reduction and acetaldehyde degradation.It is suggested that the enhanced charge separation results from the electron transfer from α-Fe2O3 to SnO2,which acts as a proper energy platform.Based on the photocurrent action spectra,it is confirmed that the coupled SnO2 exhibits longer visible-light threshold wavelength (～590 nm) compared with the coupled TiO2 (～550 nm),indicating that the energy platform introduced by SnO2 would accept more photogenerated electrons from α-Fe2O3.Moreover,electrochemical reduction experiments proved that the coupled SnO2 possesses better catalytic ability for reducing CO2 and O2.These are well responsible for the much efficient photocatalysis on SnO2-coupled α-Fe2O3.     

ZnS在TiO2纳米管上的分散对其光催化降解染料废水的影响

水热法制备了TiO2纳米管,并采用简单加热回流的方法制备了ZnS/TiO2纳米复合材料。采用TEM、XRD分析手段对产物进行表征,并对其光催化降解酸性玫瑰红B(AR)染料废水进行了研究。考察了反应物供给速率、硫化锌复合量、催化剂稳定性、光照对光催化降解效果的影响。研究表明控制反应物供给速率和硫化锌的负载量可使硫化锌在二氧化钛纳米管表面均匀分散。当染料废水初始浓度为10mg/L,ZnS:TiO2=8:1时,ZnS/TiO2复合材料光催化活性最高。且催化剂稳定性较好。     

共掺杂Cu-Ce/TiO_2光催化性能研究

采用溶胶-凝胶法,以钛酸丁酯为前驱体制备了不同Cu-Ce掺杂量的纳米TiO2光催化材料。通过模拟环境室内甲醛气体的降解实验,探讨了不同样品在日光灯和纯可见光下的光催化效果,并采用X射线衍射仪和紫外-可见分光光谱仪对其晶相结构与光学特性进行表征分析。结果表明,Cu-Ce掺杂能明显提高二氧化钛在可见光下的光催化活性,当Cu-Ce掺杂浓度为2.5%时,对甲醛气体的光催化降解效果最佳。     

掺铁TiO2纳米晶的制备及光催化性能研究

以钛酸丁酯溶液为前驱体，采用溶胶-凝胶法制备了不同掺杂量的Fe^3 -TiO2干凝胶，在空气气氛中于400℃焙烧2h，得到锐钛矿相的纳米晶，用TG-DTA，XRD，DRS，FS等手段对其进行了表征，研究结果表明，掺杂铁离子使二氧化钛纳米晶的粒径变小，吸收带边发生红移，荧光峰明显增强，分别以汞灯和氙灯为光源，通过对染料罗丹明B的光催化降解研究，发现掺入0.01?^3 -TiO2与纯TiO2相比具有更好的催化活性，掺杂量增大后，光催化降解率反而下降。     

静电纺丝法制备Fe3+/TiO2纳米纤维及表征

以聚乙烯吡咯烷酮(PVP)为纤维模板,钛酸四丁酯(Ti[O(CH2)3CH3]4)和Fe3+为前驱体,乙醇为溶剂,醋酸为催化剂,采用静电纺丝法制备不同含铁量的复合纳米纤维Fe3+/TiO2,经500℃煅烧得到以锐钛矿为主的Fe3+/TiO2纳米纤维。采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)分别表征了Fe3+/TiO2纳米纤维的形貌与晶态,计算了样品的晶粒尺寸和锐钛矿所占的比例,并比较了5%Fe3+/TiO2纳米纤维、5%Fe3+/TiO2粉体以及纯TiO2纳米纤维三者光催化降解亚甲基蓝(MB)的效果。研究表明:由静电纺丝法制备的5%Fe3+/TiO2纳米纤维的光催化降解效果比相同含铁量的粉体的降解效果好,TiO2纳米纤维比5%Fe3+/TiO2纳米纤维的光催化活性高。     

TiO2-Al2O3复合光催化剂的制备及光催化性能

以Ti（SO4）2、Al2（SO4）3·18H2O为原料,采用乙醇助水热法制备了Al2O3-TiO2复合光催化剂,并通过改变A1／Ti物质的量之比、乙醇的体积分数、水热反应温度和反应时间等得到材料制备的最佳条件。XRD分析表明样品中的TiO2以锐钛矿晶相存在,SEM显示样品粒径范围在30-50nm之间。用最佳条件制备的复合光催化剂降解甲基橙溶液,反应30min后降解率这91％,降解过程符合一级动力学方程。     

Enhanced TiO2 photocatalytic degradation of bisphenol E by beta-cyclodextrin in suspended solutions

Enhancement of beta-cyclodextrin (beta-CD) on TiO(2) photocatalytic degradation of bisphenol E (BPE, bis(4-hydroxyphenyl)ethane) was investigated under a 250 W metal halide lamp (lambda> or =365 nm) in this work. In the system of photocatalytic degradation of BPE, the photodegradation rate of BPE in aqueous solutions containing beta-CD and TiO(2) was obviously faster than that in aqueous solutions containing only TiO(2). After 40 min of irradiation, beta-CD could increase the photodegradation efficiency by about 26% for 10 mg l(-1) BPE in the UV-vis/TiO(2) system and the photodegradation of 2.5-20.0 mg l(-1) BPE in aqueous solutions was found to follow pseudo-first-order law and the adsorption constant and the reaction rate constant of BPE in the system containing beta-CD and TiO(2) are obviously higher than those in the system containing only TiO(2), the influence factors on photodegradation of BPE were studied and described in details, such as beta-CD concentration, pH, BPE initial concentration and gas medium. The formation of CO(2) as a result of mineralization of BPE was observed during the photodegradation process. After 120 min of irradiation, the mineralization efficiency of BPE reached 61% in the presence of beta-CD, whereas mineralization efficiency was only 23% in the absence of beta-CD. The enhancement of photodegradation of BPE could be dependent on the enhancement of adsorption of BPE on TiO(2) surface and moderate inclusion-depth of BPE in the beta-CD cavity.     

Photodegradation of acetaminophen in TiO(2) suspended solution

This study investigated the photocatalytic degradation of acetaminophen (APAP) in TiO(2) suspended solution under a 250 W metal halide lamp. The influence of some parameters on the degradation of acetaminophen was studied and described in details, such as initial APAP concentration, initial pH value and TiO(2) dosage. After 100 min irradiation, about 95% of APAP is decomposed in the 1.0 g L(-1) TiO(2) aqueous solution with an initial concentration of 100 micromol L(-1). The effect of adsorption at three different pH values has also been analyzed and it has been conducted that pH 3.5, at which APAP was readily adsorbed also degraded at a faster rate. Reaction rate at pH 6.9 and pH 9.5 was 2.84 and 2.96 microM min(-1), respectively. Direct hole (h(+)) oxidation and ipso-substitution was found to be the main initial step for APAP degradation. Main reaction intermediates and products were identified by GC/MS analysis. The mechanism of acetaminophen photocatalytic degradation in TiO(2) suspended solution was studied not only experimentally but also theoretically by calculating the frontier electron density of APAP. The results obtained indicated that TiO(2) photocatalytic degradation is a highly effective way to remove APAP from wastewater and drinking water without any generation of more toxic products.