Kinetics and mechanism of TNT degradation in TiO2 photocatalysis

The photocatalytic degradation of TNT in a circular photocatalytic reactor, using a UV lamp as a light source and TiO(2) as a photocatalyst, was investigated. The effects of various parameters such as the initial TNT concentration, and the initial pH on the TNT degradation rate of TiO(2) photocatalysis were examined. In the presence of both UV light illumination and TiO(2) catalyst, TNT was more effectively degraded than with either UV or TiO(2) alone. The reaction rate was found to obey pseudo first-order kinetics represented by the Langmuir-Hinshelwood model. In the mineralization study, TNT (30 mg/l) photocatalytic degradation resulted in an approximately 80% TOC decrease after 150 min, and 10% of acetate and 57% of formate were produced as the organic intermediates, and were further degraded. NO(-)(3) NO(-)(2), and NH(+)(4) were detected as the nitrogen byproducts from photocatalysis and photolysis, and more than 50% of the total nitrogen was converted mainly to NO(-)(3)in the photocatalysis. However, NO(-)(3) did not adsorbed on the TiO(2) surface. TNT showed higher photocatalytic degradation efficiency at neutral and basic pH.     

Degradation of nitrogen containing organic compounds by combined photocatalysis and ozonation

The combination of TiO2-assisted photocatalysis and ozonation in the degradation of nitrogen-containing substrates such as alkylamines, alkanolamines, heterocyclic and aromatic N-compounds has been investigated. A laboratory set-up was designed and the influence of the structure of the N-compound, the TiO2 and ozone concentration on the formation of breakdown products were examined. The experimental results showed that a considerable increase in the degradation efficiency of the N-compounds is obtained by a combination of photocatalysis and ozonation as compared to either ozonation or photocatalysis only. The mineralization of the model substances was monitored by measurements of the TOC and ion-chromatographic determinations of the formed NO2- and NO3-. The temporal changes of concentrations of breakdown products, such as NH4+, short chain alkyl- and alkanolamines were determined by single column ion chromatography (SCIC) and as well as by electrospray mass spectrometry (EI-MS).     

Photocatalytic oxidation of gaseous DMF using thin film TiO2 photocatalyst

The heterogeneous photocatalytic oxidation of gaseous N,N'-dimethylformamide (DMF) widely used in the manufacture of synthetic leather and synthetic textile was investigated. The experiments were carried out in a plug flow annular photoreactor coated with Degussa P-25 TiO2. The oxidation rate was dependent on DMF concentration, reaction temperature, water vapor, and oxygen content. Photocatalytic deactivation was observed in these reactions. The Levenspiel deactivation kinetic model was used to describe the decay of catalyst activity. Fourier transform infrared (FTIR) was used to characterize the surface and the deactivation mechanism of the photocatalyst. Results revealed that carbonylic acids, aldehydes, amines, carbonate and nitrate were adsorbed on the TiO2 surface during the photocatalytic reaction. The ions, NH4+ and NO3-, causing the deactivation of catalysts were detected on the TiO2 surface. Several treatment processes were applied to find a suitable procedure for the regeneration of catalytic activity. Among these procedures, the best one was found to be the H2O2/UV process.     

固定化催化剂TiO2膜光催化降解三氯乙醛的研究

研究了负载于玻璃上的固定化催化剂TiO2膜光催化降解水中三氯乙醛的效果,探讨了TiO2膜光催化降解三氯乙醛的机理,考察了溶液pH值和三氯乙醛初始浓度埘TiO2膜光催化降解三氯乙醛的影响,并研究了固定化催化剂TiO2膜光催化降解三氯乙醛的动力学.结果表明,固定化催化剂TiO2膜光催化降解水中三氯乙醛的效果良好,当三氯乙醛初始浓度为2.25 mg/L时,在紫外光照时间3 h下,三氯乙醛的降解率高达100%.在相司紫外光照时间下,三氯乙醛的光催化降解率随着三氯乙醛初始浓度的增大而下降.在溶液pH=6.5时,三氯乙醛的降解效率最高.固定化催化剂TiO2膜光催化降解三氯乙醛的反应遵循一级反应动力学,反应速率常数随三氯乙醛初始浓度的增大而减小.     

TiO2光催化剂在污水处理中的应用

在污水处理方面TiO2光催化剂以其独特的氧化活性、光学性能和无机化能力引起了人们极大的关注.对TiO2光催化原理、农药、染料和环境荷尔蒙等有机污染物的分解,提高催化效率的方法以及其实用技术等方面,分别作了综合评述.     

附载型复合光催化剂TiO2·SiO2/beads降解有机磷农药

研究以四异丙醇钛 [Ti( iso- O C3 H7) 4]、硅酸乙酯为原料 ,以空心玻璃微球为载体 ,用溶胶—凝胶法制备可漂浮附载型复合光催化剂 Ti O2 · Si O2 / beads的过程 ,利用附载型复合光催化剂降解有机磷农药。结果表明 ,复合型光催化剂 Ti O2 · Si O2 摩尔比存在最佳值 ,n ( Ti O2 ) / m ( Si O2 ) =30 / 70时 ,光催化剂活性最高 ,其活性是同样降解条件下、同样含量 Degussa P- 2 5Ti O2 的 2倍左右。该光催化剂比表面大 ,吸附性强。并用 XRD和 SEM对附载型复合光催化剂进行表征     

Photocatalytic oxidation of xenobiotics in water with immobilized TiO2 on agitator

A novel photocatalytic oxidation reactor, using Degussa P-25 TiO2 as a stationary phase with a thickness of 1.5-2.0 um on the blades of agitator, was developed to study the photocatalytic oxidation of xenobiotics. Particularly in this device, separation of photocatalyst from the purified water after oxidation reaction was not necessary, and no other aeration equipment was required to supply oxygen. To examine the efficiency of this device, photocatalytic degradation of xenobiotic organics such as carbofuran was studied as an example. Results indicated that carbofuran could be degraded completely with mineralization efficiency of 20% after 6 hours of oxidation under the imposed conditions. The mineralization rate of carbofuran was found to follow the pseudo-first order reaction kinetics. Moreover, the rate constant of mineralization was found to be proportional to TiO2 film area and the square root of UV light intensity. These results implied the mineralization efficiency of carbofuran could be improved through increasing TiO2 film area and UV light intensity. Accordingly, this novel device showed potential application for degrading xenobiotics in water.     

Effect of ZnFe2O4 doping on the photocatalytic activity of TiO2

The photocatalytic oxidation of the organic pollutants with the TiO2 as photocatalyst has been widely studied in the world, and many achievements have been got. The degradation of pollutants is highly related with the photocatalytic activity of TiO2. It is demonstrated that doping ions or oxides to TiO2 is one way to enhance the photocatalytic activity of TiO2. In this paper, the ZnFe2O4-doped TiO2 nanoparticles were prepared from butyl titanate by a sol-gel method and characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that when TiO2 was doped with ZnFe2O4, its particle size will decrease and its crystal structure will partly transform from anatase to rutile. The photocatalytic activity of the elaborated powders was studied following the degradation of Rhodamine B. The results showed that doping ZnFe2O4 to TiO2 will enhance the photocatalytic activity of TiO2 and that ZnFe2O4-doped TiO2 in the coexistence of anatase and rutile has higher efficiency for the degradation of Rhodamine B than that in the anatase phase alone. Also the different role of O2 in the direct photolysis and photocatalysis of Rhodamine B was discussed.     

Photocatalytic degradation of isoproturon herbicide over TiO2/Al-MCM-41 composite systems using solar light

The present investigation covers immobilization of TiO2 using a simple solid state dispersion technique over mesoporous Al-MCM-41 support for the treatment of isoproturon herbicide. Catalysts are characterized by XRD, X-ray photo electron spectroscopy (XPS), surface area, UV-Vis diffused reflectance spectra (DRS), SEM and TEM. A detailed photocatalytic degradation study of isoproturon under solar light in aqueous suspensions is reported. The 10 wt% TiO2/Al-MCM-41 composite system found to be optimum with high degradation activity. The reaction follows pseudo-first order kinetics. The parameters like TiO2 loading over Al-MCM-41, amount of catalyst, concentration of substrate, pH effect, durability of the catalyst, activity comparison of TiO2 and Al-MCM-41 supported system are studied. The mineralization of isoproturon is monitored by TOC. Based on the degradation products detected through LC-MS, a plausible degradation mechanism is proposed. The data indicates that TiO2/Al-MCM-41 composite system is an effective photocatalyst for treatment of isoproturon in contaminated water.     

Solar light induced and TiO2 assisted degradation of textile dye reactive blue 4

Aqueous solutions of reactive blue 4 textile dye are totally mineralised when irradiated with TiO2 photocatalyst. A solution containing 4 x 10(-4) M dye was completely degraded in 24 h irradiation time. The intensity of the solar light was measured using Lux meter. The results showed that the dye molecules were completely degraded to CO2, SO4(2-), NO3-, NH4+ and H2O under solar irradiation. The addition of hydrogen peroxide and potassium persulphate influenced the photodegradation efficiency. The rapidity of photodegradation of dye intermediates were observed in the presence of hydrogen peroxide than in its absence. The auxiliary chemicals such as sodium carbonate and sodium chloride substantially affected the photodegradation efficiency. High performance liquid chromatography and chemical oxygen demand were used to study the mineralisation and degradation of the dye respectively. It is concluded that solar light induced degradation of textile dye in wastewater is a viable technique for wastewater treatment.     

The preparation of Zn2+-doped TiO(2) nanoparticles by sol-gel and solid phase reaction methods respectively and their photocatalytic activities

The photocatalytic oxidation of the organic pollutants with TiO(2) as photocatalyst has been widely studied in the world, and many achievements have been made. The degradation of pollutants is highly related to the photocatalytic activity of TiO(2). It is demonstrated that doping ions to TiO(2) is one way to enhance the photocatalytic activity of TiO(2). In this paper, Zn(2+)-doped TiO(2) nanoparticles were prepared through sol-gel and solid phase reaction methods, characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The photocatalytic activity of the elaborated powders was studied following the degradation of Rhodamine B. The results showed that the photocatalytic activity of Zn(2+)-doped TiO(2) prepared by sol-gel method is close to that of pure TiO(2) particles, however, the photocatalytic activity of Zn(2+)-doped TiO(2) prepared by solid phase reaction method is much higher than that of pure TiO(2) particles. The most efficient degradation of Rhodamine B was found with TiO(2) particles doped with 0.5% Zn(2+) in mole and calcined at 500 degrees C. Also the reason for the enhancement of the photocatalytic activity of TiO(2) by Zn(2+) doping through solid phase reaction method was discussed.     

Study on the photocatalytic degradation of glyphosate by TiO(2) photocatalyst

In this paper, the photocatalytic degradation of glyphosate selected as the deputy of organic pollutant in aqueous solution with TiO(2) powder as a photocatalyst has been studied. The effects of various parameters, such as the amount of the photocatalyst, illumination time, initial pH value, electron acceptors, metal ions, and anions on the photocatalytic degradation of glyphosate were investigated. From the studies, the best condition for the effect of the parameters on the photocatalytic degradation of glyphosate was obtained. The results show that the optimum amount of the photocatalyst used is 6.0 g l(-1) for the photocatalytic reactions. The photodegradation efficiency of glyphosate increases with the increase of the illumination time. With the addition of Fe(3+), Cu(2+), H(2)O(2), K(2)S(2)O(8) or KBrO(3), the photocatalytic degradation of glyphosate is accelerated. However, with the addition of Na(+), K(+), Mg(2+), Ca(2+), Zn(2+), Co(2+) and Ni(2+), or with the addition of trace amounts of Cl(-), Br(-), SO(4)(2-), there are no obvious effects on the reactions. Acidic or alkaline mediums are favorable for the photocatalytic degradation of glyphosate. The possible roles of the additives on the reactions and the possible mechanisms of effect were discussed.     

Effects of dissolved oxygen, pH, and anions on the 2,3-dichlorophenol degradation by photocatalytic reaction with anodic TiO(2) nanotube films

In this study, the highly-ordered TiO(2) nanotube (TNT) arrays on titanium sheets were prepared by an anodic oxidation method. Under UV illumination, the TNT films demonstrated the higher photocatalytic activity in terms of 2,3-dichlorophenol (2,3-DCP) degradation in aqueous solution than the conventional TiO(2) thin films prepared by a sol-gel method. The effects of dissolved oxygen (DO) and pH on the photocatalytic degradation of 2,3-DCP were investigated. The results showed that the role of DO in the 2,3-DCP degradation with the TNT film was significant. It was found that 2,3-DCP in alkaline solution was degraded and dechlorinated faster than that in acidic solution whereas dissolved organic carbon removal presented an opposite order in dependence of pH. In the meantime, some main intermediate products from 2,3-DCP degradation were identified by a (1)H NMR technique to explore a possible degradation pathway. A major intermediate, 2-chlororesorcinol, was identified from the 2,3-DCP decomposition as a new species compared to the findings in previous reports. Photocatalytic deactivation was also evaluated in the presence of individual anions (NO(3)(-), Cl(-), SO(4)(2-), and H(2)PO(4)(-)). The inhibition degree of photocatalytic degradation of 2,3-DCP caused by these anions can be ranked from high to low as SO(4)(2-)>Cl(-)>H(2)PO(4)(-)>NO(3)(-). The observed inhibition effect can be attributed to the competitive adsorption and the formation of less reactive radicals during the photocatalytic reaction.     

Photooxidation mechanism of nitrogen-containing compounds at TiO2/H2O interfaces: an experimental and theoretical examination of hydrazine derivatives

The photocatalytic oxidation of oxalyldihydrazide, N,N'-bis(hydrazocarbonyl)hydrazide, N,N'-bis(ethoxycarbonyl)hydrazide, malonyldihydrazide, N-malonyl-bis[(N'-ethoxycarbonyl)hydrazide] was examined in aqueous TiO2 dispersions under UV illumination. The photomineralization of nitrogen and carbon atoms in the substrates into N2 gas, NH4+ (and/or NO3-) ions, and CO2 gas was determined by HPLC and GC analysis. The formation of carboxylic acid intermediates also occurred in the photooxidation process. The photocatalytic mechanism is discussed on the basis of the experimental results, and with molecular orbital (MO) simulation of frontier electron density and point charge. Substrate carbonyl groups readily adsorb on the TiO2 surface, and the bonds between carbonyl group carbon atoms and adjacent hydrazo group nitrogen atoms are cleaved predominantly in the initial photooxidation process. The hydrazo groups were photoconverted mainly into N2 gas (in mineralization yields above 70%) and partially to NH4 ions (below 10%). The formation of NO3- ions was scarcely recognized.     

Photocatalytic degradation of the herbicide pendimethalin using nanoparticles of BaTiO3/TiO2 prepared by gel to crystalline conversion method: a kinetic approach

Photocatalytic degradation of the herbicide, pendimethalin (PM) was investigated with BaTiO3/TiO2 UV light system in the presence of peroxide and persulphate species in aqueous medium. The nanoparticles of BaTiO3 and TiO2 were obtained by gel to crystallite conversion method. These photo catalysts are characterized by energy dispersive x-ray analysis (EDX), scanning electron microscope (SEM), x-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) adsorption isotherm and reflectance spectral studies. The quantum yields for TiO2 and BaTiO3 for the degradation reactions are 3.166 Einstein m(-2) s(-1) and 2.729 Einstein m(-2) s(-1) and catalytic efficiencies are 6.0444 x 10(-7) mg(-2)h(-1)L2 and 5.403 x 10(-7) mg(-2)h(-1)L2, respectively as calculated from experimental results. BaTiO3 exhibited comparable photocatalytic efficiency in the degradation of pendimethalin as the most widely used TiO2 photocatalyst. The persulphate played an important role in enhancing the rate of degradation of pendimethalin when compared to hydrogen peroxide. The degradation process of pendimethalin followed the first-order kinetics and it is in agreement with Langmuir-Hinshelwood model of surface mechanism. The reason for high stability of pendimethalin for UV-degradation even in the presence of catalyst and oxidizing agents were explored. The higher rate of degradation was observed in alkaline medium at pH 11. The degradation process was monitored by spectroscopic techniques such as ultra violet-visible (UV-Vis), infrared (IR) and gas chromatography mass spectroscopy (GC-MS). The major intermediate products identified were: N-propyl-2-nitro-6-amino-3, 4-xylidine, (2, 3-dimethyl-5-nitro-6-hydroxy amine) phenol and N-Propyl-3, 4-dimethyl-2, 6-dinitroaniline by GC-MS analysis and the probable reaction mechanism has been proposed based on these products.     

添加壳聚糖溶胶-凝胶法制备的TiO2光催化剂及其光催化性能研究

采用添加壳聚糖（CTS）的溶胶-凝胶法制备了具有较高光催化活性的TiO2光催化剂,并用XRD、TEM、BET和IR等手段对其进行表征。结果表明,CTS的添加使TiO2衍射强度增强、分散性提高、比表面积增大从而使光催化活性提高;用所制备的催化剂光催化降解甲基橙反应60min后,其去除率由不添加CTS所制备TiO2的32％提高到48％,TOC去除率由14％提高到23％。     

H4SiW12O40/TiO2/beads光催化降解亚甲基蓝的研究

以钛酸四丁酯为原料,空心微珠为载体,采用溶胶-凝胶法制备TiO2/beads光催化剂载体,然后浸渍法制备出H4SiW12O40/TiO2/beads表面负载修饰型复合光催化剂,并运用SEM、XRD、FT-IR和DRS对催化剂进行表征和分析。研究了H4SiW12O40/TiO2/beads对亚甲基蓝降解的光催化活性,考察了光强度、pH值、曝气量、底物浓度和催化剂用量等对催化效率的影响。实验结果表明,在中性条件下,H4SiW12O40/TiO2/beads催化剂的投加量为0.25 g/L,浓度为7.5 mg/L的亚甲基蓝溶液在250 W的紫外灯和600 W的可见光灯下光照60 min降解率分别可达到94.5%和55%。     

Degradation mechanism and the toxicity assessment in TiO2 photocatalysis and photolysis of parathion

The photocatalytic degradation of methyl parathion was carried out using a circulating TiO2/UV reactor. The experimental results showed that parathion was more effectively degraded in the photocatalytic condition than the photolysis and TiO2-only condition. With photocatalysis, 10mg/l parathion was completely degraded within 60 min with a TOC decrease exceeding 90% after 150 min. The main ionic byproducts during photocatalysis were measured. The nitrogen from parathion was recovered mainly as NO3-, NO2- and NH4+, 80% of the sulfur as SO4(2-), and less than 5% of the phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and paraoxon were also identified, and these were further degraded. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by photocatalysis and photolysis. A Microtox test using V. fischeri showed that the toxicity, expressed as the relative toxicity (%), was reduced almost completely after 90 min under photocatalysis, whereas only an 83% reduction was achieved with photolysis alone. Another toxicity test using D. magna also showed that the relative toxicity disappeared after 90 min under photocatalysis, whereas there was a 65% reduction in relative toxicity with photolysis alone. The pattern of toxicity reduction parallels the decrease in parathion and TOC concentrations.     

Performance of photocatalytic reactors using immobilized TiO2 film for the degradation of phenol and methylene blue dye present in water stream

TiO2 thin film photocatalyst was successfully synthesized and immobilized on glass reactor tube using sol-gel method. The synthesized TiO2 coating was transparent, which enabled the penetration of ultra-violet (UV) light to the catalyst surface. Two photocatalytic reactors with different operating modes were tested: (a) tubular photocatalytic reactor with re-circulation mode and (b) batch photocatalytic reactor. A new proposed TiO2 synthesized film formulation of 1 titanium isopropoxide: 8 isopropanol: 3 acetyl acetone: 1.1 H2O: 0.05 acetic acid (in molar ratio) gave excellent photocatalytic activity for degradation of phenol and methylene blue dye present in the water. The half-life time, t1/2 of photocatalytic degradation of phenol was 56 min at the initial phenol concentration of 1000 microM in the batch reactor. In the tubular photocatalytic reactor, 5 re-circulation passes with residence time of 2.2 min (single pass) degraded 50% of 40-microM methylene blue dye. Initial phenol concentration, presence of hydrogen peroxide, presence of air bubbling and stirring speed as the process variables were studied in the batch reactor. Initial methylene blue concentration, pH value, light intensity and reaction temperature were studied as the process variables in the tubular reactor. The synthesized TiO2 thin film was characterized using SEM, XRD and EDX analysis. A comparative performance between the synthesized TiO2 thin film and commercial TiO2 particles (99% anatase) was evaluated under the same experimental conditions. The TiO2 film was equally active as the TiO2 powder catalyst.     

TiO2光催化涂料的制备及其降解甲醛研究

自制TiO2光催化涂料,重点对所制备的涂料在室内进行降解甲醛研究,考察了在不同分散剂、不同光催化剂以及不同甲醛初始浓度、不同光源、不同温度和不同湿度等环境因素下涂料对甲醛降解率的影响。结果表明,选用聚丙烯酸钠离子型分散剂,铜金属掺杂TiO2光催化剂制备的光催化涂料对甲醛降解率达80％以上且具有良好的耐久性,在室温（20℃左右）湿度50％日光灯照射下,甲醛初始浓度5μL时效果最佳。