TiO2 mediated photocatalytic degradation studies of Reactive Red 198 by UV irradiation

Photocatalytic degradation of an aqueous solution of azo dye (Reactive Red 198) used in textile industries by UV irradiation was investigated. The effect of initial dye concentration, TiO(2) loading, pH and H(2)O(2) on degradation rate was ascertained and optimized conditions for maximum degradation were determined. The kinetics of photocatalytic degradation was found to follow a pseudo-first order according to Langmuir-Hinshelwood model. The degradation experiment under optimized reaction conditions was investigated under sunlight.     

TiO2-UV photocatalytic oxidation of Reactive Yellow 14: effect of operational parameters

The photocatalytic decolourisation and degradation of an azo dye Reactive Yellow (RY14) in aqueous solution with TiO(2) as photocatalyst in slurry form has been carried out using UV-A radiation (365 nm). The effect of various parameters such as catalyst loading, radiation intensity and initial dye concentration on the dye removal was investigated to find optimum conditions. The decolourisation and degradation kinetics have been analysed. Both follow modified Langmuir-Hinshelwood kinetic (L-H) model. A study on the effect of electron acceptors on photooxidation reveals that both decolourisation and degradation increase in the presence of H(2)O(2), (NH(4))(2)S(2)O(8), KBrO(3), to certain dosage beyond which the enhancement effect is negligible. But negative effects are observed in the presence of NaCl or Na(2)CO(3).     

TiO_2-Al_2O_3负载型催化剂的制备及其光催化性能

以钛酸四丁酯和氢氧化钠为反应物,采用两步水热法制备TiO2纳米线,并将其原位负载于Al2O3载体上,研究它们对甲基橙的光催化降解性能。结果表明,锐钛矿相TiO2主要呈纳米线和八面体状负载在Al2O3载体上,当TiO2负载质量分数为30%,焙烧温度为400℃,催化剂用量为1.332 0 g/L时,TiO2-Al2O3负载型催化剂光催化降解甲基橙的性能最佳,光照5 h后,甲基橙在紫外和太阳光下的降解率分别达到58.9%和55.6%。相同实验条件下,TiO2-Al2O3负载型催化剂对甲基橙的降解率比单纯TiO2提高了35.1%。     

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.     

Photocatalytic degradation of triazinic ring-containing azo dye (Reactive Red 198) by using immobilized TiO2 photoreactor: bench scale study

The decolorization and degradation of triazinic ring-containing azo dye by using TiO(2)-immobilized photoreactor is reported. A simple and easy method was used for the immobilization of photocatalyst. Reactive Red 198 (RR 198) was used as model compound. Photocatalytic degradation processes were performed using a 5 L (bench scale) solution containing dye. Batch mode immersion type method was used for the treatment of dye solution. UV-vis, ion chromatography (IC) and chemical oxygen demand (COD) analyses were employed to evaluate the results of the photocatalytic degradation of RR 198. Dye solution was completely decolorized in relatively short time (35 min) after UV irradiation in combination with hydrogen peroxide. The results verified that all of the dye molecules were destructed. Kinetics analysis indicates that the dye photocatalytic decolorization rates followed first order model (R(2) = 0.99). Ion chromatography analysis was used to investigate the formation and destruction of aliphatic carboxylic acids and formation of inorganic anions during the process. Formate and oxalate anions were detected as main aliphatic carboxylic intermediates, which were further oxidized slowly to CO(2). UV/TiO(2)/H(2)O(2) process proved to be capable of successful decolorization and degradation of the RR 198.     

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.     

Effect of surface plasmon resonance on the photocatalytic activity of Au/TiO2 under UV/visible illumination

In this study, gold-loaded titanium dioxide was prepared by an impregnation method to investigate the effect of surface plasmon resonance (SPR) on photoactivity. The deposited gold nanoparticles (NPs) absorb visible light because of SPR. The effects of both the gold content and the TiO2 size of Au/TiO2 on SPR and the photocatalytic efficiency were investigated. The morphology, crystal structure, light absorption, emission from the recombination of a photoexcited electron and hole, and the degree of aggregation were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible-diffuse reflectance spectra (UV-VIS-DRS), photoluminescence (PL) spectroscopy, and turbidimetry, respectively. Photocatalytic activity was evaluated by the decolorization of methyl orange solution over modified titania under UV and UV/GLED (green light emitting diode) illumination. Au/TiO2 NPs exhibited an absorption peak (530-570 nm) because of SPR. The results of our photocatalytic experiments indicated that the UV-inducedly photocatalytic reaction rate was improved by simultaneously using UV and green light illumination; this corresponds to the adsorption region of SPR. Au/TiO2 could use the enhanced electric field amplitude on the surface of the Au particle in the spectral vicinity of its plasmon resonance and thus improve the photoactivity. Experimental results show that the synergistic effect between UV and green light for the improvement of photoactivity increases with increasing the SPR absorption, which in turn is affected by the Au content and TiO2 size.     

Nanostructured mesoporous Au/TiO2 for photocatalytic degradation of a textile dye: the effect of size similarity of the deposited Au with that of TiO2 pores

Mesoporous Au/TiO₂ nanocomposites with different Au particle size (7.3–11.8 nm) were synthesized via deposition–precipitation method. The synthesized nanocomposites have been characterized by XRD, TEM, XPS, DLS, ICP-OES, N₂ sorpometry, and UV–Vis spectroscopy. Au/TiO₂ showed higher quantum yield and greater photocatalytic efficiency compared to pure TiO₂ under both ultraviolet and sunlight illumination. The increase of the photocatalytic efficiency of TiO₂ upon deposition with gold nanoparticles, Au NPs, is due to the interface electron transfer from Au nanoparticles to TiO₂ under visible light illumination and from TiO₂ to Au nanoparticles under UV illumination. For the first time, the effect of Au particle sizes when it is very similar to the interparticles pores of TiO₂ has been investigated. The highest reaction rate (5.7 × 10^?2 min^?1) and degradation efficiency of Safranin-O (SO) dye (97 %) were observed when the deposited gold nanoparticles are the smallest among the studied samples (sAu/TiO₂). In spite of blocking a high percentage of the TiO₂ pores, the sAu/TiO₂ sample demonstrated a complete degradation of SO dye in 50 min which is more efficient than any other reported catalysts in the literature.     

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.     

Photocatalytic properties of silver nanoparticles decorated nanobranched TiO2 nanofibers

In this study, nanobranched TiO2 nanofibers and silver loaded nanobranched TiO2 nanofibers were prepared by electrospinning technique followed by TiCl4 aqueous solution treatment and silver photodeposition method. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were employed to investigate the morphology of the products. X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) were conducted on the samples to study their chemical composition as well as crystallographic structure. The photocatalytic activities of these produced nanofibers were examined with two organic dyes, methylene blue and methyl orange, under ultraviolet (UV) light irradiation. The effect of nanobranches and silver modification on TiO2 nanofibers was revealed in the photocatalysis process. The photocatalytic degradation rates of silver loaded on nanobranched TiO2 nanofibers were 1.6 and 1.7 times as that of pure TiO2 nanofibers in the presence of methylene blue and methyl orange, respectively, which indicated silver nanoparticles combined nanobranches modified on the surface of TiO2 nanofibers could enhance the photocatalytic ability.     

TiO2/膨胀石墨复合材料的制备及其对亚甲基兰的光催化降解

采用快速升温法制备出以膨胀石墨为载体的TiO2/膨胀石墨光催化剂,用SEM及XRD对其表面形貌及结构进行表征,研究了该负载型光催化剂在紫外光照射下的催化能力,探讨了在催化剂中TiO2的负载量、亚甲基兰溶液的初始浓度及其pH值对光催化剂的降解能力的影响.结果发现,负载量为10%的光催化剂对40mg/L的亚甲基兰溶液5h的光降解率达到58.8%.     

TiO2／膨胀石墨复合材料的制备及光催化性能的研穷

采用快速升温法制备出以膨胀石墨为载体的TiO2／膨胀石墨光催化剂，用SEM及XRD对其表面形貌及结构进行表征，研究了光催化剂在紫外光照射下的催化能力，探讨了目标降解物溶液的初始浓度及其pH值对光催化剂的降解能力的影响。结果发现，负载量为10％的光催化剂对40mg／L的亚甲基兰溶液5h的光降解率达到58．83％，甲基橙为51．12％。     

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.     

One-dimensional TiO2 nanomaterials: preparation and catalytic applications

This work reports on the syntheses of one-dimensional (1D) H2Ti3O7 materials (nanotubes, nanowires and their mixtures) by autoclaving anatase titania (Raw-TiO2) in NaOH-containing ethanol-water solutions, followed by washing with acid solution. The synthesized nanosized materials were characterized using XRD, TEM/HRTEM, BET and TG techniques. The autoclaving temperature (120-180 degrees C) and ethanol-to-water ratio (V(EtOH)/V(H2O) = 0/60 approximately 30/30) were shown to be critical to the morphology of H2Ti3O7 product. The obtained H2Ti3O7 nanostructures were calcined at 400-900 degrees C to prepare 1D-TiO2 nanomaterials. H2Ti3O7 nanotubes were converted to anatase nanorods while H2Ti3O7 nanowires to TiO2(B) nanowires after the calcination at 400 degrees C. The calcination at higher temperatures led to gradual decomposition of the wires to rods and phase transformation from TiO2(B) to anatase then to rutile. Photocatalytic degradation of methyl orange was conducted to compare the photocatalytic activity of these 1D materials. These 1D materials were used as new support to prepare Au/TiO2 catalysts for CO oxidation at 0 degrees C and 1,3-butadiene hydrogenation at 120 degrees C. For the CO oxidation reaction, Au particles supported on anatase nanorods derived from the H2Ti3O7 nanotubes (Au/W-180-400) were 1.6 times active that in Au/P25-TiO2, 4 times that in Au/Raw-TiO2, and 8 times that on TiO2(B) nanowires derived from the H2Ti3O7 nanotubes (Au/M-180-400). For the hydrogenation of 1,3-butadiene, however, the activity of Au particles in Au/M-180-400 was 3 times higher than those in Au/W-180-400 but similar to those in Au/P25-TiO2. These results demonstrate that the potential of 1D-TiO2 nanomaterials in catalysis is versatile.     

Photocatalytic degradation of methyl orange: influence of H2O2 in the TiO2-based system

The purpose of this study was to investigate the photocatalytic oxidation of a reactive azo dye. The photocatalytic activity of the TiO2 was studied using a reactor equipped with UV-A sources, with maximum emission at 365 nm. The photocatalytic activity of the TiO2 powder (99.9% anatase) and thin films has been measured through the decomposition of methyl orange solutions. The thin film was prepared by doctor blade and spray pyrolysis deposition (SPD). The TiO2 suspensions were prepared at 1 g/L concentration, and the initial methyl orange concentration was fixed at 7.8125 mg/L. The influence of the TiO2 (powder or thin films) and/or O2 and H2O2 on the photobleaching rate, was tested under different experiments, at pH = 5. Thin films (doctor blade) of TiO2 formed of mezo-sized aggregates formed of nanosized anatase crystallites show better photobleaching efficiency than thin film (SPD) due to their large internal surface. The rate is even higher in H2O2 compared to oxygen environment.     

Sonochemical degradation of Basic Blue 41 dye assisted by nanoTiO2 and H2O2

The sonolysis of Basic Blue 41 dye in aqueous solution was performed at 35 kHz using ultrasonic power of 160 W and aqueous temperature of 25+1 degrees C within 180 min. The TiO2 nanoparticles were used as a catalyst to assist the sonication process. The effect of experimental parameters such as pH, H2O2 concentration and initial dye concentration on the reaction were investigated. It was recognized that in lower pH values the dye removal rate decreased. However, dye removal increased via increase in H2O2 concentration and lowering the initial dye concentration. All intermediate compounds were detected by integrated gas chromatography-mass spectrometry (GC/MS) and also ion chromatograph (IC). During the decolorization, all nitrogen atoms and aromatic groups of Basic Blue 41 were converted to urea, nitrate, formic acid, acetic acid and oxalic acid, etc. Kinetic studies revealed that the degradation process followed pseudo-first order mechanism with the correlation coefficient (R2) of 0.9918 under experimental conditions. The results showed that power ultrasound can be regarded as an appropriate tool for degradation of azo dyes to non-toxic end products.     

Effect of deposition of Ag on TiO2 nanoparticles on the photodegradation of Reactive Yellow-17

Nanoparticles of TiO(2) were synthesized by sol-gel technique and the photodeposition of about 1% Ag on TiO(2) particles was carried out. Ag-deposited TiO(2) catalyst was characterised by XRD, TEM and UV-vis spectroscopy. The Ag-TiO(2) catalyst was evaluated for their photocatalytic activity towards the degradation of Reactive Yellow-17 (RY-17) under UV and visible light irradiations. Then the results were compared with synthesized nano-TiO(2) sol and P-25 Degussa and the enhanced degradation was obtained with Ag-deposited TiO(2). This enhanced activity of Ag-TiO(2) may be attributed to the trapping of conduction band electrons. The effect of initial dye concentration, pH and electron acceptors such as H(2)O(2), K(2)S(2)O(8) on the photocatalytic activity were studied and the results obtained were fitted with Langmuir-Hinshelwood model to study the degradation kinetics and discussed in detail.     

Semiconductor-mediated photocatalysed degradation of two selected azo dye derivatives, amaranth and bismarck brown in aqueous suspension

Semiconductor-mediated photocatalysed degradation of two selected azo dye derivatives such as amaranth (1) and bismarck brown (2) has been investigated in aqueous suspension by monitoring the change in substrate concentration employing UV spectroscopic analysis technique as a function of irradiation time. The degradation was studied under different conditions such as types of TiO(2), pH, substrate concentration, catalyst concentration, and in the presence of electron acceptors such as hydrogen peroxide (H(2)O(2)), potassium bromate (KBrO(3)) and ammonium persulphate (NH(4))(2)S(2)O(8) besides air. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 showed comparatively highest photocatalytic activity. The dye derivative, bismarck brown (2) was found to degrade faster than amaranth dye (1).     

Discoloration of a red cationic dye by supported TiO(2) photocatalysis

The degradation under UV, visible and sunlight irradiation of C.I. Basic Red 46 (BR 46) dye used for acrylic fibers dyeing has been studied in a lab-scale continuous system with two different immobilized TiO(2) systems. Catalyst I was based on TiO(2) particles deposited on cellulose fibers; Catalyst II combined TiO(2) particles deposited on a layer of cellulose fibers (as in Catalyst I) with a layer of carbon fibers and finally a layer of cellulose fibers. The treatment of aqueous dye solutions and industrial wastewater contaminated with the same dye has been evaluated in terms of color removal and chemical oxygen demand (COD) decrease. With UV light, aqueous solutions containing dye were decolorized slightly more rapidly with Catalyst II than with Catalyst I. Sunlight was also very effective and experiments involving sunlight irradiation showed Catalyst II to be the more efficient, giving more than 90% discoloration after 20 min of treatment. Comparing the discoloration yield by adsorption or under visible light for both catalysts, it was observed that the difference between them is below 5%. The adsorption kinetics was found to follow a second-order rate law for Catalyst I and a first-order rate law for Catalyst II. The kinetics of photocatalytic degradation under UV or sunlight were found to follow a first-order rate law for both catalytic systems. Under sunlight the COD removal yield for textile wastewater reaches 33% with Catalyst I against 93% with Catalyst II.     

Photocatalytic decolorization and degradation of dye solutions and wastewaters in the presence of titanium dioxide

In this study, the photocatalytic degradation of two commercial azo dyes in the presence of TiO(2) suspensions as photocatalyst has been investigated. The degradation of the dyes follows a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Under the certain experimental conditions, in the presence of TiO(2) P-25 decolorization is achieved within 100 min of illumination, while in the presence of TiO(2) Hombikat UV-100 complete color disappearance is accomplished in less than 50 min of light exposure. The influence of various parameters, such as the type and mass of the catalyst, the initial concentration of the dye, etc. on the degradation process was examined. The mineralization of organic carbon was also evaluated by measuring the dissolved organic carbon (DOC) of the dye solutions. Moreover, the toxic properties of the dye solutions treated by photocatalysis were examined by the use of a Microtox bioassay (Vibrio fischeri). Finally, experiments using real textile wastewater were also carried out, in order to examine the effectiveness of the method to a more complex substrate.