Aqueous Suspensions Of Titanium Dioxide Research Articles

Photocatalytic Reduction of Carbon Dioxide in Aqueous Suspensions of a Titania Semiconductor

The photocatalytic reduction reactions of CO2 in aqueous suspensions of titanium dioxide (TiO2) semiconductor with photodeposited Pt and Cu cocatalysts have been studied. It has been found that the composition and amount of CO2 reduction products significantly depend on the nature of the cocatalyst supported onto TiO2. A mechanism for the formation of CO2 reduction products has been proposed.

Viscosity of aqueous suspensions of titanium dioxide (anatase) nano-particles

Viscosity of aqueous suspensions of titanium dioxide (anatase) nano-particles

Box-Wilson design modeling of photocatalytic degradation of industrial dye and wastewater in semi-pilot solar photoreactor

This work focuses on the treatment of a dye solution, C.I. Basic Blue 41 (BB41), and industrial wastewater by UV/TiO2 photocatalytic process using aqueous catalyst suspensions of titanium dioxide (TiO2), Degussa P25. The procedures were carried out in a semi-pilot scale prototype solar photoreactor under solar radiation. Response surface methodology (RSM) based on Box-Wilson design was applied to assess individual effects of the five main independent parameters: initial dye concentration ([BB41]), TiO2 concentration ([TiO2]), flow rate (Q) initial pH and accumulated solar energy (Qvn) on the decolorization efficiency and to optimise the UV/TiO2 process. Photocatalytic mineralisation was carried out at the optimal conditions found by RSM and results were evaluated by total organic carbon (TOC) abatement for BB41 sloution and industrial wastewater. The optimal conditions found by RSM were: 0.4 g/L, 14.04 mg/L, 1,479.6 L/h, 5.52 and 80 KJ/L for TiO2 concentration, initial dye concentration, flow rate, initial pH and accumulated solar energy, respectively. Photocatalytic mineralisation results show that for accumulated visible solar energy equal to 377.714 kJ/L (after 6 hours of irradiation), under these conditions, the percentage of the initial TOC reduction is about 88% and 85.5% for industrial waste and BB41 solution, respectively.

The hydration effect of singly charged ions on the electrosurface properties of titanium dioxide aqueous suspensions

The effect of ordering/disordering degree of water molecules in the vicinity of singly charged cations (Li+, Na+, K+, Rb+, Cs+) and anions (F−, Cl−, Br−, I−) on the electrosurface properties of aqueous suspensions of rutile-type titanium dioxide is discussed. The influence of mentioned ions presence on the position of the isoelectric point, which is one of the integral estimates of the suspensions electrosurface properties was examined. It was accepted that displacement of the isoelectric point is caused by different binding of cations and anions to the titanium dioxide surface. The magnitude of this displacement estimates the relative binding of cations and anions to the surface, which depends on the ordering/disordering degree of water molecules. The dependences were found to have a maximum and a minimum in the case of cations and anions, respectively. The extreme values were determined when the water molecules structure in the vicinity of ions was undisturbed and corresponded to the structure of bulk water. The results obtained are relevant for highly dispersed systems, for which it is important to maintain a stable electrolyte balance and to avoid a significant redistribution of ions between their bulk and surface parts.

Determination of the quantum yield of a heterogeneous photocatalytic reaction employing a black body photoreactor

Abstract Quantum yields of the photocatalytic DCA degradation in aqueous titanium dioxide suspensions (Hombikat UV100, Aeroxide P25) were determined employing a black body like photoreactor. The amounts of photons absorbed by the photocatalysts per unit time were determined by chemical actinometry varying the photon flux and the photon flux density. The photocatalytic DCA degradation experiments were performed under zero order conditions regarding the concentration of the probe compound. The obtained results suggest that the quantum yield of the photocatalytic DCA degradation depends on the photon flux density. Only the low flux density resulting from a large surface area of the light inlet seems to allow the determination of a quantum yield as a photocatalyst-inherent property.

(Invited) Effect of Particle Size on Photocatalytic Reaction Kinetics Including Multielectron-Transfer Processes

Oxidation of water into molecular oxygen (O2 + 4H+ + 4e– → 2H2O) must be the largest-scale chemical reaction occurring on the earth as a part of photosynthesis by plants, and the corresponding backward half-cell reaction, reduction of oxygen into water (O2 + 4H+ + 4e– → 2H2O) might proceed in the same scale by the activity of plants and animals to get energy by combustion of chemicals keeping the concentration of oxygen on the earth. It is well known that the forward and backward reactions are counter oxidation and reduction reactions, respectively, of photocatalytic water splitting/carbon-dioxide fixation and photocatalytic decomposition of organic compounds by semiconductor particles. Standard electrode potential (SEP) of this four electron-transfer redox (O2 + 4H+ + 4e– = 2H2O) is 1.23 V (versus SHE = standard hydrogen electrode potential (0 V) in definition). Almost all the papers reporting oxygen evolution use this SEP, while those of photocatalytic organics decomposition tend to use SEP for one-electron transfer, O2 + e– = O2•– (–0.28 V), for discussion. One of the possible reasons for such difference is that it is convenient to presume the production of superoxide anion radical which may produce "reactive oxygen species (ROS)" to decompose organic compounds. Anyway, it can be stated that those proposed number of transferred electrons seems speculative without any experimental evidence. We have been studying light-intensity dependence (LID) of photocatalytic reaction rates using highly intense UV-LEDs with intensity maximally ca. 3 W cm-2. For oxygen evolution from aqueous titania suspensions in the presence of electron acceptors such as iodate (IO3 –) or iron(III) ions under deaerated conditions, small anatase (8 nm) and rutile (13 nm) particles show bimodal, at first second and then first order, LID in the lower and middle intensity range while large anatase and rutile particles show simple first-order LID in the whole intensity range. This is attributable to two-electron (positive hole) transfer process in the initial step. An interesting feature is that forth-order LID was observed with small anatase particles at high (2.5 W cm-2) intensity to suggest shift of the kinetics to four-electron transfer process [1]. For oxygen reduction, LID analyses for the rate of oxidative decomposition of acetic acid by a bismuth tungstate photocatalyst suggested that two-electron oxygen reduction predominantly proceeds [2]. On the basis of these results, "effective particle size" defined as size of particle (or particle aggregates) in which multiple electrons (positive holes) are accumulated to induce multielectron processes is proposed. This "effective particle size" may govern the effect of size on photocatalytic reaction rates. [1] Takeuchi, S.; Takashima, M.; Takase, M.; Ohtani, B. Chem. Lett. 2018, 47, 373-376. [2] Hori, H.; Takashima, M.; Takase, M.; Ohtani, B. Catal. Today 2018, 313, 218-223.

In Ukrainian

The purpose of this research article is to study the influence of additives of cationic surfactant - benzethonium chloride and the pH of the initial solutions from which suspensions were prepared on the electro-surface properties of titanium dioxide of rutile modification in its aqueous suspensions as well as to detect changes in the ratio between positively charged and negatively charged surface hydroxyl groups due to adsorption of surfactant molecules. In this study, we used powdered rutile-form titanium dioxide (average particle diameter 0.23 µm and specific surface area 14.6 m 2 /g), the surface of which was modified with inorganic oxides (Al 2 O 3 , 4 %, and SiO 2 , 2 %) and graft hydrocarbon chains in order to impart required optical properties and regulate of hydrophobic–hydrophilic balance. Benzethonium chloride is an industrial surfactant that is widely used to regulate the colloidal and chemical properties of many disperse systems. According to the results of the research, it has been found that additives of benzethonium chloride to aqueous suspensions of titanium dioxide have a significant effect upon its electro-surface properties. By using the 2-pK model of a double electric layer and a multistage model of surfactant adsorption on a solid surface, it has been found that the adsorption of benzethonium chloride molecules results in a decrease in the number of surface neutral hydroxyl groups and in the redistribution of superficial positive and negatively charged hydroxyl groups. The character of the redistribution of these groups depends on the pH of the aqueous solutions on the basis of which the suspensions of titanium dioxide were prepared. By evaluating the effect of adsorption of benzethonium molecules on the electro-surface properties of titanium dioxide in its aqueous suspensions, three sites of their dependence on the pH of the initial solutions can be distinguished: the first in the range from pH ≈ 2 to pH ≈ 5, the second in the range from pH ≈ 5 to pH ≈ 9 and the third in the range from pH ≈ 9 to pH ≈ 12. The dependence analysis of the adsorption of benzethonium chloride molecules on the pH of the initial solutions shows that adsorption increases slightly in the first section, does not show any significant fluctuations in the second one, and increases significantly in the third one due to an increase in the pH of the output solutions. The adsorption quantities of benzethonium chloride on titanium dioxide which have been theoretically predicted according to the proposed model, are in good agreement with the experimental results. An increase in the concentration of benzethonium chloride in suspensions involves the displacement of the isoelectric point of the investigated suspensions of titanium dioxide into the alkaline region. The obtained results are in good agreement with the experimental results of the study of the dependence of the zeta potential of titanium dioxide suspensions on the concentration of benzethonium chloride. The found dependencies allow to purposefully regulate properties of aqueous suspensions of titanium dioxide for production of necessary technological compositions.

Light propagation model of titanium dioxide suspensions in water using the radiative transfer equation

Constructions of numerical schemes for solving the radiative transfer equation (RTE) are crucial to evaluate light propagation inside photocatalytic systems. We develop accurate and efficient schemes of the three-dimensional and time-dependent RTE for numerical phantoms modeling aqueous titanium dioxide suspensions, in which the anisotropy of the forward-directed scattering varies and the strength of absorption is comparable to that of scattering. To improve the accuracy and efficiency of the numerical solutions, the forward-directed phase function is renormalized in the zeroth or first order with a small number of discrete angular directions. Then, we investigate the influences of the forward-directed scattering on the numerical solutions by comparing with the analytical solutions. The investigation shows that with the anisotropy factor less than approximately 0.7 corresponding to the moderate forward-directed scattering, the numerical solutions of the RTE using the both of the zeroth and first order renormalization approaches are accurate due to the reductions of the numerical errors of the phase function. With the anisotropy factor more than approximately 0.7 corresponding to the highly forward-directed scattering, the first order renormalization approach still provides the accurate results, while the zeroth order approach does not due to the large errors of the phase function. These results suggest that the developed scheme using the first order renormalization can provide accurate and efficient calculations of light propagation in photocatalytic systems.

Highly Crystalline Nanoparticle Suspensions for Low-Temperature Processing of TiO2 Thin Films.

In this work, we present preparation and stabilization methods for highly crystalline TiO2 nanoparticle suspensions for the successful deposition of transparent, photocatalytically active TiO2 thin films toward the degradation of organic pollutants by a low temperature deposition method. A proof-of-concept is provided wherein stable, aqueous TiO2 suspensions are deposited on glass substrates. Even if the processing temperature is lowered to 150-200 °C, the subsequent heat treatment provides transparent and photocatalytically active titania thin layers. Because all precursor solutions are water-based, this method provides an energy-efficient, sustainable, and environmentally friendly synthesis route. The high load in crystalline titania particles obtained after microwave heating opens up the possibility to produce thin coatings by low temperature processing, as a conventional crystallization procedure is in this case superfluous. The impact of the precursor chemistry in Ti(4+)-peroxo solutions, containing imino-diacetic acid as a complexing ligand and different bases to promote complexation was studied as a function of pH, reaction time and temperature. The nanocrystal formation was followed in terms of colloidal stability, crystallinity and particle size. Combined data from Raman and infrared spectroscopy, confirmed that stable titanium precursors could be obtained at pH levels ranging from 2 to 11. A maximum amount of 50.7% crystallinity was achieved, which is one of the highest reported amounts of anatase nanoparticles that are suspendable in stable aqueous titania suspensions. Decoloring of methylene blue solutions by precipitated nanosized powders from the TiO2 suspensions proves their photocatalytic properties toward degradation of organic materials, a key requisite for further processing. This synthesis method proves that the deposition of highly crystalline anatase suspensions is a valid route for the production of photocatalytically active, transparent films on heat-sensitive substrates such as polymers.

Photocatalytic degradation of an antiparkinson drug entacapone in an aqueous suspension of titanium dioxide

Photocatalytic degradation of an antiparkinson drug entacapone in an aqueous suspension of titanium dioxide

Optimization of photocatalytic decolorization of C.I. Basic Blue 41 in semi‐pilot scale prototype solar photoreactor

AbstractBACKGROUNDThe photocatalytic decolorization of C.I. Basic blue (BB41) in aqueous catalyst suspensions of titanium dioxide (TiO2), Degussa P25, was carried out in a semi‐pilot scale prototype solar photoreactor equipped with compound parabolic collectors (CPCs). The experiments on the solar reactor were performed with and without collectors. Response surface methodology (RSM) was applied to assess individual and interactive effects of the four main independent parameters (initial dye concentration, TiO2concentration, flow rate and initial pH) on the decolorization efficiency, the central composite design (CCD) was used for optimization of UV/TiO2 process.RESULTSThe presence of the collectors has increased the rate of decolorization of 50% for an initial dye concentration of 40 mg L−1 and after 80 kJ L−1 of visible energy accumulated. Predicted values of decolorization efficiency according to RSM were in close agreement with the experimental values (R2 = 0.9626, Adj‐R2 = 0.9252). Optimization results showed that maximum decolorization efficiency was achieved at the optimum conditions catalyst concentration 0.577 g L−1, initial dye concentration 17.933 mg L−1, flow rate 1446.8 L h−1 and initial pH 4.6 for 60 kJ L−1 of VIS energy accumulated.CONCLUSIONThe photocatalytic decolorization of a textile dye, C.I. Basic Blue 41, in a tubular solar prototype photoreactor was optimized. Response surface methodology based on the central composite design has been shown to be a powerful tool in the development of any photocatalytic process due to its impact on the economy and practicability of the process. © 2014 Society of Chemical Industry

TiO2 photocatalytic degradation of caffeine and ecotoxicological assessment of oxidation by-products

<div> <p>The photocatalytic degradation of caffeine has been investigated in aqueous suspensions of titanium dioxide (TiO<sub>2</sub>) by monitoring process efficiency at varying TiO<sub>2</sub> (25 - 175 mg l<sup>-1</sup>) and initial drug concentrations (0.5 - 9.5 mg l<sup>-1</sup>). The use of the response surface methodology (RSM) allowed to fit the optimal regions of the parameters leading to the degradation of the pollutant. Also, a single polynomial expression modelling the reaction was obtained. In parallel a set of bioassays (<em>Daphnia magna</em>, <em>Pseudokirchneriella subcapitata </em>and <em>Lactuca sativa)</em> was performed to evaluate the process in terms of detoxification of caffeine oxidation by-products under chronic and acute tests. Results clearly demonstrate that caffeine is quickly degraded, but not mineralized as quickly, and that persistent toxic organic intermediates resist further oxidation.</p> </div> <p> </p>

Effect of Aqueous Suspensions of Titanium Dioxide in Photoreactor with Radiation Source on Color Changes of Three Contemporary Composite Resins

The study performed to assess the effect of titanium dioxide using (Photoreactor) with the source of radiation on the color change of the three contemporary dental fillings by composite resin material. The resins were divided into three groups head of considering the type of charge and each group of which is composed of five discs and each disc thickness of 2 mm and diameter of 5 mm and manufactured by the mold of Teflon material and then been refined and soften the disc surface and stored in distilled water for one week at 37 °C in order to complete the polymerization. After the completion of the first week is staining the surface of disks and putting it in a solution of iodine mouth wash (AVALON pharma ® ) at 37 °C for a period of just one week after the completion of this week has been directed drive and put it in aqueous suspension consisting of titanium dioxide in Photoreactor Radiation with 355 NM periods of time 0, 5, 10, 15 and 30 seconds. Colorimetric readings were taken of the tablets based on, before staining substance iodine solution, after staining discs textured iodine solution and after treatment disks Palmalq water for titanium dioxide. In addition, the absorbance was measured after each period of time and put the disks. Palmalq watery results were analyzed statistically. There were significant effects on pay chromatography and the palace of color where are different for each group from the other and come the second group of the most influential change chromatography and minors chromatography and then finished second the third set. Finally, comes the first group, as well as influenced by absorbance time in extrusive and different for each group of the three groups of disk attributed to their chemical composition

Heterogeneous Photocatalytic Degradation of Triton X-100 in Aqueous TiO2 Suspensions

The increasing utilization of surfactants generates a great amount of wastes. Surfactants and their more toxic degradation by-products in the environment affect the biota greatly. In particular, the low biodegradation of nonionic surfactants requires efficient oxidation treatments. In addition, the extracted contaminants by high concentrations of non-ionic surfactants in soil remediation may be completely treated using advanced oxidation process and thus the degradation of non-ionic surfactants needs to be checked in this case. The photocatalytic degradation of Triton X-100, a non-ionic surfactant, in aqueous titania suspensions was investigated as a function of catalyst dosage, pH, addition of hydrogen peroxide, potassium persulfate, and Tert-butyl alcohol. For the treatment of 20 mg/L Triton X-100 solutions, the optimum catalyst dosage and pH were determined to be 1 g/L and 6, respectively. The degradation efficiency of Triton X-100 by potassium persulfate was higher than that by hydrogen peroxide when the same mol of oxidants were used. Tert-butyl alcohol can strongly inhibit the photocatalytic oxidation reactions of Triton X-100. The degradation rates as a function of initial surfactant concentrations were interpreted by using a Langmuir-Hinshelwood model. With 0.2 g/L titania or even an additional 0.1 g/L hydrogen peroxide to completely degrade 1 mg/L phenanthrene in a 2 g/L Triton X-100 solution within 30 min, in this case the degradation efficiency of Triton X-100 was less than 5%. This proved that the strategy that surfactants were used as solubilizing agents for the removal of contaminants from soils followed by heterogeneous photocatalytic degradation was feasible.Within 120 min, 2 g/L of Triton X-100 can be degraded up to 67% by the addition of both 1 g/L titania and 1 g/L hydrogen peroxide. Under the right conditions, Triton X-100 can be completely degraded.

An integrated chemical and ecotoxicological assessment for the photocatalytic degradation of vancomycin

The photocatalytic degradation of an antibiotic, vancomycin B hydrochloride (VAN-B), has been investigated in aqueous suspensions of titanium dioxide (TiO2) by monitoring the change in its concentration as well as the production of ammonia and chlorides as a function of irradiation time. The removal of 50 mg L−1 VAN-B solution yields maximum concentrations of 2.45 and 2.53 mg N-NH3 L−1 after 120 min of photocatalytic oxidation using 0.1 and 0.2 g TiO2 L−1, respectively. When 0.2 g TiO2 L−1 were applied up to 87% of the stoichiometric amount of chloride was reached within 120 min of irradiation, corresponding to 0.087 mmol L−1.A set of bioassays (Daphnia magna, Pseudokirchneriella subcapitata and Ceriodaphnia dubia) was performed to evaluate the potential detoxification of VAN-B and its by-products of oxidation under chronic and acute tests. The toxicity of the treated VAN-B samples varied during the oxidation, due to the formation of some intermediate products more toxic than VAN-B. Despite almost total removal of VAN-B that was achieved within 120 min of irradiation, a significant increase in toxicity was observed in chronic tests proving that the chronic assays are more appropriate than acute ones to detect the impact of by-products formed during the photocatalytic degradation of antibiotics.

The effect of poly(methacrylic acid) on electrosurface properties of titanium dioxide in aqueous suspensions

The electrosurface properties and aggregation stability of aqueous titanium-dioxide suspensions are studied in wide ranges of medium pH values and poly(methacrylic acid) concentrations. Using the 2pK model, the ionization constants of surface hydroxyl groups of titanium dioxide are found and it is established that the adsorption of poly(methacrylic acid) macromolecules substantially decreases the fraction of neutral (uncharged) hydroxyl groups and affects the ratio between the positively and negatively charged surface hydroxyl groups.

Influence of supports on photocatalytic degradation of phenol and 4-chlorophenol in aqueous suspensions of titanium dioxide

The photocatalytic degradation of phenol and 4-chlorophenol (4-CP) in aqueous suspensions with the use of titanium dioxide (TiO2) under UV irradiation was examined. The effects of different supporting materials mixed physically with TiO2 were studied to achieve maximum degradation efficiency. Among the three supports, namely activated carbon (AC), silica (SiO2) and zeolite (ZSM-5), all exhibited paramount efficiency for degradation of phenol and 4-CP and was better than TiO2 alone. The optimum concentration was found to be 50 mg for all supporting materials. The efficiency order of the three supports was as follows: AC > ZSM-5 > SiO2, respectively. Whilst, the degradation of phenol and 4-CP was improved from 70.6% to 87.6% and 80.6% to 89.7%, respectively, within 120 min photocatalysis in the presence of optimal amount of AC. The degradation was also comparatively enhanced in the presence of cheaper rice husk and the activity was closed to ZSM-5 and lower than AC.

Solar Photocatalytic Decolorization of Two Azo Dye Derivatives, Acid Red 17 and Reactive Red 241 in Aqueous Suspension

The photocatalytic decolorization approach using sunlight has potential applications in the treatment of effluents from textile dye industries. With this aim, the decolorization of two representative commercially used textile azo dye derivatives such as AR17 and RR241 have been investigated under sunlight and atmospheric oxygen in aqueous suspension of titanium dioxide by monitoring the change in concentration using UV-Vis. Spectrophotometry. A detailed decolorization kinetics of both dye derivatives have been investigated under variety of conditions such as type of TiO2 powders (Anatase/Anatase-rutile mixture), catalyst dose, substrate concentration, pH and electron acceptors (H2O2 and KBrO3). The highest decolorization rate for dye derivative AR17 and RR241 were observed at pH 7.5 and 6.0, respectively. The photocatalyst Degussa P25 having 80:20 anatase:rutile mixture was found to be better for the decolorization of both the dyes as compared to two other photocatalysts tested. The decolorization rate was enhanced in the presence of electron acceptors such as H2O2 and KBrO3. Results demonstrated that the decolorization of dyes under sunlight is strongly influenced by different parameters investigated in this paper.

Photocatalytic degradation of atenolol in aqueous titanium dioxide suspensions: Kinetics, intermediates and degradation pathways

Abstract Photocatalytic degradation of atenolol (ATL) was investigated in aqueous suspensions using TiO2 as photocatalyst. Complete degradation of 37.6 μM ATL was obtained after 60 min irradiation in pH 6.8 Milli-Q water in the presence of 2.0 g L−1 Degussa P25 TiO2. Degradation of ATL followed pseudo-first-order reaction kinetics. Hydroxyl radical (HO ) was determined to be the predominant reactive species during photocatalysis by means of radical probes. Major transformation products were elucidated by high performance liquid chromatograph-mass spectrometry (HPLC–MS/MS) technique. ATL photodegradation pathways included generation of 3-(isopropylamino)propane-1,2-diol and p-hydroxyphenylacetamide through ether chain cleavage, hydroxylation and the formation of 4-[2-hydroxy-3-(isopropylamino)propoxy] benzaldehyde. Frontier electron densities calculation verified the formation of mono-hydroxylation products with HO primarily attacking on benzene ring, which is in agreement with LC–MS/MS analysis. Five carboxylic acids, i.e., oxalic, glyoxylic, malonic, oxamic and formic acids were identified by ion exchange chromatography by comparison with authentic standards. Photocatalytic degradation efficiency of ATL was highly dependent on the properties of the water matrix, such as pH, the presence of organic and inorganic species (e.g., humic substance, HCO3−). River water matrix was found to play a detrimental effect on ATL photocatalytic degradation with a longer irradiation time required for complete elimination of mother compound and intermediate products. Degussa P25 exhibited the highest photocatalytic activity for oxidizing ATL as well as intermediates compared to Aldrich rutile, Millennium PC500 and Hombikat UV100.

Photocatalysed decolourization of two textile dye derivatives, Martius Yellow and Acid Blue 129, in UV-irradiated aqueous suspensions of Titania

Photocatalysed decolourization of two textile dye derivatives, Martius Yellow and Acid Blue 129, has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The decolourization was studied by monitoring the decrease in dye concentration as a function of irradiation time employing the UV spectroscopic analysis technique. The decolourization kinetics was investigated under different conditions such as types of TiO2 (Anatase [Hombikat UV-100 and PC500]/Anatase–Rutile mixture [Degussa P25]), initial reaction pH, catalyst dosage, dye concentration and in the presence of electron acceptors such as potassium bromate, hydrogen peroxide and ammonium persulphate. The decolourization of both dyes was also investigated under sunlight. The decolourization rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient for the decolourization of dye derivative Martius Yellow, while UV100 was better for the decolourization of Acid Blue 129. All the electron acceptors markedly enhanced the decolourization rate of Martius Yellow, while only KBrO3 as an electron acceptor shows pronounced effect for the decolourization of Acid Blue 129 in the presence of TiO2 and air.