Aqueous Suspensions Of Titanium Dioxide Research Articles

Photocatalytic degradation of Reactive Brilliant Blue KN-R by TiO 2/UV process

The photocatalytic degradation of Reactive Brilliant Blue KN-R has been investigated under UV irradiation in aqueous suspension of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in dye concentration using UV spectroscopic technique. The effects of key operation parameters such as initial dye concentration, catalyst loading, hydrogen peroxide dosage as well as initial pH value on the decolorization extents were studied. The decolorization of the organic molecule followed a pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. Under the optimum operation conditions, approximately 97.7% color removal was achieved with significant reduction in TOC (57.6%) and COD (72.2%) within 3 h. Moreover, the degradation products were analyzed by GC–MS technique and probable pathways for the formation of products were proposed.

Photocatalyzed reaction of indole in an aqueous suspension of titanium dioxide

The photocatalyzed oxidation of indole (1) in an aqueous suspension of titanium dioxide has been investigated and an attempt has been made to identify the products formed during the photooxidation process by gas chromatographic–mass spectrometric (GC–MS) analysis. Photolysis of an aqueous solution of indole (1) in the presence of titanium dioxide and oxygen led to the formation of 2,3-dihydroindole-2-one (6) and 1H-indole-2,3-dione (7). A probable pathway for the formation of these products has been proposed.

A comparative photocatalytic activity of titanium dioxide and zinc oxide by investigating the degradation of vanillin

The photocatalytic degradation of an organic pollutant such as vanillin has been investigated in aqueous suspensions of titanium dioxide and zinc oxide by monitoring the change in substrate concentration employing UV spectroscopic analysis and decrease in Total Organic Carbon (TOC) content as a function of irradiation time under a variety of conditions. The degradation of the model compound was studied under different conditions such as pH, catalyst concentration, substrate concentration and in the presence of an electron acceptor such as hydrogen peroxide besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Degussa P25 was found to be more efficient as compared with other photocatalysts, Hombikat UV100 and ZnO.

Photocatalytic degradation of C.I. Acid Blue 80 in aqueous suspensions of titanium dioxide under sunlight

The dye C.I. Acid Blue 80 (AB80) was easily degraded by TiO2-P25 assisted photocatalysis in aqueous dispersion under irradiation of sunlight. The optimal reaction conditions were [TiO2] = 2.0 g/L, pH = 10, [H2O2] = 5 mmol/L. The photocatalytic reaction followed pseudo-first order kinetics. The adsorption of AB80 onto TiO2 was in accord with Langmuir equation.

Electrophoretic Deposition on Anodes from Aqueous Titania Suspensions with Titanate Solution

Titanate aqueous solution (TTIP-Lac) prepared by direct reaction of titanium tetraisopropoxide (TTIP) with lactic acid (Lac) in water shows characteristics of a polyanion and acts as a dispersant for preparing titanate suspension. Electrophoretic deposition (EPD) of aqueous titania suspensions was investigated with TTIP-Lac as a dispersant and hydroquinone (HQ) as an effective additive for bubble-free EPD of the aqueous system. The oxygen produced electrolytically by the EPD process at basic pH would be consumed by the chemical oxidation of HQ to quinone (Q). Bubble-free titania depositions were fabricated on anodes by EPD. A fired density with 99% theoretical density was obtained.

Ozone enhanced activity of aqueous titanium dioxide suspensions for photodegradation of 4-chloronitrobenzene

The TiO 2/UV/O 3 process has been employed to remove 4-chloronitrobenzene (4-CNB) and compared to UV/air, O 3, TiO 2/O 3, TiO 2/UV/O 2 and UV/O 3 five parallel oxidation pathways. The reaction activities of these six processes were tested in aqueous using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. Moreover, the effects of ozone dosage, catalyst dosage and initial solution pH on the degradation of 4-CNB by TiO 2/UV/O 3 process were also investigated. Results showed that the TiO 2/UV/O 3 is the most efficient process for complete mineralization of 4-CNB since the combination of photocatalytic oxidation with ozone has a synergistic effect. The relative intensity of DMPO- OH follows the order of UV/air < O 3 < TiO 2/O 3 < UV/O 3 < TiO 2/UV/O 2 < TiO 2/UV/O 3. In TiO 2/UV/O 3 process, the ozone and catalyst dosage are found to have a significant impact on the process efficiency whereas initial pH has relatively less effect. Chlorine atoms of 4-CNB are absolutely oxidized to chloride anions when the ozone dosage in the range of 5–18 mg/min, or the catalyst dosage ranging from 1.0 to 2.0 g/L. Part of chloride anions would be further oxidized to chlorate(V) ions if the ozone dosage exceeds 24 mg/min, or the catalyst dosage exceeds 2.0 g/L.

Effect of Lamp Power and Its Position on Photocatalytic Degradation of Phenol in Aqueous Suspension of TiO2

The photocatalytic degradation of phenol under irradiation with UV light was investigated in aqueous suspension of nano titanium dioxide (TiO2). The effects of photocatalyst such as TiO2 (anatase) and TiO2-P25 and power of UV-lamp along with position on the photocatalytic degradation of phenol have been studied. The degradation kinetics was analyzed by the change in phenol absorbance employing UV-vis spectrometry as a function of irradiation time. The degradation follows first order kinetics. TiO2-P25 was found to be more reactive than TiO2 (anatase) which is attributed to small crystalline size. Horizontal position of the lamp was found to be better than vertical position of lamp. The degradation was also enhanced with increased in power of UV lamp. [DOI: 10.1380/ejssnt.2009.804]

Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home-prepared titanium dioxide

Abstract Oxygenated aqueous suspensions of home-prepared (HP) and commercial TiO2 catalysts were used in a batch photoreactor for carrying out the oxidation of benzyl alcohol (BA) and 4-methoxybenzyl alcohol (MBA) under different operative conditions. HP catalysts were synthesized from TiCl4 and underwent a hydrolysis treatment of different times under mild conditions. The textural characterization of catalysts was carried out with XRD, SEM observations, BET surface area and porosity measurements. For both alcohols the main oxidation products were the corresponding aromatic aldehydes and CO2. The HP catalysts exhibited selectivity values towards the aldehyde production up to 28% (BA conversion: 50%) and 41% (MBA conversion: 65%), about four times higher than those of commercial TiO2. The addition of an aliphatic alcohol (methanol, ethanol, 2-propanol or tert-butanol) in small amounts with respect to water decreased the overall oxidation rate of aromatic alcohols but enhanced the selectivity for aldehyde formation up to 1.5 times. The reactivity results suggest that: (i) the aromatic alcohol molecules interact with the TiO2 surface in different ways that eventually determine two parallel reaction pathways (partial oxidation or mineralization); (ii) the aliphatic alcohols preferentially compete with aromatic alcohols for the mineralizing pathway.

Photocatalyzed Degradation of a Pesticide Derivative Glyphosate in Aqueous Suspensions of Titanium Dioxide

The photocatalytic degradation of a herbicide derivative, glyphosate [(N‐phosphonomethyl) glycine] has been investigated in aqueous suspensions of titanium dioxide at different pH values. This compound was found to degrade more efficiently under alkaline pH, where no adsorption takes place on the surface of the catalyst in the dark. The main degradation route involves the cleavage of the P–C bond giving rise to sarcosine and glycine as the intermediate products formed during the photooxidation process.

Photocatalytic degradation of two selected dye derivatives in aqueous suspensions of titanium dioxide

The photocatalytic degradation of two selected dye derivatives, CI Fast Green FCF (1) and CI Acid Blue 1 (2, Patent blue VF) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the change in substrate concentration employing UV spectroscopic technique as a function of irradiation time under a variety of conditions. The degradation was studied under different conditions such as different types of TiO2, pH, catalyst concentration, substrate concentration and in the presence of different electron acceptors such as hydrogen peroxide (H2O2), potassium bromate (KBrO3) and ammonium persulphate (NH4)2S2O8) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst Hombikat UV100 was found to be more efficient for the degradation of Fast Green FCF, whereas Degussa P25 was found to be better for the degradation of Patent Blue VF. Dye (2) was found to degrade more efficiently compared to dye (1).

Photocatalytic reduction of Cr(VI) in aqueous titania suspensions exposed to concentrated solar radiation

A laboratory scale parabolic trough collector has been tested for photocatalytic reaction application to wastewater treatment under different reaction conditions. The photocatalytic reduction of Cr(VI) to Cr(III), using TiO2 suspensions under solar irradiation, has been investigated. The influence of reaction conditions has been illustrated using an organic additive (citric acid) in varying doses and also by performing the reaction at different pH values and doses of TiO2. An attempt has also been made to investigate the reuse performance of the photocatalyst. The rate of reduction was found to increase steadily with increasing concentration of organic additive, TiO2 dose and decreasing pH. Complete reduction of Cr(VI) to Cr(III) was achieved in 2 h and very low catalyst concentration at pH 2. The reuse studies showed that the catalyst can be used 2–3 times for lower Cr(VI) concentrations.

Semiconductor-Mediated Photocatalyzed Degradation of a Pesticide Derivative, Glyphosate in Aqueous Suspensions

The photocatalytic degradation of a herbicide derivative, glyphosate [(N-phosphonomethyl) glycine] has been investigated in aqueous suspensions of titanium dioxide at different pH values. The model compound was found to degrade more efficiently under alkaline pH where little or no adsorption of glyphosate occurs on the surface of the catalyst in the dark. The main degradation route involves the cleavage of the P-C bond giving rise to sarcosine and glycine as the intermediate products formed during the photooxidation process.

Photodegradation of 2-naphthol in water by artificial light illumination using TiO2 photocatalyst: Identification of intermediates and the reaction pathway

Abstract The kinetics of the photocatalytic degradation of 2-naphthol has been investigated in aqueous suspensions of titanium dioxide (TiO 2 ) under a variety of conditions, which is essential from application point of view. The degradation was studied using different parameters such as types of TiO 2 , catalyst concentration, substrate concentration, reaction pH and in the presence of different electron acceptors such as hydrogen peroxide (H 2 O 2 ), potassium bromate (KBrO 3 ) and potassium persulphate (K 2 S 2 O 8 ) besides molecular oxygen. The degradation rates were found to be strongly influenced by all the above parameters. The photocatalyst “Degussa P-25” was found to be more efficient as compared with other photocatalysts. The degradation kinetics fit well to the Langmuir–Hinshelwood rate law. It was found that an optimal concentration of 5 × 10 −4 mol/l Ag + in TiO 2 achieved the fastest 2-naphthol degradation under the experimental conditions. However, with the addition of Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , Co 2+ and Ni 2+ , there are no obvious effects on the reactions. An analysis of total organic carbon (TOC) showed that a complete mineralization of 2-naphthol can be easily achieved. The intermediate products were identified by HPLC–MS technique. A detailed degradation pathway could be proposed.

Photoassisted mineralization of aromatic and aliphatic N-heterocycles in aqueous titanium dioxide suspensions and the fate of the nitrogen heteroatoms

The photoassisted degradation of aromatic heterocycles (pyrrole, imidazole, pyrazole, isoxazole, oxazole and thiazole) and N-containing alicycles (aliphatic heterocycles: pyrrolidine, 4-butanelactam and 5-pentanelactam) was examined in liquid–solid dispersions. Complete mineralization (TOC) of the aromatic heterocycles was attained within ca. 1h of UV irradiation of the TiO2/heterocycle system in acidic (pH 3), near-neutral (pH 6.0–7.6) and alkaline (pH 11) media. Mineralization kinetics were, in general, not appreciably influenced by the presence of acid but tended to be somewhat slower in alkaline media. N-alicycles were photomineralized more slowly than were the aromatics. The former could be mineralized in acidic and near-neutral media in less than 2h, but not in alkaline media in which pyrrolidine, 4-butanelactam and 5-pentanelactam (and for comparison 4-butanelactone) were not mineralized even after 3h of UV irradiation. Final products were, in all cases, CO2, NH4+ and NO3− ions and SO42− ions in the case of thiazole. Nitrogen (N2) gas was detected only during the photooxidation of pyrazole (contains two adjacent N heteroatoms) but not imidazole in which the N atom are separated by a C atom. The molar ratio NH4+/NO3− depended closely on the chemical structure of the substrates at the longer irradiation times. The site and mode of adsorption of these heterocycles onto the TiO2 particle surface were inferred from point charge calculations and the point of zero charge of the TiO2 (pHpzc ∼6.7); the position of elecrophilic attack by the photogenerated OH radicals was deduced from calculated frontier electron densities.

Photocatalytic oxidation mechanism of benzonitrile in aqueous suspensions of titanium dioxide

The photocatalytic oxidation of benzonitrile was carried out in aqueous suspensions (pH 11) of commercial polycrystalline TiO 2 (Merck and Degussa P25) irradiated by ultraviolet light. The rate of decomposition was dependent on the concentration of benzonitrile and followed a pseudo-first order kinetics. The complete mineralization of a 0.70 mM benzonitrile solution was achieved in ca. 8 h by using TiO 2 Degussa P25, whereas the substrate was only partially mineralized even after 14 h of irradiation in the presence of TiO 2 Merck. The final oxidation products were carbonate and nitrate. The appearance and the evolution of organic and inorganic intermediate species were also investigated and allowed to hypothesize the reaction pathways.

Heterogeneous photocatalytic degradation of the pharmaceutical agent salbutamol in aqueous titanium dioxide suspensions

The present paper deals with the photocatalytic transformation of salbutamol [2-(tert-butylamino)-1-(4-hydroxyl-3-hydroxymethylphenyl)ethanol] under simulated solar irradiation using titanium dioxide as a photocatalyst. The investigation has involved a kinetic study of the drug decomposition, the identification of intermediate compounds, the assessment of mineralization, as well as toxicity evaluation. The variation of TiO2 concentration and pH on the reaction rate was investigated. The use of the response surface methodology allowed to fit the optimal values of the parameters leading to the degradation of the micro-pollutant. High resolution mass spectrometry was employed in assessing the temporal course of the photocatalyzed process. According to our findings, a tentative degradation pathway is proposed for the photocatalytic degradation of salbutamol based on the formation of both oxidative and reductive compounds. 2-(Methylamino)-1-(4-hydroxyl-3-methylphenyl)ethanol, 2-(tert-butylamino)-1-(4-hydroxylphenyl)ethanol, 2-(tert-butylamino)-1-(3,4-dihydroxyphenyl)ethanol, 2-(tert-butylamino)-1-(4-hydroxyl-3-methylphenyl)ethanol, and 2-(tert-butylamino)-1-(3,4-dihydroxyphenyl)ethanone are initially formed, which are then transformed into 2-(tert-butylamino)-acetic acid and hydroquinone. All these intermediates are easily degraded themselves and until 2h of irradiation 2-(tert-butylamino)-acetic acid is the only compound recognized to endure.Photomineralization of the substrate was rather a quick process; within 2h of irradiation nitrogen is completely mineralized, where the amino moiety is mainly transformed into NH4+ and in a lesser extent into NO3− ions (ratio 2:1). Carbon complete mineralization is achieved within 3h of irradiation. Finally, Microtox bioassay (Vibrio fischeri) was employed in evaluating the ecotoxicity of solutions treated by photocatalysis.

Photocatalytic removal of hazardous dye cyanosine from industrial waste using titanium dioxide

In this paper, photocatalytic degradation studies of a hazardous water soluble xanthene dye cyanosine in aqueous suspensions of titanium dioxide under a variety of conditions, viz., catalyst concentration, substrate concentration, pH, temperature and electron acceptor hydrogen peroxide (H 2O 2) have been reported. It was observed that photocatalytic degradation by TiO 2 is an effective, economic and faster mode of removing cyanosine from aqueous solution. The optimum conditions for the degradation of the dye was dye concentration 1 × 10 −4 M, pH 8, catalyst concentration 0.04 g/L and temperature ±30 °C. Chemical oxygen demand and dye absorbance of the photodegraded dye solution substantially decreased.

Visible-Light-Mediated TiO2 Photocatalysis of Fluoroquinolone Antibacterial Agents

This study reports on the photocatalytic transformation of fluoroquinolone antibacterial agents (ciprofloxacin, enrofloxacin, norfloxacin, and flumequine) in aqueous titanium dioxide (TiO2) suspensions irradiated with ultraviolet (UV; lambda > 324 nm) or visible light (lambda > 400, > 420, or > 450 nm). Visible-light-mediated fluoroquinolone degradation is unexpected from direct photolysis or established TiO2 band gap photoexcitation mechanisms, which both require UV light. Visible-light-mediated photocatalysis requires an appropriate conduction band electron acceptor (e.g., O2, BrO3-), but is not dependent upon hydroxyl radical, superoxide, or other reactive oxygen species generated upon TiO2 band gap excitation. The process slows considerably when fluoroquinolone adsorption is inhibited. Whereas fluoroquinolone decomposition in UV-irradiated TiO2 suspensions is accompanied by mineralization, no changes in dissolved organic carbon occur during visible-light-photocatalyzed degradation. Results are consistent with a proposed charge-transfer mechanism initiated by photoexcitation of surface-complexed fluoroquinolone molecules. Complexation to the TiO2 surface causes a red shift in the fluoroquinolone absorption spectrum (via ligand-to-metal charge transfer), enabling photoexcitation by visible light. Fluoroquinolone oxidation then occurs by electron transfer into the TiO2 conduction band, which delivers the electron to an adsorbed electron acceptor. The lack of organic carbon mineralization indicates formation of stable organic byproducts that are resistant to further degradation by visible light. In UV-irradiated TiO2 suspensions, the charge-transfer mechanism acts in parallel with the semiconductor band gap photoexcitation mechanism.

Heterogeneous photocatalysed decolorization of two selected dye derivatives neutral red and toluidine blue in aqueous suspensions

The photocatalysed decolorization of two selected dye derivative neutral red ( 1 ) and toluidine blue ( 2 ) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The decolorization was studied by monitoring the change in concentration of organic dyestuff employing UV spectroscopic analysis technique as a function of irradiation time. The decolorization was investigated using various parameters such as, different types of TiO 2 , reaction pH, catalyst concentration, concentration of organic dyestuffs, and in the presence of electron acceptors like hydrogen peroxide (H 2 O 2 ) and potassium bromate (KBrO 3 ) besides molecular oxygen with an aim to determine the optimal decolorization condition for the decomposition of compounds under investigation.

Photocatalytic Degradation of Monolinuron and Linuron in an Aqueous Suspension of Titanium Dioxide Under Simulated Solar Irradiation

The photocatalytic degradation of two phenylurea herbicides, monolinuron (MLN) and linuron (LN), was investigated in an aqueous suspension of TiO2 using simulated solar irradiation. The objective of the study was to compare their photocatalytic reactivity and to assess the influence of various parameters such as initial pesticide concentration, catalyst concentration and photonic flux on the photocatalytic degradation rate of MLN and LN. A comparative study of the photocatalytic degradation kinetics of both herbicides showed that these two compounds have a comparable reactivity with TiO2/simulated sun light. Under the operating conditions of this study, the photocatalytic degradation of MLN and LN followed pseudo first-order decay kinetics. The kobs values indicated an inverse dependence on the initial herbicide concentration and were fitted to the Langmuir-Hinshelwood equation. Photocatalytic degradation rates increased with TiO2 dosage, but overdoses did not necessarily increase the photocatalytic efficiency. The degradation rate of MLN increased with radiant flux until an optimum at 580 W m‑2 was reached and then decreased. Under these conditions, an electron-hole recombination was favored. Finally, the photocatalytic degradation rate depended on pH, where an optimum was found at a pH value close to the pH of the point of zero charge (pH = 6).