Presence Of Titanium Dioxide Research Articles

Artifactual formylation of the secondary amine of duloxetine hydrochloride by acetonitrile in the presence of titanium dioxide: Implications for HPLC method development

Duloxetine hydrochloride, a secondary amine containing pharmaceutical, currently marketed as Cymbalta™, is shown to undergo N-formylation as an artifact of sample preparation prior to HPLC analysis for impurities. The reaction was discovered as a result of an investigation into variability in the levels of N-formyl duloxetine observed upon HPLC analysis. The reaction is catalyzed by sonication and/or light in the presence of titanium dioxide and is proposed to occur via a radical-initiated mechanism. The mechanism is supported by controlled sample preparation studies with deuterium-labeled acetonitrile and LC/MS studies that showed incorporation of one deuterium into N-formyl duloxetine. This discovery is broadly relevant because sonication is commonly used to aid dissolution of pharmaceuticals in acetonitrile for HPLC analysis, titanium dioxide is a commonly used excipient, the amount of light found in modern analytical laboratories is sufficient to cause the reaction to occur, and secondary amines are present in the structures of many pharmaceuticals. The artifactual reaction was effectively eliminated by changing the sample solvent to methanol and replacing sonication with shaking to aid sample dissolution.

Photocatalytic degradation of lindane by polyoxometalates: Intermediates and mechanistic aspects

The photocatalytic degradation of lindane (γ-1,2,3,4,5,6-hexachlorocyclohexane) has been studied in the presence of the polyoxometalate PW 12O 40 3− in aqueous solutions. Lindane is fully decomposed to CO 2, Cl − and H 2O, while a great variety of intermediates has been detected using GC–MS, including aromatic compounds (dichlorophenol, trichlorophenols, tetrachlorophenol, hexachlorobenzene, di- and trichloro-benzenodiol), non-aromatic cyclic compounds (penta-, tetrachlorocyclohexene, heptachlorocyclohexane), aliphatic compounds (tetrachloroethane) and condensation products (polychlorinated biphenyls). The number and nature of the intermediates implies that the mechanism of decomposition of lindane is based on both oxidative and reductive processes. Common intermediates have been reported during photolysis of lindane in the presence of titanium dioxide. A similar overall mechanism of polyoxometalates and TiO 2 photocatalysis through the formation of common reactive species is suggested.

Adsorption and photodegradation of Procion yellow H-EXL dye in textile wastewater over TiO 2 suspension

Removal of a commercial dye (Procion yellow H-EXL) in both synthetic and real wastewater from textile industry over TiO 2 suspension has been investigated. The study included both adsorption process (over TiO 2) and photocatalytic degradation process in the presence of UV illumination (UV/TiO 2). The processes were carried out in aqueous solutions containing the dye in the presence of titanium dioxide, TiO 2, (Degussa P-25) upon UV irradiation of 100 W. The photocatalytic process used the photogenerated holes (at the surface of TiO 2) and hydroxyl radicals (at the solution bulk) as oxidizing species for the dye. Different parameters affecting the adsorption and photocatalytic degradation processes such as solution pH, initial dye concentration, and TiO 2 dosages were investigated, Results obtained revealed that various dye concentration loads were removed at optimum solution pH = 5 with TiO 2 dosage of 1 g/L. The dye removal % is inversely proportional to its concentration, the lower the dyes concentration, the higher the efficiency of dye removal. The efficiency values of both adsorption and photocatalytic degradation processes reached maximum values of 46.4 and 100%, respectively, with dye concentration of 10 mg/L. The photocatalytic degradation of the investigated dye exhibited pseudo first-order kinetics according to the Langmuir–Hinshelwood's heterogeneous catalytic model

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.

Photodimerization and photooxygenation of 9-vinylcarbazole catalyzed by titanium dioxide and magnesium perchlorate

Photoreaction of 9-vinylcarbazole in acetonitrile in the presence of titanium dioxide and a catalytic amount of magnesium perchlorate gave 3,6-di(9-carbazolyl)-1,2-dioxane as a photooxygenated product via photodimerization of 9-vinylcarbazole. The photoreaction proceeds via an electron transfer mechanism, where magnesium perchlorate accelerated formation of the photooxygenated product.

Photocatalytic treatment of indoor air: Optimization of 2-propanol removal using a response surface methodology (RSM)

This paper presents an experimental design methodology for the optimization of the photocatalytic removal of 2-propanol also called isopropyl alcohol (IPA) at indoor air concentration level (ppbv). The response surface methodology (RSM) for the modelization and optimization of the photodegradation of 2-propanol in the presence of titanium dioxide was used. The effect of four different process parameters on the yield of 2-propanol mineralization was determined. Experiments were performed using an annular flow-through reactor with TiO2 as photocatalyst, 2-propanol as a volatile organic compound (VOC) model, under different ranges of relative humidity (RH: 0–60%), inlet concentration (100–700ppbv) and flow rate (100–500mLmin−1), TiO2 loading (5–20gm−2). Analysis of reaction intermediates was conducted using an automated thermal desorption technique coupled with gas chromatography–mass spectrometry (ATD–GC–MS) whereas a gas chromatograph equipped with a pulsed discharge helium photoionization detector (GC–PDHID) was used for on-line measurements of CO and CO2 at ppbv level. RH was found as the principal parameter that affect significantly the mineralization and the formation of acetone, the principal reaction intermediate from the photocatalytic oxidation of 2-propanol. For example an immediate and total removal of 2-propanol at very low % of RH along with a high rate of mineralization without any by-products was found. Many strong interactions between the parameters were also found ([2-propanol]–flow rate, RH–[TiO2], [2-propanol]–RH). The model obtained (R2=0.9965) shows a satisfactory correlation between the values of experimental data and predicted values of 2-propanol mineralization (CO2).

The recovery and recycling of mercury from fluorescent lamps using photocatalytic techniques

AbstractBACKGROUND: Release of mercury from fluorescent lamps must be minimized to avoid its hazardous effects on human beings and other living organisms. Because of this, increasing attention is given to the improvement of existing techniques for its recovery as well as the development of new ones. This paper describes the application of heterogeneous photocatalysis for the selective reduction of mercury from fluorescent lamps. The whole process involves mercury chemical extraction using aqueous solutions of sodium hypochlorite. After pH adjustment of the resulting aqueous solution, the photocatalytic reduction of mercury is performed in the presence of titanium dioxide and citric acid as an auxiliary organic agent.RESULTS: Mercury removal from the aqueous solution is higher than 99% and the final residual concentration is 4 ppb. A mixture of different mercury compounds is obtained in solid form deposited on the titanium oxide photocatalyst which can easily be redissolved into a small volume of sodium hypochlorite. Metallic mercury could be obtained from the residual Hg(II) solution by conventional cementation techniques with iron as reducing agent.CONCLUSION: Results show high efficiencies of the photocatalytic technique for recovery and recycling of mercury from fluorescent lamps. Copyright © 2009 Society of Chemical Industry

Oxidation of organics in retentates from reverse osmosis wastewater reuse facilities

The use of membrane processes for wastewater treatment and reuse is rapidly expanding. Organic, inorganic, and biological constituents are effectively removed by reverse osmosis (RO) membrane processes, but concentrate in membrane retentates Disposal of membrane concentrates is a growing concern. Applying advanced oxidation processes (AOPs) to RO retentate is logical because extensive treatment and energy inputs were expended to concentrate the organics, and it is cheaper to treat smaller flowstreams. AOPs (e.g., UV irradiation in the presence of titanium dioxide; UV/TiO 2) can remove a high percentage of organic matter from RO retentates. The combination of AOPs and a simple biological system (e.g., sand filter) can remove higher levels of organic matter at lower UV dosages because AOPs produce biologically degradable material (e.g., organic acids) that have low hydroxyl radical rate constants, meaning that their oxidation, rather than that of the primary organic matter in the RO retentate, dictates the required UV energy inputs. At the highest applied UV dose (10 kWh m −3), the dissolved organic carbon (DOC) in the RO retentate decreased from ∼40 to 8 mg L −1, of which approximately 6 mg L −1 were readily biologically degradable. Therefore, after combined UV treatment and biodegradation, the final DOC concentration was 2 mg L −1, representing a 91% removal. These results suggest that UV/TiO 2 plus biodegradation of RO retentates is feasible and would significantly reduce the organic pollutant loading into the environment from wastewater reuse facilities.

A study on synergistic effect of photocatalytic ozonation for carbaryl degradation

The combination of UVA radiation and ozone, in the presence of titanium dioxide, has been investigated as a potential destructive technology for the treatment of pesticide wastewaters. The contribution of single ozonation (O 3), photolytic ozonation (O 3/UV), and photocatalysis (TiO 2/UV) to degradation of carbaryl, a carbamate pesticide is assessed and compared with that of combined photocatalytic ozonation process (TiO 2/UV/O 3). For 40 mg/L of carbaryl (500 mL) at pH 6 and with 0.28 g/h of ozone and 1 g/L of TiO 2, 92% COD reduction was achieved in 180 min. Under this experimental condition, 76.5% TOC removal and increase of BOD 5/COD ratio to 0.38 was also observed. The synergistic effect occurs in the combined photocatalytic ozonation process which is proved by the significant improvement in the mineralization rate constant (0.09 min –1) when compared with the sum of mineralization rate constant of photocatalysis and ozonation (0.05 min –1). Further synergistic effect was noticed at acidic and neutral pH, but synergism was lost at alkaline pH due to faster self decomposition of ozone.

Photocatalytic degradation of Bisphenol A (BPA) using immobilized TiO 2 and UV illumination in a horizontal circulating bed photocatalytic reactor (HCBPR)

Photocatalytic degradation of Bisphenol A (BPA) in the presence of titanium dioxide (TiO 2) and ultraviolet (UV) illumination was performed in a self-designed horizontal circulating bed photocatalytic reactor (HCBPR). TiO 2 catalyst was immobilized on the surface of polyurethane foam (PF) cubes via microwave-assisted liquid phase deposition. The effects of initial BPA concentration, initial pH, TiO 2 dosage and temperature on BPA photodegradation were investigated in order to obtain the optimum operational conditions. The results reveal that the BPA degradation efficiency can be effectively improved by increasing pH from 3.4 to 12.3 or decreasing the initial BPA concentration from 50 to 10 ppm. The optimum TiO 2 carrier dosage (the ratio of the volume of PF carriers to the effective reaction volume of HCBPR) was about 1%. Besides, the effect of temperature on BPA photodegradation was found to be unremarkable in the range of 21.2–30.5 °C. Total organic carbon (TOC) was used to evaluate the mineralization of BPA during the photodegradation process. Under the optimum conditions, 95% removal of TOC and 97% removal of BPA can be achieved after 6 h of UV radiation, which demonstrates the high photodegradation efficiency of BPA in HCBPR.

Kinetic investigation of Cu(II) ions photoreduction in presence of titanium dioxide and formic acid

The photoreduction of Cu(II) in presence of an organic species as sacrificial agent has been investigated by many research groups but some controversial results are reported in literature. In this work, the photoreduction process of Cu(II) in presence of formic acid is investigated aiming at clarifying the reaction mechanism and assess the reaction kinetics. The effect of operating conditions such as TiO 2 load, initial concentration of sacrificial agent, pH and ionic strength was studied. The results of the work are: (1) the system reactivity does not depend neither on pH (in the range 2.0–3.5) nor on ionic strength of the solution; (2) formic acid is adsorbed on TiO 2 surface; (3) the nature of anionic species can influence the Cu(II) photoreduction (e.g. the addition of sulphate or phosphates reduces the reaction rates); and (4) FA can be completely mineralized during this photoxidation process; for example, this is observed for a TiO 2 load of 0.1 g/L after a reaction time of about 240 min. A simplified kinetic model is developed to describe the behavior of the system and validated by analysing the data collected during the experimental work.

Influence of hydroxypropyl-β-cyclodextrin on the photostability and antiradical activity of Trolox

Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a derivative of vitamin E, can undergo photolysis upon UV irradiation. In the present study the photodegradation kinetics of Trolox were thus investigated in different systems in the absence and in the presence of titanium dioxide, a physical sunscreen present in several cosmetic products, that can act as photocatalyst. In all the considered media Trolox degraded under UVB light following pseudo-zero order kinetics, probably by a mechanism of photooxidation. The rate of Trolox photodegradation was lower in O/W emulsions than in aqueous solution and in gel; furthermore it was significantly influenced by the presence of TiO2. Aiming to increase Trolox stability, it was complexed with hydroxypropyl-β-cyclodextrin: the inclusion complex was characterized by phase solubility studies, spectrophotometry and differential scanning calorimetry. The irradiation experiments indicated that complexation with hydroxypropyl-β-cyclodextrin was effective in reducing the photodegradation rate of Trolox. Moreover the host molecule favored the uptake of Trolox into the porcine skin, as shown by in vitro permeation studies. Nevertheless the assay of peroxidation, based on the reaction of malondialdehyde with thiobarbituric acid, indicated that the antioxidant activity of Trolox was maintained even after inclusion in cyclodextrin.

Photocatalytic degradation of indole in UV/TiO2: optimization and modelling using the response surface methodology (RSM)

The aim of our research is to apply experimental design methodology to the optimization of photocatalytic degradation of indole present in wastewater. Heterogeneous photocatalysis for the oxidation of organic biorecalcitrant pollutants in water is an environmental promising method. We used the response surface methodology (RSM) for the modelization and optimization of the photodegradation of indole in the presence of titanium dioxide. The effect of indole concentration, UV intensity and stirring speed on the yield of indole degradation was determined. According to the mathematic optimization of the process, the optimum point when 100% of degradation is achieved is given by the following values: UV intensity = 250 W/m2, stirring speed = 536.36 tr/min and initial indole concentration = 10.10 mg/l.

Photocatalytic reduction of methylene blue by formaldehyde in the presence of titanium dioxide and cadmium sulfide sensitized by (1-phenyl-5,6-benzoquinoline-2)-2,4-dihydroxystyryl iodide

New heterostructures of a dye, (1-phenyl-5,6-benzoquinoline-2)-2,4-dihydroxystyryl iodide, with TiO2 and CdS were obtained and their photocatalytic activity in the reduction of methylene blue by formaldehyde was established under different irradiation conditions and with different dye concentrations. Explanations for the behavior found are proposed.

Photocatalytic Ozonation of Winery Wastewaters

The combination of UV-A/vis radiation and ozone, in the presence of titanium dioxide, has been investigated as a potential destructive technology for the treatment of winery wastewaters. The contribution of the adsorption stage, single ozonation, photolytic ozonation, and photocatalysis has previously been assessed. Adsorption onto the TiO 2 surface accounts for a 15-20% removal of the initial chemical oxygen demand (COD). The rest of the subsystems attain COD conversion values in the range of 37-43%. The photocatalytic ozonation of the effluent, under the operating conditions investigated, increases the COD depletion to a value close to 80%. The working pH was studied in the range of 3-11, the optimum value being located in the acidic region (pH 3). A saturation-like behavior is experienced when the amount of TiO 2 used is varied in the interval of 0-3 g L(-1). Contrary to the use of ozone alone, the system UV-A/vis/O3/TiO2 leads to the total mineralization of the COD removed. A proposed pseudoempirical model suggested the existence of a synergistic effect when radiation, ozone, and titanium dioxide are combined.

Preparation and characterization of titanium dioxide nanocomposite fibers

Titanium dioxide and polypropylene fibers were prepared by melt-compounding and sputter coating, respectively. Energy dispersive x-ray analysis (EDX) confirmed the presence of titanium dioxide in the fibers. Through the application of environmental scanning electron microscopy (ESEM) and scanning probe microscopy (SPM), it was found that incorporating the titanium dioxide by melt-compounding caused severe aggregation of the titanium dioxide nanoparticles at the polypropylene fiber surface. Indeed, coverage of the fiber surface by titanium dioxide was poor. By contrast, the coverage of the sputter coated fiber surfaces was much more consistent, although aggregation of the titanium dioxide nanoparticles still appeared quite extensive. The behavior of the nanocomposite fiber surfaces was investigated using dynamic contact angle measurements by the Wilhelmy technique. Only a small increase in hydrophilicity of the polypropylene fibers was observed after melt-compounding with titanium dioxide, but a larger increase was noted after sputter coating. UV irradiation appreciably enhanced the hydrophilicity of the fiber surfaces in both cases.

Photocatalytic promoted oxidation of phenolic mixtures: An insight into the operating and mechanistic aspects

The photocatalytic oxidation of a phenolic mixture (gallic acid, tyrosol and syringic acid) has been carried out in the presence of titanium dioxide and a selected inorganic peroxide, namely persulphate, monopersulphate or hydrogen peroxide. The results obtained in UVA irradiated solutions reveal that hydrogen peroxide is the most effective option. The influence of some relevant operating parameters (i.e. initial concentration of phenols, hydrogen peroxide or titanium dioxide) has been investigated. In all cases a saturation-like behaviour has been observed. Thus, an increase in oxidation efficiency is observed when raising, up to a certain value, the initial amounts of reagents/catalyst added to the reactor. Nevertheless, a further increase of any of the previous parameters does not lead to the expected enhancement of the process. From the concave shape of the parent compounds’ depletion profiles, it is suggested that the system proceeds through an autocatalytic route, likely involving the action of organic radicals. A pseudoempirical model has been used to acceptably model the experimental data obtained.

Application of Photocatalytic Oxidation in the Presence of TiO2 in Small Sewage Treatment Plants

In many small rest centers, bungalows, including those located at the seaside, there are various facilities which during the holiday season generate highly concentrated sewage. An example may be car washes at gas stations, small sandwich bars, and camping sites. One of the possibilities of solving the problem of treating sewage generated in such places are small treatment plants which can operate periodically and are characterized by low running costs. This possibility is offered by a photocatalytic oxidation in the presence of titanium dioxide as a preliminary treatment process and the next biological treatment in a so‐called household sewage treatment plant. In particular, it is suitable for strongly insulated areas. The stage of chemical oxidation was a subject of our research and was performed using model solutions of surfactants and commercially available car shampoos. Promising results of their degradation were obtained.

Selective photocatalytic oxidation of steroid estrogens in water treatment: urea as co-pollutant

The objective of the present research concerns the competitive photocatalytic oxidation (PCO) and adsorption of steroid estrogens (SEs) on titanium dioxide in presence of urea. The results showed the indifference of SEs towards the presence of urea in concentrations characteristic for the domestic sewage. The selective PCO of SEs appeared to be feasible in alkaline media, in which the PCO exhibited the highest efficiency. Ethanol used for hydrophobic SEs dissolution in water appeared to be interfering with the PCO.

Preparation of TiO 2/PANI composites in the presence of surfactants and investigation of electrical properties

“In situ” polymerization was carried out in the presence of titanium dioxide (TiO 2) to synthesize TiO 2/polyaniline (TiO 2/PANI) composite in an aqueous medium containing anionic (sodium dodecylbenzenesulfonate), DBSNa, cationic (tetradecyltrimethylammonium bromide), TTAB, and nonionic surfactants (poly(ethylene oxide) (20) sorbitan monolaurate), Tween 20). The composites were characterized by FTIR, UV–vis spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Gouy balance measurements. The FTIR and UV–vis spectra reveal that the interaction between TiO 2/PANI composite and surfactants. The anionic and cationic surfactants incorporated with TiO 2/PANI composite structure. The stability of the composites in terms of direct-current electrical conductivity retention was studied in isothermal conditions. Electrical conductivity measurements indicate that the conductivity of TiO 2/PANI synthesized in the presence of the cationic surfactant has the highest conductivity value. All composites showed negative mass magnetic susceptibility values.