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Query: KEGG:D01931 (TiO2)
 11,320 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The combination of TiO2-assisted photocatalysis and ozonation in the degradation of nitrogen-containing substrates such as alkylamines, alkanolamines, heterocyclic and aromatic N-compounds has been investigated. A laboratory set-up was designed and the influence of the structure of the N-compound, the TiO2 and ozone concentration on the formation of breakdown products were examined. The experimental results showed that a considerable increase in the degradation efficiency of the N-compounds is obtained by a combination of photocatalysis and ozonation as compared to either ozonation or photocatalysis only. The mineralization of the model substances was monitored by measurements of the TOC and ion-chromatographic determinations of the formed NO2- and NO3-. The temporal changes of concentrations of breakdown products, such as NH4+, short chain alkyl- and alkanolamines were determined by single column ion chromatography (SCIC) and as well as by electrospray mass spectrometry (EI-MS).
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PMID:Degradation of nitrogen containing organic compounds by combined photocatalysis and ozonation. 1010 56

A laboratory scale flow-through model reactor for the degradation of persistent chemicals using titanium dioxide (TiO2) as photocatalyst immobilized on glass beads is presented. In the test system with a volume of 18 L contaminated water is pumped to the upper part of the floating reactor and flows over the coated beads which are exposed to UV-radiation. The degradation of two dyes of different persistence was investigated. Primary degradation of methylene blue did not fit a first order kinetic due to coincident adsorption onto the photocatalyst and direct photolysis, resulting in a half-life of 6 h. A filtrate of a green algae suspension accelerated the colour removal. In contrast, reactive red 2 was degraded only by photocatalysis; neither adsorption nor direct photolysis led to a colour removal. The course of primary degradation followed a first order kinetic with a half-life of 18 h and a rate constant of 0.04 h-1. Analysis of the degradation products indicated mineralization by detection of NO2- and NO3-, accompanied by a decrease of pH and an increase of conductivity. A successful adaptation of the model reactor (scale 1:10) to dimensions required for surface waters and waste water treatment plants would be a cost-efficient and environmentally sustainable application of photocatalysis for the treatment of industrially polluted water and could be of relevance for third world countries, particularly those favoured by high solar radiation.
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PMID:Model reactor for photocatalytic degradation of persistent chemicals in ponds and waste water. 1063 46

The photocatalytic oxidation of oxalyldihydrazide, N,N'-bis(hydrazocarbonyl)hydrazide, N,N'-bis(ethoxycarbonyl)hydrazide, malonyldihydrazide, N-malonyl-bis[(N'-ethoxycarbonyl)hydrazide] was examined in aqueous TiO2 dispersions under UV illumination. The photomineralization of nitrogen and carbon atoms in the substrates into N2 gas, NH4+ (and/or NO3-) ions, and CO2 gas was determined by HPLC and GC analysis. The formation of carboxylic acid intermediates also occurred in the photooxidation process. The photocatalytic mechanism is discussed on the basis of the experimental results, and with molecular orbital (MO) simulation of frontier electron density and point charge. Substrate carbonyl groups readily adsorb on the TiO2 surface, and the bonds between carbonyl group carbon atoms and adjacent hydrazo group nitrogen atoms are cleaved predominantly in the initial photooxidation process. The hydrazo groups were photoconverted mainly into N2 gas (in mineralization yields above 70%) and partially to NH4 ions (below 10%). The formation of NO3- ions was scarcely recognized.
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PMID:Photooxidation mechanism of nitrogen-containing compounds at TiO2/H2O interfaces: an experimental and theoretical examination of hydrazine derivatives. 1105 95

The photooxidation of C2H5NH2, (C2H5)2NH, HOC2H4NH2, (HOC2H4)2NH and (HOC2H4)3N using TiO2 and Pt/TiO2 as photocatalysts has been investigated. A laboratory set up was designed and a study on the influence of the concentration of the photocatalyst, the pH-value and the structure of the amine performed. The photocatalytic process was optimized with respect to the concentrations of the model substances during degradation. The decrease of the amine concentrations was found to be maximum at a pH of 10. The time-dependence of the formation of cationic breakdown products, such as NH3/NH4 and short-chain alkyl- and alkanolamines was studied by analyses with single column ion chromatography. The experimental data show that the photodegradation follows a Langmuir-Hinshelwood kinetic. The mineralization of the model substances also was monitored by measurements of the decrease of the TOC and of the formation of NO2 and NO3. The different mineralization efficiencies for the model substances studied are discussed with regard to their structure and adsorption behaviour on the photocatalyst. A possible breakdown mechanism involving the electrophilic attack of the hydroxyl radical is given. The applicability of the TiO2-assisted photocatalytic degradation of C2H5NH2 and (C2H5)2NH was tested at the pilot plant-scale with real solar radiation. The degradation rates and products obtained were similar to those found in the laboratory experiments.
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PMID:Degradation of short-chain alkyl- and alkanolamines by TiO2- and Pt/TiO2-assisted photocatalysis. 1105 97

In this paper photoinduced degradation of reactive yellow 17 (RY 17) dye has been studied employing TiO2 in the form of slurry in a batch reactor. UV lamps were used as the source for irradiation. The disappearance of the dye in the solution follows approximately pseudo-first order kinetics. The apparent rate constant decreases with increase in initial concentration of the dye. The addition of oxygen, hydrogen peroxide and persulphate ion influences the degradation rate of the dye. The formation of CO2, SO4(2-), NO3- and NH4+ ions have been identified in the mineralisation process. The decolourisation and mineralisation were followed by UV-Visible spectrophotometer and high performance liquid chromatography respectively. The results reveal that photocatalytic degradation may be a useful technique in the removal of reactive dyes in wastewater from textile industries.
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PMID:Kinetics of photocatalytic degradation of reactive yellow 17 dye in aqueous solution using UV irradiation. 1138 21

The formation of nitrophenols was studied as a consequence of ultra violet (UV) irradiation of aqueous solutions of phenol and nitrate in the range of pH 1-12. The study was performed both in homogeneous phase and in the presence of water-suspended TiO2. The effects of pH, dissolved oxygen and 2-propanol as .OH scavenger have been evaluated. A reaction mechanism is proposed, based on the experimental results.
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PMID:Formation of nitrophenols upon UV irradiation of phenol and nitrate in aqueous solutions and in TiO2 aqueous suspensions. 1144 6

The photo-catalytic degradation pathway and degradation products of methylene blue, rhodamine B, methyl orange, and malachite green in aqueous TiO2 suspension irradiated by high pressure mercury lamp by means of UV-visible absorption spectra and ion chromatography were investigated. The photo-catalysis degradation of dye solutions with charges was greatly effected by pH value owing to the electrostatic model. The photo-degradation rate of dyes anion increased with the decrease of pH value, in contrast, the photo-degradation rate of dyes cation increased with the increase of pH value. And the absorption peaks diminished with a blue shift. After illuminated for 30 minutes, a part of dye chemicals were completely mineralized and transferred into inorganic species including chloride ion, ammonium ion, nitrate ion, sulfate ion. And the addition of 100 mmol/L H2O2 promoted the formation of inorganic species. In this study, the quantity of ammonium ion was much more than that of nitrate ion. That indicated the formation of nitrate is from ammonium. The purification rate of COD in four kinds of dye solution was 71.7%-88.7%. The decrease of COD of dyes solution implies the feasibility of the environmental application of photo-catalyzed process.
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PMID:TiO2-assisted photo-catalysis degradation process of dye chemicals. 1159 Jul 21

The photocatalytic oxidation of the non-biodegradable p-nitrotoluene-o-sulfonic acid (p-NTS) in homogeneous (photo-Fenton reactions) and heterogeneous (with TiO2) solutions has been studied at a pilot-scale under solar irradiation at the Plataforma Solar de Almeria (PSA). In this study two different reactors were tested: a medium concentrating radiation system (Heliomans, HM) and a non-concentrating radiation system (CPC). Their advantages and disadvantages for p-NTS degradation have been compared and discussed. The degradation rates obtained in the CPC collector are around three times more efficient than in the HM collectors. However, in both systems, 100% of the initial concentration of p-NTS was removed. Kinetic experiments were performed in both systems using TiO2 suspensions. During the photodegradation, the disappearance of p-NTS was followed by HPLC, the mineralization of the solution by the TOC technique, the evolution of NO3-, NO2-, and SO4(2-) concentration by ionic chromatography, the toxicity by the standard Microtox test, and the biodegradability by BOD5 and COD measurements. The obtained results demonstrated the utility of the heterogeneous catalysis (using TiO2 as catalyst) as a pretreatment method that can be followed by a biological process.
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PMID:Concentrating versus non-concentrating reactors for solar photocatalytic degradation of p-nitrotoluene-o-sulfonic acid. 1169 62

Effective and compact deodorization systems have been required for the measure of small-scale emission sources of offensive odors usually found in urban areas. We have developed a sheet material with titanium dioxide (TiO2) photocatalyst supported on fiber activated carbon (FAC) for a compact deodorization system. In the deodorization system using the TiO2/FAC sheet and a ultraviolet lamp, malodorants can be collected on the TiO2/FAC sheet by adsorption and then decomposed by photocatalysis with UV-irradiation. In this study, we obtained basic information about the removal and the decomposition of malodorants in the photocatalytic deodorization system using the TiO2/FAC sheet. The malodorants used in this study were methyl mercaptan, ammonia, and hydrogen sulfide. In addition, two kinds of light sources, a black light bulb (BLB; dominant wavelength: 365 nm) and an ultraviolet germicidal lamp (UV2; dominant wavelength: 254 nm) were used to analyze the effect on removal and decomposition characteristics by different dominant wavelengths. The removal rates of malodorants from the gas phase were determined in the deodorization system in the presence or absence of the TiO2/FAC sheet and UV-irradiation in order to study each removal effect due to adsorption onto the TiO2/FAC sheet, direct photolysis by UV-irradiation, and photocatalytic decomposition. The effect of adsorption onto the TiO2 /FAC sheet was pronounced in this batch-type experiment. The effect of photocatalysis was observed from the removal rates of methyl mercaptan. The percent oxidation of ammonia to nitrate and that of methyl mercaptan to sulfate were examined by determining products, i.e. nitrate and sulfate ions, with purified water after the reaction. The formation of nitrate or sulfate was not observed without UV-irradiation using the BLB, while the reactions progressed in the presence of the TiO2/FAC sheet. When the UV2 lamp was used, the oxidation of methyl mercaptan to sulfate occurred without the TiO2/FAC sheet. This suggests that the decomposition characteristics of malodorants were dependent on the wavelength of the light source.
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PMID:Removal and decomposition of malodorants by using titanium dioxide photocatalyst supported on fiber activated carbon. 1176 52

TiO2-mediated photocatalytic degradation process was employed to treat aqueous 2-, 3- and 4-NT (nitrotoluene) pollutants. The NT disappearance and TOC removal rates for three isomers showed no significant differences. Three hydroxylated aromatic intermediates resulting from the photocatalytic degradation of 4-NT were identified; this suggested two (initial) degradation pathways. Formation of acetic acid, formic acid, and formaldehyde was also noted. The mineralization products included NH4+, NO3- and CO2. N2 bubbling or the presence of a positive hole acceptor during 4-NT degradation resulted in a high 4-aminotoluene formation. This indicated an effective reduction of 4-NT's nitro group to amino moiety. Generally, Pt-loaded TiO2 (Pt-TiO2) had no influence on the disappearance rate of 4-NT. However, the use of Pt-TiO2 along with a higher light intensity source resulted in an accelerated TOC removal.
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PMID:Photocatalytic degradation of nitrotoluene in aqueous TiO2 suspension. 1176 18


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