Investigation of dye functional group on the photocatalytic degradation of dyes by nano-TiO2

The photocatalytic degradation of five anionic, eight cationic and three solvent dyes using combustion-synthesized nano-TiO2 (CSTiO2) and commercial Degussa P-25 TiO2 (DP-25) were evaluated to determine the effect of the functional group in the dye. The degradation of the dyes was quantified using the initial rate of decolorization and mineralization. The decolorization of the anionic dyes with CSTiO2 followed the order: indigo carmine > eosin Y > amido black 10B > alizarin cyanine green > orange G. The decolorization of the cationic dyes with DP-25 followed the order: malachite green > pyronin Y > rhodamine 6G > azure B > nile blue sulfate > auramine O approximate to acriflavine P approximate to safranin O. CSTiO2 showed higher rates of decolorization and mineralization for all the anionic dyes compared to DP-25, while DP-25 was better in terms of decolorization for most of the cationic dyes. The solvent dyes exhibited adsorption dependent decolorization. The order of decolorization and mineralization of the anionic and cationic dyes (a) with CS TiO2 and DP-25 was different and correlated with the surface properties of these catalysts (b) were rationalized with the molecular structure of the dye and the degradation pathway of the dye. (C) 2009 Elsevier B.V. All rights reserved.

Dye sensitized visible light degradation of phenolic compounds

The present research work reports the eosin Y (EY) and fluorescein (FL) sensitized visible light degradation of phenol, 4-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) using combustion synthesized nano-TiO2 (CS TiO2). The rate of degradation of the phenolic compounds was higher in the presence of EY/CS TiO2 compared to FL/CS TiO2 system. A detailed mechanism of sensitized degradation was proposed and a mechanistic model for the rate of degradation of the phenolic compound was derived using the pyramidal network reduction technique. It was found that at low initial dye concentrations, the rate of degradation of the phenolic compound is first order in the concentration of the dye, while at high initial dye concentrations, the rate is first order in the concentration of the phenolic compound. The order of degradation of the different phenolic compounds follows: CP > TCP > DCP > phenol. The different phenolic and dye intermediates that were formed during the degradation were identified by liquid chromatography-mass spectrometry (LC-MS) and the most probable pathway of degradation is proposed. (C) 2010 Elsevier B.V. All rights reserved.

Metal doped nanosized titania used for the photocatalytic degradation of rhodamine B dye under visible-light

Metal-doped anatase nanosized titania photocatalysts were successfully synthesized using a sal gel process. Different amounts of the dopants (0.2, 0.4, 0.6, 0.8 and 1.0%) of the metals (Ag, Ni, Co and Pd) were utilized. The UV-Vis spectra (solid state diffuse reflectance spectra) of the doped nanoparticles exhibited a red shift in the absorption edge as a result of metal doping. The metal-doped nanoparticles were investigated for their photocatalytic activity under visible-light irradiation using Rhodamine B (Rh B) as a control pollutant. The results obtained indicate that the metal-doped titania had the highest activity at 0.4% metal loading. The kinetic models revealed that the photodegradation of Rh B followed a pseudo first order reaction. From ion chromatography (IC) analysis the degradation by-products Rhodamine B fragments were found to be acetate, chloride, nitrite, carbonate and nitrate ions.

Photoelectrochemical degradation of eosin yellowish dye on exfoliated graphite-ZnO nanocomposite electrode

In the quest for harnessing more power from the sun for water treatment by photoelectrochemical degradation, we prepared a novel photoanode of exfoliated graphite (EG)-ZnO nanocomposite. The nanocomposite was characterised by X-ray diffractometry, energy dispersive spectroscopy, Brunauer-Emmett-Teller surface area analyser, thermal gravimetric analyser, and X-ray photoelectron spectroscopy. The EG-ZnO nanocomposite was fabricated into a photoanode and applied for the photoelectrochemical degradation of 0.1 x 10(-4) M eosin yellowish dye in 0.1 M Na2SO4 under visible light irradiation. The degradation was monitored with a visible spectrophotometer. The photoelectrochemical degradation process resulted in enhanced degradation efficiency of ca. 93 % with kinetic rate of 11.0 x 10(-3) min(-1) over photolysis and electrochemical oxidation processes which exhibited lower degradation efficiencies of 35 and 40 % respectively.

Monitoring catalytic degradation of dye molecules on silver-coated ZnO nanowire arrays by surface-enhanced Raman spectroscopy

Catalytic degradation of organic dye molecules has attracted extensive attention due to their high toxicity to water resources. In this paper, we propose a novel method for the fabrication of uniform silver-coated ZnO nanowire arrays. The degradation of typical dye molecule rhodamine 6G (R6G), as an example, is investigated in the presence of the as-prepared silver-coated ZnO nanowire arrays. The experimental results show that such composite nanostructures exhibit high catalytic activity, and the reaction follows pseudo-first-order kinetics. Furthermore, these nanowire arrays are desirable SERS substrates for monitoring the catalytic degradation of dye molecules. Compared with traditional UV-visible spectroscopy, SERS technology can reflect more truly the catalytic degradation process occurring on the surface of the catalysts.

Degradation and adsorption of AZO RR239 dye in aqueous solution by nanoscale zerovalent iron particles immobilized on sawdust

Carra sawdust pretrated with formaldehyde was used to adsorb RR239 (reactive azo dye) at varying pH and zerovalent iron (ZVI) dosage. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model. Batch experiments suggest that the decolorization efficiency was strongly enhanced with the presence of ZVI and low solution pH. The kinetics of dye sorption by mixed sorbent (5 g of sawdust and 180 mg of ZVI) at pH 2.0 was rapid, reaching more than 90% of the total discoloration in three minutes.

Surface-enhanced Raman study of electrochemical and photocatalytic degradation of the azo dye Janus Green B

The photocatalytic degradation of Janus Green B azo dye over silver modified titanium dioxide films was investigated by surface-enhanced Raman spectroscopy (SERS). An optimized SERS-active substrate was employed to study the photodegradation reaction of Janus Green B. Considering that photocatalytic degradation processes of organic molecules adsorbed on TiO2 might involve either their oxidation or reduction reaction, the vibrational spectroelectrochemical study of the dye was also performed, in order to clarify the transformations involved in initial steps of its photochemical decomposition. In order to understand the changes in Raman spectra of Janus Green B after photodegradation and/or electrochemical processes, a vibrational assignment of the main Raman active modes of the dye was carried out, based on a detailed resonance Raman profile. Products formed by electrochemical and photochemical degradation processes were compared. The obtained results revealed that the first steps of the degradation process of Janus Green B involve a reductive mechanism. (C) 2007 Published by Elsevier B.V.

Influence of particle size on the photoactivity of Ti/TiO2 thin film electrodes, and enhanced photoelectrocatalytic degradation of indigo carmine dye

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Photoelectrocatalytical degradation of basic blue 41 dye using nanoporous semiconductor of Ti/TiO2

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of color removal and degradation of a reactive textile azo dye on nanoporous TiO2 thin-film electrodes

The feasibility of the photobleaching of a textile azo dye, reactive orange 16 (C.I. 17757), in aqueous solution using titanium dioxide thin-film electrodes prepared by the sol-gel method was investigated. The best conditions for maximum photoelectrocatalytic degradation were found to be pH > 10 for Na2SO4 medium and pH < 6 for NaCl. In both situations, an applied potential of +1.0 V and low dye concentration are recommended, when 100% of color removal is obtained after 20 min of photoelectrocatalysis. The effects of side reaction pathway on the degradation rate of dye in sulfate and chloride medium were presented and the best performance are optimized to situations closed to that verified in the textile effluent. The influence of variables as applied potential, pH, supporting electrolyte and dye concentration on the kinetics of photoelectrochemical degradation also were investigated. Oxalic acid is identified by HPLC and UV-Vis spectrophotometric methods as the main degradation product generated after 180 min of photoelectrocatalysis of 4 x 10(-5) mol l(-1) dye in sodium sulphate pH 12 and NaCl pH 4.0 and a maximum reduction of 56 and 62% TOC was obtained, respectively. (C) 2004 Elsevier Ltd. All rights reserved.

Degradation of metallophtalocyanine dye by combined processes of electrochemistry and photoelectrochemistry

Photoelectrocatalytic degradation of metallophtalocyanine reactive dye (turquoise blue 15) was performed using a Ti/TiO2 thin film photoanode prepared by sol-get method. Hundred percent of color removal and almost complete mineralization (95% at pH 2 and 85% at pH 8) where achieved after 6 h of photolectrocatalytic oxidation of 2.5 x 10(-5) mol L-1 AT15 dye in Na2SO4 mol L-1 under E = +1.2 V versus SCE. The method limitation occurs at dye concentration higher than 4 x 10-5 mol L-1, where the degradation rate becomes markedly slower. An important improvement in color removal and TOC reduction for 1 x 10(-3) mol L-1 metallophtalocyanine dye was achieved using a combined process. After 4 h of potential controlled electrolysis at -1.2 V on a cathode of platinum followed by 6 h of photoelectrocatalytic oxidation leads to 100% of color removal and 83% of TOC decay and eletrodeposition of 69% of the released copper originally presented as copperphtalocyanine complex, by electrodeposition on the cathode without any other treatment. (C) 2005 Elsevier Ltd. All rights reserved.

Assessment of the breakdown products of solar/UV induced photolytic degradation of food dye tartrazine

The food dye tartrazine (CI 19140) was exposed to UV irradiation from an artificial source, a mercury vapor lamp, and a natural one, sunlight. It was observed that conditions such as energy dose, irradiation time, pH and initial dye concentration affected its discoloration. There was 100% of color removal, after 30 min of irradiation, when a dye solution 1 x 10(-5) mol L-1 was submitted to an energy dose of 37.8 J cm(-2). Liquid Chromatography coupled to Diode Array Detection and Mass Spectrometry confirmed the cleavage of the chromophore group and the formation of five by-products at low concentration. Although by-products were formed, the Salmonella/microsome mutagenicity assay performed for both, the dye solution at a dose of 5.34 mg/plate and the solutions obtained after exposure to UV irradiation, did not present mutagenic activity for TA98 and TA100 with and without S9. (C) 2014 Elsevier Ltd. All rights reserved.

Enhanced photoabsorption properties of composites of Ti/TiO2 nanotubes decorated by Sb2S3 and improvement of degradation of hair dye

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)