Photodecomposition Of Methylene Blue Research Articles

Photodecomposition effects of graphene oxide coated on TiO2 thin film prepared by electron-beam evaporation method

Morphological, structural and photocatalytic properties of graphene oxide (GO)/TiO2 thin-film deposited on quartz substrate were investigated. The TiO2 film was prepared by electron-beam evaporation and the GO film by spin coating method. The photocatalytic activities of the GO/TiO2 film were evaluated by photodecomposition of methylene blue. There was synergistic effect between TiO2 and GO which causes a rapid photo-induced charge separation and the reduction of the recombination of electron–hole pairs under the UV–visible light irradiation. GO on TiO2 film also promotes the properties of adsorption of the dye, photon scattering probability, and interacting surface area. As a result, it leads to the enhancement of the efficiency of the photodegradation in GO/TiO2 film.

An aqueous synthesis of photocatalyst by selective dissolution of titanium oxide/hydroxyapatite composite

A novel synthesis method of a highly active photocatalyst was proposed. Titanium dioxide (TiO 2) nano-particles were prepared by three-step procedure, precipitation of hydroxyapatite (HAp) on TiO 2 particles, heat treatment of the TiO 2/HAp composites, and acid treatment in hydrochloric acid. The unique point of this procedure is the selective dissolution of HAp to obtain exposed TiO 2 surfaces. The HAp precipitation was achieved by stirring TiO 2 powders in the mixtures of Ca(NO 3) 2 and NH 4H 2PO 4 aqueous solutions at pH 8.5. Then, the heat-treated TiO 2/HAp composites were treated with hydrochloric acid. The precipitated HAp avoided the direct contact of TiO 2 particles and suppressed the phase transformation from anatase-to-rutile >200 °C. The HAp also suppressed a decrease of specific surface area of TiO 2 during the heat treatment. The photocatalytic activities were evaluated from an absorbance decrease of methylene blue (MB) under ultraviolet (UV) irradiation. The MB photodecomposition was approximated to the first-order reaction and the reaction rate constants of the obtained TiO 2 powders heated at various temperatures were higher than those of conventional TiO 2 powders heated at same temperatures. The enhanced photocatalytic activity is attributed to the suppression effects for the phase transformation to rutile phase and the decreasing of specific surface area in the heat treatment.

Photoenhanced Degradation of Methylene Blue on Cosputtered M:TiO2 (M = Au, Ag, Cu) Nanocomposite Systems: A Comparative Study

Titania thin film system containing noble metallic nanoparticles such as Au, Ag, and Cu have been prepared by utilizing radio frequency reactive magnetron cosputtering method. The structural and morphological properties of the thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Surface chemical composition of the films was determined by X-ray photoelectron spectroscopy (XPS). Optical properties of the TiO2 annealed films containing Au, Ag, and Cu metallic nanoparticles were investigated by UV−visible spectrophotometry showing surface plasmon resonance of the metals. The photocatalytic activity of all synthesized samples annealed at 600 °C in an Ar + H2(80 + 20%) environment was evaluated by measuring the rate of photodegradation reaction of methylene blue (MB) under similar conditions in the presence of UV and visible light irradiation. The Au:TiO2 and Cu:TiO2 thin film systems significantly enhanced photodecomposition of MB resulting in 80 and 90% of its initial concentration after 200 min photoirradiation, respectively. The increase in the surface roughness measured by AFM observation and the presence of the Ti3+ oxygen vacancy in the photoirradiated thin films were found responsible for the enhancement of the MB photodegradation reaction. The photoenhancement of the studied was determined in the following order: Cu:TiO2 > Au:TiO2 > Ag:TiO2 > TiO2.

Adsorption and photocatalytic properties of TiO2/mesoporous silica composites from two silica sources (acid-leached kaolinite and Si-alkoxide)

Two different mesoporous silicas (MPS) were synthesized by hydrothermal treatment in NaOH solution of two SiO2 sources. These were microporous silica (MicroPS) derived from selectively acid leached metakaolinite and tetraethylorthosilicate (TEOS). The hydrothermal syntheses of the MPSs were performed at a ratio of SiO2/cetyltrimethyl- ammonium bromide (CTABr)/NaOH/H2O = 1/0.1/0.3/150. The specific surface areas (S BET) of the MPSs from MicroPS (MPS(M)) and TEOS (MPS(T)) were 1070 and 1020 m2/g, respectively. Composites of MPS (75 mass%) with TiO2 (25 mass%) were prepared using both SiO2 and two commercial TiO2 powders, P25 and ST-01. The adsorption–desorption behavior of methylene blue (MB) by the four resulting composites and the two MPSs alone was unique in showing partially reversible behavior. The maximum MB adsorption, observed in the composite of ST-01 with MPS(M), designated (S/M), was 0.034 mmol/g. The rates of MB adsorption in the dark and photodecomposition under UV illumination were considerably different for the four composites and two TiO2 powers, and followed the order ST-01 < S/T < P25 < P/T ≈ P/M ≪ S/M. The removal rate of MB by the composite S/M by adsorption and photodecomposition was further enhanced by heating at 700 °C. Direct photodecomposition of MB without adsorption in the dark was greatly enhanced in the composites, especially in that composed of MPS(M) and ST-01.

Various factors affecting photodecomposition of methylene blue by iron-oxides in an oxalate solution

The effect of various factors on the photodecomposition of methylene blue (MB) by iron oxides calcined at various temperatures in various concentrations of oxalate solutions was investigated by illuminating with UV, visible and solar radiation. Iron oxides were prepared by a gel evaporation method and calcined at 200–700 °C. XRD showed that the as-synthesized iron oxides were amorphous, but formed maghemite (γ-Fe 2O 3) at 200–400 °C and hematite (α-Fe 2O 3) at ≥500 °C. The effect of the various iron oxides, their contents, the oxalate concentration and wavelength of the light source (UV, visible and solar) were all found to strongly influence MB photodecomposition. The optimal contents of the iron oxides increased greatly from 25 to 2000 mg/L at higher calcining temperatures. The MB photodecomposition rate at each optimal iron oxide content was related to the calcining temperature in the order 700 °C < uncalcined < 500 °C < 400 °C < 300 °C. The MB degradation was confirmed to occur by visible light illumination. Excellent photodecomposition was found at pH 2–5, but the photodegradation decreased greatly at pH > 6, consistent with the presence of iron–oxalate complexes. A much higher concentration of hydroxyl radicals was generated in the present system compared with those from a commercial TiO 2 (ST-01), as determined by the coumarin method. Since this process does not require the addition of hydrogen peroxide and shows good efficiency even under solar light, it is an economically viable method for pre-treating and/or decolorizing wastewaters containing dyes.

Structural and adsorption characteristics and catalytic activity of titania and titania-containing nanomaterials

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, 1H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO 2 for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S BET value and smallest particle size of the materials studied. However, this activity calculated per m 2 is higher for PC-105, possessing a much smaller S BET value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica–titania mixed oxide ST20. Calcination of PC-500 at 650 °C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 °C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.

Gold Nanoparticle Incorporation into Porous Titania Networks Using an Agarose Gel Templating Technique for Photocatalytic Applications

Porous titania networks containing gold nanoparticles have been synthesized and tested in photocatalytic applications. The porous structure was controlled using a templating technique, while a range of gold concentrations and a variety of routes were investigated to incorporate the gold nanoparticles. The influence of these parameters on the final structure (surface area and pore size), the gold crystal size, distribution, and content, and the photocatalytic activity of the porous materials were investigated. UV−vis diffuse reflectance spectra of the Au/TiO2 materials showed strong absorbance at approximately 580 nm, indicating the successful incorporation of the gold species. X-ray diffraction analysis ascertained that the titania materials were crystalline (anatase phase) with gold peaks observed only when the gold content was greater than 0.25 wt %. Gold distribution and content in the materials were measured using secondary ion mass spectrometry and inductively coupled plasma mass spectrometry. From transmission electron microscopy analysis, the gold particle size and distribution varied with both the material preparation method and the concentration of gold used in the synthesis. Photocatalytic activity was dependent on the gold particle size and gold quantity. The highest photocatalytic activity under UV light irradiation as monitored by the photodecomposition of methylene blue was obtained for the Au/TiO2 sample containing 2.0 wt % gold prepared by the deposition of gold onto prefabricated porous TiO2.

Preparation and photocatalytic properties of Cr/Ti hollow spheres

Cr/Ti hollow spheres were prepared using poly-(styrene-methyl acrylic acid) latex particles as a template. The photodecomposition of the methylene blue (MB) was evaluated on these Cr/Ti hollow spheres under visible light irradiation. The catalyst samples were characterized by XRD, TEM, UV-DRS, SEM, and BET, and the prepared sample was obtained with the formation of predominant rutile. The observation from UV-DRS showed that the increase of Cr 3+ contents shifted the light absorption of the specimens to the visible region. In this study, the 0.5% Cr/Ti hollow sphere exhibited the highest MB photodecomposition. The BET surface area was found to be ∼25.5 m 2 g −1 for the 0.5% Cr/Ti hollow sphere. The modification of the TiO 2 surface by chromium ion improved the photocatalytic activity under visible light.

Degradation of methylene blue in aqueous dispersion of hollow titania photocatalyst: Study of reaction enhancement by various electron scavengers

Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles (averaged diameter: 200 nm) as a template in conjunction with the sol–gel method. Utilization of 0.20 mol/L titanium tetrabutoxide and 25 g/L latex led to the formation of anatase particles having shell thickness of about 15 nm and void diameter of about 150 nm. Photocatalytic activity of the titania hollow spheres was examined by focusing on its enhancement by electron scavengers in the photocatalytic decomposition of methylene blue (MB). The electron scavengers employed were inorganic oxidants such as ClO − 3, BrO − 3, IO − 4, H 2O 2, and S 2O 2− 8. Differences in electronegativity, atomic radius of the halogens, and the number of highly reactive radical and nonradical intermediates were proven to be important criteria for an electron scavenger to yield high efficiency in the MB photodecomposition. Based on the results, the effect of the oxidants used were found to be in the order of S 2 O 8 2 − > IO 4 − > BrO 3 − > H 2 O 2 > ClO 3 − .

Preparation of TiO2/SiO2 hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO2 hollow spheres preparation. TiO2-doped SiO2 hollow spheres were obtained by using the appropriate amount of Ti(SO4)2 solution on SiO2 hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO2-doped SiO2 hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO2-doped SiO2 hollow sphere has shown higher surface area in comparison with pure TiO2 hollow spheres. The 40 wt% TiO2-doped SiO2 hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m2g−1. The photodegradation rate of MB using the TiO2-doped SiO2 catalyst was much higher than that of pure TiO2 hollow spheres.

The effect of nanosized titania-silica film composition on the photostability of adsorbed methylene blue dye

The effect of nanosized porous films (average density 10 g/m2) of TiO2. TiO2/SiO2, and SiO2 on the photostability of adsorbed methylene blue (MB) dye during UV irradiation in air was investigated by optical spectroscopy and laser-induced mass spectrometry. The effectiveness of the photodecomposition of MB decreases in the order TiO2 > TiO2/SiO2 > SiO2 with rate constants 1E-2, 0.6E-2, and 0.3E-2 min−1 respectively. A mechanism including the participation of both excited states of the dye molecules and photoexcited titanium dioxide is proposed for the photodecolorization of MB adsorbed on the surface of the investigated films.

Degradation of methylene blue in aqueous dispersion of hollow titania photocatalyst: Optimization of reaction by peroxydisulfate electron scavenger

The submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles as a template in sol–gel method. Photocatalytic activity of the hollow spheres was investigated by focusing on the effect of electron scavengers in the photocatalytic decomposition of methylene blue (MB). Photocatalytic activities of titania hollow spheres were significantly enhanced by the addition of peroxydisulfate as an electron scavenger. The rate constant for photodecomposition of MB was increased more than two times by the addition of peroxydisulfate. The significant increase in the photodecomposition rate seems to be related to electrons scavenging as well as production of additional oxidizing species. It was found that the optimum concentration of peroxydisulfate was 10 mM. Further increase in the concentration of peroxydisulfate is not recommended due to the saturation of reaction rate by the excess amount of SO 4 2 − species.

Photodecomposition of methylene-blue by highly-dispersed nano TiO2/Ag catalyst

A highly dispersed nano-TiO2/Ag catalyst is synthesized in an alkaline solution. The photocatalytic activity required for the removal of dimethyl-blue is enhanced with the effectiveness of dispersion and the proportion of nano-TiO2.

Application of carbon-coated TiO 2 for decomposition of methylene blue in a photocatalytic membrane reactor

An application of carbon-coated TiO 2 for decomposition of methylene blue (MB) in a photocatalytic membrane reactor (PMR), coupling photocatalysis and direct contact membrane distillation (DCMD) was investigated. Moreover, photodegradation of a model pollutant in a batch reactor without membrane distillation (MD) was also examined. Carbon-modified TiO 2 catalysts containing different amount of carbon and commercially available TiO 2 (ST-01) were used in this study. The carbon-coated catalyst prepared from a mixture of ST-01 and polyvinyl alcohol in the mass ratio of 70/30 was the most effective in degradation of MB from all of the photocatalysts applied. Photodecomposition of MB on the recovered photocatalysts was lower than on the fresh ones. The photodegradation of MB in the PMR was slower than in the batch reactor, what probably resulted from shorter time of exposure of the catalyst particles to UV irradiation. The MD process could be successfully applied for separation of photocatalyst and by-products from the feed solution.

Hybridization of adsorptivity with photocatalytic activity—carbon-coated anatase

Carbon-coated anatase catalysts were prepared from poly(vinyl alcohol) (PVA) and TiO 2 of anatase structure. Powders of PVA and commercial TiO 2 (ST-01) were mixed with different mass ratios and were heated at 700 and 900 °C under nitrogen. Such prepared catalysts were tested for adsorption and decomposition of two different dyes: methylene blue (MB) and Reactive Black 5 (RB5). Photoactivities of carbon-coated anatase catalysts were compared with ST-01. Carbon coating anatase suppressed anatase transformation to rutile at high temperatures. It was experimentally proved that this suppression appeared in samples with carbon content above 5 mass%. The crystalline structure of anatase was improved in catalysts heated at 900 °C. Although the sintering of anatase crystals was depressed by the carbon layer, the BET surface area of catalysts decreased, but not so much as it was observed in ST-01 heated at 700 °C. Adsorption of both dyes, MB and RB5 on carbon-coated samples was much more higher than on the original ST-01 and that heated at 700 °C. MB photodecomposition was much more higher on carbon-coated TiO 2 catalysts than on ST-01. But Reactive Black 5 was decomposed faster on ST-01 than on carbon-coated TiO 2. It can be explained by different mechanism of photodecomposition. Surface diffusion of adsorbed species through the carbon layer slowed down the rate of decomposition. High crystalline structure of anatase seems to be important in the photodecomposition process.