Organic Dyes In Aqueous Solution Research Articles

Enhanced Photocatalytic Activities of Multi-Modified TiO2 Films on Common Glass Substrates

Boric acid-treated and sulfur ion-doped multi-modified TiO2 films with high photocatalytic activities were prepared on soda–lime glass (Na2O · CaO · 6SiO2) substrates via the sol–gel method. The as-prepared specimens were characterized using high-resolution field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectra, UV–vis diffuse reflectance spectroscopy, and Brunauer–Emmett–Teller surface area. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solutions. Compared with boric acid treatment and sulfur surface doping, the integration of both methods gave the best results. It is believed that high photocatalytic activity is correlated with the microstructure of the TiO2 film.

Sonocatalytic performance of AgBr in the degradation of organic dyes in aqueous solution

Abstract AgBr sonocatalysts were prepared by a simple method. The AgBr sonocatalysts exhibited excellent sonocatalytic activities against the decolorization of methylene blue, rhodamine B, and methyl orange. By determining the content of OH radicals in the ultrasonic degradation of organic dyes, many OH radicals were detected, which may be responsible for the high sonodegradation rate over AgBr under ultrasonic radiation. Based on the effects of the initial dye concentration on the sonodegradation, we also discussed and analyzed the kinetic data, and the results are consistent with the first-order kinetic rate equation.

Effects of V and Zn codoping on the microstructures and photocatalytic activities of nanocrystalline TiO2 films

Abstract To enhance the photocatalytic activity of TiO 2 , V and Zn co-doped TiO 2 films were synthesized by the sol–gel method. The experimental results indicated that the films were composed of round-like nano-particles or aggregates. V and Zn codoping could not only obviously increase the specific surface area of TiO 2 but also result in the narrowed band gap of TiO 2 sample. The photocatalytic activities of the TiO 2 films were evaluated by the photocatalytic decomposition of organic dyes in aqueous solution. Compared with un-doped TiO 2 film or single doped TiO 2 film, V and Zn co-doped TiO 2 film exhibited excellent photocatalytic activities under both UV light and visible light. The improvement mechanism by V and Zn codoping was also discussed.

Photoinduced Reactions between Pb3O4 and Organic Dyes in Aqueous Solution under Visible Light

Pb(3)O(4) could react with organic dyes in aqueous solution under visible light irradiation, in which Pb(3)O(4) was transformed into Pb(3)(CO(3))(2)(OH)(2) along with oxidation of the organic dyes. Cu(2+) has considerable effect on the reaction. In the presence of Cu(2+), MO (20 ppm) and RhB (10(-5) mol L(-1)) were completely degraded under visible light within 6 and 20 min, respectively, while both Pb(3)O(4) and Cu(2+) keep almost stable during photodegradation. The mechanisms of the reactions with and without Cu(2+) ions were studied. The photochemical system of Pb(3)O(4) cooperating with Cu(2+) ions is probably used for the treatment of organic pollutants in water under visible light.

Enhanced Photocatalytic Activity of Co Surface Doped Nanocrystalline TiO2-SiO2 Composite Films

In order to enhance the photocatalytic activity of the TiO2 films, Co surface doped TiO2-SiO2 composite films were synthesized by the improved sol-gel method, in which tetrabutyl titanate (Ti(OC4H9)4) and tetraethyl orthosilicate were chosen as the precursors and cobaltous nitrate hexahydrate (Co(NO3)2·6H2O) was chosen as cobalt source. The field emission scanning electron microscopy and X-ray diffraction results indicated that the films were composed of nanoparticles or aggregates. The photoluminescence results revealed that the recombination rate of the photogenerated electrons and holes was prohibited via SiO2 composite and Co doping in TiO2 film. The Brunauer–Emmett–Teller results showed that the surface area of the modified TiO2 was 301.7 m2 g−1, while that of the pure TiO2 was 68.4 m2 g−1. The photocatalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. With the SiO2 composite and Co doping, the modified TiO2 films with high photocatalytic activity and clearly responsive to the visible light were obtained. The mechanisms of photoactivity enhancement for composite films have also been discussed.

Evaluation of electro-coagulation method for decolorization and degradation of organic dyes in aqueous solutions

This research has two parts: at first part electro coagulation (EC) method was used to remove the dye Direct Black 22 (DB22 (in aqueous media. All experiments were done in a 2 liter reactor with two electrodes made of steel (SS-304) as cathodes and one aluminum electrode as anode. Parameters affecting the process, such as anode material, electrolyte concentration, current density, initial pH of solution and the initial dye concentration, were investigated. Total amount of consumed energy was used for determination of optimal conditions. According to the results obtained for DB22 at optimized conditions, color and COD removal percentage were 92% and 85%, respectively. In addition, the current efficiency for aluminum anode in removal of DB22 was 90%. At the second part of the research work, color removal by EC for six different dyes was evaluated. The results showed that dye structure and anode type are very important factors on performance of the process.

Microstructures and photo-catalytic properties of B3+ and F− co-doped TiO2 films

The nano-crystalline B3+ and F− co-doped titanium dioxide films were successfully prepared by the improved sol–gel process. The as-prepared specimens were characterised using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), the Brunauer–Emmett–Teller (BET) surface area, X-ray photo-electron spectroscopy, photoluminescence spectra and UV–Vis diffuse reflectance spectroscopy. The photo-catalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. The results of XRD, FE-SEM and BET analysis indicated that the TiO2 films were composed of nano-particles. B3+ and F− co-doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Diffuse reflectance measurements showed that co-doping could clearly extend the absorbance spectra of TiO2 into visible region. Compared with pure TiO2, B3+ doped or F− doped TiO2 film, the B3+ and F− co-doped TiO2 film exhibited excellent photo-catalytic activity. It is believed that the surface microstructure of the films and the doping methods of the two ions are responsible for improving the photo-catalytic activity.

Nanocrystalline TiO2 based films onto fibers for photocatalytic degradation of organic dye in aqueous solution

Nanocrystalline titania (TiO2) synthesized via sol–gel, by using an alkoxide precursor were deposited onto commercially available silica and alumina fibers, namely E-Glass and Nextel 650, respectively. Different processing conditions and material preparation parameters, such as amount of TiO2, film composition and annealing temperature were tested in order to obtain nanocrystalline TiO2 with different morphological and structural characteristics. The materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer, Emmett, and Teller (BET) surface area measurements. The photocatalytic activity of the obtained coated fibers was investigated by monitoring the degradation of a model molecule, an azo dye (Methyl Red), under UV irradiation in aqueous solution. The detected photocatalytic performance of the sol–gel derived nanocrystalline TiO2 was explained on the basis of mechanism associated to the photocatalytic decomposition of organic molecules using semiconductor oxides and accounted for the structural and morphological characteristics of the TiO2 based coating. The materials with the most suited characteristics for photocatalysis were used to scale up the deposition onto a larger sample of fiber and then tested in a photocatalytic reactor. A commercially available TiO2 standard material (TiO2 P25 Degussa) was used as reference, in order to ultimately assess the viability of the coating process for real application.

Microstructures and Photocatalytic Properties of S Doped Nanocrystalline TiO2 Films

The nanocrystalline S doped titanium dioxide films were successfully prepared by the improved sol-gel process. Here TiO(C4H9O)4 and CS(NH2)2 were used as precursors of titania and sulfur, respectively. The as-prepared specimens were characterized using x-ray diffraction (XRD), x-ray energy dispersive spectroscopy (EDS), high-resolution field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of organic dyes in aqueous solution. The results of XRD, FE-SEM, and BET analyses indicated that the TiO2 films were composed of nanoparticles. S doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO2 film, S doped TiO2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the modified films is responsible for improving the photocatalytic activity.

Microwave-assisted synthesis of BiOBr/graphene nanocomposites and their enhanced photocatalytic activity

BiOBr/graphene nanocomposites were synthesized by a green single-step microwave strategy and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of the as-prepared BiOBr nanoplates and BiOBr/graphene nanocomposites for the photodegeneration of organic dyes in aqueous solution under visible light irradiation was investigated. The results show that BiOBr/graphene nanocomposites have a higher photocatalytic activity than bare BiOBr nanoplates.

Novel TiO2/C nanocomposites: Synthesis, characterization, and application as a photocatalyst for the degradation of organic pollutants

Novel TiO2/carbon nanocomposites were prepared through the pyrolysis of TiO2/poly(furfuryl alcohol) hybrid materials, which were obtained by the sol–gel method, starting from titanium tetraisopropoxide (TTIP) and furfuryl alcohol (FA) precursors. Six different TiO2/C samples were prepared based on different TiO2 nanoparticle sizes and TiO2/FA ratios. All of the samples were characterized using X-ray diffraction, infrared, and Raman spectroscopy. The results indicated effective FA polymerization onto the TiO2 (anatase) nanoparticles, polymer conversion to disordered carbon following the pyrolysis, and a simultaneous TiO2 anatase–rutile phase transition. The resulting TiO2/carbon composites were used as photocatalysts in the advanced oxidative process (AOP) for the degradation of reactive organic dyes in aqueous solution. The results indicate excellent photocatalytic performance (degradation of 99% of the dye after 60min) with several advantages over traditional TiO2-based photocatalysts.

Highly active photocatalytic ZnO nanocrystalline rods supported on polymer fiber mats: Synthesis using atomic layer deposition and hydrothermal crystal growth

Photocatalytically active zinc oxide nanocrystalline rods are grown on high surface area polybutylene terephthalate (PBT) polymer fiber mats using low temperature solution based methods, where the oxide crystal nucleation is facilitated using conformal thin films formed by low temperature vapor phase atomic layer deposition (ALD). Scanning electron microscopy (SEM) confirms that highly oriented single crystal ZnO nanorod crystals are directed normal to the starting fiber substrate surface, and the extent of nanocrystal growth within the fiber mat bulk is affected by the overall thickness of the ZnO nucleation layer. The high surface area of the nanocrystal-coated fibers is confirmed by nitrogen adsorption/desorption analysis. An organic dye in aqueous solution in contact with the coated fiber degraded rapidly upon ultraviolet light exposure, allowing quantitative analysis of the photocatalytic properties of fibers with and without nanorod crystals present. The dye degrades nearly twice as fast in contact with the ZnO nanorod crystals compared with samples with only an ALD ZnO layer. Additionally, the catalyst on the polymer fiber mat could be reused without need for a particle recovery step. This combination of ALD and hydrothermal processes could produce high surface area finishes on complex polymer substrates for reusable photocatalytic and other surface-reaction applications.

Microstructures and photocatalytic properties of Ag + and La 3+ surface codoped TiO 2 films prepared by sol–gel method

Ag + and La 3+ surface codoped TiO 2 films were successfully prepared by the improved sol–gel and doping processes. The as-prepared specimens were characterized using differential thermal analysis-thermogravimetry (DTA–TG), X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area, Photoluminescence spectrum (PL) and UV–vis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. The results of XRD, FE-SEM and BET analyses indicated that the TiO 2 films were composed of nano-particles or aggregates with a size of less than 10 nm. With the codoping of Ag + and La 3+, TiO 2 films with high photocatalytic activity and clearly responsive to the visible light were obtained. The improvement mechanism by ions doping was also discussed.

Sol-gel synthesis of silver/titanium dioxide (Ag/TiO 2) core-shell nanowires for photocatalytic applications

Silver/titanium dioxide (Ag/TiO 2) core-shell nanowires were synthesized by direct coating of TiO 2 shells on the surface of silver nanowires (AgNWs) through a simple sol-gel process. TEM image and EDX elemental analysis had confirmed the presence of TiO 2 coating on the surface of AgNWs. The thickness of titanium dioxide coating was about 10 nm. These Ag/TiO 2 core-shell nanowires showed good photocatalytic activities in the decomposition of methylene blue as a model organic dye in aqueous solution under UV light irradiation. Ag/TiO 2 core-shell nanowires are potentially useful in photocatalytic applications.

Microstructures and Photocatalytic Properties of Fe3+/Ce3+ Codoped Nanocrystalline TiO2 Films

Fe3+ and Ce3+ codoped titanium dioxide films with high photocatalytic activity were successfully obtained via the improved sol–gel process. The as-prepared specimens were characterized using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy, Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy, photoluminescence (PL) spectra, and UV–Vis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of various organic dyes in aqueous solutions. The results of XRD, FE-SEM, and BET analyses indicated that the TiO2 film had nanostructure. With the codoping of Fe3+ and Ce3+, TiO2 photocatalysts with smaller crystal size, larger surface area, and larger pore volume were obtained. Moreover, codoped ions could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO2 film, Fe3+ doped or Ce3+ doped TiO2 film, the Fe3+/Ce3+ codoped TiO2 film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the films and the doping methods of the ions are responsible for improving the photocatalytic activity.

Sonocatalytic performance of Er 3+:YAlO 3/TiO 2–Fe 2O 3 in organic dye degradation

In this study, the Er 3+:YAlO 3 as up-conversion luminescence agent, which can transfer the visible light part in the sonoluminescence to ultraviolet light, was synthesized by nitrate–citrate acid and sol–gel method. And then the Er 3+:YAlO 3/TiO 2–Fe 2O 3 composite as a sonocatalyst was prepared by ultrasonic dispersion and liquids boil method. The prepared Er 3+:YAlO 3/TiO 2–Fe 2O 3 composite was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The sonocatalytic activity of Er 3+:YAlO 3/TiO 2–Fe 2O 3 composite was examined through the degradation of organic dye in aqueous solution under ultrasonic irradiation. The influences of key preparation conditions such as Ti/Fe molar ratio, heat-treated temperature and heat-treated time on the sonocatalytic activity of Er 3+:YAlO 3/TiO 2–Fe 2O 3 composites were studied. The results indicated that the Er 3+:YAlO 3/TiO 2–Fe 2O 3 composite with 1:1 molar ratio of Ti/Fe heat-treated at 500 °C for 20 min displays the highest sonocatalytic performance in the degradation of Acid Red B. For the degradation of other organic dyes, the Er 3+:YAlO 3/TiO 2–Fe 2O 3 composite also demonstrates a good sonocatalytic activity.

Ag/GaP nanoparticles with photooxidation property under visible light

This article reports the use of Gallium phosphide (GaP) and Ag/GaP nanoparticles, which can harness visible light to decompose organic dye in aqueous solution. The Ag(1.139 wt%)/GaP and Ag(5.225 wt%)/GaP nanoparticles were prepared by the liquid phase reduction of silver nitrate with hydrazine hydrate. The application of X-ray fluorescence and high-resolution transmission electron micrograph morphology has provided direct evidence of the presence of silver on the GaP nanoparticles. Under visible light, the experiments on the photocatalytic degradation of crystal violet in solution over the GaP and Ag/GaP nanoparticles were carried out. The results reveal that small size and number density of Ag domains deposited on GaP nanoparticles have enhanced photocatalytic efficiencies, as compared to large size and number density of Ag domains. This study suggests the potential of both GaP and Ag/GaP nanoparticles as photofunctional materials for waste-water cleaning.

Liquid Crystals: Vertically Aligned Graphene Layer Arrays from Chromonic Liquid Crystal Precursors (Adv. Mater. 4/2011)

The inside cover shows the optical texture of a “chromonic liquid crystal”, formed by a disklike organic dye in aqueous solution. The disks stack into supramolecular rods, which then self-avoid at high concentration to make ordered liquid phases, as reported by Fei Guo, Robert Hurt, and co-workers on p. 508. They show that chromonic precursors can be used to fabricate vertically aligned graphene layer arrays on substrates by liquid coating and carbonization. The arrays can be aligned or patterned using local shear forces and have unique high-activity graphene edge-rich surfaces.

Chemical synthesis of Ni/TiO2 nanophotocatalyst for UV/visible light assisted degradation of organic dye in aqueous solution

The Ni/TiO2 nanoparticles with different Ni dopant content were prepared by a modified sol–gel method. The structure and photoinduced charge properties of the as-prepared catalysts were determined using X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy techniques, and the photocatalytic efficiency of these catalysts was tested using an organic dye. It was shown that Ni modification could greatly enhance the photocatalytic efficiency of these nanocomposite catalysts by taking the photodegradation of methyl orange as a model reaction. With appropriate ratio of Ni and TiO2, Ni/TiO2 nanocomposites showed the superior photocatalytic activity than the single TiO2 nanoparticles. Surface photovoltage spectra demonstrated that Ni modification could effectively inhibit the recombination of the photoinduced electron and holes of TiO2. This electron–hole pair separation conditions are responsible for the higher photocatalytic performance of Ni/TiO2 nanocomposites in the visible region of electromagnetic spectrum.

MnII—A fascinating oxidation catalyst: Mechanistic insight into the catalyzed oxidative degradation of organic dyes by H2O2

The use of simple MnII ions as efficient catalyst precursors for the oxidation of different highly stable organic dyes using H2O2 as an environmentally benign oxidant under mild reaction conditions, is presented. The role of a series of aromatic dyes in the in situ formation and stabilisation of the active catalyst was studied in detail using stopped-flow techniques and UV–Vis detection. DFT calculations were employed to predict the nature of the role of the substrate in the stabilisation of highly reactive MnII intermediates. Furthermore, low-temperature EPR measurements were performed in order to characterize the in situ formed catalytically active MnIVO intermediate responsible for the fast and versatile oxidation of organic dyes in aqueous solution.