Solvothermal synthesis of lanthanide-functionalized graphene oxide nanocomposites

We propose a facile approach to the preparation of graphene oxide (GO) composites with lanthanide (Ln) oxide/hydroxide nanoparticles (Ln = La, Eu, Gd, Tb) under relatively mild conditions by two different procedures of solvothermal synthesis. The mechanism of GO-Ln nanocomposite formation is thought to involve the initial coordination of Ln3+ ions to the oxygen-containing groups of GO as nucleation sites, followed by f Ln2O3 and Ln(OH)3 nanoparticle growth. The nanocomposites obtained preserve the intrinsic planar honeycomb-like structures of graphene as proven by the typical G and D bands in the Raman spectra. Fourier-transform infrared and X-ray photoelectron spectroscopy confirm the interaction between oxygen-containing groups of GO and Ln ions. The size and distribution of Ln oxide/hydroxide nanoparticles on GO sheets, estimated from scanning and transmission electron microscopy images, vary broadly for the different lanthanides. The size can span from sub-nm dimensions for Eu oxide to more than 10 μm for Eu hydroxide nanoparticles. The most homogeneous distribution of Ln oxide/hydroxide nanoparticles was found in La-containing composites. Thermogravimetric analysis demonstrated that all the GO-Ln nanocomposites are thermally less stable, by up to 30 °C than pristine GO.</p

Eco-friendly synthesis of graphene oxide–palladium nanohybrids

Nanostructured hybrids of graphene oxide and palladium were fabricated by means of one-step solvent-free gas phase treatment of graphene oxide with the aliphatic amines 1-octadecylamine and 1,8-diaminooctane, followed by in situ decoration with palladium in the liquid medium using palladium chloride as the precursor and citric acid as a mild and environmentally friendly stabilizing and reducing agent. The proposed synthesis method represents an eco-friendly alternative for obtaining nanohybrids of graphene oxide and palladium nanoparticles under mild conditions. Spectroscopic studies evidenced -COOH group derivatization of graphene due to the amidation reaction; transmission electron microscopy demonstrated the formation of nanometer-sized crystalline palladium particles and evidenced that the diamine-functionalization results in a larger particle sizes than observed for monoamine- or non-functionalized substrates. The hybrids obtained have a slightly lower thermal stability than pristine graphene oxide.</p

Synthesis of BiOI/Mordenite Composites for Photocatalytic Treatment of Organic Pollutants Present in Agro-Industrial Wastewater

Recently, bismuth oxyiodide (BiOI) is an attractive semiconductor to use in heterogeneous photocatalysis processes. Unfortunately, BiOI individually shows limited photocatalytic efficiency, instability, and a quick recombination of electron/holes. Considering the practical application of this semiconductor, some studies show that synthetic zeolites provide good support for this photocatalyst. This support material permits a better photocatalytic efficiency because it prevents the quick recombination of photogenerated pairs. However, the optimal conditions (time and temperature) to obtain composites (BiOI/ synthetic zeolite) with high photocatalytic efficiency using a coprecipitation-solvothermal growth method have not yet been reported. In this study, a response surface methodology (RSM) based on a central composite design (CCD) was applied to optimize the synthesis conditions of BiOI/mordenite composites. For this purpose, eleven BiOI/mordenite composites were synthesized using a combined coprecipitation-solvothermal method under different time and temperature conditions. The photocatalytic activities of the synthesized composites were evaluated after 20 min of photocatalytic oxidation of caffeic acid, a typical organic pollutant found in agro-industrial wastewater. Moreover, BiOI/mordenite composites with the highest and lowest photocatalytic activity were physically and chemically characterized using nitrogen adsorption isotherms, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and diffuse reflectance spectroscopy (DRS). The optimal synthesis conditions prove to be 187 °C and 9 h. In addition, the changes applied to the experimental conditions led to surface property modifications that influenced the photocatalytic degradation efficiency of the BiOI/mordenite composite toward caffeic acid photodegradation

Sprayed Pyrolyzed ZnO Films with Nanoflake and Nanorod Morphologies and Their Photocatalytic Activity

There is an increasing interest on the application of ZnO nanorods in photocatalysis and many growth methods have been applied, in particular the spray pyrolysis technique which is attractive for large scale production. However it is interesting to know if the nanorod morphology is the best considering its photocatalytic activity, stability, and cost effectiveness compared to a nonoriented growth. In this work we present a systematic study of the effect of the precursor solution (type of salt, solvent, and concentration) on the morphology of sprayed ZnO films to obtain nanoflakes and nanorods without the use of surfactants or catalysts. The surface properties and structural characteristics of these types of films were investigated to elucidate which morphology is more favorable for photocatalytic applications. Wettability and photocatalytic experiments were carried out in the same conditions. After UV irradiation both morphologies became hydrophilic and achieved a dye discoloration efficiency higher than 90%; however, the nanoflake morphology provided the highest photocatalytic performance (99% dye discoloration) and stability and the lowest energy consumption during the synthesis process. The surface-to-volume ratio revealed that the nanoflake morphology is more adequate for photocatalytic water treatment applications and that the thin nanorods should be preferred over the large ones

Photocatalytic Performance of ZnO: Al Films under Different Light Sources

ZnO and Al doped ZnO films were produced by spray pyrolysis. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy, and photoluminescence. Their photocatalytic activity was evaluated by the decomposition of the methyl orange dye using different light sources: ultraviolet light, artificial white light, and direct sunlight. The films were also tested under darkness for comparison. The ZnO films were able to degrade the test pollutant under UV and sunlight in more than a 60% after 180 min of irradiation and a scarce degradation was obtained using white light. However, the Al doped ZnO films presented a very high degradation rate not only under UV and sunlight (100% degradation), but also under white light (90% degradation after the same irradiation time). An unexpected high degradation was also obtained in the dark, which indicates that a nonphotonic process is taking place parallel to the photocatalytic process. This can be due to the extra electrons—provided by the aluminum atoms—that migrate to the surface and produce radicals favoring the decomposition process even in the dark. The high activity achieved by the ZnO: Al films under natural conditions can be potentially applied to water treatment processes

Spray deposited β-Bi2O3 nanostructured films with visible photocatalytic activity for solar water treatment

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DEPOSITED Bi2O3 THIN FILMS ON SINTERED SILICA SURFACE FOR PHOTOCATALYTIC WATER TREATMENT

Increasing concerns on water pollution encourage to investigate new techniques for controlling associated problems with practical and sustainable approaches. Heterogeneous photocatalysis is reported as the green, sustainable and clean process by using metal oxide semiconductors in removing dyes, medicines and insecticides from water. In this study deposition of nano sized Bismuth oxide (Bi2O3 NPs) thin film on sintered silica discs(30mm dia) was achieved by spray pyrolysis technique, by spraying crystal clear solution (containing Bismuth Acetate (CH3CO2)3Bi dissolved in 1 Molar CH3COOH) onto the sintered silica substrate kept at 450 °C. Deposited disc were characterized by Field emission scanning electron microscopy (FESEM), X-ray Diffraction (XRD) for evaluation of obtained crystallinity and phases, diffused reflectance spectroscopy (DRS) to determine energy band gap possessed by films. Photocatalysis was performed under visible light to analyse the photocatalytic activity of deposited thin films

Bismuth-based nanomaterials: Photo catalyst for water dye degradation

Growth of nano sized Bismuth oxy chloride (BiOCl) and Bismuth Oxide (Bi2O3) thin film on glass was achieved by Metal Organic Chemical Vapour Deposition (MOCVD) method. It was synthesized from solutions containing Bismuth chloride (BiCl3) in Acetone and Bi(NO3)3:5H2O in 1M HNO3.The BiCl3 solution was carried by nebulisation effect by Argon gas and Bi(NO3)3:5H2O by Oxygen in the reactor. The temperature degrades the chemical composition into nano thin films of desire particles on the glass surface. The expected reaction is mentioned below. NPs growth takes place on glass substrate at 600°C. Self assembly of BiOCl and Bi2O3 crystals were observed on the glass substrates. Obtained thin films were characterized by Field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDS). Further, thin films of BiOCl and Bi2O3 were evaluated for photocatalytic study. BiOCl NPs thin film was tested against methyl orange dye and Bi2O3 thin film was tested against Acid blue 113 dye under UV light. Analysis results are interesting, 90 % of dye absorption was observed in both the films. As this is the preliminary expt. on growth and dye degradation study with both the films, the data is not comparable. The study only confirms the preliminary observation on dye degradation by UV-vis spectroscopy. Further, the detailed study is in a process

Synthesis and properties of Bi5Nb3O15 thin films prepared by dual co-sputtering

International audienceBismuth-based oxides have gained attention because of their particular electronic configuration that enhances the mobility of photogenerated carriers. In this work, we focused on the synthesis, and the evaluation of the physical and photocatalytic properties of Bi5Nb3O15 films. Bismuth niobate films were deposited by dual magnetron co-sputtering, starting from Bi2O3 and Nb independently driven targets. Although the substrates were heated at 150 degrees C during the deposition, the films were amorphous; therefore, they were annealed at 600 degrees C in air for 2 h to obtain the nanocrystalline Bi5Nb3O15 orthorhombic phase. The Bi5Nb3O15 compound is an interesting material for applications in microelectronics due to its high-k dielectric value at the radiofrequency range; another possible and reported application is as photocatalyst for degradation of organic pollutants and water splitting processes. The films structure was confirmed by X-ray diffraction (theta-2 theta and in-plane modes). The Raman and infrared spectra were measured and compared with calculated vibrational modes since they have not been reported in the past. The optical properties (refractive index, extinction and absorption coefficients) of the Bi5Nb3O15 films were estimated using UV-VIS reflectance and transmittance spectroscopy. The optical band gap was estimated assuming an indirect fundamental inter-band transition at 3.25 eV. The prospective to use the Bi5Nb3O15 films as a photocatalyst was evaluated through the measurement of the photo-discoloration of indigo carmine (IC) dye solutions (5 ppm) under UV light irradiation at three pHs: 3.5, 7 and 11. The results showed a decrease in the absorbance spectrum of the IC solution as a function of irradiation time only at acidic pH where almost 100% of degradation was achieved at 270 min; this behavior is probably due to the increment of the adsorption of IC molecules on the positively charged surface. A similar response was observed after 5 cycles without any structural change of the films. (C) 2016 Elsevier B.V. All rights reserved

Efficient α/β-Bi2O3 composite for the sequential photodegradation of two-dyes mixture

A mixture of α/β-Bi2O3 and α-Bi2O3 powders were obtained by a simple solid state reaction–annealing route at 550 °C. The structure, optical properties and surface area of the commercial α and β-Bi2O3 and the synthesized α-phase and α/β-composite were well characterized by X-ray diffraction, diffuse reflectance spectra and N2 physisorption. The annealed sample at 550 °C showed 20% of β-phase, forming a heterojunction of α/β-Bi2O3 whereas annealing at elevated temperature (650 °C) lead to the α-phase. Optical properties showed that the presence of the β-phase is mainly responsible for narrowing the energy band gap. The photocatalytic activity of the commercial α and β-Bi2O3 and the synthesized α-phase and α/β-composite were investigated in degradation of single dyes, Indigo Carmine (IC) and Rhodamine-B (RhB) under both UV and visible light-induced photocatalysis. For the best photocatalyst, the photodegradation in a two-dye mixture solution was systematically studied considering the type of dye, the adsorption capacity of the samples and the behavior of dye photodegradation. The photocatalytic performance of α/β-Bi2O3 was comparatively much higher than the commercial α and β-Bi2O3, indicating that better performance of efficient charge separation and transfer across α/β-Bi2O3 composite was obtained. Possible mechanism of the single dye and two-dye mixture degradation was given by using α/β-Bi2O3 composite