PABA-assisted hydrothermal fabrication of W18O49 nanowire networks and its transition to WO3 for photocatalytic degradation of methylene blue

W₁₈O₄₉ nanowire networks have been fabricated by a facile hydrothermal method. In this method, p-aminobenzoic acid (PABA) was used as an assistant agent to control the morphology transformation. W₁₈O₄₉ and its products annealed at different temperature were characterized by XRD, SEM, TEM, UV–vis absorption spectroscopy, XPS, TGA, and FTIR. Formation mechanism and thermal stability of W₁₈O₄₉ nanowire networks were studied in detail. The experiment data showed that PABA played an important role in the induced crystal growth of W₁₈O₄₉ nanowires along [0?1?0] axis. In transformation, the structure of samples was controlled: from irregular particles to nanowire networks. W₁₈O₄₉ nanowire networks were annealed at different temperature. The nanowire networks collapsed at 450?°C, while WO₃ nanocrystals were obtained. The W₁₈O₄₉ nanowire networks annealed at 400?°C have a superior photocatalytic performance to degrade methylene blue and its specific surface area was up to 147?m²?g^?1.     

Photocatalytic degradation for methylene blue using zinc oxide prepared by codeposition and sol-gel methods

Zinc oxide nanoparticle was obtained by zinc hydrate deposited on the silica nanoparticle surface and zinc hydrate was dispersed in starch gel. The structure of zinc oxide particle was characterized by nitrogen adsorption-desorption and XRD, the morphology was observed by TEM. The result showed that the zinc oxide nanoparticle deposited on the silica nanoparticle surface was well-dispersed and less than 50nm, displayed higher photocatalytic activity for methylene blue degradation. However, the zinc oxide nanoparticle in a size of 60nm was derived from starch gel and showed poorer photocatalytic activity. It provided a simple and effective route to prepare zinc oxide nanoparticle with higher photocatalytic activity through depositing zinc oxide on the silica particle surface, moreover, the catalyst is easier to recover due to its higher density.     

Effect of Fe-doped TiO2 nanoparticle derived from modified hydrothermal process on the photocatalytic degradation performance on methylene blue

Anatase Fe-doped TiO2 nanoparticles with 10-15 nm particles sizes were directly prepared with amorphous TiO2 nanoparticles and Fe(NO3)3.9H2O by hydrothermal method. The TiO2 crystallite grain sizes decreased with the increase of Fe contents. When Fe contents increased, the diffuse reflectance spectra of Fe-doped TiO2 nanoparticles displayed a red shift in the band gap transition. And the absorbing band edge moved to visible range when the Fe contents were more than 2 mol%. XPS analysis showed that Fe3+ was not on the surface of TiO2 nanoparticles, but inserting into the matrix interior. As a result, the photoactivity degradation of MB on Fe-doped TiO2 nanoparticles decreased.     

Comparative study of the structural, optical and photocatalytic properties of semiconductor metal oxides toward degradation of methylene blue

Indium oxide (In₂O₃), zinc oxide (ZnO), stannic oxide (SnO₂), and titanium dioxide (TiO₂) thin films were prepared on glass substrates using electron beam evaporation. The samples characterized by UV-vis spectroscopy, diffraction ray-X and scanning electron microscopy techniques. The photocatalytic degradation of methylene blue in an aqueous solution, as a model compound, was investigated using different metal oxides in an attempt to compare the decomposition reaction rate. The progress of degradation was monitored using UV-vis spectrophotometry. The effects of various experimental parameters such as initial concentration of methylene blue (5-10 mg/l), pH of the solution (2-8), annealing temperature (250-550 °C), and catalyst nature and its microstructure were systematically studied in order to achieve maximum degradation efficiency. The results obtained were fitted with the Langmuir-Hinshelwood model to study the degradation kinetics and discussed in detail. Nearly complete degradation was obtained at optimal operational parameters including the higher annealing temperature of thin film and the increase in MB solution pH. The degradation with In₂O₃ was more efficient than with SnO₂, ZnO and TiO₂ films.     

Effects of optical band gap energy,band tail energy and particle shape on photocatalytic activities of different ZnO nanostructures prepared by a hydrothermal method

The dependence of the crystallite size and the band tail energy on the optical properties, particle shape and oxygen vacancy of different ZnO nanostructures to catalyse photocatalytic degradation was investigated. The ZnO nanoplatelets and mesh-like ZnO lamellae were synthesized from the PEO₁₉-b-PPO₃ modified zinc acetate dihydrate using aqueous KOH and CO(NH₂)₂ solutions, respectively via a hydrothermal method. The band tail energy of the ZnO nanostructures had more influence on the band gap energy than the crystallite size. The photocatalytic degradation of methylene blue increased as a function of the irradiation time, the amount of oxygen vacancy and the intensity of the (0 0 0 2) plane. The ZnO nanoplatelets exhibited a better photocatalytic degradation of methylene blue than the mesh-like ZnO lamellae due to the migration of the photoelectrons and holes to the (0 0 0 1) and (0 0 0 −1) planes, respectively under the internal electric field, that resulted in the enhancement of the photocatalytic activities.     

Fabrication of TiO2/Ti electrode by laser-assisted anodic oxidation and its application on photoelectrocatalytic degradation of methylene blue

A TiO2/Ti mesh electrode by laser calcination was prepared in this article. The resulting TiO2 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS), and it illuminated that the prepared electrode mainly consisted of anatase TiO2 nanoparticles on its surface and exhibited a superior photocatalytic activity. The photodegradation of methylene blue (MB) using the proposed electrode under different experimental conditions was investigated in terms of both UV absorbance at 664 nm and chemical oxygen demand (COD) removal. The electrical bias applied in photoelectrocatalytic (PEC) oxidation was also studied. The experimental results showed that under the optimal potential of +0.50 V (versus SCE), UV absorbance and COD removal during the photodegradation of MB by the proposed TiO2/Ti mesh electrode were 97.3% and 87.0%, respectively. Through the comparison between photocatalytic (PC) oxidation and photoelectrocatalytic (PEC) oxidation, it was found that PEC oxidation was a convenient and effective way to mineralize the organic matters and that laser-treated photoelectrode exceeded the oven-treated one.