Photocatalyst TiO2–Co: the effect of doping depth profile on methylene blue degradation (original) (raw)
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Journal of Physics: Conference Series, 2014
TiO 2 thin films were deposited by reactive DC-magnetron sputtering at different Ar/O 2 ratios in the gas mixture. The photocatalytic activity (under UV light irradiation) of these films was evaluated upon degradation of aqueous solutions of methylene blue (MB), a model organic pollutant. Upon photocatalysis, the TiO 2 films showed structural, morphological and compositional changes that were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and energy dispersive X-ray (EDX).
Molecules
TiO2 thin films were deposited on quartz substrates by metal–organic chemical vapor deposition (MOCVD) at temperatures of 250, 350, and 450 °C. X-ray diffraction (XRD) data revealed the production of a pure anatase phase, a decrease in crystallite size, and a textural change as deposition temperature increased. Atomic force microscopy (AFM) was used to study the morphological properties and confirm XRD results. UV-Vis.-NIR spectroscopy was used to investigate the optical properties of the samples. The effect of deposition temperature on wettability was investigated using contact angle measurements. Sunlight photocatalytic properties increased with the increase in deposition temperature for methyl orange and methylene blue. Films were post-annealed at 500 °C for 2 h. The effect of annealing on all the above-mentioned properties was explored. The kinetic analysis demonstrated superb agreement with the kinetic pseudo-first-order model. The rate of photocatalytic degradation of MB was ~...
Nanomaterials
TiO2-SiO2 thin films were created on Corning glass substrates using a simple method. Nine layers of SiO2 were deposited; later, several layers of TiO2 were deposited, and their influence was studied. Raman spectroscopy, high resolution transmission electron spectroscopy (HRTEM), an X-ray diffractometer (XRD), ultraviolet-visible spectroscopy (UV-Vis), a scanning electron microscope (SEM), and atomic force microscopy (AFM) were used to describe the sample’s shape, size, composition, and optical characteristics. Photocatalysis was realized through an experiment involving the deterioration of methylene blue (MB) solution exposed to UV-Vis radiation. With the increase of TiO2 layers, the photocatalytic activity (PA) of the thin films showed an increasing trend, and the maximum degradation efficiency of MB by TiO2-SiO2 was 98%, which was significantly higher than that obtained by SiO2 thin films. It was found that an anatase structure was formed at a calcination temperature of 550 °C; ph...
TiO2-Based Nanopowders and Thin Films for Photocatalytical Applications
… of Nanoscience and …, 2010
TiO 2-based nanopowders are elaborated by flame spray synthesis, FSS from organic precursors of titanium and chromium with the Cr content changing from 0 to 15 at.%. Well-crystallized nanopowders with high specific surface area SSA reaching 107 m 2 /g for undoped TiO 2 and 177 m 2 /g for TiO 2 +15 at.% Cr are obtained. Thin films are deposited by rf reactive sputtering from metallic Ti and Ti-Cr targets in Ar + O 2 flow controlled atmosphere. The adjustable area of Cr/Ti allows to obtain up to 16 at.% Cr in TiO 2 thin films. X-ray diffraction, transmission electron spectroscopy, TEM, atomic force microscopy, AFM and optical spectrophotometry over the ultraviolet UV and visible VIS range of the light spectrum have been performed in order to characterize the nanomaterials. The particle size of nanopowders is within the range of 5-42 nm. Anatase is the predominating polymorphic form while the amount of rutile increases with Cr content to reach of about 25 wt.% at 15 at.% Cr. The post-deposition annealing of thin films in air at temperatures from 770 K to 1280 K modifies the phase composition, leads to irreversible transformation from anatase to rutile and affects the surface roughness. Structural and optical properties of TiO 2-based nanopowders and thin films are compared. The effect of grain size and the level of chromium doping on the band gap E g is discussed. Photocatalytic activity of the nanopowders is tested for degradation of methylene blue, MB.
Al doping effect on the morphological, structural and photocatalytic properties of TiO2 thin layers
Thin Solid Films, 2016
In this study, Al-doped TiO 2 films are deposited by sol-gel dip-coating method. Structure, surface morphology, optical properties and photocatalytic degradation of Methylene blue have been investigated. The films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV-Visible spectroscopy and scanning electron microscope (SEM) equipped with electron dispersive x-ray (EDX). XRD analysis confirms the formation of single nanocrystalline anatase phase. The crystallite size is in the order of 17 nm and seems not affected by the presence of Al. AFM analysis reveals that the surface topography of TiO 2 :Al films is significantly affected by Al content. The optical properties are found not affected and all TiO 2 :Al thin films show high visible infrared transmission and high optical gap energy. The phocatalytic efficiency has been improved by Al doping; with the highest degradation rate of methylene blue observed for TiO 2 :0.2 %Al.
Surface morphology and active sites of TiO2 for photoassisted catalysis
Research on Chemical Intermediates, 2017
The main aim of this work is to discriminate the closely related adsorption and catalytic degradation processes that occur during a photocatalytic reaction. Very high-surface-area TiO 2 and Pd-doped TiO 2 were synthesized by microwaveassisted hydrothermal synthesis and used for degradation of methylene blue as a model pollutant dye. Thorough structural, morphological, and surface analyses of the synthesized catalysts were conducted to investigate key material properties that influence adsorption and catalytic performance. The adsorption capacity of the catalysts was determined by fitting adsorption data using the Langmuir isotherm model, and the photocatalytic activity of the synthesized samples was evaluated by periodically measuring the concentration of methylene blue as it was photocatalytically degraded under ultraviolet (UV) light. The results indicated that noble-metal incorporation compromised adsorption but favored catalytic performance.
Journal of the Korean Physical Society
Mono, co-and tri-doped TiO2 thin films with the transition metals (vanadium and/or chrominium) and a nonmetal (nitrogen) have been fabricated by sol-gel method. X-ray diffraction results clearly reveal anatase crystal structure for all obtained samples and doping with any dopants doesn't change the anatase phase of TiO2. Compared to TiO2, three types of doped TiO2 thin films exhibit a red-shift in the absorption edge and have much better photocatalytic properties for methylene blue degradation in visible light region. The maximum visible-photocatalytic performance was achieved for tri-doped TiO2 sample. The mechanism for enhancing visible-photocatalytic activity of co-doped and tri-doped TiO2 thin films was also examined.
International Journal of Photoenergy, 2008
The preparation of cobalt-modified TiO 2 (Co-TiO 2 ) was carried out by the incipient impregnation method starting from commercial TiO 2 (Degussa, P-25) and cobalt acetate. XPS data show that cobalt is incorporated as divalent ion, and it is likely present within few subsurface layers. No appreciable change in structural-morphologic properties, such as surface area and anatase/rutile phase ratio, was observed. Conversely, Co addition brings about conspicuous changes in the point of zero charge and in surface polarity. Diffuse reflectance spectra feature a red shift in light absorption that is dependent on the amount of cobalt. The influence of cobalt addition on the performance of TiO 2 as a photocatalyst in the degradation of 4-chlorophenol and Bisphenol A is investigated. The results show that the modified oxide presents a higher photoactivity both for illumination with UVvisible (λ > 360 nm) and visible light (λ > 420 nm; λ > 450 nm), and that this enhancement depends on the amount of the added species and on the final thermal treatment in the preparation step. We also show that Co-TiO 2 is a more active catalyst than pure TiO 2 for the reduction of O 2 in the dark, which is an important reaction in the overall photocatalytic processes.
This study involves the investigation of altering the photocatalytic activity of TiO 2 using composite materials. Three different forms of modified TiO 2 , namely, TiO 2 /activated carbon (AC), TiO 2 /carbon (C), and TiO 2 /PANi, were compared. The TiO 2 /carbon composite was obtained by pyrolysis of TiO 2 /PANi prepared by in situ polymerization method, while the TiO 2 /activated carbon (TiO 2 /AC) was obtained after treating TiO 2 /carbon with 1.0 M KOH solution, followed by calcination at a temperature of 450 ∘ C. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermogravimetric analysis (TG-DTA), Brunauer-Emmet-Teller (BET), and UV-Vis spectroscopy were used to characterize and evaluate the prepared samples. The specific surface area was determined to be in the following order: TiO 2 /AC > TiO 2 /C > TiO 2 /PANi > TiO 2 (179 > 134 > 54 > 9 m 2 g −1). The evaluation of photocatalytic performance for the degradation of methylene blue under UV light irradiation was also of the same order, with 98 > 84.7 > 69% conversion rate, which is likely to be attributed to the porosity and synergistic effect in the prepared samples.