Controlling the growth of nanosized titania via polymer gelation for photocatalytic applications (original) (raw)
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Photocatalytic Activity of Sol-Gel-Derived Nanocrystalline Titania
Journal of Physical Chemistry C, 2007
Nanocrystalline titania (TiO 2 ) powders have been synthesized via sol-gel, using an alkoxide precursor, under different processing conditions, and their photocatalytic activity has been investigated as a function of processing and material parameters through the decomposition of the methylene blue (MB) dye under exposure to the ultraviolet (UV) radiation (λ ) 200-400 nm) in an aqueous solution. The nanocrystalline TiO 2 powders with different morphology, crystallinity, average nanocrystallite size, surface area, and phase structure are obtained by controlling the ratio of molar concentrations of water and alkoxide (R) within the range of 5-60 and calcining the as-synthesized amorphous powders at higher temperatures (400-800°C). The nanocrystalline TiO 2 powders have been characterized using the scanning electron microscope (SEM), X-ray diffraction (XRD), and the Brunauer, Emmett, and Teller (BET) surface area measurement techniques while their photocatalytic activity was monitored using a UV-visible spectrometer. The photocatalytic activity of sol-gel-derived nanocrystalline TiO 2 is observed to be a function of R and calcination temperature. The maximum photocatalytic activity is observed for the largest R value and the intermediate calcination temperature as an optimum effect produced by the variation in the morphology, the average nanocrystallite size, the surface area, the phase structure, and the crystallinity of the powders. The dependence of photocatalytic activity on the average nanocrystallite size reveals the existence of a critical size (∼15 nm), below and above which the photocatalytic activity is observed to be reduced. The observed photocatalytic characteristics of sol-gel-derived nanocrystalline TiO 2 have been explained based on the existing mechanism associated with the photocatalytic decomposition of organic molecules using semiconductor oxides.
MaterialsScienceinSemiconductorProcessing, 2014
Titanium dioxide nanoparticles with average particle size of about 5 nm to 60 nm were readily synthesized via a simple, fast and low cost method; polyacrylamide gel method. Furthermore, the effect of the used acid and solvent together with calcination temperature , on crystallite size, morphology, band gaps of resultant material were investigated. The products were characterized by means of thermo gravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectroscopy analysis. The XRD results show that the presence of different anions in the precursor solution leads to the formation of samples with different anatase/rutile ratios. Their photocatalytic activities were evaluated by photocatalytic degradation of Yellow GX aqueous solution under ultraviolet radiation. The results show that the photocatalyst (TEPC I), containing 79% anatase exhibits the highest photocatalytic activity, which is due to a synergistic effect between anatase and rutile.
Journal of Sol-Gel Science and Technology, 2008
Nanocrystalline titania powders have been synthesized via conventional and modified sol-gel using an alkoxide precursor for different R, the ratio of molar concentration of water to that of alkoxide precursor, and calcination temperature. The apparent first-order reaction rate-constant obtained for the powder synthesized via conventional sol-gel is comparable with that of commercial Degussa-P25. Conventional sol-gel has been modified using the hydroxypropyl cellulose polymer to increase the specific surface area of the photocatalyst; and hence, to further enhance its photocatalytic activity. Although higher specific surface area and smaller average nanocrystallite size have been obtained for the powders synthesized via modified sol-gel, they exhibit reduced photocatalytic activity relative to that of powders synthesized via conventional sol-gel. The deactivation of the present photocatalyst has been explained on the basis of reduced surface-purity of the powders after processing via modified sol-gel as induced by the presence of surface-residual organic compounds.
Controlled Nanophase Development in Photocatalytic Titania
MATERIALS TRANSACTIONS, 2003
Acid catalyzed hydrolysis of titanium butoxide was used to synthesize homogenous titania gels, which were converted to the anatase and rutile polytypes through controlled firing. The mechanism of this phase transformation was investigated by quantitative powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Condensation to titania is a function of annealing time, temperature and atmosphere. In air, calcinations below 600 C favored the formation of anatase, with rutile only appearing at >600 C. However, in situ transformation where titania nanoparticles were treated under vacuum in the TEM required heating at higher temperatures up to 900 C. This is may be due to the formation of surface layers of reduced titanium oxide that passivate and retard the anatase to rutile transformation. Grain growth and specific surface area varied inversely, with especially rapid crystallization observed at and beyond the transformation temperature. Potential photocatalytic activity was identified with ultraviolet-visible (UV-Vis) spectroscopy. A red shift of the absorption edge for nano-titania was observed due to quantum size effects.
Journal of Photochemistry and Photobiology A: Chemistry, 2005
Nanocrystalline (14-18 nm) anatase TiO 2 powders with high photocatalytic activity are synthesized by a sol-gel method followed by supercritical drying in isopropanol. The photocatalytic behavior is studied in the model reaction of phenol photodegradation in water. The relationship between photoactivity, crystal structure, texture, charge-carrier lifetimes, bandgap energies and thermal treatment of products is discussed. The effective method of synthesis of photocatalysts based on TiO 2 -sol-gel method followed by supercritical drying in isopropanol is presented. It shows, that the obtained powders can be used in photocatalytical depollution without additional thermal treatment.
Advanced Powder Technology, 2014
In this study, polyacrylamide gel method was used for preparation of pure and mixed phase TiO 2 nanoparticles. The influence of synthesis conditions on the physicochemical properties of products was investigated. It was found that the type of acid, which was used for acidifying the precursor solution together with calcination temperature can affect the phase structure, crystalline size, morphology and thereby photocatalytic activity of obtained TiO 2 nanoparticles. Different trends were observed during the phase transformation, particle growth, shift in energy of band gap with the change in tensile strain to compressive strain of the prepared TiO 2 nanomaterial. X-ray diffraction (XRD) showed that prepared nanocrystals, which were calcined at 450 °C have pure anatase and anatase-rutile mixed structures. The prepared samples having crystallite size between 5 nm and 60 nm were observed at different calcination temperatures. In addition, the photocatalytic activities of the prepared samples were evaluated by monitoring the degradation of Cresol Red (CR). The results show that the photocatalyst (TEC I), exhibits the highest photocatalytic efficiency where 94.7% of CR can be decomposed after UV exposure for 75 min.
Sol-gel preparation of surfactants assisted Titania for solar photocatalysis
Focus on Surfactants, 2020
A typical sol-gel process with little modifications was developed to enhance the sun light photo catalysis. The synthesis of sodium influenced TiO 2 particles was done using surfactants like Cetyl Trimethyl Ammonium Bromide (CTAB), Polyvinyl Pyrrolidone (PVP) and Sodium Dodecyl Sulfate (SDS) to obtain better surface morphology by sol-gel process with surfactant assisted templating mechanism. X-ray patterns show the formation of anatase TiO 2. Methylene Blue (MB) was used as a model dye for photo catalytic degradation with various surfactant assisted titania nano particles in solar irradiation.
Journal of Physical Chemistry C, 2008
Mixed-phase nanocrystalline titania (TiO 2 ) with varying rutile content has been synthesized via solvent mixing and calcination (SMC) treatment of sol-gel-derived nanocrystalline anatase-TiO 2 and rutile-TiO 2 precursors. The mixed-phase nanocrystalline TiO 2 processed via sol-gel SMC has been characterized using X-ray diffraction, the scanning electron microscope, high-resolution transmission electron microscope, and ultraviolet-visible (UV-vis) diffuse reflectance spectroscope for analyzing its morphology, phase contents, nanocrystallite size distribution, and band gap. The photocatalytic activity of mixed-phase nanocrystalline TiO 2 processed via sol-gel SMC is measured by monitoring the degradation of the methylene blue dye in an aqueous solution, under the UV-radiation exposure, using the UV-vis absorption spectroscope. It is demonstrated that the photocatalytic activity of mixedphase nanocrystalline TiO 2 processed via sol-gel SMC is a function of rutile content with the maximum photocatalytic activity observed for 40 wt% rutile. Thus, the synergistic effect has been observed between anatase-TiO 2 and rutile-TiO 2 , which has been satisfactorily explained using a new model based on the band-gap variation in the connected nanocrystallites as a function of the size distribution and the phases involved, which overcomes the limitations of the existing models proposed earlier in the literature.
Titania Nanoparticles Synthesized by Sol-Gel Technique
Abstract: Titania (TiO2) nanoparticles were prepared by combining bulk titania with trisodium citrate solution at room temperature without calcination. The formation of titania nanoparticles was confirmed from XRD and by the dominant FTIR peaks at 621 cm-1, 412 cm-1. UV-Visible analysis shows the occurrence of strong red shift, confirming the presence of nanoparticles which is essential for higher photo catalytic activities. TGA analysis reveals that the synthesized titania nanoparticles were thermally stable up to 700 °C. SEM image shows that the particles of the synthesized sample are in nanometer range which is in accordance with UV-Visible studies.
Catalysts
Titania photocatalysts have been intensively examined for both mechanism study and possible commercial applications for more than 30 years. Although various reports have already been published on titania, including comprehensive review papers, the morphology-governed activity, especially for novel nanostructures, has not been reviewed recently. Therefore, this paper presents novel, attractive, and prospective titania photocatalysts, including zero-, one-, two-, and three-dimensional titania structures. The 1D, 2D, and 3D titania structures have been mainly designed for possible applications, e.g., (i) continuous use without the necessity of particulate titania separation, (ii) efficient light harvesting (e.g., inverse opals), (iii) enhanced activity (fast charge carriers’ separation, e.g., 1D nanoplates and 2D nanotubes). It should be pointed out that these structures might be also useful for mechanism investigation, e.g., (i) 3D titania aerogels with gold either incorporated inside...