An Improved Photocatalyst of TiO2/SiO2 Prepared by a Sol-Gel Synthesis (original) (raw)
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Influence of the Percentage of TiO2 Doped into SiO2 Matrix on Photocatalysis
ISRN Nanomaterials, 2012
The sol-gel process was employed in the preparation of titania-doped spherical nanosilica for application in photocatalysis. To this end, the silica matrix was doped with 1 and 10% titania, and the catalytic activity of the resulting solids in the degradation of rhodamine was tested. The synthesized materials were thermally treated at 120, 400, and 800°C. Differential thermal analysis did not evidence the titania-phase transition from anatase to rutile. Scanning electron microscopy revealed the formation of monodisperse spherical nanoparticles with sizes varying between 400 and 500 nm. The UV-Vis absorption spectra showed that the silica doped with 10% titania promoted 86% rhodamine degradation within 90 minutes, as compared to 40% in the case of the silica containing 1% titania. The silica matrix was demonstrated to affect the titania-phase transformation.
The advancements in sol–gel method of doped-TiO 2 photocatalysts
A critical review on the advancements in sol-gel method of doping TiO2 photocatalysts is provided. Various sol-gel and related systems of doping were considered, ranging from co-doping, transition metal ions doping, rare earth metal ions doping to other metals and non-metals ions doping of TiO2. The results available showed that doping TiO2 with transition metal ions usually resulted in a hampered efficiency of the TiO2 photocatalyst, though in some few cases, enhancements of the photocatalytic activity of TiO2 were recorded by doping it with some transition metal ions. In most cases, co-doping of TiO2 increases the efficiency of its photocatalytic activity. The review reveals that there are some elemental ions that cannot be used to dope TiO2 because of their negative effects on the photocatalytic activity of the catalyst, while others must be used with caution as their doping will create minimal or no impacts on the TiO2 photocatalytic efficiency.
Applied Catalysis A-general, 2006
The use of titania–silica materials in photocatalytic processes has been proposed as an alternative to the conventional TiO2 catalysts, in order to facilitate the separation of the solids after the reaction. However, despite the large number of works in this field, up to date it is not totally clarified the mechanism governing the photocatalytic activity of the mixed TiO2/SiO2 oxides. In the present work, several titania–silica materials have been prepared through a sol–gel method controlling the main variables to obtain materials with different textural properties, degree of titanium incorporation and dispersion of such species and crystallinity of titanium dioxide. Characterization of the samples and correlation with their activity for the photocatalytic oxidation of cyanide has permitted to determine that the main factors conditioning the photoactivity of these materials are: (i) textural properties and accessibility of the titania surface, (ii) formation of anatase nanocrystals of suitable size and band gap energy and (iii) quality of the titania crystal network, improved by the use of a hydrothermal crystallization procedure.
Catalysis Today, 2005
Immobilization of TiO 2 on silica materials has been commonly proposed in order to make easier the separation of the catalyst after the photocatalytic reactions in aqueous systems. The main drawback of the supported photocatalysts is that they usually show lower activities in comparison with powdered TiO 2 materials. The aim of this work is to elucidate the structure of some silica-supported TiO 2 photocatalysts recently developed as well as to evaluate the role that the porous structure of the support can play in the observed photocatalytic activities. In comparison with the use of an amorphous silica support, the use of the mesostructured silica SBA-15 produces an ordered structure in which TiO 2 crystals of similar sizes, independently of titania loading, are located inside the mesoporous channels of the support. The photocatalytic treatment of several cyanide-containing compounds is analyzed and the results are explained in terms of the structure of every catalyst. Depending on the model compound, the characteristic structure of the TiO 2 /SBA-15 materials allows increasing up to eight times the activity achieved by the Degussa P25 TiO 2 . The main conclusion of this work is the strong influence of the textural properties of the support on the catalytic activity of immobilized TiO 2 photocatalysts. #
Catalysts, 2020
The objective of this work is to improve the efficiency of TiO2 photocatalysts by activation treatments and by modification with palladium nanoparticles and doping with SiO2. The influence of the additive loading was explored, and two activation treatments were performed: UV exposition and H2 reduction. TiO2/SiO2/Pd photocatalysts were synthesized by an original cogelation method: a modified silicon alkoxide, i.e., [3-(2-aminoethyl)aminopropyl]trimethoxysilane (EDAS), was used to complex the palladium ions, thanks to the ethylenediamine group, while the alkoxide groups reacted with TiO2 precursors. Pure TiO2 was also synthesized by the sol–gel process for comparison. X-ray diffraction evidenced that the crystallographic structure of TiO2 was anatase and that Pd was present, either in its oxidized form after calcination, or in its reduced form after reduction. The specific surface area of the samples varied from 5 to 145 m2 g-1. Transmission electron microscopy allowed us to observe ...
Journal of Materials Chemistry, 2000
TiO 2 (anatase)-based photocatalyst powders containing up to 20 mol% calcium, strontium or barium ions were prepared from a-titanic acid by calcining gels prepared from triethanolamine-based sols at 600 ³C. The powders were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse re¯ectance ultraviolet spectrophotometry, nitrogen sorption porosimetry and in situ infrared spectroscopy to examine surface adsorbed species. Compositions containing greater than 15 mol% alkaline earth ions resulted in largely amorphous materials. The residual anatase showed decreased crystallite sizes and increased crystallographic cell volumes with increasing concentration of alkaline earth ions, while the BET surface areas of the materials increased from around 80 m 2 g 21 (no additive) to 160 m 2 g 21 at higher levels of additive. Electronic spectroscopy showed that the band gaps of the materials increased with increasing Ca 2z content, due to the decreasing particle sizes. Under the synthesis conditions used, no other crystalline phase was observed, except rutile (v1% w.r.t. anatase). The photocatalytic decomposition of oxalic acid was used as a model system to determine the relative in¯uences of the additives on the photocatalytic activities. Titania containing 20 mol% alkaline earth ions showed approximately double the photocatalytic activity of similarly prepared anatase without additive. Half of the enhancement occurred for titania samples containing only 2 mol% alkaline earth ions. Comparisons of the physico-chemical properties of the photocatalysts with oxalic acid decomposition rates were carried out to determine the factors in¯uencing the photocatalytic activity.
Novel Silica Gel Supported TiO2 Photocatalyst Synthesized by CVD Method
Langmuir, 2000
TiO2 in anatase crystal phase is a very effective catalyst in the photocatalytic oxidation of organic compounds in water. To improve the recovery rate of TiO2 photocatalysts, which in most cases are in fine powder form, the chemical vapor deposition (CVD) method was used to load TiO2 onto a bigger particle support, silica gel. The amount of titania coating was found to depend strongly on the synthesis parameters of carrier gas flow rate and coating time. XPS and nitrogen ads/desorption results showed that most of the TiO2 particles generated from CVD were distributed on the external surface of the support and the coating was stable. The photocatalytic activities of TiO2/silica gel with different amounts of titania were evaluated for the oxidation of phenol aqueous solution and compared with that of Degussa P25. The optimum titania loading rate was found around 6 wt % of the TiO2 bulk concentration. Although the activity of the best TiO2/silica gel sample was still lower than that of P25, the synthesized TiO2/silica gel catalyst can be easily separated from the treated water and was found to maintain its TiO2 content and catalytic activity.
Effects of SiO2 addition on TiO2 crystal structure and photocatalytic activity
Journal of the European Ceramic Society, 2010
A series of TiO 2 -SiO 2 mixtures -having the following stoichiometry Ti 1−x Si x O 2 , with x = 0, 0.1, 0.3 and 0.5 atoms per formula unit -were prepared by using precursor oxides and fired at three temperatures (900, 1000 and 1200 • C). The modifications in the structure and, consequently, on the photocatalytic activity, induced by the addition of SiO 2 into the TiO 2 powder, were thoroughly investigated by using various analytical techniques: X-ray powder diffraction, electron microscopy (FE-SEM and TEM), XPS, FT-IR, DRS and BET analysis. The results underlined as essentially no solid solution occurs between the two crystalline end-members. Nevertheless, silica addition caused a retarding effect on anatase-to-rutile phase transformation and on the crystallite growth.
Chemistry of …, 2008
The sol-gel synthesis of TiO 2 from TiCl 4 assisted by the triblock copolymer EO 20 -PO 70 -EO 20 (EO ) -CH 2 CH 2 O-, PO ) -CH 2 (CH 3 )CHO-) as templating agent was carried out by systematically changing H 2 O:Ti (r w ) and HCl:Ti (r a ) molar ratios. Mesoporous and nanocrystalline TiO 2 samples with well-defined and controlled phase composition (anatase, rutile, and mixed phase) were obtained after calcination at 400°C and characterized for the morphology, particle size, and shape using TEM, HRTEM, XRD, and surface area measurements. The role of r w and r a and influence of the copolymer in determining the phase composition was demonstrated. Rutile becomes the main phase by increasing r w . In fact, the decrease of Ti concentration slows down the condensation rate, favoring formation of rutile seeds in the gel. The photocatalytic activity of TiO 2 in the UV photomineralization of phenol depends on the phase composition and oxidizing agent, H 2 O 2 or O 2 . When the oxidation is performed by H 2 O 2 , rutile, formed by large crystalline rods with high aspect ratios (size 15-20 × 100-120 nm), shows higher catalytic activity with respect to the small, almost cubic, anatase particles (5-15 nm). If O 2 is used, the catalytic activity generally decreases and the behavior of polymorphous species is reverse. EPR investigation of the paramagnetic charge carriers, formed under UV irradiation at 10 K, showed the resonance lines of holes trapped at Olattice sites and electrons trapped at Ti 3+ and O 2 sites. The rutile crystalline rods present the largest quantity of Oand Ti 3+ centers. The overall results suggest correlation between TiO 2 particle size and shape and the photocatalytic activity and indicate that electron-hole recombination is the most probable rate-controlling process.
Synthesis, characterization and photocatalytic properties of sol–gel TiO2 films
Ceramics International, 2011
The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO 2 as a photocatalyst. Starting TiO 2 solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO 2 films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO 2 films were studied by means of atomic force microscopy (AFM). Structural properties of TiO 2 were identified by Xray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO 2 films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model. The addition of PEG to the TiO 2 solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO 2. The TiO 2 film prepared with PEG is characterized by higher roughness parameters (R a , R max , R q , R z and Z max), a lower amount of the rutile phase of TiO 2 , a higher amount of the anatase phase of TiO 2 and a better photocatalytic activity compared to the TiO 2 film without the addition of PEG.