Aerosol-Assisted Production of Mesoporous Titania Microspheres with Enhanced Photocatalytic Activity: The Basis of an Improved Process

Abstract

An aerosol-based process was used to prepare mesoporous TiO(2) microspheres (MTM) with an average diameter in the range of 0.5-1 microm. The structural characteristics and photocatalytic properties of the synthesized materials were determined. As-prepared MTM materials and those heated in air from 400 to 600 degrees C exhibited mesoporous texture with a narrow size distribution and an inorganic framework that consisted of 4-13 nm anatase crystallites. Pore volumes for the MTM materials were in the range of 0.17-0.34 cm(3) g(-1). Microspheres heated to 400 degrees C presented a locally ordered mesopore structure and possessed X-ray diffraction d spacings between 9.8 and 17.3 nm. Heating above 400 degrees C resulted in a loss of the mesoscopic order, a decrease of the surface area, retention of the porosity, and an increase of the anatase nanoparticle size to 13 nm. The accessibility of the pore volume was measured by monitoring the uptake of gallic acid (GA) using Fourier transform IR. The MTM materials made excellent catalysts for the photodegradation of GA, with the performance being higher than that of an equivalent sample of Degussa P25. The present MTM materials are advantageous in terms of their ease of separation from the aqueous phase, and hence a novel photocatalytic process is proposed based on separate adsorption and photocatalytic decomposition steps with an improved and more rational use of both catalyst and sunlight.

Critical aspects in the production of periodically ordered mesoporous titania thin films

“…Recent works performed with powder mesoporous titania systems assign an equivalent importance to crystallinity and accessible porosity in the photocatalysis process. 127,128 In the case of films, ordered MTTFs are more active than non-ordered porous ones, and cubic structures are more efficient than hexagonal ones, in both cases due to improved molecule diffusion to the active centres. 65,112,125,126 Again, optimisation of the synthesis design (i.e., choice of the porogen, template : precursor ratio, stabilization process and post-treatment) permits the achievement of highly accessible pore structures with better performance.…”

General Information to Obtain Spherical Particles with Ordered Mesoporous Structures

“…Aerosol-assisted synthesis of ordered mesoporous oxides is summarized in Table 2. Only mesoporous simple oxides (e.g., SiO 2 , TiO 2 , ZrO 2 , Al 2 O 3 ) prepared using EO n PO m EO n triblock copolymers [37][38][39][40][41] are listed. It is considered that such oxide species adequately interact with PEO units under acidic conditions below the isoelectric points.…”

Photocatalytic and Photoelectrochemical Characteristics of Mesoporous Titanium Dioxide Microspheres

“…The phase composition, crystallinity, size, and shape of the products of these processes are very sensitive to the structure of the Ti(IV) precursor, the nature of the solvent, and the conditions of the sol-gel transformation. By using templates and introducing various additives that affect the interaction between the TiO 2 particles during the formation of the porous framework it is possible to achieve a wide variety of TiO 2 microspheres with hierarchical organization [5,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…Penetration of the light beam into the depth of the microspheres and multiple refraction and reflection of the light in their volume increase the likelihood of absorption of light and lead to a substantial increase in the photoactivity of the TiO 2 [4,5], particularly in processes involving the degradation of dyes [9-12, 18, 22] and a series of other organic compounds [3,[13][14][15][16][17]19], the oxidation of NO x [21], and the reduction of Cr(VI) [10], CO 2 [20], and water [23]. In photoelectrochemical systems electrodes based on porous microspheres (MS) of TiO 2 can generate a higher photocurrent than photoanodes of analogous composition made from nonporous nanocrystalline TiO 2 [23,24].…”