The adsorption isotherms of catechol (1,2-dihydroxybenzene) and gallic acid (3,4,5-trihydroxybenzoic acid) onto titanium dioxide (Degussa P-25) were measured at various pH values and room temperature using attenuated total reflection Fourier transform infrared (FTIR-ATR) data, processed by singular value decomposition. The affinity is largely pH independent, although the deprotonatation of the carboxylic group in gallic acid might produce a slight increase in the affinity. Catechol was shown to form two complexes, with Langmuir stability constants log K of 4.66 (strong mode) and 3.65 (weak mode). Both complexes have the same spectral signature, and mononuclear and binuclear chelate structures are proposed for them. Gallic acid chemisorbs by complexation through two -OH groups and forms one complex only, log K = 4.70. The third -OH and the pendant carboxylate do not influence much the stability of the surface complex. Comparison with literature data demonstrates that the affinity of 4-chlorocatechol is also similar, whereas 2,3-dihidroxynaphthalene and 4-nitrocatechol form more stable complexes, probably because of the solvation contribution to the overall Gibbs adsorption energy. All quoted constants refer to the surface complexation equilibria written as follows: ([triple bond]Ti-OH)2 + H2L = ([triple bond]Ti)2-L + 2H2O, i.e., as electroneutral processes. The FTIR-ATR spectra of the surface complexes are also discussed.

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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.