Effect of Surface Chemistry and Crystallographic Parameters of TiO2 Anatase Nanocrystals on Photocatalytic Degradation of Bisphenol A

Abstract

The photocatalytic activity of a series of anatase TiO2 materials with different amounts of exposed (001) facets (i.e., 12% (TiO2-1), 38% (TiO2-3), and 63% (TiO2-3)) was tested in a batch slurry reactor towards liquid-phase bisphenol A (BPA, c0(BPA) = 10 mg/L, ccat. = 125 mg/L) degradation. Photo-electrochemical and photo-luminescence measurements revealed that with the increasing amount of exposed anatase (001) facets, the catalysts generate more electron-hole pairs and OH∙ radicals that participate in the photocatalytic mineralization of pollutants dissolved in water. In the initial stages of BPA degradation, a correlation between % exposure of (001) facets and catalytic activity was developed, which was in good agreement with the findings of the photo-electrochemical and photo-luminescence measurements. TiO2-1 and TiO2-3 solids achieved 100% BPA removal after 80 min in comparison to the TiO2-2 sample. Adsorption of BPA degradation products onto the TiO2-2 catalyst surface was found to have a detrimental effect on the photocatalytic performance in the last stage of the reaction course. Consequently, the global extent of BPA mineralization decreased with the increasing exposure of anatase (001) facets. The major contribution to the enhanced reactivity of TiO2 anatase (001) surface is the Brønsted acidity resulting from dissociative chemisorption of water on a surface as indicated by FTIR, TPD, and MAS NMR analyses.

Structure and photocatalytic activity of flame-synthesized titanium dioxide catalysts

“…The key role of particle morphology is well-known in heterogeneous catalytic processes as crystal facet-dependent catalytic activity has been pointed out many times [221][222][223]. Specifically to TiO2 applications, similar results have started to reveal themselves in the near past [76][77][78][79], emphasizing the significance of anatase crystalline shape. The natural crystal form of this phase is a truncated tertragonal bipyramid having dominating facets (~ 94% of the overall surface area, [38])…”

“…The former can actually be considered as adsorbed protons on the 2-fold coordinated bridging oxygen atom (Ti-OH + -Ti), while the latter is equally regarded as a hydroxide ion bound to the 5-fold coordinated Ti 4+ atoms or as the product of the dissociative adsorption of water at these sites [39]. In fact, the OH-group density is mainly determined by the crystal structure [76][77][78][79] of the catalyst and it can hardly be adjusted posteriorly without inducing changes in other properties. Later on, a detailed description on surface characteristics and their role in photocatalysis will be presented.…”

“…It means, on the one hand, a more efficient spatial charge separation that works against recombination. Secondly, the fortunate combination of higher OH-group density and the increased availability of holes at the {001} facets results in a significantly enhanced charge trapping and subsequent OH-radical production [79,229]. However, maximizing the {001}/{101} surface ratio does not always bring the desired performance improvement, as in some cases, an optimum value could be detected for certain applications [230].…”