Orientation Dependence of Photochemical Reactions on TiO₂ Surfaces

Abstract

The photochemistry of oriented rutile surfaces has been examined using the photoreduction of Ag+ to Ag metal from an aqueous solution onto the TiO2 surfaces. The photochemical reaction rates and quantum yields of rutile films were found to be a function of the orientation of the rutile surface. The (100) and (110) rutile orientations have lower photoreduction rates than the (101), (111), and (001). This dependence of the photochemical reaction rates on film surface orientation is observed over a range of light intensities, illumination wavelengths, and film thicknesses. Atomic force microscopy has been used to characterize the morphologies of the film surfaces and the photoreduced Ag at these surfaces. Several properties of rutile, such as the surface morphology, surface chemistry, space charge phenomena, and charge transport, are discussed in relation to their possible contributions to the orientation dependence of the photochemistry on the rutile films.

Functional links between stability and reactivity of strontium ruthenate single crystals during oxygen evolution

“…We note that under-coordinated polar surfaces such as the (110) and the (111) provide additional adsorption sites (in our case for the adsorption of OH À ) and are typically more reactive 59 . The subject of chemical anisotropy at oxide surfaces has been explored for some time with photocatalytic reactions 60 , and very recently for oxygen surface exchange 61 . In the latter studies, the (001) perovskite surface always exhibited the slowest exchange rates because of its relatively high stability.…”

Water adsorption on rutile TiO2(110) for applications in solar hydrogen production: A systematic hybrid-exchange density functional study

“…[5][6][7] However, the required solar-to-fuel efficiencies have been unattainable at a reasonable cost, 8 and there is ample motivation to enhance the photochemical conversion efficiency of the photocatalytic material. A dependency of photocatalytic activity on the surface facet has become evident from a number of experimental studies, [9][10][11][12] though the reasons for this dependency are unknown (see Ref. 13 for proposed mechanisms).…”

Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO4

“…Thus, certain facets of a semiconductor prefer reduction while others favour oxidation [18][19][20] . However, reports on the reduction and oxidation reaction facets on the same semiconductor crystal (such as TiO 2 ) were often contradictory in the literature [21][22][23][24][25][26] . For example, it was reported that rutile {011} and anatase {001} faces provided the sites for oxidation, while the rutile {110} and anatase {101} faces offered the sites for reduction 24 .…”

“…However, some references observed higher photocatalytic oxidation activity of organics on anatase nanocrystals with well-faceted {101} surfaces than that of the above-mentioned {001} facet [30][31][32] . Farneth et al 21 concluded that the fine Ag particles are mostly deposited by reduction of Ag þ on the {110} face of TiO 2 , while Hotsenpiller et al 22 reached the conclusion that the Ag particles were photocatalytically deposited at higher velocities on the {001} and {011} facets than on the {110} and {010} facets. A possible reason for the contrary conclusions is that the reaction selectivity on different facets is also affected by adsorption/desorption behaviours of reactant molecules and reaction intermediates on different facets 33,34 .…”