Formic Acid Adsorption on Anatase TiO₂(001)−(1 × 4) Thin Films Studied by NC-AFM and STM^†

Abstract

Atomic resolution scanning tunneling microscopy (STM), noncontact atomic force microscopy (NC-AFM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and formic acid adsorption experiments were used to characterize the (001) surface of anatase TiO2. A combination of NC-AFM and STM imaging was used to distinguish features due to geometrical and electronic effects. The contrast in images of the bare (1 × 4) surface and the formate-covered surface is dominated by the surface topography in both NC-AFM and STM, although electronic effects in the troughs contribute features to the STM images that are absent from NC-AFM images. High-resolution imaging by STM and NC-AFM revealed that the highest point of the ridge of the (1 × 4) structure consists of a single row of atoms. Formate adsorbs at under-coordinated Ti sites in the added rows with a minimum separation of 2a 0 and never adsorbs in the trenches even though the trenches also likely expose under-coordinated Ti atoms. The sticking probability of formate on the anatase TiO2(001)−(1 × 4) surface is near unity initially, and falls dramatically once the saturation coverage of 1/8 ML is reached. We show that of the current models for the (1 × 4) reconstruction, an added row plus surface oxygen vacancy model and the recently proposed add-molecule model are in best agreement with all of the data.

Selective photoredox activity on specific facet-dominated TiO2 mesocrystal superstructures incubated with directed nanocrystals

“…The effect of steric hindrance by TiO 2 and adsorbed molecules is therefore, explicitly ruled out. According to the literature [62][63][64], the anatase {0 0 1} surface has a strong ability to adsorb hydroxyl and carboxylic groups (as well as water molecules) dissociatively onto the undercoordinated Ti cations. It can therefore, be reasonably concluded that S M basal /S M lateral with synergetic nanocrystal engineering plays an essential role in determining the dye adsorption capability, because the surface areas of the TMC samples are very similar.…”

Adsorption of formic acid on rutile TiO2 (110) revisited: An infrared reflection-absorption spectroscopy and density functional theory study

“…6 Formate adsorption on TiO 2 has been studied extensively. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Previous studies of adsorption of formic acid (HCOOH) on rutile TiO 2 (110) surfaces have shown that upon adsorption it dissociates into a formate ion (HCOO -) and a proton (H + ), which bind to lowcoordinated Ti and O surface atoms, respectively. 22,23 The adsorption structure of small molecules, such as HCOOH, can be studied favourably by infrared spectroscopy, and in particular infrared reflection-absorption spectroscopy (IRRAS) has been employed to study e.g.…”

Growth and surface structure of vanadium oxide on anatase (0 0 1)

“…X-ray photoelectron diffraction data were consistent with an epitaxial vanadia layer; however, no ordered LEED patterns were obtained. The lack of any discernible order in LEED may have been due to the condition of the anatase (0 0 1) substrate surface which displayed only a (1 · 1) pattern rather than the (4 · 1) reconstruction now considered to be the favored termination for stoichiometric anatase (0 0 1) [15,16]. Thus the structure of vanadia layers on TiO 2 remains an open question.…”