Structure and Vibrational Spectrum of Formate and Acetate Adsorbed from Aqueous Solution onto the TiO₂ Rutile (110) Surface

Abstract

The adsorption of formate and acetate from aqueous solutions at pH 3-9 onto the TiO 2 rutile (110) surface was studied by ATR-FTIR spectroscopy. The spectra indicated that there was only one type of adsorbed species, and that formate and acetate were adsorbed in a similar manner. On the basis of the measured ν as -(COO)ν s (COO) splitting (∆ν as-s ) of 191 and 87 cm -1 , for formate and acetate, respectively, the monodentate (ester type) binding mode could be excluded. Ab initio calculations at the Hartree-Fock level showed that for pentacoordinated Ti IV , present in the (110) surface, the chelating bidentate binding mode is unstable with respect to the rearrangement to the monodentate or the bridging bidentate mode. The computed vibrational frequencies of formate and acetate adsorbed in a bridging bidentate mode onto Ti clusters with 2-5 Ti centers, representing the (110) surface, agreed with experiment and thus showed that this methodology can be used for the determination of the structures of adsorbates on, for example, metal oxide surfaces in contact with aqueous solutions.

Characterisation, phase stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

“…11 shows DRIFT spectra of formic acid preadsorbed on different co-doped samples (solid, thick curves). By comparisons with previous reports [65][66][67][68] it is evident from Fig. 11 that formic acid dissociates on all samples to form bidentate and monodentate coordinated formate molecules on the surface of the particles with their typical vibrational  as (OCO) and (C=O) bands occurring at 1560 cm -1 and 1670 cm -1 , respectively.…”

“…Additionally, an absorption band at 1580 cm -1 contributes to the broad absorption band in the 1550-1600 cm -1 region as suggested from the asymmetric shape of the broad absorption band, and deduced from peak deconvolution (not shown). This absorption band can be attributed to un-coordinated formate ions (aqueous-like) [66,67]. This is further supported by the strong absorbance of this band seen on the amorphous TiZrY5 sample, which contains more adsorbed OH/H 2 O as shown by XPS (Section 3.1).…”

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

“…The mode at 1582 cm -1 is attributed to hydrogen bonded formate ions (outer-sphere complexes) present on the surface, guided by previous reports. 16,50 The band at 1562 cm -1 is due to the  a (OCO) mode of the minority species. Within the threelayer model, coupling to the E n,p component yields only R/R 0 < 0 (R a /R 0 > 1, emission bands), see eqn.…”

“…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.…”

Polyelectrolyte Multilayer Template Assisted in-Situ Synthesis of the Inorganic Nanostructures

“…The films are formed of the monodispersed TiO 2 crystallites, whereas the average TiO 2 crystallite size below 15 nm is obtained. Due to the extreme sensitivity of titanium iso-propoxide to water, high reaction rates of hydrolysis and condensation in the sol-gel process normally result in large, polydispersed particles yielding high surface roughness of the TiO 2 film [38].…”