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Ordered Carboxylates on TiO2(110) Formed at Aqueous Interfaces.

Grinter DC, Woolcot T, Pang CL, Thornton G - J Phys Chem Lett (2014)

Bottom Line: The three molecules display quite different adsorption behavior, illustrating the different interadsorbate interactions that can occur.Acetic acid forms a well-ordered (2 × 1) acetate overlayer similar to that observed following deposition from vapor.Benzoic acid forms a (2 × 2) overlayer, which is stabilized by intermolecular interactions between the phenyl groups.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry & London Centre for Nanotechnology, University College London , 20 Gordon Street, London, WC1H 0AJ, United Kingdom.

ABSTRACT

As models for probing the interactions between TiO2 surfaces and the dye molecules employed in dye-sensitized solar cells, carboxylic acids are an important class of molecules. In this work, we present a scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) study of three small carboxylic acids (formic, acetic, and benzoic) that were reacted with the TiO2(110) surface via a dipping procedure. The three molecules display quite different adsorption behavior, illustrating the different interadsorbate interactions that can occur. After exposure to a 10 mM solution, formic acid forms a rather disordered formate overlayer with two distinct binding geometries. Acetic acid forms a well-ordered (2 × 1) acetate overlayer similar to that observed following deposition from vapor. Benzoic acid forms a (2 × 2) overlayer, which is stabilized by intermolecular interactions between the phenyl groups.

No MeSH data available.


Related in: MedlinePlus

Acetic acid (0.38 ML)on rutile TiO2(110) after deposition from a 10 mM aqueousacetic acid solution. (A) STM image of the ordered overlayer (50 ×50 nm2 (inset: 7 × 7 nm2), Vs = 1.2 V, It = 0.2 nA). (B)Schematic model of an acetate (2 × 1) overlayer. (C) LEED pattern(21 eV) showing the TiO2(110)(1 × 1) (orange) andthe acetate-(2 × 1) (blue).
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fig2: Acetic acid (0.38 ML)on rutile TiO2(110) after deposition from a 10 mM aqueousacetic acid solution. (A) STM image of the ordered overlayer (50 ×50 nm2 (inset: 7 × 7 nm2), Vs = 1.2 V, It = 0.2 nA). (B)Schematic model of an acetate (2 × 1) overlayer. (C) LEED pattern(21 eV) showing the TiO2(110)(1 × 1) (orange) andthe acetate-(2 × 1) (blue).

Mentions: Room-temperatureexposure of TiO2(110) to acetic acid in the vapor phaseis well-understood: a homogeneous, ordered (2 × 1) overlayeris observed at saturation coverage.23 Adsorptionis dissociative and results in acetate bonded in a bidentate configurationbetween adjacent Ti5c sites, equivalent to the type i formatementioned above.23−25 Tao et al. report that at low coverages, adsorbedacetate moieties do not cluster and are instead arranged diffusely,indicative of a repulsive interaction between the molecules.23 STM of TiO2(110) following exposureto a droplet of 10 mM acetic acid shows a relatively well-orderedoverlayer of 0.38 ML coverage (Figure 2A) withspacing indicative of (2 × 1) periodicity relative to the substrate.A ball model illustrating the structure of the overlayer is shownin Figure 2B. The half-integer spots foundin LEED along [001] (Figure 2C) confirm thelonger-range order of the acetate overlayer compared with that forformate. The STM image inset in Figure 2A showsthe domain structure that results from the (2 × 1) periodicity,with domains out of registry by one unit cell along [001] depictedin blue and red. The acetate moieties appear to align in phase withnearest neighbors in both [001] and [1̅10] directions, withshort chains formed both along and across rows.


Ordered Carboxylates on TiO2(110) Formed at Aqueous Interfaces.

Grinter DC, Woolcot T, Pang CL, Thornton G - J Phys Chem Lett (2014)

Acetic acid (0.38 ML)on rutile TiO2(110) after deposition from a 10 mM aqueousacetic acid solution. (A) STM image of the ordered overlayer (50 ×50 nm2 (inset: 7 × 7 nm2), Vs = 1.2 V, It = 0.2 nA). (B)Schematic model of an acetate (2 × 1) overlayer. (C) LEED pattern(21 eV) showing the TiO2(110)(1 × 1) (orange) andthe acetate-(2 × 1) (blue).
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getmorefigures.php?uid=PMC4273618&req=5

fig2: Acetic acid (0.38 ML)on rutile TiO2(110) after deposition from a 10 mM aqueousacetic acid solution. (A) STM image of the ordered overlayer (50 ×50 nm2 (inset: 7 × 7 nm2), Vs = 1.2 V, It = 0.2 nA). (B)Schematic model of an acetate (2 × 1) overlayer. (C) LEED pattern(21 eV) showing the TiO2(110)(1 × 1) (orange) andthe acetate-(2 × 1) (blue).
Mentions: Room-temperatureexposure of TiO2(110) to acetic acid in the vapor phaseis well-understood: a homogeneous, ordered (2 × 1) overlayeris observed at saturation coverage.23 Adsorptionis dissociative and results in acetate bonded in a bidentate configurationbetween adjacent Ti5c sites, equivalent to the type i formatementioned above.23−25 Tao et al. report that at low coverages, adsorbedacetate moieties do not cluster and are instead arranged diffusely,indicative of a repulsive interaction between the molecules.23 STM of TiO2(110) following exposureto a droplet of 10 mM acetic acid shows a relatively well-orderedoverlayer of 0.38 ML coverage (Figure 2A) withspacing indicative of (2 × 1) periodicity relative to the substrate.A ball model illustrating the structure of the overlayer is shownin Figure 2B. The half-integer spots foundin LEED along [001] (Figure 2C) confirm thelonger-range order of the acetate overlayer compared with that forformate. The STM image inset in Figure 2A showsthe domain structure that results from the (2 × 1) periodicity,with domains out of registry by one unit cell along [001] depictedin blue and red. The acetate moieties appear to align in phase withnearest neighbors in both [001] and [1̅10] directions, withshort chains formed both along and across rows.

Bottom Line: The three molecules display quite different adsorption behavior, illustrating the different interadsorbate interactions that can occur.Acetic acid forms a well-ordered (2 × 1) acetate overlayer similar to that observed following deposition from vapor.Benzoic acid forms a (2 × 2) overlayer, which is stabilized by intermolecular interactions between the phenyl groups.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry & London Centre for Nanotechnology, University College London , 20 Gordon Street, London, WC1H 0AJ, United Kingdom.

ABSTRACT

As models for probing the interactions between TiO2 surfaces and the dye molecules employed in dye-sensitized solar cells, carboxylic acids are an important class of molecules. In this work, we present a scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) study of three small carboxylic acids (formic, acetic, and benzoic) that were reacted with the TiO2(110) surface via a dipping procedure. The three molecules display quite different adsorption behavior, illustrating the different interadsorbate interactions that can occur. After exposure to a 10 mM solution, formic acid forms a rather disordered formate overlayer with two distinct binding geometries. Acetic acid forms a well-ordered (2 × 1) acetate overlayer similar to that observed following deposition from vapor. Benzoic acid forms a (2 × 2) overlayer, which is stabilized by intermolecular interactions between the phenyl groups.

No MeSH data available.


Related in: MedlinePlus