Characterization of hydroquinone and related compounds adsorbed at Pt(111) from aqueous solutions: electron energy-loss spectroscopy, Auger spectroscopy, LEED, and cyclic voltammetry

Abstract

Tennessee Eastman Co., and Dow Coming Corp. for their generous support under the Presidential Young Investigator Award (Grant No. CPE-8351190). We thank Prof. C. B. Richardson of the University of Arkansas for his technical advice.

Molecular Orientation of Hydroquinone Adsorbed at a Platinum(111) Thin-Layer Electrode

“…According to theoretical estimates based on Van Der Waals radii, horizontal HQ should achieve a packing density of 0.309 nmol/cm 2 (3). Estimates based upon LEED patterns of HQ at ordered Pt(111) surfaces led to a packing density of 0.276 nmol/cm 2 (5). Experimental values from this study are within the margins defined by these two values in this low concentration range.…”

“…A horizontal orientation of the adsorbed HQ molecule results from adsorption at HQ concentrations below 0.1 mM (3,5). According to theoretical estimates based on Van Der Waals radii, horizontal HQ should achieve a packing density of 0.309 nmol/cm 2 (3).…”

“…The horizontal form was reported to reorient to the vertical form when a surface containing the horizontally adsorbed form of HQ was exposed to a solution containing a higher HQ concentration (4). Measurements of HQ packing density by means of Auger electron spectroscopy (AES), however, were not indicative of a transition from horizontal to vertical orientation versus HQ concentration at Pt(111) surfaces (5,6). Divergence pertaining to the surface orientation of adsorbed HQ also exists among other studies: Surface IR displayed new absorption bands of adsorbed HQ from adsorption at higher HQ concentrations, which were indicative of edgewise adsorbed HQ (7,8); TLE-GC studies found a maleic acid peak, which was attributable to oxidation of an edgewise adsorbed HQ at the TLE surface (9).…”

Electrochemical processes for in-situ treatment of contaminated soils. Annual progress report, September 1996--May 1997

“…The values of Qu are approximately the same for the series of chlorophenols indicating a common mode of binding. If the molecules are assumed to bind in an orientation in which the plane of the phenol ring is parallel to the adsorbing surface the area covered is 1.2-1.85 m 2 /g assuming a surface area of 0.532 nm 2 /molecule (Lu, et al, 1988). Since the surface area of the kaolinite is 6.9 m 2 /g only a portion of the surface is covered with phenol.…”

Effect of van der Waals interactions on the chemisorption and physisorption of phenol and phenoxy on metal surfaces

“…Pd(110), 13 Au(111), 14 and Pt(111), 15,16 theoretical studies are limited to Rh(111) and Pt(111), 17,18 Ni(111), Ni(110) and Ni(221), 19,20 and Pd(111). 18,21 Most of these studies reported that while the C-ring of PL and PX was nearly parallel to the surface plane on Cu(110), Ni(111), 12 and Pt(111), 16 PX has tilted geometries on Ag(110) 8 and Mo(110).…”