Structure and stability of arsenate adsorbed on α-Al 2 O 3 single-crystal surfaces investigated using grazing-incidence EXAFS measurement and DFT calculation

Abstract

Direct characterization of contaminants on single-crystal planes is required because the 12 specific adsorption characteristics on different exposed crystal planes constitute their actual behavior 13 at water-mineral interfaces in aquifers. Here, the structure and stability of arsenate on α-Al2O3 (0001) 14 and ( 0 2 11 ) surfaces were characterized by using a combination of grazing-incidence extended X-ray

Density Functional Theory Study of Arsenate Adsorption onto Alumina Surfaces

“…The As-O surf distances range from 1.718 Å to 1.870 Å for the most favorable structures. All these distances are in agreement with the experimental value of 1.69 Å [13]. Although this value is measured for a microscopic sample spanning planes other than the (012), the agreement is reasonable.…”

“…the various types of oxygen functional groups. Following the language in current literature, arsenate can bind in a bidentate mononuclear (BM) fashion or a bidentate binuclear (BB) one [12][13][14]. A BM adsorption occurs when the two oxygen atoms bound to the arsenate are bound to the same Al atom.…”

“…There is a consensus in literature as to how arsenate binds to aluminum or iron surfaces, based on EXAFS data [11][12][13][14]. When arsenate binds to α-alumina, γ-alumina, and gibbsite, these studies reveal that arsenate preferentially binds to the aluminum surface in a bidentate, binuclear manner (which can also be called corner-sharing).…”

“…Building on earlier work on clean single-crystal mineral surfaces studied under ultra-high vacuum conditions [3][4][5][6], experimental studies of hydrated surfaces have emerged to address questions, such as how exposed surfaces transform under geochemical conditions [7][8][9][10]. Experimental studies of Al and Fe (hydr)oxide surfaces are prolific [11][12][13][14][15][16][17], as these materials have a natural abundance and reactivity towards aqueous contaminants. As an example, numerous studies conducted by Catalano and co-workers can be mentioned [18][19][20][21].…”

“…The study has also revealed that the average Al-As distance for the inner-sphere adsorption is~3.2 Å. EXAFS studies show that the As(V)-O surf bond distance on α-alumina, gibbsite, and γ-alumina are 1.69 ± 0.005 Å, 1.68 ± 0.02 Å and 1.69 ± 0.01 Å, respectively. For all these surfaces, the coordination number of As is~4 [12][13][14]. Using bond geometry analysis, we modelled a variety of configurations for As adsorption in order to compare EXAFS bond distances with our computational studies.…”