Surface mechanism of molecular recognition between aminophenols and iron oxide surfaces

Evidence is presented for the surface mechanism of molecular recognition be tween 2-aminophenol and hematite in a process involving aminophenol -OH and -NH2 groups. The aim of the present study war; to correlate the adsorption of some aminophenols on hematite with the degradation features observed in the dark or in the light. The hydroxyl group in the ortho position was obs erved to be a preferred position for chelation compared to the meta or para positions. Chelation was detected by diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). Both the -NH2 and -OH groups participate in the adsorption of aminophenol onto hematite. The bridging bidentate format ion during the adsorption of 2-aminophenol is supported by the simultaneous shifts of the vibrational frequencies of C=C from 1513 to 1501 cm(-1) and from 1403 to 1395 cm(-1). The matching of atomic distances between Fe-Fe bo nds in the alpha -Fc(2)O(3) crystal and the N-O bond in 2-AP allows for the formation of the bridged bidentate structure, Evidence was found that adso rption enhances degradation in dark processes. The degradation of aminophen ols in the dark produced long-lived intermediates that precluded further de gradation. Acceleration of the degradation was observed during a photochemi cally induced charge-transfer process. Highly oxidative radicals generated only under light significantly increased the degradation efficiency of 2-AP and 4-AP. The degradation of 2-aminophenol on hematite proceeded more favo rably than the degradations of 3- and 4-aminophenol because of the formatio n of a strong surface complex between 2-aminophenol and hematite that facil itates charge transfer to the oxide surface.