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Abstract
The formation and entrapment of tris(8-hydroxyquinoline)aluminum (Alq3) molecules on the surface of anodic porous alumina (APA) immersed in an ethanol solution of 8-hydroxyquinoline (HQ) were investigated by absorption, fluorescence, and Raman spectroscopies. The effects of the selected APA preparation conditions (galvanostatic or potentiostatic anodization method, anodizing current and voltage values, one- or two-step anodizing process, and sulfuric acid electrolyte concentration) on the adsorption and desorption of Alq3 species were examined. Among the listed parameters, sulfuric acid concentration was the most important factor in determining the Alq3 adsorption characteristics. The Alq3 content measured after desorption under galvanostatic conditions was 2.5 times larger than that obtained under potentiostatic ones, regardless of the adsorbed quantities. The obtained results suggest the existence of at least two types of adsorption sites on the APA surface characterized by different magnitudes of the Alq3 bonding strength. The related fluorescence spectra contained two peaks at wavelengths of 480 and 505 nm, which could be attributed to isolated Alq3 species inside nanovoids and aggregated Alq3 clusters in the pores of APA, respectively. The former species were attached to the adsorption sites with higher binding energies, whereas the latter ones were bound to the APA surface more weakly. Similar results were obtained for the Alq3 species formed from the HQ solution, which quantitatively exceeded the number of the Alq3 species adsorbed from the Alq3 solution. Alq3 molecules were formed in the HQ solution during the reaction of HQ molecules with the Al3+ ions in the oxide dissolution zone near the oxide/electrolyte interface through the cracks and the Al3+ ions adsorbed on surface of pore and cracks. In addition, it was suggested that HQ molecules could penetrate the nanovoids more easily than Alq3 species because of their smaller sizes, which resulted in higher magnitudes of the adsorption.
Highlights
Anodic porous alumina (APA) has been used in various industrial applications because of the excellent corrosion and abrasion resistance properties, while its high porosity makes it suitable for decorative coloration techniques such as electroplating, painting, and dyeing [1,2,3]
Mohammadpour et al [16] prepared two APA samples containing cylindrical nanopores with diameter around nm; one sample was immersed in a 1 mM solution of Alq3 in chloroform for h followed by thorough rinsing with pure chloroform, while the other sample was dipped and dried several times in a 10 mM solution of Alq3
APA surfaces under various conditions listed in
Summary
Anodic porous alumina (APA) has been used in various industrial applications because of the excellent corrosion and abrasion resistance properties, while its high porosity makes it suitable for decorative coloration techniques such as electroplating, painting, and dyeing [1,2,3]. Mohammadpour et al [16] prepared two APA samples containing cylindrical nanopores with diameter around nm; one sample was immersed in a 1 mM solution of Alq in chloroform for h followed by thorough rinsing with pure chloroform, while the other sample was dipped and dried several times in a 10 mM solution of Alq3 The former sample exhibited a fluorescence peak at 498 nm, and the second one—a peak at 510 nm. According to the obtained steady-state and time-resolved data, the former peak could be attributed to the Alq molecules dispersedly embedded in the APA nanovoids with sizes of 1–2 nm, while the latter one corresponded to the Alq aggregates adsorbed on the APA pore surface. The details of the mechanism describing Alq embedment in the APA matrix should be studied more thoroughly
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