Formation and Entrapment of Tris(8-hydroxyquinoline)aluminum from 8-Hydroxyquinoline in Anodic Porous Alumina

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.

Formation of Flower-Like Crystals of Tris(8-hydroxyquinoline)aluminum from 8-Hydroxyquinoline on Anodic Porous Alumina

“…The PL peak of the as-prepared APA sample (a) exhibits a peak at around 450 nm due to APA defects [29]. At 1 mM (b), the PL spectrum shows two peaks at 473 and 505 nm, which are the same results found in our previous study of APA treated in HQ in EtOH at 60 ∘ C [27]. The former and latter peaks are assigned to the isolated Alq 3 species in nanovoids, while the aggregated Alq 3 species are assigned to the nanopores in the APA.…”

“…As a result, there have been many studies of APA composites with highly fluorescent Alq 3 [22][23][24][25][26]. In a previous study, we reported that Alq 3 was formed on APA immersed in an ethanol solution of 8-hydroxyquinoline (HQ) at 60 ∘ C [27]. The PL spectra showed two peaks at wavelengths of 480 and 505 nm, which were attributed to isolated Alq 3 inside the nanovoids and aggregated Alq 3 in the nanopores of the APA, respectively.…”

Superhydrophobic and luminescent highly porous nanostructured alumina monoliths modified with tris(8-hydroxyquinolinato)aluminium

“…The luminescence quantum efficiency for the AlQ 3 in NOAQ material is about 2%, which is typical for AlQ 3 in an amorphous state [40][41][42]. One can see that for the NOAQ material, a blue-shift of the photoluminescence spectra is not observed (in comparison to the pure AlQ 3 complex) as it is for other similar systems [24,[43][44][45][46][47]. This is probably due to the high content of the complex in the pores of the NOAQ matrix, which makes its behavior close to the bulk AlQ 3 .…”

“…S1) is presently considered as one of the most reliable emitting materials because of its excellent stability and luminescent properties [22,23]. Immobilization of the AlQ 3 complex in porous matrices can serve as an alternative method for obtaining luminescent 3D materials for optical applications [24,25].…”

Adsorption of the Cationic Dye Methylene Blue on Anodic Porous Alumina in Sodium Dodecyl Sulfate Solutions

“…The applications of anodized aluminum include production of capacitors and abrasion resistant surfaces, coloring, and forming functional nanomaterials. − In particular, anodic porous alumina (APA) films have recently gained attention in nanotechnology, because of their ordered pores and the excellent transparency of the APA film surface . As a result, APA is considered a promising platform for preparing optical applications. − …”