Abstract
The test alumina (the so-called ι-Al2O3) was thermally recovered at 1,100°C from chitosan-AlOx hybrid films and found to contain Na and Ca impurity ions inherited from the parent chitosan. Two different modifications of pure alumina, namely, γ- and α-Al2O3, were adopted as control samples. The test and control aluminas were examined for 1) the bulk elemental constitution by atomic absorption spectroscopy (AAS), 2) the surface chemical composition by X-ray photoelectron spectroscopy (XPS), 3) the bulk phase composition by X-ray powder diffractometry (XRD), ex-situ Fourier-transform infrared spectroscopy (IR), and Laser Raman (LRa) spectroscopy, 4) the surface area, topography, and morphology by N2 sorptiometry, and atomic force (AFM) and scanning electron microscopy (SEM), 5) the surface adsorptive interactions with pyridine and 2-propanol gas-phase molecules by in-situ IR spectroscopy of the adsorbed species, and 6) the surface catalytic interactions with 2-propanol gas-phase molecules by in-situ IR spectroscopy of the gas phase. Results obtained could clearly show that the test alumina (ι-Al2O3) is only hypothetically pure alumina since in reality its bulk structure is majored by mullite-type Na-aluminate (Na0.67Al6O9.33/NaAlO2) and minored by Na-β-alumina (Na1.71Al11O17) and β-alumina (NaAl11O17). Consistently, observed Na-influenced modifications of the surface chemistry, topology, and morphology, as well as adsorptive and catalytic interactions with pyridine and 2-propanol gas-phase molecules, showed significant deviations from those exhibited by the control pure aluminas (γ- and α-Al2O3).
Highlights
Iota-alumina (ι-Al2O3) is, hypothetically, the end-member of the compositional series (Al2[Al2+2xSi22x]O10-x) of mullite minerals (Schneider et al, 2015; Lenz et al, 2020), where x corresponds to the number of oxygen vacancies per unit cell
1,700°C; Duvigneaud (1974) synthesized alkali-doped aluminas and Perrotta and Young (1974) produced silica-free aluminate crystallized from gels in the (Na,K)2O-BaO-Al2O3 system; Korenko et al (2008) and Kucharík et al (2010) obtained ι-Al2O3 in deeply under-cooled cryolite-alumina melts from rapid solidification process; and Ebadzadeh and Sharifi (2008) reported that they have synthesized ι-alumina phase via sol-gel processing of a mixture of dissolved aluminum nitrate and carboxymethyl cellulose
The presence of Na and Ca ions solely in ι-Al2O3 is reminiscent to the presence of chitosan (CS) in the parent hybrid film of the recovered oxide
Summary
Iota-alumina (ι-Al2O3) is, hypothetically, the end-member of the compositional series (Al2[Al2+2xSi22x]O10-x) of mullite minerals (Schneider et al, 2015; Lenz et al, 2020), where x corresponds to the number of oxygen vacancies per unit cell. Na-influenced modifications of the so-called ι-alumina bulk phase composition, as well as of its surface accessibility, topography, morphology, and acid-base properties (vs pure γ-Al2O3 and α-Al2O3 for control purposes) employing N2 sorptiometry, atomic force (AFM) and scanning (SEM) electron microscopy, ex-situ Fourier-transform infrared spectroscopy (IR), Laser Raman (LRa) spectroscopy, and insitu IR spectroscopy of pyridine adsorption and 2-propanol catalytic decomposition.
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