High-temperature stable transition aluminas nanoparticles recovered from sol–gel processed chitosan-AlOx organic–inorganic hybrid films
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Five and ten weight percent-alumina-containing chitosan-AlOx films were prepared via sol–gel processing. The films were AlOx-agglomerate-free. These organic–inorganic films were degraded by heating at 500 °C. The solid powder residues were found by means of thermogravimetry, X-ray diffractometry, infrared spectroscopy, and electron microscopy to consist of alumina (Al2O3) nanoparticles entraping volatile components, whose thermal removal encouraged ambient oxygen uptake. The surface microstructure and morphology of the recovered alumina nanoparticle were inspected by high-resolution transmission and scanning electron microscopy. Also, the surface chemistry and texture were evaluated by X-ray photoelectron spectroscopy and N2 sorptiometry. Coalescences of globular nanoparticles of γ-/η-Al2O3 were the dominant composition of the 800 °C calcination product of the recovered alumina, irrespective of the alumina-content of the film. Upon increasing the calcination temperature up to 1100 °C, an enhanced polymorphic transition into agglomerated nanoparticles of the seldom encountered Iota-(ι-)Al2O3 took place. The high thermal stability of the otherwise unstable transition aluminas (at ≥950 °C) may suggestively owe to its polymorphic interdependence and/or persistent nanoscopic nature (average particle size = ca. 3–4 nm; specific surface area = ca. 80–60 m2/g). The surface chemical composition for the recovered transition aluminas nanopowders promises versatile acid–base properties for catalysis applications. Accordingly, the highly abundant bio-waste, chitosan, was successfully utilized as a novel synthesis medium for catalytic-grade alumina nanoparticles.
KeywordsAlumina Sol–gel synthesis Nanoparticle Chitosan Organic–inorganic composite Bio-waste materials
The authors gratefully acknowledge the support provided by the Research Administration of Kuwait University, under Grant Number’s SC06/13 and GS 03/01, GS01/01, GS01/03, GS01/05 and GE03/08. They also appreciate help given by the Nanoscopy Science Center at Kuwait University in performing AFM, TEM and HRTEM measurements.
This work was supported by Kuwait University [grant number SC06/13].
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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