High-temperature stable transition aluminas nanoparticles recovered from sol–gel processed chitosan-AlOx organic–inorganic hybrid films

• Published in: Journal of sol-gel science and technology 2018-05, Vol.86 (2), p.410-422
• Main Authors: Al Sagheer, Fakhreia, Nahar, Shamsun, Nazeer, Ahmed Abdel, Bumajdad, Ali, Zaki, Mohamed I.
• Format: Article
• Language: English
• Subjects: Alumina; Aluminum oxide; Catalysis; Ceramics; Chemical composition; Chemical synthesis; Chemistry and Materials Science; Chitosan; colloids; Composites; etc.; fibers; Glass; High temperature; Inorganic Chemistry; Materials Science; Microscopy; Morphology; Nanoparticles; Nanotechnology; Natural Materials; Optical and Electronic Materials; Organic chemistry; Original Paper: Nano-structured materials (particles; Photoelectrons; Roasting; Scanning electron microscopy; Sol-gel processes; Surface layers; Thermal stability; Thermogravimetry; Transitional aluminas; X ray photoelectron spectroscopy
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-018-4617-y

Five and ten weight percent-alumina-containing chitosan-AlO x films were prepared via sol–gel processing. The films were AlO x -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 (Al 2 O 3 ) 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 N 2 sorptiometry. Coalescences of globular nanoparticles of γ-/η-Al 2 O 3 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-)Al 2 O 3 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 m 2 /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. The highly abundant bio-waste material, chitosan , is successfully employed as a synthetic medium for catalytic-grade alumina nanoparticles. This novel sol–gel synthesis process resulted in nearly 100%-recovery of nanoparticle transition γ-/η- and ι-Al 2 O 3 and may be utilized in fabricating other materials/metal oxides