Abstract
In this investigation, well defined mesoporous zirconia nanoparticles (ZrO2 NPs) with cubic, tetragonal or monoclinic pure phase were synthesized via thermal recovery (in air) from chitosan (CS)- or polyvinyl alcohol (PVA)-ZrOx hybrid films, prepared using sol–gel processing. This facile preparative method was found to lead to an almost quantitative recovery of the ZrOx content of the film in the form of ZrO2 NPs. Impacts of the thermal recovery temperature (450, 800 and 1100 °C) and polymer type (natural bio-waste CS or synthetic PVA) used in fabricating the organic/inorganic hybrid films on bulk and surface characteristics of the recovered NPs were probed by means of X-ray diffractometry and photoelectron spectroscopy, FT-IR and Laser Raman spectroscopy, transmission electron and atomic force microscopy, and N2 sorptiometry. Results obtained showed that the method applied facilates control over the size (6–30 nm) and shape (from loose cubes to agglomerates) of the recovered NPs and, hence, the bulk crystalline phase composition and the surface area (144–52 m2/g) and mesopore size (23–10 nm) and volume (0.31–0.11 cm3/g) of the resulting zirconias.
Highlights
Sol-gel processing has, been frequently used to produce hybrid nanocomposites[4], implementing hydrolysis/condensation of metal alkoxides, under favourable conditions, to form metal oxide network structures within polymeric matrices
TG curves obtained for CS-ZrOx and polyvinyl alcohol (PVA)-ZrOx hybrid films are compared to those given rise by the pure CS and PVA polymers in supplementary Fig. S1
It is obvious from the figure that TG curves of the pure CS and PVA indicate that their stepwise thermal decomposition results in 100% mass loss at ≥500 °C
Summary
Sol-gel processing has, been frequently used to produce hybrid nanocomposites[4], implementing hydrolysis/condensation of metal alkoxides, under favourable conditions, to form metal oxide network structures within polymeric matrices. Speaking, zirconia may exist in three different true polymorphs under atmospheric pressure[13,14]: (i) monoclinic (m-ZrO2) at 2300 °C Each of these polmorphs may, exist in either of the following states[14]: metastable (often sustained by the co-existence of a true phase), stabilized (by foreign agents) and strained state (due to high temperature, or while being transformed). Pure c-ZrO2 finds useful applications in automobile industry, and the manufacturing of oxygen sensors, fuel cells and optic fibers[18], whereas pure t-ZrO2 finds applications in the manufacturing of ceramics, sensors, coatings and medical implants ...etc[19] Because of these properties and applications, which can be optimized for specific functions, different approaches have been employed[20,21,22] for the selective synthesis of pure m-ZrO2, t-ZrO2, and c-ZrO2 phases. Polyvinyl alcohol (PVA), a synthetic polymer that has been used as the organic phase in the preparation of various organic/inorganic hybrid films[31], is analogously capable of immobilizing metal ionc species due to its hydrophilicity and hydroxylation
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