Characterization of iron(III) oxide/hydroxide nanostructured materials produced by sol–gel technology based on the Fe(NO3)3·9H2O–C2H5OH–CH3CHCH2O system

Nanostructured iron oxide/hydroxide materials were synthesized by sol–gel technology, starting from the ternary system Fe(NO3)3·9H2O/ethanol/propylene oxide. Evaporative drying and supercritical fluids extraction were used as drying techniques to produce xerogels and aerogels, respectively. The materials were physically, structurally and chemically characterized, to analyze their suitability for surface-dependent applications and the influence of the drying technique on their properties. In addition, the chemistry involved in the sol–gel synthesis of iron oxides/hydroxides with the referred ternary system is reviewed. The produced materials were composed by aggregates of nanometric crystallites: ∼1 nm for xerogels and ∼5 nm for aerogels. Their high porosity and surface area (xerogels – 50% and 150 m2 g−1; aerogels – 90% and 400 m2 g−1) make them suitable for surface-dependent processes, being the aerogels far more adequate. The FTIR, XRD and Mössbauer spectroscopy results gave some insight on the composition of these materials, showing that the 2-line ferrihydrite is their most probable constituent phase. Finally, it was concluded that the continuous supercritical fluids extraction is the best drying procedure for these materials, since it preserves the mesoporous structure of the gels. When evaporative drying is used, the pores shrinkage leads to a predominantly microporous structure.

► Synthesis and characterization of iron oxide/hydroxide xerogels and aerogels. ► Sol–gel chemistry of the ternary system Fe(NO3)3·9H2O/ethanol/propylene oxide. ► Aggregates of nanometric crystallites with very high porosity and surface area. ► 2-Line ferrihydrite is their most probable constituent phase of these materials. ► Continuous supercritical fluids extraction is the best drying procedure for gels.