Sol–gel synthesis of iron(III) oxyhydroxide nanostructured monoliths using Fe(NO3)3·9H2O/CH3CH2OH/NH4OH ternary system

Iron(III) oxyhydroxide xerogels were prepared through sol–gel technology, using iron(III) nitrate nonahydrate as precursor, ethanol as solvent and ammonium hydroxide as gelation agent. This base is used for propylene oxide substitution, which was the gelation agent in previous works. Synthesis of a gel using NH4OH as a gelation agent is an innovative result with this type of precursor, since with metal salts the addition of a strong base commonly results in precipitation of the solid. The gel synthesis was achieved by controlling the base addition time. The dried material has a residual amount of organic impurities, in contrast with the significant amount detected in xerogels prepared using propylene oxide. The iron phase prevailing in the produced xerogels can be defined as γ-FeO(OH) (lepidocrocite), according to FTIR and Mössbauer analyses. The xerogels are formed by large clusters of well connected nanocrystallites of this phase. XRD revealed a crystalline phase retained inside the iron oxyhydroxide amorphous structure, which corresponds to NH4NO3 and results from the combination of NO3− and NH4+ ions in solution. The produced xerogel has a promising composition to be an oxidizing composite for the energetic materials area.

► γ-FeO(OH) xerogels were produced using iron(III) nitrate nonahydrate precursor.
► Monolithic gels were never obtained with this precursor and NH4OH gelation agent.
► Large clusters of well connected nanocrystallites of iron oxyhydroxide.
► NH4NO3 by-product is retained inside the iron oxyhydroxide structure.
► Promising oxidizing composite for the energetic materials area.