γ-irradiation generated ferrous ions affect the formation of magnetite and feroxyhyte

1,10-phenanthroline spectrophotometric method was used in order to systematically measure the quantity of Fe2+ ions that were generated upon gamma-irradiation of alkaline Fe(III) aqueous solutions in the presence of diethylaminoethyl (DEAE)-dextran. gamma-irradiation was performed in a range of doses from 5 to 130 kGy and the dose rate was similar to 26 kGy h(-1). The results showed that gamma-irradiation reduces Fe3+ to Fe2+; the reduction was initially very fast, but quickly slowed down and then reached a plateau of 100% reduction. The quantity of Fe2+ in gamma-irradiated suspensions and isolated solid products roughly overlap up to 45% of Fe2+, because in this range the inverse spinel structure of substoichiometric magnetite nanoparticles was able to capture 30.1% of Fe2+. The stoichiometries of the formed magnetite nanoparticles were very similar, which indicated that the absorbed dose did not have a significant influence on the magnetite stoichiometry, even though Fe2+ molar fraction increased from 22 to 45% as a function of absorbed dose. When gamma-irradiation generated 69% or more of Fe2+ the powder samples consisted exclusively of Fe(III), i.e. of delta-FeOOH nanodiscs and poorly crystallized delta-FeOOH nanoparticles about 4 nm in size. The volume-averaged domain sizes and crystal aspect ratio of the delta-FeOOH nanodiscs increased from 16 nm to 25 nm and from 1.6 to 2.1 with the increase of absorbed dose, respectively. The use of DEAE-dextran in the gamma-irradiation synthesis enabled the generation of up to 100% of Fe2+ and synthesis of extremely stable aqueous suspensions of superparamagnetic magnetite nanoparticles as well as the synthesis of delta-FeOOH nanodiscs with high aspect ratios.