Thermally induced solid-state reaction of Fe2(SO4)3 with NaCl or KCl: a route to β-Fe2O3 synthesis

beta-Fe2O3 is a rare crystalline polymorph of the ferric oxide family with an interesting application potential, e.g., in photocatalysis. In this study, the effect of different alkali salts addition, namely NaCl and KCl, on the preparation of beta-Fe2O3 via thermally induced solid-state reaction was investigated. Two series of samples were prepared by calcining two different mixtures, Fe-2(SO4)(3) + NaCl (molar ratio 1:3) and -Fe-2(SO4)(3) + KCl (molar ratio 1:3) at temperatures from 350 to 700 degrees C. Although the addition of either alkali salt led the preparation of beta-Fe2O3 particles in wide temperature range up to 650 degrees C, differences in the overall phase composition and beta-Fe2O3 purity were observed between the two series. The addition of KCl to -Fe-2(SO4)(3) allowed the preparation of pure beta-Fe2O3 (>= 95%) in relatively wide temperature range of 450.600 degrees C, while in the case of NaCl, pure beta-Fe2O3 (>= 95%) was found only in samples calcined at 500 degrees C and 550 degrees C. Other phases could be identified as additional ferric oxide polymorphs, beta-Fe2O3 and alpha-Fe2O3. The in situ XRD results suggest that, in the case of NaCl +-Fe-2(SO4)(3) reaction, simultaneous formation of beta-Fe2O3 and alpha-Fe2O3 may be possible between 350 and 500 degrees C, depending on the reaction conditions.