Iron carbonate nanospheres were synthesized via hydrothermal treatment of aqueous solutions of iron sulfate, ascorbic acid and ammonium carbonate with a molar ratio of 1 : 1 : 3, respectively, at 140 °C for 1.5 h. Pure α-Fe2O3 nanoparticles with an average crystallite size of 10.5–32 nm were produced by thermal decomposition of FeCO3 at 400–600 °C for 2 h. The compositions of the products were identified by means of XRD, FE-SEM, HR-TEM, FT-IR, BET, zeta potential and thermal analysis. The adsorption properties of α-Fe2O3 were evaluated using reactive red 195 (RR195) dye. Various parameters influencing the adsorption process were investigated, using a batch technique. The results show that α-Fe2O3 nanoparticles show good adsorption capacity and the dye removal percentage reaches about 98.77% in 10 min. Plus, increasing the surface area of the α-Fe2O3 nanoparticles from 107.7 to 165.6 m2 g−1 increases the adsorption capacity from 4.7 to 20.5 mg g−1. Moreover, the adsorption data fit the Langmuir isotherm model well and the thermodynamic parameters exhibited an endothermic and spontaneous nature for the adsorption of RR195 dye on the hematite adsorbent.