Octyltrimethylammonium bromide-assisted synthesis of maghemite powder by thermal decomposition of ferric nitrate and its properties

Maghemite (γ-Fe2O3) powder was prepared by one-step thermal decomposition of ferric nitrate (Fe(NO3)3⋅9H2O) with the aid of octyltrimethylammonium bromide (OTAB). The effect of OTAB on the formation of γ-Fe2O3, structural properties and magnetic properties of the γ-Fe2O3 powder has been studied by X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, magnetic measurements and nitrogen adsorption–desorption. It is found that OTAB has a great influence on the thermal decomposition products of Fe(NO3)3⋅9H2O. With no OTAB addition, the thermal decomposition of Fe(NO3)3⋅9H2O produces only hematite (α-Fe2O3). In contrast, when OTAB is added to Fe(NO3)3⋅9H2O, a pure γ-Fe2O3 is formed, and its crystallite size can be controlled from 7.4 to 27.8 nm by varying the calcination temperature. Magnetic properties of γ-Fe2O3 powder are found to be strongly dependent on the calcination temperature. The saturation magnetization of γ-Fe2O3 powder increases from 28.6 to 67.5 emu g−1, when the calcination temperature increases from 160 to 200 °C. The sample obtained at 200 °C is nearly flake-like in shape and possesses a mesoporous structure with a Brunauer–Emmett–Teller surface area of 121.3 m2 g−1.