Synthesis of Mesoporous Magnetite and Evaluation of Its Dye Adsorption Capacity

Abstract

The effect of synthesis conditions on the structure of magnetic mesoporous iron oxide (MMIO) and the capacity of MMIO to adsorb bromophenol blue (BPB) were examined. MMIO with a relatively large surface area (70 m²/g) and composed of only Fe₃O₄ could be obtained by adjusting the pH of the surfactant aqueous solution to 5.5. The surface area decreased as the calcination temperature of MMIO increased in the range of 250–500°C, probably because the size of mesopores increased with the progressive sintering of Fe₃O₄ particles. In order to synthesize MMIO with a large surface area and composed of a single phase of Fe₃O₄, calcination at a low temperature of about 300°C was found to be necessary. It was also found that the added surfactant acted as a dispersant. The maximum amount of BPB adsorbed by MMIO (solution pH, 5.5; calcination temperature, 300°C) was achieved when the BPB solution pH was 4.0. The amount of BPB adsorbed at saturation was 34 µmol/g. To examine the mechanism of BPB adsorption on MMIO, the adsorption isotherm was analyzed with the Langmuir and Freundlich equations. The mechanism was found to be of the Langmuir type, with a monomolecular layer of BPB adsorbed on the surface of MMIO.