Preparation Of Mesoporous γ-Fe₂O₃Nanopowder, Mesoporous TiO₂/γ-Fe₂O₃Nanocomposite And Their Adsorption Abilities

Nowadays, increasing amount of wastewater containing fluoride ionand azo-dyes is being released into the environment, which causes greatthreat for human health. Adsorption method is believed to be the mostconvenient, effective, less expensive and it is widely used in water treatment.Mesoporous magnetic materials possess a high surface area and a large porevolume, and they can be easily separated from treated water with an externalmagnetic field. Based on such consideration, it is a best choice to be used inthe water treatment. The contents of the work involved the preparation andcharacterization of mesoporous γ-Fe₂O₃nanopowder、 mesoporousTiO₂/γ-Fe₂O₃nanocomposite, as well as the investigation of adsorptionperformance of these materials.Firstly, mesoporous γ-Fe₂O₃nanopowder was synthesized by thermaldecomposition method using cationic surfactant cetyltrimethylammoniumbromide （CTAB） as a template. The synthesized mesoporous γ-Fe₂O₃nanopowder was characterized by X-ray powder diffraction （XRD）,vibrating-sample magnetometer （VSM）, N2adsorption-desorption （BETmethod）, thermogravimetric （TG）, infrared spectroscopy （IR）, transmissionelectron micrograph （TEM）, and scanning electron micrograph （SEM）. Theresults show that the saturation magnetization of the mesoporous γ-Fe₂O₃nanopowder decreases and the specific surface area increases with theincrease of usage of template. The average crystallite size of mesoporousγ-Fe₂O₃nanopowder ranges from20to30nm. Secondly, the adsorption abilities of mesoporous γ-Fe₂O₃nanopowderfor F^-、Congo red and OrangeⅡ have been studied. The adsorption rate of F-fits well with pseudo-second-order kinetics equation; and, the adsorptioncapacity for F-increases with the increase of surface area of mesoporousγ-Fe₂O₃, indicating that the surface area of the mesoporous γ-Fe₂O₃is one ofthe major factors which greatly influence F-adsorption capacity. Theadsorbed percentage of F-reaches the maximum when the solution pH=3.The maximum adsorption capacity is determined to be9.0mg/g for thesample whose surface area is149.8m³/g. The adsorption of F-onmesoporous γ-Fe₂O₃can be well described using Langmuir adsorptionmodels, and the γ-Fe₂O₃nanopowder can be reusable. The OrangeⅡadsorption data can be well depicted using Langmuir and Freundlichisotherms and the maximum adsorption capacity is estimated to be61.7mg/g from Langmuir isotherm. When the pH of Orange Ⅱsolution variedfrom2.5to8.7, the adsorption capacity of OrangeⅡ decreases from18.0to0.8mg/g, showing that the adsorption is strongly influenced by solution pH.The maximum adsorption capacity for Congo red is estimated to be17.2mg/g, and the pH of the solutions has little effect on adsorption. The studieson adsorption mechanism suggest that Congo red is adsorbed on mesoporousγ-Fe₂O₃via van der Waals attraction force.Thirdly, mesoporous magnetic TiO₂/γ-Fe₂O₃nanocomposite wasprepared by solid-phase method using mesoporous TiO₂and γ-Fe₂O₃nanopowder as raw materials, and its adsorption abilities for Cong red wasalso investigated. The saturation magnetization of the TiO₂/γ-Fe₂O₃nanocomposite is measured to be22.8emu/g; and, BET measurements showthe formation of mesoporous TiO₂/γ-Fe₂O₃with an average pore size of3.4nm and a surface area of86.3m²/g. The adsorption rate of Cong red fits wellwith pseudo-second-order kinetics equation, and the maximum adsorptioncapacity is determined to be126.6mg/g. By an increase in solution pH from2.5～9.8, the adsorbed percentage of Congo red decreases from ca.99.9to3.4%, which indicates that the adsorption for Congo red is strongly influenced by solution pH.