Fabrication of magnetic Fe3O4/MnO2/TiO2/polypyrrole heterostructure for efficient adsorption of Mn7+ from aqueous solution

Magnetic Fe3O4/MnO2/TiO2/polypyrrole (PPy) heterostructure as adsorbent for adsorbing Mn7+ was synthesized by combining hydrothermal method and chemical oxidation method. The heterostructure was characterized by field-emission scanning electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometer. Its saturation magnetization is 18.88 emu/g, so it is easy to separate it from the solution. The feasibility of Fe3O4/MnO2/TiO2/PPy heterostructure to remove Mn7+ was researched in detail. It is found that the optimal pH is 2. The initial adsorption rate can reach 4.60 mg/g min. At 288.15 K, the maximum equilibrium adsorption capacity is 202.8 mg/g. Adsorption kinetics follows a pseudo second order model, as well as is determined by through membrane diffusion processes. The Langmuir isotherm model is used to describe the adsorption isotherm behavior. Besides, thermodynamic parameters indicate spontaneous adsorption behavior, and entropy of the endothermic reaction increases. Finally, the cycle test results show that the adsorbent has better cycle performance, displaying broad application prospects.