Synthesis of magnetic core-shell amino adsorbent by using uniform design and response surface analysis (RSM) and its application for the removal of Cu, Zn, and Pb.

The magnetic FeO was synthesized by using a one-step solvothermal method. Then, anhydrous ethanol as a solvent, tetramethyl ammonium hydroxide (TMAOH) as an auxiliary agent, tetraethyl orthosilicate (TEOS) as a silicon source, and (3-aminopropyl) triethoxysilane (APTES) as amino source were used to prepare FeO@mSiO-NH by using the sol-gel method. Uniform design U14*(14) and the response surface method (RSM) were used to optimize the synthesis ratio. According to the results of TEM, SEM, N adsorption-desorption test, VSM, and XRD, it found that the best coating effect obtained when the relative molar ratio of TMAOH:TEOS:APTES:FeO was 5:4:6:0.45. The results of EDS and elemental analysis confirmed the success of amino group coating; VSM magnetization after surface modification was 32 emu/g; BET results show that specific surface area is 236 m/g, size 5 nm, and the pore volume is 0.126 cm/g. The removal of Cu, Zn, and Pb by FeO@mSiO-NH was studied at the optimal initial pH value 6 of the adsorption test system. The isothermal adsorption results show that the Langmuir model and Redlich-Peterson model are more suitable than the Freundlich model to describe the adsorption behavior, and Cu, Zn, and Pb adsorption is mainly single molecular layer. The maximum adsorption capacity qm of the Langmuir model for Cu, Zn, and Pb removal was 48.04 mg/g, 41.31 mg/g, and 62.17 mg/g, respectively. The adsorption kinetic rates of Cu, Zn, and Pb on FeO@mSiO-NH relatively more suitable for pseudo-second-order kinetic model, i.e., R, were ranged between 0.995 and 0.999, and the suitable reaction time was 60 min. These results proved that FeO@m-SiO-NH prepared by using this method is easy to synthesize, has easy recovery, is ecofriendly, and can be potential adsorbent for Cu, Zn, and Pb removal.