Magnetic Ni/α-Ni(OH)2 porous superstructures: synthesis, influencing factors and applications in the removal of heavy metals

Abstract

Magnetic Ni/α-Ni(OH)₂ porous superstructures with the BET surface area of 114 m² g⁻¹ have been successfully prepared in one step by a simple mixed solvothermal route in the absence of any surfactant or template at 170 °C for 8 h, employing NiCl₂·6H₂O and NaBH₄ as the reactants, a mixture of ethylene glycol (EG) and N,N-dimethylformamide (DMF) with the volume ratio of 3 : 2 as the solvent. The as-obtained porous superstructures were characterized by various means including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transformation infrared spectrometry (FTIR) and energy dispersive X-ray spectrometry (EDS). The magnetic property measurement showed that the saturation magnetization (Ms) and the coercivity of the final product were 6.62 emu g⁻¹ and 141.1 Oe, respectively. Research discovered that some factors could affect the formation of the magnetic porous superstructures, including the original EG/DMF volume ratio, the reaction temperature and the original Ni²⁺/NaBH₄ molar ratio. Importantly, the present porous superstructures presented good capacities for selective adsorption of Pb²⁺ and Cu²⁺ ions from a mixed solution containing Pb²⁺, Cd²⁺ and Cu²⁺ ions. The removal efficiencies for two ions reached 65% and 70% within 50 min, respectively. Simultaneously, the adsorbent could be easily separated from water and reused owing to its magnetism, which exhibit potential application in environmental treatment and protection.