Fe-based ceramic nanocomposite membranes fabricated via e-spinning and vacuum filtration for Cd²⁺ ions removal

In this work, vacuum filtered and polymer mixed e-spinning membranes (ESPMs) made from or doped with Fe-based nanomaterials were successfully fabricated to remove Cd²⁺ ions from a neutral aqueous solution. The used Fe-based nanomaterials including FeOOH precursor Nanowires (NWs), α-Fe₂O₃ NWs and Fe₃O₄ nanoparticles (NPs) were synthesized by elevating the hydrothermal reaction temperature from 250 °C to 500 °C or doing post-heating treatment. The adsorption results showed that vacuum filtered membranes (VFMs) overall performed a better Cd²⁺ ions removal behavior than e-spinning ones. Among them, VFM made from Fe₃O₄ NPs has the highest adsorption capacity (qt) with the adsorption amount of Cd²⁺ ions reaching about 29.3 mg/g within only 2 min due to the high specific surface area of NPs. Models of pseudo-first-order, pseudo-second-order and intraparticle diffusion were used to study the kinetics of Cd²⁺ ions removal process, and a high correlation coefficient (R²) of 0.99 was obtained when pseudo-second-order model was used. It was calculated that the equilibrium rate constant of VFM made from Fe₃O₄ NPs has reached about 0.28 g mg^-1 min^-1, much smaller than those of other membranes, which indicated a high Cd²⁺ ions removal efficiency.