Biocompatible Fe3O4@SiO2-NH2 nanocomposite as a green nanofiller embedded in PES–nanofiltration membrane matrix for salts, heavy metal ion and dye removal: Long–term operation and reusability tests

High purity amorphous silica (95.55%) was simply extracted from rice husk and used as a shell for Fe3O4 magnetic nanoparticles. The obtained eco–friendly nanomaterial was functionalized by (3–Aminopropyl)trimethoxysilane and characterized by SEM, FT–IR, XRD, VSM, TEM and zeta potential analyses. The synthesized Fe3O4@SiO2–NH2 nanocomposite was embedded into the polyethersulfone membranes with different concentrations via phase inversion method. The effects of Fe3O4@SiO2–NH2 on various properties of the prepared nanofiltration membranes including membrane morphology, hydrophilicity, porosity, and mechanical stability were investigated using SEM image, water contact angle test, porosity measurement and mechanical property analysis, respectively. The performance of Fe3O4@SiO2–NH2 nanocomposite modified membranes was evaluated by measuring the pure water flux, salts rejection, Cd(II) ions removal, MR dye retention, and antifouling property. The results showed that the pure water flux was significantly increased in Fe3O4@SiO2–NH2 modified membranes due to the presence of hydrophilic functional groups on the Fe3O4@SiO2–NH2 surface. In addition, the significant enhancement in efficiency of modified membranes for removal of Cd(II) ions and MR dye was observed due to the adsorption properties of Fe3O4@SiO2–NH2 nanocomposite. Among the modified membranes with different concentrations of Fe3O4@SiO2–NH2, the 0.5 wt% concentration of nanocomposite showed the highest efficiency for the removal of Cd(II) ions (93%) and MR dye (97%). Membrane reusability study indicated a slightly decrease (≈7%) in Cd(II) ions removal after five continuous cycles. Membrane long–term filtration study showed a little reduction in permeate flux with unchanged MR dye retention during long–term filtration, which confirmed the stability of modified membrane.