Porous SiO₂ coated Al_xFe_yZr_1-x-yO₂ solid superacid nanoparticles with negative charge for polyvinylidene fluoride (PVDF) membrane: Cleaning and partial desalinating seawater

In this work, porous SiO2 coated AlxFeyZr1-x-yO2 solid superacid nanoparticles with negative charge (CS-SAFZr) were synthesized via hydrolysis, sulfation and sulfonation, and characterized by SEM, TEM, XRD, BET and so on. The results show that the size of CS-SAFZr nanoparticles prepared under the optimum preparation conditions is around 80 nm, thickness of the porous SiO2 shell is about 20 nm, Hammett acidity is -16.197 and ion exchange capacity (IEC) is 0.98 mmol.g(-1). Correspondingly, ferrum (Fe) and aluminum (Al) elements are successfully doped into the ZrO2 lattice and the doped nanoparticles present a specific surface area of 396.2 m(2) g(-1) with abundant hydroxyl and sulfonic acid groups on the surface. To investigate the properties of the nanoparticles as the filler, polyvinylidene fluoride (PVDF) was used as a candidate to prepare CS-SAFZr/PVDF ultrafiltration (UF) composite membranes and the performance were characterized via cleaning and desalinating seawater. Results indicate that the CS-SAFZr nanoparticles strengthen their compatibility with the membrane via hydrogen bonds and improve performances of PVDF membrane. The suspended solid and conductivity decline ratio of permeate seawater was 1.8 mg L-1 and 13.20% respectively, indicating that CS-SAFZr/PVDF membrane performs seawater cleaning and partial desalination. Therefore, CS-SAFZr nanoparticles can be a promising candidate to modify PVDF membrane for cleaning and desalinating seawater.