Design Of Magnetic And Flexible Silica Nanofibrous Membranes For Liquid Separation

As magnetic materials are widely used in the field of informatization, automation and national defense construction, it is of great significance to develop high performance magnetic materials. Magnetic inorganic nanofibers, combining thermostability, corrosion resistance, nano-effect and magnetic anisotropy, hold great promise for widespread application in biomedicine, environmental protection and so on. In recent years, researchers have made great progress in the field of electrospun magnetic inorganic nanofibers. However, as with most of the existing inorganic materials, the resulting magnetic nanofibrous membranes are generally brittle and have small recoverable deformation before failure. The ability to maintain structural integrity upon large deformation for magnetic inorganic nanofibrous membranes is not only crucial for building new types of flexible devices, but also important for future development of silica-based ultralight cellular membranes for bioengineering and environmental remediation. Thus, it is highly desirable to develop new strategy to tackle this challenging but very important problem.In this work, we present a robust methodology for creating flexible and magnetic NiFe2O4@SiO2 nanofibrous membranes(NiFe2O4@SNM) with a hierarchical porous structure that consists of NiFe2O4 nanoparticles(NiFe2O4 NPs) anchored silica nanofibers. The premise for our design is that the electrospun silica nanofibers are used as templates for the non-agglomerated and firm growth of NiFe2O4 NPs by a facile zein dip-coating method. The concentration of NiFe2O4 NPs is influential in micromorphology, microstructure and mechanical property of NiFe2O4@SNM. High concentration makes the NiFe2O4 NPs agglomerate and damages the tensile breaking strength and flexibility. When the concentration comes to 4%, NiFe2O4@SNM exhibit the integrated properties of extraordinary flexibility(39 mN), high porosity(0.051 cm3 g-1), large surface area(40.05 m2 g-1) as well as homogeneous dispersion of NiFe2O4 NPs.Benefiting from the hierarchical structure consist of NiFe2O4 NPs and silica nanofibers, the resulting magnetic SNM possess good magnetic responsiveness, superhydrophilicity with a water contact angle of 0°, and robust under water oleophobicity with an underwater oil contact angle of 147°. Therefore, the NiFe2O4@SNM exhibited excellent adsorption ability in removal of MB dye that it could achieve complete adsorption in 20 min, and the aqueous suspension after adsorption could be purified easily by an external magnet without tedious separation process. In addition, the NiFe@SNM can effectively separate the oil/water emulsions solely driven by gravity with a high separation flux of 3177 ± 214 L m-2 h-1. Significantly, the successful synthesis of such fascinating materials may provide a versatile platform for further exploring the application of silica in a selfsupporting, structurally adaptive, and 2D membrane form.