Biomimetic preparation of a polycaprolactone membrane with a hierarchical structure as a highly efficient oil–water separator

Abstract

A superhydrophobic, superoleophilic and eco-friendly polycaprolactone composite (PCL_C) membrane with a hierarchical microsphere structure was developed by alternated electrospinning/electrospraying technology. The PCL_C membrane was subtly designed with two parts to imitate the lotus leaf structure: low surface energy SiO₂ nanoparticles on the surface of PCL smooth microspheres (PCL_M) imitate the hydrophobic bio-wax of the lotus leaf surface, and PCL porous microspheres (PCL_M-porous) imitate the surface nano-protrusions of the lotus leaf. The average size of the potholes on the PCL_M-porous surface was only about 300 nm. The combination of small potholes and the hierarchical structure of the PCL_C and SiO₂ nanoparticles contributed to the superhydrophobicity and superoleophilicity of the PCL_C membrane. The water contact angle (WCA) of PCL_C could reach 162.0 ± 1.5°. Compared with membranes based on PCL_M-porous (WCA = 148.9 ± 1.2°) and 4% SiO₂ nanoparticles on PCL_M (WCA = 158.6 ± 2.3°), the PCL_C membrane not only showed higher superhydrophobicity but also ultra-high oil–water separation efficiency, oil flux and stability. Most importantly, the PCL_C membrane exhibited excellent oil adsorption performance for four different oils with different densities, and the separation efficiency remained ultrahigh (>99.93%) even after 10 cycles. This innovative work may provide an effective strategy for the design of biomimetic biopolymers with promising applications in the field of eco-friendly separators.