Morphology and surface wettability of the membranes were investigated using FE-SEM and contact angle meter. Fig. 2 shows the FE-SEM images of pure BC, PPy/BC4 and SPPy/BC4. From the images, we can see that the exquisite three-dimensional network structure maintained through the composite process and surface treatment. The obvious change is the diameters of fibers varied from about 50 nm to 100 nm, and then to 150 nm. It can be explained that the fiber surface was firstly coated with continuous PPy, thus leading to the increase of the fiber diameter. The diameters of the coated BC fibers with PPy were further increased by the polysiloxane coating. The inset of Fig. 2c shows the energy-dispersive spectrum (EDS) of SPPy/BC4. There are N and Si elements in the composite, which indicated that PPy have been fabricated successfully by in situ synthesis and the fibers are coated with polysiloxane.