Co-sintering synthesis of bi-layer titania ultrafiltration membranes with intermediate layer of sol-coated nanofibers

The preparation of titania ultrafiltration membranes with intermediate layer of sol-coated nanofibers is briefly described. In this process, titiania nanofibers cover on the porous substrate to produce uniform layer with high porosity and flux. The use of titania nanoparticles from sol has been found to bring an improvement on the mechanical strength of the titania nanofiber membrane due to the formation of sintering neck between nanofibers with colloidal particles (sol) at lower sintering temperature. In order to reduce the pore size and achieve high separation efficiency, titania colloidal particulate sol is used to coat on the top of the titania nanofiber layer and then co-sintered at the suitable sintering temperature of the titania gel (480 °C) to prepare ultrafiltration membranes. Furthermore, the coating times of titania sol are optimized based on the measurements supplied by permeation and separation performance and a delicate control of the coating times indeed plays a key role in the preparation of the defect-free membrane with high performance. In this work it is found that the prepared membrane has homogeneous surface without obvious defects in case of three coatings of titania sol co-sintered with the fiber layer at 480 °C. Property tests display that the pure water flux reaches 1100 L m−2 h−1 bar−1 while the molecular weight cut-off is 32,000.