Enhancing the flux of brackish water TFC RO membrane by improving support surface porosity via a secondary pore-forming method

Abstract

A secondary pore-forming method for improving support surface porosity to enhance the flux of TFC RO membrane was proposed. With this method, well-dispersed SiO2 nanospheres were used for preparing polysulfone (PSf)/SiO2 nanocomposite supports via immersion precipitation, and then the supports were treated by a hot NaOH solution. The PSf/SiO2 nanocomposite supports prepared by this method can experience two pore formation processes, which include the leaching out of the SiO2 nanospheres during immersion precipitation (the first pore formation process) and the removal of those SiO2 nanospheres embedded in the support surface by alkali treatment after the solidification of support (the second pore formation process). These two pore formation processes were studied. The results showed that (1) these two pore formation processes occurred during the preparation of PSf/SiO2 nanocomposite support, (2) the secondary pore-forming method was better than the immersion precipitation method for improving support surface porosity and (3) the support surface porosity was improved at most 291% by the secondary pore-forming method. TFC RO membranes were fabricated on pure supports, nanocomposite supports experiencing the first pore formation process only and nanocomposite supports experiencing two pore formation processes via interfacial polymerization, respectively. The brackish water desalination performance of the TFC RO membranes was evaluated using 2000ppm NaCl solutions under the condition of 1.55MPa transmembrane pressure. The influence of support surface porosity on the flux and rejection of TFC RO membrane was firstly analyzed by experimental approach. The results showed that improving the support surface porosity was beneficial for the improvement of the flux and rejection of TFC RO membrane. The flux and rejection of the TFC RO membranes fabricated on PSf/SiO2 nanocomposite supports experiencing two pore formation processes were improved compared to those fabricated on the other two supports. At an optimal condition, the flux was improved obviously with the rejection increasing simultaneously compared to the TFC RO membranes fabricated on the pure supports: a 55.4% increase in flux from 35.4 to 55.0L/(m2*h) with an increase in rejection from 98.74% to 99.10%.