Fabrication of organic-inorganic nanofiltration membrane using ordered stacking SiO2 thin film as rejection layer assisted with layer-by-layer method

In the past decades, application of nanomaterials in fabrication of organic-inorganic composite nanofiltration (NF) membrane for membrane performance improvement has been intensively studied. Herein, novel SiO 2 organic-inorganic NF membrane was achieved using an ultrathin and ordered stacking SiO 2 thin film as rejection layer assisted with layer-by-layer method. The resultant membrane showed a great enhancement in hydrophilicity with a membrane surface charge of −44   mV. It exhibited typical characteristics of negatively charged NF membranes because of the rejection against negatively charged methyl blue and methyl orange was 99.5% and 97.6%, while the rejection for positively charged methylene blue decreased to 90.1%. Correspondingly, the water flux declined from 20   L/m 2 ·h to 9.1   L/m 2 ·h using 20   ppm dye solutions as feed solution at 4   bar. In addition, the salt rejection of the produced membrane followed the sequence of MgSO 4 (88.7%)   >   Na 2 SO 4 (82.1%)   >   MgCl 2 (64.5%)   >   NaCl (43.1%), which was in accordance with the size exclusion and Donnan effect. The SiO 2 organic-inorganic membrane presented a remarkable stability under high operating pressure as well as long-term NF test. To conclude, this work paves a new avenue to fabricate highly permeable and selective NF membrane by using inorganic thin film as rejection layer.