Nanofiltration Membranes with Cellulose Nanocrystals as an Interlayer for Unprecedented Performance
Nanofiltration membranes are of great interest in brackish water desalination and drink water purification. How to promote the permeation and separation performance remains a big challenge in advanced nanofiltration membranes. Herein, we report triple-layered composite nanofiltration membranes constructed by the interfacial polymerization of diamine and acyl chloride on a cellulose nanocrystal interlayer supported by microporous substrate. The cellulose nano-crystal interlayer plays a crucial role in the polyamide skin layer formation and the following nanofiltration process. It can store aqueous diamine monomers and slow down the interfacial polymerization for a relative low cross-linking degree of the skin layer. This hydrophilic interlayer also facilitates the water permeation through a “dragging effect”. The constructed membranes exhibit an ultra-high permeation flux up to 204 Lm-2h-1 under 0.6 MPa with a Na2SO4 rejection above 97%, which is the highest reported result to our knowledge. The ultra-high water permeation flux enables the nanofiltration at low operating pressure, making it an energy-saving process. Moreover, the low cross-linking degree of the skin layer results in a high monovalent/divalent ions separation ratio.