Highly Permeable Nanofibrous Membranes for Energy Efficient Water Purification

摘要

INTRODUCTION Ultra-fine cellulose nanofibers (UCNs) with diameters in the range of 5 nm can be prepared from bleached wood pulp using the TEMPO/NaBr/NaCIO oxidation method in aqueous conditions followed by mild mechanical treatment.~1 The unique features of UCNs include small diameter, high surface to volume ratio, easy surface functionality, good chemical and mechanical properties, which are suitable for a wide range of applications including the barrier layer in water filtration membranes.~1 To support these ultra-fine nanofibers, electrospun nanofibers (diameter - 150 nm) fabricated from polymer (e.g., polyacrylonitrile, PAN) solution in an electrostatic field, are often used as scaffolds. These scaffolds offer high porosity (- 80 %), good permeability and relatively low fouling potential due to the interconnected porous structure. Furthermore, non-woven microfibrous polyethyleneterephthalate (PET) mats with fiber diameters of - 20 μm and porosity of - 60 % made by melt-blowing can be used as the bottom substrate support to provide good mechanical properties of the composite membrane.~2 Two different ways of integrating UCNs into the electrospun scaffold have been demonstrated to create highly permeable microfiltration (MF) and ultrafiltration (UF) membranes with significant energy-saving benefits.~(3-6) In addition, the UF fibrous structure can be used as a platform to create highly permeable nanofiltration (NF) membranes containing a nanocomposite barrier layer with directed water channels, as formed at the interface between the interconnected UCN and the polymer matrix, to guide the transport of water molecules in a directed manner.~7