Fabrication And Desalination Performance Study Of Thin Film Composite Membranes With SWCNT Support Layer

Water shortage has become a global challenge.Due to the low energy consumption and high efficiency,membrane separation technology with the core of membrane separation has been widely used in the desalination of seawater and brackish water,wastewater treatment and other processes to produce potable fresh water.Thanks to its structure,thin film composite(TFC)membrane is the most widely studied separation membrane with the best performance in the field of desalination.However,TFC NF membranes are still faced with the trade-off between permeability and selectivity.In recent years,a series of high-throughput and high rejection membranes with ultrathin polyamide(PA)active layer have been fabricated with the porous ultra-thin films of nanomaterials as support layer.Generally,the separation performance can be further improved by introducing nanoparticles into the PA layer to fabrication thin film nanocomposite(TFN)membrane.However,the thickness of PA layer is as low as a dozen nanometers in TFC membrane with nanomaterials support layer.It is still a challenge to add nanoparticles uniformly and controllably in such a thin PA layer to fabricate new TFN NF membrane.On the other hand,the support layer with nanomaterials is usually small in area due to the limitation of fabrication method.Therefore,the large-area fabrication of TFC membranes with nanomaterials support is still a challenge.In this paper,a new method of introducing porous nanomaterials uniformly and controllably into ultra-thin PA layer was designed to futher improve the separation performance of this new type of TFC NF membrane,and a new TFN NF membrane with nanomaterials support layer was obtained.At the same time,a new method for large-area fabrication of single-walled carbon nanotube(SWCNT)support layer has been designed to achieve the exploration of large-area fabrication of this new type of NF membrane.The special research contents are as follows:(1)New type of TFN NF membrane with SWCNT support layer.In order to further improve the permeability of TFC NF membrane,SWCNT was used as the support layer and ultra-small UIO-66-NH2 nanoparticles was used as nanofiller to fabricate TFN NF membrane with ultra-thin active layer(20±3 nm).Effectively improved the water permeability of NF membrane.Benefiting from the ultra-thin thickness of active layer and the high loading mass of nanoparticles with unique porous structure,water permeability up to 46 L m-2 h-1 bar-1 along with a Na2SO4 rejection of 97.1%was achieved,which is 53%increase of the TFC NF membrane without the addition of UIO-66-NH2 nanoparticles(2)Large-area TFC NF membrane with brush painting method.In order to achive the large-scale fabrication of TFC NF membrane,a brush painting method was designed for the controllable and large-scale fabrication of SWCNT support layer.The mechanical and chemical stability of the SWCNT support layer were carefully examined.Based on the SWCNT support layer fabricated by brush painting,TFC NF membrane with an ultra-thin PA layer(～15 nm)was fabricated.The obtained TFC NF membranes exhibited extremely high water permeability of～40 L m-2 h-1 bar-1,a high Na2SO4 rejection of 96.5%and high monovalent/divalent ion permeation selectivity.This work provides an efficient way for the large-scale fabrication of new type of TFC membranes with nanomaterials as support layer.(3)New type of TFC reverse osmosis(RO)membrane with SWCNT support layer.In order to expand the application of SWCNT support layer in the fabrication of TFC membrane,we desighed a TFC RO membrane with SWCNT support layer,and explored the influence of SWCNT wettability on the morphology and desalination of TFC RO membrane.The number and size of vesicles on the surface of TFC RO membrane can be effectively reduced with the reducing of SWCNT wettability.