| Forward osmosis (FO) technology can realize the spontaneous separation of solution driven by the difference of osmotic pressure between the feed and draw solution across a semipermeable membrane at atmospheric pressure, which shows great potential to solve the contradiction between energy and water treatment. However, the development of this technology was retardant by the shortage of high performance special membrane. Because the osmotic water flux of traditional membranes used in hydraulic pressure driven process is far lower than the predicted value, the productivity and application of the technology were influenced. At the same time, the membrane fouling due to the rough surface and special chemical structure of polyamide should be considered. Therefore, to develop novel high performance FO membrane, which can alleviate the negative effect of internal concentration polarization, improve the water flux and anti-fouling ability without sacrificing the selectivity of membrane, has become a challenging topic.Blending modification is a feasible way to improve the properties and broaden the application field of polymer materials. In this study, some modifiers, e.g. muti-walled carbon nanotubes (MWCNT), reduced graphene oxide modified graphitic carbon (CN/rGO), MMT@SPES, were blended with polyethersulfone to prepare the substrate of thin film composite membrane. These prepared membranes show higher water flux than the pristine membrane. Additionally, we modified the polyamide by a simple second interfacial polymerization method. The resulted membranes showed difference chemical structure, surface morphology, and application performance. The main contents in the present work are as following:(1) Nanocomposite MWCNT/PES substrates of TFC membrane were obtained by dispersing carbox-ylated MWCNTs within PES via solution blending with Polyvinyl Pyrrolidone as auxiliary dispersing agent. The results show that the membrane with appropriate MWCNT amount loading would harvest higher water flux due to more pores induced by MWCNTs as well as97%salt rejection. Furthermore, the tensile strength of the substrates with MWCNTs is also greater than that of the neat PES, which was not influenced by the enhanced porosity.(2) A porous layered material, CN/rGO, was synthesized as amodifier for porous polyethersulfone (PES) substrate for the preparation of thin film composite (TFC) polyamide forward osmosis (FO) membrane. The osmotic water flux of TFC membrane with0.5wt%CN/rGO in the substrate reached41.4LMH using2M NaCl as draw solution and deionized water as feed, which was around20%greater than with the control membrane without CN/rGO. The FO performance improvement should be attributed to the modified structure and more wettable wall of pores of substrate.(3) Montmorillonite (MMT) was introduced to electrostatic interact with SPES and then blended with PES dope solution to prevent hydrophilic polymer from leaching in non-solvent-induced phase separation (NIPS) process, to prepare the asymmetric substrate of thin film composite forward osmosis (TFC FO) membrane. The immobilization-effect of MMT on SPES has been examined by FT-IR and XPS analysis. It was found that the water permeability of substrates was dramatically enhanced from60.9LMH/bar to460LMH/bar upon addition of MMT@SPES owing to the increased hydrophilicity. The pore structure of the substrates with less than300kDa MWCO was appropriate for the formation of polyamide layer. The FO performance of resultant TFC membranes based on such substrates was evaluated in FO mode. Compared to the modified membrane with that based on PES/SPES substrate when they are at similar thickness of100μm, the osmotic water flux of membrane with PES/MMT@SPES(40) was improved by4folds and the reverse salt leakage reduced about the half thanks to the enhanced wettability of substrate and narrower pore size distribution of composite substrate. Based on the results, it can be confirmed that anchoring hydrophilic polymer in membrane substrate matrix is a practical method to improve the performance of TFC FO membrane.(4) High performance thin film composite forward osmosis (TFC-FO) membranes were prepared by ethane diamine (EDA) and2-[(2-aminoethyl)amino]-ethane sulfonic acid monosodium salt (SEA) in stiu modifying nascent polyamide (PA) active layer by second interfacial polymerization (SIP). EDA would contribute to better antifouling ability. While SEA would enhance the wettability of membrane, consequently resulting in higher water flux without scarifying the selectivity. But SEA-M didn’t show better anti-fouling tendency despite it has a smoother and better wettable surface. The role of initial osmotic water flux and its effect on membrane fouling tendency was also evaluated. Experiment results demonstrated that higher initial water flux would accelerate the formation of foulant cake and subsequently result in remarkable decline of flux. Compared with the surface properties of membrane, the initial water flux is the key factor on the development of a fouling cake. |
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