| Nanofiltration (NF) is considered as an attractive new membrane separation technology, which has been widely used in the pretreatment of seawater desalination, wastewater treatment, industries such as food and paper, etc. The selective separation layer of NF membrane is usually prepared by interfacial polymerization (IP). Aromatic polyamide (PA) NF membrane has been regarded as the focus of many scholars’ studies, because its high salt rejection and water flux, wide pH range of application, good chemical stability, etc. For traditional preparation procedure of interfacial polymerization PA composite NF membrane, a porous support layer is firstly submerged in an aqueous solution containing a high reactive monomer for a certain time, then it is taken out and immerse into an organic solvent solution containing another high reactive monomer for a certain time to occur interfacial polymerization. Therefore, the composite NF membrane is composed of two layers: thick porous support layer with good mechanical properties, and a ultra-thin active separation layer with higher fiux and rejection as well.In this study, we introduce a preparation method of PA thin film composite (TFC) NF membranes by IP. For the PA membranes, caustic modified polyacrylonitrile (PAN) ultrafiltration (UF) membrane is used as substrate; polyethyleneimine (PEI) and trimesoyl chloride (TMC) are used as functional monomers of aqueous and organic phases, respectively. We extensively investigated the effect of preparation parameters on the performance of the prepared composite membranes, including the monomer concentrations of aqueous and organic phases, the concentration of supporting electrolyte in the aqueous phase, the aqueous immersion time, the IP reaction time, and the heat treatment temperature and time. Various properties (morphology, structure, chemical composition, and hydrophilicity of the skin separation layer) of the prepared PA composite NF membranes were further extensively characterized by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Contact Angle (CA) analyzer, respectively. The separation performance, the chlorine resistance and the solvent resistance of the prepared PA composite NF membranes were also extensively studied as well.The results of the FTIR and XPS spectrums clearly demonstrated the formation of amide bond. The SEM and the AFM images showed that the prepared PA composite NF membranes surface was smooth. The streaming potential test results indicated that the PA composite NF membranes exhibited negative charge. The CA analysis showed that the prepared NF membrane surface has excellent hydrophilicity. The membrane preparation conditions were optimized as following:aqueous solution of 0.4 wt% PEI with 0.5 mol·L-1 NaCl as supporting electrolyte; organic solution of 0.2 wt% TMC; aqueous immersion time of 10 min; IP reaction time of 60 s; heat treatment at 70℃ for 15 min. Under the optimized conditions, by testing single salt aqueous solution of 2000 mg.L-1 Na2SO4 and NaCl, respectively, excellent separation performance (rejections of 97.63% and 66.62%, respectively) and high permeation flux (38.25 L·m-2·h-1 and 43.0 L·m-2·h-1, respectively) could be achieved (at 1.0 MPa and room temperature (20℃)). In addition, the TFC NF membranes showed excellent solvent resistance to methanol, n-hexane, acetone and ethyl acetate, proving great potential in solvent resistant nanofiltration (SRNF) applications. |
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