| Poly(vinylidene fluoride)(PVDF) with the advantages of good mechanicalproperties, chemical resistance, thermal stability and low price has been widely usedin the field of membrane separation. However, due to its hydrophobicity in nature,PVDF membranes face the problems of lower permeability and easily absorbingfoulants. Therefore, modifying PVDF membrane is considered as a key to solve theproblems.To improve the hydrophilicity and anti-fouling property, the methods ofblending modification and surface modification were utilized to prepare PVDFultrafiltration membranes in this study. For blending modification, different kinds ofadditives, including bio-inspired small molecular monomer dopamine, poly(ethylene glycol) diglycidyl ether (epoxy function PEO), and the reactant ofdopamine and epoxy functional PEO, were used to investigate the effects on themembranes morphologies and performance. Fourier transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy (XPS) results were used to analyzethe surface chemical structure and composition. X-ray diffraction (XRD) was usedto analyze the crystal structure of modified membranes, and investigated the effectsof different crystal structures on the membranes’ hydrophilicity. Hydrophilicity ofmembranes was characterized by contact angle. Pure water flux and BSA rejectionratio were measured to research the permeability and selectivity of membranes. Theanti-fouling performance of membranes was judged by analysis of membranefouling mechanism. The effects of different additives on membranes morphologieswere observed by scanning electron microscope (SEM). The results indicated thatmixing an appropriate ratio of dopamine and epoxy functional PEO with PVDFcasting solution could obtain the membranes with better permeability, selectivityand anti-fouling property. And the contact angle decreased by around30ocomparedto pure PVDF membrane.As dopamine is easily oxidated and self-polymerized under suitable conditionsand form strong adhesive polydopamine, utilizing the property of polydopamine inthe surface modification fo membranes is another part in this study. Firstly, PVDFmembranes were prepared via the immersion precipitation phase inversion. Then,put PVDF membranes immersing in the dopamine buffer solutions, and explore theeffects of different concentration of dopamine, different pH value, and differentcoating time on the performance and mophologies of membranes. The optimizedmembrane was obtained according to the coating conditions. Fourier transforminfrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) resultswere used to analyze the surface chemical structure and composition. The results proved the formation of polydopamine coating due to the presence of peaks ofhydroxyl and C=C bond. According to the results of measurements, the water flux ofmodified membrane was132.8L/m2�'h, increased by45%comparing withunmodified membrane. And the BSA rejection was improved from84.0%to91.5%.Water recovery flux can get to82%comparing with70%of unmodified membrane.Anti-fouling performance has been enhanced. |
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