Fabrication and characterization of polyvinylidene fluoride based hollow fiber ultrafiltration membranes blended with nanoparticles

With the increasing importance of water treatment and wastewater recovery, the use of membrane processes to obtain drinking and tap water has been spreading rapidly in the world. Polyvinylidene fluoride (PVDF) membranes have been extensively used in ultrafiltration (UF) membranes because of its superior properties such as high mechanical strength, thermal stability, and chemical resistance. Nevertheless, PVDF membranes may susceptible to biofouling because of its strong hydrophobicity. Therefore, various hydrophilic modification techniques have been used to improve the antifouling property, permeability and separation performance as well as mechanical properties of the membranes. Blending with nanoparticles can be considered as a practical way in adaptation to large scale production of antifouling membranes. In this study, halloysite nanotubes (HNTs) and hexagonal boron nitride nanoparticles (h- BNNPs) were functionalized by 3-Aminopropyltriethoxysilane (APTES) in order to increase the dispersion of nanofiller in PVDF matrix by reducing surface energy of nanoparticles. Pilot scale PVDF based hollow fiber UF membranes formed of different concentrations of nanofillers (0, 0.2, 0.4, 0.6 wt.%) were fabricated via the dry-wet spinning method to study influences of nanoparticles on the morphology and separation performance of PVDF membranes in terms of pore size, hydrophilicity, mechanical strength, pure water permeability (PWP) and molecular weight cut-off (MWCO) values. The Fourier-transform infrared (FT-IR) and thermogravimetric analysis (TGA) showed that APTES was successfully grafted on the surface of the nanoparticles. In addition,Powder X-ray diffraction (XRD) measurements were performed to investigate the effect of silane coupling agents on the crystalline structure of HNTs. The morphologies and pore size distributions of the developed HF membrane were characterized by scanning electron microscope (SEM). From the SEM images, the addition of HNTs and h-BN within the membrane structure suppressed macrovoids related to the increase of dope viscosities. The hydrophilicity of the PVDF hollow fiber membranes were improved significantly with the addition of A-HNTs and A-hBN, due to the change in membrane surface energy by silane treatment of nanoparticles. According to the filtration experiments, the PWP results gradually increased with the increase of nanoparticles depended on the hydrophilicity and porosity of the membrane. 0.6 A-HNT and 0.4 A-hBN achieved the maximum value at 639 and 674 L/m2.h.bar, respectively which increased by 62% and 70% compared with the standard PVDF membrane. Additionally, the antifouling property was improved in accordance with the reduction of the contact angle and increase in the hydrophilicity of the PVDF membrane. In this thesis study, h-BN was used for the first time in pressure-driven membrane processes. It was found that, with the addition HNTs and h-BNNPs, the CA of the modified membranes decreased, improving the hydrophilicity, permeability and antifouling property of the PVDF UF membrane. These results are in accordance with the previous studies revealing the effects of inorganic nanoparticles on the performance of membranes.