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The hydrophobic membranes have been widely explored to meet the membrane characteristics for the membrane distillation (MD) process. Inorganic metal oxide nanoparticles have been used to improve the membrane hydrophobicity, but limited studies have used nano clay particles. This study introduces halloysite nanotube (HNT) as an alternative material to synthesis a hydrophobic poly(vinylidene fluoride) (PVDF)-HNT membrane. The PVDF membranes were fabricated using functionalized HNTs (e.g., carnauba wax and 1H,1H,2H,2H-perfluorooctyl-trichlorosilane (FOTS)). The results were determined by Fourier transform infrared-attenuated total reflection, scanning electron microscope, goniometer and porometer to determine the desired hydrophobic membrane for direct contact membrane distillation (DCMD). The addition of FOTS-HNT (fs-HNT) and carnauba wax-HNT (fw-HNT) in the PVDF membrane enhanced the water contact angle (CA) to 127° and 137°, respectively. The presence of fw-HNT in the PVDF membrane exhibited higher liquid entry pressure (LEP) (2.64 bar) compared to fs-HNT in the membrane matrix (1.44 bar). The PVDF/fw-HNT membrane (Pfw-HNT) obtained the highest flux of 7.24 L/m2h with 99.9% salt removal. A stable permeability in the Pfw-HNT membrane was obtained throughout 16 h of DCMD. The incorporation of fw-HNT in the PVDF membrane had improved the anti-wetting properties and the membrane performance with the anti-fouling effect.

This work focused on the addition of different pore formation-controlling agent to a polysulfone/cellulose acetate blend membrane via immersion precipitation using phase inversion technique to improve the fouling resistance and selective polyphenol removal of apple juice. The membranes were prepared by blending hydrophilic polyvinylpyrrolidone (PVP) and amphiphilic Pluronic F127 (Plu) with polysulfone/cellulose acetate matrix in N-methyl-2-pyrrolidone. The morphology, mechanical strength, flux permeation, flux recovery ratio, and polyphenol separation of these membranes were characterized. It was found that the fabricated membranes with addition of PVP and Plu were more effective than the membrane without a pore formation-controlling agent. The flux recovery of the membranes with combined pore formers after ultrafiltration of bovine serum albumin increased from 12.4% to 66.9%. The selectivity of polyphenols increased from 6% to 79% with an improved flux recovery of 79%, which shows the reduction of yellowish-brown pigment in apple juice.

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