Fluorographite-co-polydimethylsiloxane coated polyvinylidene-fluoride membrane for desalination of highly saline water with humic acid in direct contact membrane distillation

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Membranes with amphiphobic properties are crucial for desalination of concentrated saline water with organic foulant by membrane distillation. In this research, we coated Fluorographite (FGi) particles on polyvinylidene-fluoride (PVDF) flat sheet membranes with 0.8% v/v polydimethylsiloxane (PDMS) as binder by filtration coating method. We evaluated its amphiphobicity via contact angles which were observed by DI water, canola oil and organic solutions as mimicking for oleophobicity. Surface modifications by FGi particles on the surface of membranes was introduced with PDMS binder which brought bifunctionality of amphiphobicity to enhance hydrophobicity and oleophobicity. We also investigated performance of coated membranes in direct contact membrane distillation (DCMD) with 1 molar concentrated NaCl solution along with humic acid being organic foulant and compared with virgin membrane (M1 membrane) and Liquid entry pressure (LEP) was also evaluated. LEP was measured by dynamic method which shown considerable improvement in coated membranes. M3 membrane showed overall better performance in terms of salt rejection higher than 99.87% and flux as compared to M1 membrane. Furthermore, the evaluation of surface characterizations was done by FESEM with EDX, AFM and FTIR. Surface morphology confirmed the coating of FGi on membrane surface while EDX evidenced increase in atomic percent of fluorine in turn F:C ratio.HighlightsSurface modifications by FGi particles with PDMS binder of PVDF microporous membranes shown improvement in DCMD.LEP with DI water & performance of M2-M4 modified membranes in DCMD was enhanced with 1M NaCl & 10 ppm HA feed solution.Amphiphobicity was evidenced by CA with low surface tension liquids upto 38 dyne/cm as well as with canola oil.EDX analysis proved enhancement in FC ratio and membrane surface analysis lead to understand enhanced performance in DCMD.

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