Polyacrylonitrile ultrafiltration membranes incorporating graphene oxide fillers modified with Zeolitic Imidazolate Framework-8 and 3-aminopropyltriethoxysilane for dye and salt removal in real textile wastewater

Chemical grafting of graphene oxide (GO) with 3-aminopropyltriethoxysilane (APTES) reduced GO-sheet aggregation, improved their dispersion and interaction with the polymer matrix. Zeolitic Imidazolate Framework (0.1-1.5 wt%) were grown on GO-APTES forming ZIF-8 @GO-APTES nanocomposites. The incorporation of these composites into polyacrylonitrile (PAN) ultrafiltration (UF) membranes resulted in increased hydrophilicity (contact angle decreasing from 69.5 degrees to 25.9 degrees), and pure water flux (increasing from 31.3 L.m-2 h(-1) to 101.3 L. m(-2) h(-1)). The dye rejection in synthetic and colour removal in real textile wastewater increased in the composite membranes. Methyl orange rejection increased from 61 % to above 75 % whilst for methylene blue it increased from 33 % to 40 %. Colour removal in real textile wastewater increased with the increasing loading of ZIF-8 @GO-APTES in the membranes, increasing from 63 % for PAN membrane to 96 % in the composite membrane with high loading of ZIF-8 @GO-APTES. Relatively high metal ions (Pb, Zn, Ca, Cr, and Mg) rejection was also observed, increasing from 40 % in PAN and GO@PAN membranes to between 60 % and 80 % as filler content was increased. The difference in solute rejection with filler loading was attributed to electrostatic interactions due the presence of the functional nanocomposites embedded in the membrane surface layer. The rejection fractionally increased as the ZIF-8 component in the filler increased within the same series and generally more as the overall loading of ZIF-8 @GO-APTES in the PAN membranes was increased, further confirmation the electrostatic-based rejection mechanism. The ZIF-8 @GO-APTES/PAN membranes showed high antifouling properties with FRR of 93.4 % compared to 43.5 % for pristine PAN membranes.