Abstract
Wider adoption of membrane technology is hindered by fouling and flux/rejection challenges.
Recent practice in mitigating these is to incorporate hydrophilic and porous
fillers. Herein the addition of hydrophilic graphene oxide (GO) in conjunction with porous
mixed ZIFs (ZIF-67/ZIF-8) crystallites were used as inorganic fillers in the preparation
of polyphenylenesulfone (PPSU) ultrafiltration (UF) membranes. The morphology of the
resultant composite membranes was assessed using atomic force microscopy (AFM) and
scanning electron microscopy (SEM) whilst surface hydrophilicity through water contact
angle. The pure water flux (PWF) and membrane permeability were found to increase
with increasing filler content. This was attributed to the combined hydrophilicity of GO
and porous structure of the ZIF materials because of increasing alternative water pathways
in the membrane matrix with increasing filler content. Furthermore, the increase in
the ZIF component led to increasing bovine serum albumin (BSA) fouling resistance as
demonstrated by increasing fouling recovery ratio (FRR). The dye rejection was due to
a combination of electrostatic interaction between the fillers and the dyes as well as size
exclusion. The chemical interactions between the ZIFs and the dyes resulted in slightly
different rejection profiles for the smaller dyes, the cationic methylene blue being rejected
less efficiently than the anionic methyl orange, potentially leading to their separation. The
larger anionic dye, Congo red was rejected predominately through size exclusion.