1 research outputs found
Improved Antifouling Properties of Polyamide Nanofiltration Membranes by Reducing the Density of Surface Carboxyl Groups
Carboxyls are inherent functional groups of thin-film
composite
polyamide nanofiltration (NF) membranes, which may play a role in
membrane performance and fouling. Their surface presence is attributed
to incomplete reaction of acyl chloride monomers during the membrane
active layer synthesis by interfacial polymerization. In order to
unravel the effect of carboxyl group density on organic fouling, NF
membranes were fabricated by reacting piperazine (PIP) with either
isophthaloyl chloride (IPC) or the more commonly used trimesoyl chloride
(TMC). Fouling experiments were conducted with alginate as a model
hydrophilic organic foulant in a solution, simulating the composition
of municipal secondary effluent. Improved antifouling properties were
observed for the IPC membrane, which exhibited lower flux decline
(40%) and significantly greater fouling reversibility or cleaning
efficiency (74%) than the TMC membrane (51% flux decline and 40% cleaning
efficiency). Surface characterization revealed that there was a substantial
difference in the density of surface carboxyl groups between the IPC
and TMC membranes, while other surface properties were comparable.
The role of carboxyl groups was elucidated by measurements of foulant-surface
intermolecular forces by atomic force microscopy, which showed lower
adhesion forces and rupture distances for the IPC membrane compared
to TMC membranes in the presence of calcium ions in solution. Our
results demonstrated that a decrease in surface carboxyl group density
of polyamide membranes fabricated with IPC monomers can prevent calcium
bridging with alginate and, thus, improve membrane antifouling properties