Influence of polydopamine deposition conditions on hydraulic permeability, sieving coefficients, pore size and pore size distribution for a polysulfone ultrafiltration membrane

Abstract

Membrane surface modification with polydopamine (PDA) coatings can reduce fouling in oily water filtration due, at least in part, to enhanced surface hydrophilicity. In this study, polysulfone (PSf) UF membranes were coated with PDA. PDA coating conditions (solution concentration and deposition time) were varied, and the effect of coating conditions on membrane molecular weight cutoff (MWCO) and hydraulic permeability was measured. Membrane MWCO decreased and PDA film thickness increased as initial dopamine coating solution concentration or deposition time increased. The MWCO decrease confirmed that PDA restricted the membrane pores. While the PDA coating thickness on membrane surfaces grew progressively with increasing initial dopamine concentration or coating time, coating inside the membrane pores was limited by the finite membrane pore size. A tradeoff between selectivity and hydraulic permeability of unmodified and PDA-modified membranes was noted. This tradeoff is reminiscent of that observed in other separation membranes. Zydney's hindered solute transport model of flow through porous membranes was used to estimate changes in membrane mean pore size and pore size distribution. Based on the modelling results, membrane mean pore radius increased at low initial dopamine concentrations or short deposition times and decreased at high initial dopamine concentrations or long deposition times with increasing initial dopamine concentration or increasing PDA coating time. The pore size distribution narrowed as the membranes were modified with PDA. The porosity to thickness ratio of PDA-modified membranes remained unchanged or was only slightly higher than that of unmodified membranes.

Hydrophilic modification of polypropylene ultrafiltration membrane by air‐assisted polydopamine coating

“…The presence of foulants in the feed water leads to deposition and accumulation on the membrane surface and internal pores blocking. For porous membranes like UF, pore size reduction and pore blocking are the major factors influencing the water flux decrease . The decrease of water flux would not only cause inconvenience for practical operation, but also increase the operating costs due to the requirement of membrane cleaning and replacement .…”

“…For porous membranes like UF, pore size reduction and pore blocking are the major factors influencing the water flux decrease. 1,6 The decrease of water flux would not only cause inconvenience for practical operation, but also increase the operating costs due to the requirement of membrane cleaning and replacement. 7,8 Membrane fouling also leads to higher energy needed to keep the membrane performance constant.…”

Effect of polydopamine deposition conditions on polysulfone ultrafiltration membrane properties and threshold flux during oil/water emulsion filtration

“…However, application of coatings or grafting materials to membrane surfaces may introduce additional mass transfer resistance to the membrane, resulting in reduced pure water permeance [3,7,8]. For porous membranes, the permeance decrease is often due to membrane separation layer thickness increase and pore size reduction or pore blockage caused by surface modification [9,10]. During constant global (i.e., overall) permeate flux filtration, pore blockage or pore size decrease could increase local convective permeate flux through the pores, enhancing the forces responsible for bringing foulants to the membrane surface, thereby increasing fouling [6].…”

“…Nevertheless, severe reductions in membrane pure water permeance due to application of the PDA coating on porous membranes should be minimized to avoid, at fixed global or overall 2 flux, increases in local permeate flux due to pore narrowing or blocking as a result of PDA modification, which could exacerbate fouling [20]. Generally, the pure water permeance of these membranes can be controlled by varying PDA modification conditions such as coating solution concentration and coating time [8,9,17,20]. Since even a minimal application of PDA to the membrane surface can significantly improve surface hydrophilicity, and more substantial applications of PDA have little effect on hydrophilicity, PDA can be used to examine the effect of changing pore size in a hydrophilic membrane.…”

Permselectivity of Electrodeposited Polydopamine/Graphene Composite for Voltammetric Determination of Dopamine

“…These results demonstrated that at less scan cycles (such as 2 scan cycles) PDA film was uncontrolled which exhibited high permeability to cationic and anionic species while at more scan cycles (such as 15 scan cycles) hindered cationic and anionic species. Probably reasons were that thickness , pore size and structures of PDA film have been changed before reaching 15 scan cycles. However, the PDA modified electrode electropolymerized for more than 15 cycles was somewhat less sensitive to detect a low concentration dopamine.…”