Manipulating the multifunctionalities of polydopamine to prepare high-flux anti-biofouling composite nanofiltration membranes

Abstract

A high-flux anti-biofouling composite nanofiltration (NF) membrane was facilely prepared by simultaneously manipulating the three functionalities (adhesion, reaction and separation) of polydopamine (PDA) via a two-step dip-coating method. Stemming from the adhesion and separation functionalities, PDA was in situ deposited on a polyethersulfone (PES) substrate and formed an ultrathin dense layer, which endowed the membrane with a satisfying rejection for a broad range of small organic molecules (methyl orange of 65.65%, orange GII of 79.05%, congo red of about 98.78%, methyl blue and alcian blue of nearly 100%) and a relatively high water flux of 249.45 L m⁻² h⁻¹ MPa⁻¹ under the operation pressure of 0.2 MPa. Stemming from the reaction functionality, PDA could reduce silver ions when exposed to AgNO₃ solution and trigger the in situ generation of silver nanoparticles (AgNPs) on the membrane surface, which conferred excellent anti-biofouling properties to the membrane with low bioadhesion and high antibacterial efficiency (almost 100%) against Escherichia coli. Moreover, the adhesion and reaction functionalities have a close relation to the separation functionality of PDA. The effects of PDA deposition time, AgNO₃ treatment time and AgNO₃ concentration on the separation performance of the resulting composite NF membranes were systematically investigated.