Evaluation of innovative dual-layer modified polyethersulfone membranes in the control of biofouling

This study uniquely demonstrates the innovative combination of aminophenol and phenolic acids through laccase-catalyzed processes on polyethersulfone (PES) surfaces. Firstly, PES membranes were modified via laccase-catalyzed polymerization of 3-aminophenol (3-AP), then a second layer with either 4-hydroxybenzoic acid (B), gallic acid (G), syringic acid (S), or vanillic acid (V) was integrated using the same laccase-catalyzed polymerization method. The B/3-AP/PES and S/3-AP/PES membranes (using 4-hydroxybenzoic acid and syringic acid as the second modification layer) had better hydrophilicity as the contact angle was reduced from 44.1° (one-layered 3-AP/PES) to 23.8° and 27.9°, respectively, alongside significant increases in the root-mean-square (RMS) roughness (59 nm for unmodified PES vs. 180.2 and 385 nm for B/3-AP/PES and S/3-AP/PES, respectively). Atomic Force Microscopy (AFM) imaging revealed brush-like architectures for 3-AP/PES and B/3-AP/PES, while it was pancake-like in S/3-AP/PES. MIC testing showed that bacterial inhibition could reach 99.9%. Microbial evaluations of biofilm formation showed that B/3-AP/PES gave the highest reduction in the detached bacterial count (77%); this was concomitant with lower hemocytometer cell counts. Scanning Electron Microscopy (SEM) confirmed the reduction of bacterial adhesion. This study introduces a new approach of enzymatically grafting aminophenol layer as a stable anchoring platform for dual-layered modification by natural phenolic compounds.