Surface modification of polyethersulfone membranes with alkaline protease-activated L-histidine zwitterion carbon dots to improve anti-protein fouling

Abstract In this study, L-histidine zwitterionic carbon dots (HZCDs) were synthesized using the hydrothermal method. The synthesized HZCDs were used to modify polyethersulfone (PES) membranes. Additionally, the HZCDs-modified membranes were activated using the protease enzyme to prepare protease-activated composite membranes. The prepared materials underwent extensive characterization and validation using various techniques, including Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analyses. The blending or activation of HZCDs by the protease enzyme reduced the contact angle of the prepared membranes. The contact angle decreased from 78.75° to 50.12° and 40.02° for 2.0 wt.% HZCDs-PES and PES/Protease-HZCDs membranes, respectively. As the contact angle decreased, the hydrophilic nature of the prepared membranes increased, reflecting a strong affinity for water and efficient wettability. In this context, the pure water flux (PWF) values of PES membranes increased from 140.5 ± 5.3 to 248.7 ± 8.4 L/m 2 .h with rising HZCDs amount from 0 to 2 wt.% HZCDs-PES. Additionally, PWF values for protease-activated composite membranes increased from 140.5 ± 5.3 to 321.1 ± 9.2 L/m 2 . h. BSA flux values of PES membranes increased from 56.4 ± 2.4 to 82.9 ± 0.9 L/m 2 .h with increasing HZCDs amount from 0 to 2.0 wt.% HZCDs-PES. Besides, BSA values for protease-activated composite membranes increased from 56.4 ± 2.4 to 89.8 ± 2.2 L/m 2 .h. The purpose of this modification was to impart hydrophilic properties to the PES membrane and address the issue of membrane fouling, which is a common problem in filtration processes. 2.0 wt.% HZCDs-PES and enzyme-activated membranes PES membranes demonstrated 100% BSA removal efficiency. Also, 2.0 wt.% HZCDs-blended membranes and 2.0 wt.% protease-HZCDs-blended membranes demonstrated remarkable antifouling properties up to 87.7% and 88.8% flux recovery ratio (FRR), respectively. In contrast, BSA flux recovery reached only 67.8% for the pristine PES. When compared to pristine PES membranes, enzyme-activated membranes demonstrated superior filtration and protein rejection efficiencies.