Ta-Fe in-situ coating PES membrane and its application in oily wastewater treatment: Insight into modification and anti-fouling mechanisms

Membrane fouling is a serious problem that limits the widespread application of membrane technology. Herein, we propose an effective modification method by in-situ modifying polyethersulfone (PES) ultrafiltration membrane with tannic acid (TA) and Fe3+ chelates to improve its pollution resistance. The TA-Fe3+ complexes could deposit on the PES membrane surface and form a hydration layer by Van Der Waals force, hydrogen bonding force, and hydrophobic association. The modified membrane (PES\TA\Fe3+) had enhanced fouling resistance and membrane flux due to its dual advantages of abundant OH groups and favorable spatial structure. After modification, the roughness of membrane surface increased from 219 nm to 257 nm, and its water contact angle decreased from 58.9° to 26.5°, endowing the PES\TA\Fe3+ membrane with a strong resistance to oil droplets through electrostatic repulsion, steric hindrance effect, and hydrogen bonding force. Polyaluminum chloride-polydimethyldiallylammonium chloride (PAC-PDMDAAC) could alleviate 85 % membrane fouling resistance. PAC-PDMDAAC mainly mitigated irreversible membrane fouling by removing oil droplets and forming large and loose flocs. While the use of PES\TA\Fe3+ membrane mainly reduced the adsorption resistance and the resistance of membrane itself. The anti-fouling performance of PES\TA\Fe3+ membrane changed with pH owing to the changes in the properties of TA-Fe3+ complexes. The hydrophilic layer would be decomposed under alkaline conditions due to the deprotonation of TA and excessive hydrolysis of Fe3+. This study provides an efficient anti-fouling strategy and reveals the modification and anti-fouling mechanisms of the hydrophilic membrane, providing theoretical guidance for the further development of membrane technology.