Construction of sandwich-structured photocatalytic membranes to regulate the conversion of natural organic matter: Enhancement of anti-fouling performance

Membrane fouling induced by natural organic matter (NOM) is a challenge for wider application of photocatalytic membranes (PMs). In this study, Bi2O3-TiO2 (BT) and powdered activated carbon (PAC) were coated on the ultrafiltration (UF) membrane surface with sandwich structure (BT/PAC-UF), to mitigate membrane fouling of PMs under the ultraviolet (UV) irradiation. When exposed to UV irradiation, the BT/PAC coating demonstrated superior performance in mitigating membrane fouling, achieving a higher flux recovery rate of 43.1 % and a lower irreversible fouling rate of 57.5 %, compared to individual PAC and BT coating layers. Additionally, after BT/PAC coating under UV irradiation, the removal efficiencies of dissolved organic carbon (DOC), UV254, and protein-like fluorescents improved to 63 %, 59 %, and 73.4 %, respectively, and the interfacial energy also increased to 6.30 mJ/m2, surpassing that achieved by PAC and BT coatings. In contrast to BT-UF under UV irradiation, the removal efficiencies of low molecular weight (LMW) Acids and Neutrals were increased 21 % and 66 % in BT/PAC-UF, respectively. The Lifshiitz-van der Waals energy (Delta GLW) had the highest Mantel correlation with the membrane resistance, followed by surface hydrophilicity energy (Delta Gsls). The removal efficiencies of humic-like and protein-like fluorescents showed high negative correlation with Delta GLW and Delta Gsls (Pearson's r = -0.98). The BT/PAC coating can reduce the content of humic-like and protein-like fluorescents, leading to a reduced attraction of the natural organic matter (NOM) to the membrane. Meanwhile, the required volume for the changed from pore blocking to cake filtration was reduced most from 320 ml to 180 ml by the BT/PAC coating. The UF membrane fouling of PMs caused by NOM was mitigated eventually.