Photocatalytic TiO2@MIL-88A (Fe)/polyacrylonitrile mixed matrix membranes: Characterization, anti-fouling properties, and performance on the removal of natural organic matter

Photocatalytic membrane reactors (PMRs), coupling photocatalysts and membranes in a single system, have shown a considerable potential to reduce membrane fouling, which is one of the major drawbacks of using membranes to treat water and wastewater. In this study, the visible light-activated photocatalysts were incorporated into the polyacrylonitrile (PAN) casting solution to synthesize the photocatalytic composite membranes. The physicochemical properties and the morphology of the membranes and photocatalysts were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction analysis (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-visible DRS), photoluminescence (PL), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET), porosimetry, and contact angle analyses. The performance of the synthesized photocatalytic mixed matrix membranes (MMMs) in treating water containing humic acid, as one of the major components in natural organic matter (NOM) existing in drinking water sources, was investigated. Under visible light irradiation, the PAN/TiO2@MIL-88A (Fe) MMMs simultaneously adopted photocatalysis and membrane separation in the PMR and thereby enhanced humic acid removal and anti-fouling properties. The best synthesized photocatalytic membrane could remove 92.4% of the humic acid once exposed to visible light. The optimum membrane had suitable water permeability, a high flux recovery ratio (99.5%), and a 13.5% decline in the humic acid flux after a 10-h run, considerably lower compared to the corresponding decline of the pristine membrane (37.5% over the same period). The remarkable properties of the PAN/TiO2@MIL-88A (Fe) membrane, including its high anti-fouling specification, confirm the appropriateness of the synthesized MMM for treating water involving humic acid.