Photocatalytic self-cleaning membrane with polyaniline/NH2-MIL-125 heterojunction for highly oil-water/seawater separation and bacterial inactivation

Abstract

Emulsified oils and microbial contaminations in water environments have posed huge risks to human health and ecological balance. In this work, we fabricated a polyaniline/NH2-MIL-125 (PANI/MIL) heterojunction decorated hydrolyzed polyacrylonitrile (HPAN) membrane with photocatalytic self-cleaning property for oil–water separation and bacterial inactivation. In which, PAN membrane was prepared by electrospinning and then HPAN membrane was obtained by alkaline hydrolysis. The photo-responsive PANI/MIL heterojunction was immobilized on HPAN membrane by vacuum-assisted assembly using protocatechuic acid (PCA) as the binder. The resultant PANI/MIL@HPAN composite membrane has a wettability of in-air superamphilicity and underwater superoleophobicity as well as surface nano-micro heterostructure. The composite membrane showed good separation efficiency (above 99.4%) and high flux (1446–3744 L m−2h−1) in a series of oil-in-water/seawater emulsions separation. In particular, the membrane can effectively deal with viscous oil fouling under visible light to achieve a desired flux recovery ratio (FRR) after separating crude oil from water, which was ascribed to the self-cleaning capacity originating from the surface coating photocatalyst. Meanwhile, the multifunctional composite membrane showed 100% photocatalytic inactivation efficiency against pathogenic Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus (6 log units) in water under visible light with low power intensity. The oil–water separation performance as well as photocatalytic inactivation efficiency of PANI/MIL@HPAN are superior to MIL@HPAN. The studies on the wettability, photothermal properties and photoelectric properties suggested that the coupling of conductive polymer PANI can simultaneously enhance the underwater superoleophobicity of the composite membrane, as well as improve the photocatalytic activity by creating a type II heterojunction to promote the separation of charge carriers and amplifying the photothermal effect, making the PANI/MIL@HPAN multifunctional membrane achieve the improved oil/water separation performance and antibacterial activity synergistically. This work provides a new strategy for developing effective self-cleaning membranes both toward oil/water separation and bacterial inactivation applications based on MIL metal–organic framework coupling with conductive polymers.