Flower-like ZnO/BiOI p–n heterojunction composite membrane composed of nanosheets for enhanced photodegradation of water-soluble pollutant and high efficiency oil–water emulsion separation

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The emulsified oil wastewater produced from the petrochemical industries and people’s daily life would cause severe harm to the ecological environment if improperly treated. Thus, the development of membranes with efficient oil–water separation and self-cleaning property remains a key global research direction. In this study, p-n heterojunctions membrane with BiOI@ZnO hierarchical flower-like-nanosheets structures (BiOI@ZnO@SSM) has been successfully fabricated through two-step electrodeposition method. The BiOI@ZnO@SSM is capable of separating water and oil from emulsified oil wastewater and performing efficient adsorption and photocatalytic degradation of organic pollutants in water. The separation efficiency of BiOI@ZnO@SSM for numerous oil-in-water (O/W) emulsions exceeded 99.3 % as well as a fast permission flux up to 299.8 L·m−2·h−1. And the degradation efficiency of BiOI@ZnO@SSM for Rhodamine B (RhB) can reach to 99.0 % in 80 min under visible-light irradiation, which is 1.5 times as high as that of ZnO@SSM. The obviously enhanced photocatalytic activity of BiOI@ZnO@SSM is due to the formation of p-n heterojunction between p-type BiOI and n-type ZnO, which broadens the light absorption range, promotes the effective separation and prolongs the lifetime of electron and hole pair and realizes efficient degradation of organic pollutants. Meanwhile, multidimensional and hierarchical nanoflowers structure is not only helpful to improve the utilization of light, but also can increase more catalytic active sites. After ten cycles, this membrane maintained high emulsion separation efficiency of 99.6 % and the photodegradation efficiency remained above 94.5 %, demonstrating its good recyclability and stability. This durable and multifunctional heterojunction composite membrane with a flower-like structure is of great application potential in dealing with practically emulsified wastewater.