Surface-engineered graphene-based multi-level filter materials for one-step separation of complex oil-in-water emulsions

Positively charged, negatively charged, and uncharged graphene sheets are integrated into a 3D material to form the novel filter material capable of efficiently separating multiple oil-in-water emulsions in one-step. [Display omitted] •The filter materials are integrated with three different charged graphene sheets.•The filter materials can separate varieties of type and content of oil-in-water emulsions.•The type and proportion of functional groups in filter materials can be adjusted.•One-step separation of complex oily wastewater is realized under gravity. Global daily oil consumption reaches nearly 100 million barrels, a figure which consequently leads to the generation of substantial volumes of oily wastewater during the processes of oil production and transportation. Existing advanced materials exhibit remarkable properties for emulsions stabilized by specific surfactants. However, these materials face limitations in practical application due to the intricate composition of surfactants present in real-world oily wastewater. In this paper, we aim to tackle this issue by presenting a solution that involves the utilization of surface-engineered graphene-based multi-level filter materials (GMFMs). These specially prepared GMFMs incorporate positively charged, negatively charged, and uncharged graphene sheets, which synergistically combine to form a porous structure with unique wettability. This innovative design allows the filter material to exhibit exceptional separation capabilities for complex emulsions. The surface-engineered GMFMs exhibited exceptional efficiency in the separation of mixed surfactant-stabilized emulsions and industrial wastewater. Operating at a high throughput of approximately 5000 L m−2 h−1, these GMFMs achieved an impressive oil removal efficiency of 99.8 % or higher after just one-step separation. The combined efficiency, reusability, and broad applicability of GMFMs facilitate efficient separation of oil-in-water emulsions on a large scale, promising a sustainable solution to the pressing issue of oily wastewater treatment.