Mussel-Inspired Robust Peony-like Cu3(PO4)2 Composite Switchable Superhydrophobic Surfaces for Bidirectional Efficient Oil/Water Separation

To alleviate the economic and environmental damage caused by industrial discharges of oily wastewater, materials applied for efficient oil/water separation are receiving significant attention from researchers and engineers. Among others, switchable wettable materials for bidirectional oil/water separation show great potential for practical applications. Inspired by mussels, we utilized a simple immersion method to construct a polydopamine (PDA) coating on a peony-like copper phosphate surface. Then, TiO2 was deposited on the PDA coating surface to build a micro-nano hierarchical structure, which was modified with octadecanethiol (ODT) to obtain a switchable wettable peony-like superhydrophobic surface. The water contact angle of the obtained superhydrophobic surface reached 153.5 degrees, and the separation efficiency was as high as 99.84% with a flux greater than 15,100 L/(m2 center dot h) after 10 separation cycles for a variety of heavy oil/water mixtures. Notably, the modified membranes have a unique photoresponsiveness, transforming to super hydrophilic upon ultraviolet irradiation, achieving separation efficiencies of up to 99.83% and separation fluxes greater than 32,200 L/(m2 center dot h) after 10 separation cycles for a variety of light oil/water mixtures. More importantly, this switch behavior is reversible, and the high hydrophobicity can be restored after heating to achieve efficient separation of heavy oil/water mixtures. In addition, the prepared membranes can maintain high hydrophobicity under acid-base conditions and after 30 sandpaper abrasion cycles, and damaged membranes can be restored to superhydrophobicity after a brief modification in the ODT solution. This simple to-prepare, easy-to-repair, robust membrane with switchable wettability shows great potential in the field of oil/water separation.

Automated summary

To address the economic and environmental damage caused by industrial discharges of oily wastewater, researchers and engineers are focusing on efficient oil/water separation materials. Switchable wettable materials for bidirectional oil/water separation, inspired by mussels, have shown great potential for practical applications. By utilizing a simple immersion method, polydopamine (PDA) coating was constructed on a peony-like copper phosphate surface, followed by deposition of TiO2 to build a micro-nano hierarchical structure. The resulting membrane demonstrated high separation efficiency and unique photoresponsiveness, making it a promising solution for oil/water separation.