Robust bio-inspired superhydrophilic and underwater superoleophobic membranes for simultaneously fast water and oil recovery

Designing a stable and uniform hydrophilic material for separation of oil and water is strongly desired for sustainable management of oily wastewater. Herein, a stable and uniform bio-inspired coating onto the non-woven fabric substrate with superhydrophilicity and underwater superoleophobicity via rapid co-deposition of dopamine and polyethylenimine was demonstrated. Ammonium persulfate outperformed other oxidants (e.g., Cu2+-H2O2 and NaIO4) to rapidly trigger the co-deposition of dopamine and polyethylenimine for homogeneous superhydrophilic and underwater superoleophobic surface engineering. Furthermore, the co-deposition conditions, i.e., concentration of ammonium persulfate and exposure duration, have a positive dependence on the hydrophilicity and underwater oleophobicity of the coated fabric membranes. Specifically, the superhydrophilicity and underwater superoleophobicity (underwater oil contact angle of 165.4 +/- 1.1 degrees, sliding angle of 2.5 +/- 0.5 degrees) can be obtained for the coated fabric membranes at the optimal co-deposition condition (i.e., 28.5 mmol L-1 persulfate and coating duration of 7 h), showing a great potential in gravitational oil-water separation (permeation flux >115,000 L m(-2) h(-1); oil rejection >99.2%). Integrating with a superhydrophobic copper mesh, the oil-water mixed solution can be continuously and sufficiently separated, realizing simultaneous recovery of pure oil and water from oily wastewater. In addition, the bio-inspired coating displays a strong long-term chemical robustness and stability in extreme environments (i.e., acidic/alkaline solutions and oils). The study provides a facile, cost-effective and practical strategy in constructing superhydrophilic and underwater superoleophobic interfaces for sustainable treatment of oily wastewater.

Automated summary

A stable and uniform bio-inspired coating with superhydrophilicity and underwater superoleophobicity was achieved on a non-woven fabric substrate through rapid co-deposition of dopamine and polyethylenimine. The co-deposition conditions, particularly the concentration of ammonium persulfate and coating duration, played a crucial role in determining the hydrophilicity and underwater oleophobicity of the coated fabric membranes. This study provides a facile and cost-effective strategy for constructing superhydrophilic and underwater superoleophobic interfaces for sustainable treatment of oily wastewater.