Mussels-inspired design a carbon nanotube based underwater superoleophobic/hydrophobic Janus membrane with robust anti-oil-fouling for direct contact membrane distillation

Membrane distillation is an emerging technique effective in desalination and other membrane separation processes. However, hydrophobic membrane fouling caused by non-polar foulants limits the practical oily wastewater application. In this study, an underwater-super-oleophobic/hydrophobic Janus membrane with flux enhancement and robust anti-oil-fouling property was fabricated through formation of a carbon nanotube/PDA/PEI hydrophilic surface coating on a PVDF membrane. The process comprised construction of carbon nanotube layer and bioinspired-adhesive polydopamine/Polyethyleneimine (PDA/PEI) which enhanced hydrophilicity and stability of the membrane. Integration of the hydrophilic property of PDA/PEI and the multiscale structures of CNT endowed the membrane with air-hydrophilicity, underwater superoleophobicity and anti-oil-fouling properties. Introduction of CNT increased the mass and heat conduction performance of the membrane, which was attributed to increased flux. Use of PDA/PEI firmly fixed the carbon nanotube layer on the membrane surface and effectively increased hydrophilicity of the membrane surface. Increase in hydrophilicity resulted in improved underwater-superoleophobicity of the modified membrane. The anti-oil-fouling properties of the Janus membrane were explored by treatment with saline feed containing 1000 mg L−1 mineral oil. The Janus membrane showed an excellent enhanced flux and oil repellent during the test. Our study provides an ideal strategy to tailor Janus membrane with excellent surface wettability for oily wastewater treatment.