Carbon nanotube based Janus composite membrane of oil fouling resistance for direct contact membrane distillation

A novel Janus composite membrane via hydrophilization of conventional PVDF hydrophobic membrane based on multiwall carbon nanotube (CNT) functionalized with carboxylic groups was investigated for use in membrane distillation. The modified membrane exhibited in-air water hydrophilicity and underwater oleophobicity. Interestingly, despite of the smaller effective pore size than that of the virgin membrane, the vapor flux was not compromised in the modified membrane, while a slight flux enhancement was observed, probably due to the high water permeability and heat conduction of the CNT layer, as suggested by the mass-heat transfer studies. Moreover, antifouling properties of the modified membrane were noted for treating a hexadecane emulsion of 1000 mg/L. The variation in the decrease in flux and the increase in conductivity was in line with force analysis between membrane and oil droplet, and the superior performance of modified membrane to the virgin membrane may be attributed to the good hydrophilicity of the functionalized CNT layer. Our results confirmed the hypothesis that CNT with high mass-heat transfer capability, homogeneously coated in a hydrophilic layer, may be promising candidate for fabricating a new-generation of fouling-resistant Janus membrane to treat oily wastewater.