Fabrication of a novel underwater-superoleophobic/hydrophobic composite membrane for robust anti-oil-fouling membrane distillation by the facile breath figures templating method

Membrane fouling is a major obstacle for the practical application of membrane distillation (MD). Herein, for robust anti-oil-fouling MD, we report a facile breath figures templating (BFT) method to develop novel composite membranes comprising a hydrophobic polytetrafluoroethylene substrate and a hydrophilic cellulose acetate coating with through-pores. The effects of dosage of cellulose acetate and template agent, and exposure time in vacuum and humid atmosphere on membrane morphology and performance were systematically studied. It was found that the higher template agent concentration slowed solvent volatilization and facilitated through-pores formation, and that humidification also facilitated through-pores formation and promoted the emergence of a spongy cross-section in the coating. As cellulose acetate concentration increased, the pore size became smaller while the porosity and underwater oleophobicity were enhanced. The fabricated PTFE-9CA composite membrane was the most effective in resisting oil-fouling as the dense and rough coating rendered the surface underwater superoleophobicity. During MD test with a saline feed containing 1000 mg/L crude oil, the permeate flux of the PTFE-9CA membrane maintained at about 16.85 kg/m(2) h, and the salt rejection was nearly 100%. The facile modification strategy to develop a composite membrane has great potential to promote MD dealing with challenging wastewaters enriched with salts and hydrophobic organics.

Automated summary

A facile breath figures templating (BFT) method was used to develop a composite membrane for robust anti-oil-fouling membrane distillation. By controlling the concentration of cellulose acetate and template agent, as well as exposure to different environments, the morphology and performance of the membrane could be systematically studied and improved. The fabricated PTFE-9CA composite membrane showed great potential in resisting oil-fouling and maintaining high salt rejection during MD testing.