One-step removal of all pollutants to produce clean water: Construct a novel dual-functional aramid nanofibre membrane for simultaneous oil-in-water separation and single-ring aromatic compound removal

The coexistence of insoluble oil droplets and dissolved harmful substances in oily wastewater are challenging for the production of clean water by membrane treatment. Accordingly, the development of an innovative membrane that will concurrently remove oil and hazardous compounds in one-step to obtain purer water is of great significance. In this study, a novel dual-functional aramid nanofibre (ANF) membrane was prepared from poly-pseudorotaxane polymer with superhydrophilic armour composed of cyclodextrin (CD). To obtain the molecular armour, an inclusion complex of CD and p-phenylenediamine (PPD) was prepared and then used in the synthesis of modified poly(p-phthaloyl-p-phenylenediamine) (CD@PPTA). The β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) could be anchored on the PPTA polymer chains like a molecular coating. The superhydrophilic and underwater superoleophobic β-CD@ANF and γ-CD@ANF membranes were constructed through the non-solvent-induced phase-inversion technique. The gratifying flux recovery (96.62%) and oil rejection (98.29%) under low pressure (0.40 bar) filtration indicated that the design of the membrane enabled its excellent anti-pollution capability. Furthermore, their ability to remove single-ring aromatic substances from the aqueous phase endowed the γ-CD@ANF membrane with excellent applicability to industrial applications. Interestingly, when treating oil-in-water emulsions containing phenol or benzoic acid, the oil separation efficiency was also enhanced. Through mechanistic analysis, this study demonstrated a new effective membrane for the simultaneous purification of practical oily wastewater containing hazardous compounds to achieve one-step removal of all pollutants to produce clean water.