Fast preparation of a polydopamine/ceramic composite nanofiltration membrane with excellent permselectivity

Fabrication of a dense polymer/ceramic composite membrane with high permeability remains a great challenge. In this study, a highly selective polydopamine (PDA)/ceramic composite nanofiltration (NF) membrane was prepared by using an Al₂O₃ ceramic membrane with pore size of 0.1 μm as the support layer. In order to improve the membrane formation rate, KMnO₄ was introduced to oxidize the dopamine to improve the reactivity, and Na₂CO₃ was used to adjust the pH value of the dopamine solution. When the addition amount of KMnO₄ is 0.2 g L^-1 and that of Na₂CO₃ is 1 g L^-1, a functional layer can be formed within 10 min. PDA and polyethyleneimine (PEI) were added to the functional layer to adjust the selectivity of the composite membrane. The composite membrane showed a rejection of 99.7% towards Congo red dye with a high flux of 165 L (m² h bar)^-1 at ambient temperature. After 3 h treatment with Congo red, the fouling resistance of the membrane was improved compared with that of the ceramic based membrane. The surface morphology and composition of the composite membrane were also characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), which confirmed the successful preparation of the PDA/ceramic composite membrane.