Fabrication of ultrafiltration membrane surface with synergistic anti-fouling effect of “dispersion-impedance” and anti-fouling mechanism of dye

Four kinds of hydrophilic chains with diverse microstructures, namely anhydride (MA), melamine (MEL), polyethylene glycol (PEG)-g-MEL and MEL-g-polyethyleneimine (PEI) were introduced into the membrane surface by the "surface deposition and grafting" method in this work. The influence of the flexibility and rigidity for the grafting chains on the anti-fouling capacity to the positively charged alcian blue (AB8GX) and the negatively charged methyl blue (MB) was investigated. The results revealed that the impact of flexibility and rigidity for the grafting chains is more significant on both the adhesion of dye on the membrane surface and the microstructure of the fouling layer formed on the membrane surface than the hydrophilicity and the charging property of the membrane surface. The "dispersion–impedance" dual synergistic mechanism of anti-dye-fouling combined with flexible chain of PEI and rigid chain of MEL was explained through analyzing and characterizing the degree of dye accumulation on the membrane surface and the adhesion between dye and the membrane surface. More specifically, the PEI chain induces a dispersing capacity on the dyes, while the MEL chain can hinder the association between the dye molecules and the adhesion and aggregation on the membrane surface to further retard the adsorption of dye on the membrane surface. The steric hindrance effect of the MEL-g-PEI chains further increases the difficulty of dyes to approach and attach on the upper surface of membrane. They will all significantly weaken the adhesion force for dyes on the membrane surface and delay the formation of irreversible fouling. This work provides not only an idea for the development of membrane surfaces with high anti-dye-fouling properties, but also provides fruitful insights by revealing the anti-dye-fouling mechanism of the membrane surfaces.