In XPS, pristine PP membranes (Figure ) showed nearly exclusively aliphatic C-(C,H) signal (Figure ), no nitrogen, and only traces of oxygen. Upon addition of PDA (Figure ) signals for oxygen and nitrogen logically appeared. Notably, the N/C ratio of the PP_PDA reaches a similar value to that of the theoretical value of the polydopamine polymer (N/C PDA = 0.125), suggesting the formation of a PDA coating of at least 10 nm thickness at the PP surface . As expected, the grafting of GDE (Figure ) on the amine residues present at the PP_PDA surface increased the oxygen surface concentration at the expense of nitrogen (Table , line 6), and the addition of PEI on PP_PDA_GDE (Figure ) resulted in a marked increase in the nitrogen content (and N/C ratio) (Table , line 7).