Achieving overall rejection of pharmaceuticals and personal care products of different polarities by controlling interlayer charging environment of graphene oxide membrane using carbon quantum dots

To realize overall rejection of numerous pharmaceuticals and personal care products (PPCPs) with varieties in hydrophilicity (dissolubility giving either negative or positive charges and non-dissolubility) and hydrophobicity, a diverse interlayer charging environment was controlled by intercalating two-dimensional carbon quantum dot (CQD)-like nanoparticles into graphene oxide membrane (GOM). It was found that ethylenediamine-added sucrose-derived CQD with a positively charged surface in aqueous solution is appropriate for such a purpose because of the strong electrostatic attraction by the graphene oxide (GO) surface of opposite charge. The CQD contains plenty of pyridine groups of stronger basicity and pyrrole groups of weaker basicity, which contribute majorly to anchoring the CQD onto GO surface and to donating positive charges in GOM interlayer, respectively. This unique membrane design strategy allows coexisting of both negatively and positively charged groups in a slightly expanded hydrophilic interlayer space of GOM. As the result, not only rejections were promoted for the negatively dissociative PPCPs (from 77 % to all more than 86%) and neutral PPCPs (from 25 % to all more than 56%) but also rejections of the positively dissociative PPCPs became remarkable (from null to all more than 56%). The research result provides a promising methodology of changing chemical environment of a simpler membrane material other than nanofiltration or reverse osmosis to achieve an all-together rejecting effect toward PPCPs of various polarities.