A covalently cross-linked graphene oxide (GO) membrane was prepared by a facile vacuum filtration method followed by a cross-linking process using tannic acid-functionalized GO (TA-GO) and hyper-ranched polyethyleneimine (PEI). The TA-GO was prepared by a simple and environmentally friendly method using GO and a renewable plant-based polyphenol, tannic acid (TA), and it was covalently cross linked by PEI via the reaction between catechol groups in TA and amine groups in PEI to form covalent bonds in a weak alkaline environment producing the cross-linked GO membrane. The cross-linked GO membrane showed excellent dimensional stability and ions separation performance. In particular, the cross-linked GO membrane containing TA showed excellent antibacterial activity against Escherichia coil (E. coil) due to the intrinsic bactericidal properties of the TA moieties. Furthermore, the membrane exhibited higher water flux and rejections toward NaCl and MgSO4 than the commercial nanofiltration (NF) membranes. (C) 2016 Elsevier B.V. All rights reserved.