Acid response nanochannels of graphene oxide membranes for fast nuclide ions separation

Separation of nuclides from radioactive wastewater is crucial for the safe disposal of nuclear wastes and the sustainable development of resources. However, it still poses great challenges due to the high acidity and high salty of complex composition in radioactive wastewater. Herein, a pH-responsive graphene oxide (GO) membrane, known as a pGO membrane, was developed for fast and efficient selective separation of Sr2+ nuclide ions from highly acidic radioactive wastewater containing multiple mixed salt ions. Different from traditional GO membranes, the interlayer spacings of pGO membranes can be adjusted and increased with increasing acidity in the surrounding solutions due to the presence of grafting molecule polyethylenimine(PEI) within the modified nanochannels of the pGO membrane. The resulting acidic environmentally adaptable membrane has enlarged and positively charged nanochannels in highly acidic solutions. This structure effectively blocks larger and highly charged hydrated Sr2+ nuclide ions while allowing smaller and lowly charged monovalent salt ions (such as Cs+, K+, Na+) to rapidly transport through the membrane. As a result, the pGO membrane exhibits high selectivity for Sr2+/monovalent salt ions with high permeability for monovalent ions. Overall, this work provides a novel sieving method for the separation of radionuclides in highly acidic solutions.