Effective removal of manganese in graphene oxide via competitive ligands and the properties of reduced graphene oxide hydrogels and films

Reduced graphene oxide (rGO) has tremendous importance due to its potential applications in electronics, catalysis and sensors. However, the properties of rGO are often affected by the impurity of manganese ions, and their removal from graphene oxide (GO) is time and labor-consuming due to their strong interaction with oxygen-containing groups of GO. In this paper, we use citric acid, sulfosalicylic acid and tartaric acid as competitive ligands to make manganese ions removal easy. The results show that under the same purifying conditions, the presence of competitive ligands can increase the purifying efficiency, and the lowest content of manganese is only one-third of that in GO without competitive ligands. The hydrogels and films of rGO have been prepared, and their properties such as capacitance and conductivity have also been evaluated. The results show that the microstructure of hydrogels is affected by the added ligands. The hydrogels prepared from GO which is purified in the presence of sulfosalicylic acid exhibit well-defined pore structure and the capacitive performance such as rate capability and the cycling stability is the best. It is proved that adding competitive ligands is an effective approach to remove manganese impurity in GO.