Co-adsorption of an anionic dye in the presence of a cationic dye and a heavy metal ion by graphene oxide and photoreduced graphene oxide

To investigate the adsorption behavior of contaminants with different adsorbents and co-adsorbates under identical conditions, the adsorption capacities of anionic orange II (OII) dye onto graphene oxide (GO) and photoreduced GO (PRGO) in a single-component system and in the presence of cationic methylene blue (MB) dye as well as heavy metal ion Pb2+ were explored. In this work, PRGO was prepared by solar light irradiation of a GO dispersion. GO and PRGO were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. The adsorption isotherms of OII, MB, and Pb2+ onto GO and PRGO in single and binary systems have been studied and analyzed by the Langmuir model. In the single system, the adsorption capacity of OII on GO can be promoted from 8.4 mg g−1 to 32.5 mg g−1 after solar light irradiation. While the adsorption capacities of MB and Pb2+ are not affected by the photoreduction process. In the binary system, a marked synergistic effect for the adsorption of OII has been determined in the presence of both MB and Pb2+, where the adsorption capacity of OII on PRGO has been improved from 8.4 mg g−1 to 295 mg g−1 and 105 mg g−1, enhancements of 35- and 12.5-fold, respectively. In contrast, the presence of OII leads to a mildly antagonistic effect on the adsorption of MB and Pb2+. These findings show that the adsorption of anionic dyes by graphene-based materials can be strongly improved in the presence of either cationic dyes or heavy metal ions, which will be of great value in practical applications.