Preparation and characterization of a novel freestanding flexible reduced graphene oxide composite membrane for adsorption of isoflavone in Radix Puerariae Lobatae

In this work, a novel freestanding flexible reduced graphene oxide (rGO) composite membrane was prepared, using polystyrene microspheres as the spacer to decrease the GO sheet self-stacking, silane coupling agents as the cross-linker to enhance the toughness, and treatment with ammonia followed by hydrochloric acid to partially reduce GO and increase the adsorption capacity. The morphologies and structures of the materials were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. The adsorption capacity toward genistein of the rGO composite membrane was 367.5 mu mol g(-1), which was much higher than other adsorbents under similar conditions in literature. Moreover, the rGO composite membrane had much higher adsorption capacity toward genistein and daidzein than the other three isoflavones (genistin, daidzein, and puerarin) due to hydrophobic interaction and hydrogen bond. Separated only once by the rGO composite membrane, the mass purity of daidzein and genistein in the purified extract was 31.31 % and 5.89 %, respectively, which was about 6 times of their mass purity in the crude extract of Radix Pueraria lobata.