Exploring the impact of close-cell structures of three-dimensional graphene on BPA adsorption via 1H NMR relaxation and isotope tracing

During the self-assembly of graphene oxide (GO) into three-dimensional graphene-based materials (3D GMs), close-cell structures are formed. However, the specific effects of these structures on the adsorption of 3D GMs remain unclear. To address this, we synthesized a series of 3D GMs with varying proportion of close-cell structures to systematically investigate their impact on Bisphenol A (BPA) adsorption. Prolonged ultrasonic treatment for GO suspension reduced GO sheet size and increased the abundance of close-cell structures in 3D GMs. Raman spectroscopy, isotope tracing, thermogravimetric analysis, and 1 H NMR measurements revealed that freeze-thawing converts confined water into free water, suggesting the destruction of close-cell structures. The freeze-thawing treatment enhanced the BPA adsorption capacity of graphene hydrogel (GH), and this enhancement was more pronounced with the decreased size of GO nanosheets. This result demonstrated that GH samples with a higher abundance of close-cell structures generated more newly exposed adsorption sites for BPA during freeze-thawing. Furthermore, adsorption experiments in real environmental water (Dianchi Lake) demonstrated that although the BPA adsorption on freeze-thawing graphene hydrogel (FGH-60 m) decreased by 43% compared to in pure water, it still exhibited higher BPA adsorption than that of GH-60 m in lake water. This indicates that the close-cell structures retain significant potential for pollutants adsorption in practical environmental applications.