Abstract
In this study, two kinds of composites with the structure of graphene oxide (GO) sheets wrapped magnetic nanoparticles were investigated on their regeneration. The composites have a similar core-shell structure, but the interactions between the core and shell are quite different, which are electrostatic and covalent. They were characterized by scanning/transmission electron microscopy, power X-ray diffraction, and vibrating sample magnetometer analysis. Their morphologies and structures of the samples had been revealed using methylene blue and Pb(II) as adsorbates during regeneration. The results showed that the composites with covalent bonding interaction could maintain a stable core-shell structure and present a good regeneration performance for adsorption-desorption of methylene blue and Pb(II). The composites with electrostatic interaction could approximately preserve its core-shell structure and could be recyclable for adsorption-desorption of methylene blue, however, they would disintegrate its core-shell structure during adsorption/desorption of Pb(II), thus greatly decreasing their regeneration performance. The regeneration mechanisms of the composites were analyzed, which could provide a useful theoretical guide to design the GO sheets wrapped magnetic nanoparticles composites.
Highlights
Due to the unique structure and excellent characteristics, graphene and its derivatives have attracted more and more interests in the scientific community (Geim and Novoselov, 2007; Smith and Rodrigues, 2015; Nandhanapalli et al, 2019)
From the Scanning electron microscopy (SEM) image (Figure 1a), it could be clearly observed that the Fe3O4 NPs or Fe3O4 NP aggregations are tightly wrapped by the silk-like graphene oxide (GO) sheets
The good structure of the Fe3O4@GO-e sample could be ascribed to the utilization of Fe3O4 NPs with large surface area, rich -OH groups on the surface introduced by SiO2 coating, and PDDA with positive charges which could strongly attract the negative GO sheets
Summary
Due to the unique structure and excellent characteristics, graphene and its derivatives have attracted more and more interests in the scientific community (Geim and Novoselov, 2007; Smith and Rodrigues, 2015; Nandhanapalli et al, 2019). Fe3O4 NPs have been successfully encapsulated with GO sheets though electrostatic interaction and covalent bonding, and both of the GO-based composites exhibited excellent adsorption toward contaminants in solution (Hu et al, 2017, 2020). Our investigations are focused on the regeneration processes and the mechanisms of two kinds of Fe3O4@GO composites, which had been successfully synthesized in our previous study. Both of the Fe3O4@GO samples have similar a core-shell structure, in which GO sheets are tightly connected with magnetic NPs, the interactions linking the core and shell are quite different, which are electrostatic and covalent, respectively. For Pb(II) desorption, the regeneration of the sample was performed by soaking it in the presence of 0.01 M of HCl under ultrasonication for 30 min
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