Formation mechanism of a ternary nanohybrid based on magnetite-chitosan-graphene oxide according to HSAB theory

Abstract

Magnetic nanohybrids containing chitosan (CS) and/or graphene have promising applications in environmental remediation. In this study, a ternary nanohybrid based on magnetite (M)-CS-graphene oxide (GO) (MCSGO) was prepared in a facile manner via simultaneous reduction–precipitation at room temperature. The as-prepared nanohybrid was characterized by field-emission scanning electron microscopy/energy dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller/Barrett–Joyner–Halenda analysis, thermogravimetric–differential thermal analysis, and vibrating sample magnetometry. Most importantly, the mechanism associated with the formation of MCSGO was determined using hard-soft acid-base (HSAB) theory and spectroscopic analyses. HSAB theory predicted the following dominant interactions in MCSGO based on electron transfer calculations and energy lowering between the couplet components: (1) CS-Fe3O4: NH2→Fe(III); (2) GO-Fe3O4: Ar-O-Ar→Fe(III); and (3) GO-CS: O(Ar-OH)→-OH (→ denotes the direction of electron flow and Ar denotes the aromatic ring). The CS-Fe3O4 and GO-Fe3O4 interactions were much stronger than that for GO-CS. The predictions obtained by HSAB theory were supported by X-ray photoelectron spectroscopy, Fourier transformation infrared spectroscopy, ultraviolet–visible spectra, and fluorescent spectra. According to HSAB theory and spectroscopic analyses, a mechanism was proposed for the formation of MCSGO based on electron transfer-induced energy lowering. In addition, MCSGO still adsorbed 199.41 mg g−1 and 193.96 mg g−1 of Hg(II) and Zn(II), respectively, after six consecutive cycles, thereby demonstrating its favorable removal efficiency. The results obtained in this study may facilitate the development of efficient adsorbents based on the MCSGO architecture for environmental remediation.