Fluorescent magnetic chitosan-based hydrogel incorporating Amino-Functionalized Fe3O4 and cellulose nanofibers modified with carbon dots for adsorption and detection of Cr (VI)

A fluorescent magnetic chitosan-based hydrogel (FMCH) incorporating Amino-Functionalized Fe3O4 nanoparticles (AF-Fe3O4 NPs) and cellulose nanofibers (CNFs) modified with carbon dots (CDs) was successfully synthesized via the crosslinking method. The FMCH was used as an adsorbent for removing Cr (VI) from aqueous solution and it exhibited encouraging adsorption performance for Cr (VI). The composition and structure of FMCH were characterized and its Cr (VI) sorption performance was evaluated. The results demonstrated that this hydrogel had 3D porous structures and a higher adsorption ability of Cr (VI). The maximum adsorption capacity of this hydrogel was measured to be 212.1 mg/g at 25 °C and pH 5.0. The performance of the FMCH in Cr (VI) adsorption was evaluated through a contrast experiment with the normal chitosan hydrogel without CNFs and AF-Fe3O4 NPs. The effect of the initial concentration of Cr (VI) and contact time were also evaluated. The results confirmed that the adsorption isotherm was according to the Freundlich model, and the adsorption kinetics followed the pseudo-second-order model. Furthermore, as a fluorescent sensor for Cr (VI), the detection sensitivity and selectivity were examined. The quantitative detection of Cr (VI) was achieved in the linear range of 20–800 mg/L. Meantime, the mechanism for highly efficient adsorption and detection of FMCH for Cr (VI) was analysed by FTIR and XPS. These results showed that the excellent sorption and sensing abilities of Cr (VI) may be mainly attributed to the porous structures which provided many active sites and ion transport channels and the additional AF-Fe3O4 NPs and CNFs modified with CDs improving the sorption ability of Cr (VI) and providing a rapid visual response to Cr (VI). It showed that the FMCH can be widely used for Cr (VI) detection and removal in wastewater.