Preparation and Characterization of Polyacrylonitrile/Aluminum Oxide Nanofiber Adsorbent Modified with 2-Amino-3-Methyl-1-Hexanethiol for the Adsorption of Thorium (IV) Ion from Aqueous Solution

In this study, a novel polyacrylonitrile/aluminum oxide ($\mathrm{PAN}/\mathrm{Al}-{\mathrm{O}}_{\mathrm{NPs}}$) nanofiber adsorbent modified with 2-amino-3-methyl-1-hexanethiol (AMH) was synthesized by a combination of hydrothermal and electrospinning and evaluated as an adsorbent for removing thorium (IV) (${\mathrm{Th}}^{4+}$) ion from aqueous solution. The $\mathrm{PAN}/\mathrm{Al}-{\mathrm{O}}_{\mathrm{NPs}}/\mathrm{AMH}$ was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Brunauer–Emmett–Teller (BET) analysis. Response surface methodology (RSM) was used in the optimization of ${\mathrm{Th}}^{4+}$ adsorption for parameters such as pH, initial metal ion concentration (${\mathrm{Th}}^{4+}$ concentration), and contact time. Design-Expert 7 was used for modeling these three variables. Statistical measures validated the developed model ($R^2=0.9415$). In addition, the adsorption kinetics was well defined by the pseudo-second-order equation ($R^2=0.98$) whereas the adsorption isotherms were better fit by the Langmuir model ($R^2=0.95$). The adsorption capacity of $\mathrm{PAN}/\mathrm{Al}\text{-}{\mathrm{O}}_{\mathrm{NPs}}/\mathrm{AMH}$, $472\mathrm{mg}{\mathrm{Th}}^{4+}{\mathrm{g}}^{-1}$ composite, led to 98% removal at 25°C. Moreover, thermodynamic parameters were determined which showed the endothermic nature of the reactions. The loaded ${\mathrm{Th}}^{4+}$ can be easily regenerated with ${\mathrm{HNO}}_3/\mathrm{HCl}$. Also, the desorption level of ${\mathrm{Th}}^{4+}$ by the $\mathrm{PAN}/\mathrm{Al}\text{-}{\mathrm{O}}_{\mathrm{NPs}}/\mathrm{AMH}$ using $0.4\mathrm{M}{\mathrm{HNO}}_3/0.2\mathrm{M}\mathrm{HCl}$ was more than 92%.