Antimony Removal from Aqueous Solution Using Novel α-MnO₂ Nanofibers: Equilibrium, Kinetic, and Density Functional Theory Studies

Herein, we report the synthesis and characterization of a novel α-MnO 2 nanofibers (MO-2) prepared via morphological and phase transitions from δ-MnO 2 nanoparticles under hydrothermal reaction in the presence of graphene oxide (GO) for the first time. The MO-2 shows long, compact, and uniform nanofiber morphology. The adsorption properties of antimonite (Sb(III)) and antimonate (Sb(V)) on MO-2 were investigated using batch experiments of adsorption isotherms and kinetics. Experimental results show that the adsorption behavior of Sb on MO-2 is spontaneous, exothermic, and pH-dependent and follows the monolayer Langmiur isotherm model, pseudo-second-order kinetic model and external mass transfer model. MO-2 has maximum Sb(III) and Sb(V) adsorption capacities of 111.70 and 89.99 mg/g, respectively. Density functional theory (DFT) calculations indicate that both Sb(III) and Sb(V) have monodentate and bidentate complexes on the (110) facet. The adsorption energies ( E ad ) analysis demonstrates that the formed monodentate and bidentate complexes of Sb(III) (−2.31 and −2.70 eV, respectively) and Sb(V) (−2.17 and −2.85 eV, respectively) on the (110) facet are stable. And it can be confirmed that Sb(III) and Sb(V) are chemisorbed on the surface of MO-2 according to the analyses of partial density of state (PDOS) and Dubinin–Radushkevich (DR) isotherm model.