Efficient removal of fluorine by carbon fiber supported Mg-Fe binary metal oxide composite adsorbent and mechanism analysis based on DFT

Improving the adsorption capacity and efficient separation of fluorine removal adsorbents will greatly enhance their cost-performance in applications. In order to explore the excellent performance of fluoride removal adsorbents, in this work, MgO, Fe2O3, and Fe3O4 nanoparticles were loaded onto carbon fiber by microwave pyrolysis to prepare a magnetic composite adsorbent material (MgO/Fe2O3/Fe3O4/CF) for fluoride removal. To verify the payload of metal oxide on the carbon foam, the adsorbent was thoroughly characterized. In application, the adsorption process is consistent with the pseudo-second-order kinetic model and Langmuir isotherm model, and the highest adsorption capacity reached 249.0 mg/g. Such a high adsorption capacity is rare among the complex adsorbents reported in the past. In addition, a possible mechanism was proposed by the analysis of EDS, XRD, FTIR, XPS, and water chemical equilibrium parameters. The reactivity, adsorption energy between F- and metal oxides, and interaction configurations of F- with hydrated ions were calculated using Density Functional Theory (DFT). Moreover, the Gibbs free energy change (Delta G) of ion exchange reactions between anions (OH-, Br- , Cl-, CO32-, NO3-, SO42-, HCO3-, and PO43-) and different forms of fluorine in solution was calculated to express the inhibitory behavior. Finally, the adsorbent can be separated efficiently from the water by means of an applied magnetic field, and then it can be recycled. In summary, the research content in this paper not only discusses an excellent fluorine removal material but also makes up for the partial absence of the influencing factors in the adsorption mechanisms of MgO and Fe2O3.