Removal of Aqueous Phenol by Adsorption and Oxidation with Doped Hydrophobic Cryptomelane-Type Manganese Oxide (K-OMS-2) Nanofibers

Molecular adsorption and oxidation at manganese oxide/liquid interfaces has attracted increased interest due to its importance in the development of heterogeneous catalysts, microbial fuel cells, and selective adsorption materials. Here we report the adsorption and oxidation of phenolic compounds on Cu2+, Co3+, and Ce4+ doped K-OMS-2 nanofibers. Different metal ion doped K-OMS-2 catalysts show distinct adsorption and oxidation ability. The structure and compositions of doped K-OMS-2 catalysts were characterized by X-ray diffraction and atomic absorption analyses. The relationships of catalyst structure-catalytic properties were discussed. The adsorbed polymeric nanospheres on doped K-OMS-2 nanofibers were investigated by field emission scanning electron microscopy, Fourier transform infared spectroscopy, transmission electron microscopy, and energy dispersive X-ray analyses. These nanospheres were totally oxidized to CO2 in oxygen or air at 553-603 K catalyzed by doped and undoped K-OMS-2 itself. OMS-2 was regenerated with air or oxygen. The chemisorption and oxidation of phenol in an anaerobic environment (N-2) demonstrate that lattice oxygen of cryptomelane is involved in these processes. Free-radical mechanisms are proposed for the oxidation of phenol in O-2 and for the formation of phenolic nanospheres. Compared with undoped K-OMS-2, metal ion doped K-OMS-2 shows higher adsorption capacity of phenolic compounds and higher phenol removal rate.