Construction of core-shell mesoporous carbon nanofiber@nickel cobaltite nanostructures as highly efficient catalysts towards 4-nitrophenol reduction

Abstract We herein report small sized nickel cobaltite (NiCo 2 O 4 ) nanosheets (103–144 nm × 71–97 nm) firmly coated on mesoporous carbon nanofibers (MCNFs), as active and stable catalysts for degradation of 4-nitrophenol in sewage with NaBH 4 as the reductant. MCNFs with surface O-functionalities were first constructed by morphology-conserved transformation of zinc-trimesic acid fibers, which provide scaffolds to anchor trisodium citrate-induced Ni-Co hydroxide nanosheets. Upon calcination, the resultant core-shell MCNF@NiCo 2 O 4 nanostructures were fabricated and characterized by SEM, TEM, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption/desorption techniques. The anchored NiCo 2 O 4 nanosheets were dense (75 wt%) but well-dispersed on the surface of MCNF (pore size 4.0 nm), and proved to be highly active and stable towards the reduction of 4-nitrophenol to 4-aminophenol. It showed a large activity factor of 2.53 s −1  g −1 , exceeding most transition metal oxide catalysts, and MCNF@NiCo 2 O 4 could be cycled at least 20 times without obvious loss of activity. Temperature-programmed desorption and reduction by hydrogen (H 2 -TPD and H 2 -TPR) studies showed that, the metal oxide dispersion and thereby the amount of H 2 adsorbed were enhanced, and the interfacial interaction was also strengthened. These should be responsible for the excellent activity and stability of MCNF@NiCo 2 O 4 towards 4-nitrophenol reduction.