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 (NiCo2O4) 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 NaBH4 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@NiCo2O4 nanostructures were fabricated and characterized by SEM, TEM, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and N2 adsorption/desorption techniques. The anchored NiCo2O4 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@NiCo2O4 could be cycled at least 20 times without obvious loss of activity. Temperature-programmed desorption and reduction by hydrogen (H2-TPD and H2-TPR) studies showed that, the metal oxide dispersion and thereby the amount of H2 adsorbed were enhanced, and the interfacial interaction was also strengthened. These should be responsible for the excellent activity and stability of MCNF@NiCo2O4 towards 4-nitrophenol reduction.