Fig. 1: Structural characterization of the nanocomposite catalysts.

a Scheme of catalyst fabrication. b–e TEM images and EDX elemental mappings of bulk Mn3O4 NPs and Mn3O4@nACNT. Representative HRTEM images of the bulk Mn3O4 NPs (f), and those confined in 120ACNT (g), 55ACNT (h), and 20ACNT (i). j Size-distribution histograms of Mn3O4 NPs in different catalysts. k XRD patterns of the catalysts.