Covalently linked porphyrin-graphene oxide nanocomposite: synthesis, characterization and catalytic activity

The work presented in this paper illustrates a synthetic endeavour devoted to the design and modification of an important donor–acceptor porphyrin-graphene oxide (Por-GO) nanocomposite. The resulting novel Por-GO architecture was thoroughly characterized with respect to their spectroscopic and catalytic properties. The functionalization of GO is mediated by an axial ligand on the respective metalloporphyrin having an amide linker between the graphene oxide and the porphyrin moiety. The successful functionalization of GO with axial ligand modified Ni(II)-porphyrin forming covalently linked Por-GO nanocomposite with good dispersion stability in organic solvents was confirmed by various spectroscopic techniques viz., Fourier Transform Infrared Spectroscopy, Ultraviolet Visible Absorption Spectroscopy, Powder X-ray Diffraction, Scanning Electron Microscopy and High-resolution Transmission Electron Microscopy. Finally, the catalytic reduction of 4-Nitrophenol to 4-Aminophenol by sodium borohydride (NaBH4−) as reductant and synthesized nanocomposite as a catalyst was monitored spectrophotometrically. The aqueous solution of 4-Nitrophenol is yellow in color and shows intense absorption in the visible range. The completion of reduction reaction was confirmed by the change of yellow color to completely colourless solution corresponding to the reduced product (4-Aminophenol). Furthermore, the complete disappearance of the absorption peak related to 4-Nitrophenolate and emergence of a new peak exhibiting large hypsochromic shift corroborate the formation of 4-Aminophenol. The whole process of reduction completes within an hour as evident by time-dependent UV–Vis spectra. The Por-GO nanocomposite exhibit excellent catalytic activity.