Sulfurized Graphene as Efficient Metal-Free Catalysts for Reduction of 4-Nitrophenol to 4-Aminophenol

The development of metal-free catalysts for hydrogenation reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) has been of great increasing scientific and industrial importance. Herein, we reported the preparation of sulfurized graphene (SG) nanomaterials by a well developed ball-milling method. The as-prepared SG nanomaterials were systematically characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared, and X-ray photoelectron spectroscopy. The SG exhibited flake-like morphology with average size of 100 nm, and the S doping (3.4 atom %) into the nanocarbon molecules results in asymmetry of electron density distribution, providing high catalytic performance for catalytic reduction of 4-NP to 4-AP by using NaBH4 as the reducer. The related catalytic mechanism and reaction path of the reduction were investigated. The effects of different initial 4-NP concentrations, initial reductant concentrations, catalyst dosages, and reaction temperatures were presented, which have not been reported so far. The thermodynamic parameters including activation enthalpy and entropy were determined.