Synthesis of Ferrocene-Modified Carbon Nitride Photocatalysts by Surface Amidation Reaction for Phenol Synthesis

A polymeric Fc-CO-NH-C3N4 (Fc-CN) material was synthesized by amidation reaction of ferrocenecarboxylic acid (Fc-COOH) with NH2 groups on the surface of mesoporous graphitic carbon nitride (MCN). The properties of the as-synthesized samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV-Vis diffuse reflectance spectra, N-2 adsorption-desorption isotherm, photoluminescence spectroscopy, transmission electron microscopy, electron paramagnetic resonance, (photo) electrochemical measurement and X-ray photoelectron spectroscopy. The resultant catalysts were investigated as heterogeneous catalysts for the selective oxidation of benzene to phenol using H2O2 as a green oxidant under visible light irradiation. The results reveal that Fc-modified samples can not only extend the visible light absorption, but also accelerate the bulk-to-surface charge transfer and separation via surface dyadic structures, both of which are favorable for phenol production from benzene photocatalytic hydroxylation with H2O2. Under the optimal conditions, up to 16.9 % phenol yield (based on benzene) is obtained by Fc-CN/(1.5)-5 sample, and the corresponding Fe content is about 0.64 wt%. Furthermore, after the second run, no significant decrease of the activity (in term of TOF) and the selectivity is found in Fc-CN/(1.0)-5 sample. Combined with the experimental results and Fenton-chemistry, a possible photocatalytic reaction mechanism on the hydroxylation of benzene to phenol at neutral medium with visible light is proposed.