Enhanced Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over g-C3N4 Quantum Dots-Modified Fe-SBA-15 Catalysts: Synergistic Effect Among Fe Species, g-C3N4 QDs, and Porous Structure

g-C3N4 quantum dots (QDs) attract considerable attention due to its remarkable applications in various fields such as catalysis, ion detection, and biosensors. Herein, the inner surface of the hexagon channels of Fe-SBA-15 was adorned by g-C3N4 QDs to enhance direct hydroxylation of benzene with H2O2 to afford phenol. The crystal texture, porous properties, inner structure, morphology, elemental distribution, chemical composites, and bonding energy of the synthesized CN-QDs/Fe-SBA-15 were thoroughly analyzed and characterized using X-ray diffraction, N-2 adsorption-desorption, transmission electron microscopy (TEM), scanning electron microscopy-energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, high-angle annular dark-field scanning TEM, X-ray photoelectron spectroscopy, and UV-vis and Fourier-transform infrared spectroscopies. The catalytic performance of the synthesized g-C3N4 QD-decorated Fe-SBA-15 was explored for one-step direct oxidation of benzene, with H2O2 as a green oxidant to obtain phenol. The structural characterization and catalytic investigation revealed that benzene molecules were adsorbed on the surface of CN-QDs by noncovalent interactions and activated by the terminal groups, that is, N-defects/C-OH present on the edges of CN-QDs. Then, the activated benzene was attacked by the hydroxyl radical generated by iron-peroxo-capturing hydrogen ion to produce phenol. The mesoporous structure of Fe-SBA-15 not only deals with the stability and aggregation of g-C3N4 QDs but also ensures the uniform dispersion of Fe species on the inner surface of the channel. The maximum yield of phenol obtained was 41.2% in this catalytic system, which is crucially dependent on the synergic effect between g-C3N4 QDs and Fe-SBA-15.