Sustainable and green synthesis of C- and N-doped nanoporous g-C₃N₄: powerful sunlight-responsive photocatalysts for aerobic oxidation of toluene

Choosing green alternatives for chemical templates and doping agents is still challenging for scientists. In this study, for the first time, N- and C-doped graphitic carbon nitrides were synthesized via a green, sustainable, and facile strategy using a naturally abundant waste material, pomegranate peels. Based on the findings, the role of pomegranate peels was not only limited to bio-templates but they also played a selective role as a doping agent in a way that an increase in its loading led to a shift from nitrogen-doped to carbon-doped graphitic carbon nitride. Comparing with the pristine g-C3N4 revealed that the presence of a bio-template elegantly altered the physical and optical properties of the prepared materials. A comprehensive analysis including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption-desorption, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy was employed to characterize the as-prepared materials. The photocatalytic potential of the synthesized graphitic carbon nitrides was investigated in the aerobic oxidation of toluene under sunlight irradiation. In this line, N-doped g-C3N4 with 0.05 wt% loading of bio-template, benefiting from the high surface area and efficient charge separation of photo-generated electron-hole pairs, was found to be the best photocatalyst, furnishing the desired product in 91% yield. Moreover, the metal-free photocatalyst could be recovered 6 times while maintaining its activity. These findings may open up a new way to synthesize metal-free photocatalysts to promote organic transformations in a more environmentally-friendly fashion.