Invited paperRapid synthesis of g-C3N4 spheres using microwave-assisted solvothermal method for enhanced photocatalytic activity

Graphitic carbon nitride (g-C3N4), comprising tri-s-triazine (C6N7) units, is a promising visible-light-active photocatalyst and is generally synthesized using thermal condensation. This study reports a time-saving microwave-assisted solvothermal synthesis (MW) in which powders were obtained at temperatures as low as 180 °C within 60-120 min. Images obtained using scanning electron microscopy and transmission electron microscopy demonstrated that the MW g-C3N4 particles had a uniform microspheric shape, whereas g-C3N4 prepared with conventional thermal condensation (TC) and solvothermal (ST) approaches exhibited plate-like layered structures with buckles on their surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicated that TC g-C3N4 had terminal NH2 groups on the periphery of its tri-s-triazine units, whereas some cyano moieties were present on MW and ST g-C3N4. In a photocatalytic test, MW g-C3N4 was discovered to have enhanced photocatalytic activity in the degradation of methyl orange dye and phenol solution under visible light irradiation, which can be ascribed to its reduced charge recombination and increased light harvesting in the visible region, as evidenced by UV-vis and photoluminescence spectroscopy. The terminal NH2 groups attached to TC g-C3N4 may have consumed the photoinduced charges, thus reducing the photocatalytic activity and increasing recombination of the sample. The facile and time-saving microwave-assisted solvothermal method presented herein can thus be used for the synthesis of visible-light-active g-C3N4, which has potential photocatalysis applications.

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