Tailoring the bandgap of N-rich graphitic carbon nitride for enhanced photocatalytic activity

Nitrogen - rich graphitic carbon nitride (Ng-C3N4) with improved photocatalytic activity was engineered using a facile post-annealing treatment of pristine g-C3N4 in N2 atmosphere. The thermal annealing did not modify the crystal structure, vibrational modes, or morphology of the N-rich g-C3N4 (Ng-C3N4). However, it decreased the crystallinity by broadening the dominant X-ray diffraction (XRD) peak and increased the surface area and mesoporous nature because of the formation of carbon vacancies. Diffuse reflectance spectroscopy indicated that the bandgap of the annealed Ng-C3N4 decreased from 2.82 to 2.77 eV compared to pristine g-C3N4. The increase of nitrogen content in the annealed Ng-C3N4 was quantified by X-ray photoelectron spectroscopy (XPS), which was also used to examine the formation of carbon vacancies. Photocurrent and electrochemical impedance spectroscopy measurements showed that the annealed Ng-C3N4 had higher light absorption capacity than the pristine g-C3N4. The photocatalytic performance of the samples was investigated for the degradation of crystal violet (CV) under ultra-violet light irradiation. The annealed Ng-C3N4 sample exhibited superior photodegradation of CV over pristine g-C3N4.