Structural fine-tuning of thermal vapour condensed graphitic carbon nitride photocatalysts for enhanced activities

Abstract Graphitic carbon nitride (g-C 3 N 4 ) is a visible-light-active, metal-free semiconductor well-known for its stability, low cost, and suitable band gap for photocatalytic applications. Herein, bulk g-C 3 N 4 is synthesized via the thermal vapour condensation method by systematically varying temperature and duration, resulting in a structural modulation. X-ray diffraction reveals that a higher pyrolysis temperature of precursor melamine beyond 550 °C improves the crystallinity of g-C 3 N 4 , whereas prolonged heating at 550 °C reduces it. The UV–Vis and photoluminescence spectroscopies indicate that the reduced crystallinity and increased defect density enhance its visible light absorption and charge separation. Among the samples, g-C 3 N 4 synthesized at 550 °C for 6 h shows the best performance, achieving 99% methylene blue degradation within 90 min in a first-order kinetics. This superior activity is attributed to its partially amorphous nature, lower conduction band edge, and higher density of defect sites. The structural modulation of its effective bandgap shows a bowing behaviour as corroborated by empirical law as well as density functional theory-based estimations.