Defect-Engineered Bismuth Doping in Graphitic Carbon Nitride for High-Efficiency Solar Photocatalysis

Abstract

Bismuth-doped graphitic carbon nitride (Bi-g-C3N4) photocatalysts were synthesized via a solid-state thermal method, and the influence of Bi loading (2–10 wt %) on their structural, textural, optical, electrochemical, and photocatalytic properties was systematically investigated. Bi incorporation induced a porous morphology and localized structural modification while preserving the intrinsic heptazine framework of g-C3N4. Brunauer–Emmett–Teller (BET) analysis revealed enhanced surface area and pore development, while UV–Vis spectroscopy indicated a pronounced red shift in optical absorption with a reduced apparent optical transition energy. Electrochemical impedance spectroscopy (EIS) demonstrated a substantially lower charge-transfer resistance for the optimized BiCN-10% sample, indicating improved interfacial electron transport. Under simulated solar irradiation, BiCN-10% achieved approximately 97.6% Rhodamine B degradation within 75 min with an apparent rate constant of 2.977 h–1, representing a 3.8-fold enhancement over pristine g-C3N4. Reactive-species trapping experiments identified photogenerated electrons as the dominant contributors to the degradation process. The enhanced photocatalytic performance is attributed to the synergistic effects of improved visible-light harvesting, enhanced charge-transfer characteristics, and Bi-induced structural and morphological modifications. Although complementary spectroscopic studies are required to fully elucidate the electronic structure, the present results demonstrate that controlled Bi incorporation is an effective strategy for improving the solar-driven photocatalytic performance of g-C3N4-based materials for environmental remediation.