Graphitic‑carbon nitride based mixed-phase bismuth nanostructures: Tuned optical and structural properties with boosted photocatalytic performance for wastewater decontamination under visible-light irradiation

To enhance the activities of advanced semiconductor photocatalysts, the charge carriers must be separated effectively. One strategy for achieving this is the use of heterogeneous structures, which can be prepared by hydrothermal synthesis and post-synthetic thermal and ultrasonic treatment. Herein, we report a mixed-phase composite of basic bismuth nitrate/pentabismuth heptaoxide nitrate (PC) prepared by hydrothermal synthesis under basic conditions and post-synthetic thermal treatment. In addition, sulfur-doped-graphitic carbon nitride (S-g-C₃N₄) was prepared and combined with PC in different ratios, denoted as PC-1, PC-2, and PC-3, using sonication-assisted treatment. The characterization of these catalysts confirmed the formation of mixed basic bismuth nitrate/pentabismuth heptaoxide nitrate phases and the composite nanostructure. The developed nanostructure showed interesting morphological features, for example, layered sheets of S-g-C₃N₄. The prepared PCs were tested for their visible light responsiveness for the photocatalytic degradation of a representative organic dye (Rhodamine B). We found that the modified photocatalysts showed superior activity to that of pristine PC. The optimal photocatalyst (PC-3) was also used to degrade methylene blue and Congo red, achieving 99% degradation. Thus, we present not only an efficient photocatalyst but also insights into the post-synthetic modification of basic bismuth nitrate/pentabismuth heptaoxide nitrate with stable carbon-based nanostructures.