Enhanced photocatalytic H2 evolution and biological stimulation via the calcination of bulk g-C3N4 under different gases

Amid the pursuit of renewable energy, photocatalytic H₂ evolution (PHE) and biosynthetic processes gained attention. Bulk g-C₃N₄ (CN) was calcined under the atmosphere and various gases (air, CO₂, N₂, and Ar) to achieve ultra-thin nanosheets. Using greenhouse gas CO₂ for the calcination (CN–CO₂) results in a greater PHE rate than in the atmosphere and air, similar to inert gases N₂ and Ar. Under visible light, CN–CO₂ produced H₂ 2.6 times faster than CN. Therefore, CN–CO₂ was chosen to promote polyhydroxybutyrate (PHB) production by Cupriavidus necator H16 in hybrid photosynthetic system. The heterotrophic PHB production was increased to 9.14 g/L, which was 1.9 times higher than without the photocatalyst (4.93 g/L), and 1.1 times more than with CN (8.11 g/L). The autotrophic PHB production was also enhanced by adding CN–CO₂. In summary, the dual benefits of PHE and biological stimulation were achieved by calcining g-C₃N₄ in CO₂.