Designing carbon nitride interfaces: S-doped and NH₃-concentration influence cases

Advancing renewable technologies requires visible-light-active, stable, and earth-abundant semiconductors capable of harvesting photons, transporting charge carriers, and driving catalytic reactions.[1,2] Carbon nitrides (CNs) are promising candidates, easily synthesized from low-cost, nitrogen-rich precursors via thermal polycondensation in molten salts. They are metal-free, chemically benign, and thermally stable up to 600 °C. As n-type semiconductors with a 2.7 eV band gap and suitable band-edge positions (–0.4 V and 2.3 V vs NHE), CNs can efficiently mediate redox reactions.[3]

This talk focuses on two strategies to tailor CN performance: (i) anionic doping through precursor pre-organization and co-polymerization and (ii) atmosphere-controlled solid-state polycondensation.

The first approach (Fig. 1a) employed purpald, a novel sulfur-containing triazole derivative, co-condensed with melamine to form hybrid S-doped CNs. These materials showed improved optical and electronic properties, achieving up to 84 ± 3% benzylamine-to-imine conversion under green light (535 nm) over 48 h, due to extended absorption (~700 nm), high S content, and defect-induced intraband states. Structural analyses (XPS, TEM, EELS, elemental) confirmed uniform S incorporation.

The second approach (Fig. 1b) enables structural/crystallinity tuning by varying NH₃/Ar ratios in a continuous-flow furnace, influencing nucleation, condensation, amines ratio, and chain growth.[4] CN hybrids synthesized under 30–100% NH₃ exhibited similar band gaps (2.9 eV) and C/N ratios (0.57), but increased NH₃ concentration enhanced surface area, crystallinity, and pore volume. The highest photocatalytic and photoelectrocatalytic H₂ evolution occurred for intermediate NH₃ ratios (CN_0.5-0.7), highlighting the role of morphological variations and challenging the conventional correlation between crystallinity and activity.

Together, these findings advance defect- and atmosphere-engineered CN photocatalysts with extended visible-light activity for solar energy conversion and storage.

References
[1]Mark Isaacs, Julio Garcia-Navarro, Wee-Jun Ong, Pablo Jiménez-Calvo, Global Challenges, 2022, 7, 2200165.

[2]Pablo Jiménez-Calvo. Materials Today Catalysis, 2024, 4, 100040

[3]Gabriel Diab, Izadora F. Reis, Chong Wang, Diandra Barreto, Oleksandr Savateev, Ivo F. Teixeira, Pablo Jiménez-Calvo. Advanced Functional Materials, 2025, 2501393

[4]Maria Jerigova, Yevheniia Markushyna, Ivo F. Texeira, Bolortuya Badamdorj, Mark Isaacs, Daniel Cruz, Iver Lauerman, Miguel Ángel Muñoz-Márquez, Nadezda V. Tarakina, Nieves Lopez Salas, Oleksandr Savateev, Pablo Jimenéz-Calvo, Advanced Science, 2023, 10, 2300099