Unlocking new ionic carbon nitrides from ionic cocrystals for solar- driven fuel synthesis Anna Lo Presti, Christian Mark Pelicano, Markus Antonietti Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Potsdam 14476, Germany Solar-driven catalysis using particulate semiconductors represents a promising approach for the sustainable generation of valuable fuels. Poly(heptazine imide) (PHI), a new class of crystalline ionic carbon nitrides (CNs), has emerged as a standout photocatalyst due to its efficient visible-light absorption and optimal energy level alignment, which satisfy the requirements for driving hydrogen peroxide (H 2 O 2 ) evolution. PHIs can be synthesized from N-rich compounds either using alkali metal chloride eutectic melts or through solid-state reactions involving alkali metal chlorides. 1, 2 They can also be prepared from pre-condensed covalent CNs by post-treatment with alkali metal salts. 3 Thus, the ionothermal approach utilizing eutectic salt melts plays a vital role in most of these routes, with an excess of alkali metal salts being crucial for PHI formation. For instance, a 1:10 precursor-to-salt ratio has been found necessary to maintain liquidity and achieve sufficient crystallinity in the final products. Herein, we present an innovative strategy to unlock new ionic CNs by annealing ionic cocrystals (ICCs). These ICCs are formed through the solid-state association of neutral organic molecules with inorganic salts, particularly alkali and alkaline earth halides. 4, 5 We have identified a new PHI variant by pyrolizing a urea:LiCl:NaCl cocrystal. This variant contains substantial amount of Li, which is unusual for benchmark KPHI and NaPHI catalysts, where the amount of lithium is usually neglicibe. The optimal catalyst shows significantly improved H 2 O 2 quantum efficiency (at 410 nm excitation wavelength)—up to threefold higher than conventional NaPHI. We are currently examining how the presence of Li affects the PHI framework. Additionally, we are exploring other ICCs derived from N-rich compounds and assessing their potential for diverse photocatalytic applications. Building on these insights, the unique interactions within ICCs present a promising pathway for creating ionic carbon nitrides (CNs) with innovative material properties and enhanced photocatalytic performance. References 1. M. Pelicano, J. Li, M. Cabrero-Antonino, I. F. Silva, L. Peng, N. V. Tarakina, S. Navalón, H. García, M. Antonietti, Journal of Materials Chemistry A 2024, 12, 475-482. 2. Z. Chen, A. Savateev, S. Pronkin, V. Papaefthimiou, C. Wolff, M. G. Willinger, E. Willinger, D. Neher, M. Antonietti, D. Dontsova, Adv Mater 2017, 29. 3. V. Shvalagin, N. Tarakina, B. Badamdorj, I. M. Lahrsen, E. Bargiacchi, A. Bardow, Z. Deng, W. Wang, D. L. Phillips, Z. Guo, G. Zhang, J. Tang, O. Savateev, ACS Catal 2024, 14, 14836-14854. 4. Braga, D., Grepioni, F., Lampronti, G. I., Maini, L., & Turrina, A., Crystal growth & design, 2011, 11(12), 5621-5627. 5. Sarkar, N., Mitra, J., Vittengl, M., Berndt, L., & Aakeröy, C. B., CrystEngComm, 2020, 22(41), 6776–6779.
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