Structural Insights into Poly(Heptazine Imides): A Light-Storing Carbon Nitride Material for Dark Photocatalysis

Schlomberg, Hendrik; Kroeger, Julia; Savasci, Goekcen; Bette, Sebastian; Moudrakovski, Igor; Duppel, Viola; Podjaski, Filip; Siegel, Renee; Senker, Jürgen; Dinnebier, R. E.; Ochsenfeld, Christian und Lotsch, Bettina V. (2019): Structural Insights into Poly(Heptazine Imides): A Light-Storing Carbon Nitride Material for Dark Photocatalysis. In: Chemistry of Materials, Bd. 31, Nr. 18: S. 7478-7486

Abstract

Solving the structure of carbon nitrides has been a long-standing challenge due to the low crystallinity and complex structures observed within this class of earth-abundant photocatalysts. Herein, we report on two-dimensional layered potassium poly(heptazine imide) (K-PHI) and its proton-exchanged counterpart (H-PHI), obtained by ionothermal synthesis using a molecular precursor route. We present a comprehensive analysis of the in-plane and three-dimensional structure of PHI. Transmission electron microscopy and solid-state NMR spectroscopy, supported by quantum-chemical calculations, suggest a planar, imide-bridged heptazine backbone with trigonal symmetry in both K-PHI and H-PHI, whereas pair distribution function analyses and X-ray powder diffraction using recursive-like simulations of planar defects point to a structure-directing function of the pore content. While the out-of-plane structure of K-PHI exhibits a unidirectional layer offset, mediated by hydrated potassium ions, H-PHI is characterized by a high degree of stacking faults due to the weaker structure directing influence of pore water. Structure–property relationships in PHI reveal that a loss of in-plane coherence, materializing in smaller lateral platelet dimensions and increased terminal cyanamide groups, correlates with improved photocatalytic performance. Size-optimized H-PHI is highly active toward photocatalytic hydrogen evolution, with a rate of 3363 μmol/gh H2 placing it on par with the most active carbon nitrides. K- and H-PHI adopt a uniquely long-lived photoreduced polaronic state in which light-induced electrons are stored for more than 6 h in the dark and released upon addition of a Pt cocatalyst. This work highlights the importance of structure–property relationships in carbon nitrides for the rational design of highly active hydrogen evolution photocatalysts.

• Dokumententyp: Zeitschriftenartikel
• EU Funded Grant Agreement Number: 639233
• EU-Projekte: Horizon 2020 > ERC Grants > ERC Starting Grant > ERC Grant 639233: Fuel from sunlight: Covalent organic frameworks as integrated platforms for photocatalytic water splitting and CO2 reduction
• Publikationsform: Publisher's Version
• Fakultät: Chemie und Pharmazie > Department Chemie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 540 Chemie
• Sprache: Englisch