Thermodynamic Equilibria in Carbon Nitride Photocatalyst Materials and Conditions for the Existence of Graphitic Carbon Nitride g-C3N4

Botari, Tiago; Huhn, William Paul; Lau, Vincent Wing-Hei; Lotsch, Bettina V. and Blum, Volker (2017): Thermodynamic Equilibria in Carbon Nitride Photocatalyst Materials and Conditions for the Existence of Graphitic Carbon Nitride g-C3N4. In: Chemistry of Materials, Vol. 29, No. 10: pp. 4445-4453

Abstract

We quantify the thermodynamic equilibrium conditions that govern the formation of crystalline heptazine-based carbon nitride materials, currently of enormous interest for photocatalytic applications including solar hydrogen evolution. Key phases studied include the monomeric phase melem, the 1D polymer melon, and the hypothetical hydrogen free 2D graphitic carbon nitride phase "g-C3N4". Our study is based on. density functional theory including van der Waals dispersion terms with different experimental conditions represented by the chemical potential of NH3. Graphitic carbon nitride is the subject of a vast number of studies, but its existence is still controversial. We show that typical conditions found in experiments pertain to the polymer melon (2D planes of 1D hydrogen-bonded polymer strands). In contrast, equilibrium synthesis of heptazine (h)-based g-h-C3N4 below its experimentally known decomposition temperature requires much less likely conditions, equivalent to low NH3 partial pressures around 1 Pa at 500 degrees C and around 10(3) Pa even at 700 degrees C. A recently reported synthesis of triazine (t)-based g-t-C3N4 in a salt melt is interpreted as a consequence of the altered local chemical environment of the C3N4 nanocrystallites.

• Item Type: Journal article
• EU Funded Grant Agreement Number: 639233
• EU Projects: 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
• Faculties: Chemistry and Pharmacy > Department of Chemistry
• Subjects: 500 Science > 540 Chemistry
• ISSN: 0897-4756
• Language: English