Annealing of acetylene containing cyclotriphosphazene to generate nitrogen- and phosphorus-containing layered graphitic materials

Abstract

Carbon-based materials are important components of organic electronics, energy-harvesting devices, batteries, and sensors. Among the methods developed to produce well-defined carbon-rich materials, the pyrolysis of carbon precursors (CO₂, ethanol, CO, etc.) continues to be a common production method due to its scalability and efficiency. However, physical methods often require high temperatures (>800 C) and can lead to the formation of complex mixtures that make the isolation and purification of the desired material difficult/costly. New methods to access well-defined carbon-rich materials from self-assembled precursors have emerged as a viable approach to well-defined carbon materials but the scalability and control of these hybrid approaches remain limited. Here, we report a relatively low-cost synthesis for nitrogen- and phosphorus-containing layered graphitic materials through the simultaneous thermally driven ring-opening polymerization of cyclotriphosphazenes and crosslinking of their terminal acetylene groups. Hard and mechanically strong insoluble graphene-like films are generated at temperatures as low as 350 °C. The formation of nitrogen- and phosphorus-containing layered graphitic materials was confirmed by Raman spectroscopy. Also typical for graphene-like structures is the formation of flake-like nanosheets observed by electron microscopy. Force-curve microscopy was also used to confirm a significant increase in the hardness of the nitrogen- and phosphorus-containing layered graphitic materials films when compared to the cyclotriphosphazene precursor. This milder, additive-free method to prepare and access thin films of carbon-rich materials represents a novel tool for the design of new carbon materials and opens new avenues for these materials in emerging applications, facilitating their integration into next generation technologies.