From Heptazines to Triazines – On the Formation of Poly(triazine imide)

Abstract

Poly(triazine imide), a 2D extended carbon nitride network compound that is obtained from ionothermal synthesis in LiCl/KCl or LiBr/KBr salt melt has been known for over a decade. We now have investigated the formation process of this material starting from various triazine‐ and heptazine‐based precursors as well as the differences between ionothermal and conventional synthesis via thermal condensation. Independent of chosen starting material, melem (triamino‐s‐heptazine) is initially formed from the starting material as the imminent precursor to poly(triazine imide). We elucidate the impact of various different carbon nitride precursor compounds on the formation process, propose a mechanism for the back reaction of heptazines to triazines, and rationalize the occurring processes.

Polymer photocatalysts for solar-to-chemical energy conversion

“…65,75,76 Here, the salt melt simultaneously acts as a high-temperature flux and the constituent ions as structure directing agents, leading to a higher degree of condensation and significantly enhanced structural perfection. Two members of this class of carbon nitrides have been structurally characterized: lithium halide intercalated poly(triazine imide) (PTI/Li + X  ), 75,[77][78][79][80] and poly(heptazine imide) (M-PHI) where M is either a proton or metal counter ion, 76,[81][82][83][84] both of which consist of imide-bridged triazine or heptazine building units forming a graphite-like two-dimensional in-plane structure with regular structural voids (Figure 3b). The crystalline sheets are then stacked in the third direction with the stacking polytype depending on the pore content.…”

Emerging Concepts in Carbon Nitride Organic Photocatalysis

“…Depending on the preparation method, PTI/Li + Cl − have a band gap of 2.8‐3.2 eV, [96a,c,e,f] while the position of VB and CB have not yet been determined [104]…”

Ionic Carbon Nitrides in Solar Hydrogen Production and Organic Synthesis: Exciting Chemistry and Economic Advantages

“…Using the same organic precursor, but selecting different salts or salts mixtures, alkali metal doped covalent carbon nitrides, PHI and PTI may be synthesized. Thus Na, K and Cs based salts give metal PHIs, while using Li salts results in formation of intercalation compound – crystalline layered poly(triazine imide) (PTI) . Secondly, excess of alkali metal salt is prerequisite for PHI formation, while heating of graphitic carbon nitride or cyanamide with only few weight percent of alkali metal hydroxide gives alkali metal doped covalent carbon nitride .…”