Research investigations into carbon nitrides have recently surged because of their newly discovered chemical and physical properties that make them potentially useful as molecular filters, as photocatalysts, and for a growing list of reactions such as involving hydroxylation or transesterification. Given the growing potential applications, many of the current studies suffer characterizing the active material due to the highly amorphous character of most carbon nitride materials. Which readily form many different polymorphs which by FTIR, PXRD, and PDF can be difficult to discern between. This makes the elucidation of clear structure-property relationships difficult to establish. The preparation and characterization of a well-defined crystalline structure is the key to understanding the basic properties of this material. The use of flux synthesis methods has been shown to result in more enhanced crystalline carbon nitrides with well-defined structures. In this work is described an in-depth investigation and optimization of the synthesis of a layered carbon nitride, i.e., poly(triazine-imide) (PTI-LiCl; C6N9H2Li2Cl), with high crystallinity and decrease in defects. This is achieved by limiting exposure to water or oxygen during the reaction, decreasing reaction temperature, and using a LiCl/KCl eutectic salt flux. Its characterization has included a combination of powder X-ray diffraction, spectroscopic and microscopic techniques. Additional synthetic work has focused on the metal-cation exchange of lithium in PTI-LiCl with other divalent metal cations, e.g., from Cr(II) to Zn(II) cations. These exchanged products show subtle changes in crystalline structure and optical properties as a function of the metal cation type and concentration. A high crystallinity is maintained with divalent cations exchanged for lithium with a concentration as high as one metal per formula unit, i.e., C6N9H2MCl (M = Cr to Zn). Additionally, their structures have been characterized using the same experimental techniques as for PTI-LiCl and found to retain the same underlying carbon nitride network.

Synthesis and characterization of highly crystalline carbon nitrides and the novel use of them as a 3D polymeric ligand

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