Stability carbon nitrides

A. J. Stevens, The stability of carbon nitride materials, Harvard University, Ph.D. Thesis, 1998. 

Alkali oxides are thermodynamically stable up to very high temperatures, and even hydrides have saline character and considerable stability. Lithium nitride is a compound which can be isolated from the solution in the metal in crystalline form. Dissolved oxides have the ability to react with transition metal oxides to form complex oxides, or with hydrogen to form hydroxides of the heavier alkali metals. Lithium cyanamide is formed by means of the reaction between nitrogen and carbon dissolved in the molten metal. The reaction product in liquid sodium is sodium cyanide. 

Alkali metals are principally similar in their ability to form compounds with non-metals and to dissolve these compounds. There are, however, some differences between light alkali metals, lithium and sodium, and their heavier homologues, potassium, rubidium, and cesium. The extreme position of lithium is due to its very high affinity to form salts and to its similarity to the alkaline earth metals. Lithium oxide and hydride are the alkali compounds of highest stability. Lithium nitride is the only stable compound of this class, and probably, lithium acetylide is also the only stable alkali carbon compound, which occurs in contact with excess alkali metal. 

Improvements in the synthesis techniques and analytic equipment may help to solve these problems. It also has to be mentioned here that the stability of some of the predicted carbon nitrides was questioned in a number of studies based on chemical and thermodynamical grounds. A recent discussion of this subject and further references can be found elsewhere [17]. 

K. K. R. Datta, B. V. S. Reddy, K. Ariga, A. Vinu, Angew. Chem. Int. Ed. 2010, 49, 5961-5965. Gold nanoparticles embedded in a mesoporous carbon nitride stabilizer for highly efficient three-component coupling reaction. 

Nitrogen-doped carbon materials shows good catalysts support in terms of catalytic activity and stability [18,19]. A graphitic carbon nitride with three-dimensionally extended highly ordered pore arrays has been reported as a support for a Pt-Ru alloy catalyst of a DMFC anode. The nanostructured C3N4 has 73-83% higher power density than Vulcan XC-72, a commercial carbon black. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

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