TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The reaction between carbon dioxide and the metal nitride further produces Li2CN2. The method further comprises reacting the Li2CN2 with C3N3Cl3 to produce the second carbon nitride. The method further comprises reacting the carbon dioxide with the metal nitride in the presence of a catalyst. The method further comprises: producing a solid contaminant in the reaction between the carbon dioxide and the metal nitride to form a mixture comprising the solid contaminant and the first carbon nitride; applying a solvent to the mixture; and separating the first carbon nitride from the solid contaminant. The separating step comprises centrifugation. The method further comprises: producing a first solid contaminant in the reaction between the carbon dioxide and the metal nitride to form a first mixture comprising the first solid contaminant and the first carbon nitride; producing a second solid contaminant in the reaction between the Li2CN2 and C3N3Cl3 to form a second mixture comprising the second solid contaminant and the second carbon nitride; applying a solvent to the first or second mixture; and separating the carbon nitride from the solid contaminant. The high pressure is 1-150 (preferably 10-100) GPa, and the high temperature is 1000-3000 degrees C, preferably 2000-2500 degrees C. Preferred Components: The metal nitride comprises at least one of lithium nitride (preferred), magnesium nitride, calcium nitride, and aluminum nitride. The first carbon nitride comprises carbon nitride. The second carbon nitride comprises carbon nitride. The catalyst comprises a transition metal, which is at least one of nickel, rhodium, ruthenium, and platinum. The solid contaminant comprises metal cyanamide, metal oxide and/or metal carbonate. The solvent comprises water, and acid comprising hydrochloric acid. The metal nitride comprises lithium nitride. The first and second carbon nitrides each comprise carbon nitride. EXAMPLE - Lithium nitride (0.5 g) was loaded in a reactor (a stainless steel tube with an inside diameter of 4 mm). Before the test, the solid sample was subjected to vacuum and heated to a selected temperature. The carbon dioxide (CO2) pressure change during reaction was measured with a digital pressure gauge, which was used to calculate the amount of consumed CO2. The amount of consumed CO2 was greater at 380?C than at 350 degrees C to give carbon nitride and lithium cyanamide.