Solvent thermal constant-pressure synthesis method for controlling phase of carbon nitride material

A method for controlling the phase of carbon nitride material by solvent heating constant pressure synthesis belongs to fields of chemical production and new material. The method includes preparing carbon source solution and nitrogen source solution; feeding into a reaction kettle; applying constant pressure of 40-2,000MPa before heating; heating up to 220-1,000 DEG C at a heating rate of 0.01-60 DEG C/min; cooling after the reaction is completed; and post-treating the product. When the boron carbon nitride is synthesized by the method, temperature and pressure of the reaction system can be independently controlled, so that the reaction can be carried out under the constant pressure, and the pressure of the reaction system can be varied according to the requirement so as to control the speed and the direction of the reaction for synthesizing boron carbon nitride. The method is capable of preparing high-particle size carbon nitride crystal.