Preparation method of rod-shaped methylene blue crystal

The invention provides a preparation method of a rod-shaped methylene blue crystal and belongs to the technical field of production of chemical raw materials. The preparation method comprises the following steps: firstly, respectively dissolving calcium nitrate and ammonium monoacid phosphate in de-ionized water so as to prepare a solution A and a solution B, wherein the mol ratio of calcium nitrate to ammonium monoacid phosphate in the two solutions is 5:3; respectively regulating the pH values of the two solutions by use of ammonia, then adding methylene blue into the solution B, and dropwise adding the solution A into the constantly-stirred solution B containing methylene blue; after dropwise adding the solution A, performing hydrothermal reaction for 4 hours under a stirring condition, and then standing and aging for 12 hours; and finally sieving a reaction solution, washing a methylene blue oversize product, and drying at a temperature of 40 DEG C for 12 hours, thereby obtaining the rod-shaped methylene blue crystal with the length of 0.2-5mm. The method is simple in process, low in raw material price and easy for industrial production.