Coprecipitation is a scalable technique for atomic-level mixing of reactants. In one example, soluble transition metal salts are dissolved in water, and then added to a concentrated solution of potassium hydroxide, causing the rapid precipitation of insoluble metal hydroxides, now uniformly mixed. Often, a chelating agent such as ammonium hydroxide is added to the potassium hydroxide solution to encourage uniform nucleation. Careful control of the pH will result in a significantly more uniform distribution of the reagents.
A highly primitive coprecipitiation can be performed simply using a burette, erlenmeyer flask, stir plate, and magnetic stir bar. A more advanced version of this technique relies upon a tank reactor, which enables careful control over both pH and the concentration of the chelating agent.
Synthesis of Ni0.25Mn0.75(OH)2
- Create 10ml of a 0.5M NiSO4-6H2O and 1.5M MnSO4-H2O solution in water. (Water content of these hydrates salts can be measured using TGA)
- Add this solution dropwise to 100ml of a 2M KOH 0.05 NH4OH solution in water.
- Collect and wash the precipitate via vacuum filtration or centrifiguation until the pH of the filtrate is neutral and all residual K2SO4 is removed.