Urea Affects Tungsten Trioxide Crystal Structure

The ammonium ion in urea stabilizes the skeleton of tungsten trioxide. If the removal of ammonium trioxide in the framework of ammonium ions, will lead to the collapse of the framework of tungsten trioxide. This shows that the monovalent cation in urea plays an important role in stabilizing the structure of tungsten trioxide. Since urea hydrolyzes under hydrothermal conditions, ammonium and bicarbonate ions are released and the pH of the reaction system is slowly adjusted.

Tungsten trioxide samples were stirred, hydrothermal, tungsten trioxide sample surface without the presence of urea. This shows that urea can be removed by washing without leaving the surface of the sample of tungsten trioxide, and urea did not play a role in regulating the crystal structure in the synthesis of the sample of tungsten trioxide. In addition, during the nucleation of tungsten trioxide, the slow hydrolysis of urea increases the p H value of the system, which hinders the growth of tungsten trioxide. Making the growth of tungsten trioxide in this system is a slow growth process.

In such a slow growth process, the appropriate pH value and the presence of a certain amount of ammonium ions, making the tungsten oxide nuclei stable. Since then urea further slow decomposition, also slowed the growth of tungsten trioxide, and slow release of ammonium ions. Although the concentration of ammonium ion in the reaction system is not enough, a certain amount of ammonium ion exists in the solution. Tungsten trioxide grows slowly, will maximize the ammonium ions filled tungsten trioxide channel, thus ensuring the stability of hexagonal phase tungsten trioxide.

This process is similar to building construction. In the building process, each layer has the necessary structural stability unit, so that the entire building in the least material conditions to maintain stability. In addition, the synthesized tungsten trioxide has a very small size and a very thin thickness. Since urea releases monovalent cations and dianions during the reaction, monovalent cations act to stabilize the tungsten oxide crystal structure. Therefore, urea-decomposed carbonate ions or bicarbonate ions may adsorb on the surface of the hexagonal phase tungsten trioxide.

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