We have synthesized two samples with different pH values and we got hexagonal and spherical shaped nanoparticles.
An increase of the pH may lead to more OH- ions in the solution, which incline to combine easily with the material (e.g. Zinc for ZnO) without leaving enough zinc for ZnO growth on the substrate. In addition to thickness decrease, this can cause lower agglomeration on the surface which I think can lead to decrease in roughness.
Dear Husain: When synthesizing zeolite-like crystalline silicoaluminates, the higher the pH the higher the rate of crystallization and the smaller the resulting particle size. Under such conditions spherical aggregates are usually obtained (e.g. Y-zeolite, A-zeolites). By contrast, lowering the synthesis pH increases the crystallization time, a fact that has to be compensated by increasing both the temperature and pressure of the crystallization. In such cases, higher crystalline size, usually well defined hexagonal and/or needle-like shapes crystal are observed (e.g. MOR, MFI, MEL zeolites)
ZnO powders agglomerate when synthesized in acidic and neutral conditions (pH 6 and 7). Fine powders were obtained when the pH of the sols was increased to 9.
In general the change of pH changes the equilibrium constant of the reaction and makes more favorable hydrolysis or condensation step or makes them run at the same time.
The shape of your particles can be affected by those steps. It is possible that when the sol-gel process is fast (meaning all the steps going at the same time) your nanoparticles does not have enough time to develop properly their crystallographic structure though you obtain spherical shapes.
The sol-gel process is in general very fragile to changes of any parameter - temperature, time, pH, etc. Also the scale matters (if you have batch of 5 mL or 500 mL).
change of pH altered the equilibrium constant of the reaction, temperature and makes more favorable hydrolysis or condensation step or makes them run at the same time. Though, depend on the nature of the materials, and type of reaction with determinant reaction step.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science