Yesterday I synthesized Al2O3-SiO2 supported nickel (maybe oxide) particles. The process is like that:
-Nickel precursor: Nickel nitrate hexahydrate
-Nickel nitrate aqueus stock solution were ultrasonicated for 20 min. and then Al2O3-SiO2 support added to mix and an additional ultrasonication was applied for 20 min. 2.5 times larger amount of NaBH4 than molar amount of nitrate anions was dissolved in water and added to mix dropwise for reduction of nickel particles. Color of solution turned to dark-grey, and then the solution wait overnight without any filtration, centrifugation or washing.
When I look at the sample in the morning, I saw that its color turn to white (or so light green). I can not understand why the color changed. If someone can help me to explain this phenomenon I will be so happy.
Thanks.
I know nothing about Nickel nitrate hexahydrate or that kind of experimentation.
However, one must remember that colors is just light in different amounts in the visible spectrum.
White = maximum light or max reflection of light
Black = no light or no reflection of light
So if the colors have changed it is because the properties of the material have changed.
e.g. an oxidation can certainly change the way the light is reflected (?)
Just a thought I got when I read your question
I suggest that you use NiCl2 instead of nitrate as precursor. The produced Ni NPs might be oxidized to nickel salt in the presence of oxygen, so to prevent that perform the synthesis under inert atmosphere, such as nitrogen gas. It is rather strange for me that the NPs turned to white color, because even the NPs are oxidized they must be colored.
If you want to investigate what was happened, it is recommended to perform XRD.
Nickel aluminates and other phase may by produced due to the solution treatment.
Actually I used nickel nitrate Mohammad Kooti . I suggest that there might be three different situations; one of them is formation of different oxidation states and the other probability might be traveling of nickel/oxide particles from outer surface to pores (however temperature is too low to transport the particles.). And the last one is the formation of by-products i.e. NaBO2 or NaNO3 (as Bryan Harry Rahmat Suryanto
said).I think that powder XRD characterization gives me tactile knowledge.
Thanks all.
Go ahead dear Ceyhun and get the XRD of the composite. This will tell you clearly whether you have NiO or not.
Keeping NPs without capping agent trigger aggregation of particles and reverse the process to Ni ions or leads to Ni salts along with by products ma appears I the solution you must use a particular Capping agent you wana see you them in same nano state.