You are rite Mohammad Kooti

If there's no change in color, it means that you have no reducing agent present in the 'plant extract'. If you add a 5% solution of hydrazine hydrate (or bubble hydrogen through) to the chloroplatinic acid then you should see reduction taking place.

Platinum slurry looks dark gray, almost black.

thanks for answering

okay, let's say something doctors, i use Gallic acid as a standard for reaction with no change to black or deep brown as a control to notify the color change

i don't where is my problem, i am really feeling bad

Are you sure that the plant extract you are using has the reducing ability to convert Pt(IV) to Pt NPs? Has this extract been used by other researchers for preparation of metal NPs? If the answers to these questions is yes then try the suggested test given by Alan.

yes, their are many papers ensure the conversion in color

if i can not use hydrazine as reducing agent because plant extract should work as reducing agent ? this is the concept of green synthesis of nanopaticles

i don't know what should i do ?

May be problem is in hexachloroplatinic acid? It usually contains a huge excess of hydrochloric acid. Check the pH of the solution after reaction with "plant extract". Maybe "plant extract" just reacts with an excess of acid and therefore does not work as a reducing agent...

I hope you do not drain the solutions after unsuccessful experiments down the sewage? I remember how a very old refinery factory was liquidated in our city. Silt in sewer pipes caused great interest ...

Dear Sondos

I am not asking you to use hydrazine to prepare Pt NPs. I suggested that you take a small amount of of the reaction mixture and add some hydrazine or other reducing agent to it to see whether the reaction conditions are OK or not. If you get the Pt NPs then the problem is the plant extract you are using. If you are not getting Pt NPs even with hydrazine you will be sure that something wrong with precursor or the reaction conditions.

Good luck!!

You are rite Mohammad Kooti