Dear Kanwal, It is an interesting result that you get all sorts of morphology in a single synthesis. I assume that you are using some plant extract as a reducing agent to reduce HAuCl4. Plant extracts normally have many phytochemicals including some reducing agents. As suggested you have to use very dilute solutions. Also proper stirring should be done at the time of addition of reducing agent. The addition of reducing agent should be very slow, one drop at a time. Also try an ice bath at the time of mixing and then you can heat if required.

Dear Kanwal

I think the plant extract you are using is not properly filtered and you might have small residues of the plant on which gold NPs precipitated. The extract is acting as reducing agent and surfactant as well. The suggestions given by Ranjit can probably help you.

Hi Dr Aisha Kanwal . I hope the following link could help : https://nanocomposix.com/pages/ultra-uniform-gold-nanospheres

Ranjit Kumar.Dear Sir...

By dilute solutions, do you mean that I should have to decrease the concentration of only plant extract(reducing agent)or both HAuCl4 and plant extract?

stirring I am doing properly but I am adding a reducing agent all at once and also I am using 60°C and 80°C temperatures(for two different green sources)

first I make the HAuCl4 solution hot and then add a reducing agent.

now I will try the way you suggested..thank you so much for your valuable suggestions.

Mohammad Kooti.Dear sir.

the extract solution is properly filtered but now I will follow the suggestions given by Sir Ranjit...maybe it will work...thank you for your kind response.

Aref Wazwaz .thank you so much Sir for sharing a link.

Dear

You must take care of addition reducing agent, stirring time, filtration of plant extract.

If you want synthesize uniform shape and size particles then you must take follow the steps very carefully otherwise you wouldn't get desired size and shape particles.

Dear Kanwal,

You should dilute the plant extract. The addition of plant extract/reducing agent should always be done dropwise. This helps in attaining uniform size and morphology.

Ranjit Kumar. thank you so much sir for your valuable suggestions

Jamil Ahmed Buledi .thank you so much for your valuable suggestions.

Dear Kanwal Aisha.. The plant extract has many bio-active compounds, and most of them are involved in the green synthesis (reduction and capping steps) of the nanoparticles. Each one of these compounds may act in a different way from the other`s, so it may produce particles differ in shape and size from the other for the same metal and the same procedure in the same plant extract( the only different is the bio-active compound in the plant extract itself). So, I recommend for you if you want a uniform for shape and size of the NPs you can purify the extract bio active components separately (at least, the major bio-active ones) and examine each one separately. In this way you can judge which one is preferred for your research aim.

I was thinking that, sometimes whatever we do we can't get the required size and morphology for the obtained NPs and therefore the best idea perhaps using another plant extract. Also, some extracts are not stable for long time and at high temperature.

Mohammad Kooti, Fadwa Waleed Abdulqahar ..thank you so much for your useful information.