according to articles in this process the solution gets colorless immediately and then red (after a couple of hours) showing formation of AuNPs, but recently when I try this way, the color changes to orange at first and gold precipitates after stirring for some hours.
May be the amount of PAMAM is more, and thus the reduction process is fast. So it is getting aggregation instead of stable colloidal AuNPs. You may decrease PAMAM to some extent and try to optimize the reaction.
You can also check the pH of the solution before and after adding gold chloride.
I am sure about the pH. but I will check the effect of the ratio of materials again and inform the result. thank you so much
The change of the color of the HAuCl4 solution id due to the reduction of the Au 3+ to Au 1+ and finally to Au (0). The rate of reduction of the Au ion plays a major role in the size of the gold sol obtained and the color observed. If the rate of reduction is faster you can see only the color of the Au sol finally obtained which may be brown or red or blue in color depending upon its size.
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