Question
What is the ruling in the matter of buying and selling banknotes, not for what they are, i.e. a means of monetary exchange, rather for having a special value? To give an example, one may be interested in acquiring the green backed banknote of one-thousand Tomandenomination, which bears the picture of the late Imam Khomeini, for more than its nominal value.
Category: Buying and Selling Gold, Silver and Money
Answer:
There is no harm in that provided that dealing in such banknotes is both serious and for a sensible reason. If this sale is on credit, i.e., just a formality intended to circumvent a ribā-based loan transaction, it is ḥarām and invalid.

Refrence:
Ref: www.leader.ir