Sometimes prepositions are used as adverbs.
About as preposition :
Tell me all about it.
About as adverb :
He is about 30 years old.
Could you please give me some more examples for other prepositions.
- Three strikes and you’re out.
- She was called away.
Note that the distinction between prepositions and adverbs is not always clear: sometimes an apparent adverb can be interpreted as a preposition by assuming that words were left out:
- Three strikes and you are out [of the game].
I am also not entirely sure whether the prepositions in phrasal verbs count as adverbs.
Historically, it is often thought that all prepositions originated in adverbs in Proto-Indo-European (the common ancestor of all Indo-European languages such as English).