It depends on the meaning. Some examples:
'He became disillusioned of his belief that she loved him.' (Disabused.)
'I am disillusioned with this treatment; it doesn't seem to be working at all.' (Disappointed with something that has been going on for some time.)
'He was disillusioned at the reaction to his new play.' (Disappointed with something that happened.)
Those do not constitute an exhaustive answer.
The preposition is up.
No, the word "when" is not a preposition. It is an adverb or a conjunction used to indicate time or a condition.
The word " I " is not a preposition, it is a pronoun.
No, it is not a preposition. The word away is an adverb.
No, the word "early" is an adverb, not a preposition. It is used to describe the timing of an action or event.
The American people were disillusioned in the 1970s.
Disillusioned is used as an adjective. The more she experienced behind the scenes, the more disillusioned she grew with the entire political process.
The preposition is up.
No the word every is not a preposition.
No, the word "when" is not a preposition. It is an adverb or a conjunction used to indicate time or a condition.
Yes, the word among is a preposition.
No, it is not a preposition. The word explore is a verb.
No, it is not a preposition. The word thing is a noun.
The word " I " is not a preposition, it is a pronoun.
No, it is not a preposition. The word away is an adverb.
No, the word "early" is an adverb, not a preposition. It is used to describe the timing of an action or event.
No, it is not a preposition. The word rivers is a plural noun.