discourse vs talk about

discourse is a noun but talk about is not a noun.

Word	Noun	Adjective	Verb	Adverb
discourse	Yes	No	Yes	No
talk about	No	No	Yes	No

As verbs, discourse and talk about are synonyms defined as:

Other synonyms of discourse include discuss.

discourse (noun)	talk about (noun)
an extended communication (often interactive) dealing with some particular topic
extended verbal expression in speech or writing
an address of a religious nature (usually delivered during a church service)

discourse (verb)	talk about (verb)
talk at length and formally about a topic	to consider or examine in speech or writing
carry on a conversation	discuss or mention
to consider or examine in speech or writing