Activated Carbon/Charcoal

Will it still absorb odors if filters or containers of it are just placed in room and not hooked up to an exhaust vent?

Maybe a little, but not much. You must pull/push air through it.

Activated carbon is very porous, it's in these pores that the odors get trapped and that's how it absorbs. It won't pull things to it so you need to blow the odors through it to get them trapped.

Thanks for the info.

No, it will not work as a stand alone unit. It needs to be connected to a exhaust fan rated for that filter. You can exhaust it directly back in to the room with out the need for added exhaust duct to the outside of the garden if heat issues/fresh air exchange is not an issue. Blowers are cheap when it comes down to the bottom line. Look an ebay or Amazon for the filters/blowers. A lot of them are free shipping.