I am ignorant as far as the use of inhalable medications is concerned. However, I find it weird that you'd want to recycle oxygen: carbon dioxide removal is eit

I am ignorant as far as the use of inhalable medications is concerned. However, I find it weird that you'd want to recycle oxygen: carbon dioxide removal is either hard or requires consumables, while oxygen can be concentrates from air using a simple process that consumers only energy (by adsorbing nitrogen on surfaces of particular minerals).