Water Purifier
A Cauldron Full of Water, with a fire underneath, connected to a hopper which is connected to a chest full of empty water bottles. Also every 5 or so minutes the chest gains a bottle of exp named 'Nitrogen Gas'.
An Idea of what this would look like. Obviously the fire would be where the flooring is and the nether rack 1 below the flooring.
Oxygen Recycler
A 3x3 room, surrounded by some sort of air tight block with ONE hole in it, in this room 78 flowers should be placed around a water hole in the center of the room, (any flowers) this room should be 2 blocks high, in the ceiling above the water hole there should be a hopper. (This links in with the Nitrogen Oxidizer)
Like this (Im showing you using glass to show whats inside.
Nitrogen Oxidizer
Using the Oxygen Recycler, every 2 or so minutes the hopper will gain 1 ghast tear (named Solid or Liquid Oxygen), this is to be put in a dropper that drops items ABOVE a hopper that is next to a block that is considered powered by redstone (e.g by a lever) and when Both Nitrogen Gas, and Liquid Oxygen is above the hopper flick the lever, and they should go down into a hopper connected to another hopper connected to a chest, forming Nitrous Oxide.
An Example. (The Lever is on so the items dont fall down)
I will be thinking of more ideas in the future.