Right now your best possible action to keep the place pure would be cutting the corrupted land out, a large enough hole will do the trick until you can get a clentaminator.
First, you will want a hardmode pickaxe, orichalcum/mythril will do but adamtite/titanium is ideal, though there is not much time so make what you think is the right decision.
Corruption can spread up to 6 blocks away, so you will need to dig out an at least 6-wide tunnel separating the land, this can be a U shaped cutout of the biome or a tunnel to hell, the tunnel is a lot faster but it does mean the rest of your world is unsafe still, you can also just dig out half of the way, since you a buying time instead of a perfect solution. You can do this with a molten/nightmare pickaxe but it is way too slow to be bearable, remember to use mining gear if you have it (the miner's set, mining potion, slice of cake etc.).
Remember to dig out ~60 blocks further than where the corruption has actually reached, you want to make sure that no corrupt blocks make it to the other side while you are digging it all out. Use a biome sight potion while digging so that no sneaky blocks make it through.
Finally, the corruption has another way of spreading that will need handling, it can reach out using it's thorns which grow on grass to corrupt even further than 6 tiles. Basically, you will need to line the
corruption side of the tunnel with a non-corruptible tile like mudstone brick, grey brick, obsidian brick, it depends on what blocks you have the most of, even snow will work for this actually.
This is so that no thorns will grow inside the tunnel and reach the other side, you should only need to do this once on the side the corruption is on since there are no
forest thorns.
If you prepare and get the right boosts for it, the tunnel to hell should take 30-40 minutes :\
Oh right, you can also just make the place a hallow biome, eh your choice 
