The air purifiers won't get rid of any mold that is currently on your walls or anywhere in your house so if you have mold on your walls or any other place around or in your house then you need to physically remove and kill that mold.
But the air purifier will work to trap, get rid of and kill mold spores that are airborne.
To get rid of mold spores in the air you need an air purifier that uses a HEPA filter and I would recommend either a Hamilton Beach or Honeywell brand air purifier to kill mold as long as you use a HEPA air filter with the air purifier either one or any other air purifiers will work.