The roots that develop in water are not the same as the roots that develop in soil. The water roots are very fragile and easily broken, making the transition to soil difficult without breaking the roots up.
Edited to add: If you read the studies about plants cleaning the air closely, you will discover the plants all had activated charcoal filters. It was the charcoal.
If you are adding plants to make oxygen, you will need a lot of fast growing plants in optimal photosynthesizing conditions. I don't think you could grow enough plants to change the oxygen level in your house.
