[sannee]

A random google link says that you would need hundreds of plants per person to get sufficient oxygen production [1].

And during night, the plants would just produce CO2, which would presumably get accumulated, making the whole situation worse.

[1] - https://io9.gizmodo.com/5955071/how-many-plants-would-you-ne...

[ThePadawan]

Another random google link says it could be as little as four shoulder-height areca palms: http://www.secrets-of-longevity-in-humans.com/oxygen-produci...