How much CO2 a tree convert into oxygen per day?

While this depends on the size and maturity of the tree and whether it is in a temperate climate of a northern climate (and so is "out of business" for about half the year) there are many estimates of tree oxygen production rates. Environment Canada, Canada's national environmental agency, has calculated that one tree produces nearly 260 pounds of oxygen each year or a bit less than than a pound of oxygen a day (about 12 oz) averaged over the whole year.

Since 44 lb of CO2 contains 32 lb of oxygen, 12 oz of oxygen is liberated from the photosynthesis of about 12/16 x 44/32 = 1.03 lb of carbon dioxide.