With sufficient sunlight houseplants produce oxygen and absorb carbon dioxide.
plants respire though, and respiration produces CO2, although this the highest at night. Producing oxygen requires sunlight from photsynthesis so at night or when there isn't enough light some
plants will put out C02--I don't think it an alarmingly high level though. I am not an expert but I believe some
plants do put out oxygen at night though
succulents, and orchids I think. Keep checking back and Will Creed our houseplant expert will surely have a better answer for you.