This will probably be used in conjunction with PFC's. Solettas could also be used to release nitrogen from nitrates in the soil. Nanotechnology could also be used to melt ice and release nitrogen. Nanotechnology, however, is an invention of the future. Although a carbon dioxide atmosphere would be fine for plants, animal life requires an oxygen-containing atmosphere.
Plants take in carbon dioxide, and release sugar and oxygen.
This will be the predominant oxygenation method, but will probably take longer than a century. Black chlorophyll would shorten the time needed considerably. The Bosch process could supplement plants in oxygenation. In this process, carbon dioxide and hydrogen combine to form water and carbon. The water is electrolyzed to form hydrogen and oxygen.