They don't, they breathe. In any case, making those scrubbers is a high-energy-cost activity and would be a net loss. Instead, you use the CO2 output to produce Algae, a process already tested by the USDOE at Sandia National Labs, where they were able to capture over 80% of the CO2 output in the algae. Then you can in turn make the algae into biodiesel and fertilizer, fixing some of the carbon and getting a second use out of the rest. In other words, your idea is stupid, and slashdot is a stupider place for having to hear it - but there is a similar, working solution.