When we first started experimenting, we measured CO2 absorption by submerging and then oven drying and weighing the samples. If the sample gained weight, the assumption was it was CO2. 

In order to get more data, we purchased a sealed container and put the air pump, sample and solution in the sealed container. We also added a true CO2 sensor https://www.adafruit.com/product/4867 to the sealed container.

We showed in our paper that yes, the CO2 in the sealed container decreased in the air from 800ppm+ to less than 100 ppm. We also repeated with control examples like plain water, water with solution etc.

We are now using thermogravimetric analyzer (TGA) to study the samples and provide further data points as the the absorption of CO2 in the sample