An option for reducing the release of greenhouse gases into the atmosphere is the implementation of CO2 capture and storage (CCS) technologies. However, the costs associated with capturing CO2 by using the currently available technology of amine scrubbing are very high. An emerging second-generation CO2 capture technology is the use of calcium-based sorbents, which exploit the carbonation and calcination reactions of CaO, namely, CaO+CO2↔CaCO3. Naturally occurring Ca-based sorbents are inexpensive, but show a very rapid decay of CO2 uptake capacity with cycle number. Here, we report the development of synthetic Ca-based CO2 sorbents using a sol–gel technique. Using this technique, we are able to synthesize a nanostructured material that possesses a high surface area and pore volume and shows excellent CO2 capture characteristics over many cycles. Furthermore, we are able to establish a clear relationship between the structure of the sorbent and its performance. After 30 cycles of calcination and carbonation, the best material possessed a CO2 uptake capacity of 0.51 g of CO2 per gram of sorbent; a value that is about 250 % higher than that for naturally occurring Havelock limestone.