Fast, reversible CO<inf>2</inf> capture in nanostructured Brownmillerite CaFeO<inf>2.5</inf>

We observed rapid CO2 capture in nanostructured Brownmillerite CaFeO2.5 with no decay in capture capacity even after multiple cycles of carbonation and calcination. Industrial exhaust CO2 gas causes global warming as a greenhouse gas and there is an ever increasing need to develop materials for direct capture of CO2. In this work, we demonstrated CO2 capture effect in an oxygen-deficient perovskite CaFeO2.5 with Brownmillerite structure by first, exposing the compounds (bulk- and nano-CaFeO2.5) to ambient air for different durations and later, by studying fast carbonation-calcination cycles using thermogravimetry. We found that, while the physical properties of bulk-CaFeO2.5 remain unaltered; nano-CaFeO2.5 shows spontaneous capture of CO2 upon exposure to ambient air. Moreover, nano-CaFeO2.5 can be recovered completely by heating in air, showing that the capture of CO2 is reversible. Investigation of bulk and nano-CaFeO2.5 in a 2-min cycle of carbonation and calcination (regeneration) at 500°C revealed that the nano-CaFeO2.5 exhibited rapid CO2 capture ability within few seconds. In addition, almost no decay in CO2 capture capacity was observed even after 30 cycles of carbonation-calcination of nano-CaFeO2.5, which is quite remarkable. Such nanostructured systems can be potential candidates for practical applications of capturing CO2 from hot exhaust gases.