Titanium diboride (TiB2) derived nanosheets enhance the CO2 capturing ability of calcium oxide (CaO)

Abstract

Several two-dimensional (2D) materials are being actively explored as additives for enhancing CO2 capture owing to their high surface area, superior thermal stability, and extremely high density of catalytically active sites. The landscape of 2D materials is constantly expanding as several van der Waals and ionic layered materials are being revisited with the view of exfoliation. Recently, we have been able to nanoscale titanium diboride (TiB2), a layered metal diboride ceramic primarily investigated in its bulk form. We have developed various approaches to exfoliate TiB2 into nanosheets that contain titanium and boron atoms decorated with oxy-functional groups such as TiO2, BO33-, and BO4- known to capture CO2 gas molecules. This aspect motivated us to examine if nanosheets derived from TiB2 can enhance the capturing capacity of CO2 adsorbent material. Calcium oxide (CaO)-based materials are widely used as regenerable CO2 adsorbents at high temperatures due to their high CO2 reactivity, easy recyclability, and low cost. However, the adsorption capacity of these materials drastically decreases with multiple carbonation-calcination (decarbonation) cycles due to particle agglomeration. This shortcoming led us to investigate the effect of TiB2 based nanosheets on the CO2 capturing ability of CaO. In this work, we show that adding just 1% of nanosheets can enhance the capturing capacity of CaO up to 25% and results in lesser sintering of CaO. We also utilized minimally functionalized nanosheets derived from TiB2 to show how the density of functional groups present on the surface of these nanosheets can affect the CO2 capturing ability of CaO. We utilized these to obtain preliminary insights on the reaction mechanism of CO2 adsorption on CaO and rate parameters through the reaction kinetics. To the best of our knowledge, this is the first study presenting a new perspective on using nanoscaled metal diborides to enhance CO2 capture.