CaO recovered from eggshell waste as a potential adsorbent for greenhouse gas CO₂

The growing number of industrial carbon emissions have resulted in a significant increase in the greenhouse gas carbon dioxide (CO₂), which, in turn, will have a major impact on climate change. Therefore, the reduction, storage, and reuse of CO₂ is an important concern in modern society. Calcium oxide (CaO) is known to be an excellent adsorbent of CO₂ in a high-temperature environment. However, since deterioration of the adsorbent is likely to occur after repeated cycles of adsorption under high temperature conditions, it would be desirable to mitigate this phenomenon, in order to maintain the stability of CaO. In the present study, common eggshell waste was used as the starting material. The main component of eggshell waste is calcium carbonate (CaCO₃), which was purified to produce CaO. Different surfactants and amino-containing polymers were added to synthesize CaO-based adsorbents with different configurations and pore sizes. The amount of CO₂ adsorbed was determined using a thermogravimetric analyzer (TGA). The results showed that the CO₂ adsorption capacity of the synthetic CaO recovered from purified eggshell waste could reach 0.6 g-CO₂/g-sorbent, indicating a good adsorption capacity. CaO modified with a dopamine-containing polymer was shown to have an adsorption capacity of 0.62 g-CO₂/g-sorbent. Moreover, it showed an excellent adsorption capacity of 0.40 g-CO₂/g-sorbent, even after 10 cycles of CO₂ adsorption. The present study suggests that using eggshell waste to synthesize CaO-based adsorbents for effective CO₂ adsorption can not only reduce environmental waste, but also have the potential to capture greenhouse gas CO₂ emissions, which conforms to the principles of green chemistry.