Carbon Sequestration Behavior and Mechanism of Calcium Salts Solutions on Graphene Surface

Global warming caused by the greenhouse effect has severely reduced the living areas of life on land and at the poles. Accelerating the pace of reducing carbon emissions and innovating carbon sequestration solutions are crucial to solving the problem of mitigating the greenhouse effect. In this report, we present the direct observation of two-dimensional (2D) calcium crystals formed on reduced graphene oxide (rGO) membranes from CaCl2 and Ca(NO3)2 solutions, even at concentrations far below saturation under ambient conditions. Surprisingly, these crystals are identified as calcite (CaCO3) crystals rather than the expected Ca-Cl or Ca-NO3 crystals. Furthermore, we found that the carbon used in forming the CaCO3 crystals comes from CO2 in the air. Theoretical studies suggest that this unconventional conversion from CaCl2 and Ca(NO3)2 to CaCO3 is due to cation-π interactions between the ions and the aromatic rings present on the graphitic surfaces. Contrary to the traditional proton theory of acids and bases, strong acids displace weaker acids at the graphene interface. Our findings provide new insight into the inorganic carbon cycle in the ocean. This unexpected reaction occurs at room temperature and involves carbon-based materials, potentially reducing the cost of carbon sequestration and paving the way for new carbon sequestration strategies.