CaAl-layered double hydroxides (LDHs) exhibit different mechanisms of borate removal at varying calcination temperatures. The addition of Mg alters the structure and composition of the calcined products, ultimately impacting their adsorption process. To investigate this, CaAl-LDH and Mg-doped CaAl-LDH with and without different calcination temperatures (500 °C and 900 °C) were prepared to immobilize a wide concentration range of borate. XRD, SEM, FTIR, and EXAFS techniques were employed to study the influence of Mg doping. The results indicate that the doping of Mg increases the BET surface area and enhances the adsorption capacity of uncalcined LDHs, with the enhancement being more pronounced at high borate concentrations. For LDHs calcined at 500 °C, Mg-doped LDHs exhibited slightly better adsorption at any borate concentration due to its more favorable ettringite formation. However, for LDHs calcined at 900 °C, Mg-doped LDHs (LDO) had a slightly better adsorption effect at low borate concentrations. At high concentrations, the crystallinity and morphology of the regenerated CaMgAl-LDH deteriorated, resulting in poor adsorption effects. These findings provide valuable theoretical support for understanding the mechanisms of removing pollutants with different concentrations by different LDHs.

Incorporating biochar into cement offers an effective strategy to reduce carbon emissions. However, the structural heterogeneity of the original biochar limits its capacity for CO₂ adsorption. In this work, biochar was produced by pyrolyzing corn straw at 300, 500, and 700 °C, and its main heterogeneous component—sedimented particles (SP)—was obtained through physical separation. Subsequently, both the original biochar and SP were treated with alkali to investigate their CO₂ adsorption capacities. Furthermore, original biochar, SP, CO₂-saturated modified biochar, and CO₂-saturated modified SP were each incorporated into cement composites at dosages of 1%, 2%, 3%, and 5% by cement mass to evaluate their effects on the mechanical properties and carbon sequestration performance. The results demonstrated that SP had a higher CO₂ adsorption capacity than the original biochar, and this capacity increased further with rising pyrolysis temperature. The adsorption kinetics indicate that biochar primarily undergoes physical adsorption of CO₂, with a minor contribution from chemical adsorption. Furthermore, as the pyrolysis temperature of biochar increased, its effects on cement composites led to a trend of first increasing and then decreasing hydration product formation. The CO₂-saturated modified SP resulted in higher compressive strength compared to cement composites containing SP alone at a substitution rate of 1%. This work provides insights that promote the effective utilization of biochar in the carbon sequestration of cement composites.