Bio-inspired in situ activation strategy of photocatalysts by CO₂ mineralization in cement-based materials

Semiconductor photocatalysis integrated into cement-based materials offers a promising route for mitigating urban NO_x pollution; however, achieving high activity and selectivity with low-cost cocatalysts remains challenging. Inspired by natural biomineralization, this study proposed a CO₂ mineralization-driven in situ activation strategy that synergistically leveraged the catalytic functionality of cement-based substrates. A MgO-TiO₂-CaCO₃ (MTC) ternary composite catalytic system was fabricated through a two-step synthesis process, in which MgO-doped TiO₂ acted as a novel precursor to trigger CaCO₃ nucleation and growth, thereby enabling synergistic cocatalytic interactions. The optimized MTC-10 exhibited a NO removal efficiency nearly twice that of pristine TiO₂, while reducing NO₂ generation by half. Mechanistic investigations revealed that the synergistic coupling of MgO and CaCO₃, as alkaline earth metal oxides/compounds, introduced oxygen vacancies and enhanced surface alkalinity, inhibiting the formation of toxic NO₂/N₂O₄ intermediates. Density functional theory (DFT) calculations further demonstrated that CaCO₃ functioned as a “transfer hub”, promoting charge redistribution, accelerating carrier migration, and enhancing reactive oxygen species (ROS) generation. These processes were crucial for the complete oxidation of NO, helping to suppress the formation of of byproducts such as NO₂ and promoting the transformation of nitrite into more stable nitrate species. This work establishes a novel CO₂ mineralization-driven strategy for boosting TiO₂ photocatalysis in cement-based materials, offering a dual-benefit pathway for CO₂ utilization and selective NO_x abatement.