Development of photocatalytic carbonation coating for concrete: Enhancement of air quality and sequestration of CO₂

A new eco-friendly carbonation coating with a photocatalytic function was developed using dicalcium silicate (C₂S) and nano TiO₂, aiming to remove air pollution and enhance the durability of concrete at the same time. The photocatalytic performance, mechanical properties, and durability of the carbonated coatings incorporating different additions of TiO₂ were evaluated, and the development of carbonation products and microstructure were investigated. The results show that the photocatalytic efficiency was increased linearly from 2518 μmol·m⁻²·h to 4392 μmol·m⁻²·h as the TiO₂ doping amount was increased from 1% to 8%. In addition, the composition and microstructure analysis indicated that TiO₂ not only improved the carbonation degree of C₂S but also promoted the formation of metastable calcium carbonate, including aragonite, vaterite, and amorphous calcium carbonate, leading to a densified microstructure structure. At the same time, the improved carbonation process could capture up to 15.18% CO₂ by mass. As a result, the bonding strength was improved from 3.29 MPa to 4.69 MPa after incorporating 8% TiO₂, which is much higher than the conventional cement-based coating. Furthermore, the microhardness of the coating increased from 150 HV to 178 HV.