Calcium and Magnesium Incorporation in TiO2: Defect Driven Photocatalysis and Self-Cleaning Performance for Smart Façade Coatings

Building façades are continuously exposed to airborne pollutants, leading to surface staining, degradation and increased maintenance. To mitigate these effects, a defect-engineering approach is applied to create calcium- and magnesium-incorporated titanium dioxide (TiO 2 ) nanomaterials for self-cleaning façades. A rapid microwave-assisted solvothermal route yields phase-pure anatase nanopowders that are translated into spray-coated films on thermoplastic polyolefin (TPO), a flexible and 100% recyclable polymer substrate relevant to façade components. X-ray diffraction (XRD) confirms anatase for all nanopowders and indicates that incorporation does not lead to secondary crystalline phases. Microstructural analysis by scanning electron microscopy (SEM) shows incorporation-driven particle refinement, with particle size decreasing from 21.4 nm for TiO 2 to 12.5 nm for Ca-TiO 2 and 13.5 nm for Mg-TiO 2 . Consistently, the specific surface area increases from 137.8 m 2 ·g -1 for TiO 2 to 237.3 m 2 ·g -1 for Ca-TiO 2 and 235.6 m 2 ·g -1 for Mg-TiO 2 . Optical analysis reveals a blue shift of the absorption edge, most pronounced for Ca-TiO 2 nanomaterial. X-ray photoelectron spectroscopy (XPS) confirms incorporation of Ca and Mg, and O 1s deconvolution indicates Ca–O-related environments together with increased reactive oxygen/hydroxyl species. Density functional theory (DFT) supports a defect-driven mechanism, predicting that calcium promotes oxygen-vacancy formation more strongly than magnesium. Under simulated solar irradiation, Ca-TiO 2 exhibits the highest photocatalytic performance, achieving ∼97% Rhodamine B degradation and outperforming TiO 2 and Mg-TiO 2 . Ca-TiO 2 also shows the strongest photoinduced hydrophilicity, lowering the water contact angle from ∼84° to ∼40° after ultraviolet activation. Overall, earth-abundant calcium incorporation emerges as a practical alternative for durable self-cleaning coatings for façade-oriented smart materials.