Defect-Engineered Ca-TiO₂ Nanomaterials for Enhanced Adsorption and Photocatalytic Degradation of Water Pollutants on Sustainable Cellulose Membranes

A defect engineering strategy is employed to produce defective calcium-doped TiO₂ nanomaterials (Ca:TiO₂), which are subsequently incorporated into cellulose-based membranes. Structural defects, including vacancies, stacking faults, grain boundaries and voids emerged from the interplay between calcium doping and microwave irradiation. The 10 mol.% Ca:TiO₂ membrane achieves an 81% degradation rate and an adsorption capacity of ≈25.8 mg g⁻¹, showcasing excellent photocatalytic and adsorption performance. The enhanced performance is attributed to the high surface area of Ca:TiO₂ agglomerates, the presence of oxygen vacancies, structural defects and the abundance of surface hydroxyl groups. X-ray Photoelectron Spectroscopy (XPS) revealed that the Fermi level of the 10 mol.% Ca:TiO₂ nanomaterial is positioned near the conduction band edge, indicating a significant modification of its electronic properties, with high electrical conductivity at room temperature (RT). Density Functional Theory (DFT) calculations provided a deeper insight into the impact of calcium doping, revealing that calcium (Ca) incorporation promotes the formation of oxygen vacancies, introducing additional electronic states near the bottom of the conduction band, thereby enhancing the material's electrical conductivity. By integrating eco-friendly materials and defect-engineered nanomaterials doped with earth-abundant elements, this work aligns with sustainability principles, fostering the development of next-generation adsorptive and photocatalytic membranes.