Performance of Sm-doped TiO₂ in photocatalytic antibiotic degradation and photocatalytic CO₂ reduction

Sm-doped TiO₂ powders with different Sm loadings (0.7–2 wt.%) were successfully synthesized via a simple hydrothermal method using commercial P25 TiO₂ and self-synthesized TiO₂ as initial TiO₂ nanoparticles. Their physicochemical properties were investigated by means of powder X-ray analysis (PXRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and nitrogen physisorption. Their photocatalytic activity was first assessed in the degradation and mineralization of aqueous solutions of antibiotics ciprofloxacin (CIP) and sulfamethoxazole (SMX) under simulated solar irradiation with the 1wt.% Sm-loaded catalysts being the most active. More than 90% of CIP was degraded within 30 min and more than 85% was mineralized within 6 h of the photocatalytic process by the best performing samples (> 60% and > 80% of SMX, respectively). Residual antibiotic activity tests confirmed that CIP solutions treated with Sm-doped TiO₂ catalysts did not exhibit toxicity toward E.coli. The photocatalytic activity of Sm-TiO₂ catalysts were also investigated in photocatalytic CO₂ reduction in batch under 6 h irradiation of a 200 W Hg/Xe lamp. The maximum production of CH₄ over the Sm-doped commercial P25 TiO₂ and self-synthesized TiO₂ was 81 ppm h⁻¹ g⁻¹ and 129 ppm h⁻¹ g⁻¹, respectively. The better photocatalytic performance of the latter could be ascribed to the well-developed specific surface area and better adsorption properties of the material.