Sm doped mesoporous CeO2 nanocrystals: aqueous solution-based surfactant assisted low temperature synthesis, characterization and their improved autocatalytic activity

Abstract

Mesoporous Sm³⁺ doped CeO₂ (Ce–Sm) with a nanocrystalline framework, a high content of Ce³⁺ and surface area (184 m² g⁻¹), have been synthesized through a facile aqueous solution-based surfactant assisted route by using inorganic precursors and sodium dodecyl sulphate as a template. The XRD results indicate that the calcined Ce–Sm and even the as-prepared material have a cubic fluorite structure of CeO₂ with no crystalline impurity phase. XRD studies along with HRTEM results confirmed the formation of mesoporous nanocrystalline CeO₂ at a lower temperature as low as 100 °C. A detailed analysis revealed that Sm³⁺ doping in CeO₂ has increased the lattice volume, surface area, mesopore volume and engineered the surface defects. Higher concentrations of Ce³⁺ and oxygen vacancies of Ce–Sm resulted in lowering of the band gap. It is evident from the H₂-TPR results that Sm³⁺ doping in CeO₂ strongly modified the reduction behavior of CeO₂ by shifting the bulk reduction at a much lower temperature, indicating increased oxygen mobility in the sample which enables enhanced oxygen diffusion at lower temperatures, thus promoting reducibility, i.e., the process of Ce⁴⁺ → Ce³⁺. UV-visible transmission studies revealed improved autocatalytic performance due to easier Ce⁴⁺/Ce³⁺ recycling in the Sm³⁺ doped CeO₂ nanoparticles. From the in vitro cytotoxicity of both pure CeO₂ and Sm³⁺ doped CeO₂ calcined at 500 °C in a concentration as high as 100 μg mL⁻¹ (even after 120 h) on MG-63 cells, no obvious decrease in cell viability is observed, confirming their excellent biocompatibility. The presence of an increased amount of surface hydroxyl groups, mesoporosity, and surface defects have contributed towards an improved autocatalytic activity of mesoporous Ce–Sm, which appear to be a potential candidate for biomedical (antioxidant) applications.