Investigation of ROS scavenging properties and in vitro cytotoxicity of oxygen-deficient La2O3-x nanostructure synthesized by spray pyrolysis method

Oxygen-deficient metal oxides have seen increased application in the field of free radical biology, whereby their electronic structure imparts unique antioxidant properties. In this work, we use the facile, one-step, cost-effective method of spray pyrolysis to synthesize oxygen-deficient lanthanum oxide (La 2 O 3- x ), nanoparticles. Structural and morphological characterization revealed the formation of an aggregate of La 2 O 3- x nanocrystals in the form of hollow spheres. Photocatalytic activity (PCA) was benchmarked against commercial La 2 O 3 and Evonik Aeroxide ® TiO 2 P25 via dye degradation experiments and a significant pH dependence of PCA is reported. Furthermore, chemical assays based on the Fenton reaction verified the scavenging properties of the synthesized materials towards reactive oxygen species (ROS), with increased scavenging of hydroxyl ( ∙ OH) and superoxide (O 2 ∙– ) radicals observed at pH 4.8. Biological assays (in vitro), with a 24 h incubation period in the presence of the La 2 O 3- x nanoparticles, were conducted upon a non-malignant human keratinocyte cell line (HaCaT). The La 2 O 3- x nanoparticles showed no toxicity when compared with the control over a significant concentration range. Biocompatibility with the non-malignant HaCaT cell line suggests the future application of La 2 O 3- x as a doping material for inorganic oxides used as UV filters or as an antioxidant to mitigate oxidative stress by scavenging free radicals in conditions such as melanoma and inflammation. Graphic abstract