Green synthesis of lanthanum oxide nanoparticles using Stachytarpheta jamaicensis leaf extract for solar driven organic dye degradation and biological applications

Abstract

Metal oxide nanoparticles with superior physicochemical properties for environmental and medical applications have been developed due to recent breakthroughs in nanoscience. As part of the study, lanthanum oxide (La2O3) nanoparticles were fabricated through the use of a green method, in which leaf extract of Stachytarpheta jamaicensis (L.) Vahl was employed as a natural reducing and stabilizing agent, thus offering a green option instead of traditional chemical methods. The resulting nanoparticles were thoroughly analysed by XRD, SEM, FTIR, UV-Visible spectroscopy, DLS/zeta potential and TG/DTA tests to verify phase purity, morphology, elemental composition, functional groups, particle size distribution, and optical properties. PXRD showed the presence of a crystalline structure with an average crystallite size of 38.52 nm. UV-visible spectroscopy absorption bands at 216 and 233 nm accompanied by an absorption edge at 335 nm revealed a semiconducting optical bandgap of around 2.9 eV. La2O3 nanoparticles (0.5 mg/mL) under solar light exhibit degradation of methylene blue and Congo red at about 94.8% and 93.1%, respectively, with pseudo-first- order rate constants of 0.01134 min− 1 for MB and 0.02046 min− 1 for CR. Hydroxyl (·OH) and superoxide (O₂·−) radical species were found to be the major reason for the degradation based on trapping experiments. Besides that, La2O3 nanoparticles were shown to have a strong antimicrobial effect on Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphylococcus aureus. This work indicates that green-synthesized La2O3 nanoparticles have a good prospect of being used for wastewater treatment, Environmental degradation and other related applications in a Biomedical and environmentally friendly way.