Green and chemical fuel driven solution combustion synthesis of La2O3 nanoparticles for their photocatalytic and electrochemical studies

The present work reports the synthesis of lanthanum oxide (La₂O₃) nanoparticles (NPs) prepared by using citric acid and banana peel powder as chemical and green fuels, labelled LO-C and LO-G, respectively. The nanoparticles (NPs) were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR and diffuse reflectance spectra (DRS) to understand the morphology, crystallinity and band gap of La₂O₃ NPs. According to XRD studies, the NPs are found in a hexagonal crystal structure, with an average crystallite size of 20.78 nm for LO-C and 28.14 nm for LO-G. The morphological studies (SEM and TEM) confirm different morphologies and high crystallinity for the two samples. UV-DRS method was applied to arrive at the band gap values of 5.48 eV and 5.81 eV for LO-C and LO-G NPs, respectively. The synthesized nanoparticles were used as photocatalysts for the degradation of three anionic dyes, namely, Acid Red 88 (AR88), Acid Blue 88 (AB88) and Eriochrome Black-T (EBT). Both LO-C and LO-G achieve near complete degradation of AR 88 in 75 min with rates of 0.014 min⁻¹ and 0.019 min⁻¹, respectively. AB 88 is degraded with an efficiency of 84.5% by LO-C (90 min) and 88.45% by LO-G (90 min). LO-C and LO-G achieve 74.49% and 81.08% degradation of EBT in 120 min. The LO-G catalyst shows excellent stability towards AR 88 degradation with about 7% decrease in efficiency after five photocatalytic cycles. Further, scavenger studies indicate hydroxy radical mediated oxidation of the dye as the major mechanistic pathway involved. In addition, LO-G modified carbon paste electrode exhibited excellent sensing of paracetamol and lithium ions in 0.1 M HCl with a limit of detection of 1 × 10⁻³ mol L⁻¹. Thus, the synthesized La₂O₃ nanoparticles can act as efficient photocatalysts and good sensors.