Unveiling radical trapping in La2O3 nanoparticles under hydrothermal temperature variations for enhanced photocatalysis

The paper explores the synthesis, characterization, and photocatalytic activity of La 2 O 3 nanoparticles synthesized through the hydrothermal method at reaction temperatures of 150 °C and 200 °C, selected based on preliminary optimization and literature reports to balance nucleation, crystallinity enhancement, and defect suppression. XRD study validated the development of cubic phase La 2 O 3 with mean crystallite sizes of 17.36 nm and 20.21 nm, showing improved crystallinity with increasing temperature. Vibrational modes were observed by Raman spectroscopy, and a temperature dependent optical band gap shift was observed by the UV-Vis analysis, which is characteristic of the optical properties. It was revealed in morphological studies that the nanoparticles were rounded in shape and had sizes ranging between 52 and 60 nm. PL spectra demonstrated that higher synthesis temperatures reduced charge carrier recombination by minimizing structural defects, thereby improving optical performance. It was also found that La 2 O 3 nanoparticles obeyed the first-order kinetics in the degradation of methylene blue (MB) and rhodamine B (RhB) dyes since photocatalytic experiments were conducted. The efficiencies of the degradation in mercury light were 90.9% with MB and 85.2% with RhB, with rate constants of 1.39 x 10 - 2 min -1 and 1.08 x 10 -2 min -1 , respectively. The use of scavenger tests revealed that the primary reactive species are the hydroxyl radicals (OH) because the isopropyl alcohol had a significant impact on the photocatalytic activity, whereas EDTA and benzoquinone revealed the presence of minor roles of holes and superoxide radicals. These findings establish clear temperature, structure, and property performance relationships in La2O3 nanoparticles, demonstrating temperature-tunable bandgap engineering for optimized photocatalysis, making La 2 O 3 a promising photocatalyst for environmental remediation and advanced nanotechnology applications.