Combustion synthesis and stability of nanocrystalline La2O3 via ethanolamine-nitrate process

Pure nanocrystalline La2O3 powders were successfully prepared by the combustion method. The effect of ethanolamine-to-nitrate ratio on phase composition and crystallite size of the combustion products was systematically investigated. Pure hexagonal La2O3 powders were almost formed in stoichiometric reaction (ψ=1.15), while metallic La phase was obtained in fuel-rich conditions (ψ≥3.0). The as-synthesized hexagonal La2O3 was found to be chemically unstable in ambient air since a complete transformation to hexagonal La(OH)3 was detected after 24 h exposure to air. The resulting hexagonal La(OH)3 showed an excellent ability to remove water pollutant and could nearly remove 100% of the Congo red at room temperature with a removal capacity of 143.5 mg Congo red/g. The phosphate adsorption data on hexagonal La(OH)3 agreed well with the Langmuir model with the estimated maximum adsorption capacity of 57.8 mg/g.