CaO-containing LaCO₃OH nanogears and their luminescence and de-NOx properties

Large-scale, uniform, monodisperse LaCO₃OH cherry-blossom-like nanogears and/or nanocubes have been synthesized under hydrothermal reaction conditions. Upon the addition of only 5 mol% Ca²⁺ ions into a La nitrate salts solution with pH 8.5, LaCO₃OH crystals with novel cubic or nanogear structures are formed in the hexagonal phase. The hydrothermal reactions were carried out without the addition of a template or catalysts. Both 24 hour and 48 hour hydrothermal reactions yield 100% pure LaCO₃OH with no irregular particles. We examined the photoluminescence properties of the as-synthesized powders of the pure LaCO₃OH nanogears and found one broad emission band centered at 394 nm after excitation at λ = 280 nm. The NO reduction activity was also examined over highly dispersed CaO-containing La₂O₃ obtained after calcination the LaCO₃OH at 800^○C for 2 hours. The CaO-containing La₂O₃ catalysts showed good stability for NO reduction with CH₄ in the presence of O₂ and H₂O vapor.