Dissolution of Eu3+ cations in mesopores in amorphous Al2O3 and controlled reconstructive nucleation and growth of γ-Al2O3 nanoparticles

Dispersed Eu3+ cations in an aqueous EuCl3 solution easily incorporate in pores in a hydrogenated porous AlO(OH)·αH2O boehmite powder. H2 gas in pores and OH− anions from energized boehmite with pores covert EuCl3 into Eu2O3 in pores as per the reaction, 2 EuCl3+32H2+3 OH−→Eu2O3+6 HCl, in a closed reactor at room temperature. This is a very efficient spontaneous exothermic reaction which occurs with evolution of H2 gas and HCl vapour as per experimental conditions. The obtained Eu3+:Al2O3 product consists of dispersed Eu2O3 nanoparticles (D∼30 nm crystallite size) in an amorphous Al2O3 in a mesoporous structure. On heating, Eu2O3 nanoparticles dissolve in high surface energy pores and result in a complete amorphous structure of Eu3+: Al2O3 at ∼700 K. A controlled reconstructive nucleation and growth into γ-Al2O3 nanoparticles in D∼6.5 nm occurs from the amorphous state at ∼1000 K. Several batches of the reaction, with Eu3+ contents up to 1.5 wt.%, have been carried out and all of them have a complete dissolution of Eu3+ cations in Al2O3 at these temperatures. The results are analyzed in terms of X-ray diffraction, microstructures, and IR spectra of samples prepared under different conditions.