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A Green Route to Synthesize Pr3+/Dy3+-Doped Nd2O3 Nanoreplicas from Nd–Fe–B Magnets

Maroufi, Samane, Khayyam Nekouei, Rasoul, Sahajwalla, Veena
ACS sustainable chemistry & engineering 2018 v.6 no.3 pp. 3402-3410
X-ray diffraction, crystal structure, deformation, ecosystem services, electronic wastes, magnetic materials, nanoparticles, rare earth elements, scanning electron microscopy, shrinkage, surface area, temperature, thermal degradation, transmission electron microscopy, value-added products
This paper details a green and sustainable process for synthesizing highly concentrated Pr³⁺/Dy³⁺-doped Nd₂O₃ nanoparticles from Nd–Fe–B magnets sourced from e-waste via a facile homogeneous precipitation route under mild conditions. Rare earth elements (REEs) are under a serious crisis owing to their uncertain supply and increasing global demand. REEs’ future demand growth is mainly linked to the use of Nd–Fe–B magnets, which are currently one of the most widely used types of rare-earth magnets with extensive implementation in a variety of applications. Using REEs (i.e., Nd, Pr, and Dy) derived from Nd–Fe–B magnets, we applied a low temperature urea-based homogeneous precipitation method and synthesized crystallized RE (i.e., Nd, Pr, and Dy) OHCO₃ nanoparticles with diameters of 40–50 nm and high specific surface area of 60 m² g–¹. The synthesized REOHCO₃ was used as a precursor for the synthesis of REO nanoparticles through a thermal degradation process at 700 °C. FE-SEM images revealed that the synthesized REO nanoparticles inherited their parent’s morphology. An X-ray diffraction spectrum of the synthesized REO nanoreplicas showed a cubic phase of Nd₂O₃ with no additional peak corresponding to the secondary phases of Pr and Dy. High resolution TEM (HRTEM) micrographs and electron diffraction of the selected area (SAED) of the as-synthesized REO nanoparticles exhibited deformation in crystalline structure, shrinkage of the crystalline size, and a decrease in interplanar distance value, indicating that Nd³⁺ in the Nd₂O₃ host lattice was replaced with dopants of Pr³⁺ and Dy³⁺. Novel synthesis of Pr³⁺/Dy³⁺-doped Nd₂O₃ nanoparticles from Nd–Fe–B magnets reported in this paper confirms a new opportunity to deal with REE critical supply while transforming a globally significant waste burden into value-added products delivering economic and environmental benefits.