Dy3+-Doped Nd2O3 Nanoreplicas

Research Article Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

pubs.acs.org/journal/ascecg

A Green Route to Synthesize Pr3+/Dy3+-Doped Nd2O3 Nanoreplicas from Nd−Fe−B Magnets Samane Maroufi,* Rasoul Khayyam Nekouei, and Veena Sahajwalla Centre for Sustainable Materials Research and Technology (SMaRT), School of Materials Science and Engineering, University of New South Wales, Sydney 2052, Australia ABSTRACT: 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. KEYWORDS: E-waste, Recycling, Nd−Fe−B magnets, Precipitation, Nanoparticles

■

poses,33 and advanced materials (e.g., high temperature ceramics and superconductors).34,35 In its various nanoscale forms, REOs not only possess the outstanding properties of their bulk counterpart but display their own unique properties3,36−38 such as improved luminescence properties, enhanced emission lifetime, better quantum efficiency, attractive optical nonlinearity, excellent chemical stability, and improved catalytic activity. A range of methods to synthesize REO nanostructures with various morphologies (e.g., nanospherical particles,50 nanowires,47 nanorods,58 nanocubes,48 and nanoplates49) have been attempted and investigated. These include hydrogen plasma metal reaction,39 the colloidal precipitation route,20 the solvothermal reaction route,26,47 the hydrothermal reaction,18,20,40 the solution combustion method,14,41,42 the tartrate route,25 the sol−gel method,19,43 the microwave assisted hydrothermal method,40,44 radiofrequency inductively coupled (RF-IC) thermal plasma route,3 the inverse microemulsion technique,18,20 direct precipitation from high-boiling polyalco-

INTRODUCTION

In recent years, rare earth compounds have attracted much attention owing to their outstanding electronic, optical, and chemical properties1,2 originating from their partially shielded 4f orbital3,4 and also due to their stability, high excitation efficiency, longer luminescence lifetime, and low toxicity.5 This family of materials has been extensively used for phosphors, typically for emission of the three fundamental colors, blue, green, and red,11 catalysts,6,7 and biological labels.8−10 Neodymium (Nd) is one such important rare earth element in the lanthanide series, which has wide applications in a variety of areas such as luminescent and magnetic devices, catalysts, dielectrics, and protective coatings.12−16 Neodymium in oxide form has also been widely used in a broad range of applications,17 such as photonic applications (e.g., as phosphors providing yellow-to-violet upconversion emission),18,19 luminescent20,21 and thermoluminescent materials,20,22 catalysts20,21 or catalysts promoters (oxidative coupling of methane, N2 decomposition, dehydrogenation of alcohol, high-temperature processes),21,23,24 protective coatings,25−27 thin films,28 for the improvement of the electrical properties,29 gate dielectrics,30 photocatalytic applications,31 laser devices,32 navigation pur© XXXX American Chemical Society

Received: October 5, 2017 Revised: December 18, 2017

A

DOI: 10.1021/acssuschemeng.7b03585 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX

Research Article

ACS Sustainable Chemistry & Engineering hol solutions,18,20 the sol−gel process,4 electron-beam evaporation,45 thermal evaporation,28 and sol−gel autocombustion.46 The global supply of rare earth elements (REEs) is however under considerable strain. More than 90% of all REEs are currently extracted and processed in China. Given the increasing domestic demand from its own industries, China has gradually tightened export quotas, resulting in reduced supplies of REEs on the world market and corresponding price increases.51 These serious supply and cost challenges, as well as the inefficiencies in REE ore miningthe extraction of neodymium, for example, results in an excess of the more abundant elements, lanthanum and ceriummean other options for securing supplies of REEs are urgently needed. As many countries have no suitable ore deposits within their territories, and deposits elsewhere are both limited and finite, the recovery of REEs through recycling is essential.52 Currently, less than 1% of REEs are recovered via recycling. Nd−Fe−B permanent magnets are now one of the most widely used types of rare-earth magnets, which are implemented in a variety of applications such as electric power generation (computer and laptop hard drive) and transportation (hybrid and electrical vehicles).53,54 Given the growing demand for lightweight products with high magnetic strength to support the miniaturization of equipment in many existing and emerging applications, demand for Nd−Fe−B magnets is, likewise, expected to continue to rise, particular for the clean energy/ transport sectors.56 Industry forecasts estimate that global sales will increase to some US $12.7 billion by 2019.57 The growing stockpiles of Nd−Fe−B magnets, however, can be considered as a second valuable source of REEs (>30 wt %) for a wide range of applications. In our previous work,55 using a novel thermal isolation process, we were able to successfully recover REEs (i.e., Nd, Pr, and Dy) from waste Nd−Fe−B permanent magnets. Pulverized Nd−Fe−B permanent magnets (sourced by dismantling randomly obsolete hard drives from laptops collected from the Reverse E-waste Company, Sydney, Australia) were subjected to an oxidation process at 1000 °C for 60 min followed by carbothermal reduction at 1450 °C for 90 min using waste tire rubber-derived carbon (WTR-DC) as a reducing agent. Oxides of iron, cobalt, and nickel were reduced and separated from the oxide phase, which led to the formation of Fe-based metal and oxide phases with a clear interface. The oxide phase mainly contained REEs (i.e., Nd, Dy, and Pr) and a minor amount of B and Al. This study aims to utilize the extracted REEs from waste Nd−Fe−B permanent magnets for synthesizing crystallized rare earth (i.e., Nd, Dy, and Pr) oxide nanoparticles. First, using a simple technique (i.e., low temperature urea-based homogeneous precipitation), nanospherical particles of rare earth (i.e., Nd, Pr, and Dy) hydroxylcarbonate were synthesized. This reaction route, which requires a low temperature, is simple, convenient, cost-effective, green, and in most reported cases leads to homogeneous particles with regular shapes and a narrow size distribution. It is worth noting that nanosized rare earth carbonate (REC) compounds (i.e., rare earth carbonates RE2(CO3)3, hydroxycarbonates REOHCO3, oxycarbonate hydrates RE 2 O(CO 3 ) 2 -H 2 O, and dioxycarbonates RE2O2CO3)5 have received considerable research effort in recent years owing to their outstanding photoluminescence properties.59 The synthesized rare earth (i.e., Nd, Pr, and Dy) hydroxylcarbonate was used as a precursor for the synthesis of REO nanoparticles. The novel processes described here confirm the feasibly of synthesizing high quality value added

nanosized REO from waste materials with economic and environmental benefits.

■

EXPERIMENTAL PROCEDURE

Low-Temperature Urea-Based Homogeneous Precipitation Method. The REO separated from waste Nd−Fe−B magnets was ground using a ring mill and then subjected to analysis using an Inductively Coupled Plasma Mass Spectrometry (ICP-MS) technique. The analyzed composition of the separated oxide phase is listed in Table 1. A comprehensive characterization study of the recovered

Table 1. ICP-MS Result of REEs Separated from Nd−Pr−Dy Magnet (wt %) Al

B

Co

Fe

Ni

Nd

Pr

Dy

1.35

2.41

0.01

0.60

0.01

64.2

11.9

1.97

REO can be found in our previous work.55 A total of 0.7 g of pulverized REO sample was added to 21 mL of nitric acid (16 M) and then placed on a hot plate at a temperature of 60 °C for 1 h. The powder was leached thoroughly, and the resulting solution (i.e., RE salt) was subsequently filtered to separate any undissolved particles. In this work, urea (CO(NH2)2) was used as a source of carbonate ions. A total of 21 g of urea (0.5 M) was dissolved into 320 mL of DI water at ambient temperature. This solution was then mixed with RE salt solution, followed by adding DI water to make a total volume of 350 mL. Under a vigorous stirring, temperature was increased to 85 °C. Immediately after increasing temperature, the pH increased from 1 to 10 and stayed at this condition for about 30 min under stirring. Temperature is a significant factor in this type of reaction. According to Matijevic,60 a temperature of around 85 °C is the best choice for rare-earth carbonate synthesis when using the urea homogeneous precipitation method. At an aging temperature below 70 °C, the decomposition of urea is too slow, and no precipitation occurs. At temperatures above 100 °C, the decomposition of urea is too fast, which can lead to secondary critical supersaturation conditions and, as a result of this, a broad size distribution of the particles. The solution was then allowed to gradually cool down to room temperature overnight without any stirring. The salted powder was washed using a centrifuge, and the resulting gel-like product was dried in an oven overnight.

■

RESULTS AND DISCUSSION Characterization of the Synthesized REOHCO3. The crystalline phases of the resulting precipitate were identified by X-ray diffraction spectrum illustrated in Figure 1a. From the Xray diffraction pattern, several intensive peaks corresponding to NdOHCO3 with an orthorhombic phase and pnma space group are detected. No diffraction peaks corresponding with Pr and Dy were found in the X-ray diffraction pattern. An FTIR spectrum of the resulting REOHCO3 was also obtained, as shown in Figure 1b. The broad band between ∼2500 and 3700 cm−1 represents O−H stretching vibrations, which corresponds to structural water.59 The vibration bands at 693 cm−1, 720 cm−1, 841 cm−1, 1081 cm−1, 1425 cm−1, and 1633 cm−1 are characteristic of the main stretching vibrations of carbonate ions. Notably, the FTIR of the hydroxycarbonate sample shows only an intensive vibration peak for carbonate; no peaks for other bonding are observed, providing further evidence of the presence of carbonate as the only compound in the precipitate. Mechanism of the Formation of REOHCO3. Formation of RE hydroxycarbonate occurs via multiple steps with urea decomposed at the first step. The decomposition of urea releases ions (NH4 +, OH−, and CO 32−) slowly59 and B


Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. (a) XRD and (b) FTIR spectra of the as-synthesized REOHCO3 using CO(NH2)2 as the carbon source.

Figure 2. (a) FE-SEM, (b) TEM images of synthesized (Nd−Pr−Dy)OHCO3, (c) N2 adsorption/desorption isotherm of synthesized (Nd−Pr− Dy)OHCO3, and (d) mass loss and derivative thermogravimetric (DTG) curves of (Nd−Pr−Dy)OHCO3 at a heating rate of 5 °C min−1 under a nitrogen purge of 20 mL min−1.

sites.61 The molar ratio of urea to rare-earth salt is one of the most important factors that influence the morphology of the products. The amount of urea in a reaction medium influences both the amount of nuclei formed as well as the point when supersaturation and therefore precipitation will occur, and these factors influence the size of the formed particles.62 Characterization and Thermal Decomposition of REOHCO3. The structure and morphology of the produced REOHCO3 was investigated using FE-SEM analysis. The FESEM image of the resulting REOHCO3, in Figure 2a, indicates that the REOHCO3 consisted of nanoparticles with a diameter smaller than 50 nm. The TEM image shown in Figure 2b also confirms the REOHCO3 nanoparticles were at diameters of 40−50 nm. The nitrogen adsorption/desorption isotherms of synthesized REOHCO3 was also carried out (Figure 2c) and a BET surface area of 60.5 m2/g was measured. High specific surface of the hyrdoxycarbone of REE synthesized is this work indicates

homogeneously into the reaction system (eq 1), which avoids the localized distribution of reactant. With more NH4+, OH−, and CO32− groups entering the reaction system, the alkanity and pH of the reaction medium increases, resulting in reaction between the CO32− ion and RE salt and therefore the formation of RE carbonates (eq 2). The whole process can be simply described by the following reactions: CO(NH 2)2 + 2H 2O → CO32 − + 2NH+4

(1)

NH3H 2O → NH+4 + OH−

(2)

Nd3 + + CO32 − + OH− → NdOHCO3

(3) −

Due to the slow decomposition of urea into OH and CO32− groups, numerous nucleating sites in the form of nanoparticles are formed. Prolonging reaction time will result in the attachment of the particles through self-assembly due to mineralization of interfacial energy by reducing nucleating C


Research Article


Figure 3. (a) General XPS spectrum of as-synthesize REO nano-particles; high resolution XPS spectra of (b) Nd 3d, (c) Pr 3d, (d) Dy 3d, and (e) O 1s.

The thermal degradation behavior of REOHCO3 was studied by thermogravimetric analysis (TGA); the sample was heated from room temperature to 1000 °C at a heating rate of 20 °C/ min under a nitrogen purge of 20 mL/min. Thermogravimetric analysis (Figure 2d) shows three degradation steps upon gradual heating with a total mass loss of ∼30% corresponding to dehydration and decarbonation. Around 10% of the total mass loss is attributed to the release of water at temperatures below 200 °C, and the remaining 20% mass loss was due to the decomposition of the carbonate at ∼450 °C and its full transformation to oxides above 700 °C. The formation of oxide from a hydroxycarbonate precursor is a two step process:

Figure 4. XRD spectrum of the as-synthesized REO nanoparticles.

2NdOHCO3 → Nd 2O2 CO3 + H 2O + CO2

(4)

Nd 2O2 CO3 → Nd 2O3 + CO2

(5)

Thermal decomposition of the REOHCO3 precursor undergoes two phase transformation processes when the temperature is elevated from room temperature to 1000 °C. The first one is the transformation from REOHCO3 to RE2O2CO3 with the turning point at 451, and the second one is transformation from RE2O2CO3 to REO with the turning point at 696. In this work, a temperature of 700 °C was selected for thermal decomposition of the REOHCO3 and the formation of REO. After thermal decomposition at 700 °C, the resulting oxide sample was subjected to further characterization study. Characterization of the As-Synthesized REO. In order to address the surface chemistry occurring at the as-synthesized REO surface, the sample was subjected to XPS analysis whose results are shown in Figure 3. The survey spectrum of assynthesized REO nanoparticles (Figure 3a) indicates several

that this sample can be potentially suitable for other applications such as photoluminescence,61,63,64 water treatment,65 and as precursors for REO. The synthesized hydroxycarbonate is a promising precursor for the synthesis of REOs, as it was prepared via a very simple and cost-effective method and it possessed a homogeneous composition which can be decomposed at low temperature. In order to find the exact temperature at which the synthesized hydroxycarbonate precursor decomposes and completely transforms to oxides, thermal analysis of the precursor was carried out. Thermal decomposition of the homogeneously precipitated precursor is a simple route toward tailored REO. D


Research Article


Figure 5. (a) TEM, (b) SAED, and (c, d) HRTEM images of as-synthesized REO nanoparticles.

1301.22 eV, which can be assigned to Dy in the +3 oxidation state.71 Figure 3e displays the O 1s spectrum of the sample, which fitted by three singlet peaks corresponds to oxygen in different bonding environments. The three peaks at binding energies of 528.7, 529.60, and 531.10 eV are attributed to O in the 2− ionic state, indicating that O predominately presents as Nd2O3, Dy2O3, and Pr2O3. The peak at 531.1 eV could also be assigned to O−H,71 indicating the high affinity of as-synthesized REO nanoparticles with water vapor due to exposure to the air atmosphere to form surface O−H owing to the hygroscopic nature of lanthanide oxides.72−74 The survey spectrum in Figure 3a indicates a low level of carbon present within the sample surface which can be associated with the C−O bond due to the adsorption of CO2 on the surface of the sample. A point can be raised in this context that no peaks corresponding to the carbonate phase was detected in X-ray diffraction pattern of the as-synthesized REO nanoparticles (Figure 4). This is further evidence that the carbon element detected by XPS is due to the reaction between the surface and CO2 present in the atmosphere. The crystallographic structure of the as-synthesized REO nanoparticles was studied using the X-ray diffraction spectrum as illustrated in Figure 4. From the X-ray diffraction pattern, several intensive peaks assigned to the cubic phase of Nd2O3 with planes of (2 2 2), (4 0 0), (4 31), (4 4 0), (4 3 1), (4 4 0), (6 2 2), (6 3 1), (8 0 0), (6 6 2), and (8 4 0) are detected. As can be seen from Figure 4, no additional peak corresponding to secondary phases of Pr and Dy was observed, which implies that Pr and Dy most probably have occupied the substitutional sites, leading to the formation of Pr/Dy doped Nd2O3 nanoparticles. However, when Pr3+ and Dy3+ ions are incorporated into the periodic crystal lattice of Nd2O3, a strain

Table 2. Structural Parameters Determined through XRD (h (2 (4 (4 (4 (6 (6 (8 (6 (8

k 2 0 3 4 2 3 0 6 4

l) 2) 0) 1) 0) 2) 1) 0) 2) 0)

d (nm) 0.320 0.277 0.217 0.196 0.167 0.163 0.138 0.127 0.124

peaks which correspond to the photoelectrons ejected from the orbitals of 3d of Nd, Pr, and Dy and orbital 1s of O. Figure 3b displays a doublet corresponding to Nd 3d5/2 and Nd 3d3/2 core levels of neodymium due to spin−orbit coupling.66 This doublet spin-energy separation is around 22.43 eV. The deconvolution of the Nd 3d5/2 and Nd 3d3/2 core-level clearly indicates the presence of several peaks. The strong peaks appearing at binding energies (BE) of 982 and 1004.43 eV are associated with the presence of Nd in a +3 oxidation state.67 The strong shoulder which is seen on the lower BE sides of the Nd 3d3/2 and also the small shoulder on the higher BE sides of Nd 3d3/2 peaks correspond to the shakeoff and shakeup satellites, respectively.68,69 The high resolution spectrum of Pr is shown in Figure 3c. A binding energy of the Pr 3d5/2 core level peak at 933.20 is assigned to the presence of Pr3+.70 The shake-off satellite structure also appears on the lower BE side of the Pr 3d5/2. Figure 3d shows high resolution spectra of the Dy 3d5/2 core level of dysprosium, which appears at a binding energy of E


Research Article


Figure 6. STEM analysis of the as-synthesized REO nanoparticles.

Figure 7. (a) FE-SEM and (b) N2 adsorption/desorption isotherm of synthesized REO nanoparticles.

sample. This further confirms that Nd2O3 was doped by Pr3+ and Dy3+. Replacing Nd3+ cations with dopants of Pr3+ and Dy3+ can change the interplanar spacing. Given that the ionic radii of Pr (rPr3+ = 1.13 Å) do not differ significantly from the ionic radii of Nd (rNd3+ = 1.12 Å), the deformation in the crystalline structure of the as-synthesized sample and decrease in interplanar distance value are mostly attributed to the Dy3+ substitution. Since, the ionic radius of Dy (rDy3+ = 1.05) is smaller than that for Nd3+, Dy3+ substituting Nd3+ in Nd2O3 lattice resulted in deformation of the host crystalline structure and shrinkage of the crystalline size. Figure 5c and d represent the HRTEM micrographs with visibility of nanoparticles at a scale of 5 and 2 nm, respectively. These micrographs display the formation of fringes at 5 and 2 nm scales, where fringe width corresponds to the d-spacing values for (2 2 2) and (4 0 0) planes. It should be mentioned that all the d-spacing values have been calculated using SAED patterns and then were compared with XRD results; however, Figure 5c and d are displayed only as a visual confirmation. To investigate the distribution of Nd, Pr, Dy, and O, the synthesized REO nanoparticles were further analyzed via scanning transmission electron microscopy (STEM) using a TEM F200 of 1 nm resolution, and the results are shown in

is expected to be induced into the system, resulting in the alteration of the lattice periodicity and decrease in crystal symmetry. High resolution TEM (HRTEM) and the corresponding selected area electron diffraction (SAED) patterns of the as-synthesized REO nanoparticles were used to analyze the crystalline structure. Figure 5 displays the TEM and HRTEM images as well as SAED patterns of the sample. Figure 5a clearly shows that the synthesized oxide nanoparticles are not sintered even after calcination, and they have diameters of 20−30 nm. The representative SAED pattern of the oxide nanoparticles is shown in Figure 5b. The presence of clear rings in the SAED pattern confirms the formation of homogeneous crystallized nanoparticles of very small size. The four rings corresponding to the most intense peaks of XRD are indexed with planes of (2 2 2), (4 0 0), (4 4 0), and (6 2 2). The interplanar distance values (d value) corresponding to the electron diffractions shown in the SAED pattern were measured as 0.302, 0.259, 0.182, and 0.154 nm, respectively. From XRD, d-spacing values corresponding to characteristic peaks of the cubic phase of Nd2O3 were also determined, and the results are shown in Table 2. Compared to the d-spacing values of the cubic phase of Nd2O3 determined through XRD peaks (Table 2), interpalanar distance values decreased in the as-synthesized F



■

Figure 6. The STEM elemental mapping clearly reveals that Nd, Pr, and Dy are homogeneously distributed throughout the sample, which can be a further indication that Pr3+ and Dy3+ substituted Nd3+ in the Nd2O3 lattice. The microstructure of the as-synthesized REO product was examined by FE-SEM. As can be seen in the FE-SEM image (Figure 7), the REO sample inherited its parent’s morphology, but its size was slightly shrunk in comparison to the REOHCO3 products in that the density of the former is higher than that of the latter. REOHCO3 was converted to REO, and its surface became rough during a subsequent calcination process with the gradual elimination of H2O and CO2. Nevertheless, conversion did not lead to changes in the morphologies. The morphologies were maintained perhaps because of the higher activation energies needed for the collapse of this structure.28 The nitrogen adsorption/desorption isotherms of synthesized REO were also carried out (Figure 7b), and a BET surface area of 27.5 m2/g was measured. The synthesized highly concentrated Pr3+/Dy3+-doped Nd2O3 nanoparticles described here can be a promising candidate for catalytic application, particularly in capturing CO2. In future work, we plan to investigate the synthesized REO’s behavior as an adsorbent in adsorbing CO2.

Research Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: s.maroufi@unw.edu.au. ORCID

Samane Maroufi: 0000-0001-5553-8519 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The financial support for this research was provided by the Australian Research Council through Laureate Fellowship FL140100215.

■

REFERENCES

(1) Hadi, A.; Yaacob, I. I. Novel synthesis of nanocrystalline CeO2 by mechanochemical and water-in-oil microemulsion methods. Mater. Lett. 2007, 61 (1), 93−96. (2) Xiao, Z.; Zhou, B.; Xu, F.; Zhu, F.; Yan, L.; Zhang, F.; Huang, A. Energy transfer among rare earth ions induced by annealing process of TmEr codoped aluminum oxide thin films. Phys. Lett. A 2009, 373 (8), 890−893. (3) Dhamale, G. D.; Mathe, V. L.; Bhoraskar, S. V.; Sahasrabudhe, S. N.; Dhole, S. D.; Ghorui, S. Synthesis and characterization of Nd 2 O 3 nanoparticles in a radiofrequency thermal plasma reactor. Nanotechnology 2016, 27 (8), 85603. (4) Qu, X.; Dai, J.; Tian, J.; Huang, X.; Liu, Z.; Shen, Z.; Wang, P. Syntheses of Nd2O3 nanowires through sol−gel process assisted with porous anodic aluminum oxide (AAO) template. J. Alloys Compd. 2009, 469 (1), 332−335. (5) Kaczmarek, A. M.; Van Hecke, K.; Van Deun, R. Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials. Chem. Soc. Rev. 2015, 44 (8), 2032−2059. (6) He, H.; Ma, H.; Sun, D.; Zhang, L.; Wang, R.; Sun, D. Porous Lanthanide−Organic Frameworks: Control over Interpenetration, Gas Adsorption, and Catalyst Properties. Cryst. Growth Des. 2013, 13 (7), 3154−3161. (7) Parac-Vogt, T. N.; Deleersnyder, K.; Binnemans, K. Lanthanide(III) complexes of aromatic sulfonic acids as catalysts for the nitration of toluene. J. Alloys Compd. 2004, 374 (1), 46−49. (8) Zhang, H.; Xu, Y.; Yang, W.; Li, Q. Dual-Lanthanide-Chelated Silica Nanoparticles as Labels for Highly Sensitive Time-Resolved Fluorometry. Chem. Mater. 2007, 19 (24), 5875−5881. (9) Li, C.; Lin, J. Rare earth fluoride nano-/microcrystals: synthesis, surface modification and application. J. Mater. Chem. 2010, 20 (33), 6831−6847. (10) Beaurepaire, E.; Buissette, V.; Sauviat, M.-P.; Giaume, D.; Lahlil, K.; Mercuri, A.; Casanova, D.; Huignard, A.; Martin, J.-L.; Gacoin, T.; et al. Functionalized Fluorescent Oxide Nanoparticles: Artificial Toxins for Sodium Channel Targeting and Imaging at the SingleMolecule Level. Nano Lett. 2004, 4 (11), 2079−2083. (11) Zhao, D.; Yang, Q.; Han, Z.; Sun, F.; Tang, K.; Yu, F. Rare earth hydroxycarbonate materials with hierarchical structures: Preparation and characterization, and catalytic activity of derived oxides. Solid State Sci. 2008, 10 (8), 1028−1036. (12) Xueping, Z.; Guo, X.; Shenglin, L.; Xin, F.; Jiaojiao, Z. Catalytic effect of Gd2O3 and Nd2O3 on hydrogen desorption behavior of NaAlH4. Int. J. Hydrogen Energy 2012, 37 (10), 8402−8407. (13) Abdelkader, A. M.; Hyslop, D. J. S.; Cox, A.; Fray, D. J. Electrochemical synthesis and characterization of a NdCo5 permanent magnet. J. Mater. Chem. 2010, 20 (29), 6039−6049. (14) Yu, R. B.; Yu, K. H.; Wei, W.; Xu, X. X.; Qiu, X. M.; Liu, S.; Huang, W.; Tang, G.; Ford, H.; Peng, B. Nd2O3 Nanoparticles Modified with a Silane-Coupling Agent as a Liquid Laser Medium. Adv. Mater. 2007, 19 (6), 838−842.

■

CONCLUSIONS Highly concentrated Pr3+/Dy3+-doped Nd2O3 nanoparticles were successfully synthesized from REEs (i.e., Nd, Pr, and Dy) derived from Nd−Fe−B magnets. Using a low temperature urea-based homogeneous precipitation method, RE (i.e., Nd, Pr, and Dy) OHCO3 nanoparticles with diameters of 30−50 nm and specific surface areas of 60 m2 g−1 were synthesized. Thermal degradation of the as-synthesized hydroxycarbonate was carried out at 700 °C and resulted in full transformation of ReOHCO3 to REO. XPS analysis of the as-synthesized REO surface indicates the presence of Nd2O3, Dy2O3, and Pr2O3. The X-ray diffraction spectrum of the bulk REO nanoparticles identified the 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 the 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+. Given that the ionic radii of Pr (rPr3+ = 1.13 Å) do not differ significantly from the ionic radii of Nd (rNd3+ = 1.12 Å), the deformation in the crystalline structure of the as-synthesized sample and decrease in interplanar distance value were mostly attributed to the Dy substitution. Since the ionic radius of Dy (rDy3+ = 1.05) is smaller than that for Nd, Dy substituting Nd in the Nd2O3 lattice resulted in deformation of the host crystalline structure and shrinkage of the crystalline size. FE-SEM images revealed that the resulting Pr3+/Dy3+-doped Nd2O3 nanoparticles had a diameter of 30−50 nm with a specific surface area of 27.5 m2 g−1. The Pr3+/Dy3+ doped Nd2O3 nanoparticles synthesized in this work can be considered promising candidates for catalytic applications. The proposed sustainable process could simultaneously demonstrate new low cost means of synthesizing high quality rare earth nanoparticles and the benefits of transforming waste to value. Such sustainable, costeffective approaches to transforming waste into secondary resources and products can help address the challenge of REE’s global resource depletion. G


Research Article

ACS Sustainable Chemistry & Engineering (15) Mohan, S.; Thind, K. S.; Sharma, G. Effect of Nd3 + concentration on the physical and absorption properties of sodiumlead-borate glasses. Braz. J. Phys. 2007, 37, 1306−1313. (16) Shylesh, S.; Radhika, T.; Rani, K. S.; Sugunan, S. Synthesis, characterization and catalytic activity of Nd2O3 supported V2O5 catalysts. J. Mol. Catal. A: Chem. 2005, 236 (1), 253−259. (17) Zhu, W.; Ma, J.; Xu, L.; Zhang, W.; Chen, Y. Controlled synthesis of Nd(OH)3 and Nd2O3 nanoparticles by microemulsion method. Mater. Chem. Phys. 2010, 122 (2), 362−367. (18) Que, W.; Kam, C. H.; Zhou, Y.; Lam, Y. L.; Chan, Y. C. Yellowto-violet upconversion in neodymium oxide nanocrystal/titania/ ormosil composite sol−gel thin films derived at low temperature. J. Appl. Phys. 2001, 90 (9), 4865−4867. (19) Sreethawong, T.; Chavadej, S.; Ngamsinlapasathian, S.; Yoshikawa, S. Sol−gel synthesis of mesoporous assembly of Nd2O3 nanocrystals with the aid of structure-directing surfactant. Solid State Sci. 2008, 10 (1), 20−25. (20) Bazzi, R.; Flores-Gonzalez, M. A.; Louis, C.; Lebbou, K.; Dujardin, C.; Brenier, A.; Zhang, W.; Tillement, O.; Bernstein, E.; Perriat, P. Synthesis and luminescent properties of sub-5-nm lanthanide oxides nanoparticles. J. Lumin. 2003, 102, 445−450. (21) Dedov, A. G.; Loktev, A. S.; Moiseev, I. I.; Aboukais, A.; Lamonier, J.-F.; Filimonov, I. N. Oxidative coupling of methane catalyzed by rare earth oxides. Appl. Catal., A 2003, 245 (2), 209−220. (22) Soliman, C. Neodymium oxide: A new thermoluminescent material for gamma dosimetry. Nucl. Instrum. Methods Phys. Res., Sect. B 2006, 251 (2), 441−444. (23) Centi, G.; Dall’Olio, L.; Perathoner, S. Oscillating Behavior in N2O Decomposition over Rh Supported on Zirconia-Based Catalysts: The Role of the Reaction Conditions. J. Catal. 2000, 192 (1), 224− 235. (24) Noronha, F. B.; Aranda, D. A. G.; Ordine, A. P.; Schmal, M. The promoting effect of Nb2O5 addition to Pd/Al2O3 catalysts on propane oxidation. Catal. Today 2000, 57 (3), 275−282. (25) Zhaorigetu, B.; Ridi, G.; Min, L. Preparation of Nd2O3 nanoparticles by tartrate route. J. Alloys Compd. 2007, 427 (1−2), 235−237. (26) Zawadzki, M.; Kȩpiński, L. Synthesis and characterization of neodymium oxide nanoparticles. J. Alloys Compd. 2004, 380 (1), 255− 259. (27) Chevalier, S.; Bonnet, G.; Larpin, J. P. Metal-organic chemical vapor deposition of Cr2O3 and Nd2O3 coatings. Oxide growth kinetics and characterization. Appl. Surf. Sci. 2000, 167 (3), 125−133. (28) Kosola, A.; Päiväsaari, J.; Putkonen, M.; Niinistö, L. Neodymium oxide and neodymium aluminate thin films by atomic layer deposition. Thin Solid Films 2005, 479 (1), 152−159. (29) Nahm, C. The electrical properties and d.c. degradation characteristics of Dy2O3 doped Pr6O11-based ZnO varistors. J. Eur. Ceram. Soc. 2001, 21, 545−553. (30) Dakhel, A. A. Characterisation of Nd2O3 thick gate dielectric for silicon. Phys. status solidi 2004, 201 (4), 745−755. (31) Byrappa, K.; Sunitha, M. H.; Subramani, A. K.; Ananda, S.; Rai, K. M. L.; Basavalingu, B.; Yoshimura, M. Hydrothermal preparation of neodymium oxide coated titania composite designer particulates and its application in the photocatalytic degradation of procion red dye. J. Mater. Sci. 2006, 41 (5), 1369−1375. (32) Ikesu, A.; Aung, Y. L.; Taira, T.; Kamimura, T.; Yoshida, K.; Messing, G. L. Progress in Ceramics lasers. Annu. Rev. Mater. Res. 2006, 36, 397−429. (33) Karpen, D. N. Reduced glare neodymium oxide containing window glass. U.S. Patent Specification 6416867.9. (34) Delorme, F.; Harnois, C.; Monot-Laffez, I.; Desgardin, G. Phys. C 2002, 372, 1127. (35) Singh, J.; Soni, N. C.; Srivastava, S. L. Bull. Mater. Sci. 2003, 26, 397. (36) Xu, A.-W.; Fang, Y.-P.; You, L.-P.; Liu, H.-Q. A Simple Method to Synthesize Dy(OH)3 and Dy2O3 Nanotubes. J. Am. Chem. Soc. 2003, 125 (6), 1494−1495.

(37) Wu, G.; Zhang, L.; Cheng, B.; Xie, T.; Yuan, X. Synthesis of Eu2O3 Nanotube Arrays through a Facile Sol−Gel Template Approach. J. Am. Chem. Soc. 2004, 126 (19), 5976−5977. (38) Fang, Y.-P.; Xu, A.-W.; You, L.-P.; Song, R.-Q.; Yu, J. C.; Zhang, H.-X.; Li, Q.; Liu, H.-Q. Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes. Adv. Funct. Mater. 2003, 13 (12), 955−960. (39) Liu, T.; Zhang; Shao; Li. Synthesis and Characteristics of Sm2O3 and Nd2O3 Nanoparticles. Langmuir 2003, 19 (18), 7569− 7572. (40) Kępiński, L.; Zawadzki, M.; Miśta, W. Hydrothermal synthesis of precursors of neodymium oxide nanoparticles. Solid State Sci. 2004, 6 (12), 1327−1336. (41) Chavan, S. V.; Sastry, P. U. M.; Tyagi, A. K. Combustion synthesis of nano-crystalline Nd-doped ceria and Nd2O3 and their fractal behavior as studied by small angle X-ray scattering. J. Alloys Compd. 2008, 456 (1), 51−56. (42) Umesh, B.; Eraiah, B.; Nagabhushana, H.; Nagabhushana, B. M.; Nagaraja, G.; Shivakumara, C.; Chakradhar, R. P. S. Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors. J. Alloys Compd. 2011, 509 (4), 1146−1151. (43) Duhan, S.; Aghamkar, P. Influence of temperature and time on Nd2O3-SiO2 composite prepared by the solgel process. Acta Phys. Pol., A 2008, 113 (6), 1671. (44) Zawadzki, M. Microwave-assisted synthesis and characterization of ultrafine neodymium oxide particles. J. Alloys Compd. 2008, 451 (1), 297−300. (45) Jeon, S.; Im, K.; Yang, H.; Lee, H.; Sim, S.; Choi, T.; Jang, H.; Wang, H. Electron Technol. 2001, 6, 20. (46) Yang, W.; Qi, Y.; Ma, Y.; Li, X.; Guo, X.; Gao, J.; Chen, M. Synthesis of Nd2O3 nanopowders by sol−gel auto-combustion and their catalytic esterification activity. Mater. Chem. Phys. 2004, 84 (1), 52−57. (47) Yin, S.; Akita, S.; Shinozaki, M.; Li, R.; Sato, T. Synthesis and morphological control of rare earth oxide nanoparticles by solvothermal reaction. J. Mater. Sci. 2008, 43 (7), 2234−2239. (48) Yang, S.; Gao, L. Controlled Synthesis and Self-Assembly of CeO2 Nanocubes. J. Am. Chem. Soc. 2006, 128 (29), 9330−9331. (49) Si, R.; Zhang, Y.-W.; Zhou, H.-P.; Sun, L.-D.; Yan, C.-H. Controlled-Synthesis, Self-Assembly Behavior, and Surface-Dependent Optical Properties of High-Quality Rare-Earth Oxide Nanocrystals. Chem. Mater. 2007, 19 (1), 18−27. (50) Yan, Z.-G.; Yan, C.-H. Controlled synthesis of rare earth nanostructures. J. Mater. Chem. 2008, 18 (42), 5046−5059. (51) Sepehri-Amin, H.; Ohkubo, T.; Zakotnik, M.; Prosperi, D.; Afiuny, P.; Tudor, C. O.; Hono, K. Microstructure and magnetic properties of grain boundary modified recycled Nd-Fe-B sintered magnets. J. Alloys Compd. 2017, 694, 175−184. (52) Binnemans, K.; Jones, P. T.; Blanpain, B.; Van Gerven, T.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: a critical review. J. Cleaner Prod. 2013, 51, 1−22. (53) Nakamoto, M.; Kubo, K.; Katayama, Y.; Tanaka, T.; Yamamoto, T. Extraction of Rare Earth Elements as Oxides from a Neodymium Magnetic Sludge. Metall. Mater. Trans. B 2012, 43 (3), 468−476. (54) Saito, T.; Sato, H.; Motegi, T. Recovery of rare earths from sludges containing rare-earth elements. J. Alloys Compd. 2006, 425 (1− 2), 145−147. (55) Maroufi, S.; Khayyam Nekouei, R.; Sahajwalla, V. Thermal Isolation of Rare Earth Oxides from Nd−Fe−B Magnets Using Carbon from Waste Tyres. ACS Sustainable Chem. Eng. 2017, 5, 6201. (56) Widmer, R.; Oswald-Krapf, H.; Sinha-Khetriwal, D.; Schnellmann, M.; Böni, H. Global perspectives on e-waste. Environ. Impact Assess. Rev. 2005, 25 (5), 436−458. (57) Neodymium Iron Boron Magnets Market (2014−2019) | Neodymium Iron Boron Magnets Market Report Trends, Analysis, Forecast - Micro Market Monitor. http://www.micromarketmonitor. com/market-report/neodymium-iron-boron-magnets-reports7154231446.html. H


Research Article

ACS Sustainable Chemistry & Engineering (58) Zhao, D.; Yang, Q.; Han, Z.; Sun, F.; Tang, K.; Yu, F. Rare earth hydroxycarbonate materials with hierarchical structures: Preparation and characterization, and catalytic activity of derived oxides. Solid State Sci. 2008, 10 (8), 1028−1036. (59) Vallina, B.; Rodriguez-Blanco, J. D.; Brown, A. P.; Blanco, J. A.; Benning, L. G. The role of amorphous precursors in the crystallization of La and Nd carbonates. Nanoscale 2015, 7 (28), 12166−12179. (60) Matijevic, E. Colloid Science of Ceramic Powders. Pure Appl. Chem. 1988, 60 (10), 1479−1491. (61) Li, G.; Peng, C.; Zhang, C.; Xu, Z.; Shang, M.; Yang, D.; Kang, X.; Wang, W.; Li, C.; Cheng, Z.; et al. Eu3+/Tb3+-Doped La2O2CO3/La2O3 Nano/Microcrystals with Multiform Morphologies: Facile Synthesis, Growth Mechanism, and Luminescence Properties. Inorg. Chem. 2010, 49 (22), 10522−10535. (62) Kaczmarek, A. M.; Van Hecke, K.; Van Deun, R. Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials. Chem. Soc. Rev. 2015, 44 (8), 2032−2059. (63) Lechevallier, S.; Lecante, P.; Mauricot, R.; Dexpert, H.; DexpertGhys, J.; Kong, H.-K.; Law, G.-L.; Wong, K.-L. Gadolinium−Europium Carbonate Particles: Controlled Precipitation for Luminescent Biolabeling. Chem. Mater. 2010, 22 (22), 6153−6161. (64) Kaczmarek, A. M.; Miermans, L.; Van Deun, R. Nano- and microsized Eu3+ and Tb3+-doped lanthanide hydroxycarbonates and oxycarbonates. The influence of glucose and fructose as stabilizing ligands. Dalt. Trans. 2013, 42 (13), 4639−4649. (65) Yang, X.; Zhai, Z.; Xu, L.; Li, M.; Zhang, Y.; Hou, W. LaCO3OH microstructures with tunable morphologies: EDTAassisted hydrothermal synthesis, formation mechanism and adsorption properties. RSC Adv. 2013, 3 (12), 3907−3916. (66) Kotani, A.; Ogasawara, H. Theory of core-level spectroscopy of rare-earth oxides. J. Electron Spectrosc. Relat. Phenom. 1992, 60, 257− 299. (67) Dingzang, Z.; Dingfei, Z.; Yuping, L.; Guangshan, H.; Yinning, G.; Fusheng, P. Neodymium-based Conversion Coating on AZ31 Magnesium Alloy. Rare Met. Mater. Eng. 2017, 46 (2), 289−295. (68) Burroughs, P.; Hamnett, A.; Orchard, A. F.; Thornton, G. Satellite structure in the X-ray photoelectron spectra of some binary and mixed oxides of lanthanum and cerium. J. Chem. Soc., Dalton Trans. 1976, 17, 1686−1698. (69) Suzuki, C.; Kawai, J.; Takahashi, M.; Vlaicu, A.-M.; Adachi, H.; Mukoyama, T. The electronic structure of rare-earth oxides in the creation of the core hole. Chem. Phys. 2000, 253 (1), 27−40. (70) Mekki, A.; Ziq, K.; Holland, D.; McConville, C. F. Magnetic properties of praseodymium ions in Na2O−Pr2O3−SiO2 glasses. J. Magn. Magn. Mater. 2003, 260 (1), 60−69. (71) Abu-Zied, B. M.; Hussein, M. A.; Asiri, A. M. Structural evolution of non-isothermally formed dysprosium sesquioxide nanoparticles and their optical and electrical conductivity properties. Ceram. Int. 2017, 43, 13166. (72) Xueping, Z.; Guo, X.; Shenglin, L.; Xin, F.; Jiaojiao, Z. Catalytic effect of Gd2O3 and Nd2O3 on hydrogen desorption behavior of NaAlH4. Int. J. Hydrogen Energy 2012, 37 (10), 8402−8407. (73) Nahm, C.-W. Microstructure and electrical properties of ZnOPr6O11-CoO-Cr2O3-Dy2O3-based varistors. Mater. Lett. 2004, 58 (6), 849−852. (74) Swihart, M. T. Vapor-phase synthesis of nanoparticles. Curr. Opin. Colloid Interface Sci. 2003, 8 (1), 127−133.

I


Dy3+-Doped Nd2O3 Nanoreplicas

Recommend Documents