Electronic Supplementary Material (ESI) for ChemComm. This journal is © The Royal Society of Chemistry 2019

Supporting Information

Green separation of rare earth elements by valence-selective crystallization of MOFs

Pengfei Yang, Qixin Zhuang, Yongsheng Li and Jinlou Gu*

†Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials

Science and Engineering, East China University of Science and Technology, Shanghai

200237, China

E-mail: [email protected]

Fax: +86-21-64250740; Tel: +86-21-64252599

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1. Experimental details

1.1 Chemicals and materials.

Diammonium cerium nitrate (Ce(NH4)2(NO3)6), fumaric acid (FUM),

1,3,5-benzenetricarboxylic acid (BTC), succinic acid (SUC), sodium

1,4-benzenedicarboxylate (Na2BDC), lanthanum nitrate hexahydrate

(La(NO3)3·6H2O), praseodymium nitrate hexahydrate (Pr(NO3)3·6H2O), neodymium nitrate hexahydrate (Nd(NO3)3·6H2O), samarium nitrate hexahydrate (Sm(NO3)3·6H2O), terbium nitrate hexahydrate (Tb(NO3)3·6H2O), erbium nitrate hexahydrate (Er(NO3)3·6H2O), ttterbium nitrate pentahydrate (Yb(NO3)3·5H2O), iron(III) nitrate nonahydrate

(Fe(NO3)3·9H2O), copper(II) nitrate hydrate (Cu(NO3)2·3H2O) nickel(II) nitrate hexahydrate

(Ni(NO3)2·6H2O), and cobaltous nitrate hexahydrate (Co(NO3)2·6H2O) were provided by

Aladdin Industrial Corporation, Shanghai. Cetone, alcohol, N, N-dimethylformamide (DMF), ethanol and acetic acid (HAc) were purchased from Sinopharm Chemical Reagent Co., Ltd,

China. The applied water (18.1 MΩ·cm-1) was purified from a NW Ultra-pure Water System

(Heal Force, China). All the chemicals were used as-received without further purification.

1.2 Instruments and methods.

Powder X-ray diffraction (PXRD) patterns were measured at a scan rate of 6° min-1 on

Bruker D8 equipped with Cu Kα radiation (40 kV, 40 mA). N2 sorption isotherms were recorded on a Micromeritics Tristar 3020 porosimeter at -196 oC. All samples were activated by using the “outgas” function of the adsorption instrument for 12 h at 100 °C prior to gas adsorption/desorption measurements. The surface area and micropore volume of all samples

2 was calculated by the Brunauer-Emmett-Teller (BET) method. The molar fraction of elements, and the percentage yields of samples were calculated by inductively coupled plasma optical emission spectrometer (ICP-OES).

1.3 Synthesis of Ce-MOF-801.

The influence of the reaction temperature on the Ce-MOF-801 was investigated by systematically changing the reaction temperature (25, 40, 60, 80 and 100 oC) when the other reagents were 7.0 M HAc (10 mL), 1 mmol Ce(NH4)2(NO3)6 and 1 mmol FUM and the reaction time was set to 6 h. The yields: 252 mg for 25 oC; 255 mg for 40 oC; 226 mg for 60 oC; 150 mg for 80 oC; 64 mg for 100 oC.

The influence of reaction time on Ce-MOF-801 was investigated by regulating reaction time (10 min, 30 min, 2 h, 6 h, and 12 h) when the other reagents were 10 mL HAc (7.0 M), 1

o mmol Ce(NH4)2(NO3)6 and 1 mmol FUM and the reaction temperature was set at 40 C. The yields: 249 mg for 10 min; 252 mg for 30 min; 249 mg for 2 h; 255 mg for 6 h; 255 mg for

12 h.

The influence of the amount of HAc on Ce-MOF-801 was investigated by introducing different equivalents (eq) of HAc ( 0 eq, 10 eq, 35 eq, 70 eq and 105 eq, based on

o Ce(NH4)2(NO3)6) when the reaction temperature was set at 40 C and the reaction time was set to 6 h. The yields: 267 mg for 0 eq; 267 mg for 10 eq; 258 mg for 35 eq; 255 mg for 70 eq;

247 mg for 100 eq.

In a typical experiment, the Ce-MOF-801 was synthesized as follows: FUM (116 mg,

1.0 mmol) was placed in a glass reaction bottle (20 mL), then, an HAc solution (8 mL) was

3 added. After ultrasonication for 20 min, the HAc solution (2 mL) contained 1.0 mmol

Ce(NH4)2(NO3)6 was added rapidly under a certain reaction temperature. The glass reactor was sealed and heated using a constant temperature water bath without stirring. The light-yellow precipitate was separated from the supernatant by centrifugation and washed with H2O (once) and ethanol (twice). Finally, the obtained solids were dried under vacuum at

90 oC for 12 h.

As an optimized result, Ce-MOF-801 was obtained following the above procedures based on the reaction temperature of 40 oC, the reaction time of 6 h and the HAc solution (6 mL H2O and 4 mL HAc, 70 eq).

1.4 Separation experiment.

The Separation of Ce from other rare earth (RE) element. An extra RE(NO3)3·6H2O (RE

= La, Pr, Nd, Sm, Tb, Er, and Yb, the molar ratio of individual RE to Ce4+ is 1 : 1) was added to the aqueous solultion under otherwise the same condition for the synthesis of Ce-MOF-801.

The reaction temperature was set to room temperature, and the reaction time was set to 10 min. The obtained MOFs were marked as RE/Ce-MOF-801. The yields: about 250 mg for all

RE/Ce-MOF-801.

Large-scale Separation of Ce/La. 0.1 mol La(NO3)3·6H2O and Ce(NH4)2(NO3)6 were dissolved in HAc solution (0.2 L, 7.0 M), then the solution was added to 0.8 L FUM solution

(0.125 M) at room temperature without stirring. After 10 min, the obtained solid was separated by filtering and was washed with water. Finally, approximate 28 g Ce-MOF-801

(about 90 mmol Ce) was obtained.

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Employing Na2BDC as a crystallization ligand. Na2BDC (210 mg, 1.0 mmol) was dispersed in HAc solution (8 mL, 0.3 M) by ultrasound for 20 min. Ce(NH4)2(NO3)6 (1.0 mmol) and La(NO3)3·6H2O (1.0 mmol) was dissolved in HAc solution (2 mL, 0.3 M). Then, the two solutions were rapidly mixed at 25 oC without stirring. After 10 min, the yellow solid was isolated by centrifugation and was washed with H2O (once), DMF (once) and ethanol

(twice). Finally, the obtained sample was heated at 90 oC in a vacuum for 12 h. Yields: 264 mg.

Employing BTC as a crystallization ligand. BTC (105 mg, 0.5 mmol) was dispersed in

HAc solution (7 mL, 5.25 M) by ultrasound for about 20 min. Ce(NH4)2(NO3)6 (1.5 mmol) and La(NO3)3·6H2O (1.5 mmol) were dissolved in HAc solution (3 mL, 5.25 M). Then, the two solutions were rapidly mixed at 25 oC without stirring. After 10 min, the yellow solid was isolated by centrifugation and was washed with H2O (once) and ethanol (twice). Finally, the obtained sample was heated at 90 oC in a vacuum for 12 h. Yield: 264 mg.

Employing SUC as a crystallization ligand. SUC (118 mg, 1.0 mmol) was dispersed in

HAc solution (8 mL, 0.2 M) by ultrasound for about 20 min. Ce(NH4)2(NO3)6 (1.0 mmol) and

La(NO3)3·6H2O (1.0 mmol) were dissolved in HAc solution (2 mL, 0.2 M). Then, the two solutions were rapidly mixed at 25 oC without stirring. After 10 min, the yellow solid was isolated by centrifugation and was washed with H2O (once) and ethanol (twice). Finally, the obtained sample was dried at 60 oC in air for 3 h. Yield: 271 mg.

Separating Fe3+ from a mixed aqueous solution of Fe3+, Cu2+, Co2+ and Ni2+. 3 mmol

Fe(NO3)3·9H2O, Cu(NO3)2·3H2O, Ni(NO3)2·6H2O and Co(NO3)2·6H2O were dissolved in 4

5 mL H2O, then 2 mmol BTC was added to the solution. The mixed solution heated for 12

o hours under stirring conditions at 95 C. The obtained solid was washed with H2O (once) and ethanol (twice). Finally, the obtained sample was dried at 60 oC in air for 3 h. Yield: 475 mg.

Fig. S1 N2 sorption isotherms of the Ce-MOF-801 prepared at different temperatures.

Fig. S2 PXRD patterns of the Ce-MOF-801 prepared with different reaction time.

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Fig. S3 N2 sorption isotherms of the Ce-MOF-801 prepared with different reaction time.

Fig. S4 The BET surface area and yields of the Ce-MOF-801 prepared with different reaction time.

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Fig. S5 N2 sorption isotherms of the Ce-MOF-801 prepared with different amounts of HAc.

Fig. S6 PXRD patterns of the Ce-MOF-801 prepared with different amounts of HAc.

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Table S1 Textural properties of the Ce-MOF-801 prepared with different amounts of HAc.

(a) (b) (c) (d) The amounts of SBET Smicro Sext Vt HAc (m2/g) (m2/g) (m2/g) (cm3/g)

0 eq 484 380 104 0.501

10 eq 551 414 137 0.619

35 eq 704 577 127 0.637

70 eq 898 767 131 0.719

105 eq 851 755 95 0.560

(a) SBET is the BET specific surface area. (b) Smicro is the t-plot specific micropore surface area calculated from the N2 adsorption-desorption isotherm. (c) Sext is the extra surface area estimated by subtracting Smicro from SBET. (d) Vt is the single point adsorption total pore volume at P/P0= 0.99.

Fig. S7 SEM images of the Ce-MOF-801 prepared with different amounts of HAc.

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Fig. S8 PXRD patterns of the Ce-MOF-801 and RE/Ce-MOF-801 (RE = La, Pr, Nd, Sm, Tb,

Er and Yb).

Fig. S9 N2 sorption isotherms of the Ce-MOF-801 and RE/Ce-MOF-801 (RE = La, Pr,

Nd, Sm, Tb, Er and Yb).

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Table S2 The BET surface area (SBET) and yields of Ce-MOF-801 and RE/Ce-MOF-801(RE

= La, Pr, Nd, Sm, Tb, Er and Yb).

Ce-MOF-8 La/Ce Pr/Ce Nd/Ce Sm/Ce Tb/Ce Er/Ce Yb/Ce 01

2 SBET (m /g) 790 807 806 813 799 804 801 797

Yield (%) 87.8 88.9 87.7 87.3 87.6 87.9 87.63 88.0

Fig. S10 PXRD patterns of La/Ce-MOF-801 obtained by enlarging 100-fold La/Ce separation system.

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Fig. S11 The molar fractions of Ce and La in the initial solution, separated solution and

La/Ce-MOF-801 MOFs solid. The data were obtained in the enlarging 100-fold La/Ce separation system.

Fig. S12 PXRD patterns of Ce-UiO-66 (A), Ce-MOF-808 (B), and Ce-UiO-66-SUC (C) obtained from La/Ce separation system.

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Fig. S13 PXRD patterns of the simulated MIL-100(Fe) and MIL-100(Fe) obtained from

Fe/Cu/Ni/Co separation system.

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