Supporting Information

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1 Supporting Information Selective Electrochemical Separation and Recovery of Uranium from mixture of Uranium(VI) and Lanthanide(III) ions in aqueous medium Rahul Agarwal* +# and Manoj Kumar Sharma +# + Homi Bhabha National Institute, Mumbai , India # Fuel Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai * Corresponding Author: Tel.: ; Fax: rahulmarru@barc.gov.in; rahulagarwal715@gmail.com Table of content Figure S1. CVs of 10 mm K 3 [Fe(CN) 6 ] in 0.1 M KCl on (i) Pt and (ii) PEDOT:PSS/Pt electrode at a scan rate of 10 mv s -1...S3 Figure S2. Experimental setup for electrodeposition of UO 2 on PEDOT:PSS/Pt wire gauze electrode...s3 Figure S3. CVs of (a) Pt and (b) PEDOT:PSS/Pt electrode in (i) absence and (ii) presence of 10 mm UO 2 2+ in 0.1 M KCl at a scan rate of 50 mv s -1...S4 Figure S4. CVs of 10 mm UO 2 2+ in 0.1 M KCl on PEDOT:PSS/GC at different scan rates...s5 Figure S5. Plot of corresponding peak current ( ) vs. square root of scan rate (ʋ. ) obtained from Fig. S4...S5 Figure S6. Plot of corresponding Ln(I) vs. Ln(ʋ) obtained from Fig. S4...S6 Figure S7. CVs of 10 mm UO 2+ 2 in 0.1 M KCl on PEDOT:PSS/Pt at a scan rate of 10 mv s -1 (a) ten repetitive measurement on single electrode; (b) measurement on single electrode for 5 consecutive days and (c) measurement on 3 different PEDOT:PSS/Pt electrode...s7 Figure S8. SEM images of electrodeposited UO 2 film over PEDOT:PSS/Pt electrode...s7 Figure S9. CV of PEDOT:PSS/Pt electrode in 10 mm UO 2 2+ in 0.1 M KCl at a scan rate of 50 mv s -1 at different negative potentials...s8 Figure S10. UV-Vis spectra of UO 2 2+ in 0.1 M KCl (i) before electrodeposition, (ii) after electrodeposition and (iii) fresh 0.1 M KCl (ph=2) after stripping of electrodeposited UO 2...S8 S-1

2 Figure S11. CVs of blank, La 3+, Ce 3+ and Sm 3+ (10 mm each) in 0.1 M KCl on (a) Pt and (b) PEDOT:PSS/Pt at a scan rate of 50 mv s -1...S9 Figure S12. CVs of 10 mm Sm 3+ in 0.1 M KCl on (i) Pt; (ii) Au and (iii) GC electrode at a scan rate of 50 mv s -1...S10 Figure S13. CVs of different concentration of Sm 3+ in 0.1 M KCl on Pt at a scan rate of 50 mv s -1...S11 Table S1. Electrochemical parameters obtained from CV on PEDOT:PSS/Pt electrode in 10 mm UO 2 2+ in 0.1 M KCl at different scan rates...s11 Table S2. Electrochemical results obtained from Controlled Potential Coulometric experiments S12 Table S3. Mass Conservation during electrodeposition and stripping of UO 2 from 10 mm UO 2 2+ in 0.1 M KCl (Gravimetric method)...s12 S-2

3 Figure S1. CVs of 10 mm K 3 [Fe(CN) 6 ] in 0.1 M KCl on (i) Pt and (ii) PEDOT:PSS/Pt electrode at a scan rate of 10 mv s -1. Figure S2. Experimental setup for electrodeposition of UO 2 on PEDOT:PSS/Pt wire gauze electrode. S-3

4 Figure S3. CVs of (a) Pt and (b) PEDOT:PSS/Pt electrode in (i) absence and (ii) presence of 10 mm UO 2 2+ in 0.1 M KCl at a scan rate of 50 mv s -1. S-4

5 Figure S4. CVs of 10 mm UO 2 2+ in 0.1 M KCl on PEDOT:PSS/GC at different scan rates. Figure S5. Plot of corresponding peak current ( ) vs. square root of scan rate (ʋ. ) obtained from Fig. S4. S-5

6 Figure S6. Plot of corresponding Ln(I) vs. Ln(ʋ) obtained from Fig. S4. Repeatability and Reproducibility of electrochemical response of UO 2+ 2 /UO 2 couple on PEDOT:PSS/Pt The repeatability of electrochemical response of modified electrode for UO 2+ 2 /UO 2 2+ couple is determined by recording ten repetitive CVs of 10 mm UO 2 in 0.1 M KCl at a scan rate of 10 mv s -1 (Fig. S7a). Precise peak currents are obtained with relative standard deviation (RSD) of 0.1% for U(VI) reduction and 0.1% for U(IV) oxidation. The reproducibility of results is examined by recording CVs in the same solution for 5 consecutive days (Fig. S7b). Precise peak currents are obtained with RSD of 1.06% for U(VI) reduction and 3.37% for U(IV) oxidation. Three different modified electrodes are prepared following the same modification procedure and CVs in the same solution is recorded (Fig. S7c). Reproducible peak currents are obtained with RSD of 2.01% for U(VI) reduction and 1.64% for U(IV) oxidation. S-6

7 Figure S7. CVs of 10 mm UO 2 2+ in 0.1 M KCl on PEDOT:PSS/Pt at a scan rate of 10 mv s -1 (a) ten repetitive measurement on single electrode; (b) measurement on single electrode for 5 consecutive days and (c) measurement on 3 different PEDOT:PSS/Pt electrode. Figure S8. SEM images of electrodeposited UO 2 film over PEDOT:PSS/Pt electrode. S-7

8 Figure S9. CV of PEDOT:PSS/Pt electrode in 10 mm UO 2 2+ in 0.1 M KCl at a scan rate of 50 mv s -1 at different negative potentials: -0.5 V (black), -0.6 V (magenta), -0.7 V (blue), V (green) and -0.9 V (red). Figure S10. UV-Vis spectra of UO 2 2+ in 0.1 M KCl (i) before electrodeposition, (ii) after electrodeposition and (iii) fresh 0.1 M KCl (ph=2) after stripping of electrodeposited UO 2. Inset shows the zoomed portion of Fig. S10(ii). S-8

9 Cyclic voltammograms of Lanthanides: Figure S11. CVs of blank, La 3+, Ce 3+ and Sm 3+ (10 mm each) in 0.1 M KCl on (a) Pt and (b) PEDOT:PSS/Pt at a scan rate of 50 mv s -1. It is found that the observed reduction potential of Sm is well below to the reported value in literature. 1,2 So to confirm our results, we choose three different electrodes; (i) Pt, (ii) Au and (iii) GC and CV of Sm is carried out using these electrodes. S-9

10 Figure S12. CVs of 10 mm Sm 3+ in 0.1 M KCl on (i) Pt; (ii) Au and (iii) GC electrode at a scan rate of 50 mv s -1. From the above figure, it is observed that, the cathodic peak potential is shifted towards more negative values as we shift from Pt to Au electrode and the peak is not observed in case of GC electrode and it falls outside the electrochemical window of GC in 0.1 M KCl. So, Sm 3+ to Sm 2+ reduction potential depends on the kind of working electrode used as well as on the medium of study. It is also important to note that experimental conditions (different from standard condition) also affect the standard reduction potential of Sm 3+. To further confirm that weather this peak is due to Sm or not, we vary the concentration of Sm 3+ and record the CV as shown below: S-10

11 Figure S13. CVs of different concentration of Sm 3+ in 0.1 M KCl on Pt at a scan rate of 50 mv s -1. As we increase the Sm 3+ concentrations, both the cathodic and anodic peak increases systematically. This further proves, the peaks observed in the above figure are due to Sm only. Table S1. Electrochemical parameters obtained from CV on PEDOT:PSS/Pt electrode in 10 mm UO 2 2+ in 0.1 M KCl at different scan rates. ν / V s -1 E c p /V E c p/2 /V i c p /A E a p /V E a p/2 /V i a p /A E P (E a p -E c p )/V E 0 '/V E E E E E E E E E E E E S-11

12 Table S2. Electrochemical results obtained from Controlled Potential Coulometric experiments. Exp. No. Mass of U taken (mg) Charge/stripping step (Coulombs) Mass obtained (mg) Expected charge: Coulombs Experimentally observed: Coulombs (Average) Efficiency of separation:. 100 %=91.02%. RSD % 6.67 % Table S3. Mass Conservation during electrodeposition and stripping of UO 2 from 10 mm UO 2 2+ in 0.1 M KCl (Gravimetric method) U taken U deposited on electrode surface U left in solution Efficiency of deposition gm gm gm 98 % U on electrode U stripped in U left on electrode Efficiency of surface solution surface stripping gm gm 95 % References: 1. Timnick, A.; Glockler, G. The Half-Wave Potential of Samarium. J. Am. Chem. Soc. 1974, 70, Morss, L. R. Thermochemical Properties of Yttrium, Lanthanum, and the Lanthanide Elements and Ions. Chem. Rev. 1976, 76, 827 S-12

13 For TOC only Synopsis: A new electrochemical approach is developed for selective electrochemical recovery of uranium from mixture of uranium and lanthanides ions in aqueous medium on PEDOT:PSS/Pt electrode. Selective electrodeposition of UO 2 on modified electrode surface followed by stripping in fresh solution separates uranium from mixture solution. S-13