SUPPORTING INFORMATION. Scalable approach to highly efficient and rapid capacitive deionization with CNT-thread as electrodes

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1 SUPPORTING INFORMATION Scalable approach to highly efficient and rapid capacitive deionization with CNT-thread as electrodes Maku Moronshing, Chandramouli Subramaniam* Department of Chemistry, Indian Institute of Technology Bombay, Powai-Mumbai , INDIA. S-1

2 EXPERIMETAL SECTION Samples of twenty-ply textile cellulose yarn (cellulose thread) were obtained from Bombay Textile Research Association (BTRA, India) and also commercially procured from Associated Chemical Corporation Mumbai (India). The residence time was calculated from the volume of the flow channel and the flow rate. A constant potential was maintain through a DC power supply. This was replaced with an AA battery connected to a potentiostat for subsequent demonstration. Aliquots of solution were collected after flow through the CDI channel and analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES, ARCOS, SPECTRO Analytical Instruments GmbH). All experiments were conducted in batch mode. The electrosorption capacity (q e ) is defined by C Cf q = ( 0 ) W e * where C o and C f are the initial and final NaCl concentration (in mg.l -1 ), respectively. V is the volume (in ml) of the NaCl used and W is the mass (in g) of the active material in the working electrode. Electrosorption efficiency (EE) depicts the device efficiency in removing the salts from feed solution. ( C0 C EE= C 0 f V ) *100 where C o and C f are the initial and final NaCl concentration (in mg.l -1 ) in solution, respectively. All calculations were carried out with the total weight of CNT-thread electrodes, corresponding to active CNT-thread length of 360 cm weighing 36 mg. Electrochemical measurements were carried out using a Biologic SP-300 electrochemical workstation using a two-electrode assembly. Both the electrodes consist of a single CNT-thread S-2

3 in geometry identical to the device. Micro-Raman measurements were carried out with a Witec Alpha 300R spectroscopic system with a 532 nm excitation and 600 g.mm -1 grating. Gas sorption experiments were performed isothermally at 77 K on Quantachrome Autosorb adsorption analyzer. The Brunauer Emmett Teller (BET) method was used to calculate the specific surface areas and the pore size distributions were derived from the adsorption branches of the isotherms using Quenched Solid Density Functional Theory (QSDFT). Thermogravimetric analysis was performed on a Perkin Elmer Pyris Diamond TGA instrument. The contact angle of water on the surface of electrodes was measured by using goniometer Digidrop GBX. Conductivity measurement of the saline solution was carried out using Thermo Scientific Orion Star A215 ph/ Conductivity meter. Fourier transform- infrared spectroscopy (FT-IR) was carried out with Bruker HYPERION 300 FT-IR spectrometer. X-ray photoelectron spectroscopy (XPS) was conducted with AXIS Supra model, Kratos Analytical, SHIMADZU, employing Al Kα ( ev) source. S-3

4 Figure S1. Comparison of ASAR of different CDI electrode material reported 2-8 and the CNTs thread electrode reported here (red 4 mg.g -1.min -1 for 1000 mg.g -1 min -1 for 500 ppm, 1.72 mg.g -1 min -1 for 250 ppm and 0.36 mg.g -1.min -1 for 50 ppm. S-4

5 . Figure S2. SEM images of pristine, as-grown CNT. S-5

6 Figure S3. Low magnification SEM images of CNT-thread showing uniform immobilization of CNTs. The dotted lines act as eye-guide. S-6

7 Figure S4. Current and voltage trace of CNT-thread before and after desalination experiments S-7

8 Figure S5. FT-IR spectra of CNT-thread and CNT-thread post washing with ethanol. S-8

9 Figure S6. Carbon spectra (C1s) from X-ray photoelectron Spectrophotometry of pristine CNT, CNT-thread and cellulose yarn. S-9

10 Figure S7. Cyclic voltamogram of CNT-thread electrode with 1000 ppm NaCl S-10

11 Figure S8: Anodic current vs square root of scan rate of CNT-thread electrode with different feed concentration. S-11

12 Figure S9: Specific capacitance of CNTs thread (red circle) as compared with other material reported in literature (black quares) S-12

13 Figure S10. Ionic conductivity of the NaCl solutions for different residence times inside the capacitive deionization device. S-13

14 Figure S11. X-ray photoelectron spectra of CNT-thread before and after capacitive deionization. S-14

15 Table S1. Comparison of surface adsorption properties of pristine CNT, pure cellulose yarn and CNT-thread. Material Specific surface area (m 2 /g) Pore volume (cc/g) Pore diameter distribution (nm) Pristine CNT <1 Pristine cellulose <1 CNT-thread <1 and ~3 Table S2. Comparison of vibrational spectra features of pristine CNT, CNT-thread, ethanol washed CNT-thread and CNT-thread post desalination. Materials D-band (cm -1 ) G-band (cm -1 ) 2D-band (cm -1 ) CNT CNT-thread CNT-thread +EtOH CNT-thread post CDI The three distinct Raman peak correspond to the D-band, G-band and 2D-band from the SWCNT of the CNT-thread. The D-band (~1350 cm -1 ) arises from the defect induced on curvature of nanotube lattice. The 2D (2670 cm -1 ) is the overtone of the D-band and G-band (1590 cm -1 ) is due to first order E 2g of the graphitic carbon (tangential C-C bond stretching). S-15

16 Table S3. Comparison of ions concentration between the initial feed stock solution and the solution obtained after CDI experiments with CNT-thread that is not washed with ethanol. Sample Na + (ppm) Ca 2+ (ppm) Mg 2+ (ppm) Cl - (ppm) Initial feed stock solution Final solution after CDI REFERENCES (1) Hata, K.; Futaba, D. N.; Mizuno, K.; Namai, T.; Yumura, M.; Iijima. S. Water-Assisted Highly Efficient Synthesis of Impurity-Free Single-Walled Carbon Nanotubes. Science 2004, 306, (2) Suss, M. E.; Porada, S.; Sun, X.; Bisheuvel, P. M.; Yoon, J.; Presser, V. Water desalination via capacitive deionization: what is it and what can we expect from it? Energy. Environ. Sci. 2015, 8, (3) Kim, T.; Yoon, J. CDI ragone plot as a functional tool to evaluate desalination performance in capacitive deionization. RSC Adv. 2015, 5, (4) Shi, W.; Li, H.; Cao, X.; Leong, Z. Y.; Zhang, J.; Chen, T.; Zhang, H.; Yang, H. Y. Ultrahigh Performance of Novel Capacitive Deionization Electrodes based on A Three- Dimensional Graphene Architecture with Nanopores. Sci. Rep. 2016, 6, S-16

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