Supporting Information Tannic Acid Sorption and Its Role for Stabilizing Carbon Nanotube Suspensions Daohui Lin 1,2 and Baoshan Xing 2, * 1. Department of Environmental Science, Zhejiang University, Hangzhou, 310028, China 2. Department of Plant, Soil and Insect Sciences, University of Massachusetts, Amherst, MA 01003, USA *Corresponding author. TEL.: (413) 545-5212; fax: (413) 545-3958; e-mail: bx@pssci.umass.edu. Number of pages: 11 (this page is not included) Number of tables: 2 Number of figures: 9
Page S1 Table S1. Nonlinear isotherm models name abbrev. equation model parameters* Langmuir model LM q e = Q 0 b C e /(1 + b C e ) Q 0 (mg/g) is the maximum monolayer adsorption capacity. b constant is related to the molar heat of adsorption. Freundlich model FM q e = K f C e 1/n K f [(mg/g)/(mg/l) 1/n ] is Freundlich affinity Dual-Langmuir model DLM q e = Q 0 1 b 1 C e /(1 + b 1 C e ) + Q 0 2 b 2 C e /(1 + b 2 C e ) coefficient; 1/n is Freundlich exponential coefficient. Q 0 1 and Q 0 2 are the maximum monolayer adsorption capacities of site populations 1 and 2, respectively. b 1 and b 2 are DLM constants. Dual-model model DMM q e = Q 0 b C e /(1 + b C e ) + K d C e K d (L/g) is the partition coefficient * q e (mg/g) is equilibrium sorbed concentration; C e (mg/l) is equilibrium solution phase concentration.
Page S2 Table S2. Results of model fits to sorption data of tannic acid by carbon nanotubes a Langmuir model (LM) CNT Q 0 p of Q 0 b p of b Adj r 2 SWCNT 370 <0.01 0.097 <0.01 0.971 MWCNT10 399 <0.01 0.135 <0.01 0.971 MWCNT20 166 <0.01 0.082 0.015 0.848 MWCNT40 156 <0.01 0.106 0.013 0.851 MWCNT60 114 <0.01 0.195 0.011 0.829 MWCNT100 126 <0.01 0.086 0.025 0.809 Freundlich model (FM) CNT K f p of K f n p of N Adj r 2 SWCNT 82 <0.01 3.674 <0.01 0.950 MWCNT10 98 <0.01 3.894 <0.01 0.934 MWCNT20 39 <0.01 3.840 <0.01 0.981 MWCNT40 41 <0.01 4.135 <0.01 0.984 MWCNT60 37 <0.01 4.595 <0.01 0.967 MWCNT100 29 <0.01 3.849 <0.01 0.972 Dual-model model (DMM) CNT Q 0 p of Q 0 b p of b K d p of K d Adj r 2 SWCNT 295 <0.01 0.178 <0.01 0.265 <0.01 0.996 MWCNT10 338 <0.01 0.213 <0.01 0.232 <0.01 0.987 MWCNT20 105 <0.01 0.405 <0.01 0.205 <0.01 0.982 MWCNT40 105 <0.01 0.467 <0.01 0.179 <0.01 0.972 MWCNT60 79 <0.01 0.666 <0.01 0.168 <0.01 0.968 MWCNT100 73 <0.01 0.494 <0.01 0.170 <0.01 0.997 Dual-Langmuir model (DLM) CNT Q 0 1 p of Q 0 1 b 1 p of b 1 Q 0 2 p of Q 0 2 b 2 p of b 2 Adj r 2 SWCNT 256 <0.01 0.233 <0.01 242 <0.01 0.003 0.018 0.998 MWCNT10 250 <0.01 0.365 <0.01 215 <0.01 0.010 0.074 0.994 MWCNT20 99 <0.01 0.486 <0.01 307000 1.00 0.000 1.00 0.997 MWCNT40 100 <0.01 0.527 <0.01 506000 1.00 0.000 1.00 0.981 MWCNT60 75 <0.01 0.765 <0.01 488000 1.00 0.000 1.00 0.978 MWCNT100 73 <0.01 0.494 <0.01 456000 1.00 0.000 1.00 0.997 a Model equation and parameter definition are listed in Table S1. All estimated parameter values and their probability of assuming the null hypothesis (p) were determined by a commercial software program (SigmaPlot 9.0). Adj r 2 (also given by the program) is the fitting parameter adjusted square of correlation coefficient.
Page S3 OH H O OH H OH H HO H H OH -D-glucopyranose tannic acid digallic acid FIGURE S1. Chemical structure of tannic acid (Simon et al., 1994) and its main functional groups: -D-glucopyranose (Simionescu and Simionescu, 1976) and digallic acid (Pithayanukul et al., 2005). Pithayanukul, P., Ruenraroengsak, P., Bavovada, R., Pakmanee, N., Suttisri, R., Saen-oon, S. Inhibition of Naja kaouthia venom activities by plant polyphenols. J. Ethnopharmacol. 2005, 97, 527-533. Simionescu, N., Simionescu, M. Galloylglucoses of low molecular weight as mordant in electron microscopy II. the moiety and functional groups possibly involved in the mordanting effect. J. Cell Biol. 1976, 70, 622-633. Simon S.A., Disalvo, E.A., Gawrisch, K., Borovyagin, V., Toone, E., Schiffman, S.S., Needham, D., Mcintosh, T.J. Increased adhesion between neutral lipid bilayers: interbilayer bridges formed by tannic acid. Biophys. J. 1994, 1943-1958.
Page S4 Sorbed TA Conc., (mg/g) 350 300 250 200 150 100 50 0 0 0 40 80 120 160 Shaking Time, (h) 5 4 3 2 1 Absorbance Adsorption by SWCNT Adsorption by MWCNT100 Absorbance before centrifugation Absorbance after centrifugation FIGURE S2. Tannic acid (TA) sorption by carbon nanotubes (CNTs) and its stabilization of CNTs in aqueous phase as a function of shaking time. CNT suspendability is showed by absorbance at 800 nm of the suspensions of MWCNT100 (200 mg/l) in 100 mg/l TA solution before and after centrifuging at 3000 rpm for 20 min, respectively. Each datum point in the figure is the mean value of three replicates. The standard deviations of the three replicates are all below 5%. SWCNT is single-walled CNT; MWCNT100 is multi-walled CNT with diameter of 60-100 nm.
Page S5 -OH -CH SWCNT 1595 1260 970 1710 MWCNT10 MWCNT20 MWCNT40 MWCNT60 MWCNT100 4000 3600 3200 2800 2400 2000 1600 1200 800 400 Wavenumber, cm -1 Figure S3. DRIFTS spectra of carbon nanotubes (CNTs). Strong peak of 1595 cm -1 was attributed to the graphitic structure of the sp 2 -hybridized carbon in CNTs, while the broad 1260 cm -1 and strong 970 cm -1 peaks were probably due to the sp 3 carbon and the ring C-H deformation vibration, respectively. The C=O stretching mode (1710 cm -1 ) in the carboxylic acid was not significant, appearing (if any) as a shoulder. Broad peaks of 2800-3600 cm -1 most probably came from -OH, which may from water adsorbed by CNTs or from the carboxylic acid group attached to the defects or tube end of the CNTs. The C- H may also contribute to this peak. SWCNT is single-walled CNT. MWCNT is multiwalled CNT. The numbers after MWCNT are their outer diameters.
Page S6 Sorbed TA Conc., (mg/g) 500 400 300 200 100 A MWCNT10 SWCNT MWCNT20 MWCNT40 MWCNT60 MWCNT100 0 0 100 200 300 400 500 Sorbed TA Conc., (mg/g) 500 400 300 200 100 B 0 0 100 200 300 400 500 Sorbed TA Conc., (mg/g) 500 400 300 200 100 C 0 0 100 200 300 400 500 Equilibrium TA Conc., (mg/l) FIGURE S4. Model fits to the sorption data of tannic acid (TA) by carbon nanotubes (CNTs), among which the isotherms of MWCNT20 (red line) and MWCNT40, and MWCNT60 and MWCNT100 almost overlap due to their similar sorption affinity. (A) Langmuir model (LM); (B) Freundlich model (FM); (C) Dual-Langmuir model (DLM). SWCNT is single-walled CNT; the numbers after MWCNT (multi-walled CNT) are their outer diameters.
Page S7 80 Surface tension, mn/m 70 60 50 40 0 100 200 300 400 500 600 Tannic acid concentration, mg/l Figure S5. Surface tension of the tannic acid solutions against its concentrations. The surface tension was determined by a drop shape analysis system DSA10 (Krss). The surface tension did not change signigivantly within the test concentrations of tannic acid.
Page S8 A B 500 nm C 500 nm 500 nm Figure S6. Typical TEM images of MWCNT100 after adsorption of tannic acid (TA) at concentrations of 5 mg/l (A), 100 mg/l (B), and 500 mg/l (C). The MWCNT100 after adsorption was collected by filtering the CNT-TA suspensions, and then washed with deionized water to remove the dissolved and unsorbed TA. The resultant MWCNT100 was dried and prepared for the TEM observation. The coating of TA on the CNT surface is evident in B and C. MWCNT100 is multi-walled carbon nanotube with outer diameter of 60-100 nm.
Page S9 3420 1530 MWCNT100 CTA5 CTA50 CTA500 TA 4000 3600 3200 2800 2400 2000 1600 1200 800 400 Wavenumber, cm -1 Figure S7. DRIFTS spectra of MWCNT100 before and after sorption of tannic acid (TA). The peak of 3420 cm -1 was strengthened by the sorption of TA, which may be due to the increased -OH functional group from the adsorbed TA. 1530 cm -1 was attributed to the C-C stretching vibration from tetrasubstituted benzene rings (Simons, 1978), which is a main structure in the TA molecule. MWCNT100 is multi-walled carbon nanotube with outer diameter of 60-100 nm. CTA5, CTA50, and CTA500 are MWCNT100 after adsorption of TA at 5, 50, and 500 mg/l, respectively. Simons, W.W. The Sadtler handbook of infrared spectra. Philadelphia: Sadtler Research laboraries, 1978
Page S10 CNT100 CNT60 CNT40 CNT20 CNT10 SWCNT CNT100 Blank TA 500 mg/l FIGURE S8. Photo of 500 mg/l tannic acid (TA) solution after adding 200 mg/l carbon nanotubes, shaking for 7 days, centrifuging at 3000 rpm for 20 min, and settling for 30 days. CNT100, CNT60, CNT40, CNT20, and CNT10 are multi-walled carbon nanotubes with outer diameters of 60-100, 40-60, 20-40, 10-20, and < 10 nm, respectively; SWCNT is single-walled carbon nanotube. The 200 mg/l CNT100 blank solution without TA and 500 mg/l TA solution without CNTs are also shown (the two vials on the right).
Page S11-70.0-60.0 Zeta potential Size 1400 1200 Zeta Potential, (mv) -50.0-40.0-30.0-20.0 1000 800 600 400 Colloid Size, (nm) -10.0 200 0.0 0 100 200 300 400 500 TA Conc., (mg/l) 0 FIGURE S9. Measured zeta potential and size of the colloids in the mixture of multi-walled carbon nanotube with outer diameter of 60-100 nm (MWCNT100) and tannic acid (TA) solutions. The initial concentration of MWCNT100 is 200 mg/l. The zeta potential and size of pure MWCNT100 suspension without TA was determined after shaking the suspension before the measurement, while others were measured with supernatants of the mixtures after centrifuging at 3000 rpm for 20 min. Each data point in the figure is the mean value of three replicates. The standard deviations of the three replicates are all below 5%.