The Role of Oxygen during Thermal Reduction of Graphene Oxide Studied by Infrared Absorption Spectroscopy

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1 SUPPLEMENTARY INFORMATION The Role of Oxygen during Thermal Reduction of Graphene Oxide Studied by Infrared Absorption Spectroscopy Muge Acik, 1 Geunsik Lee, 1 Cecilia Mattevi, ǂ2 Adam Pirkle, 1 Robert M. Wallace, 1 Manish Chhowalla, 2 Kyeongjae Cho, 1 Yves Chabal* 1 1 Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, TX Rutgers University, Materials Science and Engineering, Piscataway, NJ, USA ǂ Present address: Department of Materials, Imperial College, London, UK SW7 2AZ *Authors to whom correspondence should be addressed to: chabal@utdallas.edu 1

2 Absorbance (a. u.) ν (C-O-C) α β γ ν (C-O) ν (C=O) ν (COOH, C=O) ~1652 cm -1 ν (C-O-C) 8x10-4 ~1284 cm -1 ν (C=O) ~1735 cm -1 ν (C=C, C=O) ~1580 cm -1 ν (C-OH, COOH, H 2 O) ~ cm -1 GO (single layer) Wavenumber (cm -1 ) Figure S1 Transmission infrared absorbance spectrum of GO (single layer) at room temperature. Vibrational modes are shown for hydroxyls (possible COOH and H 2 O contribution) (C-OH, cm -1 ), ketones (C=O, ~ cm -1 ), carboxyls (COOH and/or H 2 O) (~ cm -1 ), sp 2 -hybridized C=C (in-plane stretching, ~ cm -1 ), epoxides (C-O-C, ~ cm -1 and cm -1 ). The regions labeled as α- (red), β-(yellow), and γ-(green) refer to the chemical species summarized in Table S5 for the overlapped infrared frequencies at cm -1. 2

3 Absorbance (a. u.) ν (C-O-C) α β γ ν (C-O) ν (C=O) ν (C-O-C) ~1253 cm -1 ν (COOH, C=O) ~1653 cm -1 ν (C=O) ~1740 cm -1 ν (C=C, C=O) ~1590 cm ν (C-OH, COOH, H 2 O) ~ cm -1 GO (three layers) Wavenumber (cm -1 ) Figure S2 Transmission infrared absorbance spectrum of GO (three layers) at room temperature. Vibrational modes are shown for hydroxyls (possible COOH and H 2 O contribution) (C-OH, cm -1 ), ketones (C=O, ~ cm -1 ), carboxyls (COOH and/or H 2 O) (~ cm -1 ), sp 2 -hybridized C=C (in-plane stretching, ~ cm -1 ), epoxides (C-O-C, ~ cm -1 and cm -1 ). The regions labeled as α- (red), β-(yellow), and γ-(green) refer to the chemical species summarized in Table S5 for the overlapped infrared frequencies at cm -1. 3

4 Absorbance (a. u.) ν (C-O), ~ 800 cm -1 ν (C-O-C), ~850 cm -1 α β γ ν (C-O-C) ~1230 cm -1 ν (C-O) ~ cm -1 ν (C=C) ~1595 cm -1 ν (COOH) ~1725 cm -1 ν (C=O) ~1820 cm -1 ν (COOH, C-OH, H 2 O) ~ cm GO (multi layers) bulk Wavenumber (cm -1 ) Figure S3 Transmission infrared absorbance spectrum of bulk GO (multi layers) at room temperature. Vibrational modes are shown for hydroxyls with contributions from COOH and H 2 O (C-OH, cm -1 ), ketones and/or carboxyls within overlapped frequency range (C=O, COOH ~ cm -1 ), sp 2 -hybridized C=C (in-plane stretching, ~ cm -1 ), and epoxides (C-O-C, ~1350 cm -1 and cm -1 ). The regions labeled as α- (red), β-(yellow), and γ-(green) refer to the chemical species summarized in Table S5 for the overlapped infrared frequencies at cm -1. 4

5 Table S1 Simulated infrared intensities and vibrational frequencies of (a) basal plane hydroxyls, (b) edge hydroxyls, (c) carboxyls, and (d) epoxides. 5

6 Table S2 Simulated infrared intensities and vibrational frequencies of (a) ketones, (b) 1,2benzoquinones, (c) 1,3-benzoquinones, (d) benzo[de]chromene-2,3-diones, and (e) acid anhydrides. 6

7 Table S3 Simulated infrared intensities and vibrational frequencies of (a) 2-pyranones (pyrones), (b) Naptho[1,8-de][1,3]dioxin-2-ones, (c) γ-butyrolactones, and (d) 5-membered-ring lactols. 7

8 Table S4 Simulated infrared intensities and vibrational frequencies of (a) ethers (pyran-like), (b) ethers (furan-like), (c) dioxolanes, and (d) peroxides. 8

9 Table S5 Summary of corrected frequencies extracted from the simulation frequencies for overlapped regions named as α ( cm -1 ), β ( cm -1 ), and γ ( cm -1 ) showing additional contributions of various chemical species 1. Overlapped Regions Chemical Species Corrected Frequencies (cm -1 ) α ( cm -1 ) 5-membered-ring lactol 1 peroxide 1 ether (furan) 1,3 dioxolane 1,2 basal plane hydroxyl 2 edge hydroxyl 2 naptho[1,8-de][1,3]dioxin-2-one 2 acid anhydride 4 carboxyl 3 epoxide , , , β ( cm -1 ) 2-pyranone (pyrone) 1 γ-butyrolactone 1 peroxide 1,2 ether (pyran) 2 ketone 2 benzo[de]chromene-2,3-dione 2 5-membered-ring lactol 2 acid anhydride 3 epoxide 3 ether (furan) 3 1,2-benzoquinone , γ ( cm -1 ) Ether (pyran) 1 epoxide 2 peroxide 2 ketone 1,3 1,3-benzoquinone 1, , , Numbers correspond to the orders in terms of the simulated IR intensities (i. e. the strongest is 1, the weakest 4 ). 9

10 Table S6 Simulated infrared intensities and vibrational frequencies for nearby interacting oxygen groups (a) two COOH, (b) two OH, (c) one OH and a COOH, (d) two C=O, (e) an OH and a C=O, and (f) a COOH and a C=O. 10

11 Note on frequencies of Table S6-d: When ketones and OH groups are located nearby, the highest frequency is simulated as 1825 cm -1. This is because the neighboring OH bonds are coupled strongly to C=O groups with the bond lengths (1.20 and 1.23Å, respectively), which are very similar. For this reason, the original frequency goes down to almost half. Therefore, we are not able to show a C-OH contribution at ~ cm -1. Table S7 Summary of corrected frequencies extracted from the simulation frequencies for overlapped regions named as α ( cm -1 ), β ( cm -1 ), and γ ( cm -1 ) showing additional contributions from neighboring oxygen groups 1. Overlapped Regions Neighboring Groups Corrected Frequencies (cm -1 ) α ( cm -1 ) β ( cm -1 ) γ ( cm -1 ) COOH + COOH OH + OH COOH + C=O OH + COOH OH + C=O OH + OH OH + C=O OH + OH , , Numbers correspond to the orders in terms of the simulated IR intensities (i. e. the strongest is 1, the weakest 5 ). 11

12 Absorbance (a. u.) EDGE ν (-O-), ~800 cm -1 α β γ SiO 2 (TO) ν (Si-OH) SiO 2 (LO) ν (C=C) Leftover ν (C=O) GO (five layers) (b) 850 C: 750 C FWHM: ~ 50 cm -1 (a) 750 C: 650 C Wavenumber (cm -1 ) Figure S4 Tranmission infrared differential spectra of GO (five layers) at high temperature regime ( C). Changes of functional groups are given at temperatures: (a) C (black), and (b) C (blue). A new peak appears at ~800 cm -1 after 850 C anneal with a fwhm of ~50 cm -1 indicated in the inset. The vibrational stretching mode of C=C is also shown at ~1595 cm -1. A loss corresponding to Si-OH was observed at ~980 cm -1. Vibrational modes of SiO 2 (LO and TO modes) appear at ~1250 and 1080 cm -1, respectively. 12

13 Absorbance (a. u.) EDGE ν (- O-), ~800 cm -1 α β γ SiO 2 (TO) ν (Si-OH) SiO 2 (LO) ν (C=C) Leftover ν (C=O) (b) 850 C: 750 C (thin film) FWHM: ~ 44 cm -1 (a) 750 C: 650 C GO (multi layers) Wavenumber (cm -1 ) Figure S5 Tranmission infrared differential spectra of GO (multi layers, thin) at high temperature regime ( C). Changes of functional groups are given at temperatures: (a) C (black), and (b) C (green). A new peak appears at ~800 cm -1 after 850 C anneal with a fwhm of ~44 cm -1 indicated in the inset. The vibrational stretching mode of C=C is also shown at ~1595 cm -1. A loss corresponding to Si-OH was observed at ~980 cm -1. Vibrational modes of SiO 2 (LO and TO modes) appear at ~1250 and 1080 cm -1, respectively. 13

14 Absorbance (a. u.) (b) 850 C: 750 C EDGE ν (- O-), ~798 cm -1 FWHM: SiO ~ 32 cm -1 2 SiO 2 ν (C=C) (TO) ν (Si-OH) (LO) Leftover ν (C=O) (Bulk Film) (a) 750 C: 650 C α GO (multi layers) 2x10-2 β γ Wavenumber (cm -1 ) Figure S6 Tranmission infrared differential spectra of GO (multi layers, bulk) at high temperature regime ( C). Changes of functional groups are given at temperatures: (a) C (black), and (b) C (brown). A new peak appears at ~800 cm -1 after 850 C anneal with a fwhm of ~32 cm -1 indicated in the inset. The vibrational stretching mode of C=C is also shown at ~1595 cm -1. A loss corresponding to Si-OH was observed at ~980 cm -1. Vibrational modes of SiO 2 (LO and TO modes) appear at ~1250 and 1080 cm -1, respectively. 14

15 Total Infrared Absorbance (cm -1 ) Normalized Absorbance (i) std. ± 2 3% GO-5L (Sample-a) GO-5L (Sample-b) Incomplete Oxygen Removal Annealing Temperature ( C) 1.18 (ii) 1.16 std. 2% ~92 at. % GO-5L (Sample-a) GO-5L (Sample-b) Annealing Temperature ( C) Figure S7 Integrated infrared absorbance of five layered GO for two different samples. Comparison of (i) total integrated absorbance and (ii) normalized absorbance with the initial amount of oxygen (~23.4 cm -1 for sample-a and ~17.4 cm -1 for sample-b) is shown. 15

16 Total Infrared Absorbance (cm -1 ) 140 (i) std. ~ 1% GO-ML (Bulk film)-a GO-ML (Thin film)-b Incomplete Oxygen Removal Annealing Temperature ( C) Normalized Absorbance 1.4 (ii) GO-ML (Bulk film) GO-ML (Thin film) std. ~ 1% ~46 at. % ~55 at. % Annealing Temperature ( C) Figure S8 Integrated infrared absorbance for two different samples of multilayered GO (a) bulk films and (b) thin films. Comparison of (i) total integrated absorbance and (ii) normalized absorbance with the initial amount of oxygen (~103.6 cm -1 for the bulk film and ~48.3 cm -1 for the thin film) is shown. 16

17 75 C : 60 C 100 C : 75 C CO Absorbance (a. u.) 10-2 CO C : 100 C 150 C : 125 C 175 C : 150 C 200 C 350 C 450 C : 350 C 550 C : 450 C 650 C : 550 C 750 C : 650 C 2337cm C : 350 C 550 C : 450 C 650 C : 550 C 750 C : 650 C Wavenumber (cm -1 ) 2115 cm -1 Figure S9 Transmission infrared differential spectra of multilayered GO (bulk) at C are shown for the release of CO 2 (~2337 cm -1 ) and CO (~2115 cm -1 ). Table S8 Simulated infrared intensities and vibrational frequencies for (A) 1C-vacancy (monovacancy), (B) 2C-vacancy (di-vacancy) defects. 17

18 C 1s a) 5L GO O 1s b) 5L GO Photoelectron intensity (a.u.) C 1s c) 5L GO, annealed O 1s d) 5L GO, annealed Binding energy (ev) Figure S10 Normalized C 1s (a,c) and O 1s (b,d) XPS spectra for a,b) as-synthesized five layered GO on Pt foil, c,d) five layered GO after reduction by vacuum ( torr) annealing at 850 C for 5 minutes (~12 hours of total annealing and cooling time) in furnace. Peak fit residuals are shown beneath each spectrum. 18

19 Table S9 Possible radical production and propagating radicals OH + H 2 = H 2 O + H OH + H 2 O 2 = H 2 O + HO 2 HO 2 + HO 2 = H 2 O 2 + O 2 OH + HO 2 = H 2 O + O 2 OH + ROOH = RO 2 + H 2 O [R1] Ung, A. Y. M. and Back, R. A. The photolysis of water vapor and reactions of hydroxyl radicals. Canadian Journal of Chemistry. 42, (1964). Reactions in pure water vapor: OH + OH = H 2 O + O O + OH = O 2 + H OH + OH = H 2 O 2 O + HO 2 = OH + O 2 H + O 2 = HO 2 2HO 2 = H 2 O 2 + O 2 H + HO 2 = H 2 O 2 H + HO 2 = 2OH H + HO 2 = H 2 + O 2 OH + HO 2 = H 2 O + O 2 H + H 2 O 2 = H 2 O + OH H + H 2 O 2 = H 2 + HO 2 OH + H 2 O 2 = H 2 O + HO 2 OH + H 2 = H 2 O + H Reactions with CO and CO 2 radicals: OH + CO = CO 2 + H OH + CO = COOH OH + COOH = H 2 O + CO 2 2COOH = HCOOH + CO 2 OH + CO = CO 2 + H [R2] Frost, G. J., Ellison, G. B. and Vaida, V. Organic Peroxyl Radical Photolysis in the Near- Infrared: Effects on Tropospheric Chemistry. J. Phys. Chem. A 103, (1999). [R3] Gray, P. Chemistry of free radicals containing oxygen. Trans. Faraday Soc., 55, (1959). 19