nature materials SUPPLEMENTARY INFORMATION DOl10.1038/NMAT2858 Unusual infrared-absorption mechanism in thermally reduced graphene oxide M.Acik',G.Lee',C.Mattevi2,M.Chhowalla2',K.Cho'and Y.J.Chabal* Department of Materials Science and Engineering,University of Texas at Dallas,Richardson, TX75080 2Rutgers University,Materials Science and Engineering,Piscataway,NJ,USA 08854 'Present address:Department of Materials,Imperial College,London,UK SW7 2AZ *Authors to whom correspondence should be addressed to: chabal@utdallas.edu NATURE MATERIALS www.nature.com/naturematerials 1
SUPPLEMENTARY INFORMATION doi: 10.1038/nmat2858 nature materials | www.nature.com/naturematerials 1 1 SUPPLEMENTARY INFORMATION Novel infrared absorption mechanism in thermally reduced graphene oxide M. Acik1 , G. Lee1 , C. Mattevi2† , M. Chhowalla2 †, K. Cho1 and Y. J. Chabal1* 1 Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, TX 75080 2 Rutgers University, Materials Science and Engineering, Piscataway, NJ, USA 08854 Ɨ Present address: Department of Materials, Imperial College, London, UK SW7 2AZ *Authors to whom correspondence should be addressed to: chabal@utdallas.edu Unusual infrared-absorption mechanism in thermally reduced graphene oxide
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT2858 C-O-C loss COOH loss 10 C=O formation (a)175C:60c C-OH loss (b)350C:175C C=O loss (g)500C:350C baseline M(d750C:500C C-O formation G0-1L 人 900 12001500 1800 800300032003400 3600 Wavenumber(cm-1) Supplementary Figure S1 Transmission infrared differential spectra of reduced GO(single layer).Variations upon thermal annealing at (a)175C:60C (b)350C:175C (c)500C:350C (d)750C:500C are represented in the following oxygen species:hydroxyl desorption (namely phenol,C-OH)(3050-3800 cmand~1070 cm)including all C-OH vibrations from COOH and H2O,formation of ketonic groups(1600-1650 cm,1750-1850 cm)in (a)and their loss in (b), loss of carboxyl(COOH)(1650-1750 cm including C-OH vibrations at 3530 cm and 1080 cm )loss of epoxide(C-O-C)(1230-1320 cmof asymmetric stretching and-850 cmof bending motion),formation of etheric groups (900-1100 cm),all other C-O and C=O contribution in B- region(1100-1280 cm)and sp2-hybridized C=C(1500-1600 cm,in-plane vibrations). 2 NATURE MATERIALS www.nature.com/naturematerials
2 nature MATERIALS | www.nature.com/naturematerials supplementary information doi: 10.1038/nmat2858 2 ν() °° °° °° () °° ν () Supplementary Figure S1 Transmission infrared differential spectra of reduced GO (single layer). Variations upon thermal annealing at (a) 175°C:60°C (b) 350°C:175°C (c) 500°C:350°C (d) 750°C:500°C are represented in the following oxygen species: hydroxyl desorption (namely phenol, C-OH) (3050-3800 cm-1 and ~1070 cm-1) including all C-OH vibrations from COOH and H2O, formation of ketonic groups (1600-1650 cm-1, 1750-1850 cm-1) in (a) and their loss in (b), loss of carboxyl (COOH) (1650-1750 cm-1 including C-OH vibrations at 3530 cm-1 and 1080 cm- 1 ), loss of epoxide (C-O-C) (1230-1320 cm-1 of asymmetric stretching and ~850 cm-1 of bending motion), formation of etheric groups (900-1100 cm-1), all other C-O and C=O contribution in β- region (1100-1280 cm-1) and sp2 -hybridized C=C (1500-1600 cm-1, in-plane vibrations)
DOE:10.1038/NMAT2858 SUPPLEMENTARY INFORMATION Section 1. Brief description of the structural evolution of single layer GO after annealing at 175- 750°C(Fig.S1). Between 60 and 175C,epoxide species decompose completely,most of the hydroxyl and carboxyl species are removed while some C=O containing ketonic species are formed (Supplementary Fig.Sla).Hydroxyl,carboxyl and ketonic species continuously disappear between 175 and 350C while some C-O containing etheric groups are formed(Supplementary Fig.S1b).No hydroxyl groups can be observed after 350C (Supplementary Figs S1c-d) probably because they can easily decompose due to strong interaction with neighboring hydroxyl and carboxyl groups,leading to formation of intermediate ketones [S1].Interestingly,the in- plane vibration(1580 cm)of the C=C bonds is observable only below 350C(Supplementary Figs Sla-b)for two reasons:1)the amount of sp2hybridization increases when out-of-plane oxygen species,such as hydroxyl(C-OH),carboxyl(COOH)and epoxide (C-O-C)groups are removed and 2)usually weak C=C phonon absorption is enhanced when the symmetry is perturbed by neighboring oxygen. [S1]Bagri,A.et al.Structural evolution during the reduction of chemically derived graphene oxide.Nat.Chem.2,581-587(2010). NATURE MATERIALS www.nature.com/naturematerials
nature materials | www.nature.com/naturematerials 3 doi: 10.1038/nmat2858 supplementary information 3 Section 1. Brief description of the structural evolution of single layer GO after annealing at 175- 750°C (Fig. S1). Between 60 and 175°C, epoxide species decompose completely, most of the hydroxyl and carboxyl species are removed while some C=O containing ketonic species are formed (Supplementary Fig. S1a). Hydroxyl, carboxyl and ketonic species continuously disappear between 175 and 350°C while some C-O containing etheric groups are formed (Supplementary Fig. S1b). No hydroxyl groups can be observed after 350o C (Supplementary Figs S1c-d) probably because they can easily decompose due to strong interaction with neighboring hydroxyl and carboxyl groups, leading to formation of intermediate ketones [S1]. Interestingly, the inplane vibration (1580 cm-1) of the C=C bonds is observable only below 350o C (Supplementary Figs S1a-b) for two reasons: 1) the amount of sp2 hybridization increases when out-of-plane oxygen species, such as hydroxyl (C-OH), carboxyl (COOH) and epoxide (C-O-C) groups are removed and 2) usually weak C=C phonon absorption is enhanced when the symmetry is perturbed by neighboring oxygen. [S1] Bagri, A. et al. Structural evolution during the reduction of chemically derived graphene oxide. Nat. Chem. 2, 581-587 (2010)
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT2858 Edge (-O-) 1v(0- 10 (800cm1) FWHM 0850℃(G0-3L) ('n 'e)aouequosqv (100cm-1) (m)750℃(G0-3L) (im850℃(Sio /Si) (Si-OH) 800 1000 1200 1400 (a)850C:750C(G0-3L) 5x103 (b)850℃：750℃(Si0,/Si) 6009001200150018002100240027003000330036003900 Wavenumber(cm-1) Supplementary Figure S2 Transmission infrared differential (a)and absorbance (i-ii) spectra of GO (three layers:3L)at high temperatures(850-750C).A new peak appears at 800 cm with fwhm of-100 cm.A loss corresponding to Si-OH was observed at~980 cm. The inset shows the absorbance spectra at 750C (i)and 850C (ii)anneals for single layer GO and (iii)bare clean SiO2/Si surface at 850C referenced to the room temperature clean SiOz/Si surface.Absorbance unit is abbreviated as 'a.u.'. 4 NATURE MATERIALS www.nature.com/naturematerials
4 nature MATERIALS | www.nature.com/naturematerials supplementary information doi: 10.1038/nmat2858 4 Supplementary Figure S2 Transmission infrared differential (a) and absorbance (i-ii) spectra of GO (three layers: 3L) at high temperatures (850-750°C). A new peak appears at 800 cm-1 with fwhm of ~100 cm-1. A loss corresponding to Si-OH was observed at ~980 cm-1. The inset shows the absorbance spectra at 750°C (i) and 850°C (ii) anneals for single layer GO and (iii) bare clean SiO2/Si surface at 850°C referenced to the room temperature clean SiO2/Si surface. Absorbance unit is abbreviated as ‘a. u.’
DO:10.1038/NMAT2858 SUPPLEMENTARY INFORMATION 0.8 0.4 0.4 20 0.0 0.0 0.4 30 0.4 0.0 04 40 匹 0.0 0.8 0.4 50 88 0.4 0.4 70 0.0 0.0L L, 0.60.8 1.01.21.41.6 0.60.81.01.21.41.6 v(x1000cm') v(x1000cm') 0.2 d e 1296cm-1 1400 01 。“。 1300 0.0 ◆ 1200 1160cm-1 ◆ 0.1 1100 ◆ 1000 ■ 0.0 。*。。*。。,1026Cm 900 0 800 0.0 -8 6 4 -2 0 2 2 3456789“ 00 E(eV) number of O atoms Supplementary Figure S3 Cluster simulation results for finite number of edge ether.(a) Cluster models for agglomerated edge ethers increasing from two to seven,(b)their simulated IR intensities where the asymmetric C-O-C stretch mode is indicated by the red line.(c) Examination of the asymmetric C-O-C stretch mode frequency as indicated by the red line with increasing carbon rings along (middle:v=1428 cm)or away (bottom:v=1400 cm)from the NATURE MATERIALS|www.nature.com/naturematerials
nature materials | www.nature.com/naturematerials 5 doi: 10.1038/nmat2858 supplementary information 5 1296 cm-1 1160 cm-1 1026 cm-1 ∞ Supplementary Figure S3 Cluster simulation results for finite number of edge ether. (a) Cluster models for agglomerated edge ethers increasing from two to seven, (b) their simulated IR intensities where the asymmetric C-O-C stretch mode is indicated by the red line. (c) Examination of the asymmetric C-O-C stretch mode frequency as indicated by the red line with increasing carbon rings along (middle: ν=1428 cm-1) or away (bottom: ν=1400 cm-1) from the
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT2858 edge in comparison with the original model of two ethers(top:v=1419 cm).The corresponding vibration shape is given for each case.(d)Effect of asymmetric C-O-C stretch mode on electronic density of states (DOS)for 3,5 and 7 edge O atoms,together with their vibration frequencies.For each case,DOS projected onto O-t(black)and O-0(red)orbitals are shown when the system is in its ground states (dashed)or after atomic displacements (solid).(e) Asymmetric C-O-C stretch mode frequency versus the number edge O atoms.The infinite number corresponds to edge oxidized GNR for which our calculated frequency is 870 cm. Block symbols are our calculated values,whereas red ones are the corrected values by-55 cm. The asymmetric C-O-C stretch mode frequency is quite different from 800 cm when only several ether groups appear next to each other.Fig.S3 displays our simulated data with increasing the number of edge ethers from two to seven (Fig.S3a).The C-O-C asymmetric mode is as high as about 1400 cm for two edge ethers,and decreases down to 1026 cm for seven (Fig.S3b).We have confirmed that including more carbon rings in the model does not change the frequency (Fig.S3c).We also checked change of the electronic states with the C-O-C asymmetric mode vibration (Fig.S3d).The significant lowering of O-o*states (the red solid line)can be seen clearly.At seven ethers,electrons under such vibration are found to exchange their occupation between O-o*and O-m orbitals.The C-O-C asymmetric mode frequency variation with increasing the size of ether chain is plotted in Figure S3e,where tens of edge ethers are required to reach the observed 800 cm value. 6 NATURE MATERIALS www.nature.com/naturematerials
6 nature MATERIALS | www.nature.com/naturematerials supplementary information doi: 10.1038/nmat2858 6 edge in comparison with the original model of two ethers (top: ν=1419 cm-1). The corresponding vibration shape is given for each case. (d) Effect of asymmetric C-O-C stretch mode on electronic density of states (DOS) for 3, 5 and 7 edge O atoms, together with their vibration frequencies. For each case, DOS projected onto O-π (black) and O-σ (red) orbitals are shown when the system is in its ground states (dashed) or after atomic displacements (solid). (e) Asymmetric C-O-C stretch mode frequency versus the number edge O atoms. The infinite number corresponds to edge oxidized GNR for which our calculated frequency is 870 cm-1. Block symbols are our calculated values, whereas red ones are the corrected values by -55 cm-1. The asymmetric C-O-C stretch mode frequency is quite different from 800 cm-1 when only several ether groups appear next to each other. Fig. S3 displays our simulated data with increasing the number of edge ethers from two to seven (Fig. S3a). The C-O-C asymmetric mode is as high as about 1400 cm-1 for two edge ethers, and decreases down to 1026 cm-1 for seven (Fig. S3b). We have confirmed that including more carbon rings in the model does not change the frequency (Fig. S3c). We also checked change of the electronic states with the C-O-C asymmetric mode vibration (Fig. S3d). The significant lowering of O-σ* states (the red solid line) can be seen clearly. At seven ethers, electrons under such vibration are found to exchange their occupation between O-σ* and O-π orbitals. The C-O-C asymmetric mode frequency variation with increasing the size of ether chain is plotted in Figure S3e, where tens of edge ethers are required to reach the observed 800 cm-1 value
DO:10.1038/NMAT2858 SUPPLEMENTARY INFORMATION 3.0 GO-3L EDGE(-O-) 2.5 COOH,C-OH,C=O,C-O-C,C-O -×40 2.0 COOH,C-O,C-O-C* enhancement 1.5 C=O,COOH,C-O C=O COOH,C-O 0 C=O,COOH, C=O 11.0 玉 C=0,C-O,C00H* C-O,COOH/C=O* 0.5 0.0 Overlapped peak:minor contribution 075150225300375450525600675750825 900 Temperature(C) Supplementary Figure S4 Integrated absorbance vs.annealing temperature measured at 60C(GO with three layers).Each temperature is shown with a different color(60-850C from red to brown in sequence).The existing functional groups at each specific temperature are also ordered in terms of the area size.Almost all of the functional groups disappear at 500C and only C-O containing edge ether contribution remains thereafter.The peak at 800 cm indicates a maximum variation in dipole moment at 850C with a 40 times more enhancement compared to 750C.The standard deviations (s.d.0.1-3%)shown with error bars are obtained from the mean values of fluctuations in the values of total integrated areas.(*)Overlapped peak area with minor contribution from both COOH and C=O containing species. NATURE MATERIALS www.nature.com/naturematerials
nature materials | www.nature.com/naturematerials 7 doi: 10.1038/nmat2858 supplementary information 7 ° Supplementary Figure S4 Integrated absorbance vs. annealing temperature measured at 60°C (GO with three layers). Each temperature is shown with a different color (60-850°C from red to brown in sequence). The existing functional groups at each specific temperature are also ordered in terms of the area size. Almost all of the functional groups disappear at 500°C and only C-O containing edge ether contribution remains thereafter. The peak at 800 cm-1 indicates a maximum variation in dipole moment at 850°C with a 40 times more enhancement compared to 750°C. The standard deviations (s.d. 0.1-3%) shown with error bars are obtained from the mean values of fluctuations in the values of total integrated areas. (*) Overlapped peak area with minor contribution from both COOH and C=O containing species
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT2858 Supplementary Fig.S4 summarizes the TOTAL intensity of all oxide modes of GO(three layers) as a function of thermal annealing.The initial integrated intensity decreases from~1.0 cm to -0.08 cm after a 750C anneal,when only ~8-10%of oxygen remains in three layers of GO. Upon annealing to 850C,the integrated area of the edge ether (mode centered at 800 cm) increases to a value of~3.0 cm,namely by a factor of~40. (C=O,COOH) 4x102I V(C-OH) +H20 ('n 'e)eouequosqy (a)GO(multi layers) C-o. C-N,N-N) (-O-)6p3 (b) (C=C) 5x103I 700 750 800 850 900 V(C-N,N-N) (b)After 36 hours (c)After 2 days 800 12001600 2800 3200 3600 Wavenumber(cm) Supplementary Figure S5 Time-dependent study of wet chemical reduction of GO(multi layers)in aqueous media.Tranmission infrared absorbance spectra of (a)GO(multi layers) 8 NATURE MATERIALS www.nature.com/naturematerials
8 nature MATERIALS | www.nature.com/naturematerials supplementary information doi: 10.1038/nmat2858 8 Supplementary Fig. S4 summarizes the TOTAL intensity of all oxide modes of GO (three layers) as a function of thermal annealing. The initial integrated intensity decreases from ~1.0 cm-1 to ~0.08 cm-1 after a 750o C anneal, when only ~8-10% of oxygen remains in three layers of GO. Upon annealing to 850o C, the integrated area of the edge ether (mode centered at 800 cm-1) increases to a value of ~3.0 cm-1, namely by a factor of ~40. Supplementary Figure S5 Time-dependent study of wet chemical reduction of GO (multi layers) in aqueous media. Tranmission infrared absorbance spectra of (a) GO (multi layers)
DOE:10.1038/NMAT2858 SUPPLEMENTARY INFORMATION showing vibrational modes of hydroxyl (possible COOH and H2O)(C-OH,3000-3750 cm). ketone and/or carboxyl (C=O,COOH ~1700-1900 cm),sp2-hybridized C=C (in-plane stretching,~1550-1650 cm),epoxide (C-O-C,~1350 cm and 800-900 cm)and some overlapped regions such as a-region (lactol,peroxide,dioxolane,hydroxyl,C=O contribution, carboxyl and epoxide,900-1100 cm),B-region (C=O contribution,peroxide,ether,lactol, anhydride and epoxide,1100-1280 cm),and y-region (ether,epoxide and C=O contribution, 1280-1500 cm).Variations upon exposure to hydrazine monohydrate under reflux at 100C are indicated after(b)36-hour treatment and(b)2-day treatment.A new peak appears at 800 cm after 36-hour treatment disappearing after 2-day treatment.Vibrational modes of C-N(1000- 1400 cm)and N-N(~1040 cm)become visible NATURE MATERIALS www.nature.com/naturematerials
nature materials | www.nature.com/naturematerials 9 doi: 10.1038/nmat2858 supplementary information 9 showing vibrational modes of hydroxyl (possible COOH and H2O) (C-OH, 3000-3750 cm-1), ketone and/or carboxyl (C=O, COOH ~1700-1900 cm-1), sp2 -hybridized C=C (in-plane stretching, ~1550-1650 cm-1), epoxide (C-O-C, ~1350 cm-1 and 800-900 cm-1) and some overlapped regions such as α-region (lactol, peroxide, dioxolane, hydroxyl, C=O contribution, carboxyl and epoxide, 900-1100 cm-1), β-region (C=O contribution, peroxide, ether, lactol, anhydride and epoxide, 1100-1280 cm-1), and γ-region (ether, epoxide and C=O contribution, 1280-1500 cm-1). Variations upon exposure to hydrazine monohydrate under reflux at 100°C are indicated after (b) 36-hour treatment and (b) 2-day treatment. A new peak appears at 800 cm-1 after 36-hour treatment disappearing after 2-day treatment. Vibrational modes of C-N (1000- 1400 cm-1) and N-N (~1040 cm-1) become visible
SUPPLEMENTARY INFORMATION D0:10.1038/NMAT2858 1.5 5 1 0.4 (Ae)3 0 (A)3 0 0 6 (Ae)3 0 5 1 1 1 -1.5 -1.5 0.2 1.5 3 2 2 1 151 0.0 0.5 6008001000120014001600 0 . v(cm") 0.5 0.5 -1 1 15 1.5 3 6 mode 3' 0 6 8 10 12 14 16 Supplementary Figure S6 Electronic band structure change with vibrations of six normal modes for edge oxidized GNR.The change of electronic band structure is shown under vibration of six normal modes involving significant O displacements.In the band structures (right),the red lines are for excited system,and the ground state band structure is shown in the black dashed line.In the bottom,two dimensional electron density increase (solid)or decrease (dashed)is given for the mode 3'displacement.Note the contour levels are 0.1,0.2...e/A2 for the solid lines and-0.1,-0.2,...for the dashed lines. In case of edge oxidized GNR,all six vibration modes with significant O displacements are examined to check their effects on the electronic band structure (Fig.S6).Except for the mode b NATURE MATERIALS www.nature.com/naturematerials
10 nature MATERIALS | www.nature.com/naturematerials supplementary information doi: 10.1038/nmat2858 10 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Γ X E (eV) 1 2 3 4 5 6 mode ‘3’ 1 2 3 6 5 4 Supplementary Figure S6 Electronic band structure change with vibrations of six normal modes for edge oxidized GNR. The change of electronic band structure is shown under vibration of six normal modes involving significant O displacements. In the band structures (right), the red lines are for excited system, and the ground state band structure is shown in the black dashed line. In the bottom, two dimensional electron density increase (solid) or decrease (dashed) is given for the mode ‘3’ displacement. Note the contour levels are 0.1, 0.2,.. e/Ǻ2 for the solid lines and -0.1,-0.2,… for the dashed lines. In case of edge oxidized GNR, all six vibration modes with significant O displacements are examined to check their effects on the electronic band structure (Fig. S6). Except for the mode