Sulfuric Acid Intercalated Graphite Oxide for Graphene Preparation

Supporting information for Sulfuric Acid Intercalated Graphite Oxide for Graphene Preparation

Yanzhong Hong, Zhiyong Wang, Xianbo Jin*

College of Chemistry and Molecular Sciences, Hubei Key Laboratory of Electrochemical

Power Sources, Wuhan University, Wuhan, 430072, P.R. China

*Correspondence to: [email protected]

This supplement contains:

 Caption for the supplementary movie

 Table S1and S2

 Figs. S1-S9

 Supplementary discussion and references

1 Caption for Supplementary Movie

The Rapid expansion of SIGO at low temperature. In this video, the quartz crucible is preheated at 120 oC for a stable temperature and gas distribution. It is then fed with about 0.45 g SIGO (sulfuric intercalated graphite oxide) and sealed with a rubber stopper. The pressure in the crucible can be regarded as 1 atm and the plastic bag is flat before the expansion. After about 1 minute, the billowing graphene debris is found in the top end of the crucible, indicating the occurring of expansion and vigorous gas release. The plastic bag is partially inflated. The video also reveals the big volume difference between the SIGO and ESIGO (expanded SIGO).

2 Supplementary Table S1

Table S1 ｜ The sulfur content, interlayer spacing and expansion characteristics of different SIGO samples.

a SIGO Preparation Sulfur RC/S Interlayer Expansion RC/O in Samples content (wt spacing temperature ESIGOa %)a (nm)b (oC)c

SIGO1 HCl-1 8.3 14.9 1.09 none --

SIGO2 HCl-3 5.4 31.9 0.86 110 10.7

SIGO3 HCl-5 4.0 35.9 0.83 110 11.0

SIGO4 HCl-7 2.9 55.6 0.80 150 10.4

SIGO5 HCl-9 1.7 98.1 0.78 250 8.2

SIGO6 HCl-11 1.2 146 0.76 350 7.7

SIGO7 HCl-20 ~0.5 316 0.75 730 9.4

SIGO8 H2O-2 6.3 26.0 0.89 110 10.4

SIGO9 H2O-3 5.0 34.3 0.86 110 10.9

SIGO10 IS-SIGO6d 3.9 39.7 0.83 110 10.2

SIGOn is the sulfuric acid intercalated graphite oxide (SIGO) with sample number n, and

ESIGOn is the expanded SIGOn; HCl-n or H2O-n indicates the sample prepared by washing with 2 wt% HCl solution or distilled water for n times; RC/S, RC/O, carbon to sulfur and carbon to oxygen molar ration respectively. a Calculated according to the EDX analysis; b calculated according to the XRD peak position of SIGO; c The lowest temperature for the quick d expansion (within 2 min) of the SIGO; IS-SIGO6 indicates intercalating H2SO4 into SIGO6 sample by immersing in dilute H2SO4 solution (0.1 mol/L).

3 Supplementary Table S2

Table S2｜Component analysis of the SIGO before and after expansion at 120 oC.

Test 1 Test 2 Test3

Mass of SIGO (mg), m1 447 383 198

Mass of sulfuric acid in SIGO (mg), m2a 57 49 25

ESIGO before washing (mg), m3 234 202 105

Mass loss during expansion (mg), m4b 213 181 93

Washed ESIGO (mg), m5 178 152 81

Mass loss during washing (mg), m6c 56 50 24

d Measured H2SO4 in ESIGO (mg), m7 55 51 23

Gas volume as measured (ml), Ve 28 23 12

f CO2 as estimated from gas volume (mg), m8 50 41 22

g CO2 as calculated from BaCO3 (mg), m9 46 20

h H2O as estimated (mg), m10 158 133 68

Contribution of steam for the gas pressurei 88.5 % 88.8 % 88.4 %

Three parallel experiments (Test1~3) for the SIGO sample with S content of about 4.2 wt%. a b c d m2 = m1 * 4.2 %. m4 = m1 – m3. m6 = m3 – m5. Calculated from the mass of the BaSO4 precipitation formed by adding Ba2+ into the filtrate of ESIGO. e The generated gas volume V in the plastic bag as shown in Extended Data Figure 2 when the heating kept. f The estimated g mass of the generated CO2 from the volume V. Calculated from the mass of BaCO3 formed by adding the Ba2+ into the alkaline solution of the gas product. h m10 = m4 – m8. i = m10/18/ (m10/18+m8/44).

4 Supplementary Figure S1

Figure S1｜The EDX analysis of different SIGO and ESIGO samples. a, Typical SIGO samples. b, Typical ESIGO samples by expansion exfoliation of the corresponding SIGO samples at the indicated temperature. c, EDX analysis of the SIGO sample with RC/S 146 before (SIGO6) and after (SIGO10) immersed in 0.1 mol/L H2SO4 solution for 12 hrs. d, Typical comparison between the SIGO sample and its ESIGO sample obtained by the 110 oC treatment.

Figure S2｜Photos about the expansion of SIGO (sulfur content, ~4.2 wt%) at 120 oC. a and b, Before and after expansion of 447 mg SIGO sample. c, After expansion of 451 mg SIGO sample. d. The 0.198 mg SIGO sample in the quartz tube. e and f, After expansion of the sample in d. The close-up in f shows the condensed water droplet on the internal surface of the upper end of the quartz tube.

Figure S3｜Supplementary XRD patterns of typical SIGOs, ESIGO and Graphite.

Figure S4 ｜ Typical FTIR spectra of SIGO and ESIGO. Here showing the SIGO3 and ESIGO3, and the absorption peaks corresponding to various functional groups were indicated.

Figure S5 ｜ Low-magnification SEM images of the SIGO (a) and the as-exfoliated ESIGO (b).

Figure S6 ｜ Chemical analysis of the gas product of the SIGO expansion. The EDX analysis of the precipitation formed by adding the Ba2+ into the alkaline solution of the o gaseous product of the SIGO expansion at 120 C. The precipitation was almost pure BaCO3, indicating neither SO2 nor SO3 formed as gas product.

Figure S7｜Supplementary DSC analysis of typical SIGO sample. Normalized TGA and

DSC plots for SIGO with RC/S 35.9 contained in an open alumina crucible. The sample began a remarkable exothermic DSC signal at 100 oC, in line with the expansion reduction of the bulk SIGO sample at 110 oC. But here the sample lost its mass almost completely at about 170 oC due to the vigorous gas release.

Figure S8｜Typical XPS survey spectra of SIGO and ESIGO. The XPS curves of SIGO3 o (red line) with RC/S  35.9 and ESIGO3 (black line) generated from SIGO3 by 110 C treatment.

Figure S9 ｜ The specific surface area of typical ESIGO. The Nitrogen adsorption and o desorption isotherms of the ESIGO generated from SIGO with RC/S 39 at 120 C.

13 Supplementary Discussion

The quantitative analysis of the H2SO4 in the SIGO and ESIGO

The analysis was performed on the expansion of the SIGO with S content of about 4.2 wt%. After expansion, the remaining sulfuric acid in the ESIGO can be easily removed to content lower than the detection limit of EDX by just immersed in water and filtrated. The mass loss during the washing was assumed to be mainly due to the dissolution of sulfuric acid. Correspondingly, the filtrate was acidic and precipitation formed when Ba2+ was added. The mass of the sulfuric acid has also

been measured by weighing the BaSO4 precipitation as shown in Table S2.

The gas product analysis

The expansion generated gas should include mainly steam and carbon oxides. We connected the plastic bag to the side pipe of the quartz tube to make the observation directly (Figure S2, Supplementary Video). Before the expansion, the system was preheated to a stable temperature distribution from 120 oC at the bottom to room temperature at the open end of the quartz crucible. The pressure in the crucible could then keep at 1 atm and there would be no initial gas in the flat bag. After the expansion, the plastic bag was partially inflated with gas as shown in Extended Data figure 2, which would accommodate the increased gas without causing additional pressure. The gas in the bag was measured to be about 26 oC (the room temperature).

Thus, when the heating was still kept at 120 oC, the volume of the plastic bag should

be equal to the volume of the generated CO2 considering that the steam has condensed

14 on the upper inwall of the quartz crucible (Figure S2), where the temperature was measured to be about 30~40 oC. However, the whole mass loss from SIGO to ESIGO was much larger than the as indicated mass by the measured gas volume, and the difference was ascribed to the generated water.

Alternatively, with the help of argon flow, all the gaseous products, including the

water vapor, were bubbled into NaOH solution, and then precipitated with BaCl2.

After that, no droplet was found on the crucible wall, and the mass loss from SIGO to

ESIGO was almost the same as the above. The precipitation was identified to be pure

BaCO3 by XRD and EDX analysis (Figure S6), whose mass matched very well with the gas volume as measured above in the plastic bag. Thus, the mass of the generated

steam was calculated by subtracting the mass of CO2 from the total mass loss.

It can be concluded that the gas product was predominantly steam (Table S2), which contributed about 88% of the gas pressure for the expansion exfoliation of

SIGO. At the same time, since no SO2 or SO3 was found in the gaseous product, the

H2SO4 in SIGO should still remained in the ESIGO. That is in line with the mass

analysis about the H2SO4 in SIGO and ESIGO (Table S2). The SIGO samples washed with HCl solution were contaminated with small fraction of HCl, which however showed negligible influence on the expansion of the SIGO in our cases.

The FTIR spectra of SIGO and ESIGO

As shown in Figure S4, the intense infrared absorption at ~3400 and ~1030 cm-1 indicate that the SIGO samples contain large quantity of alcohol groups. Adsorbed

-1 H2O may also contribute to the ~3400 cm absorption considering the existence of

15 ~1610 cm-1 peak. However, the stretching vibrations of aromatic C=C bond can lead to the absorption at ~1610 cm-1 as wells1. The long tail of the ~3400 cm-1 peak extending to about ~2000 cm-1 indicates the existence of strongly hydrogen bonded hydroxyl most probably with carboxyl and sulfuric acids2. The peaks at 1720 and 1380 cm-1 show the vibrations of C=O and C-O in the –COOH group19. Absorption peaks corresponding to the symmetric and anti-symmetric stretching vibrations of S-O bonds in the sulfate ion can be found at ~1030 and ~1160-1220 cm-1 respectivelys2.

The intense peak at ~1220 cm-1 can also be attributed to the epoxy groups. On the other hand, the C-H bonds in the SIGO are evidenced. Stretching vibration of the C-H on the aromatic ring may lead to absorption between 3000 and 3100 cm-1. Particularly, the ~2920 and 2850 cm-1 peaks corresponding to the symmetric and anti-symmetric

stretching vibrations of -CH2 are perceptible. The peak at ~2340 indicates the

18,19,s1,s2 presence of adsorbed CO2 in the SIGO sample .

It is clearly that most of the hydrogen and oxygen containing species in SIGO have been removed after the low temperature expansions3,s4.

Supplementary references

1. Kaniyoor, A., Baby, T. T. & Ramaprabhu, S. Graphene synthesis via hydrogen induced low temperature exfoliation of graphite oxide. J. Mater. Chem. 20, 8467-8469 (2010).

2. Jeong, H. K. et al. Evidence of graphitic AB stacking order of graphite oxides. J. Am. Chem. Soc. 130, 1362-1366 (2008).

3. Bertram, A. K., Patterson, D. D. & Sloan, J. J. Mechanisms and temperatures for the freezing of sulfuric Acid aerosols measured by FTIR extinction spectroscopy. J. Phys. Chem. 100, 2376-2383 (1996).

4. Dubin, S. et al. A one-step, solvothermal seduction method for producing reduced graphene oxide dispersions in organic solvents. ACS Nano 4, 3845-3852 (2010).