Supporting Information

A Time efficient reduction strategy for bulk production of reduced graphene oxide using selenium powder as a reducing agent

Santosh K. Tiwaria, Andrzej Huczko,b Ramesh Oraona, Amrita De Adhikaria, Ganesh C.Nayak*a

aDepartment of Applied Chemistry

Indian School of Mines, Dhanbad, Jharkhand, (India) 826004 Email:*ganeshnayak2006@gmail.com

bLaboratory of Nanomaterials Physics and Chemistry, Department of Chemistry, Warsaw University, 1

Pasteur str., 02-093 Warsaw, Poland

1. Mechanism of conversion of GO to rGO

In 1927 Diels et al. reported that selenium acts as a very good dehydrogenating reagent [1].Since then a

lot of works have been carried out ondehydrogenation of fused ring systems (along with aromatization)

using selenium powder between the temperature rangeof 280-360 oC.This reaction is very popular in

steroids chemistry. For instance transformation of cholesterol to Diels’s hydrocarbon [1-5]. Likely it is

well established that in the presence of selenium powder and at temperature above 300oC side chains

having larger than methyl eliminated or degradedand rings with the ketonic group converted into –OH

group[2]. This happened due to formation of hydrogen selenideand selenium1 dioxide related compounds

[4-6]. Moreover, temperature activated decarboxylation is one of the oldest reactions in organic

chemistry [7]. In the present case, it seems that due to facilitated reaction condition between

selenium and oxygen, the decarboxylation reaction facilitated due to the formation of hydrogen

selenide, selenium dioxide etc. So removal of ketonic groups, hydroxyl groups and methylene

groups of GO is not an issue during this reaction and mechanism for these reactions in the

presence of selenium can be explained on the basis of reported works [1,4-7]. But proper

reduction of epoxy groups present in the GO is a matter of deep study and it cannot be completely

reduced at high temperature. Herein we have proposed a probable mechanism for smooth

reduction of epoxy groups due to selenium powder on the basis of result obtained.

Fig.1 Reduction of functional groups shown by circle of GO can be explained on the basis of

previous studies.

Wittig reaction is a stepwise ionic process and it is assumed that oxaphosphetanes (intermediates

is responsible for the Wittig reaction [1-5, 6]. In the present case it is assumed that at high

temperature single electron transfer (SET) between thermally activated selenium and epoxide ring

gives ionic doublet [T], which instantly converted into oxaphosphetane type intermediate [T ’]

because of energy constraints as shown in (Fig.2). In addition, along with reduction of epoxy

groups, selenium act as excellent scavenger for oxygen which prevents any possibilities structural

and lattice damage [3].

[T’]

Fig. 2 Probable mechanism of C=C bond formation using Se powder from epoxide rings.

The formation of intermediate [T] and [T‘] at 360 oC seems favourable because selenium is

partially metallic in nature with low electronegativity (borderline metalloid).So it has a tendency

to donate electrons to epoxide systems via single electron transfer mechanism. Finally high energy

oxaphosphetane type intermediate [T’] gives double bond via removal of SeO which take one

more oxygen and becomes SeO2. Previously existence of SeO was doubtful, but now emission

spectrum of the SeO provides strong support for its existence [2, 8]. So we can say that formation

of SeO2 (via SeO) responsible for reduction of epoxide groups present in GO. This imagination is

very strongly supported by the EDX spectra of prepared GO and rGO. The EDX analysis clearly

shows that GO (Fig. 3a) contains C and excess O atoms on other hand rGO (Fig. 6b) contains

predominantly C and only very trace amount of oxygen.

[T]

Fig. 3 Atomic percentage of carbon and oxygen in the prepared GO (a) and rGO (b).

References

1. Diels,o.,Nobel Lectures Chemistry, 1942-1962, 253.

2. Helten H, Schirmeister T, Engels B (2005) Theoreticalstudies about the influence of

different ring substituents on thenucleophilic ring opening of three-membered heterocycles

and possible implications for the mechanisms of cysteine protease inhibitors, J.Org. Chem.

233-237.

3. Larciprete R, Fabris S, Sun T, Lacovig P, Baraldi A, Lizzit S (2011) Dualpath mechanism

in the thermal reduction of graphene oxide, J.Am. Chem. Soc. 133:17315-21.

4. Jagdamba,S.,Yadav, L. D. S., (2004) Organic Synthesis, ISBN, 9789350061824 page533-

536.

5. Marcano DC, Kosynkin DVJ, Berlin M, Sinitskii A, Sun Z, Slesarev A (2010) Improved

synthesis of graphene oxide, ACS Nano 8:4806-4814.

6. Reddy S, Verma KK (1980) The a-X electronic band system of selenium monoxide at 1.8

μm, J. Mol. Spectrosc., 84: 89-93.

7. Vedejs E, Marth CF (1990) Mechanism of Wittig reaction: evidence against betaine

intermediates, Am. Chem. Soc. 112:3905-3909.

8. Wittig G, Lohmann L (1954) Ann 1942, 550, 260.(b) Wittig, G. Angew.Chem, 66.

2. FTIR of GO heated at 360oC in inert atmosphere without Se

To further analyse the effect of Se on reduction of GO to rGO we have heated GO in

identical experimental conditions (as mentioned in main article) but without Se powder and

consequently FTIR spectrum was recorded [1-2]. The FTIR spectrum (Fig.4) indicates presence

all characteristic functional groups of graphene oxide but intensity of some characteristic band

diminished. Form this we concluded that, only temperature (360oC) is unable to remove

completely all the functional groups present in GO [1-2].

.Fig. 4 FTIR Spectrum of GO heated at 360oC under inert atmosphere

References

1. Li D, Mueller MB, Gilje S, Kaner RB., Wallace GG (2008) Processable aqueous dispersions of

graphene nanosheets. Nature nanotech. 3:101.

2. Zhang JL, Yang H J, Shen G X, Cheng P, Zhang, et al (2010) Reduction of graphene oxide

via L-ascorbic acid. Chem. Commun., 46:1112−1114.

3. UV-Visible absorption of GO heated at 360oC in inert atmosphere without Se

The UV-visible spectrum of GO (Fig.5) clearly revels that a very weak peak at around 226-

230nm. This indicates that heating GO without Se can remove some of the oxygen functional

groups but recovery of significant conjugation is not possible.

Fig. 5 UV-Visible Spectrum of GO heated at 360oC under inert atmosphere

4. Raman spectrum of GO heated at 360oC in inert atmosphere without Se

Raman spectrum (Fig.6)of GO heated at 360 oC without selenium powder indicates that

significant amount of functional groups still present on the surface of graphene oxide because D

bands (defective mode ) are very clear in the spectrum. In addition to this there is no 2D peak in

the spectrum which is a finger print for conversion of GO to rGO

Fig. 6 Raman Spectrum of GO heated at 360oC under inert atmosphere

5. Powder XRD of GO heated at 360oC in inert atmosphere without Se

XRD analysis of GO heated without Se is shown in (Fig.7). A broad peak is observed which

indicates that complete exfoliation of GO has not occurred. This is due to residual oxygen

functional group which held the sheets together.

Fig. 7 XRD pattern of GO heated at 360oC under inert atmosphere

Fig.8 Digital images of (a) graphene oxide and (b) reduced graphene oxide