Optical Study of Graphene Quantum Dots from

Sawahlunto Coal Graphite

Dellyansyah

1,2

, Saharman Gea

2,3

, Andriayani

2,3

, Mahyuni Harahap

2,3

and Grace Nainggolan

1,2

Postgraduate Chemistry Program, Faculty of Mathematics and Natural Sciences, Universitas Sumatera Utara,

Medan, Indonesia

Cellulosic and Functional Material Research Center, Universitas Sumatera Utara, Medan, Indonesia

Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sumatera Utara,

Medan, Indonesia

Keywords: Graphene quantum dots, Sawahlunto coal graphite (BB900), optical properties.

Abstract: Graphene quantum dots (GQDs), quantum sized graphene materials, have been proposed to be candidate in

optical and energy storage devices applications due its transparant properties and high surface area. In this

work, Sawahlunto coal graphite was converted into GQDs and analysed the optical properties. The coals

were dispersed in strong acid and irradiated with ultrasound before oxidized and hydrothermalized into

GQDs. UV-vis spectroscopy and photoluminescence spectrophotometer were used to determined the

conjugate structure and emission type respectively. The UV-vis spectra showed that the product had

conjugated structure in 230 nm. Photoluminescence results confirmed that the GQDs had cyan emission.

1 INTRODUCTION

Graphene quantum dots (GQDs), one of carbon

nanomaterials always takes an advanced part in

development of modern science and technology.

This quantum size exhibits excelent progress in

optoelectronic and energy storage device (Li et al.

2015). This is due to its transparant property and

high surface area (Yan and Liu, 2014).

GQDs can be obtained from graphene, graphene

oxide (GO), carbon nanotubes (CNTs), carbon fibers

and graphite as precursor. GO is be converted to be

GQDS by Hummers method and followed by redox

treatment repeatedly. This method is simple and

efective mass production, but requires high cost

(Bak, Kim and Lee, 2016). Hence, several literatures

have reported an advance investigation of GQDs

with low cost and high yield such as using high

temperature autoclave (Sun et al. 2013) and

microwave treatment (Shin et al., 2014).

Coal, a high carbon compound material, is able

to produce graphene to subtitute graphite (Powell

and Beall, 2015). Coal from Sawahlunto, West

Sumatera is a kind of a high volatile bituminous

with 40,79% - 49,67 % of carbon. It is potentially

converted into GQDs. It had been reported that coal

from Sawahlunto can be converted into graphene by

exfoliation graphitization graphite at 900

(Purwandari et al. 2020).

In this study, GQDs were synthesized from the

coal using modified hummers asisted by

hydrothermal method. To the best of our knowledge,

there is no optical study yet about this coal graphene

quantum dots for optical applications. The GQDs

optical properties were studied by using UV-Vis

spectroscopy and photoluminescence.

2 METHODS

2.1 Materials

Sawahlunto Sijunjung coal graphite powder

(BB900) is obtained from CFM-RC Laboratory.

CPRO WELD commercial graphite powder (KG),

Merck sulfuric acid 98% (H

), pottasium

permangate (KMnO

) and EMSURE sodium

hydroxide (EMSURE) were purchased from Sigma

Aldrich.

584

Dellansyah, ., Gea, S., Andriayani, ., Harahap, M. and Nainggolan, G.

Optical Study of Graphene Quantum Dots from Sawahlunto Coal Graphite.

DOI: 10.5220/0010614000002775

In Proceedings of the 1st International MIPAnet Conference on Science and Mathematics (IMC-SciMath 2019), pages 584-586

ISBN: 978-989-758-556-2

2.2 Synthesis of Graphene Quantum

Dots (GQDS)

BB900 (200 mg) was dispersed in a 100 ml H

for a few minutes before irradiated by ultrasonic for

2-5 hours. KMnO

(1 g) was slowly added to the

mixture under ice batch to keep temperature under

C and keep until being brownish suspension.

The suspension was heated in hydrothermal

autoclave vessel at 180

C for 18-24 hour and cooled

under room temperature. The resultant hydrothermal

was injected slowly to deionized water and added

NaOH until pH become 7 under ice batch condition.

The injected suspension was then filtered using 200

nm porous membrane. The same procedure was also

used to produced GQDs from commercial graphite

powder (GK).

2.3 Characterization

2.3.1 UV-Visible

UV-Vis spectrophotometer (UV 2400 PC Series,

Shimadzu) was used to determined conjugate bond

of GQDs. UV-Vis was carried out in range 200-800

nm.

2.3.2 Photoluminescence

Photoluminescence (AURORA 4000) were used to

determine emission of this GQDs product.

Photoluminescence was carried out in range 200-800

nm with UV-light excitation in 375 nm.

3 RESULTS AND DISCUSSION

Graphene quantum dots (GQDs) in this work were

obtained from Sawahlunto coal graphite (BB900) by

using modified hummers method and assisted by

hydrothermal. Before oxidized with strong oxidator

KMnO

BB900 was dispersed in strong acid H

and irradiated using ultrasound to weaken the Van

Der Walls bond (Shin et al., 2014). The oxidized

product was hydrothelmalized to cut graphene oxide

lattice into tiny dots at high temperature (Bak, Kim

and Lee, 2016). Finally, the tiny dots was

characterized by UV-Vis spectroscopy and

photoluminescene spectroscopy.

3.1 UV-Vis Spectrocopy Analysis

The conjugate aromatic structure was investigated

by using UV-Vis spectroscopy. Figure 1 showed

that the tiny dots of Sawahlunto coal graphite

(GQDs-BB900) and comercial graphite (GK). Both

tiny dots peaks show that there were no signifikan

friction at the wavelength. GQDs-BB900 and

GQDs-GK had first UV absorptions peaks at 230 nm

and 235 nm respectively. This first absorbance

indicated π–π* C-H sp

aromatic transitions (Shin et

al., 2014). The second absorbance was also detected

at 284 nm and 299 nm for GQDs-BB900 and GQDs-

GK. This absorbance confirmed C=O n- π* domains

(Song et al. 2014). The transitions of π–π* aromatic

were generally appeared from 200 to 270 nm and

C=O n- π* transitions were above 260 nm (Chen et

al. 2018). Although there was no significant frictions

in wavelength, the spectra showed significant

spacing in intensity of first absorbances. This

friction confirm that the tiny dots from BB900 had

more conjugated aromatic structure than GK.

Figure 1 UV-vis spectra of graphene quantum dots from

Sawahlunto coal graphite (GQDs-BB900) and commercial

graphite (GQDs-GK)

3.2 Photoluminesnence Analysis

Optical properties of this study were determined by

using photoluminescence (PL) spectrophotometer.

The PL was used to detect the emission of tiny dots

of GQDs as seen in Figure 2. From the Figure, UV

light with excitation at 375 nm was irrariated againts

GQDs-BB900, a strong peak appeared between 412

and 658 nm with maximum intensity at 493 nm.

This maximum intensity indicated that the tiny dots

of Sawahlunto coal graphite emitted cyan emission.

The same excitated UV light was also used against

GQDs-GK, a stronger peak appeared between 412

and 670 nm with maximum intensity at 467 nm. The

maximum intensity indicated that the tiny dots of

commercial graphite emitted blue emission. The

wavelength of blue emission and cyan emission

were 450-485 nm and 485-500 nm respectively

(Bruno and Svoronos, 2005).

Optical Study of Graphene Quantum Dots from Sawahlunto Coal Graphite

585

Figure 2 Emission intensity of graphene quantum dots

from sawahlunto coal graphite (GQDs-BB900) and

commercial graphite (GK)

4 CONCLUSION

Graphene quantum dots (GQDs) which was

synthesized from Sawahlunto coal graphite (BB900)

by using Hummers method with hydrothermal

asissted had been done. It has conjugated aromatic

structure and cyan emission which have potential for

optical applications.

ACKNOWLEDGEMENT

The authors thank to KEMENRISTEK DIKTI and

Rector of Universitas Sumatera Utara 2020 for

financial support through DRPM-PTM 2020 with

contract number : 11/AMD/E1/KP.PTNBH/2020.

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