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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Supporting Information for

Structure Observation of Graphene Quantum Dots by Single-Layered

Formation in Layered Confinement Space

Liqing Song, Jingjing Shi, Jun Lu, and Chao Lu*

State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology,

Beijing 100029, China

ElectronicSupplementaryMaterial(ESI)forChemicalScience.Thisjournalis©TheRoyalSocietyofChemistry2015 Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014
Experimental section

Materials

All chemicals used were analytical-reagent grade and were used as received without any further

purification. Mg(NO3)2·6H2O, Al(NO3)3·9H2O, NaOH, hydrochloric acid, citrate, ammonia, were

purchased from Beijing Chemical Reagent Company (Beijing, China). Acetone was purchased

from Thermo Fisher Scientific. The deionized water from a Millipore water purification system

was used throughout the experiments.

Apparatus

The photoluminescence spectra were obtained using a F-7000 fluorescence spectrophotometer (Hitachi,

Japan) at a slit of 2.5 nm with a scanning rate of 1500 nm/min. The solid UV-Vis absorption spectra were

acquired on a Shimadzu UV-3600 spectrophotometer (Tokyo, Japan). Transmission electron microscopy

(TEM) photographs were measured on a Tecnai G220 TEM (FEI Company, USA). High resolution

transmission electron microscopy (HRTEM) was carried out on JEOL JEM-ARM200F at an acceleration

voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) measurements were performed using an

ESCALAB-MKII 250 photo electron spectrometer (Thermo, USA). The lifetime was obtained by an

Edinburgh FLS 980 Lifetime and Steady State Spectrometer. The quantum yield was measured with an

integrating sphere from the reconvolution fit analysis (Edinburgh F980 analysis software) on an

Edinburgh instrument spectrometer. 1H nuclear magnetic resonance (1H NMR) spectra and 13C nuclear

magnetic resonance (13C NMR) were recorded at room temperature with a 600 MHz Bruker (Germany)

spectrometer. The sample of S-GQDs was dissolved in D2O. Electrospray ionization Fourier transform

ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) was carried out with solarix 9.4T (Bruker,

Germany). Bruker Data Analysis was used to determine resolving power. The powder X-ray diffraction

(XRD) measurements were performed on a Bruck (Germany) D8 Advance X-ray diffractometer equipped

with graphite-monochromatized Cu/Kα radiation (λ = 1.54178 Ǻ). The 2θ angle of the diffractometer was

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014
stepped from 5° to 70° at a scan rate of 10°/min. Fourier transform infrared (FTIR) measurements were

performed using a Perkin Elmer Model 100 FTIR spectrometer (Waltham, MA, USA). Zeta potential

measurement was determined using a Malvern Zetasizer 3000HS nano-granularity analyzer. Raman

spectrum was gained by LabRAM ARAMIS Raman System (HORIBA Jobin Yvon, Japan) with 532 nm

laser radiation source. Atomic force microscopy (AFM) in tapping mode was carried out on a NanoScope

IIIa (Digital Instruments Co., Santa Barbara, CA, USA) instrument. Gel permeation chromatography

(GPC) equipped with a Waters 1525 pump and a Waters 2414 refractive index detector (set at 35˚C).

Quantum chemistry calculation

The geometrical structure, the frontier molecular orbital analysis and the optical properties of

the C27H10N2O15 were studied in detail. All calculations were performed using Gaussian 09

software package by parallel computing in the Linux system using the 16-cores server. First, the

structure optimization was using B3LYP DFT method on 6-31G(d) basis set level, and the

calculated frequency demonstrated that the optimized geometrical structure was stable. Based on

the optimized geometries, the HOMO/LUMO analyses and spectral properties could be carried

out. The UV-Vis absorption and photoluminescence spectra were computed by TDDFT.

Procedures

Synthesis of Mg-Al-citrate-LDHs

Mg-Al-citrate-LDHs were synthesized by a co-precipitation method in the solutions of constant pH

value. A mixed salt solution containing 0.045 mol Mg(NO3)2·6H2O and 0.015 mol Al(NO3)3·9H2O in 60

mL water was added dropwise to a 60 mL solution containing 0.005 mol citrate at 30˚C under vigorous

stirring. Subsequently, 2.0 M NaOH solution was added to keep a constant pH value of 10.5. Then, the

suspensions were kept at 35˚C for 6 h under N2 atmosphere. Finally, the precipitate was filtered, washed

with deionized water for three times and stored at 4˚C until further use.

Synthesis of Mg-Al-GQD-LDHs

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Mg-Al-GQD-LDHs were synthesized by a hydrothermal method. 12.25 mL Mg-Al-citrate-LDHs

(0.045 g/mL) and 2.25 mL ammonia were added into a Teflon-equipped stainless steel autoclave followed

by hydrothermal treatment at 180˚C for 8 h. The resulting precipitate was separated by centrifugation

(10000 rpm/min, 5 min), washed thoroughly with deionized water and dried in vacuum at 60˚C for 12 h.

2.25 g Mg-Al-GQD-LDHs were treated with 5 mL hydrochloric acid in order to dissolve the layers of

LDH and obtain the pure solution of the S-GQDs. In addition, in order to remove inorganic salt, acetone

was used to mix with the solution of S-GQDs. The precipitate was removed by centrifugation (10000

rpm/min, 5 min), and acetone in the supernatant was evaporated off under a stream of N2, leaving a

yellow brown powder of the S-GQDs.

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Table S1 Geometric optimized bond length and angle of the S-GQD (C27H10N2O15).

Bond length（Å）

Bond angle (°)

C27-O28
C18-C27
C18-N31
C7-N31
C3-C7
C3-C4
C4-N32
C5-O34
C2-C17
C17-C18
C26-O30

1.381
1.496
1.377
1.422
1.395
1.430
1.316
1.430
1.209
1.358
1.196

O29-C27-C18
C27-C18-N31
C18-N31-C7
N31-C7-C3
C7-C3-C4
C3-C4-N32
N32-C4-C5
C4-C5-O34
O34-C5-C6
C1-C2-C17
C2-C17-C18
C17-C26-O30
O30-C26-O28
C26-O28-C27

129.6
127.1
116.5
121.0
117.0
124.5
116.9
121.8
120.4
124.6
123.6
130.5
122.0
109.6

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Table S2 Frontier molecular orbital (HOMO and LUMO) of the S-GQD (C27H10N2O15).

Compound

C27H10N2O15

LUMO(-4.284 eV)

LUMO

C27H10N2O11

HOMO(-6.668 eV)

-4.0

-4.5

-5.0

-5.5

-6.0

-6.5

-7.0

V)
e
(
y
g
r
e
n
E

2.384

HOMO

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Figure S1. XRD pattern of Mg-Al-citrate-LDHs.

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Electronic Supplementary Material (ESI) for Chemical Science
This journal is © The Royal Society of Chemistry 2014

Figure S2. FTIR spectrum of Mg-Al-citrate-LDHs.

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