Supporting Information for
Study on the surface energies and dispersibility of graphene
oxide and its derivatives
Jinfeng dai, Guojian Wang, Lang Ma, Chengken Wu
Further experimental details
IGC measurements and theory:
For the determination of thermodynamic surface parameters, the net retention volume
Vn is computed according to Eq. (1):[1, 2]
𝑃0 −𝑃𝑤
𝑉𝑛 = 𝐹﹒𝑗﹒(𝑡𝑟 − 𝑡0 )﹒ (
𝑃0
) ﹒ (𝑇
𝑇𝑐
𝑚𝑒𝑡𝑒𝑟
)
3 (𝑃 ⁄𝑃 )2 −1
𝑗 = 2 [(𝑃𝑖 ⁄𝑃0 )3 −1]
𝑖
0
(1)
(2)
Where F is the flow rate, tr and t0 are the retention and dead times respectively, p0 is
the pressure at the flow meter, pw is the vapor pressure of water at the temperature of
the flow meter (Tmeter), and the Tc is the column temperature. j is the James-Martin
compressibility factor for the correction of gas compressibility when the column inlet
(pi) and outlet (p0) pressure are different and it is given by Eq. (2)[1, 2]
According to Fowkers[3], the surface free energy of solid, 𝛾𝑠𝑡 , which can be
considered to be a sum of a dispersive component, 𝛾𝑠𝑑 , due to van der Waals
interactions, and a specific component, 𝛾𝑠𝑃 , such as acid–base interactions,
hydrogen-bonding, or π-π stacking. The 𝛾𝑠𝑑 value of stationary phase is measured
when n-alkanes are used as probes, and can be obtained according to Dorris and Gray
method[4]. Where 𝑅𝑇 · ln 𝑉 for n-alkanes is plotted against the number of carbon
atoms of the probe, the 𝛥𝐺𝐶𝐻2 can be determined from the slope of the resulting line.
Then, the 𝛾𝑠𝑑 can be calculated using the following Eq. (3), as seen in Figure S2:
γ𝑑𝑠
=
(𝛥𝐺𝐶𝐻2 )
2
4𝛾𝐶𝐻2 ·(𝑎𝐶𝐻2 ·𝑁𝐴 )
2
(3)
Where 𝑁𝐴 is the Avogadro constant, 𝑎𝐶𝐻2 is the area of a –CH2– group (0.06 nm2)
and 𝛾𝐶𝐻2 the surface energy of a solid consisting of only –CH2– groups. The value of
𝛾𝐶𝐻2 with temperature can be obtained by Eq. (4):
𝛾𝐶𝐻2 (𝑚𝐽 · 𝑚2 ) = −0.058(𝑚𝐽 · 𝑚2 ) × 𝑇 + 52.6(𝑚𝐽 · 𝑚2 )
(4)
If the polar probes are injected, both dispersive and specific interactions are
established with the solid surface, ∆𝐺, being the adsorption free energy, defined by
Eq. (5)[2, 5, 6]:
∆𝐺 = ∆𝐺 𝑑 + ∆𝐺 𝑠𝑝
(5)
Where ∆𝐺 𝑑 is the adsorption free energy of dispersive interaction; While ∆𝐺 𝑠𝑝 is
the specific interaction contributions to ∆𝐺 which reflects specific interaction (such
as acid–base interactions, hydrogen-bonding, or π-π stacking) between chemical
surface and probes. The value of ∆𝐺 𝑠𝑝 is difficult to obtain through Dorris and Gray
method. however, 𝑅𝑇 · ln 𝑉 can be plotted against the molecular polarizabilities (PD)
of the probes according to an approach defined by Dong et al.[7] The value of ∆𝐺 𝑠𝑝
results from the distance between the
𝑅𝑇﹒ ln 𝑉 value of polar probe and the
straight n-alkanes line, as shown in Figure S3.
From these ∆𝐺 𝑠𝑝 values, polar surface energies of solid (𝛾𝑠𝑃 ) are calculated using the
following Eq. (6)[8, 9] based on the theory of Good-Van Oss[10, 11]:
∆𝐺 𝑠𝑝 = 2﹒𝑁𝐴 ﹒𝑎﹒((𝛾𝐿+ 𝛾𝑆− )1⁄2 + (𝛾𝐿− 𝛾𝑆+ )1⁄2 )
(6)
Where 𝛾𝑆+ and 𝛾𝑆− are the acidic and basic parameters of the solid surface,
respectively, and 𝛾𝐿+ and 𝛾𝐿− are the acidic and basic parameters of the probe
molecules, respectively. In our work, we adopted DCM and EtAc as a monopolar
acidic probe and a monopolar basic probe, and their acidic and basic parameters
−
+
+
(using 𝛾𝐷𝐶𝑀
as 0.0 mJ·m-2 and 𝛾𝐷𝐶𝑀
as 5.20 mJ·m-2; assuming 𝛾𝐸𝑡𝐴𝑐
to be 0.0
−
mJ·m-2 and 𝛾𝐸𝑡𝐴𝑐
to be 19.2 mJ·m-2) are provided. Consequently, the 𝛾𝑠𝑃 is
determined according to Eq. (7)[10, 11]:
𝛾𝑠𝑃 = 2(𝛾𝑠+ 𝛾𝑠− )
1⁄
2
(7)
Once the 𝛾𝑠𝐷 and 𝛾𝑠𝑃 are obtained, the total surface energy (𝛾𝑠𝑇 ) is calculated as
following Eq. (8):
𝛾𝑠𝑇 = 𝛾𝑠𝐷 + 𝛾𝑠𝑃
(8)
Tables
Table S1 The physicochemical properties of probes
𝛂
PD
AN
DN
Specific
(Å)2
(cm3﹒mol-1)*
(kJ﹒mol-1)
(kJ﹒mol-1)
Character
C6
51.5
29.9
-
-
neutral
C7
57.0
34.6
-
-
neutral
C8
62.8
39.2
-
-
neutral
C9
69.0
43.8
-
-
neutral
DCM
31.5
16.4
16.4
0
acidic
EtAc
48.0
22.2
6.3
71.7
amphoteric (stongly basic)
THF
45.0
20.0
2.1
84.4
basic
Probe
* Molecular Deformation Polarizability
Table S2 EA, XPS data of samples
Sample
Element
EA (wt %)
XPS (at %)
C
65.14
68.6
O
33.35
31.0
N
0.17
0.4
C/O
2.60
2.21
C
68.94
72.4
O
29.54
27.6
C/O
3.11
2.62
C
79.87
83.3
O
19.36
16.7
C/O
5.50
4.98
C
91.56
90.6
O
6.91
8.2
N
1.34
1.2
C/O
17.67
11.0
GO
COOH-GO
EG-rGO
rGO
Table S3 Quantitative comparison of C1s and O1s peaks for samples
C 1s (%)
O 1s (%)
Sample
sp2/284.6eV
C-O/286.3eV
C=O/288.1eV
O-C/533.2eV
O=C/531.5eV
GO
41.5
45.4
13.1
70.9
29.1
COOH-GO
49.8
33.8
16.4
41.6
58.4
EG-rGO
67.8
23.6
8.6
59.4
40.6
rGO
72.8
7.1
3.4
48.9
51.1
Figures
Fig. S1 High resolution O1s XPS spectra of GO, COOH-GO, EG-rGO and rGO
Fig. S2 The plot of 𝑅𝑇 · ln 𝑉 Vs. carbon number
Fig. S3 Determination of ∆𝐺 𝑠𝑝 for polar probes by Dong`s method
Fig. S4 Dispersion states of GO, COOH-GO, EG-rGO and rGO versus the dispersive
components (δD) of solvents
Fig. S5. AFM images of GO/DMF, COOH-GO/DMF, EG-rGO/NMP and rGO/NMP
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