University of Groningen
Nanostructured graphene
Lu, Liqiang
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2018
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Lu, L. (2018). Nanostructured graphene: Forms, synthesis, properties and applications. Rijksuniversiteit
Groningen.
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Appendix
Appendix 1 for chapter 3
Figure A1.1 Intermediates produced at different preheating temperatures: (a) 100 °C; (b) 150 °C; (c) a product reduced at 300 °C for 1h after preheating at 150 °C; (d) TEM of Ni nanoparticles formed by reduction at 300 °C for 1 h.
40 50 60 70 80 Intensity (a.u.) 2 (°C) 270 °C 300 °C 450 °C 600 °C 800 °C b for 2h
Figure A1.2 (a) SEM image of nanoporous Ni prepared at 800 °C, (b) XRD patterns of nanoporous Ni prepared at different temperature from 270 °C to 800 °C, respectively.
Figure A1.3 Nanoporous Ni prepared at 300 °C for 2 h under different flow rate of H2 (15% in Ar), (a) 200 sccm, (b) 400 sccm.
Figure A1.4 Nanoporous Ni prepared by using different precursors and reduced at different temperatures: (a) Ni(CH3COO)2·4H2O and reduced at 300 °C for 2 h, (b) NiO and reduced at 300 °C for 2 h, (c) Ni(OH)2 as the precursor, reduced at 300 °C for 2 h, (d) NiCl2 as the precursor and reduced at 700 °C for 2 h; (e and f) nickel oxalates as precursors and reduced at 450 °C for 2h.
Figure A1.5 the deposition of NiC2O4 coating on (a) internal ligaments and (b) surfaces of Ni chips. 0 100 200 300 400 500 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Volt age (V v s Li + /Li)
Specific capacity (mAh/g)
1st
2nd
3rd
4th
c
Figure A1.6 (a and b) SEM images of NiC2O4·2H2O@np-Ni nanowires, (c) the discharge and charge performances of NiC2O4·2H2O@np-Ni nanowires (loading with 2.96 mg cm-2) at 100 mA g-1.
Calculation of areal, gravimetric and volumetric capacity density of overall electrodes:
For graphite anodes, supposing the coating on copper foil contains 90% graphite, 10% binder. Applying the following parameters: the theoretical capacity 372 mAh g-1, the area of
electrodes 1 cm2, the thickness of copper foil 18 µm (in half cell), the tap density of graphite
in anode coating 1.3 g cm-3, 10% of polyvinylidene fluoride binder (PVDF) binders, the
thicknesses of graphite coating on copper foil ~60 µm, the density of copper 8.96 g cm-3.
The volume of coating (graphite, binders, and CB): Va =60×10-4 cm×1 cm2=6 ×10-3 cm3
Areal loading of graphite: mA= Va×1.3 g cm-3=6 ×10-3 cm3 ×1.3 g cm-3=7.8×10-3 g=7.8 mg
Areal capacity of graphite: CA= mA ×372 mAh g-1=7.8×10-3 g ×372 mAh g-1=2.9 mAh
Total volume of electrodes: VT=1 cm2×(60+18) ×10-4 cm=7.8×10-3 cm3
Volumetric capacity density: Cv= CA/ VT = 2.9 mAh/(7.8*10-3 cm3) ≈ 372 mAh cm-3
Areal weight of copper foil: 18×10-4 cm×1 cm2×8.96 g cm-3 = 16.1 mg
Areal weight of anode coating: 7.8 mg/0.9 = 8.7 mg.
Total weight of electrodes (including copper foil, graphite, binders): mT = 16.1+8.7 = 24.8 mg.
Gravimetric capacity density: CG = CA/mT = 2.9 mAh/24.8 mg = 0.117 mAh mg-1=117 mAh g-1.
It should be pointed out that, when using a copper foil with thickness of ~10 µm in commercial use, the maximum gravimetric capacity density and volumetric capacity density will be 164 mAh g-1 and 414 mAh cm-3.
Table A1.1 The comparison of the initial capacities of NiC2O4·2H2O with previous oxalates
MC2O4 (M=Ni, Fe, Mn, Cu, Zn, Co)
MC2O4 Initial discharge capacity
(mAh g-1)
Initial charge capacity
(mAh g-1) Ref.
NiC2O4·2H2O@np-Ni 3,154 1,910 This work
NiC2O4·2H2O/GO composites 1,109 1,072 39 CoC2O4 nanorodes 1,609 997 42 MnC2O4 500 / 43 FeC2O4 930 / 43 CuC2O4·5H2O 1,100 450 42 ZnC2O4 1,080 400 42 Fe0.75Co0.25C2O4. 1,460 ~ 1,080 40
Table A1.2 The comparison of the performances of np-Ni@NiC2O4·2H2O with different types of porous metal electrodes and typical graphite anodes Electrodes Initial discharge capacity* (mAh g-1) Initial charge capacity* (mAh g-1) Thickness of the electrodes (µm) Areal loading of active materials (mg cm-2) Areal capacity (mAh cm-2) Gravimetric capacity density# (mAh g-1) Volumetric capacity density# (mAh cm-3) Ref. NiC2O4·2H2O@ np-Ni 3,154 at 100 mA/g 1,910 at 100 mA/g ~ 100 1.2 ~ 10.1 8.8 for initial; remained at 4 after 20 cycles 189 881 This work
Cu/NP Cu/SnO2 1,780 919 10.8 0.27 0.48 for initial ~ 50 444 6
Cu/NP Cu/MnO2 1,324 1,179 10.8 ~0.0056 0.0074 for initial 0.78 ~ 6.9 41
NP Cu@Cu2O 2.35
mAh cm-2 1.61 mAh cm-2 / / 2.35 for initial / / 44
Cu/Si/Ge NW@ Ni-CF 3,273 2,373 500 0.32-1.2 2.67 for intial and stabilited at 1.27 63 53 46 ZnCo2O4@Ni-CF 2,053 1,508 1,000 2.0 4.1 for intial stabilized at 2.2 49 48 50
NiO@Ni-CF 1,126.7 802.4 500 1.24-1.86 1.4-2.1 for initial < 50 < 42 51 ZnCo2O4–ZnO–C
@Ni-CF 930 667 500 1 0.93 for initial 22 19 52
Co3O4@Co3S4@
Ni-CF 1,903 1,565 ~500 3.0 5.7 for initial ~136 ~114 53
Si-C composites 1,950 ~ 1,650 ~ 18.6 ~ 2.94 ~ 5.73 for initial ~ 282 ~ 734 54 Graphite on Cu
foil (18 µm) 372 372 78 7.8 2.94 for initial 117 ~ 372 54
Appendix 2 for chapter 4
Figure A2.1 Nanoporous graphene (NPG) in the forms of powder (left), chip (middle) and bulk (right).
Figure A2.2 SEM micrographs showing NPNi-1000 synthesized at 600 °C: (a) overview and (b) close view.
Figure A2.3 Schematic of PVP thin film coated a Ni ligament and converted to graphene (G) coating
Calculation of PVP coating converted to graphene coating on Ni:
Below conditions are required: suppose all the Ni ligaments were equivalent to a long Ni wire of diameter d and length l. Thin PVP coating and graphene coating can be seen as very thin tube compared with Ni ligaments. Thus, the thickness of PVP coating tPVP and the
thickness of graphene coating tG can be ignored when calculate the volume of PVP and
graphene coating because d >> tPVP > tG. The solubility of carbon follows the Eq. 1:
ln S = 2.480‐4,880/T (1)
where S is the solubility in grams of carbon per 100 grams of nickel. T is the temperature (K) The volume of Ni ligaments (VNi) can be presented in the following equation:
V = l × π × d × (2)
Then, the mass of Ni ligaments (MNi) can be estimated with Eq. 3,
M = ρ × l × π × d × (3)
Similarly, we have the volume of PVP coating (VPVP) in the following Eq. 4
V = l × π × d × t (4)
and the mass of PVP (MPVP) in Eq. 5:
M = ρ × l × π × d × t (5)
The volume of G coating (VG)follows Eq. 6:
V = l × π × d × t (6)
The mass G (MG) follows Eq. 7:
M = ρ × l × π × d × t (7)
The mass of carbon after heat treatment at 800 °C is 4.1 wt.% of PVP by heating PVP under H2/Ar using same condition with heat treatment of NPNi/PVP. So, the mass of carbon
MC generated from PVP at 800 °C is 0.041MPVP.
M = 0.041 × M (8)
The solubility of C in Ni is ~0.126 g at 800 °C calculated based on Eq.1. So, when the carbon in Ni at 800 °C is saturated, the amount MC0 of carbon dissolved in Ni ligaments of
MNi equals to 0.00126*MNi.
When all the solid carbon from PVP decomposition converted to graphene,
M = M ≤ M = 0.00126 M (9)
When MG=0.00126 MNi,
ρ × l × π × d × t = 0.00126 × ρ × l × π × d × (10) So,
When ρgraphite≈2.26 g cm-3 and ρNi=8.908 g cm-3, we have
t ≈ 1.24 × 10 d (12)
When the maximum ligament size is 1,500 nm, tG is ~1.9 nm.
Also, we have MG=0.041 MPVP,
So,
ρ × l × π × d × t = 0.041 × ρ × l × π × d × t (13) When ρpvp=1.2 g cm-3, we have the relationship between PVP and graphene,
t ≈ 0.0218t (14)
Also, we have tG=0.34n, where n is the number of graphene layer. So
n ≈ 0.064t (15)
Figure A2.4 (a) PVP coated nanoporous Ni by dipping the nanoporous Ni in 0.25 g mL-1 of PVP solution, (b) PVP coated nanoporous Ni by dipping the nanoporous Ni in 0.4 g mL-1 of PVP solution, (c and d) SEM and TEM of nanoporous graphene with thick walls obtained by using 0.4 g mL-1 of PVP solution.
1000 1200 1400 1600 1800 In tensi ty (a. u.) Raman shift (cm-1) D G
e
Figure A2.5 (a and b) SEM image and TEM image of the NPG prepared by using sucrose as the precursor; (c and d) SEM and N mapping of NPG prepared by using PVP and dicyandiamide as carbon sources. (e) Raman spectra of N-doped NPG.
1000 1200 1400 1600 1800 2000 Intensity (a .u .) Raman shift (cm-1) D G
b
Figure A2.6 (a) HR-TEM and (b) Raman spectra of nanoporous graphene obtained at 700 °C, showing the disordered layer structure and low graphitization.
Figure A2.7 (a) SEM of nanoporous Ni with average ligament size ~160 nm (b) low-magnification SEM image of NPG-160.
0.0 0.2 0.4 0.6 0.8 1.0 0 20 40 60 80 100 120 140 Quantity A d sorbed (cm 3 /g ST P ) Relative Pressure ( P/P0)
Appendix 3 for chapter 5
Figure A3.1 (a, b) SEM images of micron-porous Fe reduced from FeCl3 at 700 °C, (c, d) SEM images of micron-porous graphene foam synthesized by using micron-porous Fe templates, observed at different magnifications.
Figure A3.1a and b shows the microstructure of porous iron. It has a similar but less uniform porous structure in comparison with the micron-porous Ni. Figure A3.1 c and d show the as-synthesized micron-porous graphene by using porous iron as templates. It should be mentioned that, the porous graphene synthesized from the iron chloride has more fracture than by using nickel chloride as precursors, which could be due to the uniformity porous structure of iron templates.
Appendix 4 for chapter 6
Figure A4.1a is an SEM image of the Ni-C-Ni sandwich film deposited on SiO2 (300 nm
thick)/Si substrate (500 µm thick). The size of the Ni particle is less than 20 nm. The XRD pattern shown in Figure A4.1b demonstrates (111) and (200) peaks of Ni. It indicates a nanocrystalline Ni film from the large full width at half maximum (FWHM). The surface roughness was measured by using AFM. Figure A4.2 is the AFM image of Ni-C-Ni sandwich film before VTP treatment. It reveals the deposited poly-Ni has a smooth surface with an RMS toughness of ~0.1 nm. 40 45 50 55 Inte nsi ty (a.u. ) 2 theta (°) Ni (111) Ni (200) b
Figure A4.1 SEM image (a) and XRD pattern (b) of the Ni-C-Ni sandwich film deposited on SiO2 (300 nm thick)/Si substrate (500 µm thick).
Figure A4.2 AFM image of Ni-C-Ni sandwich film before annealing
Figure A4.3 High-resolution SEM images revealing the topographic contrast (a) and voltage contrast (b) of the same view field of pure nanocrystalline Ni film after VTP treatment at 350 °C for 1 h.
Table A4.1 Raman intensity ratio ID/IG and FWHM (W) of the D and G bands for the
free-surface graphene and interface graphene, respectively.
ID/IG WD (cm-1) WG (cm-1)
Free-surface graphene film 1.8 141 65
Interface graphene film 2.8 240 79
The calculation of ID/IG refers to the peak intensity of D and G peaks after
deconvolution of Raman spectra as shown in Figure A4.3b and Figure A4.3d. The full width at half-maximum (FWHM) of the D and G peaks is listed in Table A6.1. The larger FWHMs for the interface graphene film indicate that the interface graphene film has a higher content of defects and smaller distances between the defects (LD) than the free surface graphene film.
The ID/IG of free surface graphene is also smaller than the ID/IG of the interface graphene,
Figure A4.4 SAED (left), TEM (middle) and HRTEM (right) images of nc-Ni film coated amorphous carbon on Cu grids.
Figure A4.5 (left) SEM and (right) TEM images of nc-Ni film coated amorphous carbon on Cu grid after VTP at 350 °C for 12 h.
Figure A4.6 SEM images of the Ni-C-Ni sandwich film kept for 4 weeks at room temperature (~20 °C). Small graphene domains start to nucleate even at room temperature, although it took a long time. This observation is consistent with the previous results.1
Figure A4.7 HRTEM image of nc-Ni film coated amorphous carbon TEM grid kept for 2 weeks at room temperature. The white arrows show the lattice spacing of ~0.34 nm indicating graphene crystals formed at room temperature.
Figure A4.8 Cross-sectional SEM image (a) and element distribution (b-d) of the Ni-C-Ni sandwich film with 100 nm thick carbon film after processed by VTP at 350 °C for 96 h.
Ni
C
S
Ni
C
Ni
a b c dFigure A4.9 Cross-sectional SEM image (a) and element different distribution (b-d) of the Ni-C-Ni sandwich film with 10 nm thick carbon film after processed by VTP at 350 °C for 96 h. After VTP, all the C film was exhausted because the carbon middle layer disappeared.
References
[1] J. Kwak, J.H. Chu, J. Choi, S.D. Park, H. Go, S.Y. Kim, et al., Near room-temperature synthesis of transfer-free graphene films, Nat. Commun. 3 (2012) 645.
Ni
Ni
Ni
C
Si
a b c dAppendix 5 for chapter 7
In the sythesis process of GQDs, nanographite (NG) and acetylene black (AB) were used for exfoliation, respectivily. Figure A5.1 shows the photographs of as-prepared N-methyl-2-pyrrolidone (NMP) dispersions of low-defects graphene quantum dots (LD-GQDs) and high-defects graphene quantum dots (HD-GQDs). After ultrasonication, the NMP dispersions became gray or dark. It can be clearly seen that the NMP dispersion made from AB raw material has lower transparence than that made from NG raw material, which indicates more exfiolated products dispersed in the AB dispersion because of the tiny and defect-rich graphitic layers exist in AB. For other solvents such as DMSO and DMF, they have different effects for the exfoliation. As shown in Figure A5.2, no transparence change was observed for DMSO dispersion, while a brown dispersion was obtained by using DMF exfoliation. Comparing with them, dark dispersion was obtained by using NMP.
Figure A5.1. Photograph of as-prepared NMP dispersion of LD-GQDs (left) and HD-GQDs (right), respectively, made from nanographite (NG) and acetylene black (AB).
Figure A5.2. Photographs of GQDs dispersions in various solvents by using AB as precursor.
Figure A5.3. Bottom view photographs of as-synthesized GQDs in the flask bottom after removing NMP by vacuum evaporation, viewed under nature light (left) and 365 nm irradiation (right).
When excited by ultraviolet light (365 nm), the orange GQDs emit bright blue light. This is an efficient way to detect the GQDs prepared.
Figure A5.4 are the XRD patterns of raw carbon materials AB and NG. For AB, it shows hump diffraction peaks indexed to (002) and (200) lattice planes. But for NG, it shows strong diffraction peaks owing to the high crystallization and graphitization. The (002) plane spacing of AB is around 0.355 nm because of the defect-rich nanocrystalline structure.
10 15 20 25 30 35 40 45 50 (200) Intensi ty (a. u. ) 2 (°) (002) AB a 10 20 30 40 50 60 70 80 Intens ity (a .u.) 2(°) NG (002) b
Figure A5.4. XRD patterns of raw materials AB (la) and NG (b).
Table A5.1. Content of C, N, and O atoms in LD-GQDs and HD-GQDs as determined by XPS measurements Composition (at.%) LD-GQDs HD-GQDs C 84.0 79.6 C−C 74 65.0 C−(O,N) 17.7 22.0 (C=O)−NH−C 8.3 13 N 5.0 7.6 (C=O)−NH−C 97.2 96.0 N-C3 2.8 4.0 O 11.0 12.8
Figure A5.5 are the EDS spectrum of LD-GQDs and HD-GQDs. From the spectrum, the EDS peaks corresponding element C, N and O are observed in both two samples. The contents of element C, N and O are determined and shown in Table A5.2. Consist with the results of XPS, the LD-GQDs have lower content of N and O than HD-GQDs.
0 100 200 300 400 500 Inten s ity(a.u.) Energy(eV) O C N LDGQDs a 0 100 200 300 400 500 Inten s ity(a.u.) Energy (eV) C NO HDGQDs b
Figure A5.5 EDS spectrum of LD-GQDs (a) and HD-GQDs (b).
Figure A5.6 and Figure A5.7 show the SEI images and corresponding EDS element mapping of C, N, O. All the elements C, N, O are well distributed.
Figure A5.6 (a) SEI image and (b-d) element mapping for carbon (b), nitrogen(c), and oxygen(d) of sample LD-GQDs
a b
Table A5.2 The contents of element C, N, O in sample LD-GQDs and HD-GQDs determined by EDS measurements
Sample Element content
C N O
LD-GQDs 82.0% 4.4% 13.6%
HD-GQDs 76.6 % 8.0 % 15.4 %
Figure A5.7 SEI image (a) and element mapping for carbon (b), nitrogen(c), and oxygen(d) of sample HD-GQDs
Thermogravimetric analysis (TGA) measurements were carried out using a Mettler Toledo TGA/SDTA 851e thermal gravimetric analyzer at a heating rate of 10 oC min-1 from
20−700 oC under nitrogen flow (100 sccm). Figure A5.8 gives the TGA and DTG profiles of
sample HD-GQDs and LD-GQDs respectively. The weight loss of HD-GQDs is about 56% while that of LD-GQDs is about 31%. The main weight losses for two samples occur at 300-400 oC, which is ascribed to the in-plane and edge oxygenated functionalities.1 The big difference of weight loss in TGA between LD-GQDs and HD-GQDs is owing to the lower content of functional groups in LD-GQDs.
a b
0 100 200 300 400 500 600 700 40 50 60 70 80 90 100 dW /dT W ei g ht loss ( %) Temperature (o C) Red curve: TGA
Black curve: DTG -0.005 -0.004 -0.003 -0.002 -0.001 0.000 a 0 100 200 300 400 500 600 700 40 60 80 100 dW /dT We ight lo s s (%) Temperature (o C) Red curve: TGA Black curve: DTG -0.0020 -0.0015 -0.0010 -0.0005 0.0000 0.0005 b
Figure A5.8 TGA/DTG curves of HD-GQDs (a) and LD-GQDs (b) measured in N2 atmosphere
Figure A5.9 shows the atomic force microscopy (AFM) characterization of the thickness of HD-GQDs (a) and LD-GQDs (b). For HD-GQDs, the thickness distribution is 0.4-2 nm, which corresponds to maximum 6 layers GQDs. For LD-GQDs, the thickness distribution is 0.3-3 nm, which is equal to 9 or less layers GQDs.
Figure A5.9. AFM images of HD-GQDs and the height profile along the indicated line (a), and of LD-GQDs and the height profile along the indicated line (b).
Figure A5.10 presents the photographs of HD-GQDs excited by ultraviolet, blue and red laser light. It can be seen blue, green and red light emitted by HD-GQDs. This observation agrees well with the excitation-dependent PL behaviours.
Figure A5.10. The photographs of HD-GQDs sample excited by ultraviolet, blue and red light.
Figure A5.11 displays the images of bright-field image and confocal fluorescence photomicrograph under 488 nm excitation of the fibroblast L929 cells of mouse without treating with GQDs. It can be seen that without GQDs no cells are observed in confocal fluorescence photomicrograph under excitation.
Figure A5.11. The bright-field image (a) and confocal fluorescence photomicrograph under 488 nm excitation (b) of the fibroblast L929 cells of mouse without GQDs
References
[1] R.K. Biroju, G. Rajender, P.K. Giri, On the origin and tunability of blue and green photoluminescence from chemically derived graphene: hydrogenation and oxygenation Studies, Carbon 95 (2015) 228-238.
