Experimental section
以下为《Experimental section》的无排版文字预览，完整格式请下载
下载前请仔细阅读文字预览以及下方图片预览。图片预览是什么样的，下载的文档就是什么样的。
Experimental section
Chemical
Polyacrylonitrile (PAN), Zn(Ac)2, Zn(NO3)2·6H2O, 2-methylimidazole (2-MeIM), methanol, and dimethylformamide (DMF) were purchased from Sinopharm Chemical Reagent Co., Ltd.
Synthesis of integrated ZIF-8 tubes
Before the preparation of ZIF-8 tubes, Zn(Ac)2/PAN fibers were pre-prepared according to the literature [1]. Afterward, a certain amount of Zn(Ac)2/PAN fibers was immersed into a 2-MeIM methanolic solution (5 mM; 25 mL) for 30 min, decorating the fibers with the first layer of ZIF-8. Then, the first-layer ZIF-8 decorated PAN fibers were immersed into a Zn(NO3)2 methanolic solution (5 mM; 25 mL) for another 30 min, resulting in second-layer ZIF-8 decorated fibers. Continuing to immerse the obtained fibers into 2-MeIM methanolic solution and Zn(NO3)2 methanolic solution alternatively, the fibers covered with the third and fourth layers of ZIF-8 can be obtained. This process is known as the layer-by-layer growth process. The fibers covered with four layers of ZIF-8 are selected as the representative sample and abbreviated as PAN@ZIF-8 fibers. Finally, PAN@ZIF-8 fibers were gently immersed in DMF at 60 °C to remove PAN core and produce integrated ZIF-8 tubes.
Synthesis of NCTs
The obtained ZIF-8 tubes were heated at 350 °C and 900 °C in a nitrogen atmosphere, respectively. Each stage was kept for 2h. The heating rate was set to be 1 °C min-1 in the first stage (below 350 °C) and increased to be 5 °C min-1 in the second stage (350 to 900 °C). NCTs were finally obtained by immersing the carbonized product in 1 M H2SO4, followed by a drying process. After that, NCTs were directly attached to graphite paper (thickness: 1 mm) to prepare capacitive deionization (CDI) electrodes.
Characterizations
The crystal structure of the samples was characterized by powder X-ray diffraction (XRD, Ultima Rint 2000 X-ray diffractometer, RIGAKU, Japan) measurements using Cu Kα radiation (40 kV, 40 mA, 2°?min?1 scan rate). The chemical composition and state of the samples were obtained by X-ray photoelectron spectroscopy (XPS) measurements using an Imaging Photoelectron Spectrometer (Axis Ultra, Kratos Analytical Ltd.) with a monochromatic Al Kα X-ray source. The porosity of the samples was characterized by the N2 adsorption/desorption measurements using a BELSORP-mini (BEL, Japan) at 77 K. The Brunauer-Emmett-Teller (BET) method was used for estimating specific surface areas (SSAs) of samples by using adsorption branch data in relative pressure (P/P0) range of 0.05-0.5. The overall morphology of the samples was investigated by field-emission scanning electron microscope (FESEM, Hitachi SU8000, 5 kV) with a platinum coating before the FESEM observations. The field emission transmission electron microscope (TEM) images were taken by a JEOL JEM-2100.
Electrochemical analysis
The electrochemical measurements were performed on an electrochemical workstation (CS2350H) in a three-electrode system with 1 M NaCl aqueous electrolyte, a platinum (Pt) counter electrode and an Ag/AgCl reference electrode. Cyclic voltammetry and gravimetric charge-discharge measurements were carried out in the potential range of 0 to 1 V.
The specific capacitances were calculated from the discharge curves by using the following equation:
??=
??×??
????
(1)
where i is the discharge current density (A g-1), t is the discharge time (s), and ΔV is the voltage window (V).
Desalination analysis
Each CDI apparatus comprises a pair of identical electrodes (2×2 cm2), and a pair of ion-exchange membranes, and then attached to peristaltic pump, power source, and tank, constituting a continuous recycling system for subsequent batch-mode desalination experiments. In each experiment, the real-time saline concentration variation was monitored and measured at the outlet of the CDI apparatus by using an ion conductivity meter. The volume of the saline solution was fixed to 20 mL, the flow rate was 20 mL min-1, and the operating voltage was 1.2 V.
The salt adsorption capacity (Γ, mg g-1) and mean salt adsorption rate (MSAR, mg g-1 min-1) at t min were calculated as follows:
??=
(
??
0
?
??
??
)×??
??
(2)
????????=
??
??
(3)
where C0 and Ct represent the concentrations of NaCl at the initial stage and t min, respectively (mg L-1); V represents the volume of the NaCl solution (L); and m represents the total mass of the electrode materials (g).
/
Fig. S1. Schematic illustration for CDI process.
/
Fig. S2. (a) Low-resolution and (b) high-resolution FESEM images of PAN/Zn(Ac)2 composite fibers.
/
Fig. S3. (a) Low-resolution and (b) high-resolution FESEM images of PAN@ZIF-8 fibers.
/
Fig. S4. (a) Low-resolution and (b) high-resolution FESEM images of fractured ZIF-8 tubes.
/
Fig. S5. XRD patterns of ZIF-8 tubes and simulated ZIF-8.
/
Fig. S6. XRD pattern of NCTs.
/
Fig. S7. High-resolution N 1s XPS spectrum of NCTs.
/
Fig. S8. N2 adsorption/desorption isotherms of NCTs, NCPs, and ACs.
/
Fig. S9. TEM image of NCTs after long-term cycling desalination tests.
Table S1. Coefficients of Langmuir model fitting.
Isotherm
Model equation
Parameter
Value
Langmuir
??=
??
??
??
??
??
1+
??
??
??
qm
56.9
KL
0.166
r2
0.994
Table S2. Performance comparisons of NCTs and other carbon architectures.
Carbon Family
Sample
SSA (m2 g-1)
Voltage (V)
SAC (mg g-1)
Ref.
ACs
P-60
1260
1.5
5.28
[2]
Filtrasorb 400
964
1.0
13.03
[3]
AC-1-2.0
2105
1.0
9.72
[4]
C5A85K4
3649
1.2
22.2
[5]
HPC
609
1.2
10.27
[6]
CCS
2680
1.2
16.1
[7]
3DHCA
2061
1.2
17.83
[8]
PCNSs
2853
1.1
15.6
[9]
NPC
1036.2
1.2
15.5
[10]
SBB-CO2-30
1019
1.2
28.9
[11]
CTS-AC
2727
1.2
14.12
[12]
Carbon Spheres
PCS1000
1321
1.6
5.81
[13]
NPCSs1000
1640
1.2
14.91
[14]
N-PHCS
512
1.4
12.95
[15]
hCSs-800
1529
1.2
15.8
[16]
PCSs-800
485.6
1.2
18.5
[17]
CHS-1
809.91
1.6
18.88
[18]
N-HMCSs
1099
1.6
16.6
[19]
Mesostructured Carbons
OMC
844
1.2
0.68
[20]
NMCs
842.3
1.2
20.63
[21]
NOMC
459.32
1.6
26.2
[22]
OMC-O
1481
1.2
9.8
[23]
o-OMCs-1000
780.3
1.2
14.58
[24]
OMC-S
1491
1.2
0.93
[25]
ACk2
1968
1.6
11.7
[26]
Graphene
N-HMCS/HGH
337.7
1.4
37.2
[27]
GSSNA-11
664
1.2
22.09
[28]
CSG
711.9
1.5
9.60
[29]
GE/MC
685.2
2.0
0.73
[30]
MC
1700
1.2
3.5
[31]
Activated graphene
3513
2.0
11.86
[32]
G@MC-O-thin
1270
1.2
24.3
[33]
AGE-30
898
1.2
6.26
[34]
RGO/AC
779
1.2
2.94
[35]
GTAC
426.56
1.2
10.94
[36]
GS
356.0
1.2
14.9
[37]
mGE
474.0
1.2
14.2
[38]
HGF
124
2.0
29.6
[39]
Carbon Nanotubes
EPD-CNTs
82
1.2
2.33
[40]
CNTs/CNFs
211
1.2
1.61
[41]
MWCNT/PVA
208
1.2
13.07
[42]
nit-CNTs
200.9
1.2
17.18
[43]
OMC/CNT
620.9
1.2
0.63
[44]
MOF-derived Carbons
ZFCarbon
2060
1.2
8.1
[45]
e-CNF-PCP
1450.6
1.2
12.56
[46]
PC-900
1563.09
1.2
9.39
[47]
PC-900
1911
1.2
10.90
[48]
NC-800
798
1.2
8.52
[49]
PCP1200
1187.8
1.2
13.86
[50]
ZIF-8@PZS-C
929
1.2
22.19
[51]
A-NCP
2474
1.2
24.4
[52]
CNFH
696.2
1.4
43.3
[53]
aG10P
1067
1.2
36.1
[54]
NCTs
1323.5
1.2
56.9
This work
References
[1] M. Sokó?, J. Grobelny, E. Turska, Investigation of structural changes of polyacrylonitrile on swelling. Wide-angle X-ray scattering study, Polymer 28 (1987) 843-846.
[2] Y.J. Kim, J.H. Choi, Enhanced desalination efficiency in capacitive deionization with an ion-selective membrane, Sep. Purif. Technol. 71 (2010) 70-75.
[3] C.H. Hou, C.Y. Huang, A comparative study of electrosorption selectivity of ions by activated carbon electrodes in capacitive deionization, Desalination 314 (2013) 124-129.
[4] C.L. Yeh, H.C. Hsi, K.C. Li, C.H. Hou, Improve 内容过长，仅展示头部和尾部部分文字预览，全文请查看图片预览。 ganic frameworks for improved CDI performance, Chem. Eng. J. 382 (2019) 122996.
[53] M. Ding, K.K. Bannuru, Y. Wang, L. Guo, A. Baji, H.Y. Yang, Free standing electrodes derived from metal-organic frameworks/nanofibers hybrids for membrane capacitive deionization, Adv. Mater. Technol. 3 (2018) ***.
[54] Z.Y. Leong, G. Lu, H.Y. Yang, Three-dimensional graphene oxide and polyvinyl alcohol composites as structured activated carbons for capacitive desalination, Desalination 451 (2019) 172-181.
[文章尾部最后500字内容到此结束,中间部分内容请查看底下的图片预览]
以上为《Experimental section》的无排版文字预览，完整格式请下载
下载前请仔细阅读上面文字预览以及下方图片预览。图片预览是什么样的，下载的文档就是什么样的。
图片预览
