C A R B O N 4 8 ( 2 0 1 0 ) 2 8 1 2 – 2 8 1 4

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An activation-free method for preparing microporous carbonby the pyrolysis of poly(vinylidene fluoride)

Bin Xu a,*, Shanshan Hou b, Mo Chu b, Gaoping Cao a, Yusheng Yang a

a Research Institute of Chemical Defense, Beijing 100191, Chinab School of Chemical and Environmental Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China

A R T I C L E I N F O

Article history:

Received 21 February 2010

Accepted 8 April 2010

Available online 14 April 2010

0008-6223/$ - see front matter � 2010 Elsevidoi:10.1016/j.carbon.2010.04.011

* Corresponding author: Fax: +86 10 66705840E-mail address: xubinn@sohu.com (B. Xu

A B S T R A C T

A simple method for the preparation of microporous carbon was presented by pyrolyzing

poly(vinylidene fluoride) (PVDF) at high temperature under N2 atmosphere without activa-

tion or any other additional processes. The yield of PVDF-derived carbon is 35.0%. Its spe-

cific surface area reaches 1012 m2 g with a pore volume of 0.41 cm3 g�1. The carbon is

microporous with unimodal pore size distribution at 0.55 nm.

� 2010 Elsevier Ltd. All rights reserved.

Porous carbon is widely used as gas-phase and liquid-

phase adsorbent, catalyst support, electrode material for sup-

ercapacitors, etc. The porous carbon is usually produced by

carbonization of the precursor under an inert atmosphere to

eliminate non-carbon element, followed by activation of the

char with activation agent (H2O, CO2, KOH, etc.) to create por-

ous structure. The developed porosity in the carbon is formed

predominately in activation period, which is also the most

complex procedure in the overall manufacture process. Some

novel activation-free methods have been proposed such as

polymer blend carbonization [1], organic gel carbonization

[2], and template carbonization [3]. However, the additional

processes such as preparation of polymer blend, time-con-

suming supercritical drying, the introduction of the precursor

in the channel of the template and the removal of the tem-

plate are necessary, making the preparation process even

more complicated than the conventional methods. Poly(vinyl-

idene chloride) (PVDC) carbonization is certainly a simple

activation-free method for porous carbon preparation and

has attracted great attention [4–8]. In our previous reports

[7,8], porous carbon with a surface area of 1230 m2 g�1 is sim-

ply prepared by PVDC carbonation without activation. In this

letter, for the first time to our knowledge, we used homoge-

neous poly(vinylidene fluoride) (PVDF) which has similar

structure to PVDC as precursor, and obtained microporous

carbon with a surface area of 1000 m2 g�1 by applying a sim-

er Ltd. All rights reserved

.).

ple carbonization step at high temperature without activation

or any other additional processes.

The homogeneous PVDF (Kynar 761, Arkema Co.) was used

as precursor. Fig. 1 shows the thermogravimetric analysis of

PVDF. The dramatic weight loss of PVDF occurred at 400–

600 �C with the sharp peak at 462 �C. PVDF powder were put

into a tubular furnace, heated to the carbonization tempera-

ture (600–900 �C) at 10 �C/min and kept for 1 h under the pro-

tection of nitrogen (99.999%) to accomplish pyrolysis. After

cooled to room temperature, the PVDF-derived porous car-

bons were obtained.

As shown in Fig. 2, the nitrogen adsorption/desorption iso-

therms (Micrometritics ASAP 2020M) of the PVDF-derived car-

bons prepared at different temperatures are very similar.

According to the classification of IUPAC, all of the samples ex-

hibit a typical type I isotherms. The knee of the isotherms ap-

pears at very low relative pressure (p/p0 < 0.05) and the

plateau is fairly flat, indicating highly microporous carbons.

Table 1 lists the yield and properties of PVDF-derived

carbons. The yield of the carbons is about 35.0%, similar to

the theory carbon content in PVDF (37.5%). The Brunauer–

Emmett–Teller (BET) surface area and pore volume of the

PVDF-derived carbons are independent of the carbonization

temperature, and reach 1012 m2 g�1 and 0.41 cm3 g�1, respec-

tively. The surface area of the PVDF-derived carbons is

comparable to that of commercial, physically-activated

.

Fig. 3 – Pore size distribution of PVDF-derived carbons.

Fig. 2 – Nitrogen adsorption/desorption isotherms of PVDF-

derived carbons.

Fig. 1 – Thermogravimetric curve for PVDF in flow of

nitrogen gas.

Table 1 – Yield and properties of PVDF-derived carbons.

Samples Carbonizationtemp. (�C)

Yield(%)

SBET

(m2 g�1)Vt

(cm3 g�1)

PVFC600 600 35.6 963 0.399PVFC700 700 35.7 1001 0.403PVFC800 800 35.1 1012 0.410PVFC900 900 34.7 976 0.398

C A R B O N 4 8 ( 2 0 1 0 ) 2 8 1 2 – 2 8 1 4 2813

porous carbon, in spite of the elimination of the activation

step. This indicates that PVDF pyrolysis is a simple method

for the preparation of porous carbon. For the best of our

knowledge, this method has not been reported so far.

Fig. 3 presents the pore size distribution of the PVDF-de-

rived carbons calculated by density function theory. The car-

bons prepared at different carbonization temperatures

exhibit similar pore size distribution curves. All of the car-

bons are highly microporous with unimodal pore size distri-

bution at 0.55 nm.

Compared with our previous work on PVDC-derived car-

bon [7,8], PVDF shows similar properties to PVDC as carbon

precursor due to their similar structure. Porous carbons can

be obtained from both PVDF and PVDC by carbonization at

high temperature under an inert atmosphere. However, there

are some differences between them. The decomposition tem-

perature of PVDF (462 �C) is much higher than that of PVDC

(246 �C), indicating a higher thermal stability. This is attrib-

uted to the stronger bond energy of C–F bond than C–Cl bond.

The pore formation mechanism is based on the complete re-

lease of HF or HCl from the carbon chain in PVDF or PVDC at

high temperature under inert atmosphere. As the molecular

size of HF is smaller than HCl, the surface area and pore vol-

ume of the PVDF-derived carbon (1012 m2 g�1, 0.41 cm3 g�1)

are a little smaller than PVDC-derived carbon (1226 m2 g�1,

0.48 cm3 g�1) [7]. However, the carbon content in PVDF is

higher than PVDC, resulting in a higher carbon yield of

PVDF-derived carbon (35.0%) than PVDC-derived carbon

(25.0%).

Acknowledgements

This work was funded by NSFC (50802112, 20633040) and 973

Program (2009CB220100) of China.

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