Environmental Engineering Reference
In-Depth Information
methods, respectively. The carbons formed on the surface of MgO particles are
microporous, rich in the pores with the width of approximately 1 nm. The size of
mesopores formed in the carbon is found to depend on the starting MgO precur-
sors, Mg acetate mixed with PVA in solution forming mesopores with the size of
approximately 10 nm, Mg citrate those with 5 nm, and Mg gluconate those with
2-4 nm. In the case of Mg acetate/PVA mixtures, the sizes of mesopores depend
strongly on mixing method mixing in powder (powder mixing) gives a broad dis-
tribution of pore size but solution mixing gives a relatively sharp distribution of
mesopores at around 10 nm. However, Mg citrate/PVA mixtures gave almost the
same size distribution of mesopores by mixing in either powder or solution. The
substrate MgO had an additional advantage that it could be easily dissolved out at
room temperature by a diluted solution of acid, even by 1 mol/L citric acid, so that
MgO was experimentally proved to be recycled. The preparation of mesoporous
carbons using MgO template and their applications were reviewed. Porous car-
bons containing both micropores and mesopores were also prepared by using Ni
hydroxide template. Aqueous suspension of Ni (OH)
2
, which was prepared from
Ni(NO
3
)
2
and NaOH, was mixed with ethanol solution of phenolic resin and then
carbonized at 600°C after drying. By dissolving inorganic species, formed during
the process (NiO and Na
2
CO
3
), porous carbon was isolated. The carbon obtained
had S
BET
of 970 m
2
/g, total pore volume of 0.69 mL/g, and micropore volume of
0.3 mL/g, in which the predominant micropore and mesopore sizes were approxi-
mately 0.8 nm and 15 nm, respectively [26, 27].
1.1.10.3 DEFLUORINATION OF PTFE
Porous carbons were reported to be prepared through defluorination of poly tet-
rafluoroethylene (PTFE) with alkali amalgamates. The detailed studies were re-
ported for the preparation of porous carbons from PTFE by using different alkali
metals. PTFE film was pressed with lithium metal foil under 4 MPa in Ar atmo-
sphere for 48 h to defluorinate PTFE. After excess lithium metals were washed
out with methanol, the heat treatment at 700°C and washing by dilute HC1 were
carried out in order to eliminate finely dispersed LiF. Defluorination of PTFE was
also possible through heating a mixture of PTFE powders with alkali metals, Na,
K, and Rb, in vacuum at 200°C in a closed vessel. N
2
adsorption isotherms of
resultant carbons were found to depend strongly on alkali metal used. Defluori-
nation of PTFE with Na metal was found to give mesopore rich carbon and very
high S
BET
as 2225 m
2
/g. S
BET
of these carbons prepared using Na was found to in-
crease with heat treatment at a high temperature up to 1000°C, probably because
of gasification of carbon with surface oxygen functional groups. Deflourination
of PTFE using Na metal has an advantage, Na metal is much cheaper in price and
easier to handle, and so the process being simpler than using other alkali metals.
The irradiation of PTFE before carbonization is also preferable for getting
high surface area. Defluorination of PTFE was possible in 1, 2-di-methoxyethane
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