Photocatalytic cleavage of C-F bond in pentafluorobenzoic acid with titanium dioxide-P25

Article abstract of DOI:10.1016/j.jfluchem.2006.06.009

The photocatalytic C-F bond cleavage in pentafluorobenzoic acid (PFBA) with TiO₂-P25 using UV-C light has been investigated under different conditions. Complete cleavage of C-F is observed with TiO₂-P25 under UV-C light irradiation.

Full text of DOI:10.1016/j.jfluchem.2006.06.009

Journal of Fluorine Chemistry 127 (2006) 1204–1210
www.elsevier.com/locate/fluor
Photocatalytic cleavage of C–F bond in pentafluorobenzoic
acid with titanium dioxide-P25
1
L. Ravichandran, K. Selvam, M. Muruganandham , M. Swaminathan
*
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
Received 17 March 2006; received in revised form 7 June 2006; accepted 9 June 2006
Available online 15 June 2006
Abstract
The photocatalytic C–F bond cleavage in pentafluorobenzoic acid (PFBA) with TiO -P25 using UV-C light has been investigated under
2
ꢀ
ꢀ
2ꢀ
different conditions. Complete cleavage of C–F is observed with TiO -P25 under UV-C light irradiation. Oxidants such as IO
2
4
, BrO
ꢀ
3
, S
ꢁ BrO > ClO3 . C–F
2
ꢀ
O ,
8
ꢀ
ꢀ
2ꢀ
H O and ClO ions enhance the defluoridation of PFBA. The order of their activities is IO4 > H O > S O
2
2
2
3
2
2
8
3
cleavage is also influenced by the addition of inorganic anions and metal ions. The defluoridation intermediates were analyzed by GC-MS technique.
2006 Elsevier B.V. All rights reserved.
#
2
Keywords: Pentafluorobenzoic acid; TiO -P25; Defluoridation; Photocatalysis
ꢀ
1
1
. Introduction
Fluorinated chemicals are prominent xenobiotics used in
C–F bond (485.3 kJ mol ) in pentafluoropropionic acid with
a water soluble heteropoly acid [H PW O ] photocatalyst
[10].
3
12 40
pharmaceutical, agricultural and other industrial applications
due to their thermal stability and enhanced lipophilicity [1,2].
Perfluorinated acids (mainly carboxylic and sulfonic acids) and
their derivatives are widely used as emulsifying agents in
polymer synthesis, fire retardants, carpet cleaners, paper
coatings, surface treatment agents in photolithography, etc.
A review of microbial cleavage of the C–F bond had been
published [2]. In the recent years, advanced oxidation processes
have been developed for the degradation of pollutants in
wastewater. In our laboratory we had reported the degradation
of dyes by various advanced oxidation processes [11–15].
Heterogeneous photocatalysis using semiconductors such as
TiO2 or ZnO is an attractive advanced oxidation process
[16,17].
[
3–5]. The use of perfluorinated acids has steadily increased
and some of them have recently been detected in environmental
waters and in animals [6–9]. These perfluorinated acids are
quite stable and they have no known natural decomposition
In the present work, we have investigated the photocatalytic
defluoridation of pentafluorobenzoic acid (PFBA) with TiO2-
P25 using UV-C light and analysed the effect of oxidants,
inorganic ions and metal ions on this process.
[4,5]. Hence the detoxification of these perfluorinated acids
under mild conditions becomes essential.
The cleavage of C–F bond of fluorinated compound results
in the formation of fluoride ions, which can easily combine
2. Results and discussion
2
+
with Ca to form environmentally harmless CaF . In addition,
2
CaF is a raw material for the production of hydrofluoric acid,
2
2.1. Primary defluoridation
which is a starting material for many fluorinated compounds.
Hori et al. reported the photocatalytic cleavage of the strong
Initially the experiments were carried out to test the
photodefluoridation with 400 ppm of PFBA under different
conditions and the results are shown in Fig. 1. PFBA undergoes
self photolysis with 254 and 365 nm light to certain extent. The
*
Corresponding author. Tel.: +91 4144 220572; fax: +91 4144 220572.
E-mail address: chemsam@yahoo.com (M. Swaminathan).
ꢀ
1
theoretical amount of fluoride in the compound is 180 mg L
.
1
After 180 min of 365 nm irradiation of PFBA with TiO2,
Present address: Department of Environmental Engineering and Science,
Feng Chia University, Taichung, Taiwan.
69.2 mg of fluoride ion was released while the catalyst in dark
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.06.009

L. Ravichandran et al. / Journal of Fluorine Chemistry 127 (2006) 1204–1210
1205
Fig. 2. Effect of pH on adsorption of pentafluorobenzoic acid:
ꢀ1
[
PFBA] = 100 ppm; catalyst suspended = 100 mg; airflow rate = 8.1 mL s .
2
.2. Effect of pH on adsorption and deflouridation
Fig. 1. Photodegradability of pentafluorobenzoic acid (PFBA): [PFBA] = 400
ꢀ1
ppm; catalyst suspended = 175 mg; airflow rate = 8.1 mL s ; pH 7; I254 nm
.54 ꢃ 10ꢀ5 einstein L
=
ꢀ1 ꢀ1
; I365 nm = 2.08 ꢃ 10ꢀ6 einstein L
ꢀ1 ꢀ1
The effect of pH on the adsorption of PFBA is shown in
Fig. 2. The adsorption of PFBA on TiO surface increases from
2
s
s .
2
pH 1 to 3 and then decreases. The point of zero charge (PZC) of
TiO -P25 is 6.8 [21]. When the solution pH is lower than PZC,
does not facilitate the deflouridation. On irradiation by 254 nm
light with TiO , 180 mg of fluoride ion was released in 90 min.
2
the TiO surface is positively charged. The ionization of PFBA
2
2
Complete defluoridation is achieved in 90 min with 254 nm
light. The results indicate that PFBA can be effectively
degraded in presence of photocatalyst on irradiation with UV-C
light. The C–F bond is one of the strongest covalent bonds
known. The fluorine atom is larger than the hydrogen atom, so it
shields the carbon from attack more effectively than hydrogen
in water is also influenced by pH as it contains the COOH
group. The pK value of PFBA is 1.75. When pH is higher than
a
+
the pKa of PFBA, it ionizes to give solvated H and
pentafluorobenzoate anion. At pH 3 the electrostatic attraction
between positively charged TiO2 and negatively charged
pentafluorobenzoate ion leads to strong adsorption of PFBA
ꢀ1
atoms. In fluoro carbons C–C bond energy is 334.7 kJ mol
,
on the TiO surface. The effect of pH on the photocatalytic
2
ꢀ
1
whereas C–F bond energy is 485.3 kJ mol [18]. Hence more
energy is required to break C–F bond than C–C bond. The
release of fluoride ion and carbon dioxide from PFBA on
defluoridation of PFBA was investigated for pH range of 1–10.
The results are presented in Fig. 3. After 60 min of irradiation
93.6, 140, 126.6, 126.4 and 128.4 mg of fluoride ions were
released at pH 1, 3, 5, 7 and 10, respectively in presence of
irradiation with 254 nm light in presence of TiO indicates that
2
PFBA can be effectively mineralised into CO and fluoride ions
2
TiO . pH 3 is found to be more favorable for defluoridation. The
2
(Eq. (1)). The formation of intermediates before complete
mineralisation is discussed in Section 2.7:
TiO2
C6F5COOH þ 5O2ðairÞ þ 2H2Oꢀ! 7CO2 þ 5HF
(1)
hn
This mineralisation is caused mainly by hydroxy radical, a
strong oxidizing species produced by TiO on irradiation with
2
2
54 nm light (Eqs. (2)–(7)) [19,20]:
ꢀ
þ hVBþ
ꢂ
TiO þ hn ! e
(2)
(3)
2
CB
hVB þ OHðadsÞꢀ ! OH
þ
þ
ꢂ
þ
hVB þ H2OðadsÞ ! OH þ H
eCB þ O2 ! O2ꢂꢀ
(4)
(5)
(6)
ꢀ
ꢂꢀ
ꢂ
ꢀ
2
O2 þ 2H2O ! 2 OH þ 2OH þ O2
Since the defluoridation was effective with 254 nm light, the
effects of pH and oxidants on this process had been carried out
using 254 nm light to find out the optimum conditions.
Fig. 3. Effect of pH on photodefluoridation of pentafluorobenzoic acid:
ꢀ1
[
PFBA] = 400 ppm; catalyst suspended = 175 mg; airflow rate = 8.1 mL s
;
254 nm = 2.54 ꢃ 10ꢀ einstein L
5
ꢀ1 ꢀ1
s .
I

1206
L. Ravichandran et al. / Journal of Fluorine Chemistry 127 (2006) 1204–1210
Table 1
effect of pH on the photocatalytic reaction is generally
attributed to change in the surface charge property of TiO2,
which depends on pH of the solution.
Effect of oxidants on photodefluoridation of PFBA
ꢀ ꢀ1
[F ] mg L
Oxidants
Since the adsorption is maximum at pH 3 more defluorida-
tion occurs at this pH. This reveals that photocatalytic reaction
is more facilitated at the catalyst surface. At pH above 3, the
change in adsorption is not much and also the defluoridation
decreases slightly. But at pH 1 the defluoridation is less. At high
Without TiO
2
With TiO
2
KIO
4
119.6
90.1
80.2
86.0
18.6
180.0
158.3
144.0
146.4
112.5
2 2
H O
KBrO
3
(NH ) S O
4
2
2
8
acidic conditions TiO particle agglomeration may take place
2
KClO
3
and this may reduce the photo adsorption [12].
[
2 2
PFBA] = 400 ppm; catalyst suspended = 175 mg; oxidants = 125 mg; H O =
ꢀ1
0
1
.01 M; irradiation time = 30 min; airflow rate = 8.1 mL s ; I254 nm = 2.54 ꢃ
ꢀ5 ꢀ1 ꢀ1
0
einstein L
s .
2
.3. Effect of substrate concentration
The effect of initial PFBA concentration on the defluorida-
tion rate was investigated by varying the initial concentration
electron hole recombination. Inorganic oxidants such as KIO
,
4
ꢀ
1
from 100 mg to 600 mg L
at constant pH and catalyst
(NH , KClO , KBrO and H can compensate for the
2
4
)
S
2
O
8
3
3
O
2 2
loading. The results are shown in Fig. 4. From the results, it is
clear that on increase of the initial concentration increases the
time required to defluoridate the PFBA. After 60 min
irradiation, 100% fluoride ion was released when the
lack of oxygen caused either by oxygen consumption or slow
oxygen mass transfer. These oxidants on irradiation generate
other oxidizing species to accelerate the defluoridation and
hence they play a dual role in this process. This dual role is also
confirmed by the significant defluoridation caused by oxidants
alone on irradiation. The Table 1 shows the release of fluorides
ꢀ
1
concentration was 100 mg L whereas only 52.8% fluoride
ꢀ1
ion was released at the concentration of 600 mg L . The
increase of PFBA concentration decreases the defluoridation
ꢀ1
ions (mg L ) by both oxidants and the oxidants with TiO .
2
ꢂ
ꢂ
ꢀ
ꢀ
2ꢀ
ꢀ
and ClO exhibit
3
rate. The rate of defluoridation relates the amount of OH
radical formation on catalyst surface and the probability of OH
In the dark IO
4
, BrO
3
, H
2
O
2
, S
2
O
8
negligible activity. Irradiation of UV light (lmax = 254 nm)
with PFBA and oxidants alone enhances the defluoridation rate.
radical reacting with PFBA molecules. For all initial PFBA
concentrations, the catalyst concentration (175 mg) and UV
2
ꢀ
ꢀ
After 30 min of irradiation time with S
ꢀ
O
(0.01 M) and ClO
(125 mg), BrO
ꢀ
2
8
3
ꢀ
5
ꢀ1 ꢀ1
power (2.54 ꢃ 10 einstein L
s
) are same. Since the
(125 mg), IO
4
(125 mg), H
2
O
2
3
(125 mg)
released 86, 80.2, 119.6, 90.1 and 18.60 mg of fluoride ion
generation of hydroxyl radical remains constant the probability
of PFBA molecule to react with hydroxyl radical decreases.
2
ꢀ
respectively. The defluoridation efficiencies of UV/S ,
ꢀ
UV/BrO3 processes are nearly equal to the efficiency of UV/
O
2
8
ꢀ
2
.4. Effect of inorganic oxidants
TiO process is more efficient
ꢀ
than UV/TiO process whereas UV/ClO is least efficient one.
2
process (88.2 mg). But UV/IO
4
2
3
ꢀ
Usually molecular oxygen is used as a electron acceptor in
an heterogeneous photocatalytic reaction for the prevention of
The higher degree of defluoridation in UV/IO
due to formation of highly reactive intermediates, such as IO
4
process is
ꢂ
,
OH, IO , O (Eqs. (9)–(11)) [22]. Therefore defluoridation
3
ꢂ
ꢂ
ꢂ
4
occurs by free radical pathways and is more efficient at high
intensity of light:
IO4 þ hn ! IO3ꢂ þ Oꢂꢀ
ꢂꢀ
(9)
(10)
(11)
ꢂꢀ
þ Hþ ! OH
ꢂ
O
ꢂOH þ IO4ꢀ ! OH þ IO4
H O on irradiation with 254 nm light produces OH radicals:
2
ꢀ
ꢂ
ꢂ
2
hn
ꢂ
H2O2ꢀ! OH
S2O8 can generate sulfate radical anion (SO ) photolyti-
(12)
2
ꢀ
ꢂꢀ
4
ꢂꢀ
cally in aqueous solution. SO
ꢂ
then reacts with H O to
2
4
produce OH radicals:
hn
2
ꢀ
ꢂꢀ
ꢂ
S2O8 ꢀ! 2SO4
(13)
SO4 þ H2O ! OH þ SO4 þ Hþ
itself is a strong oxidant (E = 2.6 eV) and can directly
react with PFBA. Addition of these oxidants to UV/TiO2
ꢂꢀ
2ꢀ
(14)
Fig. 4. Effect of various substrate concentration of pentafluorobenzoic acid:
SO4ꢂꢀ
0
ꢀ1
catalyst suspended = 175 mg; airflow rate = 8.1 mL s ; pH 7; I254 nm
=
.54 ꢃ 10ꢀ einstein L
5
ꢀ1 ꢀ1
s .
2

L. Ravichandran et al. / Journal of Fluorine Chemistry 127 (2006) 1204–1210
1207
ꢂ
process enhances the defluoridation rate strongly when com-
pared with UV/oxidant system as seen in Table 1. 146.4, 144,
ions is due to the reaction of these ions with holes and OH
(Eqs. (18)–(22)).
1
TiO /S O , UV/TiO /BrO , UV/TiO /IO , UV/TiO2/
80, 160.3 and 71.2 mg of fluoride ions were released in UV/
ꢀ
2
ꢀ
2
ꢀ
ꢀ
SO4 þ hVBþ ! SO42ꢀ
(18)
(19)
(20)
(21)
(22)
2
2
8
2
3
2
4
ꢀ
H O and UV/TiO /ClO after 30 min of irradiation with
2
SO4 þ OH ! SO4 þ OHꢀ
2þ
ꢂ
ꢂꢀ
2
2
3
2
54 nm light.
The enhancement in UV/TiO process by the addition of
ꢀ
ꢂ
ꢂꢀ
2
HCO3 þ OH ! CO
þ H O
3
2
oxidant is due to increased charge separation. This is done by
accepting the conduction band electron (Eqs. (15)–(17)).
2
ꢀ
ꢂ
ꢂꢀ
CO3 þ OH ! OH þ CO
3
S2O8 þ eCBꢀ ! SO4ꢂꢀ þ SO42ꢀ
2
ꢀ
(15)
(16)
(17)
2
ꢀ
ꢂ
ꢂꢀ
þ OHꢀ
HPO4 þ OH ! HPO
4
BrO3 þ 6eCBꢀ þ 6Hþ ! Br þ 3H O
ꢀ
ꢀ
2
2
.6. Effect of metal ions
ClO3 þ 6eCBꢀ þ 6Hþ ! ClO2ꢀ þ H O2
ꢀ
2
The presence of dissolved metal ions is common in
ꢀ
4
The order of reactivity is:UV/TiO /IO > UV/TiO2/
2
industrial wastewater and they can sensibly affect the rate
and efficiency of photocatalytic reactions. The effect of added
metal ions on photocatalytic defluoridation is shown in Fig. 5.
2
ꢀ
ꢀ
H O > UV/TiO /S O
2
ꢁ UV/TiO /BrO > UV/TiO2/
2
2
2
8
2
3
ꢀ
ClO3
.
UV/TiO /oxidant processes are more efficient than the UV/
2+
2
Except Cu , other metal ions have not influenced the
defluoridation rate initially for 30 min. For 90 min of
irradiation, 180, 177.8, 170, 156.2 and 114 mg of fluoride
ꢀ
TiO process. The lower efficiency at UV/TiO /ClO process
2
2
3
ꢀ
is due to poor light absorption capacity of ClO3 ion.
2
+
2+
2+
ions were released by the addition of Cu , Mg , Fe , Fe
3+
2
.5. Effect of inorganic ions
+
and Ag ions respectively. The order of reactivity of these ions
2
+
2+
2+
3+
+
is Cu > Mg > Fe > Fe > Ag . The enhancement of
defluoridation by addition of these ions is due to their
acceptance of conduction band electron, which promote the
charge separation.
Wastewater contains not only organic contaminants but also
considerable amounts of inorganic anions such as nitrate,
sulfate, phosphate and carbonate, etc. Hence it is useful to study
the influence of these ions on this photocatalytic process. Two
possible ways of the inorganic ions influencing the photo-
catalytic reaction are (i) changing the ionic strength of reaction
medium and (ii) inhibition of catalytic activity of the
photocatalyst. The effects of added inorganic ions on the
defluoridation of PFBA are shown in Table 2.
nþ
ꢀ
ðnꢀ1Þ
;
M
þ eCB ! M
2þ
2þ
3þ
2þ
þ
M ¼ Cu ; Fe ; Fe ; Mg ; Ag
2
+
3+
2+
The process with Fe , Fe and Mg showed a steady
effect in the defluoridation of PFBA and at the end of 120 min,
2
100% defluoridation was achieved. For Cu ion 100%
+
The results clearly show that the addition of inorganic anions
on the photocatalytic process decreases the defluoridation rate.
After 30 min of irradiation time 86.2, 74.6, 73.4, 71.2 and
+
defluoridation was obtained in 90 min. Ag addition had
retardation effect on the defluoridation due to deposition of
7
1
2.0 mg of fluoride ions were released by the addition of
00 mg of NaNO , Na SO , NaHCO , Na CO and K HPO ,
3
2
4
3
2
3
2
4
respectively. The order of inhibition of these ions is
ꢀ
2
ꢀ
2ꢀ
ꢀ
HPO4 > CO3 > HCO > SO4 ꢁ NO . It has been
3
3
2
ꢀ
reported that HPO
has higher inhibiting capacity than
HCO3 in photocatalytic degradation of organic compounds
4
ꢀ
ꢀ
with TiO2 [23]. Addition of NO3 did not affect of the
defluoridation rate appreciably. The inhibition effect of these
Table 2
Effect of anions on photodefluoridation of PFBA
Anions
% of defluoridation
TiO
NaNO
Na SO
NaHCO
Na CO
HPO
2
88.2
84.2
75.8
46.0
52.4
63.4
3
2
4
3
2
3
K
2
4
[
PFBA] = 400 ppm; catalyst suspended = 175 mg; anions = 125 mg; irradiation
254 nm = 2.54 ꢃ 10ꢀ5 einstein
Fig. 5. Effect of addition of metal ions of pentafluorobenzoic acid:
ꢀ1
ꢀ1
time = 30 min; airflow rate = 8.1 mL s
ꢀ1
;
I
[PFBA] = 400 ppm; catalyst suspended = 175 mg; airflow rate = 8.1 mL s
;
ꢀ1
metal ions = 10 mg; I254 nm = 2.54 ꢃ 10ꢀ5 einstein L
ꢀ1 ꢀ1
L
s
.
s .

1208
L. Ravichandran et al. / Journal of Fluorine Chemistry 127 (2006) 1204–1210
Scheme 1.
silver on the TiO surface. The deposited silver blocks the
2
pentafluoropropionic acid [10] and trifluoroacetic acid [26].
The attack of OH radical may produce pentafluorophenol (2),
which produce tetrafluoroquinone (3). In general, the attack of
PFBA by OH radical replaces fluorine atoms producing more
hydroxyl functional groups and the intermediates are ultimately
mineralised to carbon dioxide and fluoride ions [27].
active sites of TiO and consequently decreases the defluorida-
2
tion rate. Similar inhibition effect was observed in the
photocatalytic and photoelectrolytic degradation of HCOOH
on Ag deposited TiO film [24]. The maximum enhancement by
2
2
+
+
Cu may be due to its regeneration from Cu by holes
(
Eq. (24)) [25].
3
. Conclusions
þ
h
þ
2þ
Cu ꢀ!Cu
.7. Photodefluoridation pathway
Irradiation of air equilibrated aqueous suspension containing
(24)
The results of this study show that the strong C–F bond can
ꢀ
be cleaved by photolysis with the oxidants such as IO ,
ꢀ
BrO3 , S O , H O and ClO and TiO -P25 using 254 nm
4
2
2ꢀ
ꢀ
2
8
2
2
3
2
light. Except for KClO , the addition of other oxidants
3
significantly enhance the UV/TiO process. Inorganic anions
2
photocatalyst TiO -P25 and pentafluorobenzoic acid being
2
inhibits the defluoridation and the order of their inhibition is
ꢀ
examined under UV 254 nm light leads to conversion of
fluorinated derivatives into detectable intermediate aromatic
products and eventually to the evolution of stoichiometry
quantities of fluoride and carbon dioxide.
2
ꢀ
2ꢀ
ꢀ
ꢀ
HPO
> CO3 > HCO3 > SO4 ꢁ NO . Addition of
4
3
2
Cu increases the defluoridation rate, whereas Ag has a
+
+
2
+
retardation effect. The maximum enhancement by Cu is
assumed to be due to its regeneration by holes. Based on GC–
MS analysis pentafluorobenzene, pentafluorophenol and tetra-
fluoroquinone have been identified as intermediates of
An attempt was made to identify the intermediate products
formed in the photocatalytic defluoridation of the pentafluor-
obenzoic acid through GC–MS analysis of the solution
obtained after 30 and 60 min irradiation. We get three
predominant peaks for retention times of 2.185, 19.45 and
photocatalytic defluoridation by TiO -P25.
2
4
. Experimental
2
0.294. These three products were identified as pentafluor-
obenzene (1), pentafluorophenol (2) and tetrafluoroquinone (3)
based on their molecular ion and mass spectrometric
fragmentation peaks and are given below.
4
.1. Materials
Pentafluorobenzoic acid (99% purity) was obtained from
Aldrich Chemical Co. and was used without further
Compound
Mass spectrum (m/z)
purification. TiO -P25 (80% anatase, 20% rutile) BET
2
2
ꢀ1
1
2
3
168, 149, 137, 118, 99, 84, 75, 61, 51, 47, 31
surface area 50 m g , mean particle size 30 nm was
supplied by Degussa. AnalaR grade reagents (NH ) S O ,
KIO , KBrO , KClO , H O (30% w/w), NaCl, NaNO3,
181, 163, 149, 135, 121, 112, 104, 92, 77, 56, 41, 29
184, 168, 156, 142, 128, 112, 100, 84, 70, 58, 44, 41
4
2 2 8
4
3
3
2 2
From Scheme 1, first band cleaved in the one electron
oxidised PFBA is the C–C bond between C F and COOH. This
Na SO , NaHCO and K HPO were used as received. All
2 4 3 2 4
experiments were carried out using deionised and double
distilled water. The pH of the solution was adjusted with
H SO or NaOH as required.
6
5
ꢂ
cleavage produces C6F5 and CO . The photo-kolbe mechan-
2
ism was proposed for a similar cleavage reported in
2
4

L. Ravichandran et al. / Journal of Fluorine Chemistry 127 (2006) 1204–1210
1209
milliliters of water and 20 mL of ionic strength adjustable
buffer (TISAB) were added to the solution. This solution was
stirred for 5 min and fluoride ion concentration was
measured. The pH of the solutions were measured using
Metrohm 744 pH meter.
4.4. GC–MS analysis
For identification of intermediate products of PFBA
photocatalytic defluoridation, the sample taken after 30, 60
and 90 min was analysed. The sample for analysis was prepared
by the following method. The centrifuge obtained after
irradiation was extracted five times with HPLC grade
dichloromethane. The extract was dried over anhydrous
sodium sulfate to remove the water present in the solution.
The solvent was removed by evaporation under reduced
pressure. The final residual mass was taken for GC–MS
analysis.
The GC (Perkin-Elmer Auto System) is equipped with an
MSHP 5 capillary column (30 mm ꢃ 250 mm) and 1micron
film thickness (Perkin-Elmer elite series) and interfaced
directly to the MS (Perkin-Elmer turbo mass spectrophot-
ometer). The GC column was operated at a temperature of
Fig. 6. Photoreactor.
4
.2. Photoreactor
The photocatalytic defluoridation has been carried out with a
5
0 8C for 2 min then increased to 280 8C at the rate of
0 8C min . The other experimental conditions are: EI impact
ꢀ1
1
Heber immersion type photoreactor model HIPR-LP 6/8/116
whose schematic diagram is shown in Fig. 6. This model
consisted of a double walled immersion well made of a quartz
ionization 70 eV, helium as carrier gas, injection temperature
260 8C, source temperature 180 8C.
3
reactorof175 cm capacity. A small diameterinlettubeextended
References
down the annular space to ensure flow of the coolant from bottom
of well upwards to outlet. In the center of cylindrical reactor, the
lamps used for light source was placed inside the quartz tube. For
the experiments, lamps with different wavelength emission were
used. One was 16 W low pressure mercury with emission mainly
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