First observation of tetranitro iron (II) phthalocyanine catalyzed oxidation of phenolic pollutant assisted with 4-aminoantipyrine using dioxygen as oxidant

Article abstract of DOI:10.1016/j.molcata.2011.06.002

A novel system for catalytic oxidation of phenol and chlorophenol pollutant in water by tetranitro iron (II) phthalocyanine (TNFe(II)Pc) is reported for the first time. In this system, several phenolic substrates (phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol) could be easily oxidized by naturally dissolved oxygen in the presence of TNFe(II)Pc, and then rapidly combined with 4-aminoantipyrine to generate the pink dye. The catalytic oxidation process and resulting products were monitored by UV-Vis spectroscopy and high performance liquid chromatography-mass spectrometer (HPLC-MS) technique. Control experiments demonstrated that the generation of superoxide anion radical was crucial for the dye formation, and a possible mechanism involved a successive single electron transfer from phenolic substrates to O₂ via the axis of TNFe(II)Pc was proposed. Potentially, this system is promising for application in chromogenic identification of phenolic pollutant. Crown Copyright

Full text of DOI:10.1016/j.molcata.2011.06.002

Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
First observation of tetranitro iron (II) phthalocyanine catalyzed oxidation of
phenolic pollutant assisted with 4-aminoantipyrine using dioxygen as oxidant
Dapeng Li, Yilin Tong, Jun Huang∗, Liyun Ding, Yunming Zhong, Dan Zeng, Ping Yan
National Engineering Laboratory for Fiber Optic Sensing Technology, Wuhan University of Technology, Wuhan 430070, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel system for catalytic oxidation of phenol and chlorophenol pollutant in water by tetranitro iron
(II) phthalocyanine (TNFe(II)Pc) is reported for the first time. In this system, several phenolic substrates
(phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol) could be easily oxidized by naturally
dissolved oxygen in the presence of TNFe(II)Pc, and then rapidly combined with 4-aminoantipyrine to
generate the pink dye. The catalytic oxidation process and resulting products were monitored by UV–Vis
spectroscopy and high performance liquid chromatography–mass spectrometer (HPLC–MS) technique.
Control experiments demonstrated that the generation of superoxide anion radical was crucial for the dye
formation, and a possible mechanism involved a successive single electron transfer from phenolic sub-
strates to O2 via the axis of TNFe(II)Pc was proposed. Potentially, this system is promising for application
in chromogenic identification of phenolic pollutant.
Received 21 April 2011
Received in revised form 1 June 2011
Accepted 2 June 2011
Available online 13 June 2011
Keywords:
Tetranitro iron (II) phthalocyanine
Phenol
Chlorophenol
Catalysis
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
Oxidation
1. Introduction
catalytic oxidation system was utilized with 4-AAP for detecting
phenols and their derivatives [12]. However, for the instability
Phenol and chlorophenol compounds such as 2-chlorophenol
(2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (DCP) are
common environmental pollutants produced from fungicide, her-
bicide, pesticide and paper manufacturing industry [1–5]. Most of
these contaminants exist in industrial wastewater and even drink-
ing water, which are extremely dangerous to the environment for
their toxicity and resistance to natural degradation [6,7]. Nowa-
days, various methods have been explored on the detection of
phenolic pollutants in water or soil. Among them, catalytic oxida-
tion of phenol assisted with 4-aminoantipyrine (4-AAP) to generate
the pink antipyrilquinoneimine dye is the representative technique
for chromogenic measurement of phenols and their derivatives
[8–14]. In general, the catalytic efficiency is closely related to the
properties of catalyst and oxidant [15]. The structure of catalyst
and its working conditions would have significant influence on the
precision and sensibility of the measurement. Moreover, from the
environmental and economic point of view, molecular oxygen is a
preferred oxidant favorable for the current development of green
chemistry.
and easy inactivation of these natural enzymes in some rigorous
conditions, biomimetic catalysts, such as porphyrin and phthalo-
cyanine metal complexes that could mimic active sites of natural
enzymes and reproduce their catalytic activity, have become the
attractive candidates to replace some natural enzymes [15]. Early
investigations had proved that iron and manganese porphyrins and
their derivatives exhibited excellent biomimetic oxidation activity
of natural cytochrome P-450 system [16,17]. Recently, Rezzano’s
group reported that mono and bimetallic polymeric porphyrin
(polyCoCuPP and polyFeCuPP) on Au support could catalyze H2O2
oxidation of phenols assisted with 4-AAP in aqueous solution [13].
In spite of these advancements in their catalytic performance, the
application of metal porphyrins still suffers from their high cost.
Therefore, some cheap and readily available phthalocyanine metal
complex, especially, the functionalized metalphthalocyanine with
tetra-substituted sulfonic groups had received much attention
[7]. Meunier’s group firstly reported that water-soluble tetra-
sulfophthalocyanine Fe(III) or Mn complexes (FePcTS, MnPcTS)
could efficiently catalyze H2O2 oxidation of polychlorophenols
and degrade them into various products with different oxidation
degrees [6,7,18,19]. Later, the catalytic co-oxidation of phenols with
4-AAP performed by different metal tetrasulfophthalocyanines in
the presence of H2O2 was observed by Santhanalakshmi [14]. How-
ever, compared with metal porphyrin, the deficient development
of metal phthalocyanine catalysis is far from satisfying [15]. More-
over, additional oxidant was necessary (such as corrosive H2O2,
KHSO5, or toxic tBuOOH (tert-butyl hydroperoxide)) in most of the
In nature, microorganisms such as Phanerochaete chrysosporium
can catalyze oxidation of lignin (natural polyphenolic compounds)
by means of a manganese peroxidase and H2O2. This natural
∗
Corresponding author. Tel.: +86 27 87651851; fax: +86 27 87665287.
E-mail addresses: lidapengabc@yahoo.com.cn (D. Li), hjun@whut.edu.cn
(J. Huang).
1381-1169/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.06.002

D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
109
documented oxidation reaction catalyzed by MPcTS. Therefore, the
exploration of novel phthalocyanine metal system with green oxi-
dant for catalytic oxidation of phenolic pollutant remains an active
topic. Furthermore, understanding the details of reaction mecha-
nism is important for the development of phthalocyanine catalysis.
In this work we show that tetranitro iron (II) phthalocyanine
(TNFe(II)Pc) could efficiently catalyze oxidation of phenols and
chlorophenols (2-CP, 4-CP and DCP) assisted with 4-AAP in aqueous
medium. The dissolved molecular oxygen as oxidant was suffi-
cient for the catalytic oxidation reaction. Although TNFe(II)Pc is
not a novel phthalocyanine metal complex [20], we found for the
first time that TNFe(II)Pc was an efficient heterogeneous catalyst
for oxidation of phenolic substrates in aqueous medium. Control
•−
experiments demonstrated that superoxide anion radical (O2
)
was the active species involved in catalytic oxidation process and
the resulting pink dye was considered to be generated from radical
coupling. Moreover, we analyzed the resultant dye and proposed a
catalytic mechanism for the chromogenic reaction.
2. Experimental
2.1. Instrumental
UV–Vis spectra were recorded on a Shimadzu UV-2450 spec-
trophotometer. IR spectra were recorded on a Thermo Nicolet
Nexus FT-IR spectrometer with the standard KBr pellet method.
Elemental analyses were performed on a Elementar Vario EL III Ele-
mental Analyzer. 1H NMR spectra were recorded on a Varian NMR
System 600 MHz Spectrometer. Nitrogen adsorption–desorption
isotherms were collected on a Micromeritics Gemini V2380 sur-
face area and porosity analyzer at 77 K after the sample had
been degassed in the flow of N2 at 200 ◦C. Catalytic reaction was
monitored by high performance liquid chromatography (HPLC,
Dalian Elite P230 series). The reaction products were identified
by HPLC–MS. HPLC analyses were carried out using Agilent 1100
instrument equipped with a SGE ␮ C18 column (150 mm × 4.6 mm).
The mobile phase consisted of acetonitrile–methanol–water mix-
ture (4:1:5, v/v) with a flow rate of 1.0 mL/min. The column
temperature was set at 25 ◦C. Mass spectrometry (MS) analyses
were performed using Applied Biosystems API2000 instrument.
Electrospray ionization (ESI) source of MS was set at the positive
ionization mode.
Scheme 1. Synthesis of 4-nitrophthalimide and tetranitro iron (II) phthalocyanine
complex.
2.3.1. 4-Nitrophthalimide
The synthesis of 4-nitrophthalimide was adopted according
to Young’s method [21]. Yield: 66%. FT-IR (KBr pellets) 3328(s),
3077(w), 3043(w), 1791(m), 1705(s), 1622(m), 1546(s), 1349(s),
1307(s), 1110(s), 1075(s), 720(s) cm−1 1H NMR (600 MHz, d6-
;
DMSO): ı 8.07 (d, 1H, J = 2.4 Hz, Ph-H), 8.43 (s, 1H, Ph-H), 8.61 (d,
1H, J = 2.4 Hz, Ph-H), 11.84 (s, 1H, NH).
2.2. Materials and reagents
Phenol, 2-chlorophenol, 4-chlorophenol, 2, 4-dichlorophenol
and 4-aminoantipyrine are of analytical reagent grade and
purchased from Sinopharm Chemical Reagent Co., Ltd. The
raw materials used for the synthesis of tetranitro iron (II)
phthalocyanine are phthalimide, urea, ammonium molybdate (VI)
tetrahydrate, iron (II) sulfate heptahydrate, concentrated H2SO4
and fuming HNO3. All these reagents are analytical pure and
used without further purification. Boric acid–borax buffer solu-
tion (0.2 M, pH 7.4 and 9.0) and Na2HPO4–KH2PO4 buffer solution
(0.2 M, pH 5.5) were used as catalytic reaction medium. Deionized
water was used in all the experiments. Methanol and acetonitrile
(HPLC grade, Sinopharm Chemical Reagent Co., Ltd.) was used as
elution solution for HPLC study.
2.3.2. Tetranitro iron (II) phthalocyanine
TNFe(II)Pc was prepared by a reported method [22], but with
some modifications. 3.84 g 4-Nitrophthalimide, 1.4 g FeSO4·7H2O,
0.05 g ammonium molybdate, and excess 12 g urea were added
into a 100 mL three-necked flask containing 20 mL nitrobenzene
under magnetic stirring. Then the mixture was heated slowly to
130 ◦C to completely dissolve all the organic solid under the protec-
tion of N2, and subsequently the temperature was raised to reflux
for 3 h. Thereafter, the mixture was cooled to room temperature
and dark blue product was obtained. The product solution was
poured into ethanol, stirred and collected by vacuum filtration to
afford the crude product. Then the crude product was added into
400 mL of 1 M HCl solution, boiled for about 30 min and then fil-
tered, washed with deionized water for several times, followed by
the further treatment with 400 mL of 1 M NaOH solution by the sim-
ilar treatment mentioned above. Finally, the TNFe(II)Pc solid was
washed with ethanol by Soxhlet extraction to remove the residual
nitrobenzene, then the dark blue solid was collected and dried at
100 ◦C overnight in vacuum. Yield: 56%. FT-IR (KBr pellets) 733(m),
760(m), 808(w), 852(w), 1097(m), 1142(m), 1254(w), 1335(s),
1517(s), 1614(w) cm−1. UV–Vis (DMSO) ꢀmax = 284, 682 nm. Anal.
2.3. Preparation and characterization of TNFe(II)Pc
There are two steps in our synthesis of TNFe(II)Pc catalyst: (I)
the nitration reaction of phthalimide to 4-nitrophthalimide; (II)
the formation of TNFe(II)Pc via the reaction of 4-nitrophthalimide,
urea, FeSO4 and ammonium molybdate. The synthetic procedure
for TNFe(II)Pc is described in Scheme 1.

110
D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
Scheme 2. Catalytic oxidation of 2-CP, DCP, 4-CP and phenol to corresponding dyes by O2 in the presence of TNFe(II)Pc catalyst and 4-AAP. The chloro-substituted
antipyrilquinoneimine is one possible isomer.
Calcd. for C32
51.62; H, 1.89; N, 22.67.
H
12FeN12O8: C, 51.36; H, 1.62; N, 22.46. Found: C,
complex [6,19,23,24], herein four types of phenolic substrate
were chosen to investigate the catalytic activity of TNFe(II)Pc in
aqueous solution. For this purpose, the absorbance increased at
510 nm during catalytic oxidation was followed due to the for-
mation of (chloro-substituted) antipyrilquinoneimine dyes [14].
Fig. 1 shows the UV–Vis absorption spectra for chromogenic reac-
tion of 2-CP, DCP, 4-CP and phenol with 4-AAP in the presence
of TNFe(II)Pc at regular intervals, respectively (Fig. 1a–d). Obvi-
ously, the intensities of characteristic peak of dye at 510 nm
gradually increased along with the gradually decreased intensi-
ties of substrates and 4-AAP in the range of 200–300 nm within
90 min, suggesting the continuous transformation of phenols or
chlorophenols with 4-AAP to dyes in the presence of TNFe(II)Pc,
while the auto-oxidation reaction without TNFe(II)Pc was neg-
ligible (see Fig. S1 in supplementary data). The UV–Vis spectra
of these four systems exhibited no obvious change after 90 min,
which meant the completion of catalytic reaction. Compared with
the absorption intensities of dye at 510 nm, the catalytic reactiv-
ity trend for different phenolic substrates was in the following
order: 2-CP > DCP > phenol > 4-CP. The above results indicated that
the oxidation reaction of all these four kinds of phenolic substrate
with 4-AAP were successfully catalyzed by TNFe(II)Pc, which was
promising for chromogenic identification as well as environmental
decontamination.
2.4. Catalytic oxidation experiment
The typical catalytic oxidation of phenolic substrates with 4-AAP
by TNFe(II)Pc catalyst was performed under the following experi-
mental procedure (see Scheme 2). A 40 mL of deionized water, 5 mL
of 4-AAP aqueous solution (1 × 10−3 mol/L), and 5 mL of substrate
solution (phenol or chlorophenol, 1 × 10−3 mol/L) were added into
a 50 mL glass beaker. The catalytic reaction was initiated by addi-
tion of 0.015 mmol of TNFe(II)Pc powder into the above solution,
followed by the ultrasonic treatment for 1 min and continuous
magnetic stirring at 20 ◦C. The suspension was filtered with a
membrane (0.22 ␮m) to remove TNFe(II)Pc particles at the regular
intervals. The filtrate was detected with UV-Vis spectrophotometer
and HPLC for process monitoring. (HPLC, Dalian Elite P230 series fit-
ted with a C 18 reverse column (200 mm × 4.6 mm) and connected
to a variable wavelength UV–Vis detector (set at ꢀ = 220 nm). The
mobile phase was composed of acetonitrile–methanol–water mix-
ture (4:1:5, v/v), with a flow rate of 1.0 mL/min. The sample inject
volume was 50 ␮L.) The phenolic substrates and 4-AAP were iden-
tified by spiking using standards via comparison of retention times
in HPLC trace.
The recycling experiments of TNFe(II)Pc were performed
under the typical conditions. After each catalytic experiment, the
TNFe(II)Pc powder was separated by centrifugation and washed
with deionized water until the pink color was disappeared. Then
the resulting TNFe(II)Pc powder was added into boiled water for
60 min to make the catalyst free from the possible residual organic
compounds. Finally, the TNFe(II)Pc powder was collected and dried
at 100 ◦C in vacuum for the next catalytic experiment.
3.2. Effect of pH on catalytic oxidation of 2-CP and DCP
For the obvious chromogenic indication in 2-CP and DCP system,
we chose them to further study the activity of TNFe(II)Pc under dif-
ferent pH conditions. It is known that the dominating species of
chlorophenol varied with pH of aqueous solution due to the exis-
tence of equilibrium between undissociated chlorophenols (below
their pKa values) and corresponding chlorophenolates (above their
pKa values), thus the catalytic oxidation of chlorophenols assisted
with 4-AAP was considered to be closely related to pH [25]. Since
the pKa for the deprotonation of 2-CP and DCP OH-group are 8.48
and 7.85, respectively, therefore, boric acid–borax buffer solution
(BBS, pH 7.4, 9.0) and Na2HPO4–KH2PO4 buffer solution (PBS, pH
5.5) as well as deionized water were used to investigate the effect
of pH on catalytic reaction.
3. Results and discussion
3.1. Chromogenic reaction of phenols and chlorophenols
catalyzed by TNFe(II)Pc
Previous reports had documented that oxidation of various
phenolic compounds could be catalyzed by phthalocyanine metal

D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
111
Fig. 1. Stacked UV–Vis absorption spectra of catalytic oxidation of various phenolic substrates with 4-AAP at regular intervals. The initial concentration of phenolic substrates
and 4-AAP was 1.0 × 10−4 M, and the dosage of TNFe(II)Pc powder was 11.3 mg.
Fig. 2 records the dye formation process in 2-CP and DCP system
at different pH on the plot of UV–Vis absorption (ꢀ = 510 nm) versus
reaction time. For 2-CP system (Fig. 2a), the catalytic reaction was
completed after 3 h at pH 7.4 and 5.5, while the catalytic reaction
still proceeded after 5 h at pH 9.0. Compared with the catalytic oxi-
dation of 2-CP in deionized water, more dyes were formed at pH
7.4 although longer reaction time (≥180 min) was required. How-
ever, the concentrations of dye at pH 5.5 and pH 9.0 after 300 min
were still lower than that in deionized water at 60 min. For com-
parison, the reaction trend of DCP at selected pH was similar to
that of 2-CP system except for the small difference at pH 5.5 and
9.0. Although the chromogenic reaction was faster in deionized
water at the early stage, the maximal conversion of chlorophenol
to dye could be achieved in buffer solution at pH 7.4, both of which
reflected the significant contribution of the molecular chlorophe-
nol rather than chlorophenolate. The detailed reasons for different
rates of dye formation and their final yields would be discussed
later.
3.3. Determination of active oxygen species
Because the solution was exposed to air and there were no other
oxidants employed in it, dissolved O2 was considered to be the
possible oxidant for the chlorophenol oxidation. To investigate the
effect of dissolved O2 on the catalytic oxidation, the reaction was
firstly carried out with continuous nitrogen-bubbling to eliminate
Fig. 2. Dye formation process in 2-CP and DCP system under different pH conditions in the presence of TNFe(II)Pc. (ꢀabs = 510 nm) (ꢀ) in deionized water; (᭹) in boric
acid–borax buffer solution, 0.2 mol/L, pH 7.4; (ꢁ) in boric acid–borax buffer solution, 0.2 mol/L, pH 9.0; (ꢂ) in Na2HPO4–KH2PO4 buffer solution, 0.2 mol/L, pH 5.5. The initial
concentration of 2-CP and DCP is 1.0 × 10−4 M and the dosage of TNFe(II)Pc is 11.3 mg.

112
D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
3.4. Catalytic process monitoring and products identification by
HPLC–MS
The produced pink dyes in 2-CP/DCP system had good stability
and low volatility, thus HPLC–MS was considered to be a suitable
analytical approach for the determination of the possible reaction
products. We firstly identified 2-CP, DCP and 4-AAP by compar-
ison of their retention time with that of standards (ꢀ = 220 nm),
while the determination of the resulting dye products was real-
ized by tuning the wavelength of UV–Vis detector to 510 nm and
only one chromatogram peak was found (see Fig S2 in supplemen-
tary data), and the corresponding retention time (9.84 min) was
same to that of P1 and P3 in Fig. 4a and c. Obviously, the con-
centration of dye increased fast in the initial 60 min, which was
consistent with the corresponding UV–Vis results (Fig. 1a and b).
Besides the dyes, one byproduct and at least three intermediate
products were observed in 2-CP/DCP system, for the concentrations
of P2 and P4 (byproducts) gradually increased in the whole catalytic
reaction, while the contents of the intermediate products increased
at the first 15 min or so and then decreased. Fig. 4b and d indicates
that the 4-AAP disappeared completely after 90 min of reaction,
while 2-CP/DCP remained less than 50%. For this reason, excess 4-
AAP was needed for complete removal of chlorophenols. On the
basis of HPLC analyses (conversion of chlorophenols and selectiv-
ity of dye in total oxidation products), we evaluate the final yields
of dye by using normalization method, 38% for 2-CP system and
25% for DCP system (yield = conversion × selectivity/100). Further-
more, we chose the reaction solution obtained at 30 min to further
identify all the products by ESI–MS, unfortunately, the obvious
molecular ion signal of the unknown byproducts and intermedi-
ate products could not be obtained for the difficulty of ionization
(see Fig. S3 in supplementary data), only the dye products of P1
and P3 were identified according to the corresponding m/z values
(m/z = 328.0 and 329.9) in Fig. S3b and e of Supplementary data.
Both of the resultant (M+H)+ signals of P1/P3 resulted from the exis-
tence of isotopic element of chlorine (35Cl and 37Cl) in dye molecule.
Moreover, the retention times of these unknown products were
also different from those of commercial 1,4-benzoquinone and
2-chloro-benzoquinone (Fig. S2 in supplementary data). There-
fore, in 2-CP and DCP system, the same dye of chloro-substituted
antipyrilquinoneimine was determined.
Fig. 3. Dye formation process in 2-CP (a) and DCP (b) system versus reaction time
under different conditions. (ꢀabs = 510 nm) (a, ꢀ) Typical catalytic reaction; (b, ꢂ)
iso-propanol 0.01 M; (c, ꢃ) in the dark; (d, ꢄ) K2Cr2O7 0.1 mM; (e, ꢁ) NaN3 0.01 M;
(f, ᭹) N2 bubbled; (g, ꢅ) K2Cr2O7 1 mM. The inset picture shows the color deepening
in 2-CP system of typical catalytic reaction (a, ꢀ).
3.5. Proposed mechanism for catalytic oxidation of phenolic
substrates
the dissolved oxygen in solution. Time courses for the dye forma-
tion process in 2-CP (a) and DCP (b) system is shown in Fig. 3.
Under anaerobic conditions (curve f), the dye formation rate was
largely prohibited compared to the typical catalysis (curve a), sug-
gesting that oxygen was crucial for the oxidation of chlorophenol.
Generally, O2 molecule can trap electron to produce active oxy-
Compared with the dye formation rate in the presence and
absence of TNFe(II)Pc (Fig. 1 versus Fig. S1 in supplementary data),
it is clear that TNFe(II)Pc catalyst is crucial for the fast formation
of dye, and the oxidation catalysis was considered to be closely
•−
related to the generation of O2 species. Therefore, understand-
gen radicals (O2 and OH•) that could initiate oxidation reaction
ing the catalytic mechanism as well as the effect of active reaction
species is of guidance for practical application of phenolic oxida-
tion chemistry. Until now, the well-developed catalysis system was
the water-soluble MPcTS (M = Fe(III), Mn) with H2O2 as oxidant,
which was used as bleaching catalysts for oxidative degradation of
chlorophenol [15]. Especially, for oxidation of 2,4,6-trichlorophenol
(TCP) catalyzed by FePcTS–H2O2 system [6,7], Meunier and Sorokin
proposed three different models of active iron-centered oxidizing
species including (X)PcSFev = O, (L)PcSFeIV = O and (L)PcSFeIII-OOH,
which depended on the nature of oxidant, the axial ligand and the
macrocycle (L = neutral ligand and X = anionic ligand). The proper
active iron–oxygen species could further abstract electrons from
TCP and achieve the initial oxidation of TCP to DCQ (2,6-dichloro-
1,4-benzoquinone).
•−
[26]. To further confirm the existence of specific reactive species,
several scavengers (iso-propanol for OH•, K2Cr2O7 and NaN3 for
O2•−) were employed. The addition of iso-propanol exhibited little
influence on the dye generation compared with the typical catal-
ysis (curve b versus curve a), suggesting that OH• unlikely takes
part in the catalytic oxidation reaction. However, when K2Cr2O7 or
NaN3 was added into the reaction solution, the generation of dye
was significantly inhibited (curves d, g and e). Especially, when the
concentration of K2Cr2O7 was increased to 0.001 M, the catalytic
reaction could hardly proceed (curve g). Therefore, the generation
of O2•− was crucial for the chromogenic reaction and a O2•− medi-
ated mechanism of TNFe(II)Pc catalysis is confirmed. Moreover, the
typical catalysis could also proceed efficiently in the dark (curve a
versus curve c), which indicates that sunlight is not essential for
chlorophenol oxidation in the presence of TNFe(II)Pc catalyst.
From the point of Meunier and Sorokin, the proposed active
iron–oxygen species was responsible for TCP oxidation, which

D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
113
Fig. 4. HPLC chromatogram of 2-CP (a) and DCP (c) system obtained after regular intervals of catalytic reaction. P1 and P3 were dye products in 2-CP and DCP system,
respectively, byproducts (p2 and P4) and several intermediate products were observed after 5 min of catalytic reaction. (b) and (d) Record the percentage data of substrate,
4-AAP and resulting dyes during catalytic reaction according to the corresponding peak areas of HPLC chromatogram.
also illuminated the donor–acceptor interactions existed in sub-
strate, catalyst and oxidant [7,27,28]. Herein, in the TNFe(II)PC
catalytic reaction system, the interactions among substrate, cat-
alyst and O2 should result in the coordination structures of
chlorophenol–TNFe(II)Pc-O2. Then the successive single electron
transfer from hydroxyl oxygen (donor) of chlorophenol to O2
(acceptor) via the axis of TNFe(II)Pc macrocycle realized the fast
oxidation of chlorophenol (see Scheme 3, a case of 2-CP), which
the low initial concentration of chlorophenol molecules at pH 7.4
buffer solution and the possibility of greater number of collisions
between radical reactants and phosphate ions in PBS contributed
to the low rate of dye formation, while the durative transforma-
tion of chlorophenolate to chlorophenol molecule was responsible
for the high yield of dye in the end. Therefore, pH is an important
parameter that determines the dominating species of chlorophenol
and influences the rate of dye formation in aqueous solution (see
Scheme 4, a case of 2-CP).
We also found that the initial rate of dye formation in 2-CP sys-
tem at higher temperature (40 ◦C) was enhanced, while less dyes
were formed at the end of catalytic oxidation (Fig. 5a). The pseudo-
first-order model was introduced to illuminate the reaction kinetic
of dye formation at different temperature [14]. It is found that the
reaction rate constant reached 110.83 × 10−3 min−1 at 40 ◦C, much
higher than that (53.38 × 10−3 min−1) of RT reaction (Fig. 5b). The
fast formation of dye at 40 ◦C was considered to be closely related to
the fast collision of radical reactants according to Arrhenius princi-
ple, while the acceleration of side reactions could be responsible for
the final low yield of dye. Furthermore, detailed HPLC results con-
firmed the low conversion of 2-CP and low selectivity of dye, which
contributed to the less amount of dye formed at 40 ◦C compared to
that at RT (see Table 1).
was responsible for the succeeding generation of p-quinoid rad-
•−
ical (possible chlorophenol oxidation product) and O2
(step I).
•−
In turn, the resulting O2 could further oxidize the amino group
of 4-AAP to produce the Antipyrine-NH• (radical form of 4-AAP)
(step II). Immediately, p-quinoid radical and Antipyrine-NH• could
combine to generate the final products of pink chloro-substituted
antipyrilquinoneimine dye (step III). This is the possible mechanism
•−
for the generation of O2 and dye formation via radical coupling.
For the phenol or 4-CP oxidation, the resulting pink dye should be
antipyrilquinoneimine (see Scheme 2).
Furthermore, following the discussion of the effect of pH on
catalysis, we found that lower pH was not suitable for•d−ye formation
(see Fig. 2). It is possible that the combination of O2 with excess
H+ would be accelerated at lower pH, which would decrease the
quantity of Antipyrine-NH• radicals (see Scheme 3, step II) and thus
resulted in the decreased yield of dye. In addition, the initial rate of
dye formation in deionized water was the highest in contrast to that
in buffer solution (see Fig. 2), which meant the fast generation of
abundant radicals of p-quinoid and Antipyrine-NH•, the interaction
of these active radicals might result in some byproduct or interme-
diate products (see Fig. 4), and thus the final dye with relatively
small quantity in deionized water could be explained. In contrast,
3.6. Recycling experiments of TNFe(II)Pc catalyst
The stability and reusage of catalyst is important for its practi-
cal application. To examine the catalytic effectiveness of the reused
catalyst, a three-cycle experiment for catalytic oxidation of 2-CP
was performed under typical conditions. It was interesting to find

114
D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
Scheme 3. Proposed mechanism for O2 oxidation of 2-CP and dye generation via radical coupling in the presence of TNFe(II)Pc.
the catalyst only exhibited slight deactivation after three cycles of
repeated experiments for 2-CP system (Fig. 6). According to the
general explanation, the possible permanent adsorption of some
species on catalyst surface could result in the deactivation of some
active sites, which should be responsible for the reduction of cata-
lyst’s activity [29]. Moreover, the loss of catalyst should be another
possible reason for the gradual reduction of activity, for it is difficult
to collect total TNFe(II)Pc powder after several cycling experiments.
Table 1
The conversion, selectivity, yield and rate constant calculated for 2-CP system and textural parameters of TNFe(II)Pc catalyst.
b
System
Conversion/selectivity
Yield (%)a
k × 10−3 (min−1
)
BET surface area (m2/g)c
9.60
Pore diameter (nm)c
36.46
2-CP (RT)
58/66
50/60
38
30
53.38
110.83
2-CP (40 ◦C)
a
Yield calculated on the basis of HPLC analysis (yield = conversion × selectivity/100).
The rate constants of dye formation at RT and 40 ◦C.
The data of TNFe(II)Pc catalyst.
b
c

D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
115
Scheme 4. The ionization equilibrium between molecular chlorophenols and
chlorophenolates, and their transformation to dyes during catalytic oxidation reac-
tion.
Fig. 6. Recycling runs in the catalytic oxidation of 2-CP in the presence of TNFe(II)Pc
catalyst under same conditions. The UV–Vis absorption was recorded at the wave-
length of 510 nm.
4. Conclusion
In summary, this study demonstrates that heterogeneous
TNFe(II)Pc could efficiently catalyze O2 oxidation of several pheno-
lic substrates assisted with 4-AAP for fast chromogenic indication
of phenolic pollutants. Control experiments testified that the gen-
•−
eration of O2
is the key step for initial chlorophenol oxidation
and subsequent formation of dyes. This low-cost catalytic system
consists of an easily accessible TNFe(II)Pc catalyst, clean and green
oxidant of oxygen from air, and common 4-AAP, which provides
an economical route for detective analysis and removal of harm-
ful phenolic pollutants. It is notable that the oxidation of 2-CP and
DCP would cause the consumption of O2 and result in a quantita-
tive relationship between the concentration of chlorophenol and
O2, which would provide the basis for the development of fiber
optic sensor based on oxygen sensing and biomimetic catalysis.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (Nos. 60877048 and 50802069), and
the Excellent Doctor Cultivation Project of Wuhan University of
Technology (2010-YB-05). We thank professor Yu Cao (College of
Chemistry, Huazhong Normal University) for the help of chemi-
cal characterization and measurement. We thank Dr. Xiaodi Du
(Department of Chemistry, Wuhan University of Technology) for
the help of HPLC measurement and analyses.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.06.002.
References
[1] M.Y. Ghaly, G. Härtel, R. Mayer, R. Haseneder, Waste Manage. 21 (2001) 41–47.
[2] C. Guillard, J. Disdier, C. Monnet, J. Dussaud, S. Malato, J. Blanco, M.I. Maldonado,
J.M. Herrmann, Appl. Catal. B 46 (2003) 319–332.
[3] K. Abburi, J. Hazard. Mater. 105 (2003) 143–156.
[4] X.M. Zhang, J. Wiegel, Appl. Environ. Microbiol. 56 (1990) 1119–1127.
[5] F.A. Banat, B. Al-Bashir, S. Al-Asheh, O. Hayajneh, Environ. Pollut. 107 (2000)
391–398.
[6] A. Sorokin, J.L. Séris, B. Meunier, Science 268 (1995) 1163–1166.
[7] B. Meunier, A. Sorokin, Acc. Chem. Res. 30 (1997) 470–476.
[8] J. Santhanalakshmi, J. Kasthuri, N. Rajendiran, J. Mol. Catal. A: Chem. 265 (2007)
283–291.
Fig. 5. (a) Comparison of dye formation process in 2-CP system at room tempera-
ture (RT) and 40 ◦C. (ꢀabs = 510 nm) (b) Kinetic plots of dye formation at RT and 40 ◦
C
on the basis of UV–Vis spectra. The correlation coefficients (R2) for fit of experi-
mental data are 0.9540 and 0.9893, respectively. (The kinetic parameter Ln S, where
S = Abs /(Abs∞ − Abst) are calculated from absorbance versus reaction time).
∞

116
D. Li et al. / Journal of Molecular Catalysis A: Chemical 345 (2011) 108–116
[9] S. Sgalla, G. Fabrizi, S. Cacchi, A. Macone, A. Bonamore, A. Boffi, J. Mol. Catal. B:
[21] J.G. Young, W. Onyebuagu, J. Org. Chem. 55 (1990) 2155–2159.
[22] B.N. Achar, G.M. Fohlen, J.A. Parker, J. Keshavayya, Polyhedron
1463–1467.
[23] M. Hassanein, M. Abdo, S. Gerges, S. EI-Khalafy, J. Mol. Catal. A: Chem. 287
(2008) 53–56.
[24] S.V. Sirotin, A.Y. Tolbin, I.F. Moskovskaya, S.S. Abramchuk, L.G. Tomilova, B.V.
Romanovsky, J. Mol. Catal. A: Chem. 319 (2010) 39–45.
[25] B. Agboola, K.I. Ozoemena, T. Nyokong, J. Mol. Catal. A: Chem. 227 (2005)
209–216.
[26] W.J. Li, D.Z. Li, J.J. Xian, W. Chen, Y. Hu, Y. Shao, X.Z. Fu, J. Phys. Chem. C 114
(2010) 21482–21492.
Enzym. 44 (2007) 144–148.
[10] M. Mifune, T. Tai, A. Iwado, H. Akizawa, J. Oda, N. Motohashi, Y. Saito, Talanta
54 (2001) 319–327.
6 (1987)
[11] B. Tang, G.Y. Zhang, Y. Liu, F. Han, Anal. Chim. Acta 459 (2002) 83–91.
[12] H. Biava, S. Signorella, Polyhedron 29 (2010) 1001–1006.
[13] R.R. Carballo, V. Campodall’ Orto, I.N. Rezzano, J. Mol. Catal. A: Chem. 280 (2008)
156–163.
[14] N. Rajendiran, J. Santhanalakshmi, J. Mol. Catal. A: Chem. 245 (2006) 185–191.
[15] A.B. Sorokin, E.V. Kudrik, Catal. Today 159 (2011) 37–46.
[16] A.M.d’A.R. Gonsalves, M.M. Pereira, J. Mol. Catal. A: Chem. 113 (1996) 209–221.
[17] B. Meunier, J. Bernadou, Top. Catal. 21 (2002) 47–54.
[18] A. Sorokin, B. Meunier, Chem. Eur. J. 2 (1996) 1308–1317.
[19] A. Sorokin, S.D. Suzzoni-Dezard, D. Poullain, J.P. Noël, B. Meunier, J. Am. Chem.
Soc. 118 (1996) 7410–7411.
[27] A.B. Sorokin, S. Mangematin, C. Pergral, J. Mol. Catal. A: Chem. 182–183 (2002)
267–281.
[28] O.V. Zalomaeva, I.D. Ivanchikova, O.A. Kholdeeva, A.B. Sorokin, New J. Chem. 33
(2009) 1031–1037.
[20] A. Shaabani, N. Safari, A. Bazgir, F. Bahadoran, N. Sharifi, P.R. Jamaat, Synth.
Commun. 33 (2003) 1717–1725.
[29] M.A. Zanjanchi, A. Ebrahimian, M. Arvand, J. Hazard. Mater. 175 (2010)
992–1000.