Synthesis of a simplified iron(III) tetraamido macrocyclic ligand (FeIII-TAML) catalyst and its catalytic activity for degradation of dye wastewater by H2O2

Article abstract of DOI:10.1080/00958972.2019.1710138

To reduce the cost of water treatment reagents, a simplified iron(III) tetraamido macrocyclic ligand compound (Fe^III-TAML) was synthesized with a total yield of 53.3%. For comparison, two second generation Fe^III-TAML catalysts were s

Full text of DOI:10.1080/00958972.2019.1710138

Journal of Coordination Chemistry
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Synthesis of a simplified iron(III) tetraamido
macrocyclic ligand (FeIII-TAML) catalyst and
its catalytic activity for degradation of dye
wastewater by H2O2
Shunlai Li, Liaoyuan Wang, Run Zhou, Cheng Zhou & Hongguang Du
To cite this article: Shunlai Li, Liaoyuan Wang, Run Zhou, Cheng Zhou & Hongguang Du (2020):
Synthesis of a simplified iron(III) tetraamido macrocyclic ligand (FeIII-TAML) catalyst and its catalytic
activity for degradation of dye wastewater by H2O2, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2019.1710138
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JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2019.1710138
Synthesis of a simplified iron(III) tetraamido macrocyclic
ligand (FeIII-TAML) catalyst and its catalytic activity for
degradation of dye wastewater by H2O2
Shunlai Li, Liaoyuan Wang, Run Zhou , Cheng Zhou and Hongguang Du
College of Chemistry, Beijing University of Chemical Technology, Beijing, China
ABSTRACT
ARTICLE HISTORY
Received 19 August 2019
Accepted 16 December 2019
To reduce the cost of water treatment reagents, a simplified
iron(III) tetraamido macrocyclic ligand compound (FeIII-TAML) was
synthesized with a total yield of 53.3%. For comparison, two
second generation FeIII-TAML catalysts were synthesized. The
synthetic route was optimized, and the total yield increased from
30.1% to 49.5%. The catalytic activity of the simplified catalyst for
degradation of dye wastewater by hydrogen peroxide was tested
and compared with that of the second generation FeIII-TAML
catalysts. The experimental results show that the simplified
KEYWORDS
Tetraamido macrocyclic
ligand; water treatment;
dye degradation; COD
catalyst has good catalytic activity. At 25ꢀC, pH ¼ 8, CFe-TAML
¼
50 mg/L, and Chydrogen
¼ 1.5 g/L, the decolorization and
peroxide
chemical oxygen demand removal of methylene blue, methyl
orange, neutral red, and Rhodamine B dye wastewater were
74.8%–96.1% and 46.9%–63.7%, respectively.
1. Introduction
Environmental pollution is becoming more serious. In industrial production, especially
in printing, dyeing, and textile fields, large amounts of wastewater are discharged
every year, containing toxic organic matter. If discharged directly without treatment, it
causes serious damage to the natural ecology [1]. Therefore, it is necessary to study
how to treat organic matter in industrial sewage more efficiently.
At present, the commonly used chemical treatment technologies of organic waste-
water are ozone oxidation, chlorine oxidation, and Fenton oxidation [2, 3]. Ultraviolet
irradiation is a common method in ozonation, which can destroy the unsaturated
CONTACT Hongguang Du
dhg@mail.buct.edu.cn
ß 2020 Informa UK Limited, trading as Taylor & Francis Group

2
S. LI ET AL.
Figure 1. The structures of three FeIII-TAML catalysts A, B, and C.
bonds of organic compounds and directly oxidize organic compounds to form small
molecules. The method has the characteristics of wide application range, high reaction
efficiency, and no secondary pollution. The disadvantages are that ozone is unstable
and its utilization rate is low; also producing ozone consumes a lot of electricity.
Sodium hypochlorite, chlorine, and chlorine dioxide are used in chlorine oxidation
processes [4]. These technologies have the advantages of low cost and simple operation.
However, its disadvantage is high toxicity, which may produce chlorinated organic
compounds with high toxicity and cause secondary pollution to the environment.
The Fenton reaction was discovered by British scientist Fenton. It mixed hydrogen
peroxide with iron salts to form a strong oxidation system, which can degrade organic
matter in wastewater. With the development of the Fenton method, optical Fenton
method [5–9] and electro Fenton method [10–14] appeared. The Fenton method can
degrade refractory substances with fast reaction speed and mild conditions. The disad-
vantage of the Fenton reaction is that it needs strong acidic conditions. Alkali should
be adjusted after the reaction to make iron ion precipitation flocculate, and acid-base
consumption is high. A large amount of ferric hydroxide sludge is produced after
the reaction.
With the development of water treatment research, enzymatic catalyst has gradually
developed. Enzyme-mimetic catalyst mainly simplifies the structure of natural enzymes,
extracts the key parts of natural enzymes, and makes them have similar catalytic activ-
ity as natural enzymes. These mimetic enzymes are usually characterized by mild reac-
tion conditions, a small amount of catalysts and high activity. Common catalysts
include metal porphyrins, metal phthalocyanines [15–17], and Schiff bases [18–20]. The
second generation of iron-tetraamido macrocyclic ligand catalyst (FeIII-TAML) [21, 22]
designed by Carnegie Mellon University in the United States is a hydrogen peroxide
mimetic enzyme. It has been reported that it has high catalytic activity for hydrogen
peroxide [23, 24] and can be used as a sewage treatment reagent [25–27]. On the
basis of its structure, the two methyl substituents at the tail were removed. A simpli-
fied FeIII-TAML catalyst A (Figure 1) was synthesized. Since the two methyl groups
were removed, 2,2-dimethylmalonyl chloride, one of the raw materials for the syn-
thetic catalyst, was replaced with dimethyl malonate, and the cost of the synthesis of
the new catalyst was nearly 10,000 times lower than that of the original catalyst.
At the same time, two other FeIII-TAML catalysts with known structures (FeIII-TAML
catalyst B and FeIII-TAML catalyst C, also shown in Figure 1) were synthesized, and the
synthetic route of catalyst B was redesigned and optimized. In this article, the catalytic
activity of catalyst A was investigated to determine the optimal conditions for its

JOURNAL OF COORDINATION CHEMISTRY
3
Figure 2. Synthetic route of dihydrogen FeIII-TAML catalyst A.
reaction. The activities of catalysts were compared by treating methylene blue, methyl
orange, neutral red, and Rhodamine B simulated dye wastewater.
2. Materials and methods
2.1. Materials
All reagents were analytical pure and solvents were dried by standard procedures
1
before use. IR spectra were recorded on a Bruker Vector22 spectrophotometer. The H
(400 MHz) and 13C{1H} (100 MHz) NMR spectra were recorded on a Bruker AVANCE AV
400 MHz spectrometer in DMSO-d6 or CDCl3. The HRMS were recorded with an Agilent
Q-TOF-6540 high resolution mass spectrometer. The dye absorbance was measured
using a 722 spectrophotometer. The elemental analyses (C, H, N) were performed on a
Elementar Vario EL CUBE.
2.2. Synthesis of dihydrogen FeIII-TAML catalyst A
The synthesis of dihydrogen FeIII-TAML catalyst A is shown in Figure 2. 2-Nitroaniline
(10.0 g, 72.4 mmol) was dissolved in xylenes (50 mL) in a 100 mL round-bottom flask.
Dimethyl malonate (0.5 eq, 4.78 g, 4.14 mL, 36.2 mmol) was added. The temperature of
the system was raised to 180 ꢀC. By controlling the temperature at the top of the
column to lower than 100 ꢀC, the distillate can be steamed out slowly in the branch
pipe of the column. After heating for 12 h, the reaction was stopped and yellow solids
precipitated after cooling to room temperature. After vacuum filtration, the solid was
1
recrystallized with anhydrous ethanol. Yield: 86% (10.71 g). H NMR (DMSO-d6): 11.09
(s, 2 H, CONH), 8.80 (d, J ¼ 4.4, 2 H, ArH), 8.26 (d, J ¼ 8.4, 2 H, ArH), 7.72 (t, J ¼ 7.6, 2 H,
ArH), 7.29 (t, J ¼ 4.4, 2 H, ArH), 3.76 (s, 2 H, CH2). 13C NMR (DMSO-d6): 165.0, 137.2,
135.9, 133.7, 125.8, 124.2, 122.8, 47.0.
A1 (5.0 g, 14.5 mmol) was dissolved in 30 mL ethyl acetate in a 250 mL round-bottom
flask. Stannous chloride (6 eq, 19.66 g, 87.1 mmol) in 4.8 mL of concentrated hydrochloric
acid was slowly dropped into the reaction system. After stirring for 4 h at room tempera-
ture, the yellow solution gradually became colorless and a white precipitate was formed.
The acid was neutralized with ice cold aqueous NaOH and the pH of the aqueous layer

4
S. LI ET AL.
Figure 3. A reported synthetic route of FeIII-TAML catalyst B.
was adjusted to 9–10, and the organic and aqueous layers were separated. The aqueous
layer was extracted three times with EA (20 mL each). All organic layers were combined,
dried over Na2SO4, and the solvent removed by rotary evaporation to afford white solid
1
A2. Yield: 92% (3.8 g). H NMR (DMSO-d6): 9.38 (s, 2 H, CONH), 7.15 (d, J ¼ 8.0, 2 H, ArH),
6.94 (t, J ¼ 8.0, 2 H, ArH), 6.73 (dd, J1 ¼ 8.0, J2 ¼ 1.2, 2 H, ArH), 6.55 (td, J1 ¼ 7.6, J2 ¼ 1.2,
2 H, ArH), 4.96 (s, 4 H, NH2), 3.50 (s, 2 H, CH2). 13C NMR (DMSO-d6): 166.1, 142.6, 126.4,
125.9, 122.7, 115.9, 115.4, 44.2.
A2 (0.5 g, 1.76 mmol) was dissolved in CH2Cl2 (150 mL) in a 250 mL round-bottom
flask. Triethylamine (2.2 eq, 392 mg, 0.54 mL, 3.87 mmol) was added with stirring.
Oxalyl chloride (1 eq, 223 mg, 1.76 mmol) dissolved in CH2Cl2 (10 mL) was added
dropwise to the solution in a dropping funnel with rapid stirring in an ice bath.
During the reaction, a white solid was produced. Stirring was continued for 6 h, the
liquid was filtered and the filtrate was evaporated. The obtained solid was recrystal-
1
lized from acetonitrile and isopropyl alcohol. Yield: 71% (0.42 g). H NMR (DMSO-d6):
10.16 (s, 2 H, CONHR), 9.65 (s, 2 H, CONH), 7.88 (m, 4 H, ArH), 7.19 (m, 4 H, ArH), 3.18 (s,
2 H, CH2). 13C NMR (DMSO-d6): 170.6, 159.2, 127.4, 126.6, 126.2, 125.3, 38.6.
A3 (0.5 g, 1.48 mmol) was dissolved in freshly distilled THF (50 mL) under nitrogen; the
solubility of the ligand was not good, and the solution was turbid. Under ice bath, n-BuLi
(4 eq, 2.19 mL, 5.91 mmol) was added slowly to the system. The ligand was gradually dis-
solved. After stirring for 15 min, FeCl3 (1 eq, 240 mg, 1.48 mmol) dissolved in freshly dis-
tilled THF (2 mL) was added to the system and the color of system became dark purple.
After stirring for 8 h at room temperature, the solution was concentrated to 10 mL and
then poured into 100 mL hexane to give a brown solid. Yield: 95% (0.42 g). FTIR (film,
cmꢁ1): 3379 (Ph-H), 2955 (R-CH2-R), 2858 (R-CH2-R), 1685 (R-CO-NR2), 1602 (Ph), 1540 (Ph),
1437, 1386, 1040, 865, 757, 516. ESI-HRMS [M-18]- m/z: calcd for C17H10FeN4O4- 390.1245,
found 390.1240. Anal Calcd: C, 49.83; H, 2.49; N, 13.38; Found: C, 49.19; H, 2.91; N, 13.50.
2.3. Redesign and synthesis of FeIII-TAML catalyst B
The synthesis of FeIII-TAML catalyst B has been reported [21, 22], but its synthesis route is
complex (Figure 3), involving the protection and deprotection of amino groups, which
increases the cost of synthesis. To simplify the route and reduce the cost, we redesigned

JOURNAL OF COORDINATION CHEMISTRY
5
Figure 4. Improved synthesis of FeIII-TAML catalyst B.
the synthetic route (Figure 4). The improved route uses 2-nitroaniline as a raw material,
and 2-nitroaniline reacts with dimethylmalonyl dichloride to form amide intermediate B1.
The two nitro groups of B1 are reduced to the amino group, and the resulting intermedi-
ate B2 is further reacted with oxalyl chloride to give TAML (B3). Finally, TAML complexes
with the iron salt in the presence of n-BuLi to form FeIII-TAML (B4). The total yield of the
improved synthetic route was increased from 30.1% to 49.5% compared with the
reported route.
2-Nitroaniline (5.0 g, 36.2 mmol) was dissolved in freshly distilled THF (100 mL) in a
250 mL round-bottom flask. Pyridine (2.2 eq, 6.3 g, 6.43 mL, 79.6 mmol) was added. The
temperature of the system is raised to 50 ꢀC. Dimethylmalonyl dichloride (0.5 eq,
3.06 g, 1.38 mmol) dissolved in freshly distilled THF (10 mL) was added dropwise to the
solution in a dropping funnel with rapid stirring in an ice bath. After 6 h, the mixture
was cooled to room temperature and suction filtered, giving a yellow oily liquid by
evaporation. Adding 20 mL of methyl tert-butyl ether and sonicating for 5 min to pre-
cipitate a large amount of yellow solid. The liquid was filtered, and the solid was
1
washed with a small amount of methanol. Yield: 86.7% (5.84 g). H NMR (CDCl3): 11.15
(s, 2 H, CONH), 8.79 (dd, J1 ¼ 1.2, J2 ¼ 8.4, 2 H, ArH), 8.23 (dd, J1 ¼ 1.6, J2 ¼ 8.4, 2 H,
ArH), 7.67 (td, J1 ¼ 1.2, J2 ¼ 7.2, 2 H, ArH), 7.22 (m, 2 H, ArH), 1.79 (s, 6 H, CH3). 13C
NMR (CDCl3): 171.7, 137.0, 136.0, 134.3, 125.8, 123.9, 122.6, 53.2, 23.7.
B1 (0.5 g, 1.34 mmol) was dissolved in ethyl acetate (20 mL) in a 100 mL round-
bottom flask. Stannous chloride (6 eq, 1.53 g, 8.06 mmol) in 1.6 mL of concentrated
hydrochloric acid was slowly dropped into the reaction system. After stirring 4 h at
room temperature, the yellow solution gradually became colorless and a white precipi-
tate formed. The acid was neutralized with ice cold aqueous NaOH, the pH of the
aqueous layer was adjusted to 9–10, and the organic and aqueous layers were sepa-
rated. The aqueous layer was extracted three times with EA (20 ml each). All organic
layers were combined, dried over Na2SO4, and solvent removed by rotary evaporation
1
to afford white solid B2. Yield: 96.1% (0.4 g). H NMR (DMSO-d6): 9.00 (s, 2 H, CONH),
6.95 (td, J1 ¼ 8.8, J2 ¼ 0.8, 4 H, ArH), 6.72 (dd, J1 ¼ 0.8, J2 ¼ 8.0, 2 H, ArH), 6.55 (td, J1
¼ 1.2, J2 ¼ 7.6, 2 H, ArH), 4.89 (s, 4 H, NH2), 1.57 (s, 6 H, CH3). 13C NMR (DMSO-d6):
172.8, 144.1, 127.5, 126.8, 122.7, 115.8, 115.4, 50.7, 23.5.

6
S. LI ET AL.
B2 (0.5 g, 1.6 mmol) was dissolved in freshly distilled THF (100 mL) in a 250 mL
round-bottom flask. Triethylamine (2.2 eq, 356.3 mg, 0.49 mL, 3.52 mmol) was added
with stirring. Oxalyl chloride (1 eq, 203 mg, 0.135 mL, 1.6 mmol) dissolved in freshly dis-
tilled THF (10 mL) was added dropwise to the solution in a dropping funnel with rapid
stirring in an ice bath. During the reaction, a white solid was produced. Stirring was
continued for 6 h, the liquid was filtered and the filtrate was evaporated. The obtained
1
solid was recrystallized from acetonitrile and isopropyl alcohol. Yield: 64.3% (0.38 g). H
NMR (DMSO-d6): 10.18 (s, 2 H, CONHR), 9.56 (s, 2 H, CONH), 7.51 (d, J ¼ 8.0, 2 H, ArH),
7.35 (d, J ¼ 7.6, 2 H, ArH), 7.26 (t, J ¼ 7.6, 2 H, ArH), 7.17 (t, J ¼ 8.0, 2 H, ArH), 1.58 (s, 6 H,
CH3). 13C NMR (DMSO-d6): 172.5, 161.8, 131.7, 130.7, 127.2, 126.5, 126.0, 125.4,
51.2, 23.3.
B3 (0.5 g, 1.36 mmol) was dissolved in freshly distilled THF (50 mL) under nitrogen;
the solubility of the ligand was not good, and the solution was turbid. Under ice bath,
n-BuLi (4 eq, 1.37 g, 2.02 mL, 5.46 mmol) was added slowly to the system. The ligand
gradually dissolved. After stirring for 15 min, FeCl3 (1 eq, 221.4 mg, 1.36 mmol)
dissolved in distilled THF (2 mL) was added to the system and the color of system
became dark purple. After stirring for 8 h at room temperature, the solution was con-
centrated to 10 mL and then poured into 100 mL hexane to give a brown solid. Yield:
92.5% (0.53 g). FTIR (film, cmꢁ1): 3415 (Ph-H), 2956 (R-(CH3)2), 2872 (R-CH3), 1640
(R-CO-NR2), 1602 (Ph), 1570 (Ph), 1472, 1398, 1354, 1039, 754, 593. ESI-HRMS [M-18]-
-
m/z: calcd for C19H14FeN4O4 418.3082, found 418.3086.
2.4. Synthesis of FeIII-TAML catalyst C
FeIII-TAML catalyst C is based on the structure of FeIII-TAML catalyst B, adding two
nitro groups. According to relevant literature, introducing electron-withdrawing groups
into FeIII-TAML can improve the catalytic activity and stability of FeIII-TAML. In this
article, we synthesized it according to the methods reported [21, 22]. Yield 38.8%. FTIR
(film, cmꢁ1): 3432, 2925, 2863, 1625, 1537, 1508, 1470, 1394, 1335, 737, 593. ESI-HRMS
[M-18]- m/z: calcd for C19H12FeN6O8 508.0072, found 508.0072.
-
2.5. Activity test method of FeIII-TAMLs
A 100 mL dye sewage solution with a mass concentration of 30 mg/L was prepared
and the initial absorbance was measured as A0. The pH was adjusted with Na2CO3/
NaHCO3 buffer. An appropriate amount of FeIII-TAML catalyst was added and mixed
well. With the reaction temperature controlled by a water bath, a certain amount of
H2O2 was added to initiate the reaction. After 30 min, the absorbance was measured
and the decolorization was calculated.
A0ꢁAt
Decolorization ¼
ꢂ100%
A0
The method for measuring chemical oxygen demand (COD) was carried out in
accordance with the national standard GB 11914-89 (Determination of COD in water
quality). Deionized water (20 mL) was added to a 500 mL reaction flask, followed by
HgSO4 (0.4 g), standard potassium dichromate solution (10 mL), and standard H2SO4-

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 5. Influence of hydrogen peroxide dosage on decolorization.
Ag2SO4 solution (30 mL). After heating to reflux for 2 h, the solution was cooled to
room temperature, and 3 drops of Ferroin solution was added as an indicator. The sys-
tem was titrated with a solution of ammonium ferrous sulfate, and the volume of the
consumed ammonium ferrous sulfate was recorded as V0. The water sample to be
tested is treated as described above, and the volume of the consumed ammonium fer-
rous sulfate is recorded as V1.
CODCr ¼ ½ðV0 ꢁ V1Þ ꢂ c ꢂ 8 ꢂ 1000ꢃ=V
In the above formula, V is the water sample volume (mL) and c is the concentration
of ammonium ferrous sulfate (mol/L).
3. Results and discussion
3.1. Effect of hydrogen peroxide dosage in the reaction
FeIII-TAML catalysts A, B, and C were selected to test the treatment of methylene blue
simulated wastewater. The effect of hydrogen peroxide dosage on the degradation of
dyes was studied at 25 ꢀC, CFe-TAML ¼ 25 mg/L, and pH ¼ 8. The reaction results are
shown in Figure 5. The decolorization increases with increase of hydrogen peroxide.
Increasing the concentration of hydrogen peroxide can increase the concentration of
high valent iron andꢄOH in the reaction system, which can degrade dyes more quickly.
However, it was also observed that the decolorization decreased if the amount of
hydrogen peroxide continued to increase. This is because excessive hydrogen peroxide
competes with substrates and combines with high valent iron produced in the reac-
tion process, resulting in lower reaction rate and decolorization. Considering the
experimental results and the cost of reagents, we consider that the optimal amount of
hydrogen peroxide used in the catalytic reaction is 1.5 g/L.

8
S. LI ET AL.
Figure 6. Influence of FeIII-TAMLs dosage on decolorization.
Figure 7. Catalytic reaction process.
3.2. Effect of FeIII-TAMLs concentration on the reaction
FeIII-TAML catalysts A, B, and C were selected to test the treatment of methylene blue
simulated wastewater. The effect of FeIII-TAMLs concentration on the degradation of
dyes was studied at 25 ꢀC, Chydrogen peroxide ¼ 1.5 g/L and pH ¼ 8. The reaction results
are shown in Figure 6. Decolorization increases with increase of catalyst concentration
in a certain range, because the increase of catalyst concentration accelerates the for-
mation of active intermediates. However, if the catalyst concentration continues to
increase, the decolorization decreases. This is because the reaction rate of catalyst
with hydrogen peroxide to produce active intermediates is faster than that of active
intermediates and substrates, which results in the loss of some active intermediates
during the reaction process, so the decolorization decreases. The reaction process is
shown in Figure 7 [28]. Considering the experimental results and the cost of reagents,
we consider that the optimal dosage of three FeIII-TAML catalysts A, B, and C is 50 mg/
L, 10 mg/L, and 50 mg/L, respectively.

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 8. Influence of pH on decolorization.
3.3. Effect of pH in the reaction
FeIII-TAML catalysts A, B, and C were selected to test the treatment of methylene blue
simulated wastewater. The effect of pH on the degradation of dyes was studied 25 ꢀC,
Chydrogen peroxide ¼ 1.5 g/L and CFe-TAML ¼ 25 mg/L. The reaction results are shown in
Figure 8. Decolorization of the reaction is low under acidic conditions because the cata-
lyst is not stable at low pH. The hydrogen ion attacking the nitrogen causes the Fe-N
bond to break and the catalyst loses its activity. With increase of pH, the decolorization
increased gradually. When the reaction pH exceeded 9, the decolorization began to
decrease, because hydrogen peroxide is a weak acid, which decomposes rapidly in
strong alkaline environment. The results show that the optimum reaction pH of FeIII-
TAML catalyst A and FeIII-TAML catalyst B is 8, and that of FeIII-TAML catalyst C is 9.
3.4. Effect of temperature in the reaction
FeIII-TAML catalyst A was selected to test the treatment of methylene blue simulated
wastewater. The effects of temperature on catalytic reaction were investigated at
Chydrogen peroxide ¼ 1.5 g/L, CFe-TAML ¼ 25 mg/L, and pH ¼ 8. The reaction results are
shown in Figure 9. When the temperature increases from 20 ꢀC to 30 ꢀC, the reaction
rate increases significantly and the decolorization increases within 30 min. This is
because the temperature provides enough energy for the reaction system to acceler-
ate the molecular motion and the rate of production of the reactive intermediates,
thereby increasing the decolorization. When the temperature increases from 30 ꢀC to
40 ꢀC, the reaction rate at 40 ꢀC is slightly lower than that at 30 ꢀC. This may be due to
two reasons: (1) with increase of temperature, the decomposition rate of hydrogen
peroxide increases, and hydrogen peroxide cannot react with catalyst to form active
intermediates, but converted into water and oxygen directly; (2) with increase of
temperature, some active intermediates lose their activity before they can fully contact
with organic pollutants, which leads to the decrease of decolorization.

10
S. LI ET AL.
Figure 9. Effect of reaction temperature on decolorization.
Figure 10. Structural formulas of four dyes.
Table 1. Degradation effect of catalyst A.
Dye
Methylene blue
Methyl orange
Neutral red
Rhodamine B
kmax (nm)
Decolorization %
COD removal %
664
96.1
63.7
464
74.8
46.9
530
83.7
50.1
554
84.0
53.6
3.5. Treatment of four kinds of simulated dye sewage
Methylene blue, methyl orange, neutral red, and Rhodamine B (Figure 10) simulated
dye wastewater were treated with the optimum reaction conditions of A, B and C. The
decolorization and COD removal were determined after 30 min. The results are shown
in Tables 1, 2, and 3, respectively. From the results of treating four dyes with three
catalysts, there are some differences in the activity of the three catalysts. The best
catalytic effect is Fe-TAML catalyst C, while the catalytic effect of Fe-TAML catalyst B is
slightly better than that of Fe-TAML catalyst A.

JOURNAL OF COORDINATION CHEMISTRY
11
Table 2. Degradation effect of catalyst B.
Dye
Methylene blue
Methyl orange
Neutral red
Rhodamine B
kmax (nm)
Decolorization %
COD removal %
664
98.9
66.6
464
79.3
57.5
530
93.7
62.9
554
95.4
60.3
Table 3. Degradation effect of catalyst C.
Dye
Methylene blue
Methyl orange
Neutral red
Rhodamine B
kmax (nm)
Decolorization %
COD removal %
664
99.6
71.8
464
95.6
62.4
530
97.2
65.3
554
99.6
76.0
The structure of the three catalysts shows that the biggest difference between Fe-
TAML catalyst C and Fe-TAML catalyst B is that there are two nitro groups in the mol-
ecule. Nitro is a strong electron-accepting group, which greatly reduces the charge of
iron in the molecule, and makes it easier to combine with hydrogen peroxide to form the
active high valent iron, so its catalytic activity is the highest. Compared with Fe-TAML
catalyst A and Fe-TAML catalyst B, there is a bare methylene in the Fe-TAML catalyst A
molecule. The secondary C-H bond of the catalyst is somewhat active, and the structure
of the catalyst is destroyed and inactivated in the strong oxidation environment.
Therefore, the activity of Fe-TAML catalyst A is slightly lower than that of Fe-TAML cata-
lyst B. In general, Fe-TAML catalyst A has the activity of catalyzing hydrogen peroxide to
degrade dye wastewater. Although it is not as good as Fe-TAML catalyst B and Fe-TAML
catalyst C, its synthesis cost is much lower than the latter, and it has more practical value.
4. Conclusion
In this article, a new simplified Fe-TAML was synthesized. Fe-TAML catalyst is a perox-
idase-like complex used to catalyze the degradation of organic pollutants in water by
hydrogen peroxide. The cost of synthesis is much lower than that of existing Fe-TAML
catalysts, and it has practical value in this field. In addition, the synthesis of dimethyl
Fe-TAML catalyst was redesigned and synthesized, which reduced the synthesis steps
and costs. Next, we will continue to design new structures of Fe-TAML catalysts to fur-
ther simplify its structure and enhance its stability in water.
Disclosure statement
There are no conflicts of interest to declare.
Acknowledgement
The authors gratefully acknowledge Professor Wang Qing for her contribution to this project.
Funding
This work was supported by the National Natural Science Foundation of China (No. 21272022).

12
S. LI ET AL.
ORCID
Run Zhou
http://orcid.org/0000-0002-1350-5409
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