Zinc(ii) triazole: Meso -arylsubstituted porphyrins for UV-visible chloride and bromide detection. Adsorption and catalytic degradation of malachite green dye

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Zinc(II) triazole meso-arylsubstituted porphyrins for

UV-visible chloride and bromide detection.

Adsorption and catalytic degradation of malachite

green dye†

Cite this: RSC Adv., 2020, 10, 22712

a

ab

c

Mouhieddinne Guergueb, Jihed Brahmi, Soumaya Nasri,* Frederique Loiseau,

´

d

e

f

a

Kaıss Aouadi, Vincent Guerineau, Shabir Najmudin

and Habib Nasri

¨

Three new triazole meso-arylporphyrins (4a–c) were synthesized by the copper(I)-catalyzed azide alkyne

cycloaddition (CuAAC) “click” reaction in high yield. The corresponding zinc(II) coordination compounds

5a–c) have also been prepared. All 4a–c and 5a–c porphyrin species were fully characterized by

elemental analysis, electrospray ionization and MALDI-TOF mass spectrometry, infrared spectroscopy,

proton nuclear magnetic resonance, UV-visible, ﬂuorescence and cyclic voltammetry. The zinc(II) 5a–c

(

ꢀ

complexes have been tested as detectors for Cl and Br anions. UV-visible titrations reveal that these

host systems exhibit strong anion binding aﬃnities. The eﬃciency of the adsorption of the malachite

green dye (MG) dye on the 4a–c free base porphyrins and the corresponding zinc(II) complexes 5a–c

was investigated by a kinetic study using these synthetic porphyrin derivatives as adsorbents. The use of

our triazole Zn(II) complexes in the catalytic degradation of the MG dye is the ﬁrst example where

a metalloporphyrin is involved in the MG dye decolorization reaction. The degradation reactions were

Received 5th April 2020

Accepted 3rd June 2020

2 2

carried out using an ecological oxidant (H O ), where the eﬃciency of the decolorization has been

characterized by UV-visible spectroscopic analysis. Several factors aﬀecting the degradation

phenomenon have been studied. The energetic parameters concerning the degradation process have

also been determined.

DOI: 10.1039/d0ra03070h

rsc.li/rsc-advances

and optical properties. Phosphines, pyridines, imidazoles and

crown ethers, to name a few, have been used to functionalize

1

. Introduction

7–10

In the elds of chemistry, biochemistry and material sciences, meso-arylporphyrins.

porphyrins and metalloporphyrins have been extensively Sharpless et al., the copper catalyzed azide–alkyne cycloaddi-

studied due to their vast range of potential applications such as: tion (CuAAC) known as “click chemistry” has been widely used

Since its introduction in 2001 by

11

1,2

3

photodynamic therapy, catalysis, as building blocks, in arti- to link moieties together in a very eﬃcient and reliable way to

12,13

4

5,6



cial photosynthetic systems and as sensors. The chemical prepare new functionalized meso-arylporphyrins. Beer et al.,

modications at the meso positions of porphyrins give rise to reported the synthesis and the characterization of several

a large number of porphyrin derivatives with unique electronic functionalized meso-porphyrins such as the “porphyrin-cage”

and the tetra-triazole-appended “picket-fence” zinc(II) coordi-

nation compounds. These species were prepared to be tested as

receptors for halide and other inorganic salts. Thus, the aim is

a

University of Monastir, Laboratoire de Physico-chimie des Mat ´e riaux, Facult ´e des

Sciences de Monastir, Avenue de l'environnement, 5019 Monastir, Tunisia. E-mail:

to investigate the role of various substituents at the porphyrin

Department of Chemistry, College of Science Al-Zul, Majmaah University, Saudi meso-positions for receptor eﬃciency.

hnasri1@gmail.com; Habib.Nasri@fsm.rnu.tn; Fax: +216 73500278

b

Arabia

Interestingly, porphyrins and metalloporphyrins have been

c

D ´e partement de Chimie Mol ´e culaire, Universit ´e Grenoble Alpes, 301 rue de la Chimie,

tested eﬀectively in the degradation of chemical dyes. Indeed,

these species constitute a large part of water pollutants due to

the sewage discharge containing carcinogenic and chronically

CS 40700, 38058 Grenoble Cedex 9, France

d

Department of Chemistry, College of Science, Qassim University, Buraidah 51452,

Saudi Arabia

14

e

toxic organic dyes, which are extensively used in textile,

printing and photographic industries. During the late decade,

Institut de Chimie des Substances Naturelles CNRS, Avenue de la Terrasse, F-91198

Gif-sur-Yvette, France

f

Randall Centre for Cell and Molecular Biophysics, Faculty of Life Sciences and several free bases porphyrins have been used as catalysts in

Medicine, King's College, 3rd Floor New Hunt's House, London SE1 1UL, UK

2

presence of TiO , in the photocatalytic degradation of dyes, e.g.

the meso-arylporphyrins substituted by phenyl carboxylic acid

†

Electronic supplementary information (ESI) available. See DOI:

0.1039/d0ra03070h

1

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groups and di-tert-butyl-substituted phenyl rings have been

15

used in the degradation of the methylene blue (MB) dye. Metal

porphyrins such as the manganese(III) metalloporphyrin based

polymers have also been used in the methylene blue dye (MB)

16

degradation in an aqueous solution of hydrogen peroxide. We

also reported the use of two 4-cyanopyridine–cobaltous-

II

porphyrin complexes type [Co (Porph)(4-CNpy)] (Porph ¼

meso-tetrakis(para-methoxyphenyl)porphyrinato and meso-tet-

ra(para-chlorophenyl)porphyrin) in the same MB dye degrada-

17

tion in presence of H O . In 2018, we reported the catalytic

2

degradation of the Calmagite dye using an aqueous solution of

0

H O with the (4,4 -bipyridine)[(tetrakis(ethyl-4(4-butyryl)oxy-

2

18

phenyl)porphyrinato)]zinc(II) complex.

Among dyes, the malachite green (MG) dye, with the formula

C(C N(CH ]Cl (Scheme 1) is widely used in the

5 6 4 3 2 2

textile and paper industry. The [C H C(C H N(CH ) ) ] cation

[C

6

H

5

6

H

4

3 2 2

) )

+

6

which gives the very intense green color to this dye exhibits

a very strong absorption band at 621 nm.

During the past two decades, reports on the enduring

carcinogenic and mutagenic characteristics of MG dye have

Scheme 2 Structure of [Zn(TAzP-XVP)] complexes. 5a: X ¼ H, 5b: X ¼

Cl and 5c: X ¼ I.

19

increased. Since 2000, the MG dye has been listed as a priority

chemical for carcinogenicity assessment by the U.S. Food and

20

Drug Administration. However, due to its eﬃcacy and low cost,

it is still used in many countries. Therefore, many treatment

technologies have been applied to decolorize MG from aqueous

been described which is the rst example of the use of a por-

phyrinic compound for the degradation of this dye.

21

medium.

Here, we describe the preparation of three new substituted

meso-arylporphyrins using the “click chemistry” strategy and

their zinc(II) corresponding complexes namely: the meso-tetra-

kis(3-methoxy-4-((1-phenyl-1H-1,2,3-triazol-4-yl)methoxy)

2

. Results and discussion

2.1. Synthesis

phenyl)porphyrin (4a) [H

chlorophenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3-methoxyphenyl)

porphyrin (4b) [H (TAzP-ClVP)], and the meso-tetrakis(4-((1-(4- triazol-4-yl)methoxy)phenyl)porphyrin (4a) [H

2

(TAzP-HVP)], the meso-tetrakis(4-((1-(4- Scheme 3 depicts the overall synthetic route for the prepa-

ration of meso-tetrakis(3-methoxy-4-((1-phenyl-1H-1,2,3-

2

(TAzP-HVP)],

iodinephenyl)-1H-1,2,3-triazol-4-yl)methoxy)-3-methoxyphenyl)

the meso-tetrakis(4-((1-(4-chlorophenyl)-1H-1,2,3-triazol-4-

porphyrin (4c) [H (T_A_z_P-IVP)] and the corresponding zinc(II) yl)methoxy)-3-methoxyphenyl)porphyrin

(4b)

[H (T_A_z_P-

2

metalloporphyrins: 5a–c with the formulas [Zn(T_A_z_P-HVP)], ClVP)] and the meso-tetrakis(4-((1-(4-iodinephenyl)-1H-

Zn(TAzP-ClVP)] and [Zn(TAzP-IVP)], respectively (Scheme 2).

1,2,3-triazol-4-yl)methoxy)-3-methoxyphenyl)porphyrin (4c)

[

All these porphyrin derivatives have been characterized by [H (T_A_z_P-IVP)], as well as the corresponding zinc(II) metal-

2

1

UV-visible, uorescence, IR and H NMR spectrometry, as well loporphyrins 5a–c with the formulas [Zn(T_A_z_P-HVP)],

as by mass spectrometry and cyclic voltammetry. The second [Zn(TAzP-ClVP)] and [Zn(TAzP-IVP)], respectively (see

part of this paper concerns the study of the chloride and synthetic procedures in the ESI†). The rst step is the

bromide ions receptor by the zinc(II) chloro–triazole and iodine– preparation

of

the

3-methoxy-4-(prop-2-ynl-yloxy)

triazole porphyrin complexes 5b–c. The other important goal of benzaldehyde (2). This derivative was prepared by reacting

the present work is to study the eﬃciency of the free base the 3-hydroxy-3-methoxy-benzaldehyde (1) with K CO and

2

3

porphyrins 4a–c and the corresponding zinc(II) complexes 5a–c the propargyl bromide in acetone under reux for 4 hours.

in the adsorption of the malachite green (MG) dye. The catalytic The second step is the synthesis of the three substituted

oxidative degradation eﬃciency of the MG dye using the three [1,2,3](triazol-4-ylmethoxy)-benzaldehyde: 3-methoxy-4-(3-

triazole meso-arylporphyrin zinc(II) compounds 5a–c have also phenyl-3H-[1,2,3]triazol-4-ylmethoxy)-benzaldehyde

(3a),

the 4-[3-(4-chloro-phenyl)-3H-[1,2,3]triazol-4-ylmethoxy]-3-

methoxy-benzaldehyde (3b) and the (4-iodine-phenyl)-3H-

[

1,2,3]triazol-4-ylmethoxy]-3-methoxy-benzaldehyde

(3c).

These compounds were prepared using the so-called “click

reaction” (CuAAC) by reacting the 3-methoxy-4-(prop-2-ynl-

yloxy)benzaldehyde (2) with the 1-azidobenzene or the 1-

azido-4-chlorobenzene or the 1-azido-4-iodinebenzene and

the diisopropylethylamine (DIPEA) reagents in the presence

2

Scheme 1 Structure of the malachite green (MG) dye.

of copper(I) (CuI) catalyst. The success of the click reaction

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Scheme 3 Synthesis of aldehydes 2–3a–c, the free base porphyrins 4a–c and the zinc(II) porphyrin complexes 5a–c.

is veried in IR by the disappearance of the two absorption fragments were observed which is a clear indication of the

ꢀ

1

bands of the azido group (n (N ) ꢁ 2130 and ꢁ2080 cm

)

stability of the 5a–c compounds in THF solutions.

as

3

and the alkyne group of compound 2 and the appearance of

ꢀ

1

a new band at 1726 cm assigned to n(C]N, N]N) of the

triazole group (Fig. SI-2†). The three triazole-meso-porphy-

rins 4a–c were prepared using a slightly modied Adler–

1

2

.3. IR and H NMR investigation

The IR spectra of the 4a–c free base porphyrins and the corre-

sponding zinc(II) metallated species 5a–c conrm the formation

2

3

Longo procedure. The metalation by the zinc(II) of the

three 4a–c porphyrins were made according to the literature

2

4

method using the zinc(II) acetate salt Zn(OAc) $2H O

2

leading to the three zinc(II) metalloporphyrins [Zn(T_A_z_P

-

HVP)] (5a), [Zn(T_A_z_P-ClVP)] (5b) and [Zn(T_A_z_P-IVP)] (5c). The

three free base porphyrins 4a–c and the corresponding

zinc(II) metalloporphyrins 5a–c were characterized by UV-

1

visible, uorescence, IR and H NMR spectroscopies as

well as by mass spectrometry.

2.2. Mass spectrometry

All synthetic compounds were characterized by ESI or MALDI-

TOF mass spectrometry (see ESI†). The MALDI-TOF spectra of

our three zinc(II) metalloporphyrins [Zn(TAzP-HVP)], [Zn(TAzP

-

ClVP)] and [Zn(T_A_z_P-IVP)] (5a–c), shown in Fig. SI-1,† were

recorded in the tetrahydrofuran solvent using the trans-2-[3-(4-

tert-butylphenyl)-2-propenylidene]malonitrile (DCTB) as matrix.

Fig. 1 IR spectra (solid state) of [Zn(TAzP-HVP)] (5a) (red color),

[Zn(TAzP-ClVP)] (5b) (black color) and [Zn(TAzP-IVP)] (5c) (blue color).

+

n+

For all three zinc(II) porphyrin species, the [M] and [M + nH]

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Table 1 UV-visible data of the three triazole meso-arylporphyrins (4a–c) and a selection of several meso-arylporphyrins and zinc(II) tetra-

coordinated metalloporphyrins. The solvent used is the dichloromethane

Free base meso-arylporphyrins

max (nm) (3 ꢂ 10^ꢀL mmol cm

3

ꢀ1

)

l

Egap-opt (eV)

Ref.

Compound

Soret band

Q bands

a

H

2

(TPP)

(TTP)

416(419)

420

513(20)

516

550(20)

552

590(6)

594

646(6)

640

1.89

1.86

1.82

1.85

1.88

1.87

1.86

26

27

4

18

b

c

(TPBP)

(TEBOP)

(TAzP-HVP) 4a

(TAzP-ClVP) 4b

(TAzP-IVP) 4c

420(513)

422(295)

420(565)

422(551)

424(576)

516(17)

517(9)

517(42)

518(35)

520(46)

552(7)

554(8)

554(19)

555(26)

555(29)

591(5)

593(5)

593(15)

594(15)

595(24)

646(4)

651(7)

650(13)

651(17)

652(18)

d

This work

Zinc(ii) meso-arylporphyrin complexes

max (nm) (3 ꢂ 10^ꢀL mmol cm

3

ꢀ1

)

l

Compound

Soret band

Q bands

Egap-opt (eV)

Ref.

a

[

Zn(TPP)]

421(524)

420

550(21)

550

591(25)

586

1.91

—

28

29

24

18

e

Zn(TMP)]

c

Zn(TPBP)]

Zn(TEBOP)]

Zn(TAzP-HVP)] 5a

Zn(TAzP-ClVP)] 5b

Zn(TAzP-IVP)] 5c

425(546)

424(219)

424(530)

426(523)

426(532)

554(24)

552(11)

551(26)

552(31)

558(29)

596(9)

594(5)

592(10)

594(15)

597(12)

1.99

2.03

2.04

2.02

2.01

d

This work

a

b

c

d

TPP ¼ meso-tetraphenylporphyrinato. TTP ¼ meso-tetratolylporphyrinato. TPBP ¼ meso-tetrakis-[4-(benzoyloxy)phenyl]porphyrinato. TEBOP

e

¼

meso-tetrakis(ethyl-4(4-butyryl)oxyphenyl)porphyrinato. TMP ¼ meso-tetrakis(2,4,6-trimethylphenyl)porphyrinato.

of the triazole meso-arylporphyrins as well as the corresponding 2.4. Photophysical properties

zinc(II) coordination compound. Indeed, the values of the n(CH)

The electronic absorption spectra of the free base porphyrins

_

stretching frequencies of the C H bonds of the triazole and the

4a–c and the corresponding zinc(II) metallated porphyrin

aryl groups of H (T -HVT) (4a), H (T -ClVT) (4b) and

2

AzP

2

AzP

species (5a–c) are depicted in Fig. SI-7 and SI-8† while the UV-

visible data are given in Table 1. The lmax values of the Soret

band of the free base porphyrins 4a–c are ꢁ420 nm while those

ꢀ

1

ꢀ1

H (T -IVT) (4c) are ꢁ3070 cm and in the [2955–2854] cm

2

AzP

range, respectively (Fig. SI-3†). For the zinc(II) corresponding

complexes 5a–c (Fig. 1), the n(CH) stretching frequencies values

are practically the same as those of the free base porphyrins 4a–

c. The presence of the triazole fragment is conrmed by a strong

ꢀ

1

absorption band at ꢁ1725 cm for both free base porphyrins

a–c and the corresponding zinc(II) complexes 5a–c. This band

4

25

is attributed to n(N]N) and n(C]N) of the triazole group. The

metallation of 4a–c porphyrins are conrmed by (i) the disap-

pearance of the absorption band correspondent to the n(N H)

_

ꢀ

1

stretching frequency of the free base porphyrins (ꢁ3280 cm

)

and (ii) by the shi of the deformation frequency d(CCH) from

ꢀ

1

ꢀ1

ꢁ

965 cm (4a–c) to ꢁ1000 cm for the zinc(II) complexes 5a–c

(

Fig. SI-3† and 1).

The proton NMR spectra of the three zinc(II) complexes 5a–c

are shown in Fig. SI-4–6.† The b-pyrrolic protons of the three

porphyrinates in complexes 5a–c resonate at about 9 ppm while

the phenylic protons resonate between 7.19 and 7.71 ppm. For

these three 5a–c species, the chemical shi values of the triazole

protons are ꢁ8 ppm and those of the O–CH

2

-triazole groups are

ꢁ

5.4 ppm. The methoxy groups for 5a–c presents singlets at Fig. 2 The emission spectra of compounds 4a–c and 5a–c. The

about 4.0 ppm.

spectra were recorded in dichloromethane solvent with a concentra-

tion ꢁ10 M. The excitation wavelength value is 430 nm.

ꢀ6

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Table 2 Emission parameter values of several meso-arylporphyrins and a selection of zinc(II) meso-metalloporphyrins

lmax (nm)

a

b

f

Compound

Q(0, 0) band

Q(0, 1) band

F

f

s

(ns)

Ref.

Free base meso-arylporphyrins

H

2

(TAzP-HVP) 4a

(TAzP-ClVP) 4b

(TAzP-_cIVP) 4c

(TPP)

655

651

650

656

653

656

651

719

715

714

717

712

719

714

0.091

0.076

0.071

0.09

0.12

0.082

0.089

8.82

7.18

7.12

—

9.6

7.16

7.42

This work

33

34

35

26

c

(TPP)

2(TMPP)

d

e

2

(TClPP)

Tetracoordinated zinc(II) meso-metalloporhyrins

[

Zn(TAzP-HVP)] 5a

Zn(TAzP-ClVP)] 5b

Zn(TAzP-IVP)] 5c

601

600

599

597

600

649

648

647

648

0.051

0.035

0.032

0.033

0.030

1.96

1.78

1.51

1.90

1.60

This work

35

c

Zn(TPP)]

f

Zn(TTP)]

36

a

b

c

d

F

f

¼ uorescence quantum yield.

s

f

¼ uorescent lifetime.

H

2

(TPP) ¼ meso-tetraphenylporphyrin.

H

2

(TMPP) ¼ meso-tetra(para-methoxy)

e

f

phenylporphyrin.

H

2

(TClPP) ¼ meso-tetra(para-chlorophenyl)porphyrin. TTP ¼ meso-tetratolylporphyrinato.

of the Q bands are ꢁ518, ꢁ550, ꢁ590 and ꢁ650 nm which are photoluminescence data of these porphyrin species are given in

typical for meso-arylporphyrins. For the tetracoordinated zinc(II) Table 2.

coordination compounds 5a–c type [Zn(Porph)] (Porph ¼ TAzP

-

Importantly, it should be noticed that porphyrin derivatives

HVP or T -ClVP or T -IVP porphyrinates), the Soret and the exhibit interesting photophysical properties especially due to

AzP

Q bands of these metalloporphyrins are, as expected, slightly the signicant aromaticity of the porphyrin macrocycle. Indeed,

redshied compared to the corresponding free base porphyrins. these species present one very weak emission transition S / S₀

2

Notably, the UV-visible data of our three free bases and the of the Soret band between the second excited singlet state S

corresponding zinc metallated porphyrins are very close to and the ground state S . The second emission transition of

those of the reported zinc(II) related species (Table 1). The porphyrin and metalloporphyrins, which is much stronger than

optical gap values (E -op) of our synthetic compounds 4a–c and the rst transition, is the S / S of the Q bands between the

a–c were determined using the Tauc's relation (eqn (1)): to the ground state S . Therefore,

only the following two S / S transitions are observed for the

2

0

g

1

0

30,31

5

rst excited singlet state S

1

0

1

0

2

(

ahn) ¼ A[hn ꢀ E -op]

(1)

g

where A is a constant parameter depending on transition

probability, hn is the incident photon energy and a is the optical

absorption coeﬃcient deduced from absorbance data. The

intercepts between the solid lines and x-axis allow the deter-

mination of E -op values (Fig. SI-9†). The optical gap energy

g

values of the free bases 4a–c are 1.88, 1.87 and 1.86 eV,

respectively, while those of the corresponding zinc(II) complexes

g

5a–c are 2.05, 2.02 and 2.01 eV, respectively. The fact that the E -

op values of the metallated porphyrins are higher than those of

the free bases is mainly due to the higher exibility of the non

metallated porphyrins which leads to the destabilization of the

HOMO–LUMO orbital energies. Thus, the net result is the

reduction of the gap energy values of these meso-porphyrins.

However, the zinc metallation of these tetradentate ligands

decreases the distortion of the porphyrin core. Therefore, the

values of the optical energy of the metalloporphyrins are usually

32

higher than those of the non metallated porphyrins. We notice

that both 4a–c porphyrins and 5a–c Zn(II) metalloporphyrins

Fig. 3 Cyclic voltammograms of complexes 5a–c. The solvent is

present E

phyrins and zinc(II) meso-arylporphyrins. Fig. 2 illustrates the

uorescence spectra of 4a–c and 5a–c, while the working electrode (B ¼ 2 mm).

g

-op values very close to the related meso-arylpor-

a mixture of dichloromethane and acetonitrile (4/1) and the concen-

ꢀ3

ꢀ1

tration is ca. 10 M in 0.1 M TBAPF , 100 mV s , vitreous carbon

6



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a

Table 3 Electrochemical data for the three free base triazole meso-arylporphyrins 4a–c and the corresponding zinc(II) complexes 5a–c and

a selection of several related porphyrins species

Oxidations

First oxid.

Reductions

First

red

Second

red.

Second oxid.

(O2, R2)

(

O1, R1)

(R3, O3)

(R4, O4)

b

1/2

Compound

E

1/2

E

1/2

E

1/2

Ref.

H

2

(TAzP-HVP) 4a

(TAzP-ClVP) 4b

(TAzP-_cIVP) 4c

(TPP) _d

0.86

0.85

0.78

1.02

0.95

0.72

0.71

0.72

0.89

0.81

0.72

1.09

1.08

1.13

1.26

1.36

1.08

1.09

1.05

1.18

1.11

1.15

ꢀ0.95

ꢀ0.76

ꢀ0.82

ꢀ1.20

ꢀ1.12

ꢀ1.36

ꢀ1.37

ꢀ1.26

ꢀ1.48

ꢀ1.42

ꢀ1.36

ꢀ1.40

ꢀ1.37

ꢀ1.55

ꢀ1.53

—

ꢀ1.70

ꢀ1.76

—

This work

40

(TBPP)

24

[

Zn(TAzP-HVP)] 5a

Zn(TAzP-ClVP)] 5b

Zn(TAzP-I_cVP)] 5c

Zn(TPP)] _d

This work

41

24

40

Zn(TBPP)]

e

Zn(DTPP)]

a

b

c

d

The potentials are reported versus SCE.

E

1/2 ¼ half wave potential. TPP ¼ meso-tetraphenylporphyrinato.

H

2

TBPP ¼ meso-{tetrakis-[4-

e

(benzoyloxy)phenyl]porphyrin. DTPP ¼ 5,15-p-ditolyl-10-phenylporphyrinato.

free base porphyrins and metalloporphyrin complexes: S [Q(0, by the single photon counting technique, and the uorescence

1

0

)] / S

species 4a–c, the emission spectra show two bands: the weak uorescence decays (s

band at lmax ꢁ 715 nm is assigned as Q(0, 1), and the stronger Fig. SI-10†). Our [Zn(Porph)] complexes (5a–c) display, as ex-

values between 7.2 and 8.82 ns which are much higher

0

and S

1

[Q(0, 1)] / S

0

. For the three free base porphyrin decays were tted to single exponentials. The representative

f

) of these four derivatives are similar (see

band at lmax ꢁ 650 nm is assigned as Q(0,0) (Fig. 2). The values pected, s

f

of each lmax of our three derivatives are very close to those of the than the corresponding free bases (4a–c) with values in the

reported meso-arylporphyrins (Table 2). The hypochromic shis range 1.51 and 1.96 ns.

of the Q(0, 0) and the Q(0, 1) of the zinc(II) metalloporphyrins

5

a–c compared to those of the corresponding free bases 4a–c are

important for consideration. The lmax values of the Q(0, 0) band

are ꢁ600 nm, while the lmax values of the Q(0, 1) bands are Cyclic voltammograms (CV) of our porphyrin derivatives 4a–c

650 nm. These shis are mainly due to the metallation of the and 5a–c were recorded at room temperature in a mixture of

2.5. Cyclic voltammetry

ꢁ

37

porphyrins. The Stocks shis values of the free bases 4a–c and dichloromethane and acetonitrile (4/1) under an argon atmo-

the 5a–c zinc(II) metalloporphyrins are small, indicating a uo- sphere with tetrabutylammonium hexauorophosphate

rescence emission with no signicant conformational change (TBAPF ) as the supporting electrolyte (0.1 M). The CV of the

6

between the fundamental and excited states.

free base porphyrins 4a–c are illustrated in Fig. SI-11,† while

The uorescence properties were studied by both steady- those of the corresponding zinc(II) complexes 5a–c are depicted

state and time-resolved uorescence techniques. As indicated in Fig. 3. The electrochemical data of our synthetic porphyrin

in Table 2, the uorescence quantum yield (F

AzP-HVP (4a) is slightly higher than those of the chloro–tri- free bases 4a–c exhibit two reversible one-electron reduction

azole and iodine–triazole free base derivatives H AzP-ClVP (4b) waves and two reversible one-electron oxidation waves, which

and H AzP-IVP (4c) with F values of 9.1%, 7.6% and 7.1%, correspond to the reduction and the oxidation of the porphyrin

f

) value of the species and several related compounds are given in Table 3. The

2

H T

2

T

2

T

f

respectively, which could be attributed to the higher molar mass ring. The half potential values (E₁_/₂) of the three triazole meso-

of the iodine (in 4c) and chlorine (in 4b) atoms compared to that arylporphyrins 4a–c are much smaller than those of the

of the hydrogen atom (in 4a). Notably, the F value of the 4a unsubstituted meso-tetraphenylporphyrin (H TPP) (Table 3).

f

2

38

porphyrin is comparable with that of the meso-tetraphenylpor- Neya et al., reported that the second reduction of the

phyrin H TPP (F values of porphyrin ring in metalloporphyrins, with non-redox-active

2

f

ꢁ 10) (Table 2). As expected the F

f

our three zinc(II) porphyrins 5a–c which are 5.1%, 3.5 and 3.1%, cationic metal centers such as Zn(II) and Mg(II), is usually not

respectively, are quite smaller than those of the related free base observed in the electrochemical window of the solvent which is

porphyrins 4a–c. We also notice that the iodine–triazole and the case for our zinc(II) derivatives 5a–c. It was also reported that

chloro–triazole zinc(II) derivatives exhibit slightly higher uo- the zinc metallation of the meso-arylporphyrins leads to the

rescence quantum yields than that of the H-triazole porphyrin shis of the characteristic reduction and oxidation potentials to

29,39

species. The lifetime of singlet excited state (s ) was measured more negative values.

In our case, only the E₁_/₂values of the

f

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24



rst reduction waves for [Zn(TazP-HVP)], [Zn(TazP-ClVP)] and arylporphyrins and the corresponding [Zn(Porph)] complexes

[Zn(T_a_z_P-IVP)] (5a–c) are shied to more negative values (Table and (iii) the iodine–triazole fee base porphyrin 4c exhibits the

3).

smallest E -el gap value (1.77 eV) compared to those of 4a–

g

In short, the CV investigation on our synthetic 4a–c and 5a–c b (1.95 and 1.87 eV, respectively) while the three zinc(II) metal-

porphyrin species show that the nature of the substituted lated porphyrins 5a–c presents very close values of E

groups on the phenyls of the meso-arylporphyrins do not have 2.14 eV.

a very signicant eﬀect on the electrochemical properties of this

type of species.

g

-el ꢁ

42

Ghosh et al., estimated the electrochemical gap energy (E

g

-

2.6. Anion binding studies

el) as the diﬀerence between the potential of the rst oxidation

potential and the rst reduction potential of the porphyrin. The

estimated energy values of the HOMO and LUMO orbitals as

The zinc(II) complexes 5b–c with the chloro–triazole and the

iodine–triazole meso-porphyrinates were tested as Cl and Br

ꢀ

anions detector by UV-visible titration. The two halide ions

titrations, carried out in dichloromethane solvent, revealed

signicant perturbation of the Soret and the Q bands of the

zinc(II) 5b–c receptors as a function of the concentration of the

tert-butyl ammonium chloride and bromide salts (TBACl and

TBABr). In the literature, several UV-visible titrations involving

the tetracoordinated zinc(II) meso-porphyrins type [Zn(Porph)]

well as the value of the E

following equations (eqn (2)–(4)):

g

-el can be calculated using the

43

E

HOMO ¼ ꢀ(Vonset-ox ꢀ Vref + 4.8) eV

(2)

(3)

(4)

E

LUMO ¼ ꢀ(Vonset-red ꢀ Vref + 4.8) eV

(

Porph ¼ meso-arylporphyrin) and neutral N-donor ligands are

E

g

-el ¼ (ELUMO ꢀ EHOMO) eV

18

reported. These investigations indicate the presence of

The E_H_O_M_Oand the E_L_U_M_Oare also known as the ionization a redshi of the Soret and the Q bands, upon addition of the

potential (IP) and the electron aﬃnity (EA), respectively. The axial ligand, of about 10 nm and 5 nm for the two bands,

V

onset-ox and the Vonset-red are the oxidation onset and the respectively, and the formation of a 1 : 1 coordination complex

reduction onset, respectively and the Vref is the reference half- type [Zn(Porph)(L)] (L ¼ N-neutral axial ligand).

wave potential. The values of EHOMO, -el were

The UV-visible titration spectra of [Zn(T_A_z_P-ClVP)] (5b)

calculated using equations eqn (2)–(4) and are reported in Table (concentration about 10 M) with Cl , in the Soret region, are

along with those of several related compounds. The energy shown in Fig. 4 and 5. The gradual addition of chloride to 5b

E

LUMO and E

g

ꢀ

6

ꢀ

4

level of the HOMO and LUMO orbitals as well as the E -el of 4a–c leads to a bathochromic shi of the Soret band from 426 nm to

g

and 5a–c are illustrated in Fig. SI-12.† From Table 4 we can 436 nm (Dl_m_a_x¼ 10 nm) with one distinct isosbestic point at

deduce: (i) except for the case of the H (TPBP) porphyrin, the 431 nm. In the Q region, the titration of the same complex 5b

2

ꢀ

electrochemical gap energy values of the zinc metal- with Cl exhibits also a redshi of the Q(0, 0) and Q(0, 1) bands.

loporphyrins are higher than those of the free base porphyrins; The titration of the same complex 5b with the bromide anion,

ꢀ

(ii) as expected, the values of the E

g

-el of 4a–c and 5a–c are using the same solvent and concentration as the Cl titration,

higher than those of the E

g

-op (optical gap energy) of the same gives a comparable result with a redshi of the Soret and the Q

species, which is also the case for all known meso- bands (Fig. 4). The isosbestic points are 431 nm for the Soret

Table 4 Values of the HOMO, LUMO orbitales energies and the

electrochemical gap energy for a selection of porphyrins species

g

E -el

Compound

EHOMO (eV)

ELUMO (eV)

(eV)

Ref.

Free base meso-arylporphyrins

a

H

2

(TPP)

ꢀ5.50

ꢀ5.87

ꢀ5.40

ꢀ5.53

ꢀ5.32

ꢀ3.49

ꢀ3.73

ꢀ3.45

ꢀ3.66

ꢀ3.56

2.01

2.14

1.95

1.87

1.77

44

24

b

(TPBP)

(TAzP-HVP) 4a

(TAzP-ClVP) 4b

(TAzP-IVP) 4c

This work

Zinc(II) meso-arylporphyrin tetracoordinated complexes

a

[

Zn(TPP)]

ꢀ5.58

ꢀ5.64

ꢀ5.24

ꢀ5.23

ꢀ5.24

ꢀ3.46

ꢀ3.27

ꢀ3.09

ꢀ3.11

2.12

2.37

2.15

2.14

2.13

45

24

b

Zn(TPBP)]

Zn(TAzP-HVP)] 5a

Zn(TAzP-ClVP)] 5b

Zn(TAzP-IVP)] 5c

This work

a

b

Fig. 4 Changes in the absorption spectra in the Soret band region of

TPP ¼ meso-tetraphenylporphyrinato. TBPP ¼ meso-tetrakis-[4-

benzoyloxy)phenyl]porphyrinato.

ꢀ6

(

complex 5b (ꢁ10 M) recorded in dichloromethane, upon addition of

ꢀ

Cl (0–500 equiv.). The inset shows enlarged view.

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region and 561 and 594 nm for the Q bands region. These values species ([Zn(PC)] with log Kas value of 4.6179 for our 5c complex

ꢀ

are practically the same as those of the Cl titration.

compared to log K_a_svalue of 4.0860 [Zn(PC)].

For the zinc iodine–triazole complex [Zn(T_A_z_P-IVP)] (5c), the

ꢀ

titrations with both the Cl and Br halide ions are very similar

2.7. Adsorption

to each other and to those of the zinc chloro–triazole complex

The adsorption process is generally due to several physico-

5b (Fig. 6 and 7). As mentioned above, the presence of isosbestic

chemical forces that occur at the solid–liquid interface such as

points is an indication of formation of a 1 : 1 receptor/anion

adduct, i.e., leading to a pentacoordinate complex type

5

0,51

52

van der Waals forces,

interactions.

hydrogen bonds and hydrophobic

53,54

To determine the eﬃciency of adsorption of the

[Zn(Porph)(L)]. The redshi of the absorption bands of metal-

MG dye on the 4a–c free base porphyrins and the corresponding

zinc(II) complexes 5a–c, we carried out a kinetic study using our

synthetic porphyrin derivatives as adsorbents. The adsorption

spectrum of MG dye as a function of time in presence of 4a–c

and 5a–c species are shown in Fig. SI-14.† The adsorption eﬃ-

ciency (R%) of the MG dye on 4a–c and 5a–c porphyrin

compounds are depicted in Fig. 8. The R% values for the 4a–c

free base porphyrins are 35.5, 37.25 and 36.5%, while those for

the 5a–c complexes are 29, 31.75 and 30.75%, respectively. The

fact that the adsorption eﬃciency of the free base porphyrins

are higher than those of the corresponding [Zn(Porph)]

complexes 5a–c could be related to the pyrrole hydrogen atoms

in 4a–c leading to hydrogen bond type interactions with the

nitrogens of the MG dye molecules. Notably, the chloro–triazole

and iodine–triazole 4b–c free base meso-arylporphyrin deriva-

loporphyrins is due to the narrowing of the HOMO–LUMO and

the energy gap is explained by the deformation of the porphyrin

46

core. This bathochromic eﬀect is also related to the electron-

withdrawing groups at the meso and b-pyrrolic positions of

4

7,48

the porphyrin macrocycle and to the nature of the metal ion.

ꢀ

In order to compare the Cl and Br detecting properties of

our zinc complexes 5a–b with those of the unsubstituted zinc(II)-

meso-tetraphenylporphyrin ([Zn(TPP)]) we also performed a UV-

visible titration in the Soret band region of this complex with

ꢀ

Cl and Br halide ions. The spectra concerning these titrations

are shown in Fig. SI-13.† The association constants values of the

ꢀ

1

[

: 1 complexes 5a–b : X (X ¼ Cl and Br ) as well as those of the

Zn(TPP)X] compounds are reported in Table SI-1.† To calculate

these associate constants Kas (and log Kas) we use the so-called

49

“

strong interactions” method (see the ESI† for details).

tives present better adsorption than that of the H-triazole T_A_z_P

-

A close inspection of Table SI-1† indicates that the iodine–

HVP species (4a). This trend is also present in the correspond-

ing zinc(II) porphyrin complexes (5a–c). This might result from

the fact that the chlorine and iodine atoms in the case of the 4b–

c and 5b–c species are involved in a n–p type interactions with

the MG molecules, which is not possible in the case of the H-

triazole 4a and the chloro–triazole 5a porphyrin species

triazole zinc derivative 5c presents a better binding aﬃnity than

ꢀ

the chloro–triazole zinc metalloporphyrin 5b for both Cl and

ꢀ

Br anions. This could be explained by the higher donor eﬀect

of the chlorine in the para position of the TAzP-ClVP porphyri-

nate than that of the iodine atom in the TAzP-IVP moiety leading

to a higher electron density on the zinc(II) center metal for 5b.

Therefore, the bonding aﬃnity of zinc(II) in 5b for the two

halides is smaller than that of the iodine–triazole zinc TAzP-IVP

55

(

Fig. SI-15†). It should also be noticed that all 4a–c and 5a–c

porphyrin compounds present p–p type interactions with the

MG dye molecules (Fig. SI-16†). Furthermore, the nitrogen atom

receptor. In contrast, the value of the log K for the 5b receptor

as

3 2

of the –(CH ) N– group of the malachite green molecule is most

ꢀ

for Cl is higher than that for Br which are 4.0245 and 3.5512,

2

+

likely coordinated to the center Zn ion as in the case of N-

donor ligands (L) which react with the tetra-coordinated

respectively. This is not the case for the 5c receptor for which

ꢀ

log Kas value, in the case of the Br anion, is higher than that for

[Zn(Porph)] species leading to penta-coordinated complexes

ꢀ

the Cl anion; i.e. log Kas is 4.6179 and 5.0566, respectively.

type [Zn(Porph)(L)].

Notably, our two receptors present much better aﬃnity

ꢀ

for Cl and Br than the zinc(II) unsubstituted meso-tetraphe-

2

.8. Adsorption kinetic

Adsorption kinetic determines the time required to reach

Beer et al., reported the use of a zinc(II) cage porphyrin equilibrium between the solute and the adsorbent and it also

complex [Zn(PC)] (PC meso-tetrayltetrakis(carbonyloxy- gives an idea of the adsorption mechanism and the mode of

methanediyl-1H-1,2,3-triazole-4,1-diylmethanediyl)tetraphenyl)- transfer between the liquid and solid phases. Several kinetic

nylporphyrin complex ([Zn(TPP)]) used as reference

(Table SI-1†).

12

¼

ꢀ

porphyrin) as receptor of several anions (such as F , Cl , Br , I

models have been developed to describe the adsorption kinetics

). This later complex presents a high binding aﬃnity and to specify the nature of the interactions at the solid–liquid

2

ꢀ

and SO

4

ꢀ

for Cl (log Kas ¼ 4.0860), but a very small association constant interface. In this work, four kinetic models have been selected

ꢀ

K

as value (<50) for Br . This can be explained by the small size of to study the kinetic behavior of the MG dye at the surface of our

the porphyrin cage which is not accommodated to host the porphyrinic compounds, namely: the pseudo rst order kinetic

highly diﬀuse bromine ion. It is interesting to note (i) that our model, the pseudo second order kinetic model, the intraparticle

56

zinc(II) chlorine porphyrin derivative (5b) has a similar bonding diﬀusion model and the Elovich model. The adsorption

ꢀ

aﬃnity for Cl ion as the [Zn(PC)] related receptor with very capacity curves as function of time for our six porphyrinic

close log Kas values (4.0224 and 4.0860, respectively) and (ii) our compounds (4a–c and 5a–c) are given in Fig. 9.

iodine–triazole zinc derivative (5c) exhibits much better

bonding aﬃnity for Cl anion than the zinc-porphyrin cage of MG dye on the 4a–c and 5a–c compounds. The data were

Fig. SI-17† illustrates the experimental data of the adsorption

ꢀ



tted using the four kinetic models and the results are given in

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Fig. 5 Changes in the absorption spectra in the Soret band region of

Fig. 7 Changes in the absorption spectra in the Soret band region of

ꢀ6

complex 5b (ꢁ10 M) recorded in dichloromethane, upon addition of

ꢀ6

complex 5c (ꢁ10 M) recorded in dichloromethane, upon addition of

ꢀ

Br (0–600 equiv.). The inset shows enlarged view.

ꢀ

Br (0–30 equiv.). The inset shows enlarged view.

Table SI-2.† The values of the amount of MG adsorption

calculated from the pseudo second order model are the closest

to those determined experimentally for all 4a–c and 5a–c

porphyrin species, which indicates the adequacy of the use of

this model to describe the adsorption phenomenon. The

The second order model equation used is as follows (eqn (5)):

t

1

t

¼

À

Á þ

(5)

^qe²^ꢂ^k2

q

t

q

e

where, q

t

and q

e

represent the amounts of the adsorbent

2

correlation coeﬃcient (R ) values of the pseudo second order

adsorbed at time t and equilibrium, respectively, while k

2

is the

model are close to 0.99. In the case of the pseudo rst order

rate constant for the pseudo second order model (g

2

model, the R parameters are between 0.86 and 0.90 for all

ꢀ1

2

mg min ). The values of k and qcal were calculated for each

compounds. For the intraparticle diﬀusion model, the correla-

tion coeﬃcient does not exceed 0.91 and in the case of Elovich

of the six porphyrinic compounds from the slope and the

intersection of the corresponding plot, respectively.

2

model, the R values are between 0.93 and 0.97. These data

indicate that the pseudo second order kinetic model is the most

appropriate for describing the adsorption of MG dye by our

porphyrin derivatives.

2

.9. Degradation of MG dye

2.9.1. Eﬀect of the initial MG concentration. In order to

obtain the optimal condition of the initial MG dye concentra-

tion, only the 5a derivative was tested. The degradation

Fig. 6 Changes in the absorption spectra in the Soret band region of Fig. 8 Adsorption eﬃciency curves of malachite green dye (C

0

¼

ꢀ

6

ꢀ1

complex 5c (ꢁ10 M) recorded in dichloromethane, upon addition of 20 mg L ) as a function of time of the porphyrin compounds 4a–c

ꢀ

Cl (0–30 equiv.). The inset shows enlarged view.

and 5a–c (m ¼ 5 mg, pH ¼ 8).

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Fig. 11 Change in the degradation eﬃciency of the MG dye on varying

ꢀ

1

Fig. 9 Adsorption capacity of the MG dye (C

0

¼ 20 mg L ) as

2 2

initial H O concentration using 5a triazole zinc(II) derivative as

a function of time for the 4a–c and 5a–c porphyrin species (m ¼ 5 mg,

pH ¼ 8). Dots represents the experimental data and the curves where

plotted using the pseudo second-order kinetic model.

a catalyst.

Thus, the eﬀect of the initial hydrogen peroxide concentration

on the malachite green dye degradation was studied using an

C

o

procedure of the MG dye consists of reacting the dye with H-

ꢀ

1

initial MG concentration of 20 mg L at room temperature

using 5a compound as a catalyst. The C initial H aqueous

concentrations used were 0, 3, 6 and 9 mg L . The increase in

triazole meso-arylporphyrin zinc(II) (5a) (m ¼ 5 mg) in the

2 2

O

ꢀ1

o

presence of an aqueous solution of H

2

O

2

(6 mg L ) at pH ¼ 8.

ꢀ1

Fig. 10 shows the evolution of the color removal against initial

MG dye concentration which shows that the degradation

kinetics of MG is slow when the initial dye concentration is

increased. This indicates that the increase of the initial

concentration of the dye leads to an increase in the number of

malachite green molecules, while the number of hydroxyl

radicals remains constant. As a consequence, there is a decrease

in the kinetics of the degradation reaction as well as the

discoloration eﬃciency. These trends are consistent with those

ꢀ1

H O concentration from 0 to 6 mg L leads to an increase in

2

the degradation eﬃciency (Fig. 11). However, for a C concen-

o

ꢀ

1

tration of 9 mg L , the discoloration eﬃciency of the MG

decreases. This phenomenon could be explained by the fact that

at high concentration, hydrogen peroxide is a powerful OHc

58

scavenger (Equations (eqn (6)–(8)).

ꢃ

H

2

O

2

þ OH /HO þ H

2

O

(6)

(7)

(8)

2

ꢃ

57

H O þ OH /OH þ O þ H O

reported in the literature.

.9.2. Eﬀect of the initial H O concentration. The 5a tri-

2

ꢃ

HO þ OH /H

2

O þ O

2

azole zinc(II) derivative was also used to obtain the optimal

condition for the initial hydrogen peroxide concentration.

2

Fig. 10 Evolution of the color removal against initial dye concentra-

ꢀ1

tion. The hydrogen peroxide concentration, C

o

is 6 mg L , 5a catalyst Fig. 12 Change of the degradation eﬃciency of the MG solution as

weight m ¼ 5 mg, pH ¼ 8 and the MG mass, m

o

is 5 mg.

function of time using 5a used as catalyst at 298, 308 and 318 K.

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Fig. SI-19a† represents the absorption curve of the MG dye in

2

.9.3. Eﬀects of pH. To investigate the eﬀects of pH on the presence of H O without catalyst (blank experiment) versus

2 2

degradation of the MG dye by complexes 5a–c, aqueous solu- time where it can be seen that the absorption remains practi-

tions with pH from 4 to 8 were adjusted by 0.1 M HCl and 0.1 cally the same for a period of 180 min. By using the same mass

NaOH. The inuence of pH on the dye oxidation was studied of the three catalysts 5a–c, the obtained degradation yields are

using ve solutions with pH values determined initially (4, 6, 8, 54.0, 52.1 and 48.9% for 5a, 5b and 5c, respectively (Fig. SI-

10 and 12) and without any modications or control of the pH 20a†). The degradation reactions were achieved aer 180 min.

during the process. The results obtained for dye removal as Fig. SI-20b† shows the degradation removal eﬃciency for

a function of the initial pH of the solution at various reaction complexes 5a–c using the same number of moles (3.35 ꢂ

ꢀ6

times are presented in Fig. SI-18.† The maximum conversion 10 mol.) for the three species. The obtained degradation

was achieved aer 3 h from the start of the reaction for a pH of yields are 54.0, 53.88 and 53.94% for 5a, 5b and 5c, respectively.

8.

These results show that using the same number of moles for our

2.9.4. Degradation with optimal conditions. The degrada- three 5a–c catalysts, the degradation eﬃciency is virtually the

tion study of the MG dye was carried out using an aqueous H

2

O

2

same (ꢁ54%). This conrms the fact that the central metal is

58

solution under optimal conditions, found for the 5a derivative, the main site of degradation of the dye and that the nature of

and applied to the two other species 5b–c (Fig. SI-19b and c†). the substituent X (X ¼ H, Cl and I) on the para-position of the

Table 5 Selection of several methods used for MG degradation with the optimal reaction conditions and yields

Degradation system and optimal

Method of degradation

reacting conditions

Degradation yield, time reaction

99.25% (60 min)

Ref.

60

Chemical method: Fenton's reagent

Fe(II)/aqueous H

2

O

2, pH ¼ 3.4,

2+

2 2 o

[H O ]

¼ 0.50 mM, [Fe ] ¼

ꢀ1

ꢄ

0.10 mM, [MG]

0

¼ 20 mg L , 30 C

Chemical method: mesoporous

carbon adsorbent

Mesoporous silica (MCM-48), pH ¼

98.2% (30 min)

53.25% (60 min)

61

62

ꢀ

3

8.5, [silica] ¼ 5.10 g/25 mL, [MG]

0

ꢀ1

ꢄ

¼

50 mg L , T ¼ 25 C

Photocatalysis method

Using naked niobium oxide (Nb O )

2 5

as a photocatalyst. weight of catalyst

ꢄ

¼

0.1 g, [MG]

o

¼ 5 ppm; T ¼ 25 C,

ꢀ2

3

mV cm light intensity, pH ¼ 6

, pH ¼ 9, [MG] ¼ 5 ꢂ

Photocatalysis method

Biodegradation method

Ag doped TiO

2

0

99.5%

63

64

ꢀ6

10

M, [catalyst] ¼ 0.12 g, 60 mW

ꢀ2

cm light intensity

System used: bacterium

Enterobacter asburiae strain XJUHX-

Maximum decolorization (>98%) in

semi-synthetic media

4TM, semi-synthetic medium

having the following composition

ꢀ

1

was used: MG: 0.100–1.00 g L

,

ꢀ1

KH

2

PO

: 2 g L , MgSO

, FeSO $7H O: 0.01 g L

sucrose: 15 g L , and beef extract:

4

: 1 g L , KCl: 0.5 g L ,

ꢀ

1

NaNO

3

4 2

$7 H O: 0.5 g

ꢀ1

L

4

2

,

ꢀ

1

ꢀ1

3

g L

System used: Pseudomonas sp.

strain DY1, [MG

] ¼ 100–

000 mg L , pH ¼ 6.6, T ¼ 28–30 C

Biodegradation method

Eﬀective decolorization: 78.9–84.3%

65

o

ꢀ1

ꢄ

1

Use of our three zinc(II) complexes 5a–c

Complex

System used

Yield

ꢀ

1

ꢀ1

[Zn(TAzP-HVP)] 5a

[Zn(TAzP-ClVP)] 5b

[Zn(TAzP-IVP)] 5c

[H

2

O

2

] ¼ C

o

¼ 6 mg L , [MG] ¼ 20 mg L

,

54.0% (180 min)

52.0% (180 min)

48.9% (180 min)

weight of catalyst (5a) ¼ m

o

¼ 5 mg, pH ¼ 8, T

ꢄ

¼

25 C

ꢀ1

[H

2

O

2

] ¼ C

o

¼ 6 mg L , [MG] ¼ 20 mg L

,

weight of catalyst (5b) ¼ m

o

¼ 5 mg, pH ¼ 8, T

ꢄ

¼

25 C

ꢀ1

[H

2

O

2

] ¼ C

o

¼ 6 mg L , [MG] ¼ 20 mg L

,

weight of catalyst (5c) ¼ m

o

¼ 5 mg, pH ¼ 8, T

ꢄ

¼

25 C

22722 | RSC Adv., 2020, 10, 22712–22725

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RSC Advances

terminal phenyl of the three triazole meso-aryporphyrins 4a–c, Table 6 Thermodynamic parameters (DS*, DH*, DG*) and activation

energy (E

a

) for complex 5a

practically has no eﬀect on this degradation.

.9.5. Eﬀect of temperature. For the zinc(II) porphyrin

derivative 5a, the eﬀect of temperature on the degradation of

2

ꢄ

T ( C)

25

35

45

ꢀ1

k

o

(min

)

0.0042

9.867

0.0046

9.867

0.0054

9.867

ꢀ

1

MG dye has been investigated. The temperatures used were 25, E_a(kJ mol

)

ꢄ

ꢀ1 ꢀ1

3

5 and 45 C (Fig. 12). As expected, the degradation eﬃciency of DS* (J mol

K

)

ꢀ265.983

ꢀ

1

DH* (kJ mol

DG* (kJ mol

)

7.308

MG dye increased from 54.0% to 64.2% as a consequence of

ꢀ

1

86.570

89.230

91.890

ꢄ

increasing the temperature from 25 to 45 C. This is due to the

fact that higher temperatures increase the reaction rate between

hydrogen peroxide and the zinc metal center. This in turn

increases the rate of generation of the OHc radical oxidizing

meaning the degradation process is endothermic and a higher

temperature facilitates degradation. The negative value of the

entropy suggests the diminution of the disorder during the

59

species.

.9.6. Comparison of our procedure with other reported

methods. Many investigations concerning the MG degradation

2

degradation process. The activation energy value is

19

have previously been reported in the literature. The most

important of which are: the chemical methods, the photo-

catalysis methods and the biodegradation methods (Table 5).

As depicted in Table 5, the degradation yields of the MG dye

obtained using our zinc(II) 5a–c (ꢁ50%) porphyrin zinc(II)

complexes are lower than those obtained using the other

methods shown in this table. It is expected that the use of other

ꢀ1

9

.867 kJ mol . Since the thermodynamic parameters found for

both 5b–c complexes are very close to those of complex 5a, only

the results founds for the latter zinc(II) derivative are reported.

3

. Conclusion

60

metal ions instead of Zn(II), such as Cu(II) or Fe(II) with our We have successfully synthesized three novel triazole meso-

three triazole porphyrins in the presence of H will lead to an arylporphyrins, the: H-triazole, chloro–triazole and iodine–tri-

increase in the degradation eﬃciency of the dye. This is due to azole meso-arylporphyrins with the respective formulas H

the fact that ferrous and cuprous ions are more eﬀective than HVP) (4a), H (TAzP-ClVP) (4b) and H (TAzP-IVP) (4c) as well as

their corresponding zinc(II) porphyrins 5a–c. The chloride and

2 2

O

2

(TAzP-

2

+

ꢃ

Zn ion in giving HO and OHc radicals.

2

Nevertheless, the obtained yields are quite acceptable for bromide binding properties of the chloro–triazole and the

a rst reported investigation on the MG degradation using iodine–triazole zinc(II) triazole meso-arylporphyrins derivatives

a porphyrin derivative. Thus, these encouraging results suggest 5b–c have been monitored by UV-visible technique. Both 5b–c

ꢀ

that our zinc(II) 5a–c can be further improved and can be receptors exhibit strong Cl and Br anion binding aﬃnities,

concomitantly used with other degradation techniques such as forming 1 : 1 stoichiometric complexes. The adsorption eﬃ-

the photodegradation where the expected yields are higher than ciency of the malachite green dye (MG) on all three base

those reported here.

.9.7. Activation energy and thermodynamic variables. To compounds revealed that: (i) the adsorption eﬃciency of the

better understand the degradation phenomenon, the pseudo free base porphyrins 4a–c are higher than those of the corre-

rst order model was used to calculate the kinetic parameters. sponding zinc(II) porphyrin complexes 5a–c, (ii) the free base

Arrhenius law (eqn (9)) was used to determine the activation chloro–triazole and iodine–triazole 4b–c porphyrin derivatives

energy (E ). The thermodynamic activation parameters of show better adsorption than that of the H-triazole T_A_z_P-HVP

enthalpy (DH*), entropy (DS*) and Gibbs free energy (DG*) were species (4a), which is also the case for the corresponding zinc(II)

porphyrins and their corresponding zinc(II) coordination

2



a

6

calculated using Eyring's equation (eqn (10) and (11)).

porphyrin complexes (5a–c) and (iii), the pseudo second order

kinetic model is the most appropriate to describe the adsorp-

tion of MG dye by our free porphyrin compounds. The degra-

dation investigation of the MG dye, using complexes 5a–c as

E

a

ln k

o

¼ ln A

o

ꢀ

(9)

RT

ꢀ

ꢁ

ꢀ ꢁ

k

o

k

DS* DH*

2 2

catalysts, carried out using an aqueous H O solution under

ln

¼ ln

þ

ꢀ

(10)

T

h

R

RT

optimal conditions, shows that the degradation yield using the

H-triazole meso-arylporphyrin zinc(II) derivative 5a is higher

than those of the chloro–triazole and the iodine–triazole meso-

arylporphyrin zinc(II) complexes 5b–c. The degradation yields

using our 5a–c species are ꢁ54% which are much smaller than

several reported MG dye degradations using other methods.

Nevertheless, this is an encouraging result as this is the rst

time a porphyrin derivative has been used for the degradation of

this dye and studies are underway to test our zinc(II) derivatives

in photochemical degradations of the malachite green and

other dyes. The thermodynamic parameters were determined

and show that the free energy is positive in all the cases indi-

DG* ¼ DH* ꢀ T DS*

(11)

where k is the kinetic rate, h and k are the Plank's and Boltz-

mann's constants, respectively. A is the Arrhenius constant and

o

ꢀ1

R is the universal gas constant (8.314 J mol

K ). The obtained

thermodynamic parameters and activation energy values are

summarized in Table 6. From these results, it can be seen that

the free energy is positive in all the cases. This indicates that the

degradation of MG dye using H O is a non-spontaneous reac-

2 2

tion regardless of temperature. The free enthalpy is positive,

2 2

cating that the degradation of MG dye using H O is a non-

RSC Adv., 2020, 10, 22712–22725 | 22723

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RSC Advances

Paper

spontaneous, temperature-dependent reaction. Furthermore, 18 R. Soury, M. Jabli, T. A. Saleh, W. S. Abdul-Hassan, E. Saint-

the enthalpy is positive which implies that the degradation

process is endothermic, while the negative value of the entropy

Aman, F. Loiseau, C. Philouze and H. Nasri, RSC Adv., 2018,

8, 20143–20156.

suggests the diminution of disorder during the degradation 19 P. N. P. Raval, P. U. Shah and N. K. Shah, Appl. Water Sci.,

process.

2017, 7, 3407–3445.

20 S. Srivastava, R. Sinha and D. Roy, Aquat. Toxicol., 2004, 66,

319–329.

Conﬂicts of interest

21 S.-Y. An, S.-K. Min, I.-H. Cha, Y.-L. Choi, Y.-S. Cho, C.-H. Kim

and Y.-C. Lee, Biotechnol. Lett., 2002, 24, 1037–1040.

There are no conicts to declare.

2

2 J. Brahmi, K. Aouadi, M. Msaddek, J.-P. Praly and S. Vidal, C.

R. Chim., 2016, 19, 933–935.

3 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher,

j. Assour and L. J. Korsakoﬀ, Org. Chem., 1967, 32, 476.

4 S. Nasri, I. Zahou, I. Turowska-Tyrk, T. Roisnel, F. Loiseau,

E. Saint-Amant and H. Nasri, Eur. J. Inorg. Chem., 2016,

Acknowledgements

The authors extend their appreciation to the deanship of

Scientic Research at Majmaah University, Saudi Arabia.

5

004–5019.

5 K. G ¨o rlitzer, S. Huth and P. G. Jones, Pharmazie, 2005, 60,

69–272.

6 K. Ezzayani, Z. Denden, S. Najmudin, C. Bonif ´a cio, E. Saint-

Aman, F. Loiseau and H. Nasri, Eur. J. Inorg. Chem., 2014,

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RSC Adv., 2020, 10, 22712–22725 | 22725

Article Doi

Zinc(ii) triazole: Meso -arylsubstituted porphyrins for UV-visible chloride and bromide detection. Adsorption and catalytic degradation of malachite green dye

DOI: 10.1039/d0ra03070h

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Article abstract of DOI:10.1039/d0ra03070h

Full text of DOI:10.1039/d0ra03070h

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