Production of nanocatalyst from natural magnetite by glow discharge plasma for enhanced catalytic ozonation of an oxazine dye in aqueous solution

Article abstract of DOI:10.1016/j.molcata.2015.05.004

Cheap natural magnetite (NM) was modified with oxygen plasma owing to its cleaning effect by chemical etching and with argon plasma due to its sputtering effect resulting in more surface roughness. These plasmas were utilized individually or in the order of first O₂ and then Ar plasmas, respectively. The performance of the plasma treated magnetites (PTMs) was higher than NM for treatment of Basic Blue 3 (BB3) in catalytic ozonation (O₃/PTM). The properties of NM and the most efficient treated magnetite (PTM₄) samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) methods. The optimal values were chosen for operational parameters including ozone concentration (0.3 g/L), initial pH (6.7) and PTM₄ dosage (600 mg/L). GC-Mass analysis was applied to detect intermediates. Environmentally-friendly treatment of the NM, simple separation of the catalyst, negligible leached iron concentration, successive reusability at milder pH and unaffected efficiency in the presence of inorganic salts are the main advantages of the PTM₄.

Full text of DOI:10.1016/j.molcata.2015.05.004

Accepted Manuscript
Title: Production of nanocatalyst from natural magnetite by
glow discharge plasma for enhanced catalytic ozonation of an
oxazine dye in aqueous solution
Author: Mojtaba Taseidifar Alireza Khataee Behrouz Vahid
Sirous Khorram Sang Woo Joo
PII:
S1381-1169(15)00177-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.05.004
MOLCAA 9490
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
25-12-2014
4-5-2015
5-5-2015
Please cite this article as: Mojtaba Taseidifar, Alireza Khataee, Behrouz Vahid,
Sirous Khorram, Sang Woo Joo, Production of nanocatalyst from natural
magnetite by glow discharge plasma for enhanced catalytic ozonation of an
oxazine dye in aqueous solution, Journal of Molecular Catalysis A: Chemical
http://dx.doi.org/10.1016/j.molcata.2015.05.004
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Production of nanocatalyst from natural magnetite by glow discharge
plasma for enhanced catalytic ozonation of an oxazine dye in aqueous
solution
Mojtaba Taseidifara, Alireza Khataeea*a_khataee@tabrizu.ac.ir ar_khataee@yahoo.com,
Behrouz Vahidb, Sirous Khorramc, Sang Woo Jood**swjoo@yu.ac.kr
aResearch Laboratory of Advanced Water and Wastewater Treatment Processes, Department of
Applied Chemistry, Faculty of Chemistry, University of Tabriz, 51666-16471 Tabriz, Iran
bDepartment of Chemical Engineering, Tabriz Branch, Islamic Azad University, 51579-
44533 Tabriz, Iran
cResearch Institute for Applied Physics and Astronomy, University of Tabriz, 51666-
16471 Tabriz, Iran
dSchool of Mechanical Engineering, Yeungnam University, 712-749 Gyeongsan, South
Korea
*Corresponding author. Tel.: +98 41 33393165; Fax: +98 41 33340191
**Corresponding author: Tel: +82 53 810 1456
1

Graphical abstract
Proposed model for the interaction of glow discharge (O2-Ar) plasma and
O3 with catalyst surface.
2

Highlights
 Modification of natural magnetite by oxygen and argon glow discharge plasma.
 Characterization of the plasma treated magnetite by XRD, FT-IR, SEM, BET and
pHPZC
.
 Application of plasma treated magnetite in heterogeneous catalytic ozonation process.
 Evaluation of effective parameters on heterogeneous ozonation process.
3

Abstract
Cheap natural magnetite (NM) was modified with oxygen plasma owing to its cleaning effect
by chemical etching and with argon plasma due to its sputtering effect resulting in more
surface roughness. These plasmas were utilized individually or in the order of first O2 and
then Ar plasmas, respectively. The performance of the plasma treated magnetites (PTMs) was
higher than NM for treatment of Basic Blue 3 (BB3) in catalytic ozonation (O3/PTM). The
properties of NM and the most efficient treated magnetite (PTM4) samples were characterized
by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-
Emmett-Teller (BET) and scanning electron microscopy (SEM) methods. The optimal values
were chosen for operational parameters including ozone concentration (0.3 g/L), initial pH
(6.7) and PTM4 dosage (600 mg/L). GC-Mass analysis was applied to detect intermediates.
Environmentally-friendly treatment of the NM, simple separation of the catalyst, negligible
leached iron concentration, successive reusability at milder pH and unaffected efficiency in
the presence of inorganic salts are the main advantages of the PTM4.
Keywords
Nanocatalyst; Magnetite nanoparticles; Catalytic ozonation; Oxygen glow discharge; Argon
glow discharge.
4

1. Introduction
Wastewater of textile industries have extensive amounts of various dyes, which are
commonly bio-resistant and as a consequence conventional biological methods are not
efficient for their remediation [1]. Moreover, other physico-chemical processes like
adsorption and coagulation merely transfer pollutants to secondary phases, that need more
treatment [2]. Hence, applications of advanced oxidation processes (AOPs) are more proper
not only for degradation, but also for mineralization of diverse contaminants with no extra
waste [3]. Among reactive oxygen species (ROS), hydroxyl radicals (•OH) have the
significant role in AOPs due to unselective reaction with organic pollutants and their
conversion to harmless compounds like carbon dioxide, water and inorganic mineral salts [4].
Ozonation treatment is one of the effective AOPs applied for the removal of persistent
organic pollutants (POPs) due to its high reactivity and disinfection ability [4, 5].
•
Degradation of POPs can be explained by decomposition of O3 to generate OH radicals in
basic mediums (Eqs. 1 and 2) or by its direct electrophilic attack in acidic conditions [6].
However, it has been known that the appropriate degradation of pollutants may be not
achieved by O3 alone process [7].
-
O3 + OH- → HO2 + O2
(1)
(2)
-
-
O3 + HO2 → •OH + O2 + O2
•
Heterogeneous catalyzed ozonation, which can be performed under ambient conditions is
more efficient process for the removal of organic pollutants like humic and oxalic acids [8]. It
can be attributed to more ozone dissolution and decomposition in the presence of solid
particles due to ozone reaction with hydroxyl groups, which is existed on the surface of
particles [9].
5

Stable form and abundance of magnetite (Fe3O4) makes it adequate for usage in the catalytic
ozonation [10]. Furthermore, applications of nano-sized catalysts in heterogeneous ozonation
results in more reaction sites and better mass transfer [8, 11]. However, different synthesis
methods for producing nano-sized magnetite require toxic and expensive reactants [10].
Plasma is ionized gas that it comprises from positive and negative ions, electrons and neutral
species, which is considered as the forth state of matter, solves the above-mentioned
problems by an environmentally-friendly method [12]. Recently, non-thermal plasma
methods including glow discharge, silent discharge, and radio frequency discharge have been
applied for surface modification of various catalysts and improvement of their performance
[13, 14]. For instance, the plasma treatment changes the surface structure and activity of
synthesized zeolites or natural clinoptilolite [13]. Besides, stability and catalytic activity of
the Pd/HZSM-5 catalyst enhance after treatment by plasma [15]. In addition, plasma-
modified Fe2O3/ZSM-5 catalyst with the high activity and selectivity for hydrogenation of
carbon monoxide is obtained using the glow discharge of oxygen and argon [16].
To the best of our knowledge, there have been no reports regarding to the surface
modification of natural magnetite particles under the glow discharge plasma for using in
water treatment process. So, in this study first, a novel method to generate nanostructured
magnetite utilizing the plasma method is presented. The characterizations of treated NM were
performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR),
Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) methods. Then, the
efficiency of PTM in heterogeneous catalytic ozonation for the decolorization of BB3 was
evaluated and compared with NM. Finally, the effect of operational parameters include dye
concentration, ozone concentration, initial pH, organic, PTM dosage and additional of
inorganic salts were carried out and some of the generated intermediates during the process
were identified by GC-Mass.
6

2. Experimental
2.1. Materials
Natural magnetite was provided from Sarab, Iran, which was very cheap and abundant.
Elemental composition of NM was identified (O, 52.85%; Fe, 10.54%; C, 21.18%; Si,
14.25% and Ti, 1.18%) by X-ray photoelectron spectroscopy (XPS) using K-ALPHA Thermo
Scientific spectrometer (UK). C.I. BB3 (color index number: 45170, molecular formula =
C20H26N3OCl, max= 654 nm and Mw = 359.89 g/mol), which is a cationic mono-oxazine dye,
purchased from Boyakhsaz Co., Iran. Its chemical structure is shown in Fig. 1.
BB3 is used extensively for dyeing of wool and acrylic fibers with lethal dose 50 (LD50) of
100 mg/kg for rats [17]. All of the other chemicals were of analytical grade and they were
provided from Merck, Germany.
2.2. Procedure of catalyst treatment and characterization methods
NM sample was crushed to prepare particles with diameter between 210 and 354 µm and the
obtained particles were washed with distilled water and they dried at 60-70 oC for 24 h. Then,
non-thermal plasma technique was used for rejuvenation of them (3 g) using a plasma reactor
made up of a Pyrex tube equipped with two electrodes on its sides (Fig. 2).
DC high-voltage (1200 V) was applied on electrodes to generate glow discharge plasma.
Oxygen and/or argon at a flow of 3 standard cubic centimeters per second were fed to the
7

plasma reactor individually to generate the plasma. Table 1 presents the type and applied time
of the mentioned gases in the plasma reactor.
After the modifying process, the PTM particles were collected for using in heterogeneous
ozonation. In order to characterization of NM and the most effective plasma treated magnetite
(PTM4), the following analyses were performed: 1) the phase identification was carried out
by X-ray diffraction (XRD) technique (PANalytical X’Pert PRO, Germany) with Cu-kα
radiation (45 kV, 40 mA, 0.15406 nm). 2) Fourier transform infrared (FT−IR) spectra of the
samples were obtained by Tensor 27, Bruker spectrometer (Germany). 3) Scanning electron
microscopy (S-4200 Hitachi, Japan) was applied to identify their morphology and
dimensions. 4) The porosity of the samples was evaluated by physical adsorption of N2 at 77
K using Nitrometrics Gmini series (Japan). 5) the pH of point of zero charge (pHPZC) was
determined according to the salt addition method [18].
2.3. Catalytic ozonation set-up and procedure
The ozonation set-up was illustrated in Fig. 3.
Experiments were carried out in batch mode by a cylindrical reactor (Pyrex, 36 cm height ×
4.5 cm internal diameter). To generate ozone, oxygen gas, which was provided by oxygen
generator (Airsep, USA), was fed into the laboratory ozone generator (Donali, Iran). Then,
the ozone was continuously fed into the solution through a diffuser at the bottom of the
reactor and its concentration was adjusted by changing the gas flow (1 to 5 L/min) with
ozone-dissolved concentration between 0.3 and 2.5 mg/L and determined by indigo
trisulfonate method according to the procedure proposed by Bader and Hoigne [19]. In each
8

experiment, 250 mL of the reaction mixture contained definite concentration of BB3 and
catalyst (NM or PTM) was prepared. Sulfuric acid and sodium hydroxide were used for pH
adjustment of the solution. Then, the solution was treated by chosen O3 dosage. At distinct
process time-intervals, samples were withdrawn by a glass syringe, and then the magnetic
catalyst particles were separated from the solution by an external magnet. Eventually, the
sample was analyzed for degradation amount of BB3 concentration by UV–Vis
spectrophotometer (WPA Lightwave S2000, England) at 654 nm. In order to identify the
BB3 degradation intermediates during O3/PTM process, GC-Mass analysis was performed
using an Agilent 6890 gas chromatograph with a 30 m–0.25 mm HP-5MS capillary column
coupled with an Agilent 5973 mass spectrometer (Agilent Technologies, Palo Alto, Canada)
[20]. Influence of inorganic salts including sodium chloride (1 mM) and sodium sulfate (1
mM) were applied as hydroxyl radical scavengers [4]; the dissolved iron concentration was
measured colorimetrically with 1,10-phenanthroline at 510 nm by UV-Vis spectrophotometer
in O3/PTM4 process [21].
3. Results and discussion
3.1. Comparison of various treatment processes for degradation of BB3 and
kinetics study
The ozonation and catalytic ozonation processes for the degradation of a model contaminant
(BB3) in aqueous solution were compared using NM and various plasma treated samples.
The adsorptions of dye by all the samples were negligible and obtained less than 7% in
optimal condition after 20 min. All of the applied AOPs in this study followed pseudo-first
order kinetic, which is in consistent with other similar studies [22, 23].
In the depicted plots of ln(A0/A) against time (t), straight lines with high correlation
coefficients (R2), which was more than 0.96, confirmed the suggested first order kinetic.
9

Then, from the slope of plots, the apparent pseudo-first order rate constants (kapp) for the
degradation of BB3 were determined and presented in Table 1. As can be seen from Fig. 4,
the degradation efficiency of BB3 after 15 min of treatment at the same operational
conditions was obtained as 51.02, 63.78 and 93.47% for O3, O3/NM and O3/PTM4 (the most
efficient plasma surface modified catalyst) processes. Hence, PTM4 was selected as the
desired catalyst for identification of this structure and further experiments in catalytic
ozonation.
3.2. Characterization of NM and PTM4
The XRD patterns of the NM and PTM4 samples are demonstrated in Fig. 5.
There are the same diffraction peaks at 2θ of 30.1, 35.5, 43.2, 53.5, 57.0 and 62.8 attributed
to (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) panels of magnetite (Fe3O4 phase),
respectively [24, 25]. Thus, these results demonstrate that the plasma treatment have no effect
on the crystal structure of the NM.
Plasma treatment caused to decrease in the absorption peaks at 400 to 4000 cm-1 in FT-IR
spectrum (Fig. 6), generally.
The peaks at 576 and 470 cm-1 correspond to Fe–O vibration [26, 27]. Moreover, the peak at
1641 cm-1 is attributed to C=O stretching vibration in carbonyl groups, which is almost
vanished in PTM4. Besides, two peaks at about 2924 and 2853 cm-1 are assigned to
asymmetric and symmetric C–H bonds, respectively [28]. The peak at 3450 cm-1 can be
10

attributed to O–H bond vibration [29]. Finally, the peak at 1046 cm-1 belongs to asymmetric
O−Si−O stretching vibration bond [13].
SEM images of NM and PTM4 samples with different magnifications are shown in Fig. 7.
Fig. 7 (a, b) demonstrates a bulk structure of the raw magnetite sample. SEM images of NM
after 15 min of treatment by O2 plasma were shown in Fig. 7 (c, d), which shows no
considerable changes on the surface of NM. Comparison of the mentioned SEM images with
Fig 7 (e, f) indicates nano-sized magnetite is formed on the surface of NM by Ar plasma-
treated process after 45 min, which shows nano-structure of the catalyst surface. Specific
surface area of the NM and PTM4 were determined as 7.65 and 11.03 m2/g, reactively. Also,
pHPZC of the NM and PTM4 were measured as 7.5 and 6.2, respectively.
3.3. Effect of plasma on the NM
The PTM4 was produced from the NM utilizing O2 plasma for 15 min, and then Ar plasma for
45 min. In the first step of the plasma treatment, as can be seen from SEM images (Fig. 7 (c,
d)), the surface of the catalyst is not changed remarkably, which indicates the pure chemical
etching resulting in formation of some gaseous products like CO2 and H2O [14, 30]. Besides,
the O2 plasma can remove the carbon from the catalyst surface and cause to better
performance by regenerating of active sites [31]. Furthermore, O3 can be generated during the
utilization of O2 plasma [32], which can decline in the bands related to the surface hydroxyl
and carbonate groups. However, after treatment by O3 and scavenging of the mentioned
species, some of the hydroxyl groups remain on the surface of the catalyst [33], which can
interact with ozone in solution in O3/PTM4 process. The decrease in FT-IR peaks in the
sample after plasma treatment confirms the mentioned mechanism, as can be observed CO
band (1641 cm-1) is disappeared almost completely but OH groups (3450 cm-1) still remained
11

on the catalyst surface. This chemical cleaning effect of the surface by retaining of hydroxyl
groups is the main reason of the better performance of the catalyst in the O3/PTM process in
comparison with O3/NM. In the second step of the plasma treatment by applying of the high
energy species generated by the Ar plasma, the surface of the catalyst was sputtered
effectively by the positive ions from the argon plasma resulting in more surface roughness
with nano-sized structure and increase in active sites of catalyst [34, 35]. Furthermore, the
rate of ozone decomposition is strongly dependent on the specific surface area [36]. In the
light of these facts outlined above, PTM4 has better performance in catalytic ozonation than
PTM3 because it was modified with Ar gas more than O2 gas. As can clearly be seen from
SEM images (Fig. 7 (e, f)). Enhancement of the specific surface area of the catalyst from 7.65
(NM) to 11.03 m2/g (PTM4) after plasma treatment verifies the above-mentioned
explanations and is the major reason for the more activity of the catalyst in the O3/PTM4
process compared to O3/NM (Fig. 4).
3.4. Effect of operational parameters on the catalytic ozonation
The effect of main operational parameters including initial BB3 and ozone concentrations,
pH, and catalyst (PTM4) dosage on the degradation of the organic contaminant was studied.
Effect of these parameters on the apparent pseudo-first order constant of degradation and
mineralization for O3/PTM4 process was illustrated in Table 2.
Amount of operational parameters except for the above-mentioned ones: [BB3]0 = 600 mg/L,
pH = 6.7, O3 concentration = 0.3 mg/L and PTM4 dosage = 600 mg/L
12

The degradation of BB3 was declined by increasing of its initial concentration (Fig. 8)
because the identical amounts of produced oxidizing species at the same operational
conditions had to degrade more BB3 and its degradation intermediates [37, 38].
As the applied ozone concentration was increased, the degradation of BB3 was enhanced due
to the production of more ROS, particularly hydroxyl radicals [39]. In addition, a high ozone
flow rate leads to the enhancement of the ozone mass transfer rate from gas phase to liquid
phase [40]. By considering the high reactivity of the ozone and approximately the same
obtained degradation efficiency of BB3 after 21 min, the flow rate of 1 L/h correspondent to
0.3 mg/L was chosen for performing of the other experiments. The degradation of BB3 was
seemed to be efficient by the indirect attack of hydroxyl radicals in the more basic medium
than the direct electrophilic attack in the acidic medium under the identical operational
conditions (Fig. 9) [36, 39]; Moreover, the pHpzc of the PTM4 was measured as 6.2. At pH>
pHpzc, the surface of the catalyst has negative charge, which can adsorb the positive charge
dye better than in pH< pHpzc, due to the electrostatic repulsion effects.
However, the obtained results for pH of 6.7 (natural pH of the dye) and 9 did not differ
considerably, hence pH of 6.7 was chosen as the optimum one. In addition, PTM4 has the
lower pHpzc (pHpzc=6.2) compared to NM (pHpzc=7.5), which can adsorb the positive charged
dye more effectively in the lower pHs, Hence, the better performance of the PTM4 was
observed in pH of 6.7 (Fig. 10).
13

Fig. 11 illustrates the interaction of O3 with the hydroxyl groups on the catalyst surface after
plasma treatment, which causes to generation of active radicals specially hydroxyl radicals to
degrade the contaminant [33, 36]:
The hydroxyl groups existed on magnetite surface can catalyze the O3 in solid phase and
make a series of chain reactions (Fig. 11). The initial step involves the formation of a surface
complex between ozone and the magnetite surface [6, 41], thus proposed mechanism for
ozone decomposition on PTM4 surface can be described as Eqs. 3-6. Similar study has been
conducted by Park et al [41].
•
PTM4-OH + O3 ↔ PTM4-OH (O3)s ↔ PTM4-O• + HO3
PTM4-O• + H2O → PTM4-OH + •OH
(3)
(4)
(5)
(6)
•
-
HO3 ↔ H+ + •O3
•
HO3 → •OH + O2
This phenomenon can be explained by the fact that with increasing PTM4 dosage, the number
of catalytic active sites is enhanced and accordingly more ozone molecules on the catalyst
•
surface are decomposed to OH [41]. However no noticeable difference in degradation
efficiency between 600 and 800 mg/L of the catalyst dosage was observed (Fig. 12).
Therefore, 600 mg/L was selected as the desired dosage of the PTM4.
3.5. Spectral changes of BB3 during the catalytic ozonation and reusability of the
catalyst
14

The changes in UV-Vis absorption spectra of BB3 during PTM catalytic ozonation are shown
in Fig. 13.
The decrease of absorption peak of BB3 at 654 nm indicated a rapid degradation of the dye
and its complete degradation was achieved after 21 min at the desired experimental
conditions. Furthermore, the absorption peak around 254 nm, gradually weakened and
removed after 21 min of the treatment, without observing a new peak, which is related to the
elimination of the aromatic rings [42].
The potential of the catalyst in successive application for removal of organic contaminants is
significant from a practical point of view. Thus, three repetitive cycles for the degradation of
BB3 were conducted (Fig. 14).
The applied catalyst was recovered by the magnetic separation and dried for the next
degradation cycle. The PTM4 exhibited the same activity as that obtained from the first run,
which demonstrated not only the stability and reusability of the catalyst, but also the
reliability of the results.
3.6. Effect of inorganic salts and dissolved iron concentration
2-
The influence of inorganic anions such as sulfate (SO4 ) and chloride (Cl-), which can be
existed in textile effluents and acted as hydroxyl radical scavengers, was determined in
O3/PTM4. Catalytic ozonation process is just negligibly affected by the mentioned inorganic
salts (Fig. 15), which is in consistent with the other study for degradation of mesoxalic and
oxalic acids by catalytic ozonation [4].
15

The iron amount in the solution was measured colorimterically based on beer-Lambert law
(Fig. 16).
After 30 min of treatment under optimal conditions the total iron amount was determined as
0.2 mg/L, which was lower than maximum concentration level of iron in drinking water (0.3
•
mg/L) [43]. Iron ions can catalyze O3 resulting in production of OH by the process of
homogenous catalytic ozonation. Firstly, this reaction gives the Ferryl intermediate (FeO2+),
which could also generate hydroxyl radical (Eqs. 7 and 8) [44, 45].
Fe2+ + O3 → FeO2+ + O2
(7)
(8)
FeO2+ + H2O → Fe3+ + •OH + OH-
3.7. Identification of intermediates in the catalytic ozonation process
In order to recognize the intermediates of BB3 degradation in the O3/PTM4 process, the dye
solution was treated for 4 min under the optimal conditions and six produced intermediates
were identified by comparison with commercial standards when the match factor of mass
spectrum was above 90% (Table 3). Degradation of the dye can take place by cleavage of
C_C or C_N bonds [46]. After opening the aromatic rings, short chained compounds like acids
were formed, which could be converted directly to CO2 for complete mineralization.
Moreover, formation of compounds 3 and 4 considered to be related to interaction of
unknown byproducts with each other quickly [47]. However, several chromatographic peaks
could not be identified owing to their low match factor. In addition, some of the intermediates
could not be recognized due to their rapid oxidization.
4. Conclusions
16

In this research, improvement of the natural magnetite activity by the low-temperature
plasma treatment in the catalytic ozonation process for degradation of the oxazine dye can be
attributed to the chemical cleaning and sputtering effects of O2 and Ar plasmas, respectively.
The most efficient modified catalyst (PTM4) was prepared by utilizing O2 and then Ar
plasmas for 15 and 45 min, respectively. The obtained results were confirmed by decreasing
of the absorption peaks in FT-IR spectra and the enhancement of surface area of PTM4
compared to the NM. SEM images demonstrated the formation of nano-structured magnetite
on the catalyst surface after plasma treatment. Based on the XRD patterns, the crystal
structure of magnetite was not altered after plasma treatment. The effect of experimental
parameters was investigated on the degradation efficiency of BB3 in O3/PTM4 process.
Decolorizarion efficiency was declined by increasing of the pollutant concentration and
enhanced by increasing of ozone concentration, PTM4 dosage and pH. The proposed plasma
treatment method for modification of the NM catalyst as a cheap and abundant material was
environmentally friendly without using toxic chemicals for its synthesis. The PTM4 can be
effectively used in the repeated runs with simple separation by the external magnetic field.
Moreover, it can be utilized in the milder pH medium and the inorganic salts have almost
insignificant effect on the process.
Acknowledgement
The authors thank the University of Tabriz (Iran) for all of the support provided.
17

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21

Figure caption
Fig. 1. Chemical structure of Basic Blue 3.
Fig 2. Schematic diagram of the glow discharge plasma system.
Fig. 3. Schematic of experimental set-up of catalytic ozonation system.
Fig. 4. Comparison of O3, O3/NM and O3/PTM4 ozonation in degradation of BB3. The inset
shows mentioned processes follow pseudo-first order kinetic. Experimental conditions:
catalyst dose: 600 mg/L, initial BB3 concentration: 90 mg/L, ozone concentration: 1.2 g/L
and initial pH: 6.7.
Fig. 5. XRD patterns of NM and PTM4 samples.
Fig. 6. FT-IR spectra of NM and PTM4 samples.
Fig. 7. SEM images of NM (a, b), NM exposure to O2 plasma (15 min) (c, d) and PTM4 (e, f).
Fig. 8. Effect of initial BB3 concentration on the degradation of BB3 during PTM4 catalytic
ozonation. The inset shows mentioned processes follow pseudo-first order kinetic.
Experimental conditions: PTM4 dose: 600 mg/L, ozone concentration: 0.3 g/L and initial pH:
6.7.
Fig. 9. Effect of ozone concentration on the degradation of BB3 during PTM4 catalytic
ozonation. The inset shows mentioned processes follow pseudo-first order kinetic.
Experimental conditions: PTM dose: 600 mg/L, initial BB3 concentration: 90 mg/L and
initial pH: 6.7.
Fig. 10. Effect of initial pH on the PTM4 catalytic ozonation of BB3. Experimental
conditions: PTM dose: 600 mg/L, initial BB3 concentration: 90 mg/L and ozone
concentration: 0.3 g/L.
Fig. 11. Proposed model for the interaction of glow discharge (O2-Ar) plasma and O3 with
catalyst surface.
22

Fig. 12. Effect of initial PTM4 concentration on the catalytic ozonation of BB3. The inset
shows mentioned processes follow pseudo-first order kinetics. Experimental conditions:
initial BB3 concentration: 90 mg/L, ozone concentration: 0.3 g/L and initial pH: 6.7.
Fig. 13. Change in UV-Visible spectra of BB3 solution PTM4 catalytic ozonation process at
different times. Experimental conditions: catalyst dose: 600 mg/L, initial BB3 concentration:
90 mg/L, ozone concentration: 0.3 g/L and initial pH: 6.7.
Fig. 14. Reusability of PTM4 on PTM4 catalytic ozonation of BB3. Experimental conditions:
PTM dose: 600 mg/L, initial BB3 concentration: 90 mg/L, ozone concentration: 0.3 g/L, and
initial pH: 6.7.
Fig. 15. Effect of addition different salts on the degradation of BB3 during PTM4 catalytic
ozonation. Experimental conditions: PTM4 dose: 600 mg/L, initial BB3 concentration: 90
mg/L, initial salts concentration: 1 mM, ozone concentration: 0.3 g/L, and initial pH: 6.7.
Fig. 16. Evolution of total iron leached from the PTM4 catalyst. Experimental conditions:
PTM dose: 600 mg/L, ozone concentration: 0.3 g/L and initial pH: 6.7.
23

Table 1. Effect of the different catalytic ozonation and ozonation on the apparent pseudo-
first-order constants of degradation and mineralization of BB3.
No. Process
Type and time of applied gases in plasma kapp (min-1) R2
1
2
3
4
O3
_
0.0510
0.0734
0.1295
0.1685
0.96
0.98
0.99
0.98
O3/NM
O3/PTM1
O3/PTM2
_
O2 (60 min)
Ar (60 min)
5
6
O3/PTM3
O3/PTM4
O2 (45 min) + Ar (15 min)
O2 (15 min) + Ar (45 min)
0.1384
0.1814
0.97
0.97
24

Table 2. Effect of the operational parameters on the apparent pseudo-first order constant of
degradation and mineralization for O3/PTM4 process.
Operational parameters
kapp (min-1)
Correlation
and amounts
coefficient (R2)
BB3 concentration
(mg/L)
60
0.2175
0.1814
0.1370
0.1122
0.99
0.97
0.96
0.95
90
120
150
pH
3
0.08
0.97
0.97
0.94
6.7
0.1814
0.26
9
O3 concentration (mg/L)
0.3
0.1814
0.20
0.97
0.99
0.97
1.2
2.5
0.21
PTM4 dosage (mg/L)
300
400
600
800
0.067
0.094
0.1814
0.202
0.99
0.98
0.97
0.99
25

Table 3. Identified by-products during catalytic ozonation of BB3 at 21 ˚C after 4 min of
reaction at pH of 6.5 and ozone flow rate of 1 L/h.
Main fragments (m/z)/
(percent)
No.
1a
Compound
Acetic acid
Structure
tR (min)
4.581
75.00 (100.00%), 116.10 (76.7%),
73.10 (13.34%), 76.00 (7.52%),
117.00 (7.46%)
CH3
COOH
147.10 (100.00%), 73.10
(86.69%), 148.10 (42.73%),
203.10 (37.34%), 188.10
(22.50%)
O
2b
Ethanimidic acid
Carbodiimide
5.092
H2N
CH3
171.10 (100.00%), 172.10
(16.28%), 173.00 (7.13%), 73.10
(7.12%), 78.00 (4.81%)
3b
5.292
HN
C
NH
CH3
2-methyl-5-(1-
methylethyl)
phenol
207.00 (100.00%), 73.10
(30.28%), 222.10 (26.26%),
208.10 (18.17%), 209.10 (5.21%)
OH
CH3
4a
12.438
CH3
OH
28.10 (100.00%), 151.00
(56.89%), 75.00 (31.69%), 32.00
(25.97%), 166.10 (16.69%)
147.10 (100.00%), 73.00
OH
5a
6.812
Benzene-1,2-diol
Propanedioic acid
O
O
6a
12.014
(67.79%), 305.20 (42.42%),
189.10 (33.03%), 75.00 (19.44%)
HO
OH
a Value corresponding to the trimethylsilyl derivative
b Value corresponding to the bis trimethylsilyl derivative
26

Fig. 1. Chemical structure of Basic Blue 3.
27

Fig 2. Schematic diagram of the glow discharge plasma system.
28

Fig. 3. Schematic of experimental set-up of catalytic ozonation system.
29