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Electro-assisted activation of peroxymonosulfate by iron-based minerals for the degradation of 1-butyl-1-methylpyrrolidinium chloride
Separation and Purification Technology xxx (xxxx) xxx–xxx
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Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Electro-assisted activation of peroxymonosulfate by iron-based minerals for the degradation of 1-butyl-1-methylpyrrolidinium chloride María Arellano, M. Angeles Sanromán, Marta Pazos
⁎
Centro de Investigación Tecnolóxico Industrial – MTI, University of Vigo, Campus As Lagoas-Marcosende, 36310 Vigo, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: 1-Butyl-1-methylpyrrolidinium chloride Peroxymonosulfate Sulfate radicals Electro-assisted activation Iron-based minerals
In the present study, the degradation of ionic liquid 1-butyl-1-methylpyrrolidinium chloride has been carried out through sulfate radicals. These radicals were generated by different methods of activation of the commercial peroxymonosulfate (PMS) formulation, Oxone®. Among them, the electro-assisted activation in presence of iron provided the best results in terms of pollutant removal and mineralization. However, radical scavenging takes place at high concentration of catalyst (Fe2+) in solution, that provokes the reduction of the removal rate. In order to control the iron self-regulation in the process, iron-based minerals such as pyrite, goethite and magnetite were studied as catalyst. This process was evaluated in detail and the key factors as catalyst concentration, oxidant dosage and applied current were analyzed. It was confirmed that the removal reaction in the heterogeneous system followed pseudo-first order kinetic model. Pyrite catalyst achieved the best results and its application was optimized. The activation of PMS (10 mM) by pyrite (1 mM) under electric field (150 mA) showed a very high pollutant degradation efficiency (over 80% TOC decay in 300 min) with a low electrical energy consumption per log-unit of pollutant concentration decrease (5.45 kWh m−3 order−1). In addition, the use of solid catalyst eased its separation from the reaction medium and its reuse at least 5 cycles, achieving in all cases a degradation efficiency near 100% in 300 min. This fact justifies the developed process as a promising treatment for a novel class of neoteric contaminants such as ionic liquids.
1. Introduction Advanced Oxidation Processes (AOPs) have gained the interest of more and more researchers, as they seem to be powerful methods for the removal of recalcitrant organic pollutants that the conventional treatments are not able to eliminate. These processes are based on the generation of powerful oxidants, which attack the pollutants until its mineralization. The most popular AOPs are based on Fenton process which generates hydroxyl radicals [1–4]. However, the generation of sulfate radicals is also taking the attention of scientific community and their application in the oxidation of several pollutants have been the subject of numerous investigations [5–9]. This is due to the fact that sulfate radicals have higher selectivity and longer half-life than hydroxyl radicals [10]. Recently, much attention has been paid to producing these radicals through activation of peroxymonosulfate (PMS) [11–14]. Therefore, the use of PMS has gained acceptance thanks to its great reactivity and its high potential in generating radicals. PMS is a potassium salt mainly used as a stable, nontoxic oxidant and easy to handle. Up to date, various methods of PMS activation to produce powerful oxidant agents such as sulfate or hydroxyl radicals have been
⁎
reported in literature, including the presence of transition metals or H2O2, heat energy, UV light, ultrasound, conduction electron and carbon catalysts [12,15]. As regards the transition metals for PMS activation, Co2+ has been widely used (Eq. (1)). However, there are some limitations in the application of homogeneous catalysts, being the most important the difficulty of their recovery. Thus, heterogeneous transition metals systems have reached a great interest [12]. HSO5− + Co2+ → SO4%− + HO− + Co3+
(1)
Carbon-based material (C), as a catalyst, has also been used for activation of PMS to generate radicals (Eq. (2)). These materials minimize the employment of metals and they can be considered as promising alternatives to toxic metals such as Co2+ [12]. HSO5− + C → SO4%− + HO− + AC+
(2)
Conversely, several studies have proved the effectiveness of employing energy for PMS activation. In this case, the peroxide bond in PMS is the target of scission and different forms of energy, such as UV irradiation or ultrasounds (Eqs. (3)–(4)), can be employed [12,14,16].
Corresponding author. E-mail address: [email protected] (M. Pazos).
https://doi.org/10.1016/j.seppur.2018.05.028 Received 28 February 2018; Received in revised form 10 May 2018; Accepted 14 May 2018 1383-5866/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Arellano, M., Separation and Purification Technology (2018), https://doi.org/10.1016/j.seppur.2018.05.028
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(3)
HSO5− + ))) → SO4%− + HO%
(4)
100
[bmpyr]Cl removal (%)
HSO5− + hν → SO4%− + HO%
In other ways, PMS, as an oxidant, can be used as electron acceptor in photocatalysis process [12]. The conduction electron decomposes PMS and generates sulfate or hydroxyl radicals (Eq. (5)). HSO5− + eCB− → SO4%− + HO− or + SO42− + HO%
(5)
Recently, electric current has also been used to activate PMS for degradation of different pollutants [17,18]. In this sense, sulfate radical can be produced by electron transfer reaction (Eq. (6)). HSO5− + e− → SO4%− + HO−
(6)
40 20
0
50
100
150
200
250
300
Time (min) Fig. 1. Evaluation of PMS activation through of the [bmpyr]Cl removal under different activation methods. In all tests it was used [bmpyr]Cl = 1.82 mM and PMS = 10 mM. For each trial, the experimental conditions were as follow: Fe2+ = 10 mM (circle), Fe2+ = 10 mM, 37 kHz, 174 W (triangle down), Fe2+ = 10 mM, UV 40 W (square), Na2SO4 = 10 mM, I = 100 mA (diamond), Fe2+ = 10 mM, Na2SO4 = 10 mM, I = 100 mA (triangle up).
2. Materials and methods 2.1. Chemicals
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1-butyl-1-methylpyrrolidinium chloride ([bmpyr]Cl) was acquired by IoLiTec. Oxone® (KHSO5·1/2KHSO4.1/2K2SO4), iron (II) sulfate heptahydrate (FeSO4·7H2O), sodium thiosulfate anhydrous (Na2S2O3) and sodium sulfate anhydrous (Na2SO4) were purchased from SigmaAldrich. Pyrite (iron (II) sulphide, FeS2), goethite (α-iron (III) oxide, FeO(OH)) and magnetite (iron (II, III) oxide, Fe3O4), used as iron sources, were acquired by Sigma-Aldrich.
On the other hand, pyrite mineral is able to regulate iron ions in the solution in the presence of O2 according to the following reaction (Eq. (8)) [24]. 2FeS2 + 7O2 + 2H2O → 2Fe2+ + 4SO42− + 4H+
60
0
Among all of the methods mentioned above, in the last years, the application of heterogeneous catalysts in AOPs has attracted the attention of the scientific community. Accordingly, solid catalysts just like zero-valent iron, magnetite and hematite were used to replace Fe2+ in different AOPs [19,20]. It is expected that these catalysts favor the self-regulation of the iron present in the media avoiding the scavenger effect. The activity of iron on the surface of catalyst it is not well defined under the electric field action in comparison to free iron and depends on the iron species present on the mineral [21,22]. Thus, it is postulated that Fe3+ on the surface of iron oxides can be converted to Fe2+ by cathodic reduction (Eq. (7)) under the electric field action [23]. ^Fe3+ + e− → ^Fe2+
80
(8)
However, most of the studies are accomplished by the removal of traditional pollutants as dyes or phenolic compounds, and a reduced number of researches has been focused their efforts on emerging pollutants such as pesticides or pharmaceuticals [12,25,26]. Lately, ionic liquids have attracted the attention due to their great versatility since they could widely be used for industrial application. Nevertheless, because of their great stability, they could move through traditional treatment systems to become persistent pollutants in the environment. Several studies have demonstrated the toxicity and low biodegradability of these compounds [27,28]. Hence, ionic liquids have been classified as a group of neoteric contaminants [29] and it is necessary to develop strategies to degrade them. In the present study, the ionic liquid 1-butyl-1-methylpyrrolidinium chloride ([bmpyr]Cl) was selected in order to evaluate the potential use of the commercial PMS formulation, Oxone®, as active oxidant for this contaminant. This compound belongs to the family of pyrrolidinium and, among different applications, it has been recently proposed as an effective corrosion inhibitor of the current collector in an electrolyte containing magnesium chloride complex [30]. To our knowledge, the present study is the first attempt in which PMS is used for the removal of ionic liquids, therefore, this fact highlights the novelty of the developed research. The aim of this research was to investigate the performance of sulfate radicals to degrade a recalcitrant contaminant [bmpyr]Cl through the examination of various methods of PMS activation, including the addition of iron or the combination with other technology such as ultrasound, ultraviolet radiation, electric field or their combinations. The electric field activation along with iron provided the best performance and this process was studied in detail and the key factors as catalyst source and concentration, PMS dosage and applied current were analyzed by which the best experimental conditions were identified.
2.2. Experimental procedures The experiments were carried out in a 600 mL cylindrical glass reactor containing 300 mL of solution. The [bmpyr]Cl initial concentration was 1.85 mM. Although the solution pH was not regulated, it was maintained around 2 during the experiments in presence of PMS. Different trials were performed in order to achieve the degradation of [bmpyr]Cl through sulfate radicals. In all of them, Oxone®, was added to the solution and different activation methods were studied: – Electrochemical experiments (EC) were accomplished with a twoelectrode system, using carbon felt as cathode and boron-doped diamond (BDD) as anode. Carbon felt (25.5 × 5 cm) was placed on the inner wall of the reactor, whereas BDD (5 × 2.5 × 0.2 cm; both sides are active) was located on the center. A constant current was applied by a direct-current power supply (Blausonic FA-350). Sodium sulfate (10 mM) was added as a supporting electrolyte. In these trials, different concentration ratios of iron and PMS were studied. – Ultrasonic (US) tests were performed in a Fisherbrand™ FB11203 Ultrasonic Cleaner with a power of 174 W and a frequency of 37 kHz [31], using the same PMS and iron concentrations of 10 mM (Fe2+/ US). – Ultraviolet (UV) light assays were carried out with a light emitting diode (LED) lamp of 40 W (λmax 365 nm) provided by LuckyLight Electronics Co, Ltd, and it was placed 1 cm from the bottom [32]. Similar that the US experiments, both concentrations of PMS and iron were 10 mM (Fe2+/UV).
2
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80
80
TOC decay (%)
100
[bmpyr]Cl removal (%)
100
60 40 20
60 40 20
0
0 0
50
100
150
200
250
0.1
300
Time (min)
1
10
25
Iron concentration (mM)
Fig. 2. Effect of iron concentration on [bmpyr]Cl removal ([Fe2+] = 0.1 mM (circle), 1 mM (triangle down), 10 mM (square), 25 mM (diamond)) (left) and TOC decay (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, I = 100 mA.
2.3.3. Iron concentration The concentration of Fe was determined by spectrophotometric method at 510 nm after complexing with 1,10-phenanthroline using a UV–Vis spectrophotometer [33].
Table 1 Pseudo-first order kinetics for the different assays. [PMS] (mM)
[Fe2+] (mM)
Source of iron
Pseudo-first order kinetics k (min−1)
R2
10
25 10 1 0.1
FeSO4·7H2O
0.0021 0.0068 0.0161 0.0144
0.9991 0.9894 0.9949 0.9837
10
25
Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4
0.0169 0.0135 0.0139 0.0190 0.0187 0.0168 0.0144 0.0150 0.0145
0.9827 0.9728 0.9876 0.9749 0.9618 0.9719 0.9944 0.9958 0.9996
Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4
0.0165 0.0147 0.0131 0.0161 0.0132 0.0127
0.9990 0.9390 0.9676 0.9889 0.9659 0.9675
10
1
25
25
10
2.3.4. Electrical energy consumption The electrical energy consumption per order of magnitude (EE/O) was calculated in order to shown the process efficiency. EE/O is defined as the amount of electrical energy in kilowatt hours (kWh) required to reduce the initial pollutant concentration by one order of magnitude in 1 m3 of contaminated water. The EE/O (kWh m−3 order−1) can be calculated from the following Eq. (9) [34,35].
EE Pel × t P × 3.84∙10−2 = = el O V × log (C0/ Cf ) V×k
(9)
where Pel is the cell power (kW), t is the time (h), V is the cell volume (m3), C0 and Cf are the initial and final pollutant concentration respectively, and k is the kinetic constant for a pseudo-first order reaction (min−1) for the removal of the pollutant concentration. 3. Results and discussion 3.1. Study of several PMS activation methods
In all assays, the solution was continuously mixed with a magnetic stirrer to avoid concentration gradients and they were conducted at room temperature. Samples were withdrawn periodically from the reactor and quenched using sodium thiosulfate.
The PMS activation was evaluated through of the efficiency on the [bmpyr]Cl removal using different methods: (i) Direct iron addition 10 mM (Fe2+), (ii) iron 10 mM in combination with ultrasounds (Fe2+/ US), (iii) iron 10 mM in conjunction with ultraviolet light (Fe2+/UV), (iv) current intensity of 100 mA (EC) and (v) EC in the presence of iron 10 mM (Fe2+/EC). The profiles of the [bmpyr]Cl reduction during the different treatments are presented in Fig. 1. It can be seen that PMS activated with iron (ratio 10 mM:10 mM) generated an initial removal around 13% and it was kept along the time. The combinations with US or UV increased slightly the initial removal values, 15.4 and 20.3% respectively. However, the removal reached at initial stage was kept constant until the end of the experiments. On the other hand, the electric field clearly improved the process, and the [bmpyr]Cl was gradually removed during the treatment reaching levels around 96.4% of reduction after 300 min of treatment. This fact demonstrates that the electric field can be an alternative to activate the generation of sulfate and hydroxyl radicals based on the chemical reactions described by Wang and Chu [18] (Eq. (6) and (10)).
2.3. Analytical methods 2.3.1. Ionic liquid concentration The degradation of [bmpyr]Cl was monitored by ionic chromatography with a conductivity detector (Metrohm 733 IC) equipped with a column Dionex™ IonPac™ CS12 (4 × 250 mm) (CACTI, University of Vigo). The isocratic eluent nitric acid/acetonitrile (4 mM HNO3 + 50% ACN) was pumped at a rate of 1 mL min−1 for 20 min. Prior to injection, samples were filtered through a 0.45 µm filter. The injection volume was set at 25 µL and the separation was carried out at 30 °C.
2.3.2. Total organic carbon The mineralization pollutant was monitored from total organic carbon (TOC) decay, measured via catalytic high-temperature combustion by multi N/C 3100 equipment (Analytic Jena) coupled with a non-dispersive infrared (NDIR) detector (CACTI, University of Vigo).
HSO5− + e− → SO42− + OH%
(10)
Contrary to what was expected, the presence of iron in the electrochemical activation of PMS, Fe2+/EC assay, reduced the removal 3
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70 60
80
TOC decay (%)
[bmpyr]Cl removal (%)
100
60 40 20
20
a
70 60
80
TOC decay (%)
[bmpyr]Cl removal (%)
30
0
100
60 40 20
50 40 30 20 10
b
0
b
0
100
70 60
80
TOC decay (%)
[bmpyr]Cl removal (%)
40
10
a
0
50
60 40 20
50 40 30 20 10
c 0
0 0
50
100
150
200
250
300
c 25
10
1
Iron concentracion (mM)
Time (min)
Fig. 3. Effect of iron source (pyrite (a), goethite (b), magnetite (c)) and its concentration on [bmpyr]Cl removal ([Fe2+] = 25 mM (circle), 10 mM (triangle down), 1 mM (square)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line), 300 min (horizontal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, I = 100 mA.
rate in comparison to that obtained using alone the electric field. Thus, the removal achieved after the treatment was around 86.3%. TOC analysis of the final samples was performed in order to validate the degradation of the pollutant in the different treatments. Only the assays using the electrochemical activation (Fe2+/EC and EC) reached a significant TOC decay, around 30%. Several authors have reported the use of electrochemical activation of PMS using iron [18,17]. Wang and Chu [18] informed a synergistic effect by coupling ferrous mediated activation of PMS with electrochemical activation of PMS. Accordingly, the electric field produces the direct activation of the PMS (Eq. (6) and (10)), and the regeneration of the catalyst (Eq. (11)) which is used in the activation of PMS (Eq. (12)). Fe3+ + e− → Fe2+
(11)
HSO5− + Fe2+ → Fe3+ + SO4%− + OH−
(12)
concentration [36]. In the PMS/EC/Fe2+ experiments, the Fe2+ is regenerated by the reduction of Fe3+ at cathode (Eq. (11)), which maintains a higher level of catalyst in the solution, while the PMS concentration is decreasing along the time. Therefore, the reduction of the degradation rate could be attributed to this fact. 3.2. Effect of Fe2+ concentration on the Fe2+/EC activation method Based on the previous results, the effect of iron concentration was investigated in order to analyze its influence on the PMS activation under electric field. In the Fig. 2 (left), the removal profiles of [bmpyr]Cl using 0.1, 1, 10 and 25 mM of iron in solution are presented. These new experiments confirm the hypothesis previously reported. An important reduction on the removal rate was observed at the highest concentration, 25 mM, and the reached pollutant removal was closely to 20%. These results are in agreement with Rastogi et al [36] who reported that the excess ferrous ions may act as sulfate radical scavengers as shown in the Eq. (13):
However, in the present study this effect was not detected. It is well known that the iron activation of PMS is influenced by catalyst concentration and different researches have reported scavenger episodes in presence of high concentration of catalyst with regard to PMS
Fe2+ + SO4%− → Fe3+ + SO42− 4
(13)
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[bmpyr]Cl removal (%)
100
70 60
TOC decay (%)
80 60 40
50 40 30 20
20
10
a
0
100
70
[bmpyr]Cl removal (%)
0
60
TOC decay (%)
80 60 40 20
50 40 30 20 10
b 0
b
0
100
70 60
80
TOC decay (%)
[bmpyr]Cl removal (%)
a
60 40 20
c 50
100
150
200
250
40 30 20 10
0 0
50
c
0
300
10
25
Iron concentration (mM)
Time (min)
Fig. 4. Effect of increased PMS dosage and different concentrations of iron (pyrite (a), goethite (b), magnetite (c)) on [bmpyr]Cl removal ([Fe2+] = 25 mM (circle), 10 mM (triangle down)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line), 300 min (horizontal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 25 mM, Na2SO4 = 10 mM, I = 100 mA.
100
80
80
TOC decay (%)
[bmpyr]Cl removal (%)
100
60 40
60
40
20
20 0 0
50
100
150
200
250
0
300
25
50
100
150
Current intensity (mA)
Time (min)
Fig. 5. Effect of current intensity on [bmpyr]Cl removal (I = 25 mA (circle), 50 mA (triangle down), 100 mA (square), 150 mA (diamond)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
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activation of PMS under electric field action.
Table 2 Pseudo-first order kinetics for assays testing current intensity. PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
25 50 100 150
EE/O (kWh m-3order-1)
3.3. Effect of iron source on the EC activation method
Pseudo-first order kinetics k (min−1)
R2
0.0041 0.0090 0.0144 0.0170
0.9960 0.9945 0.9944 0.9946
10
0.5
8
0.4
6
0.3
4
0.2
2
0.1
0
In the present research, natural iron sources pyrite (FeS2), goethite (FeO(OH)) and magnetite (Fe3O4) were evaluated for the electro-assisted activation of PMS to generate sulfate radicals. Therefore, the electro-activation of PMS process was accomplished in presence of the selected minerals (Fig. 3). Based on the previous results, the amount used of each mineral was selected in order to achieve an iron concentration in suspension of 1 mM, 10 mM and 25 mM. For all assays, complete depletion of [bmpyr]Cl was reached after 300 min (Fig. 3 left). However, the removal rates were different depending on the mineral used. Kinetic studies were performed with the obtained data. Several models were evaluated, and pseudo-firstorder kinetic model fitted well to the [bmpyr]Cl removal in the electroassisted systems, achieving the highest correlation coefficients (Table 1). This finding is in agreement with those reported by Lin et al. [38] and Cai et al. [39] who demonstrated that the pseudo-first-order model describes well the removal of the Orange II dye pollutant in the electro-assisted heterogeneous activation of peroxydisulfate or persulfate species, respectively. Among the different assays, the highest kinetic constants were obtained when pyrite was used as catalyst (Table 1); therefore, pyrite is postulated as an appropriate candidate for PMS activation under the electric field. The [bmpyr]Cl mineralization should be also analyzed in order to demonstrate the good performance of the developed treatment. Consequently, the reduction of TOC was measured in the assays (Fig. 3 right). Similarly to previous results, it was confirmed that the higher concentration of catalyst (25 mM) produced a reduction on the TOC removal rate. At the studied concentrations, pyrite achieved the highest TOC abatement (higher than 60% in 300 min). However, there was not so much difference working at low levels, 1 mM or 10 mM. The iron released in the effluent can be a drawback in the use of pyrite as catalyst, thus, iron concentration was measured in the solution at the end of the pyrite experiments and it was determined the concentrations of iron were 2.64 mM, 0.43 mM and 0.06 mM for iron suspension as pyrite 25 mM, 10 mM and 1 mM, respectively. Based on the TOC decay and iron leaching it seems that pyrite at the lower concentration (1 mM iron in suspension) was the best option for the activation of 10 mM of PMS. The obtained results also evidence that in the electro-assisted activation of PMS by pyrite a very low concentration of iron in solution is necessary which points out the applicability at industrial scale of the developed system. In order to verified the real effect of the combination of both electric field and iron, the results obtained in the optimized treatment (10 mM PMS and 1 mM iron in suspension as pyrite) were compared with and electrochemical convectional process. In both assays, the [bmpyr]Cl concentration was 1.82 mM, the current was 100 mA and the Na2SO4 concentration was 10 mM. The synergetic effect of electric field in the activation of PMS in presence of pyrite was demonstrated by the increase of the removal rate and also by the TOC abatement achieved in the combined treatment. The TOC was almost duplicated in the electroactivation process (62.8% TOC decay) in comparison to conventional electrochemical treatment (34.0% TOC decay). The concentration of PMS should be also analyzed in order to accomplish a more efficient treatment. Thus, the electro-activation of PMS was carried out increasing the initial concentration to 25 mM and several concentrations of mineral catalyst were evaluated (Fig. 4). Contrasting to previous assays, there was no significant influence in the removal profiles varying the concentration of the catalyst from 10 mM to 25 mM (Fig. 4 left). The kinetic study also demonstrated that the increase of the initial concentration of PMS did not achieved higher removal rates in comparison to previous assays working with and initial concentration of 10 mM of PMS (Table 1). This behavior was also experimented in the TOC decay profiles (Fig. 4 right). The maximum
Iron concentration (mM)
Current intensity (mA)
0.0 25
100
50
150
Current intensity (mA)
0.5
100
0.4
80
0.3
60 40
0.2
20
0.1
0
Iron concentration (mM)
[bmpyr]Cl removal and TOC decay (%)
Fig. 6. EE/O calculated in kWh m−3 order−1 (bars) and leaching of iron from pyrite (dots) in the assays testing current intensity. Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
0.0 1
2
3
4
5
Reuses of pyrite Fig. 7. Reusability of pyrite in order of [bmpyr]Cl removal (bar filled of dots) and TOC decay (bar filled of diagonal lines). Leaching of iron from pyrite represented by dots. Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe, I = 150 mA.
As described by Guinea et al. [37], other possible factor that reduces the system efficiency could be the formation of Fe3+ complexes with carboxylic acids. The kinetic study demonstrated that, for these assays, the removal rate followed pseudo-first kinetic model (Table 1). The iron concentrations of 1 and 0.1 mM obtained the highest kinetics constants, 0.0161 min−1 and 0.0144 min−1, respectively; reaching reduction degrees even highest than working with 10 mM of iron in solution. In order to determine the optimal concentration, TOC analysis were performed (Fig. 2 right). According to these decays, the concentration of 1 mM appears as the best concentration with a TOC decay higher than 60% after 300 min. These results are in agreement with Lin et al. [17] who reported that concentrations of iron higher than 2 mM decrease the efficiency of the degradation of clofibric acid in the 6
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reached removals were around 60% using the different catalysts. According to Ling et al. [40], the poor performance at high PMS concentration can be explained by the unfavorable consumption of sulfate radicals by the excessive PMS, which leads to the scavenging of sulfate radicals, generating of less reactive SO5%− as explained by Eq. (14):
were below 0.15 mM. The reported results disclosed that pyrite particles possess high stability and can be reutilized well for the activation of PMS under electro-assisted process.
HSO5− + SO4%− → SO5%− + SO42− + H+
In this study, the electro-activation of PMS in presence of iron-based mineral as catalyst was postulated as the best option in degrading the ionic liquid [bmpyr]Cl. The removal of this pollutant by the electroassisted system was observed to follow pseudo first-order kinetics. The effect of various operational parameters, such as catalyst concentration, oxidant dosage and applied current were also examined to optimize the process. Based on the test results, the activation of PMS (10 mM) by pyrite (1 mM iron in suspension) under electric field (150 mA) showed a very high pollutant degradation efficiency (over 80% TOC decay within 300 min) with a very low electrical energy consumption per log-unit of pollutant concentration decrease (5.45 kWh m−3 order−1). In addition, the catalyst can be utilized in several cycles without losing its good performance in the developed treatment. Therefore, the combination of anodic oxidation with pyrite activation of PMS is an efficient approach in eliminating complex pollutants as ionic liquids. The designed process in the present study, electro-assisted activation of PMS in presence of pyrite, is an interesting approach never reported in the existing literature. This fact points out the innovative technology presented, nevertheless more studies are required in order to scale up the process.
4. Conclusions
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Because of the overdose of PMS, the radicals remaining in the solution are still in good quantities, and the overall removal [bmpyr]Cl is not affected as long as the reaction time is sufficient. The obtained results demonstrated that the determination of an optimal PMS dosage is critical for an efficient application. 3.4. Effect of current intensity on the pyrite EC activation method Based on the previous results, pyrite (1 mM iron in solution) was selected as the best catalyst in the electro-activation of PMS (10 mM) in the degradation of [bmpyr]Cl (1.85 mM). Then, the influence of the applied current intensity was investigated with different values at the range of 25–150 mA. As depicted in Fig. 5, there was a clear relationship between the current intensities and the removal rates. Accordingly, the concentration of pollutant declined significantly at higher current values (100–150 mA). This fact was in accordance with the proposed mechanism of the process. When current intensity increased, more hydroxyl radicals are formed on the anode surface (Eq. (15)) and the generation of sulfate and hydroxyl radicals via electron transfer reaction is also raised (Eqs. (6) and (10)). Furthermore, the increase of current intensity enhanced the regeneration of Fe3+ to Fe2+, thus accelerating the activation of PMS to produce sulfate radical (Eq. (12)). M(H2O) → M(OH%) + H+ + e−
Acknowledgments This research has been financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and European Regional Development Funds (Project CTM2014-52471-R). María Arellano is grateful to Xunta de Galicia and European Union (European Social Fund – ESF) for her PhD grant.
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As a result, when the current intensity increases from 25 to 150 mA the removal percentages of [bmpyr]Cl after 60 min increased from 26.9 to 77.7% (Fig. 5 left) and the TOC decay at the end of the treatment (300 min) augmented from 8.74% to 80%, accordingly (Fig. 5 right). The kinetic study at different intensities also demonstrated that the kinetic constants raised according to the current intensity applied (Table 2). In addition, the leaching of iron was less than 0.1 mM, which is below the legal limits (0.2 mM) [41] (Fig. 6). This fact is a great advantage of the developed process with regard to the other existing technologies. Thus, the present study provides an innovative solution reducing the impact of the catalyst release in the environment. To stablish a cost-efficient treatment, the electrical consumption should be also study. For this purpose, the EE/O value was calculated for the different current intensities (Fig. 6). This value growth as the current intensity increased from 25 mA to 150 mA, reaching a maximum of 5.45 kWh m−3 order−1. Nevertheless, the EE/O values were low in comparison to existing literature. As example, Cai et al. [39] in the electro-assisted heterogeneous activation of persulfate by Fe/SBA15 for the degradation of Orange I reported a value of 9.87 kWh m−3 order−1. This fact indicates that the developed system is an efficient method for pollutant removal in a water stream [42].
References [1] N. Oturan, C.T. Aravindakumar, H. Olvera-Vargas, M.M. Sunil Paul, M.A. Oturan, Electro-Fenton oxidation of para-aminosalicylic acid: degradation kinetics and mineralization pathway using Pt/carbon-felt and BDD/carbon-felt cells, (n.d.). http:// doi.org/10.1007/s11356-017-9309-6. [2] E. Brillas, C.A. Martínez-Huitle, Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review, Appl. Catal. B Environ. (2015) 166–167, http://dx.doi.org/10.1016/j.apcatb.2014.11.016. [3] C. Salazar, C. Ridruejo, E. Brillas, J.Y. Nez, H.D. Mansilla, I. Sirés, Abatement of the fluorinated antidepressant fluoxetine (Prozac) and its reaction by-products by electrochemical advanced methods, Appl. Catal. B Environ. 203 (2017) 189–198, http://dx.doi.org/10.1016/j.apcatb.2016.10.026. [4] L. Ma, M. Zhou, G. Ren, W. Yang, L. Liang, A highly energy-efficient flow-through electro-Fenton process for organic pollutants degradation, Electrochim. Acta 200 (2016) 222–230, http://dx.doi.org/10.1016/j.electacta.2016.03.181. [5] Y. Wu, R. Prulho, M. Brigante, W. Dong, K. Hanna, G. Mailhot, Activation of persulfate by Fe(III) species: implications for 4-tert-butylphenol degradation, J. Hazard. Mater. 322 (2017) 380–386, http://dx.doi.org/10.1016/j.jhazmat.2016. 10.013. [6] C. Luo, J. Jiang, J. Ma, S. Pang, Y. Liu, Y. Song, C. Guan, J. Li, Y. Jin, D. Wu, Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: kinetics, products, and pathways, Water Res. 96 (2016) 12–21, http://dx. doi.org/10.1016/j.watres.2016.03.039. [7] L.W. Matzek, K.E. Carter, Activated persulfate for organic chemical degradation: a review, Chemosphere 151 (2016) 178–188, http://dx.doi.org/10.1016/j. chemosphere.2016.02.055. [8] Y. Fan, Y. Ji, D. Kong, J. Lu, Q. Zhou, Kinetic and mechanistic investigations of the degradation of sulfamethazine in heat-activated persulfate oxidation process, J. Hazard. Mater. 300 (2015) 39–47, http://dx.doi.org/10.1016/j.jhazmat.2015.06. 058. [9] H. Lin, J. Wu, H. Zhang, Degradation of bisphenol A in aqueous solution by a novel electro/Fe3+/peroxydisulfate process, Sep. Purif. Technol. 117 (2013) 18–23, http://dx.doi.org/10.1016/j.seppur.2013.04.026. [10] J. Wang, S. Wang, Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants, Chem. Eng. J. 334 (2017) 1502–1517, http://dx.doi.org/10.1016/j.cej.2017.11.059. [11] A. Takdastan, B. Kakavandi, M. Azizi, M. Golshan, Efficient activation of peroxymonosulfate by using ferroferric oxide supported on carbon/UV/US system: a new approach into catalytic degradation of bisphenol A, Chem. Eng. J. 331 (2018) 729–743, http://dx.doi.org/10.1016/J.CEJ.2017.09.021.
3.5. Reusability of the catalyst on the pyrite EC activation method The stability of the catalyst in a continuous process is one of the critical factors for its implementation at industrial scale. Therefore, the same pyrite particles were utilized for five consecutive cycles in order to evaluate the preservation of their catalytic activity. It could be noticed that no noticeable changes on [bmpyr]Cl removal were observed during these cycles (Fig. 7). For example, the TOC decay ranged from 79% to 68%, and the rate constants from 0.0170 to 0.0178 min−1, during the five cycles. In addition, the leaching concentrations of iron during these repeated cycles 7
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[27] A. Jordan, N. Gathergood, Biodegradation of ionic liquids – a critical review, Chem. Soc. Rev. 44 (2015) 8200–8237, http://dx.doi.org/10.1039/c5cs00444f. [28] T. Phuong, T. Pham, C.-W. Cho, Y.-S. Yun, Environmental fate and toxicity of ionic liquids: a review, Water Res. 44 (2010) 352–372, http://dx.doi.org/10.1016/j. watres.2009.09.030. [29] S.D. Richardson, S.Y. Kimura, Emerging environmental contaminants: challenges facing our next generation and potential engineering solutions, Environ. Technol. Innov. 8 (2017) 40–56, http://dx.doi.org/10.1016/j.eti.2017.04.002. [30] J.H. Ha, J.-H. Cho, J.H. Kim, B.W. Cho, S.H. Oh, 1-Butyl-1-methylpyrrolidinium chloride as an effective corrosion inhibitor for stainless steel current collectors in magnesium chloride complex electrolytes, J. Power Sources 355 (2017) 90–97, http://dx.doi.org/10.1016/j.jpowsour.2017.04.041. [31] A.B. Kurukutla, P.S.S. Kumar, S. Anandan, T. Sivasankar, Sonochemical degradation of rhodamine B using oxidants, hydrogen peroxide/peroxydisulfate/peroxymonosulfate, with Fe2+ ion: proposed pathway and kinetics, Environ. Eng. Sci. 32 (2015) 129–140, http://dx.doi.org/10.1089/ees.2014.0328. [32] A.M. Díez, E. Rosales, M.A. Sanromán, M. Pazos, Assessment of LED-assisted electro-Fenton reactor for the treatment of winery wastewater, Chem. Eng. J. 310 (2017) 399–406, http://dx.doi.org/10.1016/j.cej.2016.08.006. [33] APHA, AWWA, WPCF, Standard Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, American Water Works Association, Water Pollution Control Federation, Washington, DC, USA, 1998. [34] M.H. Chen, C.C. Chen, R.J. Wu, C.S. Lu, Heterogeneous photocatalytic degradation of disulfoton in aqueous TiO2 suspensions: parameter and reaction pathway investigations, J. Chin. Chem. Soc. 60 (2013) 380–390, http://dx.doi.org/10.1002/ jccs.201200027. [35] J.R. Bolton, K.G. Bircher, W. Tumas, C.A. Tolman, Figures-of-merit for the technical development and application of advanced oxidation technologies for both electricand solar-driven systems (IUPAC Technical Report), Pure Appl. Chem. 73 (2001) 627–637, http://dx.doi.org/10.1351/pac200173040627. [36] A. Rastogi, S.R. Al-Abed, D.D. Dionysiou, Sulfate radical-based ferrous–peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems, Appl. Catal. B Environ. 85 (2009) 171–179, http://dx.doi.org/10.1016/j. apcatb.2008.07.010. [37] E. Guinea, F. Centellas, J.A. Garrido, R.M. Rodríguez, C. Arias, P.L. Cabot, E. Brillas, Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe3+ using a boron-doped diamond electrode, Appl. Catal. B Environ. 89 (2009) 459–468, http://dx.doi.org/10.1016/j.apcatb.2009.01.004. [38] H. Lin, Y. Li, X. Mao, H. Zhang, Electro-enhanced goethite activation of peroxydisulfate for the decolorization of Orange II at neutral pH: efficiency, stability and mechanism, J. Taiwan Inst. Chem. Eng. 65 (2016) 390–398, http://dx.doi.org/10. 1016/j.jtice.2016.05.050. [39] C. Cai, Z. Zhang, H. Zhang, H. Zhang, Electro-assisted heterogeneous activation of persulfate by Fe/SBA-15 for the degradation of Orange II, J. Hazard. Mater. 313 (2016) 209–218, http://dx.doi.org/10.1016/j.jhazmat.2016.04.007. [40] S.K. Ling, S. Wang, Y. Peng, Oxidative degradation of dyes in water using Co2+/ H2O2 and Co2+ /peroxymonosulfate, J. Hazard. Mater. 178 (2010) 385–389, http://dx.doi.org/10.1016/j.jhazmat.2010.01.091. [41] Ley 5/2002, de 3 de junio, sobre vertidos de aguas residuales industriales a los sistemas públicos de saneamiento., Boletín Of. Del Estado. (2002) 13. https://www. boe.es/buscar/pdf/2002/BOE-A-2002-14187-consolidado.pdf (accessed May 7, 2018). [42] J.R. Bolton, S.R. Cater, Homogeneous photodegradation of pollutants in contaminated water. An Introduction, in: Surf. Aquat. Environ. Photochem., 1994: pp. 467–490.
[12] F. Ghanbari, M. Moradi, Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: review, Chem. Eng. J. 310 (2017) 41–62, http://dx.doi.org/10.1016/j.cej.2016.10.064. [13] N. Jaafarzadeh, F. Ghanbari, M. Alvandi, Integration of coagulation and electroactivated HSO5− to treat pulp and paper wastewater, Sustain. Environ. Res. 27 (2017) 223–229, http://dx.doi.org/10.1016/j.serj.2017.06.001. [14] R. Yin, W. Guo, H. Wang, J. Du, X. Zhou, Q. Wu, H. Zheng, J. Chang, N. Ren, Enhanced peroxymonosulfate activation for sulfamethazine degradation by ultrasound irradiation: performances and mechanisms, Chem. Eng. J. 335 (2018) 145–153, http://dx.doi.org/10.1016/j.cej.2017.10.063. [15] S. Wacławek, H.V. Lutze, K. Grübel, V.V. Padil, M. Černík, D.D. Dionysiou, Chemistry of persulfates in water and wastewater treatment: a review, Chem. Eng. J. 330 (2017) 44–62, http://dx.doi.org/10.1016/j.cej.2017.07.132. [16] Y. Rao, D. Xue, H. Pan, J. Feng, Y. Li, Degradation of ibuprofen by a synergistic UV/ Fe(III)/Oxone process, Chem. Eng. J. 283 (2016) 65–75, http://dx.doi.org/10. 1016/j.cej.2015.07.057. [17] H. Lin, J. Wu, H. Zhang, Degradation of clofibric acid in aqueous solution by an EC/ Fe3+/PMS process, Chem. Eng. J. 244 (2014) 514–521, http://dx.doi.org/10.1016/ j.cej.2014.01.099. [18] Y.R. Wang, W. Chu, Degradation of 2,4,5-trichlorophenoxyacetic acid by a novel electro-Fe(II)/oxone process using iron sheet as the sacrificial anode, Water Res. 45 (2011) 3883–3889, http://dx.doi.org/10.1016/j.watres.2011.04.034. [19] L. Gomathi Devi, M. Srinivas, M.L. Arunakumari, Heterogeneous advanced photoFenton process using peroxymonosulfate and peroxydisulfate in presence of zero valent metallic iron: a comparative study with hydrogen peroxide photo-Fenton process, J. Water Process Eng. 13 (2016) 117–126, http://dx.doi.org/10.1016/j. jwpe.2016.08.004. [20] F. Ghanbari, M. Moradi, M. Manshouri, Textile wastewater decolorization by zero valent iron activated peroxymonosulfate: compared with zero valent copper, J. Environ. Chem. Eng. 2 (2014) 1846–1851, http://dx.doi.org/10.1016/j.jece.2014. 08.003. [21] Y. Zhang, H.P. Tran, X. Du, I. Hussain, S. Huang, S. Zhou, W. Wen, Efficient pyrite activating persulfate process for degradation of p-chloroaniline in aqueous systems: a mechanistic study, Chem. Eng. J. 308 (2017) 1112–1119, http://dx.doi.org/10. 1016/j.cej.2016.09.104. [22] C.M. Sánchez-Sánchez, E. Expó Sito, J. Casado, V. Montiel, Goethite as a more effective iron dosage source for mineralization of organic pollutants by electro-Fenton process, Electrochem. Commun. (2006), http://dx.doi.org/10.1016/j.elecom.2006. 08.023. [23] V. Poza-Nogueiras, E. Rosales, M. Pazos, M.Á. Sanromán, Current advances and trends in electro-Fenton process using heterogeneous catalysts – a review, Chemosphere 201 (2018) 399–416, http://dx.doi.org/10.1016/j.chemosphere. 2018.03.002. [24] N. Barhoumi, N. Oturan, H. Olvera-Vargas, E. Brillas, A. Gadri, S. Ammar, M.A. Oturan, Pyrite as a sustainable catalyst in electro-Fenton process for improving oxidation of sulfamethazine. Kinetics, mechanism and toxicity assessment, Water Res. 94 (2016) 52–61, http://dx.doi.org/10.1016/j.watres.2016.02.042. [25] A. Ghauch, A. Baalbaki, M. Amasha, R. El Asmar, O. Tantawi, Contribution of persulfate in UV-254 nm activated systems for complete degradation of chloramphenicol antibiotic in water, Chem. Eng. J. 317 (2017) 1012–1025, http://dx. doi.org/10.1016/j.cej.2017.02.133. [26] S. Khan, X. He, H.M. Khan, D. Boccelli, D.D. Dionysiou, Efficient degradation of lindane in aqueous solution by iron (II) and/or UV activated peroxymonosulfate, J. Photochem. Photobiol. A Chem. 316 (2016) 37–43, http://dx.doi.org/10.1016/j. jphotochem.2015.10.004.
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Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Electro-assisted activation of peroxymonosulfate by iron-based minerals for the degradation of 1-butyl-1-methylpyrrolidinium chloride María Arellano, M. Angeles Sanromán, Marta Pazos
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Centro de Investigación Tecnolóxico Industrial – MTI, University of Vigo, Campus As Lagoas-Marcosende, 36310 Vigo, Spain
A R T I C LE I N FO
A B S T R A C T
Keywords: 1-Butyl-1-methylpyrrolidinium chloride Peroxymonosulfate Sulfate radicals Electro-assisted activation Iron-based minerals
In the present study, the degradation of ionic liquid 1-butyl-1-methylpyrrolidinium chloride has been carried out through sulfate radicals. These radicals were generated by different methods of activation of the commercial peroxymonosulfate (PMS) formulation, Oxone®. Among them, the electro-assisted activation in presence of iron provided the best results in terms of pollutant removal and mineralization. However, radical scavenging takes place at high concentration of catalyst (Fe2+) in solution, that provokes the reduction of the removal rate. In order to control the iron self-regulation in the process, iron-based minerals such as pyrite, goethite and magnetite were studied as catalyst. This process was evaluated in detail and the key factors as catalyst concentration, oxidant dosage and applied current were analyzed. It was confirmed that the removal reaction in the heterogeneous system followed pseudo-first order kinetic model. Pyrite catalyst achieved the best results and its application was optimized. The activation of PMS (10 mM) by pyrite (1 mM) under electric field (150 mA) showed a very high pollutant degradation efficiency (over 80% TOC decay in 300 min) with a low electrical energy consumption per log-unit of pollutant concentration decrease (5.45 kWh m−3 order−1). In addition, the use of solid catalyst eased its separation from the reaction medium and its reuse at least 5 cycles, achieving in all cases a degradation efficiency near 100% in 300 min. This fact justifies the developed process as a promising treatment for a novel class of neoteric contaminants such as ionic liquids.
1. Introduction Advanced Oxidation Processes (AOPs) have gained the interest of more and more researchers, as they seem to be powerful methods for the removal of recalcitrant organic pollutants that the conventional treatments are not able to eliminate. These processes are based on the generation of powerful oxidants, which attack the pollutants until its mineralization. The most popular AOPs are based on Fenton process which generates hydroxyl radicals [1–4]. However, the generation of sulfate radicals is also taking the attention of scientific community and their application in the oxidation of several pollutants have been the subject of numerous investigations [5–9]. This is due to the fact that sulfate radicals have higher selectivity and longer half-life than hydroxyl radicals [10]. Recently, much attention has been paid to producing these radicals through activation of peroxymonosulfate (PMS) [11–14]. Therefore, the use of PMS has gained acceptance thanks to its great reactivity and its high potential in generating radicals. PMS is a potassium salt mainly used as a stable, nontoxic oxidant and easy to handle. Up to date, various methods of PMS activation to produce powerful oxidant agents such as sulfate or hydroxyl radicals have been
⁎
reported in literature, including the presence of transition metals or H2O2, heat energy, UV light, ultrasound, conduction electron and carbon catalysts [12,15]. As regards the transition metals for PMS activation, Co2+ has been widely used (Eq. (1)). However, there are some limitations in the application of homogeneous catalysts, being the most important the difficulty of their recovery. Thus, heterogeneous transition metals systems have reached a great interest [12]. HSO5− + Co2+ → SO4%− + HO− + Co3+
(1)
Carbon-based material (C), as a catalyst, has also been used for activation of PMS to generate radicals (Eq. (2)). These materials minimize the employment of metals and they can be considered as promising alternatives to toxic metals such as Co2+ [12]. HSO5− + C → SO4%− + HO− + AC+
(2)
Conversely, several studies have proved the effectiveness of employing energy for PMS activation. In this case, the peroxide bond in PMS is the target of scission and different forms of energy, such as UV irradiation or ultrasounds (Eqs. (3)–(4)), can be employed [12,14,16].
Corresponding author. E-mail address: [email protected] (M. Pazos).
https://doi.org/10.1016/j.seppur.2018.05.028 Received 28 February 2018; Received in revised form 10 May 2018; Accepted 14 May 2018 1383-5866/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Arellano, M., Separation and Purification Technology (2018), https://doi.org/10.1016/j.seppur.2018.05.028
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(3)
HSO5− + ))) → SO4%− + HO%
(4)
100
[bmpyr]Cl removal (%)
HSO5− + hν → SO4%− + HO%
In other ways, PMS, as an oxidant, can be used as electron acceptor in photocatalysis process [12]. The conduction electron decomposes PMS and generates sulfate or hydroxyl radicals (Eq. (5)). HSO5− + eCB− → SO4%− + HO− or + SO42− + HO%
(5)
Recently, electric current has also been used to activate PMS for degradation of different pollutants [17,18]. In this sense, sulfate radical can be produced by electron transfer reaction (Eq. (6)). HSO5− + e− → SO4%− + HO−
(6)
40 20
0
50
100
150
200
250
300
Time (min) Fig. 1. Evaluation of PMS activation through of the [bmpyr]Cl removal under different activation methods. In all tests it was used [bmpyr]Cl = 1.82 mM and PMS = 10 mM. For each trial, the experimental conditions were as follow: Fe2+ = 10 mM (circle), Fe2+ = 10 mM, 37 kHz, 174 W (triangle down), Fe2+ = 10 mM, UV 40 W (square), Na2SO4 = 10 mM, I = 100 mA (diamond), Fe2+ = 10 mM, Na2SO4 = 10 mM, I = 100 mA (triangle up).
2. Materials and methods 2.1. Chemicals
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1-butyl-1-methylpyrrolidinium chloride ([bmpyr]Cl) was acquired by IoLiTec. Oxone® (KHSO5·1/2KHSO4.1/2K2SO4), iron (II) sulfate heptahydrate (FeSO4·7H2O), sodium thiosulfate anhydrous (Na2S2O3) and sodium sulfate anhydrous (Na2SO4) were purchased from SigmaAldrich. Pyrite (iron (II) sulphide, FeS2), goethite (α-iron (III) oxide, FeO(OH)) and magnetite (iron (II, III) oxide, Fe3O4), used as iron sources, were acquired by Sigma-Aldrich.
On the other hand, pyrite mineral is able to regulate iron ions in the solution in the presence of O2 according to the following reaction (Eq. (8)) [24]. 2FeS2 + 7O2 + 2H2O → 2Fe2+ + 4SO42− + 4H+
60
0
Among all of the methods mentioned above, in the last years, the application of heterogeneous catalysts in AOPs has attracted the attention of the scientific community. Accordingly, solid catalysts just like zero-valent iron, magnetite and hematite were used to replace Fe2+ in different AOPs [19,20]. It is expected that these catalysts favor the self-regulation of the iron present in the media avoiding the scavenger effect. The activity of iron on the surface of catalyst it is not well defined under the electric field action in comparison to free iron and depends on the iron species present on the mineral [21,22]. Thus, it is postulated that Fe3+ on the surface of iron oxides can be converted to Fe2+ by cathodic reduction (Eq. (7)) under the electric field action [23]. ^Fe3+ + e− → ^Fe2+
80
(8)
However, most of the studies are accomplished by the removal of traditional pollutants as dyes or phenolic compounds, and a reduced number of researches has been focused their efforts on emerging pollutants such as pesticides or pharmaceuticals [12,25,26]. Lately, ionic liquids have attracted the attention due to their great versatility since they could widely be used for industrial application. Nevertheless, because of their great stability, they could move through traditional treatment systems to become persistent pollutants in the environment. Several studies have demonstrated the toxicity and low biodegradability of these compounds [27,28]. Hence, ionic liquids have been classified as a group of neoteric contaminants [29] and it is necessary to develop strategies to degrade them. In the present study, the ionic liquid 1-butyl-1-methylpyrrolidinium chloride ([bmpyr]Cl) was selected in order to evaluate the potential use of the commercial PMS formulation, Oxone®, as active oxidant for this contaminant. This compound belongs to the family of pyrrolidinium and, among different applications, it has been recently proposed as an effective corrosion inhibitor of the current collector in an electrolyte containing magnesium chloride complex [30]. To our knowledge, the present study is the first attempt in which PMS is used for the removal of ionic liquids, therefore, this fact highlights the novelty of the developed research. The aim of this research was to investigate the performance of sulfate radicals to degrade a recalcitrant contaminant [bmpyr]Cl through the examination of various methods of PMS activation, including the addition of iron or the combination with other technology such as ultrasound, ultraviolet radiation, electric field or their combinations. The electric field activation along with iron provided the best performance and this process was studied in detail and the key factors as catalyst source and concentration, PMS dosage and applied current were analyzed by which the best experimental conditions were identified.
2.2. Experimental procedures The experiments were carried out in a 600 mL cylindrical glass reactor containing 300 mL of solution. The [bmpyr]Cl initial concentration was 1.85 mM. Although the solution pH was not regulated, it was maintained around 2 during the experiments in presence of PMS. Different trials were performed in order to achieve the degradation of [bmpyr]Cl through sulfate radicals. In all of them, Oxone®, was added to the solution and different activation methods were studied: – Electrochemical experiments (EC) were accomplished with a twoelectrode system, using carbon felt as cathode and boron-doped diamond (BDD) as anode. Carbon felt (25.5 × 5 cm) was placed on the inner wall of the reactor, whereas BDD (5 × 2.5 × 0.2 cm; both sides are active) was located on the center. A constant current was applied by a direct-current power supply (Blausonic FA-350). Sodium sulfate (10 mM) was added as a supporting electrolyte. In these trials, different concentration ratios of iron and PMS were studied. – Ultrasonic (US) tests were performed in a Fisherbrand™ FB11203 Ultrasonic Cleaner with a power of 174 W and a frequency of 37 kHz [31], using the same PMS and iron concentrations of 10 mM (Fe2+/ US). – Ultraviolet (UV) light assays were carried out with a light emitting diode (LED) lamp of 40 W (λmax 365 nm) provided by LuckyLight Electronics Co, Ltd, and it was placed 1 cm from the bottom [32]. Similar that the US experiments, both concentrations of PMS and iron were 10 mM (Fe2+/UV).
2
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80
80
TOC decay (%)
100
[bmpyr]Cl removal (%)
100
60 40 20
60 40 20
0
0 0
50
100
150
200
250
0.1
300
Time (min)
1
10
25
Iron concentration (mM)
Fig. 2. Effect of iron concentration on [bmpyr]Cl removal ([Fe2+] = 0.1 mM (circle), 1 mM (triangle down), 10 mM (square), 25 mM (diamond)) (left) and TOC decay (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, I = 100 mA.
2.3.3. Iron concentration The concentration of Fe was determined by spectrophotometric method at 510 nm after complexing with 1,10-phenanthroline using a UV–Vis spectrophotometer [33].
Table 1 Pseudo-first order kinetics for the different assays. [PMS] (mM)
[Fe2+] (mM)
Source of iron
Pseudo-first order kinetics k (min−1)
R2
10
25 10 1 0.1
FeSO4·7H2O
0.0021 0.0068 0.0161 0.0144
0.9991 0.9894 0.9949 0.9837
10
25
Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4
0.0169 0.0135 0.0139 0.0190 0.0187 0.0168 0.0144 0.0150 0.0145
0.9827 0.9728 0.9876 0.9749 0.9618 0.9719 0.9944 0.9958 0.9996
Fe2S FeO(OH) Fe3O4 Fe2S FeO(OH) Fe3O4
0.0165 0.0147 0.0131 0.0161 0.0132 0.0127
0.9990 0.9390 0.9676 0.9889 0.9659 0.9675
10
1
25
25
10
2.3.4. Electrical energy consumption The electrical energy consumption per order of magnitude (EE/O) was calculated in order to shown the process efficiency. EE/O is defined as the amount of electrical energy in kilowatt hours (kWh) required to reduce the initial pollutant concentration by one order of magnitude in 1 m3 of contaminated water. The EE/O (kWh m−3 order−1) can be calculated from the following Eq. (9) [34,35].
EE Pel × t P × 3.84∙10−2 = = el O V × log (C0/ Cf ) V×k
(9)
where Pel is the cell power (kW), t is the time (h), V is the cell volume (m3), C0 and Cf are the initial and final pollutant concentration respectively, and k is the kinetic constant for a pseudo-first order reaction (min−1) for the removal of the pollutant concentration. 3. Results and discussion 3.1. Study of several PMS activation methods
In all assays, the solution was continuously mixed with a magnetic stirrer to avoid concentration gradients and they were conducted at room temperature. Samples were withdrawn periodically from the reactor and quenched using sodium thiosulfate.
The PMS activation was evaluated through of the efficiency on the [bmpyr]Cl removal using different methods: (i) Direct iron addition 10 mM (Fe2+), (ii) iron 10 mM in combination with ultrasounds (Fe2+/ US), (iii) iron 10 mM in conjunction with ultraviolet light (Fe2+/UV), (iv) current intensity of 100 mA (EC) and (v) EC in the presence of iron 10 mM (Fe2+/EC). The profiles of the [bmpyr]Cl reduction during the different treatments are presented in Fig. 1. It can be seen that PMS activated with iron (ratio 10 mM:10 mM) generated an initial removal around 13% and it was kept along the time. The combinations with US or UV increased slightly the initial removal values, 15.4 and 20.3% respectively. However, the removal reached at initial stage was kept constant until the end of the experiments. On the other hand, the electric field clearly improved the process, and the [bmpyr]Cl was gradually removed during the treatment reaching levels around 96.4% of reduction after 300 min of treatment. This fact demonstrates that the electric field can be an alternative to activate the generation of sulfate and hydroxyl radicals based on the chemical reactions described by Wang and Chu [18] (Eq. (6) and (10)).
2.3. Analytical methods 2.3.1. Ionic liquid concentration The degradation of [bmpyr]Cl was monitored by ionic chromatography with a conductivity detector (Metrohm 733 IC) equipped with a column Dionex™ IonPac™ CS12 (4 × 250 mm) (CACTI, University of Vigo). The isocratic eluent nitric acid/acetonitrile (4 mM HNO3 + 50% ACN) was pumped at a rate of 1 mL min−1 for 20 min. Prior to injection, samples were filtered through a 0.45 µm filter. The injection volume was set at 25 µL and the separation was carried out at 30 °C.
2.3.2. Total organic carbon The mineralization pollutant was monitored from total organic carbon (TOC) decay, measured via catalytic high-temperature combustion by multi N/C 3100 equipment (Analytic Jena) coupled with a non-dispersive infrared (NDIR) detector (CACTI, University of Vigo).
HSO5− + e− → SO42− + OH%
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Contrary to what was expected, the presence of iron in the electrochemical activation of PMS, Fe2+/EC assay, reduced the removal 3
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c 0
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Fig. 3. Effect of iron source (pyrite (a), goethite (b), magnetite (c)) and its concentration on [bmpyr]Cl removal ([Fe2+] = 25 mM (circle), 10 mM (triangle down), 1 mM (square)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line), 300 min (horizontal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, I = 100 mA.
rate in comparison to that obtained using alone the electric field. Thus, the removal achieved after the treatment was around 86.3%. TOC analysis of the final samples was performed in order to validate the degradation of the pollutant in the different treatments. Only the assays using the electrochemical activation (Fe2+/EC and EC) reached a significant TOC decay, around 30%. Several authors have reported the use of electrochemical activation of PMS using iron [18,17]. Wang and Chu [18] informed a synergistic effect by coupling ferrous mediated activation of PMS with electrochemical activation of PMS. Accordingly, the electric field produces the direct activation of the PMS (Eq. (6) and (10)), and the regeneration of the catalyst (Eq. (11)) which is used in the activation of PMS (Eq. (12)). Fe3+ + e− → Fe2+
(11)
HSO5− + Fe2+ → Fe3+ + SO4%− + OH−
(12)
concentration [36]. In the PMS/EC/Fe2+ experiments, the Fe2+ is regenerated by the reduction of Fe3+ at cathode (Eq. (11)), which maintains a higher level of catalyst in the solution, while the PMS concentration is decreasing along the time. Therefore, the reduction of the degradation rate could be attributed to this fact. 3.2. Effect of Fe2+ concentration on the Fe2+/EC activation method Based on the previous results, the effect of iron concentration was investigated in order to analyze its influence on the PMS activation under electric field. In the Fig. 2 (left), the removal profiles of [bmpyr]Cl using 0.1, 1, 10 and 25 mM of iron in solution are presented. These new experiments confirm the hypothesis previously reported. An important reduction on the removal rate was observed at the highest concentration, 25 mM, and the reached pollutant removal was closely to 20%. These results are in agreement with Rastogi et al [36] who reported that the excess ferrous ions may act as sulfate radical scavengers as shown in the Eq. (13):
However, in the present study this effect was not detected. It is well known that the iron activation of PMS is influenced by catalyst concentration and different researches have reported scavenger episodes in presence of high concentration of catalyst with regard to PMS
Fe2+ + SO4%− → Fe3+ + SO42− 4
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[bmpyr]Cl removal (%)
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70 60
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20
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Fig. 4. Effect of increased PMS dosage and different concentrations of iron (pyrite (a), goethite (b), magnetite (c)) on [bmpyr]Cl removal ([Fe2+] = 25 mM (circle), 10 mM (triangle down)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line), 300 min (horizontal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 25 mM, Na2SO4 = 10 mM, I = 100 mA.
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Fig. 5. Effect of current intensity on [bmpyr]Cl removal (I = 25 mA (circle), 50 mA (triangle down), 100 mA (square), 150 mA (diamond)) (left) and TOC decay at 120 min (dot), 240 min (diagonal line) (right). Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
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activation of PMS under electric field action.
Table 2 Pseudo-first order kinetics for assays testing current intensity. PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
25 50 100 150
EE/O (kWh m-3order-1)
3.3. Effect of iron source on the EC activation method
Pseudo-first order kinetics k (min−1)
R2
0.0041 0.0090 0.0144 0.0170
0.9960 0.9945 0.9944 0.9946
10
0.5
8
0.4
6
0.3
4
0.2
2
0.1
0
In the present research, natural iron sources pyrite (FeS2), goethite (FeO(OH)) and magnetite (Fe3O4) were evaluated for the electro-assisted activation of PMS to generate sulfate radicals. Therefore, the electro-activation of PMS process was accomplished in presence of the selected minerals (Fig. 3). Based on the previous results, the amount used of each mineral was selected in order to achieve an iron concentration in suspension of 1 mM, 10 mM and 25 mM. For all assays, complete depletion of [bmpyr]Cl was reached after 300 min (Fig. 3 left). However, the removal rates were different depending on the mineral used. Kinetic studies were performed with the obtained data. Several models were evaluated, and pseudo-firstorder kinetic model fitted well to the [bmpyr]Cl removal in the electroassisted systems, achieving the highest correlation coefficients (Table 1). This finding is in agreement with those reported by Lin et al. [38] and Cai et al. [39] who demonstrated that the pseudo-first-order model describes well the removal of the Orange II dye pollutant in the electro-assisted heterogeneous activation of peroxydisulfate or persulfate species, respectively. Among the different assays, the highest kinetic constants were obtained when pyrite was used as catalyst (Table 1); therefore, pyrite is postulated as an appropriate candidate for PMS activation under the electric field. The [bmpyr]Cl mineralization should be also analyzed in order to demonstrate the good performance of the developed treatment. Consequently, the reduction of TOC was measured in the assays (Fig. 3 right). Similarly to previous results, it was confirmed that the higher concentration of catalyst (25 mM) produced a reduction on the TOC removal rate. At the studied concentrations, pyrite achieved the highest TOC abatement (higher than 60% in 300 min). However, there was not so much difference working at low levels, 1 mM or 10 mM. The iron released in the effluent can be a drawback in the use of pyrite as catalyst, thus, iron concentration was measured in the solution at the end of the pyrite experiments and it was determined the concentrations of iron were 2.64 mM, 0.43 mM and 0.06 mM for iron suspension as pyrite 25 mM, 10 mM and 1 mM, respectively. Based on the TOC decay and iron leaching it seems that pyrite at the lower concentration (1 mM iron in suspension) was the best option for the activation of 10 mM of PMS. The obtained results also evidence that in the electro-assisted activation of PMS by pyrite a very low concentration of iron in solution is necessary which points out the applicability at industrial scale of the developed system. In order to verified the real effect of the combination of both electric field and iron, the results obtained in the optimized treatment (10 mM PMS and 1 mM iron in suspension as pyrite) were compared with and electrochemical convectional process. In both assays, the [bmpyr]Cl concentration was 1.82 mM, the current was 100 mA and the Na2SO4 concentration was 10 mM. The synergetic effect of electric field in the activation of PMS in presence of pyrite was demonstrated by the increase of the removal rate and also by the TOC abatement achieved in the combined treatment. The TOC was almost duplicated in the electroactivation process (62.8% TOC decay) in comparison to conventional electrochemical treatment (34.0% TOC decay). The concentration of PMS should be also analyzed in order to accomplish a more efficient treatment. Thus, the electro-activation of PMS was carried out increasing the initial concentration to 25 mM and several concentrations of mineral catalyst were evaluated (Fig. 4). Contrasting to previous assays, there was no significant influence in the removal profiles varying the concentration of the catalyst from 10 mM to 25 mM (Fig. 4 left). The kinetic study also demonstrated that the increase of the initial concentration of PMS did not achieved higher removal rates in comparison to previous assays working with and initial concentration of 10 mM of PMS (Table 1). This behavior was also experimented in the TOC decay profiles (Fig. 4 right). The maximum
Iron concentration (mM)
Current intensity (mA)
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Fig. 6. EE/O calculated in kWh m−3 order−1 (bars) and leaching of iron from pyrite (dots) in the assays testing current intensity. Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe.
0.0 1
2
3
4
5
Reuses of pyrite Fig. 7. Reusability of pyrite in order of [bmpyr]Cl removal (bar filled of dots) and TOC decay (bar filled of diagonal lines). Leaching of iron from pyrite represented by dots. Experimental conditions: [bmpyr]Cl = 1.82 mM, PMS = 10 mM, Na2SO4 = 10 mM, pyrite = 1 mM Fe, I = 150 mA.
As described by Guinea et al. [37], other possible factor that reduces the system efficiency could be the formation of Fe3+ complexes with carboxylic acids. The kinetic study demonstrated that, for these assays, the removal rate followed pseudo-first kinetic model (Table 1). The iron concentrations of 1 and 0.1 mM obtained the highest kinetics constants, 0.0161 min−1 and 0.0144 min−1, respectively; reaching reduction degrees even highest than working with 10 mM of iron in solution. In order to determine the optimal concentration, TOC analysis were performed (Fig. 2 right). According to these decays, the concentration of 1 mM appears as the best concentration with a TOC decay higher than 60% after 300 min. These results are in agreement with Lin et al. [17] who reported that concentrations of iron higher than 2 mM decrease the efficiency of the degradation of clofibric acid in the 6
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reached removals were around 60% using the different catalysts. According to Ling et al. [40], the poor performance at high PMS concentration can be explained by the unfavorable consumption of sulfate radicals by the excessive PMS, which leads to the scavenging of sulfate radicals, generating of less reactive SO5%− as explained by Eq. (14):
were below 0.15 mM. The reported results disclosed that pyrite particles possess high stability and can be reutilized well for the activation of PMS under electro-assisted process.
HSO5− + SO4%− → SO5%− + SO42− + H+
In this study, the electro-activation of PMS in presence of iron-based mineral as catalyst was postulated as the best option in degrading the ionic liquid [bmpyr]Cl. The removal of this pollutant by the electroassisted system was observed to follow pseudo first-order kinetics. The effect of various operational parameters, such as catalyst concentration, oxidant dosage and applied current were also examined to optimize the process. Based on the test results, the activation of PMS (10 mM) by pyrite (1 mM iron in suspension) under electric field (150 mA) showed a very high pollutant degradation efficiency (over 80% TOC decay within 300 min) with a very low electrical energy consumption per log-unit of pollutant concentration decrease (5.45 kWh m−3 order−1). In addition, the catalyst can be utilized in several cycles without losing its good performance in the developed treatment. Therefore, the combination of anodic oxidation with pyrite activation of PMS is an efficient approach in eliminating complex pollutants as ionic liquids. The designed process in the present study, electro-assisted activation of PMS in presence of pyrite, is an interesting approach never reported in the existing literature. This fact points out the innovative technology presented, nevertheless more studies are required in order to scale up the process.
4. Conclusions
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Because of the overdose of PMS, the radicals remaining in the solution are still in good quantities, and the overall removal [bmpyr]Cl is not affected as long as the reaction time is sufficient. The obtained results demonstrated that the determination of an optimal PMS dosage is critical for an efficient application. 3.4. Effect of current intensity on the pyrite EC activation method Based on the previous results, pyrite (1 mM iron in solution) was selected as the best catalyst in the electro-activation of PMS (10 mM) in the degradation of [bmpyr]Cl (1.85 mM). Then, the influence of the applied current intensity was investigated with different values at the range of 25–150 mA. As depicted in Fig. 5, there was a clear relationship between the current intensities and the removal rates. Accordingly, the concentration of pollutant declined significantly at higher current values (100–150 mA). This fact was in accordance with the proposed mechanism of the process. When current intensity increased, more hydroxyl radicals are formed on the anode surface (Eq. (15)) and the generation of sulfate and hydroxyl radicals via electron transfer reaction is also raised (Eqs. (6) and (10)). Furthermore, the increase of current intensity enhanced the regeneration of Fe3+ to Fe2+, thus accelerating the activation of PMS to produce sulfate radical (Eq. (12)). M(H2O) → M(OH%) + H+ + e−
Acknowledgments This research has been financially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and European Regional Development Funds (Project CTM2014-52471-R). María Arellano is grateful to Xunta de Galicia and European Union (European Social Fund – ESF) for her PhD grant.
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As a result, when the current intensity increases from 25 to 150 mA the removal percentages of [bmpyr]Cl after 60 min increased from 26.9 to 77.7% (Fig. 5 left) and the TOC decay at the end of the treatment (300 min) augmented from 8.74% to 80%, accordingly (Fig. 5 right). The kinetic study at different intensities also demonstrated that the kinetic constants raised according to the current intensity applied (Table 2). In addition, the leaching of iron was less than 0.1 mM, which is below the legal limits (0.2 mM) [41] (Fig. 6). This fact is a great advantage of the developed process with regard to the other existing technologies. Thus, the present study provides an innovative solution reducing the impact of the catalyst release in the environment. To stablish a cost-efficient treatment, the electrical consumption should be also study. For this purpose, the EE/O value was calculated for the different current intensities (Fig. 6). This value growth as the current intensity increased from 25 mA to 150 mA, reaching a maximum of 5.45 kWh m−3 order−1. Nevertheless, the EE/O values were low in comparison to existing literature. As example, Cai et al. [39] in the electro-assisted heterogeneous activation of persulfate by Fe/SBA15 for the degradation of Orange I reported a value of 9.87 kWh m−3 order−1. This fact indicates that the developed system is an efficient method for pollutant removal in a water stream [42].
References [1] N. Oturan, C.T. Aravindakumar, H. Olvera-Vargas, M.M. Sunil Paul, M.A. Oturan, Electro-Fenton oxidation of para-aminosalicylic acid: degradation kinetics and mineralization pathway using Pt/carbon-felt and BDD/carbon-felt cells, (n.d.). http:// doi.org/10.1007/s11356-017-9309-6. [2] E. Brillas, C.A. Martínez-Huitle, Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. An updated review, Appl. Catal. B Environ. (2015) 166–167, http://dx.doi.org/10.1016/j.apcatb.2014.11.016. [3] C. Salazar, C. Ridruejo, E. Brillas, J.Y. Nez, H.D. Mansilla, I. Sirés, Abatement of the fluorinated antidepressant fluoxetine (Prozac) and its reaction by-products by electrochemical advanced methods, Appl. Catal. B Environ. 203 (2017) 189–198, http://dx.doi.org/10.1016/j.apcatb.2016.10.026. [4] L. Ma, M. Zhou, G. Ren, W. Yang, L. Liang, A highly energy-efficient flow-through electro-Fenton process for organic pollutants degradation, Electrochim. Acta 200 (2016) 222–230, http://dx.doi.org/10.1016/j.electacta.2016.03.181. [5] Y. Wu, R. Prulho, M. Brigante, W. Dong, K. Hanna, G. Mailhot, Activation of persulfate by Fe(III) species: implications for 4-tert-butylphenol degradation, J. Hazard. Mater. 322 (2017) 380–386, http://dx.doi.org/10.1016/j.jhazmat.2016. 10.013. [6] C. Luo, J. Jiang, J. Ma, S. Pang, Y. Liu, Y. Song, C. Guan, J. Li, Y. Jin, D. Wu, Oxidation of the odorous compound 2,4,6-trichloroanisole by UV activated persulfate: kinetics, products, and pathways, Water Res. 96 (2016) 12–21, http://dx. doi.org/10.1016/j.watres.2016.03.039. [7] L.W. Matzek, K.E. Carter, Activated persulfate for organic chemical degradation: a review, Chemosphere 151 (2016) 178–188, http://dx.doi.org/10.1016/j. chemosphere.2016.02.055. [8] Y. Fan, Y. Ji, D. Kong, J. Lu, Q. Zhou, Kinetic and mechanistic investigations of the degradation of sulfamethazine in heat-activated persulfate oxidation process, J. Hazard. Mater. 300 (2015) 39–47, http://dx.doi.org/10.1016/j.jhazmat.2015.06. 058. [9] H. Lin, J. Wu, H. Zhang, Degradation of bisphenol A in aqueous solution by a novel electro/Fe3+/peroxydisulfate process, Sep. Purif. Technol. 117 (2013) 18–23, http://dx.doi.org/10.1016/j.seppur.2013.04.026. [10] J. Wang, S. Wang, Activation of persulfate (PS) and peroxymonosulfate (PMS) and application for the degradation of emerging contaminants, Chem. Eng. J. 334 (2017) 1502–1517, http://dx.doi.org/10.1016/j.cej.2017.11.059. [11] A. Takdastan, B. Kakavandi, M. Azizi, M. Golshan, Efficient activation of peroxymonosulfate by using ferroferric oxide supported on carbon/UV/US system: a new approach into catalytic degradation of bisphenol A, Chem. Eng. J. 331 (2018) 729–743, http://dx.doi.org/10.1016/J.CEJ.2017.09.021.
3.5. Reusability of the catalyst on the pyrite EC activation method The stability of the catalyst in a continuous process is one of the critical factors for its implementation at industrial scale. Therefore, the same pyrite particles were utilized for five consecutive cycles in order to evaluate the preservation of their catalytic activity. It could be noticed that no noticeable changes on [bmpyr]Cl removal were observed during these cycles (Fig. 7). For example, the TOC decay ranged from 79% to 68%, and the rate constants from 0.0170 to 0.0178 min−1, during the five cycles. In addition, the leaching concentrations of iron during these repeated cycles 7
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M. Arellano et al.
[27] A. Jordan, N. Gathergood, Biodegradation of ionic liquids – a critical review, Chem. Soc. Rev. 44 (2015) 8200–8237, http://dx.doi.org/10.1039/c5cs00444f. [28] T. Phuong, T. Pham, C.-W. Cho, Y.-S. Yun, Environmental fate and toxicity of ionic liquids: a review, Water Res. 44 (2010) 352–372, http://dx.doi.org/10.1016/j. watres.2009.09.030. [29] S.D. Richardson, S.Y. Kimura, Emerging environmental contaminants: challenges facing our next generation and potential engineering solutions, Environ. Technol. Innov. 8 (2017) 40–56, http://dx.doi.org/10.1016/j.eti.2017.04.002. [30] J.H. Ha, J.-H. Cho, J.H. Kim, B.W. Cho, S.H. Oh, 1-Butyl-1-methylpyrrolidinium chloride as an effective corrosion inhibitor for stainless steel current collectors in magnesium chloride complex electrolytes, J. Power Sources 355 (2017) 90–97, http://dx.doi.org/10.1016/j.jpowsour.2017.04.041. [31] A.B. Kurukutla, P.S.S. Kumar, S. Anandan, T. Sivasankar, Sonochemical degradation of rhodamine B using oxidants, hydrogen peroxide/peroxydisulfate/peroxymonosulfate, with Fe2+ ion: proposed pathway and kinetics, Environ. Eng. Sci. 32 (2015) 129–140, http://dx.doi.org/10.1089/ees.2014.0328. [32] A.M. Díez, E. Rosales, M.A. Sanromán, M. Pazos, Assessment of LED-assisted electro-Fenton reactor for the treatment of winery wastewater, Chem. Eng. J. 310 (2017) 399–406, http://dx.doi.org/10.1016/j.cej.2016.08.006. [33] APHA, AWWA, WPCF, Standard Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, American Water Works Association, Water Pollution Control Federation, Washington, DC, USA, 1998. [34] M.H. Chen, C.C. Chen, R.J. Wu, C.S. Lu, Heterogeneous photocatalytic degradation of disulfoton in aqueous TiO2 suspensions: parameter and reaction pathway investigations, J. Chin. Chem. Soc. 60 (2013) 380–390, http://dx.doi.org/10.1002/ jccs.201200027. [35] J.R. Bolton, K.G. Bircher, W. Tumas, C.A. Tolman, Figures-of-merit for the technical development and application of advanced oxidation technologies for both electricand solar-driven systems (IUPAC Technical Report), Pure Appl. Chem. 73 (2001) 627–637, http://dx.doi.org/10.1351/pac200173040627. [36] A. Rastogi, S.R. Al-Abed, D.D. Dionysiou, Sulfate radical-based ferrous–peroxymonosulfate oxidative system for PCBs degradation in aqueous and sediment systems, Appl. Catal. B Environ. 85 (2009) 171–179, http://dx.doi.org/10.1016/j. apcatb.2008.07.010. [37] E. Guinea, F. Centellas, J.A. Garrido, R.M. Rodríguez, C. Arias, P.L. Cabot, E. Brillas, Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe3+ using a boron-doped diamond electrode, Appl. Catal. B Environ. 89 (2009) 459–468, http://dx.doi.org/10.1016/j.apcatb.2009.01.004. [38] H. Lin, Y. Li, X. Mao, H. Zhang, Electro-enhanced goethite activation of peroxydisulfate for the decolorization of Orange II at neutral pH: efficiency, stability and mechanism, J. Taiwan Inst. Chem. Eng. 65 (2016) 390–398, http://dx.doi.org/10. 1016/j.jtice.2016.05.050. [39] C. Cai, Z. Zhang, H. Zhang, H. Zhang, Electro-assisted heterogeneous activation of persulfate by Fe/SBA-15 for the degradation of Orange II, J. Hazard. Mater. 313 (2016) 209–218, http://dx.doi.org/10.1016/j.jhazmat.2016.04.007. [40] S.K. Ling, S. Wang, Y. Peng, Oxidative degradation of dyes in water using Co2+/ H2O2 and Co2+ /peroxymonosulfate, J. Hazard. Mater. 178 (2010) 385–389, http://dx.doi.org/10.1016/j.jhazmat.2010.01.091. [41] Ley 5/2002, de 3 de junio, sobre vertidos de aguas residuales industriales a los sistemas públicos de saneamiento., Boletín Of. Del Estado. (2002) 13. https://www. boe.es/buscar/pdf/2002/BOE-A-2002-14187-consolidado.pdf (accessed May 7, 2018). [42] J.R. Bolton, S.R. Cater, Homogeneous photodegradation of pollutants in contaminated water. An Introduction, in: Surf. Aquat. Environ. Photochem., 1994: pp. 467–490.
[12] F. Ghanbari, M. Moradi, Application of peroxymonosulfate and its activation methods for degradation of environmental organic pollutants: review, Chem. Eng. J. 310 (2017) 41–62, http://dx.doi.org/10.1016/j.cej.2016.10.064. [13] N. Jaafarzadeh, F. Ghanbari, M. Alvandi, Integration of coagulation and electroactivated HSO5− to treat pulp and paper wastewater, Sustain. Environ. Res. 27 (2017) 223–229, http://dx.doi.org/10.1016/j.serj.2017.06.001. [14] R. Yin, W. Guo, H. Wang, J. Du, X. Zhou, Q. Wu, H. Zheng, J. Chang, N. Ren, Enhanced peroxymonosulfate activation for sulfamethazine degradation by ultrasound irradiation: performances and mechanisms, Chem. Eng. J. 335 (2018) 145–153, http://dx.doi.org/10.1016/j.cej.2017.10.063. [15] S. Wacławek, H.V. Lutze, K. Grübel, V.V. Padil, M. Černík, D.D. Dionysiou, Chemistry of persulfates in water and wastewater treatment: a review, Chem. Eng. J. 330 (2017) 44–62, http://dx.doi.org/10.1016/j.cej.2017.07.132. [16] Y. Rao, D. Xue, H. Pan, J. Feng, Y. Li, Degradation of ibuprofen by a synergistic UV/ Fe(III)/Oxone process, Chem. Eng. J. 283 (2016) 65–75, http://dx.doi.org/10. 1016/j.cej.2015.07.057. [17] H. Lin, J. Wu, H. Zhang, Degradation of clofibric acid in aqueous solution by an EC/ Fe3+/PMS process, Chem. Eng. J. 244 (2014) 514–521, http://dx.doi.org/10.1016/ j.cej.2014.01.099. [18] Y.R. Wang, W. Chu, Degradation of 2,4,5-trichlorophenoxyacetic acid by a novel electro-Fe(II)/oxone process using iron sheet as the sacrificial anode, Water Res. 45 (2011) 3883–3889, http://dx.doi.org/10.1016/j.watres.2011.04.034. [19] L. Gomathi Devi, M. Srinivas, M.L. Arunakumari, Heterogeneous advanced photoFenton process using peroxymonosulfate and peroxydisulfate in presence of zero valent metallic iron: a comparative study with hydrogen peroxide photo-Fenton process, J. Water Process Eng. 13 (2016) 117–126, http://dx.doi.org/10.1016/j. jwpe.2016.08.004. [20] F. Ghanbari, M. Moradi, M. Manshouri, Textile wastewater decolorization by zero valent iron activated peroxymonosulfate: compared with zero valent copper, J. Environ. Chem. Eng. 2 (2014) 1846–1851, http://dx.doi.org/10.1016/j.jece.2014. 08.003. [21] Y. Zhang, H.P. Tran, X. Du, I. Hussain, S. Huang, S. Zhou, W. Wen, Efficient pyrite activating persulfate process for degradation of p-chloroaniline in aqueous systems: a mechanistic study, Chem. Eng. J. 308 (2017) 1112–1119, http://dx.doi.org/10. 1016/j.cej.2016.09.104. [22] C.M. Sánchez-Sánchez, E. Expó Sito, J. Casado, V. Montiel, Goethite as a more effective iron dosage source for mineralization of organic pollutants by electro-Fenton process, Electrochem. Commun. (2006), http://dx.doi.org/10.1016/j.elecom.2006. 08.023. [23] V. Poza-Nogueiras, E. Rosales, M. Pazos, M.Á. Sanromán, Current advances and trends in electro-Fenton process using heterogeneous catalysts – a review, Chemosphere 201 (2018) 399–416, http://dx.doi.org/10.1016/j.chemosphere. 2018.03.002. [24] N. Barhoumi, N. Oturan, H. Olvera-Vargas, E. Brillas, A. Gadri, S. Ammar, M.A. Oturan, Pyrite as a sustainable catalyst in electro-Fenton process for improving oxidation of sulfamethazine. Kinetics, mechanism and toxicity assessment, Water Res. 94 (2016) 52–61, http://dx.doi.org/10.1016/j.watres.2016.02.042. [25] A. Ghauch, A. Baalbaki, M. Amasha, R. El Asmar, O. Tantawi, Contribution of persulfate in UV-254 nm activated systems for complete degradation of chloramphenicol antibiotic in water, Chem. Eng. J. 317 (2017) 1012–1025, http://dx. doi.org/10.1016/j.cej.2017.02.133. [26] S. Khan, X. He, H.M. Khan, D. Boccelli, D.D. Dionysiou, Efficient degradation of lindane in aqueous solution by iron (II) and/or UV activated peroxymonosulfate, J. Photochem. Photobiol. A Chem. 316 (2016) 37–43, http://dx.doi.org/10.1016/j. jphotochem.2015.10.004.
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