Study on Degradation of Benzothiazolium-Based Ionic Liquids by UV-H2O2
Round 1
Reviewer 1 Report
Dear authors:
The article about the degradation of benzothiazolium based ionic liquids shows interesting results and the application of the combination UV-H2O2 seems a nice way for its degradation. Nevertheless some questions shouldbe taken into account before its publication:
Results section.
a) The scave of radicals is a mechanism that is mentioned in several situations in the manuscript (the degradation depending on the concentration of peroxide and the degradation on presence of ions). For this reason, I encourage the authors to include some references in which this mechaniems occurs in other systems. For instance:
Reinosa, J.J., Docio, C.M.Á., Ramírez, V.Z., Fernández, J.F.F. Hierarchical nano ZnO-micro TiO2 composites: High UV protection yield lowering photodegradation in sunscreens. Ceram Int. 2018; 44(3): 2827-2834.
b) In the case of the study about the effect of the concentration in IL degradation, it should be better explained the yield for 0.05mM and 0.10mM. The differences are not clearly indicated.
c) In the case of the temperatura effect, and taking into account the decomposition of hydrogen peroxide, I recommend to add the theoretical decomposition temperatura of H2O2.
d) In lines 158-159, authors express that "a neutral or weakly acidic solution is more suitable for the UV-H2O2 oxidative degradation reaction". Please, include a reference which supports this affirmation.
e) The motivation of the assay with chlorides is well explained but authors should indicate why do you choose as chlodire concentration 0.001M, 0.01M and 0.1M. Under my opinión, authors should point out the values of chlorides in waste eaters in order to compare the results with a real situation.
f) Regarding the effect of anion degradation, the motivation of this assay is not expressed in the manuscript. In addition, authors should explain the reason for choosing those anions. Moreover, the obtained results are not explained. In addition, authors indicate that the results are in figure 7b, but figure 7b corresponds to the efficiency of the different methodologies. After all these indications, I advice eliminating this assay from the manuscript.
g) In section 3.10, a mechanism explaining the efficiency of UV-H2O2 should be indicated.
Best regards
Author Response
Response to Reviewer 1 Comments
Point 1: The scave of radicals is a mechanism that is mentioned in several situations in the manuscript (the degradation depending on the concentration of peroxide and the degradation on presence of ions). For this reason, I encourage the authors to include some references in which this mechaniems occurs in other systems. For instance:
Reinosa, J.J., Docio, C.M.Á., Ramírez, V.Z., Fernández, J.F.F. Hierarchical nano ZnO-micro TiO2 composites: High UV protection yield lowering photodegradation in sunscreens. Ceram Int. 2018; 44(3): 2827-2834.
Response 1: Thank you for your comments. We have added references
Point 2: In the case of the study about the effect of the concentration in IL degradation, it should be better explained the yield for 0.05mM and 0.10mM. The differences are not clearly indicated.
Response 2: Experimental results showed that the degradation yield gradually decreased with the increase of the concentration of ILs.
|
Sequence number |
1 |
2 |
3 |
4 |
|
[ILs] (mM) |
0.05 |
0.10 |
0.15 |
0.20 |
|
k (min-1) |
0.0721 |
0.0562 |
0.0325 |
0.0242 |
|
t1/2 (min) |
9.61 |
12.33 |
21.32 |
28.64 |
|
dc/dt×10-3 (min-1×mM-1) |
2.60 |
4.05 |
3.52 |
3.49 |
The first line is the sequence number; the second line is the initial concentration of ILs; the third line is the degradation rate constant k; the fourth line is the corresponding half-life of ILs; the fifth line is the concentration of ionic liquid degradation in unit time.
From the above table, we can see that when the initial concentration of ILs is 0.10 mM, the concentration of ILs decrease most in the same period.
Point 3: In the case of the temperature effect, and taking into account the decomposition of hydrogen peroxide, I recommend to add the theoretical decomposition temperature of H2O2.
Response 3: Temperature is an important factor that affects the stability of hydrogen peroxide. Existing research shows that when the temperature exceeds 45 ℃, the degradation yield of 3% hydrogen peroxide solution will exceed 50% in 2h.
In this manuscript, the activity of hydroxyl radicals does increase with the rise of temperature, but hydrogen peroxide, which produces hydroxyl radicals, decomposes into oxygen and water more quickly, resulting in a decrease in the concentration of hydroxyl radicals.
Zhun Z, Yubin L (2004) Study on the stability of hydrogen peroxide. Heilongjiang Medicine journal: 337-338
Point 4: In lines 158-159, authors express that "a neutral or weakly acidic solution is more suitable for the UV-H2O2 oxidative degradation reaction". Please, include a reference which supports this affirmation.
Response 4: According to the existing literature, in the process of photocatalytic degradation of ILs by UV-H2O2, alkaline solution is more favorable for this process than acidic solution. In the process of pH changing from acid to alkaline, the degradation rate of ionic liquid is not rising in a straight line.
Boutiti, A., et al., Photodegradation of 1-hexyl-3-methylimidazolium by UV/H2O2 and UV/TiO2: Influence of pH and chloride. Journal of Photochemistry and Photobiology A: Chemistry, 2017. 336: p. 164-169.)
https://doi.org/10.1016/J.JPHOTOCHEM.2016.12.030
The degradation rate first increased slowly, then decreased slowly, and finally increased rapidly. The degradation rate of methylimidazolium ILs under natural pH is much lower than that under alkaline conditions, but the degradation rate of benzothiazolium ILs may be different from that of methylimidazolium ILs.
In addition, although the degradation rate is much faster at pH=12, the difference in degradation yield of ILs is much smaller than the natural pH within 10 min. (ηpH=12=94%, ηpH=5.2=93%)
Adjusting to alkaline may require additional costs (unless we have alkaline wastewater), so we think weaker acidity is more appropriate.
Point 5: The motivation of the assay with chlorides is well explained but authors should indicate why do you choose as chlodire concentration 0.001M, 0.01M and 0.1M. Under my opinión, authors should point out the values of chlorides in waste water in order to compare the results with a real situation.
Response 5: We chose this way to reflect the huge impact of chloride ions on the reaction process. It is also for comparison with other types of ILs in the existing literature.
Boutiti, A., et al., Photodegradation of 1-hexyl-3-methylimidazolium by UV/H2O2 and UV/TiO2: Influence of pH and chloride. Journal of Photochemistry and Photobiology A: Chemistry, 2017. 336: p. 164-169.)
Point 6: Regarding the effect of anion degradation, the motivation of this assay is not expressed in the manuscript. In addition, authors should explain the reason for choosing those anions. Moreover, the obtained results are not explained. In addition, authors indicate that the results are in figure 7b, but figure 7b corresponds to the efficiency of the different methodologies. After all these indications, I advice eliminating this assay from the manuscript.
Response 6: Thank you for your suggestion. I have eliminated this part.
Point 7: In section 3.10, a mechanism explaining the efficiency of UV-H2O2 should be indicated.
Response 7: Due to the synergistic effect of UV and H2O2, the degradation efficiency can be significantly improved compared to any of them alone. This phenomenon can be described by the following equation.
H2O2+hv→2·OH
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript "Study on degradation of benzothiazolium-based ILs by UV-H2O2" presents interesting and promising results in the treatment of waters contaminated with ILs.
First of all I recommend a revision of the English. Some sentences are difficult to understand. For example:
Lined 21-22: We also explored the effects of anion species, chloride ions... This sounds a little extrange. I suggest to replace anion species by "IL anionic part".
Line 23: Is really necessary to include the term "respectively"?
Lines 62-63: synthetic experiments?
Line 69: Dichlorometane, silver nitrate...
Line 73: Degraded UV wavelength?
Line 70. "Ultrapure water ..." this sentence may be deleted, considering that the water purification system is described in lines 82-83. Or was this purification water machine used to treat wastewaters?
Lines 87-88: Most of this information has been provided before. On the other hand, analytical column dimensions must be included.
Line 89: membrance?
Fig. 1. Please check the y-axis legends.
Line 105: Add an .... This does not sound very well. It looks like a recipe.
Fig. 2b is not mentioned in the text of the manuscript. Perhaps in Line 106 could be mentioned as: The obtained results are shown in Figure 2.
Please, revise the legends for the figures 2, 3, 4 and 5 in order to simplify them.
Figs. 2b and 4b: Symbols have been omitted.
I suggest to combine Fig 6a with 5a, and Fig 6b with 5b.
Section 3.8. I would recommend to title it as "Effect of IL anionic part nature on degradation".
Line 188: (see Figure 7b?)
Line 196: Please replace "anion species" by "IL anionic part nature".
Have the experimental studies carried out using wastewaters contaminated/fortified with ILs or pure water? If pure water was used, Can the authors foresee that the same results will be obtained as with wastewater? If wasterwaters were used, concerning data should be provided.
Supporting material:
Line 17: Add.... Newly, the sentence seems like a recipe.
Line 21: The rest of the ILs were... (Fig. S1).
Is really necessary to repeat Fig. 3 as Fig. 3S a and b?
Line 35: Please check, abscissa and ordinate designation.
Author Response
Response to Reviewer 2 Comments
Point 1: Lined 21-22: We also explored the effects of anion species, chloride ions... This sounds a little extrange. I suggest to replace anion species by "IL anionic part".
Response 1: Another reviewer suggested that we delete the discussion about the IL anionic part.
Point 2: Line 23: Is really necessary to include the term "respectively"?
Lines 62-63: synthetic experiments?
Line 69: Dichlorometane, silver nitrate...
Line 73: Degraded UV wavelength?
Line 70. "Ultrapure water ..." this sentence may be deleted, considering that the water purification system is described in lines 82-83. Or was this purification water machine used to treat wastewaters?
Lines 87-88: Most of this information has been provided before. On the other hand, analytical column dimensions must be included.
Line 89: membrance?
Response 2: According to your comments, I have made some modifications.
Point 3: Fig. 1. Please check the y-axis legends.
Response 3: I remade Figure 1 and used different colors to distinguish different results.
Point 4: Line 105: Add an .... This does not sound very well. It looks like a recipe.
Fig. 2b is not mentioned in the text of the manuscript. Perhaps in Line 106 could be mentioned as: The obtained results are shown in Figure 2.
Please, revise the legends for the figures 2, 3, 4 and 5 in order to simplify them.
Figs. 2b and 4b: Symbols have been omitted.
I suggest to combine Fig 6a with 5a, and Fig 6b with 5b.
Section 3.8. I would recommend to title it as "Effect of IL anionic part nature on degradation".
Line 188: (see Figure 7b?)
Line 196: Please replace "anion species" by "IL anionic part nature".
Response 4: We have modified the description of the pictures to make them easier to understand
Point 5: Have the experimental studies carried out using wastewaters contaminated/fortified with ILs or pure water? If pure water was used, Can the authors foresee that the same results will be obtained as with wastewater? If wasterwaters were used, concerning data should be provided.
Response 5: There are currently no examples of production using benzothiazolium-based ILs around us. In this manuscript, we used pure water as solvent. The results of wastewater may be worse when the substance in wastewater has strong reducibility or can absorb ultraviolet light strongly or can cause hydrogen peroxide degradation.
Point 6: Supporting material:
Line 17: Add.... Newly, the sentence seems like a recipe.
Line 21: The rest of the ILs were... (Fig. S1).
Is really necessary to repeat Fig. 3 as Fig. 3S a and b?
Line 35: Please check, abscissa and ordinate designation.
Response 6: According to your comments, I have made some modifications and remade Figure S3 and replaced some of the text in this manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear authors,
thank you very much for taking into account my recommendations.
Best regards
Author Response
Thank you very much.
Reviewer 2 Report
The quality of the manuscript has been enhanced but several defficiences in the English style are still detected. The text is totally understandable but some changes would be considered, if you consider their suitability, for example:
Line 19: Please change "results" by "data". Line 29: The term "volatile" can be deleted because the condition of low vapour pressure has been yet stated. Lines 32-33: It has "been" shown. Line 38: Replace "for effectively treating the benzothiazole ILs wastewater" by "for their effective treatment in wastewater" Line 40: I think it seems better as: "...[16,17], but these methods cannot completely..."
Line 51: I suggest to define the abbreviations BMIM and EMIM.
Line 57: photocatalytic or photo catalytic?
Line 60: Delete "benzothiazole": "... to the treatment of these ILs"
Materials and Methods: The benzothiazole ILs studied are not here included.
Line 64: The complete name of the provider should be included: "and purchased from Chengdu Kelong Chewed Reagent Factory"
Line 71: City and country for this provider has been included before, so this information may be removed from here.
Line 87: I suggest to rewrite as "HPLC analysis was performed using an LC system (Shimadzu, Kyoto, Japan) equipped with a LC 20AT pump and an HCT 360 LC column cooler/heater (Hengao Tech & Dev, Tianjin, China) and coupled to a SPD H20A PDA detector working at 278 nm. Separation was carried out using a Summetry C18 column (Waters, Massachusetts,
79 USA) of xxxxx (please include column dimensions) thermostated at 30 ºC and using a 40X60 v/v methanol:water mixture as mobile phase with a flow-rate of 1 mL min. Class-VP workstation (Shimadzu, Kyoto, Japan) was used for data acquisition.
Lines 94-95: I think I did not express myself well in the first review.I suggested rewriting the beginning of this section but not starting with the results obtained.
Line 105: H2O2 is (as?).....provider, so its initial...
Line 125: IL (no ILs) solutions .... were prepared. I think the term "respectively" can be deleted.
Line 144: Here again, can the term "respectively" be omitted?
Legend for figure 5: Effect of: ......(a) and, .....
Lines 159-160: "... ocean and river water and also in industrial wastewaters"
Lines 162-164: I suggest to rewrite as "Different concentration levels of NaCl were added to an aqueous solution containing 0.1 mM IL and 100 mM H2O2, to make chloride anion concentrations of ....."
Line 165: The results are shown in Figure 5a, where it can be seen...
Author Response
Response to Reviewer 2 Round 2 Comments
Point 1:
Line 19: Please change "results" by "data".
Line 29: The term "volatile" can be deleted because the condition of low vapour pressure has been yet stated.
Lines 32-33: It has "been" shown.
Line 38: Replace "for effectively treating the benzothiazole ILs wastewater" by "for their effective treatment in wastewater"
Line 40: I think it seems better as: "...[16,17], but these methods cannot completely..."
Line 51: I suggest to define the abbreviations BMIM and EMIM.
Line 57: photocatalytic or photo catalytic?
Line 60: Delete "benzothiazole": "... to the treatment of these ILs"
Response 1: According to your comments, I have made some modifications.
Point 2:
Materials and Methods: The benzothiazole ILs studied are not here included.
Response 2: According to your comments, I have made some modifications. The synthesis method and purity of benzothiazolium-based ILs are shown in SI.
Point 3:
Line 64: The complete name of the provider should be included: "and purchased from Chengdu Kelong Chewed Reagent Factory"
Line 71: City and country for this provider has been included before, so this information may be removed from here.
Line 87: I suggest to rewrite as "HPLC analysis was performed using an LC system (Shimadzu, Kyoto, Japan) equipped with a LC 20AT pump and an HCT 360 LC column cooler/heater (Hengao Tech & Dev, Tianjin, China) and coupled to a SPD H20A PDA detector working at 278 nm. Separation was carried out using a Summetry C18 column (Waters, Massachusetts,79 USA) of xxxxx (please include column dimensions) thermostated at 30 ºC and using a 40X60 v/v methanol:water mixture as mobile phase with a flow-rate of 1 mL min. Class-VP workstation (Shimadzu, Kyoto, Japan) was used for data acquisition.
Lines 94-95: I think I did not express myself well in the first review. I suggested rewriting the beginning of this section but not starting with the results obtained.
Line 105: H2O2 is (as?).....provider, so its initial...
Line 125: IL (no ILs) solutions .... were prepared. I think the term "respectively" can be deleted.
Line 144: Here again, can the term "respectively" be omitted?
Legend for figure 5: Effect of: ......(a) and, .....
Lines 159-160: "... ocean and river water and also in industrial wastewaters"
Lines 162-164: I suggest to rewrite as "Different concentration levels of NaCl were added to an aqueous solution containing 0.1 mM IL and 100 mM H2O2, to make chloride anion concentrations of ....."
Line 165: The results are shown in Figure 5a, where it can be seen...
Response 3: According to your comments, I have made some modifications.
Author Response File: Author Response.pdf
