Application of Phanerochaete chrysopsorium-Based Carbon Paste Electrode as an Electrochemical Sensor for Voltammetric Detection of Hg (II) in Chlor-Alkali Industrial Effluent

Round 1

Reviewer 1 Report

Comments for author File: Comments.pdf

Author Response

Manuscript ID: electrochem-1914060

Title: Application of Phanerochaete chrysopsorium based carbon paste electrode as an electrochemical sensor for voltammetric detection of Hg (II) in chlor-alkali industrial effluent

I have carefully revised the manuscript as per reviewer’s comments and hope that the revised manuscript will meet the standards required for publication.

ANSWERS TO COMMENTS OF REVIEWER’s # 1

Note: All the revisions made in revised manuscript with respect to comments of reviewer no 1 are highlighted in red color

1. In the introduction line 60-62, authors discussed about the background statement on fouling and reproducibility issues related to solid electrodes, how can they justify this statement to their usage of carbon paste electrode in the current study?

It has been mentioned in submitted manuscript that ‘Modified carbon paste electrodes have proved themselves an effective alternate of solid electrodes as they have wide potential range, robustness, stable response, low ohmic resistance and chemical inertness. Moreover the problem of passivation in this case is simply solved by renewal of their surface’ [14]

2. It is suggested to remove the word “novel” from the title

Above recommendation has been incorporated in revised manuscript. Kindly check the title in revised manuscript.

3. Author should provide proper detail on how FTIR imaging done on the electrode? Details about how the solution were prepared for the electrochemical measurements? the concentration range for the calibrations study? What was the control /blank used in the study?

Above recommendation has been incorporated in revised manuscript. Kindly check the section 2.4 and section 3.2 in revised manuscript.

4. In the line 159-168, surface characterization by FTIR authors statement says “changed their frequencies to 1721.30 cm−1 and 1123.7 cm−1 in Hg (II) loaded modified carbon paste electrode” authors should use more scientific term such as blue or red shift. Revisit and modify and justify the discussion for FTIR as it is the only method shown to explain the adsorption of Hg(II)?

Above recommendation has been incorporated in revised manuscript. Kindly check the section 3.1 in revised manuscript.

5. In the Line 173-183, authors should provide comment/justification on how the modified surface affects the anodic and cathodic peak potential and current? How much is the potential shift? what was the scanning rate or sampling rate used for CV?

Above recommendation has been incorporated in revised manuscript. Kindly check the section 3.2

6. What was the accumulation medium concentrations? I did not see at the manuscript text during discussion except at the figure caption

Above recommendation has been incorporated in revised manuscript. Kindly check the section 2.4.

7. Author discussed about the effect of electrolyte on the stripping process but what property or factor influencing the adsorption of Hg(II) to the modified platform as  compared to the control/unmodified carbon paste electrode? Specifically, carbon and role of the biomass in modification?

Above recommendation has been incorporated in revised manuscript. Kindly check the section 3.4.

8. Choice of reference electrode: is there any reason for using Calomel electrode when the stripping medium is acidic?

Calomel electrode

Calomel electrode was chosen as it was the available reference electrode. In literature, this reference electrode has been employed for acidic medium analysis

• Honeychurch, Trace Voltammetric Determination of Lead at a Recycled Battery Carbon Rod Electrode, Sensors 2019, 19(4), 770; https://doi.org/10.3390/s19040770
• Hongbo Xiao, Wenlei Wang, Shaofeng Pi, Yan Cheng, Qingji Xie, Anodic stripping voltammetry analysis of mercury(II) on a pyridine-Au/pyridine/glassy carbon electrode, Sensors and Actuators B: Chemical, 317, 2020, 128202, https://doi.org/10.1016/j.snb.2020.128202.

9. Author must show the reproducibility or stability study of the current carbon paste electrode?

During optimization of experimental parameters, mean value based on triplicate readings along with standard deviation calculation (depicted as error bars) has been considered for graph plotting. These triplicate readings for a particular experiment have been taken from the same electrode by surface renewal procedure.

10. Statement in the line 234-237, “While in alkaline medium the observed decrease in current value can be assigned to the fact that Hg (II) do exists as hydroxyl species [32] which subsequently hinders its affinity to the functional moieties present on the surface of electrode”. Authors should explain what functional moieties?

Above recommendation has been incorporated in revised manuscript. Kindly check the section 3.4.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Manuscript ID: electrochem-1914060

Title: Application of Phanerochaete chrysopsorium based carbon paste electrode as an electrochemical sensor for voltammetric detection of Hg (II) in chlor-alkali industrial effluent

I have carefully revised the manuscript as per reviewer’s comments and hope that the revised manuscript will meet the standards required for publication.

ANSWERS TO COMMENTS OF REVIEWER’s # 2

Note: All the revisions made in revised manuscript with respect to comments of reviewer no 1 are highlighted in blue color

1. Authors should check the legibility of figures and the units properly.

Figures have been improved. Kindly check the revised manuscript. Legibility of units is thoroughly checked in revised manuscript

2. Authors should mention scan rates for the electrochemical measurements.

Above recommendation has been incorporated. Kindly check section 3.2 in revised manuscript

3. How does the surface roughness changes for the modified electrode as compared to the pristine (bare carbon paste) electrode. Please comment.

Atomic force microscopic analysis based surface roughness calculation for modified and bare electrode has been carried out in our previously reported study. Thus it has not been included in our current work.

• Zaib, M. and Athar, M. Electrochemical evaluation of Phanerocheaete chrysosporium based carbon paste electrode with potassium ferricyanide redox system. Int. J. Electrochem. Sci. 2015, 10, 6690

4. Current work is based upon adsorption of Hg (II) on to electrode surface. How the electrochemically active surface area for the modified and pristine electrode compares?

Above recommendation has been incorporated. Kindly check section 3.2 in revised manuscript

5. Authors have checked for the biomass (%) loading effect in fig 3b. Does the organic species have effect on conductivity of the films which restricts electrochemical activity?

Above query has been addressed under the section 3.4 in revised manuscript

6. Fig 3a is confusing. In text, authors mentioned reduction potential, whereas, in figure it shows anodic positive current. Authors should recheck the figure and correct it.

Discussion with reference to Fig 3a has been revised. Kindly check section 3.4 (page 10) in revised manuscript

7. Authors have done interference studies from other heavy metal ions in the current manuscript. It has been found heavy metal ions tend to form amalgams. Is there any such formation possible in current scenario? How can formation of amalgams effect the stripping voltammetry measurement? Authors should comment.

Most of the reported studies related to amalgam formation are based on the interaction of divalent cations with mercury based working electrode.

• G. Anastopoulos, G.N. Nikolaidis, Mechanism of amalgam formation electrode reactions in nonaqueous solvents. Combined analysis of interfacial distance parameters and steric factors, Journal of Electroanalytical Chemistry, 571(2), 2004, 309-317
• Ronald Fawcett, Shelgon Yee, Double-layer effects on the electroreduction of lead(II) at mercury in dimethylformamide solutions, Journal of Electroanalytical Chemistry, 366, (1–2), 1994, 219-224
• Ronald Fawcett, Double layer effects in the electrode kinetics of amalgam formation reactions: Part II. A comparison of the CE and IE mechanisms, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 310(1–2), 1991, 13-25

8. After one cycle (i.e. adsorption, reduction and stripping) how much activity is retained in the modified electrode? Did the author check the reusability of the modified electrode?

During optimization of experimental parameters, mean value based on triplicate readings along with standard deviation calculation has been considered for graph plotting. These triplicate readings for a particular experiment have been taken from the same electrode by surface renewal procedure.

8. There are a few typos and grammatical mistakes in the manuscript, which needs to be rechecked and corrected.

Authors have thoroughly checked the revised manuscript.

9. References are not formatted according to journal standard so please check and correct them.

References have been formatted according to journal standard. Kindly check the reference section in revised manuscript

Author Response File: Author Response.docx

Reviewer 3 Report

The authors reported an electrochemical sensor for monitoring Hg (II) at trace levels by using differential pulse anodic stripping voltammetry with a limit of detection of 4.4ug/L which is basically higher than the WHO limit. The sensor must be checked for LODs lower than WHO limit to show its significance. The sensitivity is good, but selectivity shows variation with increasing concentration of interfering ions. The manuscript is accepted with major revision and needs to incorporate the following correction before accepting for publication:

1.     Does the introduction provide sufficient background and include all relevant references?

: Authors need to include the latest references and compare the proposed sensor with different literature already published with lower LODs for Hg(II) detection.

2.     The sensing materials/protocol before and after detection should be characterized using SEM/EDX, TEM and XRD etc.

3.     All material used will be included in the material section.

4.     The language should be polished further. Currently, there are too many very long sentences, which are not convenient for reading. Also, some typo errors must be corrected in the complete manuscript (lines 14 [min.], 43, 116 etc.)

5.     Authors must follow the same way of writing for Hg(II) or Hg²⁺ throughout the manuscript (lines 42, 43, 85 etc.).

6.     The latest publication in 2020-2022 needs to be included for LOD comparison.

7.     LOD calculation must be included in the manuscript.

8.     Conclusions must be re-written by including all the essential novelty and results obtained.

9.     In Figure 5, the caption must include the Hg(II) concentration and other interfering ions concentration. Also, the author needs to explain why he responds more with Cu(II) ions in the interference study.

10. In Conclusion, before writing “The proposed sensor has better detection limit as compared to previously reported works”; Author has to check the latest publication in 2020-2022 for LOD comparison. Table 2 also has some lower LODs compared to the present study. So, the author needs to explain the novelty and significance in more detail.

Comments for author File: Comments.pdf

Author Response

Manuscript ID: electrochem-1914060

Title: Application of Phanerochaete chrysopsorium based carbon paste electrode as an electrochemical sensor for voltammetric detection of Hg (II) in chlor-alkali industrial effluent

I have carefully revised the manuscript as per reviewer’s comments and hope that the revised manuscript will meet the standards required for publication.

ANSWERS TO COMMENTS OF REVIEWER’s # 3

Note: All the revisions made in revised manuscript with respect to comments of reviewer no 1 are highlighted in green color

1. Does the introduction provide sufficient background and include all relevant references? Authors need to include the latest references and compare the proposed sensor with different literature already published with lower LODs for Hg(II) detection.

Latest references have been added to the revised manuscript. Kindly check the reference section of revised manuscript

2. The sensing materials/protocol before and after detection should be characterized

using SEM/EDX, TEM and XRD etc.

Reviewer’s suggestion is highly appreciated. However, please acknowledge that this could be part of our future research work scope. This study focused to evaluate and statistically compare modified carbon paste electrode towards electrochemical determination of mercuric ions in standard solution and then in real samples.

3. All material used will be included in the material section.

All the materials has been mentioned in material section. Kindly check the revised manuscript.

4. The language should be polished further. Currently, there are too many very long sentences, which are not convenient for reading. Also, some typo errors must be corrected in the complete manuscript (lines 14 [min.], 43, 116 etc.)

Authors have thoroughly revised and improved the language of revised manuscript

5. Authors must follow the same way of writing for Hg(II) or Hg2+ throughout the manuscript (lines 42, 43, 85 etc.).

Above recommendation has been incorporated in revised manuscript. Kindly check revised manuscript

6. The latest publication in 2020-2022 needs to be included for LOD comparison.

Latest publications have been added for LOD comparison. Kindly check Table no 2 in revised manuscript

7. LOD calculation must be included in the manuscript.

LOD calculation has already been reported in submitted manuscript under section 3.5 titled ‘Analytical Performance’

8. Conclusions must be re-written by including all the essential novelty and results obtained.

Above recommendation has been incorporated in revised manuscript. Kindly check conclusion section in revised manuscript

9. In Figure 5, the caption must include the Hg(II) concentration and other interfering ions concentration. Also, the author needs to explain why he responds more with Cu(II) ions in the interference study.

Above recommendation has been incorporated in revised manuscript. Kindly check Fig no 5 caption in revised manuscript

1. In Conclusion, before writing “The proposed sensor has better detection limit as compared to previously reported works”; Author has to check the latest publication in 2020-2022 for LOD comparison. Table 2 also has some lower LODs compared to the present study. So, the author needs to explain the novelty and significance in more detail

Conclusion section and Table 2 have been revised

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Issues have been addressed and the manuscript has improved a lot. 

Author Response

Thanks for the comments

Reviewer 3 Report

Review comments:

The authors reported an electrochemical sensor for monitoring Hg (II) at trace levels by using differential pulse anodic stripping voltammetry with a limit of detection of 4 microgram/L which is basically higher than the WHO limit. The sensor must be checked for LODs lower than WHO limit to show its significance.

The manuscript is accepted with minor revision and needs to incorporate the following correction before accepting for publication:

1.    The sensitivity is good, but selectivity shows variation with increasing concentrations of interfering ions (Mostly Cu ions) in Figure 5. This shows that the sensor is also selective to Cu ions. So, It is necessary to check the selectivity without Hg(II) ions.

2.    The sensor must be checked for LODs lower than WHO limit to show its significance.

3.    Latest publications like https://doi.org/10.1016/j.jelechem.2022.116350 also used the electrochemical sensor for Hg(II) ions detection at the picomolar range. The author needs to justify why their proposed method is better than similarly reported sensors.

Authors need to address all these points very carefully and incorporate them in the revised manuscript before accepted for publication.

Comments for author File: Comments.pdf

Author Response

1. The sensitivity is good, but selectivity shows variation with increasing concentrations of interfering ions (Mostly Cu ions) in Figure 5. This shows that the sensor is also selective to Cu ions. So, It is necessary to check the selectivity without Hg(II) ions.

Apparently presence of Cu (II) ions has increased the peak current value. Thus, this method can be recommended suitable for cupric ions free samples. Above recommendation has been addressed in revised manuscript. Kindly check section 3.6 (page 13) in revised manuscript

2. The sensor must be checked for LODs lower than WHO limit to show its significance.

Above recommendation has been addressed in revised manuscript. Kindly check section 3.5 (page 12) in revised manuscript

3. Latest publications like https://doi.org/10.1016/j.jelechem.2022.116350 also used the electrochemical sensor for Hg(II) ions detection at the picomolar range. The author needs to justify why their proposed method is better than similarly reported sensors.

Above recommendation has been addressed in revised manuscript. Kindly check section 3.5 and Table 2 (page 12 and 22) in revised manuscript

Author Response File: Author Response.docx