Influence of Cerium and Nickel Co-Doping on ZnO Nanostructures for Electrochemical Behavior of H₂O₂ Sensing Applications

Round 1

Reviewer 1 Report

The article presents the preparation of co-doped Ce and Ni- ZnO electrodes to be applied as hydrogen peroxide sensor.

The article is well presented and with characterizations of the materials as well as their application. However, it needs to undergo an intensive English review specially in the abstract, introduction and experimental parts. Although the results and discussion session presents better writing in English, there are several language mistakes, especially in verbal tense. I suggest that all writing review of the fulltext a prior to acceptance.

There is also a need to add comparisons with the literature of all characterizations and results obtained, such as the sensitivity of the electrodes. The value obtained is high or low, compared to other studies reported in the literature? Some data presentations, electrochemical part, must also be redone

• In the sequence, I present some language mistakes (in the abstract and in the introduction parts) that hinder the understanding of what the authors wanted to say.

Abstract:

• What did you mean by: “are different optimum conditions and materials analysis.”? Review English writing
• What did you mean by: “ The results of electrochemical studies reveal that co-doped product exhibits the higher sensing response is 46.21 μA/μcm2 belongs to concentration range 15.89 μM for Ce/Ni-doped ZnO aimed at H2O2 than bare ZnO representing that it canuse potentially for future bio-medical applications.” Review English writing

Introduction:

• In the recent past, materials in nanoscale are the prime focus among the researchers because of their unique physico-chemical properties

Did you mean:

 In the recent past, materials in nanoscale were the prime focus among the researchers, because of their unique physico-chemical properties

• ZnO is a II-IV semiconductors family with a wide band gap of 3.34 eV [1].
• In the sentence :

Though a wide spread of re-ports are made available on doped ZnO nanostructures, there are few reports on co-doped ZnO nanocrystals [7-12].

Did you mean:

Although a wide spread of reports is available on doped ZnO nanostructures, there are few reports on co-doped ZnO nanocrystals [7-12].

• What did you mean with “exposure” in the sentence :

 In the current status, the exposure of hydrogen peroxide (H2O2) have gain immense significance as sensing of hazards chemicals in food, bio-medical re-sources pharmaceuticals, and environment [13-16],

• In the current status, the exposure of hydrogen peroxide (H2O2) have gain immense significance as sensing of hazards chemicals in food, bio-medical re-sources pharmaceuticals, and environment [13-16], and also cerium (Ce) and lanthanam (La) rare-earth metals doped ZnO nanostructures were detect the hazardous materials for bio-sensing applications [17-20].

Did you mean:

In the current status, the exposure of hydrogen peroxide (H2O2) have gain immense significance as sensing of hazards chemicals in food, bio-medical re-sources pharmaceuticals, and environment [13-16], and also cerium (Ce) and lanthanum (La) rare-earth metals doped ZnO nanostructures were detect the hazardous materials for bio-sensing applications [17-20].

• Previously, the few reports on ZnO nanostructures aimed at H2O2 monitoring from biological targets, such as glucose, lactose and bio-logical thin film samples [20, 21].

Did you mean:

Previously, few reports on ZnO nanostructures aimed at H2O2 monitoring from biological targets, such as glucose, lactose and bio-logical thin film samples [20, 21].

• An essential assignment of Titrimetry, spectrophotometry, chemilumi-nescence, and electrochemical such methods are used and developed to detect the H2O2

 An essential assignment of Titrimetry, spectrophotometry, chemilumi-nescence, and electrochemical methods are used and developed to detect the H2O2

• What did you mean by” to the expand?”

In this work, we have report to the expand a modified electrode of ZnO by co-doping ZnO with cerium and nickel in appropriate proportions via a facile chemical precipitation process. The personalized electrode is analyzed on behalf of its sensing activity against H2O2. From the obtained results, it is obvious that the modified electrode of ZnO shows higher sensor activity than bare ZnO.

I suggest :

In this work, we report the preparation of a modified electrode of ZnO by co-doping ZnO with cerium and nickel in appropriate proportions via a facile chemical precipitation process. The personalized electrode is analysed on behalf of its sensing activity against H2O2. From the obtained results, it is obvious that the modified electrode of ZnO shows higher sensor activity than bare ZnO.

Materials and Methods:

• This topic also need major english reviewing
• The ZnO - Ce/Ni preparation is presented in a confusing way and it is important to remember that all molar concentrantions should be presented as "mol L^-1 or mol/L" and not as "molar" or "M"
• Material Analysis and Instrumentations and Electrochemical measurements also need to be rewriten

Results and discussion:

XRD

• What is the determining factor for the increase in cell parameters with initial Ni-doping?
• What can be attributed to the decrease in intensity in the diffraction peaks with the increase in Ni concentration?

Correct the sentence:

“Further, the crystallite peaks intensity significant decreased as the Ni-content increased”

XRD, XPS, PL need to be compared to previously reported researches

There are a lot of English language mistakes throughout the results, such as:

3.3. UV-Vis reflectance spectroscopy The UV-Vis spectroscopy was studied by optical band gap of the products between 250-750 nm. Intensity of reflectance is become decreased with increase in Ni concentration

Should be :

“3.3. UV-Vis reflectance spectroscopy The UV-Vis spectroscopy was studied by optical band gap of the products between 250-750 nm. Intensity of reflectance decrease with the increase in Ni concentration”

“3.4. FT-IR analysis FT-IR spectra of pure ZnOcompared to dual-doped ZnO nanoparticles were shows in Fig. 5. IR transmittance peaks at around 428 cm-1 associated to stretching bond…”

Should be :

3.4. FT-IR analysis FT-IR spectra of pure ZnO compared to dual-doped ZnO nanoparticles were shown in Fig. 5. IR transmittance peaks at around 428 cm-1 associated to stretching bond

Electrochemical characterization

Fig 8 )a 

Transform the y-axis into microampare and decrease the number of points.

Reverse the reduction writing, it should not be presented upside down

Fig 8 c) The points in the linearization of the Ipa and Ipc must not be connected, but presented with LINEAR FITTING (regression)

What do you mean with the sentence?

“good oxidations and reductions peaks (redox) peaks were observed for entire the sweep rates”

Improve the discussion. What determines a "good redox process" is the  ΔE (∆φp = φpa − φpc)

Correct the presentation of the Nyquist diagram. The EIE data, in this type of representation, is commonly presented in a graph with the same dimension on the x and y axes and also with the same scale on both axes. This, to allow the correct visualization of the semi-circle, for example. The rectangular presentation impairs the reader's analysis of the graphs.

The x and y axes of the Nyquist diagram must be presented in the form of k(ohm) or M(ohm)

Compare the H2O2 sensitivity of 46.21 μA/μM.cm2 with some previously reported ZnO (and other oxidel-based) electrodes

Compare all electrochemical characterization with the literature. 

Author Response

Respected Reviewer/Sir/ Madam, Authors thanks to peer review valuable suggestions for the manuscript, more helpful and authors very carefully understand the review comments response reply word file separately word file and also revised manuscript yellow color-highlighted. 

The authors hope our review response may be at a satisfactory level for review corrections to the whole manuscript.   

Author Response File: Author Response.docx

Reviewer 2 Report

In this manuscript,the authors developed an electrocatalytic-amperometric detection techniques for H₂O₂sensor applications by using Ce and Ni co-doped ZnO nanoparticles successfully. The electrocatalytic active materials were cerium and nickel doped ZnO synthesized via a facile chemical precipitation technique, and also their structural and morphological structures were analyzed. However,there are some problems with the integrity of the data analysis. Therefore, this manuscript is recommended for publication after the following issues are properly addressed.

1. In the part of XPS analysis, the authors only showed the XPS spectra for Ce/Ni-doped [Ce (0.05 M), Ni (0.075 M)] ZnO nanostructure. It is better to compare the XPS spectras for pure ZnO and Zn_0.95-xCe_4+0.05Ni_xO (x = 0.025, 0.05, 0.1 and 0.125 M) with Ce/Ni-doped [Ce (0.05 M), Ni (0.075 M)] ZnO because the electrochemical sensing performance of materials is related to the electronic structure of materials.
2. The manuscript showed the HRTEM image of Ce/Ni-doped [Ce (0.05 M), Ni (0.075 M)] ZnO nanostructure and revealed that the co-doping does not tailor the actual hexagonal structure of ZnO. Maybe the authors should measure the lattice space of Ce/Ni-doped [Ce (0.05 M), Ni (0.075 M)] ZnO and pure ZnO to investigate the effect of codoping on crystal lattice. And the HRTEM images of Zn_0.95-xCe_4+0.05Ni_xO (x = 0.025, 0.05, 0.1 and 0.125 M) should be provided.
3. The author analyzed the optical properties of the co-doped material, please describe the relationship between the change of optical properties and the electrochemical sensing properties of the materials.

Author Response

Respected Reviewer, As per your valuable review comments we are carefully revised and responded to your, Authors reply may be satisfied with your peer-review comments/ questions.  

The revised manuscript highlighted your comments reply and also separately attached a word file. 

Author Response File: Author Response.docx

Reviewer 3 Report

In the current study, the authors investigate the effect of Cerium and Nickel Co-Doping on ZnO Nanostructures for Electrochemical Behavior of H₂O₂ Sensing and concluded that synthesized doped nanoparticles exhibit the higher sensing response is 46.21 μA/μM.cm2 belongs to concentration range 15.89 μM for Ce/Ni-doped ZnO aimed at H2O2 than bare ZnO. After carefully reading the whole manuscript, I have following major concerns.

1. The name of company and city name should be mentioned of all materials and equipments mentioned in the manuscript.
2. XPS analysis section should be interpret clearly rather than just reporting the data.
3. 2a is a stretched image, It should be same as Figure 2,b,c,d, and e
4. Figure 3 and b, multiple concentrations were used. Minimum concentration for Ni is 0.125M. Why the authors did not interpret it below this value? and what is the control (standard)?
5. UV-Vis reflectance spectroscopy and Photoluminescence (PL) analysis should be revised according to concentration of Ni below 0.125M and why the concentration of Ce is fixed about to 0.05M
6. I think XPS and PL emission and UV-Vis spectra results are same, no need to add further add FT-IR results.
7. What is the Limit of detection and response time of H2O2 against your proposed nanoparticle structure?
8. Figure 10 shows the results are taken one time specially Figure c and d. Figure 10 c and d should have some standard deviation to check the accuracy of the H2O2 detection.
9. Figure captions should be revised and clearly matched with the text

Author Response

Respected Reviewer, Thanks for reviewing my manuscript, more valuable comments to we are carefully rectified the mistakes error and response to your author's reply. Thanking you. 

Author Response File: Author Response.docx

Reviewer 4 Report

In this paper, the authors form Cerium and Nickel Co-Doping on ZnO Nanostructures for Electrochemical Behavior of H2O2 Sensing Applications The synthesized nanoparticles are well characterized and perform well. Before publication is considered, the level of English needs to be improved. Detailed below are additional suggestions that should be considered when submitting the revised manuscript.

1. Please redesign the abstract section to be more readable by focusing on the merit of the figures.
2. It is recommended to elaborate on the results and discussions.
3. Introduction: Essential related work may be cited if appropriate Tamilalagan, S. V. Selvi, S.-M. Chen, M. Akilarasan, S. Maheshwaran, T.-W. Chen, A. M. Al-Mohaimeed, W. A. Al-onazi, M. S. Elshikh and X. Liu, Journal of The Electrochemical Society, 2021, 168, 036501; M. Akilarasan, S. Maheshwaran, T.-W. Chen, S.-M. Chen, E. Tamilalagan, M. A. Ali, W. A. Al-onazi and A. M. Al-Mohaimeed, Microchemical Journal, 2020, 159, 105509.; 3. V. Renganathan, R. Balaji, S.-M. Chen, S. Kogularasu and M. Akilarasan, Ecotoxicology and Environmental Safety, 2019, 176, 250-257; S. Kogularasu, M. Akilarasan, S.-M. Chen, T.-W. Chen and B.-S. Lou, Materials Chemistry and Physics, 2019, 227, 5-11.
4. Some figure captions are scary examples fig. 8.
5. Authors have synthesized different ratios of Nickel Co-Doping on ZnO Nanostructures and it was well characterized through XRD, FTIR, and PL spectra. However, the electrochemical characterization of this data is missing.
6. How to author choose Ce/Ni-ZnO [Ce4+ (0.05 M) & Ni (0.075 M)] as an active electrode for H2O2 sensing?
7. In an electrochemical sensor, selectivity is one of the important parameters. The reason, why the current modified electrode is selective, should be highlighted with the proposed mechanism for this selectivity.
8. Error bar should be added to the fitting figures.
9. How author confirmed that Ce/NiZnO electrode have higher electrochemical active area than undoped ZnO?
10. Fig .9 don’t have c , d. however author mentioned Fig. 9,  c and d as a linear regression plot. Please check it.
11. Author should mentioned the applied potential for amperomertic sensing of H2O2.
12. LOD of the prepared sensor should be mentioned.
13. In addition to the above points, a thorough inspection is required, because many typographical, grammatical errors or poor English are distributed in the manuscript, the manuscript should be carefully checked, and necessary corrections should be done.

Author Response

Respected Reviewer, Thank you for reviewing my manuscript, after revision is more efficient for authors' response review corrections satisfied level, we are attached a separate word file and also review comments and modifications are highlighted in the revised manuscript.  

Thanking you Sir/ Madam. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The article presents the preparation of co-doped Ce and Ni- ZnO electrodes to be applied as hydrogen peroxide sensors.

In the first review of the article, I strongly suggested many changes in the graphics and discussions but most of them weren’t done. The data remain without comparison to the literature and many of my questions (in the first review) were not answered. Although some changes have been made, compared to the first version, there is still a clear need for a native-language review of the entire text.

An example is the preparation of materials that are presented in a very confusing way with a lot of writing and grammar mistakes:

“The typical prepararions of cerium and nickel doped ZnO, firstly zinc acetate [Zn(CH3COO)2*2H2O] weighed at 5.49g and (0.5 mol/L) of dissolved in 50 mL of deionized (DI) water with vigorously by magnetic stirrer. Additionally, cerium (III) chloride heptahydrate [(CeCl3)*7H2O] at 0.05 mol/L of prepared in 20 mL solutions was mixed above the solution mixture. After 35 min, nickel nitrate hexahydrate[Ni(NO3)2*6H2O] of preferred various molar concentrations (0.025, 0.05, 0.075, 0.1, and 0.125 mol/L) equipped in 20 mL aqueous was add slowly into above mixture of solutions.”

Based on these observations, I suggest the article to be REJECTED. The new version presented by the authors aren’t sufficient to be published.

Author Response

Authors' Response to major review second revised submission manuscript

Respected first 1#reviewer dear sir/madam,

 Thanks for the revised version peer review questions second time again we revised the whole manuscript carefully and according to the first review ann second review major revision and review comments were very carefully addressed and highlighted by a green color shadow.

Authors kindly revised the manuscript with the whole manuscript and also revised the manuscript resubmitted the second major revision satisfied level, kindly request to based on your review acceptance format level.

Thanking you for your review sir/ madam.  

Author Response File: Author Response.pdf

Reviewer 3 Report

I recommend this paper for publication.

Author Response

Authors all more Thanks to Reviewer#2 for accepting my articles 

Reviewer 4 Report

The author has addressed the reviewer's comments, therefore the manuscript has been accepted in its present form

Author Response

Thank you reviewer#4 for accepting my request, thank you sir/madam.

Round 3

Reviewer 1 Report

The text still needs English revisions. Below I suggest some modifications. Please check if the changes have not changed the meaning of the original text

Introduction

In the recent past, materials on the nanoscale were the prime focus among researchers because of their unique physicochemical properties. ZnO is an II-IV semiconductors family with a wide bandgap of 3.34 eV [1]. The peculiar conductive, photocatalytic, piezoelectric, and pyroelectric properties [2,3] of zinc oxide have made it as a promising material in sensors [3,4], photovoltaic and solar cell [5,6] applications. Although a widespread of reports is available on doped ZnO nanostructures, there are few reports on codoped ZnO nanocrystals [7-15]. In the current status, the exposure to hydrogen peroxide (H2O2) has gained immense significance as sensing of hazardous chemicals in food, biomedical resources pharmaceuticals, and the environment [16-19], as also cerium (Ce) and lanthanum (La) rare-earth metals doped ZnO nanostructures were detected the hazardous materials for biosensing applications [17-23]. Previously, few reports on ZnO nanostructures aimed at H2O2 monitoring from biological targets, such as glucose, lactose, and io-logical thin film samples [24, 25]. The fields of study about the H2O2 levels to using metal oxide nanoparticles ZnO, and tin oxide (SnO2) to resolve toxic materials using electrochemical bio-sensing applications [26]. An essential assignment of Titrimetry, spectrophotometry, chemiluminescence and electrochemical methods are used and developed to detect the H2O2 [27,28], these methods have certain limitations, for example, reagents are more expensive, the analysis time is lengthy, and continuing stability is very poor [29]. However, the drawbacks are rectified by using the electrochemical approaches to the measurement of H2O2 sensing. In the field of electrochemical biosensor applications, such as tin oxide (SnO2) [30], tungsten oxide (WO2) [31], copper oxide (CuO) [32], titanium dioxide (TiO2) [33], magnesium oxide (SnO2) [34], cuprous oxide (Cu2O) [35]and zinc oxide (ZnO) have demonstrated outstanding performance in the biosensor and bioelectronic sensor fields among those materials with promising behavior of Metal-oxide semiconductors [36]. In this work, we report the preparation of a modified electrode of ZnO by codoping ZnO with cerium and nickel in appropriate proportions via a facile chemical precipitation process. The personalized electrode is analyzed on behalf of its sensing activity against H2O2. From the obtained results, it is obvious that the modified electrode of ZnO shows higher sensor activity than bare ZnO

2.2. Synthesis of co-doped ZnO nanoparticles

For the typical preparations of cerium and nickel-doped ZnO, firstly zinc acetate [Zn(CH3COO)2*2H2O], weighed at 5.49g, and (0.5 mol/L) of dissolved in 50 mL of deionized (DI) water, with vigorous stirring by a magnetic stirrer. Additionally, a 0.05 mol/L solution of cerium (III) chloride heptahydrate [(CeCl3)*7H2O], prepared in 20 mL solutions was mixed with the above solution mixture. After 35 min, nickel nitrate hexahydrate [Ni(NO3)2*6H2O], at different molar concentrations (0.025, 0.05, 0.075, 0.1, and 0.125 mol/L) equipped in 20 mL aqueous solution was added slowly into the above mixture of solutions.” Finally, 5.64 g (1 mol/L) of (NH4)2CO3 in 50 mL of DI water was added gradually to the above the mixture. The entire mixture of solutions was continuously magnetic stirrer and finally until a get precipitate sediment has appeared. The obtained solid dispersions were cleaned using DI water with ethanol repeated numbers until the clear white powder was obtained. The optimized as-prepared metallic composites were dried overnight at 80 °C. Finally, the product was treated in annealed at 500°C for 2 hrs using a box furnace. The as-prepared powders were agate mortar grinding at Pure ZnO, ZnO: Ce (0.05 M): Ni (0.025 M), ZnO: Ce (0.05 M): Ni (0.05 M), ZnO: Ce (0.05 M): Ni (0.075 M), ZnO: Ce (0.05 M): Ni (0.1 M), ZnO: Ce (0.05 M): Ni (0.125 M). A comparable sample of pure ZnO nanocrystals was prepared under the same above experimental procedure using without the addition of Ce and Ni.

2.4. Electrochemical measurements

Electrochemical applications of H2O2 sensing were carried out in a three-electrode cell set-up using a CHI-600D electrochemical workstation. The expectable three-electrode cell with a platinum wire as the counter electrode and Ag/AgCl (dripping wet with KCl) as the reference electrode. The as-prepared all kinds of doped and undoped binary metal nanoparticles composites were drop-casting coating with modified and polished glassy carbon electrode (GCE) with dia 3 mm) and used as the working electrodes. The catalytic capability of zinc oxide toward H2O2 reduction was employed to evaluated by cyclic voltammetry (CV) and chronoamperometric (CA) techniques. The amperometric measurements mini magnetically stirring the constant electrolyte molar concentrations. All kinds of electrochemical analyses were used in phosphate buffer solution (PBS). In the direction to avoid the decomposition of H2O2, it was slowly mixed with the stock solution in PBS. The impedance analysis delivers details to find the resistance of the material

Author Response

Respected Reviewer#1/Editor (Sustainability)

Thanks for the third (3^rd) revised version peer review (minor revision), authors have completely revised the whole manuscript carefully every sentence clearly verified that scientific sentence continuity and English grammar are polished. We hope the final 3^rd review corrected sentences are highlighted and uploaded 3^rd time fully revised the whole manuscript (violet color highlighted by a green color shadow) just bellow attached revised as per reviwer#1 suggestions. Authors kindly request to based on your minor review reply/corrections. we hope to review the acceptance 3rd review revised suitably for MDPI- Sustainability.

Thanking You (Reviewer/ Editor) Sir/Madam.  

Author Response File: Author Response.docx