Synthesis of g-C₃N₄@ZnIn₂S₄ Heterostructures with Extremely High Photocatalytic Hydrogen Production and Reusability

Round 1

Reviewer 1 Report

The manuscript titled "Synthesis of g-C₃N₄@ZnIn₂S₄ heterostructures with extremely high photocatalytic hydrogen production and reusability" provides a detailed account of the synthesis of g-C₃N₄@ZnIn₂S₄ heterostructures and study the photocatalytic activity. The quality of the research work presented in the paper should be modified. Below given are some of the comments that authors should look into improving the manuscript.

1.      There are many works published using g-C₃N₄ / ZnIn₂S₄ heterostructures for HER and photocatalytic H₂ evolution. Comparatively, what is the novelty of your work?

2.      As in line 343 of page 11 it's mentioned as “different amounts of g-C₃N₄ was uniformly dissolved and dispersed in a 20 mL solution” and throughout the manuscript, it's only mentioned as “0.01g g-C₃N₄ nanostructures”. The authors should revise the experimental part as the information given contradicts it. And the data for other samples that are missing.

3.      Adding to question 2 the authors should include the data (XRD, UV, FTIR, SEM, BET, EIS, photocurrent response etc.. of other samples 0.005g, 0.025g, 0.05g.

4.      The authors have not compared the EIS, photocurrent response and photocatalytic H₂ evolution of pure ZnIn₂S₄ with g-C₃N₄@ZnIn₂S₄ heterostructures, it would be better to add those data to improve the clarity of preparing g-C₃N₄ heterostructures.

5.      What is the reason only 10 mg (0.01g) addition of g-C₃N₄ with ZnIn₂S₄ to synthesise g-C₃N₄@ZnIn₂S₄ heterostructures shows such a huge H₂ evolution?

6.      From the XPS data, it's very clear that there is a huge amount of Carbon and lesser Nitrogen showing that the CN ratio is lesser than C₃N₄. It would be better to clarify the amount of C and N using CHN analysis.

7.      EDS mapping images of the Carbon sample are missing. Better to include.

8.      A huge amount of TEOA would minimise the H₂ evolution capability. The authors have used 50% of TEOA as a sacrificial agent and demonstrated high H₂ evolution, what is the mechanism that is involved in such a huge evolution of H₂?

9.      There are several mistakes, authors should check for spelling, symbols that should be given in Italics, space between words and numbers etc.

10.  Some of the words in the figures are not clear. If the authors can modify it would be better.

minor revision needed

Author Response

Reviewers' comments:

The manuscript titled "Synthesis of g-C3N4@ZnIn2S4 heterostructures with extremely high photocatalytic hydrogen production and reusability" provides a detailed account of the synthesis of g-C3N4@ZnIn2S4 heterostructures and study the photocatalytic activity. The quality of the research work presented in the paper should be modified. Below given are some of the comments that authors should look into improving the manuscript.

Response: Thanks for the pertinent and positive comments.

1. There are many works published using g-C3N4 / ZnIn2S4 heterostructures for HER and photocatalytic H2 evolution. Comparatively, what is the novelty of your work?

Response: Thanks for your reminder. Despite their remarkable efficiency in photocatalytic hydrogen production, no research has investigated the extended durability of g-C₃N₄@ZnIn₂S₄ heterostructures under low-wattage light sources. By exploring this aspect, we can optimize photocatalyst utilization and achieve significant energy conservation from the light source.

2. As in line 343 of page 11 it's mentioned as “different amounts of g-C3N4 was uniformly dissolved and dispersed in a 20 mL solution” and throughout the manuscript, it's only mentioned as “0.01g g-C3N4 nanostructures”. The authors should revise the experimental part as the information given contradicts it. And the data for other samples that are missing.

Response: Thanks for your reminder. This sentence has been amended in the revised manuscript. A ZnIn₂S₄ reaction solution containing 1 mM ZnCl₂, 2.5 mM InCl₃, and 5 mM TAA was dissolved in a 20 mL mix solvent (15 mL DI water and 5 mL ethanol). Then, different amounts (0.005, 0.01, 0.025, and 0.05 g) of g-C₃N₄ were uniformly dispersed in the reaction solution using an ultrasonic treatment for 15 min.

3. Adding to question 2 the authors should include the data (XRD, UV, FTIR, SEM, BET, EIS, photocurrent response etc.. of other samples 0.005g, 0.025g, 0.05g.

Response: Thanks for your reminder. We have provided EIS (new Figure 8a) and photocurrent response (new Figure 8b) for the g-C₃N₄ nanostructures, g-C₃N₄@ZnIn₂S₄ heterostructures with different weights of g-C₃N₄ nanostructures and ZnIn₂S₄ nanostructures in the revised manuscript.

4. The authors have not compared the EIS, photocurrent response and photocatalytic H2 evolution of pure ZnIn2S4 with g-C3N4@ZnIn2S4 heterostructures, it would be better to add those data to improve the clarity of preparing g-C3N4 heterostructures.

Response: Thanks for your reminder. We have provided EIS (new Figure 8a) for the g-C₃N₄ nanostructures, g-C₃N₄@ZnIn₂S₄ heterostructures with different weights of g-C₃N₄ nanostructures and ZnIn₂S₄ nanostructures in the revised manuscript.

5. What is the reason only 10 mg (0.01g) addition of g-C3N4 with ZnIn2S4 to synthesise g-C3N4@ZnIn2S4 heterostructures shows such a huge H2 evolution?

Response: Thanks for your reminder. A notable difference in the EIS Nyquist curves' arc radii is that g-C₃N₄ nanostructures exhibit larger arc radii than g-C₃N₄@ZnIn₂S₄ heterostructures. In addition, g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures reveal the lowest arc radii. This result indicates that g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures possess the lowest charge transfer resistance to enhance efficiency in separating charge carriers, facilitating the fastest electron transfer process.

6. From the XPS data, it's very clear that there is a huge amount of Carbon and lesser Nitrogen showing that the CN ratio is lesser than C3N4. It would be better to clarify the amount of C and N using CHN analysis.

Response: Thanks for your reminder. Due to the unavailability of the necessary instrument for CHN data analysis in our laboratory, obtaining access to related expensive instruments is time-consuming. Consequently, the revised manuscript cannot include the CHN data.

7. EDS mapping images of the Carbon sample are missing. Better to include.

Response: Thanks for your reminder. The EDS carbon signal may not be accurate due to TEM sample preparation on a carbon-coated copper grid.

8. A huge amount of TEOA would minimise the H2 evolution capability. The authors have used 50% of TEOA as a sacrificial agent and demonstrated high H2 evolution, what is the mechanism that is involved in such a huge evolution of H2?

Response: Thanks for your reminder. The presence of TEOA serves to consume the photogenerated holes. This synergistic effect significantly reduces the possibility of carrier recombination, resulting in a notable increase in the photocatalytic activity of g-C₃N₄@ ZnIn₂S₄ and promoting efficient hydrogen generation.

9. There are several mistakes, authors should check for spelling, symbols that should be given in Italics, space between words and numbers etc.

Response: Thanks for your reminder. We have amended these mistakes in the revised manuscript.

10. Some of the words in the figures are not clear. If the authors can modify it would be better.

Response: Thanks for your reminder. We have modified the words in the figures.

Author Response File: Author Response.pdf

Reviewer 2 Report

This work reports that g-C3N4@ZnIn2S4 heterostructures were successfully synthesized through a combination of thermal annealing and hydrothermal method. Although some results seem interesting, however, after careful reading of this work, I cannot recommend publication in its present form.

1, Why this work merits publication? I cannot find significant advances with those reported previously since the g-C3N4@ZnIn2S4 has been studied intensively for the past few years. The authors should strengthen the novelty and differences of this work in the introduction part.

2, The activity is very important. The authors should list the data for H2 evolution in a table to show the improvement of this work with the literature.

3, XPS data is poor. For g-C3N4, the contaminant carbon should be very small as compared with C-N, however, in this work, this species shows very strong intensity. Also, the XPS spectra should be retreated to improve the quality.

4, Fig.1 is wrong, InCl2 should be InCl3.

5, Why Fig. 3 show no g-C3N4 in the heterostructure? The authors should show the compsite structure.

6, Fig. 8a should be re-carried out to show the semi-circle, maybe the electrode should be repeated.

7, In Fig. 9, I cannot understand the unit umol g^-1h^-1L^-1. In present, the optimal unit for H₂ production is umol h^-1.

8, Fig. 10b should show the presence of g-C3N4, only ZIS is not enough.

9, Fig. 11, the mechanism lacks evidence. The authors should explain why electron is on ZIS. Gold deposition experiment should be added.

no

Author Response

This work reports that g-C3N4@ZnIn2S4 heterostructures were successfully synthesized through a combination of thermal annealing and hydrothermal method. Although some results seem interesting, however, after careful reading of this work, I cannot recommend publication in its present form.

1. Why this work merits publication? I cannot find significant advances with those reported previously since the g-C3N4@ZnIn2S4 has been studied intensively for the past few years. The authors should strengthen the novelty and differences of this work in the introduction part.

Response: Thanks for your reminder. Despite their remarkable efficiency in photocatalytic hydrogen production, no research has investigated the extended durability of g-C₃N₄@ZnIn₂S₄ heterostructures under low-wattage light sources. By exploring this aspect, we can optimize photocatalyst utilization and achieve significant energy conservation from the light source.

2. The activity is very important. The authors should list the data for H2 evolution in a table to show the improvement of this work with the literature.

Response: Thanks for your reminder. Comparative analysis of the photocatalytic hydrogen production activity of g-C₃N₄@ZnIn₂S₄ heterostructures with other reported photocatalysts strongly supports their favorable application prospects.

3. XPS data is poor. For g-C3N4, the contaminant carbon should be very small as compared with C-N, however, in this work, this species shows very strong intensity. Also, the XPS spectra should be retreated to improve the quality.

Response: Thanks for your reminder. We will pay special attention to this part in the preparation of related XPS test pieces in the future. Obtaining access to related expensive instruments is time-consuming. Consequently, the revised manuscript cannot include the XPS data of post-photodegradation samples.

4. 1 is wrong, InCl2 should be InCl3.

Response: Thanks for your reminder. Figure 1 has been amended in the revised manuscript.

5. Why Fig. 3 show no g-C3N4 in the heterostructure? The authors should show the compsite structure.

Response: Thanks for your reminder. The crystallinity of ZnIn₂S₄ is much better than that of g-C₃N₄. This result induces that the XRD signal of g-C₃N₄ cannot be detected after decorated ZnIn₂S₄. In order to address this issue, FESEM-EDS mapping was employed to detect the N signal and confirm the presence of g-C₃N₄ in the g-C₃N₄@ZnIn₂S₄ heterostructures. During observation, the carbon signal exhibited significant intensity due to the material deposition on a carbon-coated copper grid.

6. 8a should be re-carried out to show the semi-circle, maybe the electrode should be repeated.

Response: Thanks for your reminder. We have provided the new EIS (Figure 8a)

7. In Fig. 9, I cannot understand the unit umol g-1h-1L-1. In present, the optimal unit for H2 production is umol h-1.

Response: Thanks for your reminder. This unit is primarily used to specify the weight of the photocatalyst and the reaction volume more accurately.

8. 10b should show the presence of g-C3N4, only ZIS is not enough.

Response: Thanks for your reminder. In the revised manuscript, we have provided the FESEM image (Figure 10c) and FESEM-EDS mapping image (Figure 10d).

9. 11, the mechanism lacks evidence. The authors should explain why electron is on ZIS. Gold deposition experiment should be added.

Response: Thanks for your reminder. In this study, we employ ion exchange resin to coat the materials (g-C₃N₄ and ZnIn₂S₄) onto indium tin oxide (ITO) glass, followed by measuring the flat band potential using cyclic voltammetry [1,2]. The conduction band (CB) positions of g-C₃N₄ and ZnIn₂S₄ are −1.40 eV and −0.58 eV, respectively, while their valence band (VB) positions are 1.50 eV and 1.78 eV [70,71]. Under visible light irradiation (λ_max = 420 nm), g-C₃N₄ and ZnIn₂S₄ materials undergo excitation, generating photogenerated electrons in the VB transitioning to the CB, consequently creating holes in the VB. The construction of the heterojunction facilitates the transfer of electrons from the conduction band (CB) of g-C₃N₄ to the lower surface of ZnIn₂S₄, while the photogenerated holes are transferred from the VB of ZnIn₂S₄ to the VB of g-C₃N₄. This formation of a type II heterojunction at the interface between g-C₃N₄ and ZnIn₂S₄ greatly enhances the separation efficiency of the photogenerated electron-hole pairs in g-C₃N₄. Additionally, due to the more negative conduction potential of ZnIn₂S₄ compared to the reduction potential of H⁺/H², the photogenerated electrons accumulated in the CB of ZnIn₂S₄ undergo a reduction reaction, effectively reducing H⁺ in an aqueous solution to produce H₂. Simultaneously, the presence of TEOA serves to consume the photogenerated holes. This synergistic effect significantly reduces the possibility of carrier recombination, resulting in a notable increase in the photocatalytic activity of g-C₃N₄@ ZnIn₂S₄ and promoting efficient hydrogen generation. This intricate photocatalytic process facilitates efficient charge carrier separation and promotes hydrogen production.

Reference:

1. Ge, H.; Tian, H.; Zhou, Y.; Wu, S.; Liu, D.; Fu, X.; Song, X.-M.; Shi, X.; Wang, X.; Li, N. Influence of Surface States on the Evaluation of the Flat Band Potential of TiO2. ACS Appl. Mater. Interfaces 2014, 6, 2401-2406, doi:10.1021/am404743a.
2. Bhattacharya, C.; Lee, H.C.; Bard, A.J. Rapid Screening by Scanning Electrochemical Microscopy (SECM) of Dopants for Bi2WO6 Improved Photocatalytic Water Oxidation with Zn Doping. J. Phys. Chem. C 2013, 117, 9633-9640, doi:https://doi.org/10.1021/jp308629q.

Author Response File: Author Response.pdf

Reviewer 3 Report

The current research article discussed “Synthesis of g-C3N4@ZnIn2S4 Heterostructures with Extremely High Photocatalytic Hydrogen Production and Reusability”. Authors have explained the fabrication of g-C3N4/ZnIn2S4 heterojunctions via hydrothermal and thermal methods in addition to characterization of the photocatalyst by various analytical techniques. The photocatalytic performance was evaluated by its exposure to light and hydrogen production. The article is well written and properly structured however, there are some concerns which needs to be addressed before considering the manuscript for publication.

There are some comments:

1.    The authors should add a table and compare different carbon nitride and ZnIn2S4 based materials already reported for similar photocatalytic hydrogen generation. The authors should also address that how their g-C3N4@ZnIn2S4 heterojunction is novel and better.

2.    In figure 1, the authors should provide a real image of g-C3N4 and g-C3N4@ZnIn2S4 composite or draw a similar kind of sketch of morphology as seen in the FE-SEM micrographs.  

3.    Authors, should explain about the composition of ZnIn2S4 with g-C3N4 and it should be mentioned to clarify the role of actual component responsible for enhanced the photocatalytic activity of the material, Authors should describe, why a particular composition was successful for photocatalysis.

4.    The authors should also label the FTIR spectrum (figure 4c).

5.    The EDX elemental composition of g-C3N4@ZnIn2S4 should be mentioned in table form.

6.    The DRS showing band gap energy of g-C3N4@ZnIn2S4 as 2.9 eV. But it is generally believed that band gap of g-C3N4 is around 2.7 eV. Can authors explain this variation?? Figure 7. (C)

7.    It will be good if authors could provide XPS of post photodegradation samples to compare the differences in composition and oxidation states before and after the photocatalytic hydrogen generation.

8.    Why the XRD of Pre and post experiments for g-C3N4 are different? The (002) Peak is not observed in post measurement XRD, how authors justly it?

minor formatting, spell check is required 

Author Response

Reviewers' comments:

The current research article discussed “Synthesis of g-C3N4@ZnIn2S4 Heterostructures with Extremely High Photocatalytic Hydrogen Production and Reusability”. Authors have explained the fabrication of g-C3N4/ZnIn2S4 heterojunctions via hydrothermal and thermal methods in addition to characterization of the photocatalyst by various analytical techniques. The photocatalytic performance was evaluated by its exposure to light and hydrogen production. The article is well written and properly structured however, there are some concerns which needs to be addressed before considering the manuscript for publication.

Response: Thanks for the pertinent and positive comments.

There are some comments:

1. The authors should add a table and compare different carbon nitride and ZnIn2S4 based materials already reported for similar photocatalytic hydrogen generation. The authors should also address that how their g-C3N4@ZnIn2S4 heterojunction is novel and better.

Response: Thanks for your reminder. Despite their remarkable efficiency in photocatalytic hydrogen production, no research has investigated the extended durability of g-C₃N₄@ZnIn₂S₄ heterostructures under low-wattage light sources. By exploring this aspect, we can optimize photocatalyst utilization and achieve significant energy conservation from the light source.

2. In figure 1, the authors should provide a real image of g-C3N4 and g-C3N4@ZnIn2S4 composite or draw a similar kind of sketch of morphology as seen in the FE-SEM micrographs.

Response: Thanks for your reminder. We have corrected this morphology in the new Figure 1.

3. Authors, should explain about the composition of ZnIn2S4 with g-C3N4 and it should be mentioned to clarify the role of actual component responsible for enhanced the photocatalytic activity of the material, Authors should describe, why a particular composition was successful for photocatalysis.

Response: Thanks for your reminder. The average HER values of as-prepared photocatalysts were 10.4 (g-C₃N₄ nanostructures), 2056.2 (0.005 g g-C₃N₄ nanostructures), 2377.6 (0.01 g g-C₃N₄ nanostructures),1355.1 (0.025 g g-C₃N₄ nanostructures), 448.7 (0.05 g g-C₃N₄ nanostructures) and 921.2 μmolh⁻¹g⁻¹L⁻¹ ZnIn₂S₄ nanostructures, respectively. The average HER of g-C₃N₄@ZnIn₂S₄ heterostructures gradually increased as the weight of g-C₃N₄ nanostructures increased. However, a notable decline in the average HER was observed when the weight of g-C₃N₄ nanostructures exceeded 0.01 g. This outcome could be attributed to the higher weights of g-C₃N₄ nanostructures, which might cause an excessive generation of g-C₃N₄ nanostructures and subsequently decrease the efficiency of electron-hole pair transfer, thereby inhibiting the overall photocatalytic hydrogen production efficiency. This result is consistent with the above EIS (The g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures reveal the lowest arc radii. This result indicates that g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures possess the lowest charge transfer resistance to enhance efficiency in separating charge carriers, facilitating the fastest electron transfer process) and photocurrent response (The g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures exhibited significantly higher photocurrent density than g-C₃N₄ nanostructures and g-C₃N₄@ZnIn₂S₄ heterostructures with other weights, indicating a substantial improvement in the efficiency of separating photogenerated electrons and holes.) measurements. In addition, g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01g g-C₃N₄ nanostructures revealed almost 228.6 and 2.58 times higher than g-C₃N₄ nanostructures and ZnIn₂S₄ nanostructures, respectively.

4. The authors should also label the FTIR spectrum (figure 4c).

Response: Thanks for your reminder. We have labeled these peaks in the new Figure 4c.

5. The EDX elemental composition of g-C3N4@ZnIn2S4 should be mentioned in table form.

Response: Thanks for your reminder. The TEM-EDS elemental composition of g-C₃N₄@ZnIn₂S₄ is 81.58 (C), 6.24 (N), 3.17 (Zn), 3.40 (In), and 5.61 (S), respectively. The EDS carbon signal may not be accurate due to TEM sample preparation on a carbon-coated copper grid. An organic layer on carbon or copper tape can influence the composition analysis using FESEM EDS.

6. The DRS showing band gap energy of g-C3N4@ZnIn2S4 as 2.9 eV. But it is generally believed that band gap of g-C3N4 is around 2.7 eV. Can authors explain this variation?? Figure 7. (C)

Response: Thanks for your reminder. This phenomenon shall be attributed to the impact of the reaction precursor and the annealing temperature of g-C₃N₄, causing a shift in the energy gap [1,2].

7. It will be good if authors could provide XPS of post photodegradation samples to compare the differences in composition and oxidation states before and after the photocatalytic hydrogen generation.

Response: Thanks for your reminder. Obtaining access to related expensive instruments is time-consuming. Consequently, the revised manuscript cannot include the XPS data of post-photodegradation samples.

8. Why the XRD of Pre and post experiments for g-C3N4 are different? The (002) Peak is not observed in post measurement XRD, how authors justly it?

Response: Thanks for your reminder. The crystallinity of ZnIn₂S₄ is much better than that of g-C₃N₄. This result reveals that XRD cannot effectively detect the g-C₃N₄ on the g-C₃N₄@ZnIn₂S₄. Therefore, this study mainly confirmed the heterostructure formation by detecting the N signal through an EDS mapping image of FESEM.

Reference:

1. Alaghmandfard, A.; Ghandi, K. A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)–Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing. Nanomaterials 2022, 12, doi:10.3390/nano12020294.
2. Pham, T.-T.; Shin, E.W. Influence of g-C3N4 Precursors in g-C3N4/NiTiO3 Composites on Photocatalytic Behavior and the Interconnection between g-C3N4 and NiTiO3. Langmuir 2018, 34, 13144-13154, doi:10.1021/acs.langmuir.8b02596.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The quality of the research work is improved after the revision. Below are some comments that authors should look into improving the manuscript.

1. The authors have mentioned EIS displays lower arc radii in the manuscript, but from Figure 8a, it’s not visible; better to include a figure for visibility.

2. The authors should provide all samples' charge transfer resistance values from the EIS spectra.

3. It would be better to display a table comparing the H₂ evolution of the gC₃N₄@ZnIn₂S₄ with other reported samples

4. Some figures are not visible.

Comments for author File: Comments.pdf

Author Response

Reviewers' comments:

The quality of the research work is improved after the revision. Below are some comments that authors should look into improving the manuscript.

Response: Thanks for the pertinent and positive comments.

1. The authors have mentioned EIS displays lower arc radii in the manuscript, but from Figure 8a, it’s not visible; better to include a figure for visibility.

Response: Thanks for your reminder. The charge transfer resistance values of g-C₃N₄ nanostructures, g-C₃N₄@ZnIn₂S₄ heterostructures with different weights of g-C₃N₄ nanostructures, and ZnIn₂S₄ nanostructures, as shown in Table S1. The g-C₃N₄@ZnIn₂S₄ heterostructure with 0.01 g g-C₃N₄ nanostructure exhibits the lowest charge transfer resistance. This result indicates that g-C₃N₄@ZnIn₂S₄ heterostructures with 0.01 g g-C₃N₄ nanostructures possess the lowest charge transfer resistance to enhance efficiency in separating charge carriers, facilitating the fastest electron transfer process.

2. The authors should provide all samples' charge transfer resistance values from the EIS spectra.

Response: Thanks for your reminder. The charge transfer resistance values of g-C₃N₄ nanostructures, g-C₃N₄@ZnIn₂S₄ heterostructures with different weights of g-C₃N₄ nanostructures, and ZnIn₂S₄ nanostructures, as shown in Table S1. The g-C₃N₄@ZnIn₂S₄ heterostructure with 0.01 g g-C₃N₄ nanostructure exhibits the lowest charge transfer resistance.

3. It would be better to display a table comparing the H2 evolution of the gC3N4@ZnIn2S4 with other reported samples.

Response: Thanks for your reminder. Comparative analysis of the photocatalytic hydrogen production activity of g-C₃N₄@ZnIn₂S₄ heterostructures with other reported photocatalysts strongly supports their favorable application prospects, as shown in Table S2.

Table S2 List of photocatalytic hydrogen evolution for the g-C₃N₄@ZnIn₂S₄ heterostructures and other similar photocatalysts reported in the literature.

4. Some figures are not visible

Response: Thanks for your reminder. We have amended these figures in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

I am satisfied with the answers and revisions by the authors, and now recommend publication in its present form.

Some minor typos should be checked.

Author Response

Reviewers' comments:

I am satisfied with the answers and revisions by the authors, and now recommend publication in its present form.

Thanks for the pertinent and positive comments.

Author Response File: Author Response.docx