Review Reports - Single-Layered Biosynthesized Copper Oxide (CuO) Nanocoatings as Solar-Selective Absorber

Round 1

Reviewer 1 Report

There is no obvious innovation and application value in the manuscript

Author Response

Response; Thank you for the comments. The research article is aimed at developing an alternative surface coatings as spectrally selective absorber, and spectrally selective CuO coating surfaces via biosynthesis has not been reported yet.

Reviewer 2 Report

This manuscript reported the green synthesis of copper oxide (CuO) nanoparticles and deposited them on stainless steel (SS) substrates using spin-coater at 700, 800, 900 and 1000 rpm. The morphological surface, structural, and compositional analysis of the obtained nanocoatings were studied using SEM, XRD, EDX, and Raman spectroscopy. However, this paper contains many weak points, it must be improved. Overall, this paper is not suitable for publication in this form, which needs to be rewritten in light of the recommendations mentioned below.

Some major concerns are shown as following:

1. Introduction: The literature review in this part is insufficient.

2. The article has many formatting problems, please check the full text carefully and make corrections: 1) Punctuation should be followed by a space; 2) There should be a space between the number and the unit; 3) The format of the unit is inconsistent.

3. Please unify the format of the references.

4. In order to facilitate readers to quickly and accurately understand the preparation process of nanocoatings prepared in the paper, please add the preparation flow chart of relevant samples in the paper.

5. The cause analysis of the experimental phenomenon is not enough in the manuscript, so the authors are requested to add the relevant chemical reaction formula and schematic diagram of the samples prepared, and provide a more detailed explanation of the relevant reasons.

6. In order to facilitate readers to understand the properties of the nanocoatings prepared in this paper, the authors are asked to compare the main properties and prices of the samples prepared in this paper with the list of values in the literature.

Author Response

We are grateful to the editors and reviewers for their appreciations to our manuscript and their constructive criticism on certain issues. We agree with the reviewer’s comments and accordingly, the text and figures of the manuscript has now been modified and the changes that have been made in the revised manuscript.

Please note that the changes effected in the text are highlighted in red.

Reviewr-2;

Some major concerns are shown as following:

Introduction: The literature review in this part is insufficient.

Response; We agreed with the reviewer's comment. The literature review has been modified, please refer to the introduction section on page (1 & 2) of the manuscript.

The article has many formatting problems, please check the full text carefully and make corrections: 1) Punctuation should be followed by a space; 2) There should be a space between the number and the unit; 3) The format of the unit is inconsistent.

Response; We agreed with the reviewer's comments. Accordingly, the punctuation, space and unit inconsistent have been updated and reviewed.

Please unify the format of the references.

Response; The reference format has been updated, and reviewed. Please refer to the references section on page (15-18) of the manuscript.

In order to facilitate readers to quickly, and accurately understand the preparation process of nanocoatings prepared in the paper, please add the preparation flow chart of relevant samples in the paper.

Response; Thank you for the comments. The schematic representation of the preparation process, and deposition of CuO as absorber surface has included, please refer to the methodology section in figure-1 on page (3) of the manuscript.

The cause analysis of the experimental phenomenon is not enough in the manuscript, so the authors are requested to add the relevant chemical reaction formula and schematic diagram of the samples prepared, and provide a more detailed explanation of the relevant reasons.

Response; Thank you for the comments. Accordingly, a chemical reaction diagram that illustrate the preparation process of CuO has included, please refer to the Result and discussion section in figure-2 on page (5) of the manuscript.

In order to facilitate readers to understand the properties of the nanocoatings prepared in this paper, the authors are asked to compare the main properties and prices of the samples prepared in this paper with the list of values in the literature.

Response; Thank you for the comments. Recently, in the literature several multi-layers absorber surfaces have reported for solar energy harvesting using conventional physical and chemical procedures. Herein, we demonstrated a single layered CuO nanocoatings via green synthesis which is environmentally friendly, and clean synthesis technique. However, we do not figure out the list of prices compared with in the literature. The assessment will be addressed when this research is further converting into projects in the future.

Reviewer 3 Report

In this paper, the cactus pear extracts were used as chelating and stabilizing agent for green synthesis of CuO nanoparticles, then the green synthesized CuO nanoparticles were deposited on stainless steel substrate using a spin coater. This paper can be reconsidered after some major revisions.

1. The quality of SEM images in Fig. 1 is poor. The author needs to redo the experiment to get new high-quality pictures.

2. Almost all curves need to be redrawn to meet the magazine format requirements.

3. The appropriate surface roughness can determine the optical property of absorber surfaces. The coatings tended to be slightly thicker with rough surfaces at lower RS of the spin coater. However, which is the optimal RS value for the spin coater? The author needs to do more experiments so as to obtain the inflection point.

Author Response

Please note that the changes effected in the text are highlighted in red.

Reviewer-3

The quality of SEM images in Fig.1 is poor. The author needs to redo the experiment to get new high-quality pictures.

Response; Thank you for the comments. The SEM images has been remeasured, please refer to the surface morphology section in figure-3 on page (6) of the manuscript.

Almost all curves need to be redrawn to meet the magazine format requirements.

Response; Thank you for the comments. Accordingly, the curves have been redrawn. Please refer to figure 5, figure 6, and figure 9 of the manuscript.

The appropriate surface roughness can determine the optical property of absorber surfaces. The coatings tended to be slightly thicker with rough surfaces at lower RS of the spin coater. However, which is the optimal RS value for the spin coater? The author needs to do more experiments so as to obtain the inflection point.

Response; Thank you for the comments. The research article is aimed at developing of spectrally selective CuO absorber surface with a higher solar absorptance (α ≥ 0.90) as a function of rotational speed (RS) of spin coater. The authors carried out more experiments even below 700 rpm (at 500, and 600 rpm), with no significance change in solar absorptance (α) value however the thermal emittance (ε) is high due to scattering of sunlight and radiation lose in the IR region, for instance at 600 rpm the emittance (ε) was 0.38, this accompanied by increase in surface roughness and thickness of the nanocoatings. The optimal value was achieved at RS of 700 rpm with 0.90 absorptance (α), and relatively better emissivity (ε=0.31); Moreover, better spectral selectivity is observed at 700 rpm.

Round 2

Reviewer 1 Report

I think it's acceptable

Reviewer 2 Report

The authors have revised the manuscript carefully based on referees' comments. The scientific quality of this paper is improved. The manuscript can be accepted at the present version.