Modified Approach Using Mentha arvensis in the Synthesis of ZnO Nanoparticles—Textural, Structural, and Photocatalytic Properties

Round 1

Reviewer 1 Report

Stoyanova et al. prepared ZnO nanoparticles using extract of Mentha Arvensis (MA) leaves as stabilizing/reducing agent, followed by hydrothermal treatment at 180°C. The as-prepared sample was characterized using a wide range of techniques including XRD, IRS, SEM, EPR, BET, TEM, IR,  and so on. The results and scientific content of this manuscript look interesting and of promising interest. However the authors should spend some time in revising their manuscript before it can be accepted for publication.

1. The authors presented 1 image/graph in each Figure, totalling 16 individual Figures in this paper. This is unusual for Research Article. The authors should consider putting several images/graphs together in one Figure and name them Figure 1a, 1b, 1c etc.

2. Figure 1 (schematic) should be re-drawn for better illustration.

3. Figure 5 shows the EDX spectrum of the sample. The raw data should be used to plot this graph.

4. Y-axis in some Figure 10 and 11 is missing.

5. Some recent advances on ZnO structures and applications can be found below and should be referred:

- Bu et al. Rechargeable sunlight-promoted Zn-air battery constructed by bifunctional oxygen photoelectrodes: Energy-band switching between ZnO/Cu2O and ZnO/CuO in charge-discharge cycles. Chemical Engineering Journal, 2021, 133559.
- Xiang et al. Enhanced Piezo-Photoelectric Catalysis with Oriented Carrier Migration in Asymmetric Au−ZnO Nanorod Array. Small, 2020, 16, 1907603.
- Gao et al. Synthesis of ultra-long hierarchical ZnO whiskers in a hydrothermal system for dye-sensitised solar cells. RSC Advances, 2016, 6, 109406-109413.

Author Response

Answers to reviewers comments to Ref: Applsci-1553128

 

Dear Prof. Fang ,

We are very thankful to the editor and reviewer comments and recommendations about the paper entitled „Modified approach using Mentha Arvensis in synthesis of ZnO nanoparticles – textural, structural and photocatalytic properties” by D. Stoyanova et al. The newly inserted text in the revised version is highlighted in yellow color. The reference list and the figures were revised and appear with new numbers.

Answers to the reviewer 1:

1. The authors presented 1 image/graph in each Figure, totalling 16 individual Figures in this paper. This is unusual for Research Article. The authors should consider putting several images/graphs together in one Figure and name them Figure 1a, 1b, 1c etc.

A1: The remark was taken into consideration.

2. Figure 1 (schematic) should be re-drawn for better illustration.

A2 For better illustration of the details, concerning the ZnO  particles formation we have added new scheme (Fig 1-b).

3. Figure 5 shows the EDX spectrum of the sample. The raw data should be used to plot this graph.

A3:  We have made consultation with the EDX specialist. The EDX apparatus was generated  the raw data and the figure have plotted automatically. 

4. Y-axis in some Figure 10 and 11 is missing.

A4: The remark was taken into consideration.

5. Some recent advances on ZnO structures and applications can be found below and should be referred:

- Bu et al. Rechargeable sunlight-promoted Zn-air battery constructed by bifunctional oxygen photoelectrodes: Energy-band switching between ZnO/Cu2O and ZnO/CuO in charge-discharge cycles. Chemical Engineering Journal, 2021, 133559.
- Xiang et al. Enhanced Piezo-Photoelectric Catalysis with Oriented Carrier Migration in Asymmetric Au−ZnO Nanorod Array. Small, 2020, 16, 1907603.
- Gao et al. Synthesis of ultra-long hierarchical ZnO whiskers in a hydrothermal system for dye-sensitised solar cells. RSC Advances, 2016, 6, 109406-109413.

A5:We have added the proposed references as ref. 3, 4 and 5.  

 

Author Response File: Author Response.docx

Reviewer 2 Report

My Review reports about this manuscript is attached. 

Comments for author File: Comments.pdf

Author Response

Answers to reviewers comments to Ref: Applsci-1553128

 

Dear Prof. Fang ,

We are very thankful to the editor and reviewer comments and recommendations about the paper entitled „Modified approach using Mentha Arvensis in synthesis of ZnO nanoparticles – textural, structural and photocatalytic properties” by D. Stoyanova et al. The newly inserted text in the revised version is highlighted in yellow color. The reference list and the figures were revised and appear with new numbers.

Answers to reviewer 2

1) Introduction of manuscript is very poor in terms of literature survey with respect green synthesis of nanoparticles using plant extracts specially Mentha plant and ZnO nanoparticle.

А: We are very thankful for the reviewer remark and have enriched the information in the Introduction par with corresponding literatures. (ref. N  3,4,5, 27,28).

2) Author should to discuss some more recent references and clearly discus and prove the novelty of this study as compared to studies reported in literature. In fact in literature various studies are reported based ZnO nanoparticle synthesis using Mentha plant. I am listing only few of them, for Instance, Appl. Sci. 2020, 10, 5054; doi:10.3390/app10155054; https://doi.org/10.1016/j.matpr.2021.01.971;

 

https://doi.org/10.1016/j.micpath.2019.04.022 .

 

A2 We are very thankful for the reviewer remark. We have added the proposed references concerning the Mentha mediated ZnO synthesis in part Introduction (ref. N 35 and 38 ).

 

3) Sub-section 2.2: Authors reported that: “After that 12 g of MA leaves were ground into powder using a mortar and the powder was mixed with 230 ml double distilled water”. Authors should clarify that what are scientific reasons behind election of this specific ratio?

1. A3/ The specific ratio MA-water in our experiment  is based on the data in Rad et al  Rad S.S., Sani A. M., Mohseni S., Biosynthesis, characterization and antimicrobial activities of inc oxide nanoparticles from leaf extract of Mentha Pulegium (L), Microbial Pathogenesis, 2019, 131, 239-245. doi: 10.1016/j.micpath.2019.04.022.  The authors have obtained well crystallized nanosized ZnO, which  has potential for many biological applications. Based on our experience we have proved, that the hydrothermal synthesis of ZnO was carried out under mild conditions with selected type of precipitants results in mesoporous nanosized ZnO particles, which are highly active photocatalysts./ref 17/.

 

4) Is authors characterized the phytochemical constituents of Mentha plant leafs?

5) It will be better if authors will specify the name of specific phytochemicals which are useful in the synthesis ZnO nanoparticles from the Zn2+ ions.

 

A4 and A5:  The present paper is the start of research work in the field of green synthesized ZnO particles. In this connection the aim of the present article is only to clarify the effect of the introducing of the MA extract on the some physicochemical features and on the photocatalytic activity. For this reason, the investigation of composition of Mentha Arvensis leafs is planned as future experiment in order to obtain deep insight concerning the specific phytochemicals playing reducing and stabilizing role. According to the results from the gas chromatographic analysis of Mentha Arvensis presented in ref. [Manuja R., Prasad B. et al., Mater Today, Proc, in press, https://doi.org/10.1016/j.matpr.2021.01.971] the main constituents are: cellulose (38-42%), hemicellulose (27-30%) and lignin (12-8%). These data were added in Experimental part in the revised version of the article and in new Scheme 2 (which represents the reducing/stabilizing role of these phytochemicals in Mentha Arvensis).

6) During the synthesis of nanoparticles authors are reporting just very common tend which are already reported in several other studies in literature. It will be better for readers, if authors will clarify the specific role of plant extract and thermal treatments in an autoclave with clear scientific proves.

 

A6 : In the available literature exist plenty of papers, concerning ZnO green synthesis, which involve the precipitation and in some cases additional thermal treatment. Among the ZnO powders preparation techniques, the hydrothermal method is a low cost and fast synthesis method, offering potential capability to obtain lowly aggregated ZnO structures with different morphologies, narrow grains size distributions and high degree purity without any heat treatment at high temperature. The our previous experiments concerning ZnO partciles synthesis involves the use of urea as precipitating agent in view of the highest photocatalytic efficiency in the oxidative degradation of RB5 dye. The using of urea as precipitating agent ensures the homogeneous precipitation, while NaOH leads to faster precipitation and lower surface area. The samples, obtained using urea possess the higher specific surface area and greater share of mesopores. Only a few studies report the preparation of ZnO by  hydrothermal treatment of precipitate, obtained using plant extract [Zare et al, Scientific Reports. 2019, doi:10.1038/s41598-019-44309-w]. In the present study we have used the advantages of the both : the hydrothermal synthesis and the application of plant extract as stabilizing/reducing agent. As a result high effective ZnO photocatalysts with high specific surface area (80-140 m2/g) and larger share of mesopores ( 16-17 nm) were obtained. The higher surface area and pores sizes ensures better charge diffusion, mass transportation and faster reaction rate of discoloration. On the contrary, common green synthesis (with conventional precipitant  NaOH) without hydrothermal activation leads to preparation of particles with lower specific surface  area and smaller pore sizes.[ Vinayagam et al, Applied Nanoscience,2021, doi 10.1007/s13204-021-01816-5]The proposed synthesis involving 3 stages: precipitation by means of Mentha Arvensis extract, hydrothermal treatment and final low temperature treatment give rise to effective control of the texture and morphology, thus ensuring the successfully preparation of highly active photocatalyst.

 

7) Is it possible to prepare ZnO nanoparticles either only plant extract or only thermal treatment by adopting same procedure as reported in this study?

A7 We synthesized powder with only MA plant without thermal treatment, but the samples obtained are amorphous and no porous (as could be seen on the photo below) For this reason the samples have not exhibited  any photocatalytic activity.For this reason these experiments were not presented in the article.

 

The sample, denoted with code G0 in our article was prepared by the same technology (the same conditions of the hydrothermal treatment and thermal treatment  as other bio-synthesized samples (G1, G2), without participation of Mentha extract.As can be seen form the results in atricle, it possesses different morphology, crystallographic phase composion and particles size, which reflects on its  photocatalytic efficiency.

 

8) It is not clear to me, How the increasing concentration of plant extracts results in broadening of the peaks of XRD analysis (Fig.2).

It is well known, that the plant extract used in biosynthesis of oxide particles plays role as stabilizing, capping agent as well as steric hindrance thus preventing agglomeration process. Consequently the increasing of the plant concentration of the bio synthesized samples leads to decreased particle sizes. For better illustration of this effect we have added new scheme 2 in the revised version .  The decreasing of the particles size with the increasing of the plant content are also obtained by other research groups ( for instance  M. G. Demissie, F. K.Sabir, G. D. Edossa, B. A. Gonfa, https://doi.org/10.1155/2020/7459042]- this reference is added in revised version.

 

9) Section 3: Instead of using common sentences of other published articles, authors should clearly mention the name of constituents of plant extract which are working as reducing, stabilizing and capping agents for the ZnO nanoparticles.

A9 According to the results from the gas chromatographic analysis of Mentha Arvensis presentedby   et al the main constitutens are : cellulose (38-42%), hemicellulose (27-30%) and lignin (12-8%). The role of these constituents as reducing/stabilizing agents is illustrated  in  Scheme 2 in the revised version.[Manjula R.,et al, Doi: 10.1016/j.matpr.2021.01.971].

 

10) Author should provide error bar in Fig. 15 and 16

A10: It was taken into consideration. The Figures have revised with the error bars (now Figure 11a and 11b)

 

11) It will be better if authors provide the mechanistic aspects diagram of proposed photocatalytic degradation process for selected dye using ZnO nanoparticles.

A11  The reviewer's comment is taken into consideration and  the probable mechanism of dye discoloration is summarized in sheme, as new Figure 11.

 

12) English of the manuscript must be improved.

A12: The reviewer's comment is taken into consideration. The English text has been improved by the Editor of journal “Nanoscience and Nanotechnology” of the Bulgarian Academy of Sciences ISSN:1313-8995 following the Instructions of “American Chemical Society Style Guide – A Manual for Authors and Editors” Janet S. Dodd, Editor, Marianne C. Brogan, Advisory Editor, ACS Washington DC 198

 

 

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

The authors revised their manuscript as required. However, the authors should put individual Figures (Figure Xa, b, c and d) together in one Figure. Otherwise, this paper can now be accepted for publication.

Author Response

The authors revised their manuscript as last required.

Author Response File: Author Response.doc

Reviewer 2 Report

The authors improved the manuscript significantly, thus manuscript can be accepted.

Author Response

The authors thank you to the reviewer for his precise review of theirs manuscript.