Size-Controlled ZnO Nanoparticles Synthesized with Thioacetamide and Formation of ZnS Quantum Dots
Round 1
Reviewer 1 Report
The manuscript is very interesting due to the possibility of applying the solutions presented in this material. ZnS quantum dots have been known for a long time, but work is still ongoing to optimize their production methods and use them as luminescent materials in electronics.
The layout of the article is unquestionable, as is the design of the research.
However, the manuscript contains several fragments that require clarification or correction:
1) Line 70
The abbreviation "ZAD" is not often used. Although there is an explanation in the text, I suggest writing the chemical name in "2.1 Materials" - Zinc Acetate Dihydrate (ZAD, 99.0%)
2) Lines 82 and 83
Since I did not find an explanation neither in the manuscript nor in the reference material [41], please describe what the "two-step purification process to remove the residue" looks like.
3) The most important and the essence of the entire material is the authors' indication of the "decomposition" of ZnO during the formation of ZnS (reaction with TAA). Of course, the authors justify this with appropriate research (XRD), and in lines 223-225 we read: "Our results enable a broader understanding of the synthetic mechanisms involved in the use of TAA as sulfur source in the formation of ZnO/ZnS nanocomposites." There is a substantive inconsistency here. So do we only have ZnO structures after reaction with TAA, or do we have a composite of ZnO and ZnS?
4) If the authors actually suggest the ZnO ->ZnS process, they should propose a mechanism for this process. We do not see such a "proposal" in Scheme 1.
Author Response
See the attached response file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript by Ju-Seong Kim et al. reports on size-controlled ZnO nanoparticles synthesized with thioacetamide and the formation of ZnS quantum dots. The authors employ sol-gel and hydrothermal methods to prepare the size-controlled blue, green, and yellow ZnO quantum dots and nanocrystalline ZnO nanoparticles and subsequently mixed (reacted) with the thioacetamide for investigating the ZnS formation. The authors have investigated the materials by means of X-ray diffraction, Transmission Electron Microscope, UV-vis, and Photoluminescence spectroscopic. In general, the question, employed methodology, and the material (ZnS) itself are interesting. However, the presented data requires further extended and comparative discussions and clarification, mainly considering the previous literature. First of all, the introduction fails to provide reasonable information about the fundamental properties of ZnS and ZnO nanoparticles/quantum dots. I suggest the authors enhance these discussions by considering different methods, nanoparticle stabilization approaches, formation pathways, and the critical role of different techniques on the final nanoparticle properties. Also, instead of "abstract" discussions of prior properties of ZnS, ZnO NPs/QDs, their very important application areas, such as solar cells, photocatalysis, etc., can be mentioned (i.e., Catalysts 2022, 12(11), 1316). In the current state, it is difficult to understand the main idea of the manuscript from the abstract and conclusions. Therefore, I suggest the authors improve these parts. The main problem is as follows. Although the authors present sufficient results to prove ZnS formation from ZnO NPs/QDs, the process itself is rather unclear. So what is the main driving force to convert stable ZnO to ZnS, such as temperature, polarity, or any other properties of solvents, reaction kinetics, etc. So, the main parameters that influence this chemical reaction should be clearly discussed. It is well known that the properties (i.e., the energy gap, PL emission, etc.) of ZnO and ZnS (similar to other nanomaterials) are very sensitive to vacancy states, which are, in turn, related to the preparation techniques (i.e., Materials Letters 162 (2016) 121–125 and Chemical Physics Letters 646 (2016) 69–74). I suggest the authors implement further comparative discussions in this aspect. So if the ZnS derived from ZnO contains less or more vacancy states or defective structure in comparison with one-step chemical synthesis. In addition to the conceptual and discussion-related issues, the manuscript contains many typos, missing articles, grammatical errors, back-and-force, as well as repetitive statements, which must be corrected before the second review process.
The manuscript contains many typos, missing articles, grammatical errors, back-and-force, as well as repetitive statements, which must be corrected before the second review process.
Author Response
See the attached response file.
Author Response File: Author Response.pdf
Reviewer 3 Report
I recommend the paper for publication in Electronic Materials after addressing several issues.
Figure 1 caption: “(a) B_ZnO QDs, (b) G_ZnO QDs, (c) Y_ZnO QDs, and (d) NC_ZnO NPs.”
There are no labels (a), (b), (c), (d) in the figure.
Lines 166-167: “In the absorption spectra of B_ZnO QDs, after synthesizing for 5 min with TAA a new absorption peak at 266 nm except the peak at 322 nm newly occurred”
It won’t hurt to explain to which material the peak at 322 nm is related and why it “completely disappeared after synthesizing for 10 min with TAA”.
It also would to helpful to provide deconvolution of the peaks.
The spectra shown in Fig. 4 (except of spectra (a), (b) and (c) for ZnO without TAA) show some sharp equidistant lines predominantly in the blue-UV spectral region, which seem to be an artifact caused by an interference in the optical spectrometer, which does not belong to the measured samples. Can the authors explain the nature of these features?
From the facts that all ZnS particles are of the same size, regardless the size of ZnO particles “…only spherical ZnS QDs with similar diameters of 2.2 nm were observed in all samples,” (lines 146-147) and the ZnO-related peak in the absorption spectra do not move as ZnO is consumed by growing ZnS it may be concluded that ZnS does not form “shells” on the surfaces of ZnO QDs, but rather forms ZnS nuclei and consume Zn from surrounding. Is it so? What is the author’s view on the mechanism of ZnS growth?
The main goal of ZnS growth on ZnO QDs is to improve PL from ZnO. Moreover, such improvement is well known and mentioned by the authors (Refs. 27, 28, for example). It remains unclear why the authors did not achieve the enhancement of ZnO PL. I think that some speculations could be added regarding this finding.
Author Response
See the attached response file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for making corrections to the manuscript.
Reviewer 2 Report
The authors have adequately addressed the reviewers' questions and concerns. The manuscript can be accepted for publication in Electronic Materials.
