Mechanochemically Synthesized Chalcogenide Cu₃BiS₃ Nanocrystals in an Environmentally Friendly Manner for Solar Cell Applications

Round 1

Reviewer 1 Report

Well writtend and documented research study

Author Response

We thank the reviewer for the positive evaluation of our work.

Reviewer 2 Report

Ternary wittichenite Cu3BiS3 nanocrystals were prepared mechanochemically using a planetary ball mill from elemental copper, bismuth and sulphur in a stoichiometric ratio in only 5 minutes. Cu3BiS3 nanocrystals show ~26% enhancement on the photoresponsive current. The present paper needs major revision.

Abstract needs improvement in terms of conclusion and results.

State of the art results have to contain also the authors results, not only their research basis.

Section 3 has no comparison with state of the art and no relevant results discussion. Please improve it and add value to your experiment.

Explain outcomes from Figure 8, also.

Nevertheless, what is the added value of this research? What are the applications? What is this study accuracy and repeatability?

Conclusion is weak.

Author Response

We thank to the reviewer for favorable comments and suggestions. We incorporated corresponding changes into body of the manuscript and prepared the responses for Reviewer.

Author Response File: Author Response.docx

Reviewer 3 Report

The research paper focuses on mechanochemical synthesis of nano-sized Cu3BiS3 crystals and their characterization be series of physicochemical analyses (XRD, TEM/EDX, Raman, UV-vis, photoluminescence etc.) The research is original and could be interesting for the readership of the Crystals. However, authors add missing experimental details, better analyze own data and make better comparison their results with the known literature data on Cu₃BiS₃. A text correction by a native speaker is required.

There are some concerns that need to be addressed:

1)     I have noticed many deficiencies in English grammar and style. A text correction by a native speaker is required. Some examples:

·        Abstract. “Ternary wittichenite Cu₃BiS₃ nanocrystals were prepared mechanochemically using a planetary ball mill from elemental copper, bismuth and sulphur in a stoichiometric ratio in only 5  minutes… Cu₃BiS₃ was nanocrystalline with approximate crystallite size”

·        Lines 30-31. “copper-bismuth-sulphide (Cu-Bi-S) materials have received significant attention in solar cell research as alternative absorbers due to their low-toxicity, low cost and earth-abundant elements”

·        Lines 75-80. “Mechanochemistry using tools of high-energy milling is a scalable and reproducible method. Moreover, the  mechanochemically synthesized compounds are composed of morphologically inhomogeneous, weakly crystallized and structurally disordered nanoparticles. Mechanochemical solid-state approach represents an environmentally friendly alternative to the classical methods and has been successfully applied also for the ternary chalcogenide synthesis by our group”

Etc.

2)     Particles size of Cu, Bi and S used for the synthesis should be indicated.

3)     Please indicated purity and supplier of the Ar used. Please indicate how the milling jar was filled under Ar atmosphere – it was done using glowbox? Milling was done without cooling breaks? Please indicate balls-to-powder ration (BPR). What was the yield of Cu₃BiS₃ phase?

4)     Generally, EDX analysis should be carried out using 5-6 points and on different particles, and then the results of the analysis should be averaged. How the EDX analysis was standardized? Please make an ICP/MS analysis in order confirm EDX results and be sure that amorphous phases are absent (especially amorphous sulphur, which could be easily amorphous in harsh condition used for the synthesis).

5)     Please provide in SI Raman spectra in 4000-100 cm^-1 range. Please make all bands assignment for Raman spectra.

6)     Please update the quality of the graphics in the article up to 300 dpi. The numbers on some Figures are hardly visible: Figures 4-5

7)     According to Figure 3 the agglomerate has 600nm x 1200 nm dimensions, according Figure 5 the particle size is 1.5 μm. What was medium particle size? Isotherm of N₂ adsorption and desorption at 77K should be provided in SI. As it reported in ref. 19, a specific BET surface for particles with medium size as 30 nm and 90 nm were 17.6 and 4.0 correspondingly, so if the determined particle size is 38 nm the BET specific surface should be comparable with reported in ref. 19 values, however if the particle size is between 350-600 nm thus specific BET surface 0.7-2.7 seems reasonable.

Author Response

We thank to the reviewer for favorable comments and suggestions. We incorporated corresponding changes into body of the manuscript and prepared the responses for Reviewer.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Article was revised.

Author Response

We thank the reviewer for the positive evaluation of our work.

Reviewer 3 Report

In general, I satisfied with authors reply and changes made.

I have several remarks:

1) The details of sample preparation for ICP-OES is missing. Sample was digested used HNO₃, aqua regia or HCl/HNO₃/HF mixture. 

2) Space group should be P2₁2₁2₁ instead "P₂₁₂₁₂₁".

3) It is written that  "the Cu₃BiS₃ sample was unstable under the beam irradiation." - at which temperature measurements were carried out? In the case of such instability lower temperatures could be used.

4) "It must be taken into account that in the mechanosynthesis method, all the elements that are introduced as  precursors will be present in the final product of the reaction, irrelevant of the fact wheter or not the reaction has been completed." - I tend to disagree with that since the "final product" generally is regarded as the synthesized phase namely Cu₃BiS₃. There are numerous cases when the introduced reagents formed only mechanical mixture without forming a new phase. Moreover in some cases the final product could be washed out from the reagents or purified by recrystallisation or sublimation.

Author Response

We thank to the reviewer for the comments and suggestions. We have  incorporated the corresponding changes into the re-revised manuscript.

Author Response File: Author Response.docx