Stable Carbon Dots from Microwave-Heated Carbon Nanoparticles Generating Organic Radicals for In Situ Additions

Round 1

Reviewer 1 Report

The article by

Weixiong Liang et al. entitled

„Stable Carbon Dots from Microwave-Heated Carbon Nanopar ticles Generating Organic Radicals for in situ Additions” is in a scope of a journal Polymer MDPI.

Purchased carbon carbon dota were functionalized with N-ethylcarbazole (NEC) using microwave-assisted method.

The prepared functionalized carbon dots were caracterized using UV-vis, fluorescence, TEM, AFM and quantitative proton and ¹³C NMR methods. Applied methods provided evidences on functionalization by cleaving alpha-hydrogen. NEC functionalized carbon dots exhibited high structural stability stability.

The manuscript is recommened for publication after satifying the remarks and questions raised below.

Section 2. Experimental Section 2.1. Materials describing the commercial purchased materials and chemicals does not provide characteristic of carbon dots and purity of applied chemicals.

Temperature was not monitored in Suplementary Materials section 2.

Fig. 3. Absorption spectra for N-ethylcarbazole (NEC) and diamine 2,2’-(ethylenedioxy)bis(ethylamine) (EDA) functionalized carbon dots are shown and discussed in the region 400 nm – 700 nm. However, the most interesting reagion of ππ* C=C absorption between 230 nm to ca. 290 nm, redshifted due to functional groups of larger atomic number and nitrogen amine groups (at ca. 340 nm), are missing. In my opinion this may reveal differences, which should be discussed (absorption peak shifts and/or intensity changes).

Section 5. Results and Discussion

In my opinion result presented in Fig. 6 and Fig. 7 (NMR methods) should be better described. Comparison of peak areas (intensities) and FWHM is better to be presented in a Table. This will make the discussion of results more clear.

Author Response

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Reviewer 2 Report

In this paper, the authors presented the surface functionalization of preexisting small carbon nanoparticles with N-ethylcarbazole radical addition.

The paper is properly divided in sections and sub-sections but needs some corrections before its publication in the journal.

-        The authors should avoid the use of acronyms in the keywords;

-        The authors used multiple references, for example 13-20 in the introduction section: they should try to evidence the contribution of the single reference;

-        The authors should better describe the experimental apparatus for the microwave irradiation, even if reported in the supplementary materials;

-        Which temperature is reached during the microwave irradiation? Which is the duration of the irradiation? Which is the MW power used?

-        The conclusions section should be separated;

 

-        The authors should refer in the main text to the supplementary materials;

Author Response

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Reviewer 3 Report

The manuscript "Stable Carbon Dots from Microwave-Heated Carbon Nanoparticles Generating Organic Radicals for in situ Additions" is an interesting and practical study on microwave treatment of small carbon nanoparticles. However, in my opinion, it is difficult to recognize it as completely original, given the previously published work by the same authors - Xianyan Ren, Weixiong Liang, Ping Wang, Christopher E. Bunker, Montrez Coleman, Lindsay Rose Teisl, Li Cao, Ya-Ping Sun, A New Approach in Functionalization of Carbon Nanoparticles for Optoelectronically Relevant Carbon Dots and Beyond, Carbon (2018), doi: 10.1016/j.carbon.2018.09.085, which is open-access. The article [X. Ren et al Carbon 141 (2019) 553] details a new approach in the functionalization of small carbon nanoparticles under a microwave-assisted reaction, where carbon nanoparticles were also functionalized by N-ethylcarbazole (NEC) under a microwave-assisted reaction. A significant part of the Figures in the submitted manuscript are somewhat modified figures from the article [X. Ren et al Carbon 141 (2019) 553]. There is a reference to this work in the submitted manuscript (line 90), but information about the results obtained in an earlier paper is not available in the reviewed manuscript. In my opinion, results from [X. Ren et al Carbon 141 (2019) 553] should be written directly in a new article and readers' attention should be focused on new and original results that supplement those previously obtained. There is no doubt that over the three years of work, the authors have made progress in understanding the mechanisms of functionalization of carbon nanoparticles by N-ethylcarbazole, so my wish does not seem excessive

When discussing NMR spectra of functionalized nanodiamonds, it would be appropriate to refer to the almost classic review by A.M. Panich, Nuclear magnetic resonance studies of nanodiamond surface modification, Diamond & Related Materials (2017).

Also, when finalizing the text of the manuscript, in my opinion, it would be worthwhile to dwell in more detail on the discussion of one of the key results of the article - the sample stability based on the deviations of fluorescence quantum yields. I am sure that the readers of the article would be grateful if the authors justify the choice of solvent and measurement temperature, indicate the excitation wavelength, and also provide a brief analysis of reasons why quantum yields deviate from average values.

Author Response

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Round 2

Reviewer 2 Report

In my opinion, the authors properly revised the manuscript