Photoreactive Carbon Dots Modified g-C₃N₄ for Effective Photooxidation of Bisphenol-A under Visible Light Irradiation

Comments/suggestion/question

Response

Iqbal et al. modified the g-C3N4 with carbon dots for photocatalytic removal of BPA. The manuscript is well organized. The catalysts were also well characterized, and the structural-activity relationship was well illustrated. This manuscript can be accepted after solving the following minor concerns:

Thank you. We appreciate the comment.

Concerns:

1.        The resolution of Figures and schemes is not enough, at least 300 dpi is required, especially for Scheme 1.

Thank you for the comment. Figure 1 was replotted and resized to make it clearer. Figures 3 (e) and (f) were replaced with updated images. However, due to the limitation of the instrument in our facility, the quality of the images was limited. The DFT pore size distribution has been removed from Figure 4 as insets and placed in the Supplementary Materials, as Figure S1. Figures 5 and 6 were replotted and resized. Scheme 1 was redrawn.

2.        The third column in table 1 is not clear. For example, which outcome/remarks are corresponding to the photocatalyst of “High surface area C-dots/g-C 3 N4”?

Thank you for the comment and the question. Table 1 reports examples of carbon dots and g-C₃N₄-based photocatalysts and their application. Column 3, Table 1 is intended to highlight the outcome and the role of the carbon dots as reported by the authors. The third column heading has been changed to “Outcome and role of CDs/CQDs” to avoid confusion. We have removed “high surface area" from “High surface area C-dots/g-C₃N₄”. Please refer to Table 1, page 3.

3.        The mentioned peaks in FT-IR should better be marked in the Figures to make it clear.

Thank you for the suggestion. The wavenumbers have been included. Please refer to Figure 1(b) page 4.

4.        Some important papers about photocatalysts should be referenced to improve the quality of this manuscript (e.g. Catalysts 2022, 12, 1005).

Thank you for suggesting an interesting paper. We have included it as reference 70 in the revised manuscript.

Comments/suggestion/question

Response

The manuscript reports the facile synthesis of CDs/g-C3N4 and the degradation of bisphenol A by using visible light. As compared with the previous studies, the photocatalyst is consisted from the less toxic materials, and is more stable, which is confirmed by the well experiments. The catalyst has been characterized in detail, and the degradation pathway of BPA has also been carefully analyzed using LC/MS. Although it is not very advanced, it does report useful information. If the following points are resolved, I would like to recommend the publication.

Thank you. We appreciate the comments.

1  Role of carbon dots

  Authors described that the addition of CQDs enhanced the light absorption capacity of the nanocomposite and suppressed the photoinduced e-/h+ recombination rate. The latter is supported by the PL spectra. However, the former is not clear. How does the absorption of the CQDs contribute to activity?  

Thank you for the comment. The proof can be seen from the UV Vis analysis (page 8). Data collected from the analysis shows shifting of the band edge and band gap energy after incorporation of the CDs compared to pure g-C₃N₄. The shifting is caused by the enhancement in the light absorption.

2  Degradation pathways of BPA

In scheme 1, there are some mistake. The m/z value of hydroquinone is 110. The hydroxylated BPA (m/z 259) can not afford 4-isopropenylphenol (m/z 134). The intermediate (m/z 152) would be 4-(2-hydroxyprop-2-yl)phenol. Please see the literature (Langmuir 2017, 33, 10468.).

Thank you for the comment. We have rewritten the section. Please refer to pages 12 and 13. We have included the reference as reference 64.

3  Degradation of endocrine disruptor by the heterogeneous photocatalysts

  The heterogeneous photocatalysts can decompose organic compounds with very low concentration, and thus, are suitable for the degradation of endocrine disruptor. Consequently, authors should confirm the complete removal of BPA. Please see the literature (ACS Catal. 2013, 3, 903.). 

Thank you for the comment. The synthesized photocatalyst was unable to remove the BPA completely. The removal only reaches 90%.

The recommended paper is very interesting. We will definitely cite in our future study.