Research on Cu-Site Modification of g-C3N4/CeO2-like Z-Scheme Heterojunction for Enhancing CO2 Reduction and Mechanism Insight
Chengyang Feng
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this work, the authors developed a Cu@g-C3N4/CeO2 Z-scheme heterojunction photocatalyst for the highly selective reduction of CO2 to CO. The authors systematically analyzed the mechanisms behind the structure and performance enhancement of the catalyst. However, there are still some issues that need to be resolved before publication. I recommend accepting the paper after major revisions.
1. The authors present the optimized structures of CeO2, g-C3N4, and Cu@g-C3N4/CeO2 in Figure 1. The authors should provide details about the optimization process in the Experimental Section, including specifics related to theoretical calculations.
2. According to the photodeposition synthesis strategy used, the Cu species in the prepared samples should exist in the form of nanoparticles. Therefore, the modeling (Figure 1) and schematic diagram (Figure 8) may be incorrect. This could lead to a misunderstanding that the Cu species are single-atom layers or monodisperse.
3. In Figure 3c, the C 1s peak of g-C3N4 appears to differ significantly from what is reported in the literature, with an additional peak at 281.3 eV. This peak disappears in the Cu@g-C3N4/CeO2 composite. The authors need to provide an explanation for this. Additionally, the authors should describe the assignments for each subpeak after deconvoluting the C 1s peak.
4. A similar phenomenon is observed in Figure 3d. In the composite, the peak at 532.2 eV in the O 1s spectrum disappears. The authors need to analyze this change.
5. The authors observed significant shifts in the peaks of the monomeric materials and composite materials in the XPS spectra, attributing this to the interaction between g-C3N4 and CeO2. This analysis seems reasonable. However, given the significant peak shifts, did the authors calibrate the XPS data using the C 1s peak? If not, please calibrate the data.
6. TRPL spectroscopy was used to analyze the photogenerated carrier separation efficiency of the samples. However, the data separation in Figure 4b is not very pronounced. It is recommended that the authors show the fluorescence decay time constants and fit the carrier lifetimes. Some recent papers that demonstrate this type of analysis can be referenced and cited: 10.1039/D3EE03032F.
7. As a Z-scheme heterojunction photocatalyst, determining the band structure of each component is very important. The authors should calculate the band gaps of the samples using UV-Vis DRS. The following papers can be referenced and cited: 10.1002/adfm.202309761.
8. The authors conducted CO2 reduction experiments using the developed photocatalyst and detected the formation of CO. Are there other products present in the system, such as CH4 and H2?
Comments on the Quality of English LanguageLanguage needs to be improved to a certain extent.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsComment 1: The authors stated in the abstract: “high photocatalytic efficiency of 92%” What do the authors refer to as efficiency?
Comment 2: In the (Cu@g-C3N4/CeO2) composite, where is Cu deposited: on g-C3N4, CeO2, or both?
Comment 3: Why was g-C3N4/CeO2 not characterized and tested?
Comment 4: On page 8, line 236, the authors state: “peak at 1472 cm-1 belonged to the COOH*43,44, which is the critical intermediate from CO2 to CO, besides, the peaks at 1123 and 1063 cm-1 belonged to HCO3− and the peaks at 1398 cm-1 was considered to be the CO32-“ Authors are advised to carefully review the cited papers and accurately identify maxima, as well as to investigate both symmetric and asymmetric vibrations of carbonate.
Comment 5: The Figure 8 shows Schematic diagram of the mechanism of CO2 reduction by Cu@g-C3N4/CeO2 under visible light irradiation.
Did the authors detect oxygen?
What is the summary reaction?
Do the authors suggest that Cu acts as a connection between CeO2 and g-C3N4?
Is this figure constructed using flat band potentials and band gaps derived from the measurements?
Comment 6: The experimental data lack sufficient information.
For example:
page 10 line 311 “Gas products were detected by a gas chromatography (GC 5890N) equipped with hydrogen flame ionization detector (FID)” There is no data provided about the column or carrier gas.
page 10 line 304 “In situ Fourier transform infrared spectroscopy (in situ FTIR) was carried out to research the CO2 photoreduction process (Thermo Fisher Nicolet iS-10)”. Data on in situ adsorption/reaction measurements should be provided here.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript is subjected to some improvement before being accepted for publication:
1. Section 3.1.2 – 3.1.5: The synthesis methods reported in this study are authors own method or they adopted from other studies, if not then provide appropriate reference.
2. Line # 120: The elemental composition value in % should be provided from XPS analysis.
3. Line # 74: The novelty and objectives of current research should be presented in detail and more clear way.
4. Did author check the optimum results of Cu@g-C3N4/CeO2 at different operating parameters?
5. The comparison of current study results with related published studies should be discussed for better understanding.
6. Introduction section: Some references are outdated such as 2014,2016, authors are required to add appropriate recent references.
7. Authors need to check the reference style according to journal guidelines.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe revision has improved the quality of the manuscript greatly. I think the present paper is suitable for publication.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have revised accordingly
