Cyano/Hydroxyl Groups Co-Functionalized g-C3N4 for Photocatalytic NO Removal: A Synergistic Strategy towards Inhibition of Toxic Intermediate NO2
, Yu Huang 4,5, Shuwei Wei 1, Mohsen Padervand 6,*, Shahnaz Ghasemi 7 and Chuanyi Wang 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript Cyano/hydroxyl groups co-functionalized g-C3N4 for photo-2 catalytic NO removal: a synergistic strategy towards inhibition 3 of toxic intermediate NO2 reports on development of cyano/hydroxyl groups-modified g-C3N4 (DCN-O-R) photocatalysts for NO selective conversion. The manuscript is well written and only minor grammatical errors should be addressed as detailed below:
1. Line 36-44 of the introductions are comments to the authors about the manuscript. That whole paragraph should be completely removed from this manuscript.
2. The band gap of semiconductor is excited when the energy of photon equals or exceeds its band gap…… this statement should be rephrased for correct meaning.
3. XPS spectra were provided for all the samples but in the figure caption it states that the results are for DCN-O-R. This should be corrected.
4. Line 280 ….key pint of our findings…correct this statement.
5. It could be better to include a comparative table of the current results with other previous findings
Comments on the Quality of English LanguageMinor revisions required
Author Response
Please see the attachment
Author Response File: 
Author Response.doc
Reviewer 2 Report
Comments and Suggestions for AuthorsThis review concerns manuscript titled: “Cyano/hydroxyl groups co-functionalized g-C3N4 for photocatalytic NO removal: a synergistic strategy towards inhibition of toxic intermediate NO2” submitted for consideration to Catalysts. The present work reports on the synthesis and characterization of cyano/hydroxyl groups co-functionalized g-C3N4 and its testing toward NO removal by photocatalytic oxidation. The work is interesting, novel, well executed, and the manuscript is of high technical and scientific quality. I recommend publication after the minor corrections listed below are addressed by the authors.
1. First paragraph of the introduction seems to be leftover from template guide. It should be removed before publication.
2. Experimental section refers readers to SI for all experimental details. However, the details are included in the appendix A to the present manuscript (and also in the SI). I would recommend including these details in the experimental section instead of the appendix or SI.
3. Fig. S1 in SI has incorrect formula for ammonium chloride (should be NH4Cl instead of NH3Cl).
4. I would also suggest moving Fig. S1 to the main manuscript. Seems impractical to have prospective readers have to hunt for SI online to be able to see the synthesis scheme, when synthesis is key part of the manuscript.
5. ROSs is used throughout the manuscript but only defined at the end in the experimental section. It should be defined at the first place it is used.
6. Information on how BET surface area and BJH pore size distribution were calculated should be provided in the experimental section (relative pressure range, cross-sectional area, adsorption or desorption branch, statistical film thickness curve, assumed pore shape, etc.).
7. Manuscript would benefit from diligent proofreading and spellchecking. For example: key pint on page 8 was probably supposed to be key point.
Author Response
Please see the attachment
Author Response File: Author Response.doc
Reviewer 3 Report
Comments and Suggestions for Authors1) First Paragraph, lines 36-44, should be removed. It is instructions on how to write the Introduction section. Apparently, it is a mistake, but I wonder how 11 authors oversee this mistake where each of them is expected to have read the final manuscript and approved it.
2) Two of the authors are zoologists. Their role in preparing this manuscript must be verified.
3) Two of the authors just helped in writing and editing (the draft was written by the first author). An author must significantly contribute to the manuscript!!!
4) According to reference 36 (lines 84-88), the HOMO and LUMO are located in the functional groups (CN and OH) (the excited electron is thus localized!). A few lines after (90-93), reference 37 mentions that the functional groups modulate the band structure. Which statement is the right one, that of ref 36 or ref 37?
5) In the last paragraph of the introduction the authors start using abbreviations without introducing them, for example, DCN-O-R and ROS. The problem becomes crucial when the authors present the results of the CN, DCN, DCN-O-R and DCN-O-P catalysts while the reader doesn’t have any idea of these designations. They are explained in the experimental part at the end of the manuscript in Appendix A. Please amend this situation; the catalyst designations must be explained at the beginning when the reader is first confronted with them.
6) Line 130: I believe the conclusion that “CN shows a smooth surface block structure” is not justified. It looks like the sample hasn’t been well prepared for the TEM measurement. The agglomeration of particles over each other results in an unclear picture (blackness, hindered transmission). I suggest either replacing the TEM micrographs of CN with better ones or, if not available, simply deleting them. Keep those of DCN-O-R, they are very good.
7) Line 135: Please delete the estimation of pore size by TEM to be 20-60 nm (It is not clear and not really conclusive). Leave the pore size for the BET measurements.
8) Line 142-143: delete “proving that they are mesoporous” because such hystereses have also been observed for microporous materials.
9) FTIR, Line 161: Please discuss how IR spectroscopy differentiates between triazine-based g-C3N4 and heptazine-based g-C3N4.
10) EPR, lines 169-176: EPR measures unpaired electrons. Where do unpaired electrons come from in your system? This has to be explained in detail in the paragraph about EPR.
11) XPS, lines 186-191: “The C 1s high-resolution spectra of CN, DCN and DCN-x, as shown in Fig. 3c, could be fitted into three peaks at the binding energies of 284.8, 285.8, and 288.3 eV, which are assigned to N-C=N, C-NHx or -C≡N [50], and sp2-hybridized carbon, respectively [51]. Compared to CN, the intensities of the characteristic peaks of DCN and DCN-x located at the binding energy of 286.37 eV increased, indicating that DCN and DCN-x contain high concentrations of -C≡N group. In the sentence above, there are three peaks designated to four types of carbon atoms (highlighted in yellow). Also, the peak at 286.37 attributed to the cyano group (highlighted in red) appears at a different position than reported above (yellow highlighted). Please explain.
12) Based on your XPS results, please make a table with the ratio N-to-C and O-to-C in all four catalysts.
13) I didn’t understand what is meant by N-vacancies. Please make an illustration of a nitrogen vacancy and explain how the presence of such vacancies can be experimentally observed without ambiguity.
14) In their application of Tauc’s formula, the authors assumed indirect allowed transitions. Any explanation for this? Have you tried to analyze assuming direct allowed transitions?
15) Lines 213-215: “In addition, the absorption tails of DCN and DCN-x in the range of 450-600 nm have obviously surges, indicating that the samples have an intermediate band gap [42].” The tail is most probably due to localized states at lower energies. This fits well with the interpretation given by ref 36 (comment #4 above). We don’t speak of intermediate bands unless there is more than one electronic system. Please correct the sentence.
16) Line 226: The authors say that the “intermediate band gap” was estimated to be 2.5 eV. First, it is not clear how this is determined. Please make a Figure only with the curve for DCN-O-R and show the two straight lines. I believe it is incorrectly determined. Moreover, you have to explain how this “intermediate band gap” is produced (is there another electronic system?). It is the localized electronic system that produces the tail and causes absorption at lower energies.
17) In Figure 4d, the VB edge of 1.93 is drawn between 2 and 3; it should be below 2.
18) Please make a plot of the reaction set-up.
19) The reaction was conducted in a continuous-flow glass reactor. Apparently, the reaction takes place in the gas phase and the authors use NOx analyzer which is used to determine the NOx concentrations in air. Under such conditions, the nitrates postulated to have formed cannot leave the catalyst surface; they stay on the surface, accumulate and poison the catalyst. Please comment on this.
20) The authors use scavenging agents to clarify the role of radicals in question. The mentioned scavenging agents are usually used in solution, not in gas phase reactions. I am confused!! Did the authors conduct the scavenging experiments under conditions different than those under which the gas-phase photocatalytic NO removal was performed?
21) Fig.5: The reactor used is a continuous-flow reactor. This means a steady state concentration will be reached within a specific time after admitting the reactants. Then, the concentration at the outlet remains constant. Indeed, this is the case with NO, the steady state (not equilibrium!!) is reached within three minutes, its concentration remains thereafter constant. But how come NO2 remains increasing whereas NO concentration is constant? NO2 is the reaction product; its production is controlled by NO removal. Please explain this discrepancy.
22) Fig.5: The initial concentration of NO was 800 ppb. For DCN, the removal was about 40%, which means that 320 ppb of NO reacted. However, only 140 ppb NO2 are formed. Please explain where the rest of the reacted NO has gone.
23) Lines 279-281: Do you want to inhibit the generation of NO2 or enhance its further reaction? If you want to inhibit it, then you must explain to what NO is being converted.
24) Please give the experimental details of the fluorophotometric measurements of H2O2.
25) Lines 361-362: “The sharp band at 1193 cm-1 describes the NO intermediate generated following the NO chemisorption on DCN-O-R surface”. What intermediate? Be specific.
26) Line 394 and Figure 8: The oxidation of NO by h+ doesn’t give NO2 directly. You need oxygen. Where does it come from? Write the corresponding chemical equation.
27) Figure 7: Please show the absorption range above 3000 cm-1. I expect to see negative bands due to the loss of H atom of hydroxyl groups.
28) Figure 7d: There are many negative bands (one above 1200 cm-1 and one below 2200 cm-1). Please explain the origin of these negative bands.
29) Fig7c and d: Please explain the negative band above 900 cm-1.
30) Fig7a; Absorption features between 1045 and 1085 were left without comments.
31) Nitrates usually show a very strong characteristic IR band due to the asymmetric stretch vibration above 1400 cm-1. It is absent in this work, what raises doubt about the identification of nitrate. The bands around 900-1200 cm-1 known for nitrate are much weaker in intensity than the asymmetric stretch vibration. Please comment on this. Without clarifying this issue, the formation of nitrate cannot be confirmed.
Comments for author File: 
Comments.pdf
needs minor editing
Author Response
Please see the attachment
Author Response File: Author Response.doc
Round 2
Reviewer 3 Report
Comments and Suggestions for Authors
Comments and Suggestions for Authors
My comments on the authors' responses are marked in red after each response.
1) First Paragraph, lines 36-44, should be removed. It is instructions on how to write the Introduction section. Apparently, it is a mistake, but I wonder how 11 authors oversee this mistake where each of them is expected to have read the final manuscript and approved it.
Response: Thanks for the reviewer’s helpful comments. As suggested, the first paragraph was removed.
Still, I wonder how 11 authors oversee this mistake where each of them is expected to have read the final manuscript and approved it.
2) Two of the authors are zoologists. Their role in preparing this manuscript must be verified.
Response: Thanks for the reviewer’s helpful comments. These two authors provided great assistance in revising the article and provided some guidance in drawing.
This doesn’t answer my concern about what zoologists have to do with this subject. I leave it to the editor to decide.
3) Two of the authors just helped in writing and editing (the draft was written by the first author). An author must significantly contribute to the manuscript!!!
Response: Thanks for the reviewer’s helpful comments. Two of the authors have also provided a lot of help in other areas, especially in conceptualization, methodology, data calculation, writing original draft preparation, etc., but the most important ones are writing and editing. So they made a huge contribution to the manuscript.
This doesn’t answer my concern about the role of two specific authors from Iran whose role, as stated in the manuscript in the section on authors’ contributions, was just writing and editing. I leave it to the editor to decide.
4) According to reference 36 (lines 84-88), the HOMO and LUMO are located in the functional groups (CN and OH) (the excited electron is thus localized!). A few lines after (90-93), reference 37 mentions that the functional groups modulate the band structure. Which statement is the right one, that of ref 36 or ref 37?
Response: Thanks for the reviewer’s helpful comments. There are different perspectives on the role of functional groups, which is not comprehensive. This work explores the role of different functional groups more comprehensively. From this perspective, reference 37 is more valuable. Thus, reference 36 has been removed from the manuscript.
OK
5) In the last paragraph of the introduction the authors start using abbreviations without introducing them, for example, DCN-O-R and ROS. The problem becomes crucial when the authors present the results of the CN, DCN, DCN-O-R and DCN-O-P catalysts while the reader doesn’t have any idea of these designations. They are explained in the experimental part at the end of the manuscript in Appendix A. Please amend this situation; the catalyst designations must be explained at the beginning when the reader is first confronted with them.
Response: Thanks for the reviewer’s helpful comments. The CN, DCN, DCN-O-R, DCN-O-P samples, and ROS were explained when they first appeared in the manuscript. OK
6) Line 130: I believe the conclusion that “CN shows a smooth surface block structure” is not justified. It looks like the sample hasn’t been well prepared for the TEM measurement. The agglomeration of particles over each other results in an unclear picture (blackness, hindered transmission). I suggest either replacing the TEM micrographs of CN with better ones or, if not available, simply deleting them. Keep those of DCN-O-R, they are very good.
Response: Thanks for the reviewer’s helpful comments. The TEM image of CN has been deleted.
OK
7) Line 135: Please delete the estimation of pore size by TEM to be 20-60 nm (It is not clear and not really conclusive). Leave the pore size for the BET measurements.
Response: Thanks for the reviewer’s helpful comments. We have corrected it in the revised manuscript as following:
“As shown in Fig. 2d, many mesopores with the pore sizes ranging from 20 to 60 nm can be clearly observed on the DCN-O-R surface.” has been removed from the manuscript.
OK
8) Line 142-143: delete “proving that they are mesoporous” because such hystereses have also been observed for microporous materials.
Response: Thanks for the reviewer’s helpful comments. As suggested, “proving that they are mesoporous” has been removed from the manuscript.
OK
9) FTIR, Line 161: Please discuss how IR spectroscopy differentiates between triazine-based g-C3N4 and heptazine-based g-C3N4.
Response: Thanks for the reviewer’s helpful comments. If a characteristic peak located at 995 cm-1 is displayed in the infrared spectrum, it corresponds to the respiratory pattern of the triazine ring. However, if a characteristic peak located at 810 cm-1 is displayed, it is attributed to the typical out of plane bending vibration of the heptazine ring. This distinguishes the two groups triazine and heptazine on g-C3N4. Such observation is consistent with what previously reported “Liu, J.; et al. Creating triazine units to bridge carbon nitride with titania for enhanced hydrogen evolution performance. Journal of Colloid and Interface Science. 2022, 608: 2768-2778.”
Please add to the manuscript that the formation of triazine-based C3N4 can be excluded, as evidenced by the absence of its characteristic band at 995 cm-1.
10) EPR, lines 169-176: EPR measures unpaired electrons. Where do unpaired electrons come from in your system? This has to be explained in detail in the paragraph about EPR.
Response: Thanks for the reviewer’s helpful comments. We have corrected it in the revised manuscript as following:
The paragraph of the EPR has added “The absence of nitrogen atoms leads to the presence of nitrogen vacancies in the g-C3N4 structure. After the N atom is lost, there are no paired electrons on the C atom, and the EPR signal will be enhanced.
OK
11) XPS, lines 186-191: “The C 1s high-resolution spectra of CN, DCN and DCN-x, as shown in Fig. 3c, could be fitted into three peaks at the binding energies of 284.8, 285.8, and 288.3 eV, which are assigned to N-C=N, C-NHx or -C≡N [50], and sp2-hybridized carbon, respectively [51]. Compared to CN, the intensities of the characteristic peaks of DCN and DCN-x located at the binding energy of 286.37 eV increased, indicating that DCN and DCN-x contain high concentrations of -C≡N group.” In the sentence above, there are three peaks designated to four types of carbon atoms (highlighted in yellow). Also, the peak at 286.37 attributed to the cyano group (highlighted in red) appears at a different position than reported above (yellow highlighted). Please explain.
Response: Thanks for the reviewer’s helpful comments. The high-resolution spectral positions of C-NHx and -C≡N in C1s are very close and generally difficult to distinguish. We have corrected it in the revised manuscript as following:
“The C 1s high-resolution spectra of CN, DCN and DCN-x, as shown in Fig. 3c, could be fitted into three peaks at the binding energies of 284.8, 285.8, and 288.3 eV, which are assigned to N-C=N, C-NHx or -C≡N [49], and sp2-hybridized carbon, respectively [50].” has been modified to “The C 1s high-resolution spectra of CN, DCN and DCN-x, as shown in Fig. 3c, could be fitted into three peaks at the binding energies of 284.8, 286.37, and 288.3 eV, which are assigned to N-C=N, C-NHx or -C≡N [49], and sp2-hybridized carbon, respectively [50].”
OK
12) Based on your XPS results, please make a table with the ratio N-to-C and O-to-C in all four catalysts.
Response: Thanks for the reviewer’s helpful comments. A table has been created based on the XPS results and placed in the supporting information.
The values reported in Table S1 haven’t been commented on in the manuscript. First, the ratio is below the ideal ratio of 1.33. Moreover, there is an obvious decrease in the N/C ratio and an increase in the O/C ratio, especially in DCNO-R. That deserves an explanation.
|
photocatalysts |
N/C |
O/C |
|
CN DCN DCNO-P DCNO-R |
1.190 1.176 1.173 1.049 |
0.053 0.053 0.063 0.069 |
13) I didn’t understand what is meant by N-vacancies. Please make an illustration of a nitrogen vacancy and explain how the presence of such vacancies can be experimentally observed without ambiguity.
Response: Thanks for the reviewer’s helpful comments. In the g-C3N4 crystal structure, one nitrogen atom is connected to two carbon atoms. When nitrogen atoms are missing, nitrogen vacancies are formed. After the N atom is lost, there are no paired electrons on the C atom, and the EPR signal will be enhanced. Therefore, the presence of nitrogen vacancies in g-C3N4 materials can be analysed through EPR testing.
Please add an illustration of N-vacancy in the manuscript.
14) In their application of Tauc’s formula, the authors assumed indirect allowed transitions. Any explanation for this? Have you tried to analyze assuming direct allowed transitions?
Response: Thanks for the reviewer’s helpful comments. Assuming that the transition method is a direct transition. The bandgap energy (Eg) of the samples were estimated by the Tauc formula (αhυ) = A (hυ - Eg)2. The fitted bandgap is 2.8 eV, even higher than pure g-C3N4. The calculation results are obviously unreasonable, so the transition method tends to be considered as an indirect transition.
OK
15) Lines 213-215: “In addition, the absorption tails of DCN and DCN-x in the range of 450-600 nm have obviously surges, indicating that the samples have an intermediate band gap [42].” The tail is most probably due to localized states at lower energies. This fits well with the interpretation given by ref 36 (comment #4 above). We don’t speak of intermediate bands unless there is more than one electronic system. Please correct the sentence.
Response: Thanks for the reviewer’s helpful comments. Impurities, defects, surface adsorbents, etc. can all cause electronic localization in semiconductor materials. The presence of localized electronic systems may alter the band structure and molecular orbital structure of the sample. We have corrected it in the revised manuscript as following:
The “In addition, the absorption tails of DCN and DCN-x in the range of 450-600 nm have obviously surges, indicating that the samples have an intermediate band structure” has been changed to “In addition, the absorption tails of DCN and DCN-x in the range of 450-600 nm have obviously surges, suggesting that the samples have the intermediate band structure”.
Still, I don’t understand what the authors mean by intermediate band structure. Why intermediate? The 2.5 eV-gap corresponds to the main band structure. In addition to the main band structure there are delocalized energy levels (not bands) corresponding to the surface defects and contaminants, as correctly stated in the authors’ response in point #16. Unless you can clarify this issue, I suggest deleting the word intermediate in “intermediate band structure”.
16) Line 226: The authors say that the “intermediate band gap” was estimated to be 2.5 eV. First, it is not clear how this is determined. Please make a Figure only with the curve for DCN-O-R and show the two straight lines. I believe it is incorrectly determined. Moreover, you have to explain how this “intermediate band gap” is produced (is there another electronic system?). It is the localized electronic system that produces the tail and causes absorption at lower energies.
Response: Thanks for the reviewer’s helpful comments. We have corrected it in the revised manuscript as following:
Figure 4b has been modified. And “Structural defects, impurities, and other surface adsorbents can lead to electron localization. Therefore, the localized electrons in DCN and DCN-x may be caused by cyanide groups, resulting in absorption tails in the range of 450-600nm.” has been added to the manuscript.
OK
17) In Figure 4d, the VB edge of 1.93 is drawn between 2 and 3; it should be below 2.
Response: Thanks for the reviewer’s helpful comments. As suggested, the position of the VB edge has been adjusted to the appropriate position, as shown in Figure 5d.
OK
18) Please make a plot of the reaction set-up.
Response: Thanks for the reviewer’s helpful comments. As suggested, The reaction device diagram has been placed in the supporting information, as shown in Figure S1.
OK
19) The reaction was conducted in a continuous-flow glass reactor. Apparently, the reaction takes place in the gas phase and the authors use NOx analyzer which is used to determine the NOx concentrations in air. Under such conditions, the nitrates postulated to have formed cannot leave the catalyst surface; they stay on the surface, accumulate and poison the catalyst. Please comment on this.
Response: Thanks for the reviewer’s helpful comments. Some nitrates will flow out with the airflow, while others will stay on the surface of the catalyst. After a certain period of use, the catalyst needs to be cleaned and regenerated.
It is not true that some nitrates can leave the catalyst surface in the airflow. Nitrate is an anion. It needs an opposite charge to get stabilized. It cannot leave the surface alone. Surface nitrates will decompose, releasing NO2!!!!! Either they accumulate and poison the catalyst, or they decompose, releasing NO2. This must be clarified. How would you regenerate the catalyst without producing NO2?
20) The authors use scavenging agents to clarify the role of radicals in question. The mentioned scavenging agents are usually used in solution, not in gas phase reactions. I am confused!! Did the authors conduct the scavenging experiments under conditions different than those under which the gas-phase photocatalytic NO removal was performed?
Response: Thanks for the reviewer’s helpful comments. According to the survey, some papers have used the aforementioned scavengers for capture experiments in gas-phase reactions, such as “Zhu, Q. H.; et al. Efficient full spectrum responsive photocatalytic NO conversion at Bi2Ti2O7: Co-effect of plasmonic Bi and oxygen vacancies. Applied Catalysis B: Environmental. 2022, 319.” and “Xin, Y.; et al. Photocatalytic NO removal over defective Bi/BiOBr nanoflowers: The inhibition of toxic NO2 intermediate via high humidity. Applied Catalysis B: Environmental. 2023, 324: 122238.” Specifically, Take 5 mL of anhydrous ethanol, 50 mg of sample, and some capture agents, and sonicate for 10 minutes. Conduct NO removal test after drying.
OK
21) Fig.5: The reactor used is a continuous-flow reactor. This means a steady state concentration will be reached within a specific time after admitting the reactants. Then, the concentration at the outlet remains constant. Indeed, this is the case with NO, the steady state (not equilibrium!!) is reached within three minutes, its concentration remains thereafter constant. But how come NO2 remains increasing whereas NO concentration is constant? NO2 is the reaction product; its production is controlled by NO removal. Please explain this discrepancy.
Response: Thanks for the reviewer’s helpful comments. In fact, Figure 6b shows the concentration change of NO2 after turning on the light. However, the concentration remained almost unchanged before turning on the lights.
The answer is not satisfactory. Under irradiation, NO reaches a steady state but NO2 not!!!!!
22) Fig.5: The initial concentration of NO was 800 ppb. For DCN, the removal was about 40%, which means that 320 ppb of NO reacted. However, only 140 ppb NO2 are formed. Please explain where the rest of the reacted NO has gone.
Response: Thanks for the reviewer’s helpful comments. The NO oxidation products are generally NO2 and NO3-. When the oxidation ability of the system is stronger, the final product tends to form NO3-. In addition to NO2, part of NO in the system are deeply oxidized to NO3-.
Not satisfactory. It is just speculation. There is no real evidence for the formation of NO3- in such quantities.
23) Lines 279-281: Do you want to inhibit the generation of NO2 or enhance its further reaction? If you want to inhibit it, then you must explain to what NO is being converted.
Response: Thanks for the reviewer’s helpful comments. NO2 is more toxic than NO, so inhibiting NO2 production is the ultimate goal. NO is oxidized to NO2 and further oxidized to NO3-. So, you shouldn’t use the words “inhibition of NO2 generation”. Instead, you must speak of the enhancement of further reaction to NO3-.
24) Please give the experimental details of the fluorophotometric measurements of H2O2.
Response: Thanks for the reviewer’s helpful comments. We have corrected it in the revised manuscript as following:
“Place 50 mL of H2O and 50 mg of catalyst in a beaker. Stir for 30 minutes under dark conditions. Take 3 mL of suspension and filter the catalyst. Add 100 uL (0.1 g/L) of horseradish enzyme to the liquid, wait for 10 minutes, H2O2 reacts with horseradish enzyme to generate fluorescence signals. And then add 1 mL of NaOH (0.1 mol) to stop the reaction. Turn on the light and take a sample every 10 minutes according to the above method. Using fluorescence spectrophotometry to analyze the concentration of produced H2O2, in which the excitation wavelength was set at 409 nm and the emission wavelength at 326 nm.” The above content has been added to the experimental section.
OK
25) Lines 361-362: “The sharp band at 1193 cm-1 describes the NO intermediate generated following the NO chemisorption on DCN-O-R surface”. What intermediate? Be specific.
Response: Thanks for the reviewer’s helpful comments. During the photocatalytic removal of NO by g-C3N4, a sharp band at 1193 cm-1 was observed in the catalytic reaction, which is considered a typical vibration of bidentate nitrite. Such observation is consistent with what previously reported. “Li, J. L.; et al. Ti3C2 MXene modified g-C3N4 with enhanced visible-light photocatalytic performance for NO purification. Journal of Colloid and Interface Science. 2020, 575: 443-451.” We added this paper as reference 59. And the “NO intermediate” in the manuscript has been changed to “biometric nitrate”
What is biometric nitrate? I don’t understand this term. Biometric usually refers to metrics of a living body!!!!
26) Line 394 and Figure 8: The oxidation of NO by h+ doesn’t give NO2 directly. You need oxygen. Where does it come from? Write the corresponding chemical equation.
Response: Thanks for the reviewer’s helpful comments. The reaction device is shown in Figure S1, and the gas in the reaction device is composed of air and NO. Oxygen comes from air. The main reaction equations are as follows:
DCN-O-R + hÊ‹ → e- + h+
O2 + e- → ·O2-
NO + h+ → NO+
NO+ + O2 → NO2
NO2 + ·O2- → NO3-
NO + ·O2-→ NO2-/NO3-
2NO2- + ·O2- → 2NO3-
OK
27) Figure 7: Please show the absorption range above 3000 cm-1. I expect to see negative bands due to the loss of H atom of hydroxyl groups.
Response: Thanks for the reviewer’s helpful comments. There is indeed a negative band at 3500 cm-1. As shown in the following figure.
Add to the figure and comment on it.
28) Figure 7d: There are many negative bands (one above 1200 cm-1 and one below 2200 cm-1). Please explain the origin of these negative bands.
Response: Thanks for the reviewer’s helpful comments. The occurrence of negative bands above 1200 cm-1 and below 2200 cm-1 may be due to strong characteristic peaks around this frequency range, making it appear like a negative peak. This phenomenon also occurred in reference 58.
Not satisfactory. Please provide an explanation.
29) Fig7c and d: Please explain the negative band above 900 cm-1.
Response: Thanks for the reviewer’s helpful comments. The occurrence of negative bands above 900 cm-1 may be due to strong characteristic peaks around this frequency range, making it appear like a negative peak.
Not satisfactory. Please provide an explanation.
30) Fig7a; Absorption features between 1045 and 1085 were left without comments.
Response: Thanks for the reviewer’s helpful comments. This phenomenon may be due to changes in the stretching vibration intensity of C-O during the reaction process. This phenomenon also occurred in reference 58.
You have to be more specific and add your comments to the manuscript.
31) Nitrates usually show a very strong characteristic IR band due to the asymmetric stretch vibration above 1400 cm-1. It is absent in this work, what raises doubt about the identification of nitrate. The bands around 900-1200 cm-1 known for nitrate are much weaker in intensity than the asymmetric stretch vibration. Please comment on this. Without clarifying this issue, the formation of nitrate cannot be confirmed.
Response: Thanks for the reviewer’s helpful comments. There is no characteristic IR band (as shown in the figure) at 1400-1600cm-1. The spectral bands near 900-1200cm-1 can demonstrate the formation of nitrate.. Similar experimental results were observed in references 27, 57, etc.
Not satisfactory. You cannot have the nitrate bands at 900-1200 without having those at 1400-1600 cm-1. This raises doubt on the identification of the nitrate species unless you can provide an explanation for the absence of the asymmetric vibration of nitrate.
Comments on the Quality of English Language
minor editing needed
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
