Photocatalytic Degradation of Diclofenac by Nitrogen-Doped Carbon Quantum Dot-Graphitic Carbon Nitride (CNQD)

Round 1

Reviewer 1 Report

In this paper, nitrogen-doped carbon quantum dot (NCQD)/graphitic carbon nitride (CNS) composites with different contents of NCQD (2, 4, 6, 8 wt%) were synthesized. The presence of NCQD on the surface of nanosheets of graphitic carbon nitride (CNS) contributed to forming a better phase composition and morphology evolution. The photocatalytic activity of the synthesized materials was assessed during the degradation of diclofenac (DCF) in aqueous solution under visible light irradiation. As a result, improved photocatalytic efficiency in DCF degradation was observed for all the CNQD composites in comparison with bulk graphitic carbon nitride (bCN) and CNS. I have done a thorough reading for this paper. The manuscript focuses on an important topic, and the idea of this paper is relatively clear. Overall, the manuscript is well organized, and therefore I recommend acceptance for publication on Catalysts after the authors have revised their manuscript according to the following comments:

1.  The EDX mapping for carbon C, N, and O of NCQDs in Figure 2 is not clear. Please update the images.

2.  The author mentioned “Table 1. Surface properties of bCN, CNS and CNQD photocatalysts.” Please confirm Table 2 or Table 1. And explain why the pore size of CNS was smaller than bCN.

3. The author mentioned “There are no significant shifts in the deconvoluted peaks of the N1s spectra between CNS and CNQD-6, which strongly suggest that coupling interactions exist between NCQD and CNS in the hybrid nanostructures.” Please explain it in more detail

4.      The author mentioned “CNQD-6 removal efficiency was reduces by only about 10% even in the third cycle and this result reveal its excellent reusability and photostability properties.”. In order to prove the excellent properties, the reusability and photostability properties of catalysts in other literatures should also be listed in this manuscript.

5.      Please carefully check and unify the writing of unit and Figure, like “ml/mL” “Fig./Figure”.

Author Response

1. The EDX mapping for carbon C, N, and O of NCQDs in Figure 2 is not clear. Please update the images.

• The images of Figure 2 (EDX mapping for carbon C, N, and O of NCQDs) are updated.

 

2. The author mentioned “Table 1. Surface properties of bCN, CNS and CNQD photocatalysts.” Please confirm Table 2 or Table 1. And explain why the pore size of CNS was smaller than bCN.

• The table number for the surface properties is updated (Table 2).
• The revised sentence for this result is in line 235 – 256.
• Line 241 – 248 specifically explain difference pore size of bCN and CNS: “The pore size distribution peak of CNS is located at 9 nm, smaller than the bCN, located at 16 nm. The total pore volumes of bCN and CNS obtained are 0.6 cm³/g and 0.5 cm³/g, respectively. The results were similar to those observed [75], which indicates that the two-step polymerization could facilitate the formation of small pores in the complete polymerization process. The smaller pore size of CNS might be due to the well and tight contact between the layer of CNS nanosheets, while the bigger pore size might be due to the aggregation of the sphere bulk structure of bCN.”

  

3. The author mentioned “There are no significant shifts in the deconvoluted peaks of the N1s spectra between CNS and CNQD-6, which strongly suggest that coupling interactions exist between NCQD and CNS in the hybrid nanostructures.” Please explain it in more detail

• The description of Figure 8 (XPS spectra) was revised and further explain the C1s and N1s spectral peak.
• The revised sentence is in Line 271-278: “Figure 8c shows the N 1s spectrum of CNS, which revealed three peaks, situated at 398.67, 399.92 and 401.00 eV, which corresponded to sp2 of tri-s-triazine rings (C–N=C), bridged nitrogen atoms groups (N≡C) and amino functional groups (C–N–H) bonds, respectively [65,79]. The slight shifts in the peaks of N1s spectra of CNQD-6 situated at 398.30, 399.56 and 400.65 eV after the NCQDs modification, which suggest that the NCQDs might load onto the surface of CNS via the formation of C–N=C, N≡C and N–H bonds, while the original structure of CNS almost did not change which was similar to the reported literature [76].”

 

4. The author mentioned “CNQD-6 removal efficiency was reduced by only about 10% even in the third cycle and this result reveal its excellent reusability and photostability properties.”. In order to prove the excellent properties, the reusability and photostability properties of catalysts in other literatures should also be listed in this manuscript.

• The description regarding to the reusability and photostability properties of graphitic carbon nitride are updated and the related literature are cited.
• The revised sentence is in line 416-423: “This shows that the CNQD-6 removal efficiency was reduced by about 10% even in the third cycle. This result reveals its excellent reusability and photostability properties, similar as reported literature [63,87]. The C–N=C sp2-hybridized aromatic N atoms were reported as the critical component of g-C₃N₄, which is associated with the in-plane π-conjugated bond and plays a significant role in absorption, closely related to the photocatalytic performance [88]. Only a slight loss of the C–N=C bond was ob-served and reported by [87] during the photostability test, indicating the excellent sta-bility properties of g-C₃N₄.

5. Please carefully check and unify the writing of unit and Figure, like “ml/mL” “Fig./Figure”.

The unit and Figure were updated accordingly.

Reviewer 2 Report

Manuscript ID: catalysts-2279730

Huzaikha Awang and co-authors reported " Photocatalytic Degradation of Diclofenac by Nitrogen-doped 2 Carbon Quantum Dot-Graphitic Carbon Nitride (CNQD) ". Although the topic is interesting, but some important aspects were not performed. Following comments should be addressed before possible consideration for publication in worthy Journal of catalysts. I believe it will not take a long for the authors to work on this revision. My comments are,

1.      In abstract add numerical values from results

2.      Novelty is not specified in introduction section

3.      Suggestion  other latest and modified methods to control or degradation of diclofenac (DCF) in introduction

4.      No methods discussed to synthesize Carbon Quantum Dots (CQDs)  materilals & their modifications as carbon nitride materials (CNS)

5.      Nitrogen doped but urea quantum dots and citric acid used how HOC(CO2H)(CH2CO2H)2.

6.      Headings and detail work in experiment looking not relatable

7.      In experimental scheme is not include and it’s attached in results. Shift Scheme1 in experimental section

8.      In 324-326 cite reference

9.      In introduction section cite these latest references on degradation and carbon nitride based materials, like https://doi.org/10.3390/app11199000, Chemical Physics Letters 805 (2022) 139939, Optical Materials 126 (2022) 112199.

10.  Fig 4 consisting further sub-figs but not explained in caption. Caption should be corrected accordingly.

11.  This is interesting to note that there 311 is no diffraction peak for NCQD in the CNQD photocatalyst due to the minimal mass 312 loading on the CNS nanosheets same as reported by previous studies then how their activity changed . Therefore, 313 it can be concluded that, the structural integrity of CNS remained intact when loaded with 314 NCQDs, which suggested that there was no disruption to the structural identity of CNS 315 when NCQDs were added and allowing the modulation of its optical properties. In ftir also no difference same. How?

12.  In conclusion add more data from results

13.  There are so many typo grammatical errors in whole manuscript,should be revised by some native speaker and formatting should be checked.

Author Response

1. In abstract add numerical values from results

• The abstract was revised and the important numerical values (photocatalytic degradation of DCF) of optimal CNQD-6 was stated.

 

2. Novelty is not specified in introduction section.

• The novelty of this work was specified in introduction section.
• The sentence is in line 96-103: “The NCQD/g-C₃N₄ composites were reported to have excellent efficiency in photocatalytic degradation, such as methylene blue (MB) degradation [52] and DCF degradation [25,63]. However, it should be noted that although the hybridisation of NCQDs and g-C₃N₄ had been reported, the synthesis method, morphology, physico-chemical and photoelectrochemical properties of NCQD/g-C₃N₄ composites still need more detailed research and differ from one research paper to another. To the best of our knowledge, there is still less work that investigates the photocatalytic of NCQDs/g-C₃N₄ nanosheets for photocatalytic degradation of DCF under visible light irradiation.”

 

3. Suggestion other latest and modified methods to control or degradation of diclofenac (DCF) in introduction.

• The latest and modified methods to control or degradation of diclofenac (DCF) has been added in introduction.
• The sentence is in line 58-66: “Currently, several identified methods, including photocatalytic degradation, have been employed to capture or degrade DCF [1,25-28], such as adsorption [24], ozonation [29], photo-electrocatalytic degradation [30] and bioremediation [31]. It was suggested that the organic contaminants in wastewater must be removed using highly consistent, ecologically friendly, and economical treatment procedures [28,32]. Photocatalytic degradation can be described as an ecologically friendly and economical treatment procedure because it can fully degrade the resistant pollutants and mineralize the organic pollutants into carbon dioxide and water using only photocatalyst and light irradiation [33-37].”

 

4. No methods discussed to synthesize Carbon Quantum Dots (CQDs) materilals & their modifications as carbon nitride materials (CNS).

• The method to synthesize Nitrogen Carbon Quantum Dots (NCQDs) materials & their modifications as carbon nitride materials has been discussed.
• The sentence is in sub-sentence 3.3 Preparation of Nitrogen-doped Carbon Quantum Dots (NCQDs).

 

5. Nitrogen doped but urea quantum dots and citric acid used how HOC(CO2H)(CH2CO2H)2.

• Line 85-91: “Heterogeneous doping of CQDs with atoms of nitrogen [52], palladium [53], sulfur [54] and phosphorous [55] has been demonstrated to be able to enhance photocatalytic performances. The majority of research has focused on nitrogen-doped CQDs (NCQDs) because of their high quantum yield (QY), narrowed band gap due to an increase in electron density, and longer absorption wavelength [54]. The NCQDs can be synthesize by using the nitrogen containing precursors such as urea [52,56-58] and ethylenediamine [59].”

 

6. Headings and detail work in experiment looking not relatable.

• The Headings and detail work in experiment was revised.

 

7. In experimental scheme is not include and it’s attached in results. Shift Scheme1 in experimental section

• The Schematic illustration was shifted in the experimental section and rename as Scheme 2.

 

8. In 324-326 cite reference.

• Line 324-326 has been revised and cited.
• The revised sentence was currently located in line 190-198: “The CNS and CNQD photocatalysts exhibited similar XRD characteristic peaks at 2θ = 13.2° and 27.40°. The intensity of diffraction peaks 002 of CNQD composites were slightly changed compared to CNS, indicating the changes in CNQD composites crystal size. The same characteristic peaks demonstrated that the graphite-like phase structure of CNS did not change with the introduction of NCQDs, which was in line with the SEM analysis as depicted in Figure 3. The structural integrity of CNS remained intact when loaded with NCQDs, similar as reported by previous studies [57,67].”

9. In introduction section cite these latest references on degradation and carbon nitride based materials, like https://doi.org/10.3390/app11199000, Chemical Physics Letters 805 (2022) 139939, Optical Materials 126 (2022) 112199.

• The introduction section was revised and cited with several latest references.
• The revised sentence in line 71-75.

 

10. Fig 4 consisting further sub-figs but not explained in caption. Caption should be corrected accordingly.

• The photos of CNQD photocatalysts in Figure 4 were introduced and describe in caption.

 

11. This is interesting to note that there is no diffraction peak for NCQD in the CNQD photocatalyst due to the minimal mass loading on the CNS nanosheets same as reported by previous studies then how their activity changed. Therefore, it can be concluded that, the structural integrity of CNS remained intact when loaded with NCQDs, which suggested that there was no disruption to the structural identity of CNS when NCQDs were added and allowing the modulation of its optical properties. In ftir also no difference same. How?

• This mentioned sentence was revised.
• The revised sentence is in line 190-198 : “The CNS and CNQD photocatalysts exhibited similar XRD characteristic peaks at 2θ = 13.2° and 27.40°. The intensity of diffraction peaks 002 of CNQD composites were slightly changed compared to CNS, indicating the changes in CNQD composites crystal size. The same characteristic peaks demonstrated that the graphite-like phase structure of CNS did not change with the introduction of NCQDs, which was in line with the SEM analysis as depicted in Figure 3. The structural integrity of CNS remained intact when loaded with NCQDs, similar as reported by previous studies [57,67].”
• The XPS discussion in Line 271-278 shows the slight shifts in peaks of N1s spectra: “Figure 8c shows the N 1s spectrum of CNS, which revealed three peaks, situated at 398.67, 399.92 and 401.00 eV, which corresponded to sp2 of tri-s-triazine rings (C–N=C), bridged nitrogen atoms groups (N≡C) and amino functional groups (C–N–H) bonds, respectively [65,79]. The slight shifts in the peaks of N1s spectra of CNQD-6 situated at 398.30, 399.56 and 400.65 eV after the NCQDs modification, which suggest that the NCQDs might load onto the surface of CNS via the formation of C–N=C, N≡C and N–H bonds, while the original structure of CNS almost did not change which was similar to the reported literature [76].”
• The introduction of NCQDs did not affect the morphology and structure of CNS. The physicochemical and photoelectrochemical properties of CNQD composites were studied and showed a slight alteration compared to bCN and CNS, which affect the photocatalytic degradation of DCF.

 

12. In conclusion add more data from results

• The conclusion has been revised and the data from results had been added.

 

13. There are so many typo grammatical errors in whole manuscript, should be revised by some native speaker and formatting should be checked.

• The formatting has been revised and carefully checked.

Reviewer 3 Report

The manuscript entitled “Photocatalytic Degradation of Diclofenac by Nitrogen-doped Carbon Quantum Dot-Graphitic Carbon Nitride (CNQD)” describes nitrogen-doped carbon quantum dot (NCQD)/graphitic carbon nitride (CNS) composites with different contents of NCQD (2, 4, 6, 8 wt%) and evaluated as photocatalyst for diclofenac degradation in aqueous solution under visible light irradiation. Among them, 6 wt% NCQD loaded g-C3N4 nanosheets affords superior photodegradation activity for diclofenac. This is an interesting work. However, there are still several points found in the manuscript requiring further elucidations after my reading in depth.

1.     The novelty of the work should be established compare your results with the carbon nitride-related diclofenac degradation literature.

2.     Provide a tabular form of the literature performance results with the present work.

3.     Add references to g-C3N4 catalysts for diclofenac introduction (DOI: 10.1016/j.jece.2021.105827) and charge-transfer (DOI: 10.1021/acs.nanolett.8b02740) and EIS data (DOI:10.1016/S1872-2067(20)63647-6) and so on.

4.     Typological errors such as spaces, subscripts, superscripts, etc.

 

5.     Figure 11: Include other samples data (CNQD-2, CNQD-4, CNQD-8, and bCN) for understanding for readers

Author Response

1. The novelty of the work should be established compare your results with the carbon nitride-related diclofenac degradation literature.

• The novelty of this work was specified in introduction section.
• The sentence is in line 96-103: “The NCQD/g-C3N4 composites were reported to have excellent efficiency in pho-tocatalytic degradation, such as methylene blue (MB) degradation [52] and DCF degradation [25,63]. However, it should be noted that although the hybridisation of NCQDs and g-C₃N₄ had been reported, the synthesis method, morphology, physico-chemical and photoelectrochemical properties of NCQD/g-C₃N₄ composites still need more detailed research and differ from one research paper to another. To the best of our knowledge, there is still less work that investigates the photocatalytic of NCQDs/g-C₃N₄ nanosheets for photocatalytic degradation of DCF under visible light irradiation.”

 

 

2. Provide a tabular form of the literature performance results with the present work.

• The table of literature performance results to compare with the present work has been provide in the photocatalytic performance results (Figure 3).

 

3. Add references to g-C3N4 catalysts for diclofenac introduction (DOI: 10.1016/j.jece.2021.105827) and charge-transfer (DOI: 10.1021/acs.nanolett.8b02740) and EIS data (DOI:10.1016/S1872-2067(20)63647-6) and so on.

• Several literatures regarding to carbon nitride-related diclofenac degradation were added in the introduction section.
• The reference for EIS data also has been added.

 

4. Typological errors such as spaces, subscripts, superscripts, etc.

• The formatting had been carefully checked and revised accordingly.

5. Figure 11: Include other samples data (CNQD-2, CNQD-4, CNQD-8, and bCN) for understanding for readers.

• The data depicted is for pristine CNS and CNQD-6 catalysts (which shows the best performance). The others sample do not been tested.

Round 2

Reviewer 2 Report

Manuscript No: catalysts-2279730

Title: Photocatalytic Degradation of Diclofenac by Nitrogen-doped 2 Carbon Quantum Dot-Graphitic Carbon Nitride (CNQD)

The authors have improved the manuscript but still some changes are required.

1.      Should provide clean file along with track changes file.

2.      In introduction section cite these latest references on degradation and carbon nitride based materials, like https://doi.org/10.3390/app11199000, Chemical Physics Letters 805 (2022) 139939, Optical Materials 126 (2022) 112199.

3.      Effect of pH of diclofenac (DCF) should be studied

4.      Effect of Concentration of diclofenac (DCF) should be studied

5.      Author mentioned in manuscript diclofenac (DCF) but in keywords Diclofenac sodium (DCF). What this actually is ?

6.      Kinetic study for the degradation of Diclofenac sodium (DCF with CNQD shoyld be discussed in details

7.      Authors have sited 88 references which is unacceptable. References should be reduced to 60 to 65.

Author Response

1. Should provide clean file along with track changes file.

• The track changes function is used in this revised manuscript.

 

2. In introduction section cite these latest references on degradation and carbon nitride based materials, like https://doi.org/10.3390/app11199000, Chemical Physics Letters 805 (2022) 139939, Optical Materials 126 (2022) 112199.

 

• Manuscript “A Comparative Study of Cerium- and Ytterbium-Based GO/g-C₃N₄/Fe₂O₃ Composites for Electrochemical and Photocatalytic Applications” has been cited as a reference number 38.

 

• Manuscript “Facile synthesis of Yb³⁺-Zn²⁺ substituted M type hexaferrites: Structural, electric and photocatalytic properties under visible light for methylene blue removal” has been cited as a reference number

 

• Manuscript “Photo-Fenton activated C₃N_4x/AgO_y@Co_1-xBi_1-yO₇ dual s-scheme heterojunction towards degradation of organic pollutants” has been cited as a reference number 44.

 

3. Effect of pH of diclofenac (DCF) should be studied

• The effect of pH of DCF from previous literatures has been added and highlighted in this report (Line 374 – 407).

 

4. Effect of Concentration of diclofenac (DCF) should be studied

• The effect of initial concentration of DCF from previous literatures has been added and highlighted in this report (Line 374 – 407).

 

5. Author mentioned in manuscript diclofenac (DCF) but in keywords Diclofenac sodium (DCF). What this actually is?

• The precursor of pollutant is diclofenac sodium (DCF, Sigma Aldrich, Germany) and the first mentioned diclofenac sodium is in introduction (line 46).

 

6. Kinetic study for the degradation of Diclofenac sodium (DCF with CNQD should be discussed in details

• The kinetic study has been revised and discussed and detail in this report (Line 431 – 466).

 

7. Authors have sited 88 references which is unacceptable. References should be reduced to 60 to 65.

Deleting any (arbitrarily chosen) references in our manuscript for no obvious reasons (“too many” is not a substantial reason) would be a violation of the standards of good scientific conduct. We are dedicated to obeying the codex of good scientific conduct as released of DFG in 2019 (Link: https://www.dfg.de/download/pdf/foerderung/rechtliche_rahmenbedingungen/gute_wissenschaftliche_praxis/kodex_gwp.pdf). Therefore, we did not delete any of the references because they are essential for the manuscript.