Comparative Study on Enhanced Photocatalytic Activity of Visible Light-Active Nanostructures for Degradation of Oxytetracycline and COD Removal of Licorice Extraction Plant Wastewater

Round 1

Reviewer 1 Report

In the manuscript, the authors prepared TiO₂ modified with L-Histidine, L-Methionine and L-Asparagine, respectively, to prepare photocatalysts with different N, S, and C doping. The results of photocatalytic degradation show that the modified TiO₂ does exhibit more excellent photocatalytic activity. The experimental design is logical, the thinking is clear, and it has a certain degree of novelty. However, many imprecise places in the manuscript need to be corrected, and major revisions must be made before it can be considered for publication.

1. In line 22, "PL" analysis should be written as "PL analysis".

2. How did the author distinguish between bCOD and nbCOD? In Figure 2, why are the values of bCOD and nbCOD so high when the reaction time is 0? According to Line 224, the total COD value obtained by adding the three in Figure 2 seems to be incorrect. Authors, please double-check.

3. When the abbreviation of a proper noun appears for the first time, the author needs to add the corresponding full name, such as BOD5, etc.

4. In Figure 6, each table requires a corresponding photocatalyst label. For the infrared test results, how did the author attribute the 3400 cm^-1 peaks to both the hydroxyl group and the NH₂? Also, please mark the peak at 600 cm^-1 for L- Asparagine-TiO₂. I don't see a peak in the graph that is identifiable and distinguishable from the other two catalysts.

5. For Figure 6d, the authors should make corresponding tangents to confirm the bandgap width.

6. From the XRD and FT-IR results, the difference between C, N doped-TiO₂ and C, N, and S doped cannot be determined. The author must provide the XPS spectra of the three catalysts and the corresponding fine spectra.

7. The author needs to determine the energy band structure of L-histidine-TiO2, and also needs to supplement the active species capture experiment. Only by combining the two can the relationship between the energy band position and the generation of free radicals be obtained, and a reasonable photocatalytic degradation mechanism can be proposed.

8. The author needs to number all formulas sequentially instead of using "1,2,3" repeatedly.

9. Suggestion: consider citing some similar photocatalytic degradation research reports. Such as Liu C, Mao S, Wang H, et al. Chemical Engineering Journal, 2022, 430: 132806; Liu C, Mao S, Shi M, et al. Journal of Hazardous Materials, 2021, 420: 126613; Chemical Engineering Journal, 2022, 449: 137757.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors made a comprehensive study about the TiO2 modification with L-18 Histidine, L-Methionine and L-Asparagine and their application in the photocatalytic degradation of oxytetracycline and COD removal in licorice extraction wastewater. The authors designed the work in a systematic way and performed valuable experimental work. However, some points are important to be addressed before going to publication.

-           The English should be improved, mainly in the introduction.

-           Materials characterization should be presented before the other results

-           Line 51-54. The information presented here belongs to the results section. The authors could provide, instead, other references that report the characterization of LEPW.

-           It is not really necessary to present pseudo-second order fittings in the main manuscript if the pseudo-first order fit is better. It is well known that these processes usually follow pseudo-first order kinetics. I suggest creating supplementary material, where the pseudo-second order fittings can be presented, as well as figures with repeated information, such as Fig 2 (which shows the same as table 3).

-           The authors should provide information about the adsorption process during longer periods than 30 min. Reactions with at least the same period of photocatalytic treatment are necessary.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors addressed very well most of my comments. Paper could be published now.