Photocatalytic Liquid-Phase Selective Hydrogenation of 3-Nitrostyrene to 3-vinylaniline of Various Treated-TiO2 Without Use of Reducing Gas
Round 1
Reviewer 1 Report
Catalysts
Manuscript ID: catalysts-456267
Title: Photocatalytic liquid-phase selective hydrogenation of 3-nitrostyrene to 3-vinylaniline of various treated-TiO2 without use of reducing gas.
Reviewer comments:
The authors have produced an interesting study concerning the preparation of different titania-based photocatalytic layers for the selective hydrogenation of 3-nitrostyrene to 3-vinylaniline. The work has been undertaken diligently and the interpretation of the data supports the conclusions. However, some points should be modified and investigated. I would suggest publishing it on Catalysts only after major revisions.
(1) The authors should revise English language; for example pag.1 line 27-28: “The selective hydrogenation of organic molecule is one the most important in chemical industry” should be “The selective hydrogenation of organic molecules is one of the most important goals for the chemical industry”….
(2) Introduction:
-the authors should uniform the temperature data; sometimes they are expressed in Kelvin degrees, sometimes in Celsius one;
-the Introduction section should be modified adding some recent works about this topic as discussion of the state of art (for example Yoshida, Hiroshi, et al. "Influence of crystallite size of TiO 2 supports on the activity of dispersed Pt catalysts in liquid-phase selective hydrogenation of 3-nitrostyrene, nitrobenzene, and styrene."Catalysis Letters 145.2 (2015): 606-611; Nuzhdin, A. L., et al. "Study of Catalyst Deactivation in Liquid-Phase Hydrogenation of 3-Nitrostyrene Over Au/Al 2 O 3 Catalyst in Flow Reactor." Catalysis Letters 147.2 (2017): 572-580).
(3) Materials and methods:
-line 233: the ratio between 3-nitrostyrene and catalyst is sustainable from an industrial point of view? (200μmol of 3-nitrostyrene for 0.2 g of catalyst);
-the authors should provide a list of all the reagents used; for example, in the case of 3-nitrosytrene data about % of purity are necessary;
-line 237: the authors said: “the substrate and products were analysis by GC-FID which were calibrated with authentic concentration of sample”; the authors should explain the expression “authentic concentration” and correct English grammar (“which were” should be “which was”);
-the authors should add some data about the mercury lamp used for the photocatalytic tests: distance from the sample, irradiating power, etc…
(4) Results and discussion
-line 59: the authors said that the UV irradiation was performed for 6 hours….the authors should discuss the choice of this specific time (is there a study about different times of irradiation?);
-the powders related to the products obtained should be characterized by thermogravimetric analyses in order to quantify the components;
-in all the manuscript the authors discuss the topic of this research from an industrial point of view, but it is not clear the real application of the photocatalytic materials developed…..for example Sabatini and all in Catalysts, (2018), DOI: 10.3390/catal8110568, discuss the preparation of a floating hybrid device for the purification of waste water. In this case it is not clear the application of the photocatalytic layers prepared in a photocatalytic device. The authors should discuss this point adding some info about prospective applications.
Author Response
Overall Opinion
The authors have produced an interesting study concerning the preparation of different titania-based photocatalytic layers for the selective hydrogenation of 3-nitrostyrene to 3-vinylaniline. The work has been undertaken diligently and the interpretation of the data supports the conclusions. However, some points should be modified and investigated. I would suggest publishing it on Catalysts only after major revisions.
We thank you for your kind comments. English usage has been improved throughout the manuscript. We have carefully revised our manuscript according to your comments and reported as follow:
(1) The authors should revise English language; for example pag.1 line 27-28: “The selective hydrogenation of organic molecule is one the most important in chemical industry” should be “The selective hydrogenation of organic molecules is one of the most important goals for the chemical industry”….
The sentence has been modified and shown in the Introduction section on page 1 line 28.
MODIFICATION
“The selective hydrogenation of organic molecules is one of the most important goals for the chemical industry.”
(2) Introduction:
-the authors should uniform the temperature data; sometimes they are expressed in Kelvin degrees, sometimes in Celsius one;
All temperature unit has been changed to Celsius degree. The correction is in the Abstract on page 1 line 16.
MODIFICATION
“In order to study those effects, P25-TiO2 semiconductor used as a photocatalyst were calcined at different temperatures (600-900oC) under various gas flow (Air, N2 and H2).”
-the Introduction section should be modified adding some recent works about this topic as discussion of the state of art (for example Yoshida, Hiroshi, et al. "Influence of crystallite size of TiO 2 supports on the activity of dispersed Pt catalysts in liquid-phase selective hydrogenation of 3-nitrostyrene, nitrobenzene, and styrene."Catalysis Letters 145.2 (2015): 606-611; Nuzhdin, A. L., et al. "Study of Catalyst Deactivation in Liquid-Phase Hydrogenation of 3-Nitrostyrene Over Au/Al 2 O 3 Catalyst in Flow Reactor." Catalysis Letters 147.2 (2017): 572-580).
The Introduction has been modified and the recent reference works have been added in Introduction section on page 1-2.
MODIFICATION
“Generally, 3-VA is produced by the selective hydrogenation reaction of 3-nitrostyrene (3-NS) [1, 2]. This reaction normally operated under medium to high temperature (T > 393K) and hydrogen pressure (PH2 > 3bar) using noble metal as the catalysts [3-5]. The selective hydrogenation of 3-NS to 3-VA is very challenging because there are two reducible functional groups which could be hydrogenated in 3-NS. The reaction mechanism of 3-NS hydrogenation was proposed by Haber et al. [1]. This process had two different reaction routes including the direct paths to 3-VA and condensation route. 3-ethylnitrobenzene (3-ENB) and 3-ethylaniline (3-EA) were produced under this process resulted from the over hydrogenation of 3-NS. In order to improve the catalytic performance, many change in pretreatment conditions [6,7], reaction mediums [6,8], catalyst supports [8, 9], and the addition of promoters [10] had been investigated.”
(3) Materials and methods:
-line 233: the ratio between 3-nitrostyrene and catalyst is sustainable from an industrial point of view? (200μmol of 3-nitrostyrene for 0.2 g of catalyst);
The amounts of nitroaromatic compounds and the catalysts used in the photocatalytic hydrogenation reaction are shown in Table 1. ณn this work, we used the ratio of nitrostyrene to catalyst similar to that of Inamura et al [2-4].
Table 1 Amounts of nitroaromatic compounds and catalyst used in the photocatalytic hydrogenation reaction
Researchers | Nitroaromatic content | Amount of catalysts | Ref. |
Zand et al. Imamura et al. Imamura et al. Imamura et al. Hakki et al. | 2 mmole of nitrobenzene 50 mmole of nitrobenzene 50 mmole of nitrostyrene 65 mmole of m-nitrobenzenesulfonic acid 100 mmol of m-nitrotoluene | 5 mg 50 mg 50 mg 50 mg 25 mg | [1] [2] [3] [4] [5] |
References
1. Z. Zand, F. Kazemi, S. Hosseini, Tetrahedron Letters 55 (2014) 338–341
2. K. Imamura, T. Yoshikawa, K. Hashimoto, H. Kominami, Applied Catalysis B: Environmental 134–135 (2013) 193–197
3. K. Imamura, K. Nakanishi, K. Hashimoto, H. Kominami, Tetrahedron 70 (2014) 6134-6139
4. K. Imamura, S. Iwasaki, T. Maeda, K. Hashimoto, B. Ohtanib, H. Kominami, Physical Chemistry Chemical Physics 13 (2011) 5114–5119
5. A. Hakki, R. Dillert, D. W. Bahnemann, Physical Chemistry Chemical Physics 15 (2013) 2992--3002
-the authors should provide a list of all the reagents used; for example, in the case of 3-nitrosytrene data about % of purity are necessary;
The properties of reagent used in this study have been added in Materials and Methods section on page 12 line 264.
MODIFICATION
“200µmol of 3-nitrostyrene (96%, Aldrich Chem. CO. Ltd), 20ml of isopropanol (99.95%, Fisher Chem. CO. Ltd) and 0.2g of catalyst were transferred into pyrex glass tube reactor and sealed by septum.”
-line 237: the authors said: “the substrate and products were analysis by GC-FID which were calibrated with authentic concentration of sample”; the authors should explain the expression “authentic concentration” and correct English grammar (“which were” should be “which was”);
Authentic concentration is the concentration of product and substrate in solution prepared by us to use as the calibration value. English has been corrected and shown in Materials and Methods section on page 12 line 271.
MODIFICATION
“The substrate and products were analysis by GC-FID, which was calibrated with authentic concentration of both samples.”
-the authors should add some data about the mercury lamp used for the photocatalytic tests: distance from the sample, irradiating power, etc…
Mercury lamp data has been added in Materials and Methods section on page 12 line.267
MODIFICATION
“catalyst were photo-irradiated under mercury mixed lamp Philips 500W E40 (λ > 300nm, UV98.5% and visible1.5%) for 6h”
(4) Results and discussion
-line 59: the authors said that the UV irradiation was performed for 6 hours….the authors should discuss the choice of this specific time (is there a study about different times of irradiation?);
We select this time because the %NS conversion is not too high or too low, which is good to use for catalytic activity comparison. Because, the error is much higher when the %NS conversion is low, on the other hands, the high %NS conversion is hard to compare especially when the conversion reached 100%. We also had the plot between %NS conversion vs irradiation time as shown in Figure 1.
Figure 1: Plots between %NS conversion and %VA selectivity with reaction time
-the powders related to the products obtained should be characterized by thermogravimetric analyses in order to quantify the components;
The spent catalysts has been characterized by thermogravimetric analyses and the results are shown in Results and Discussion section on page 11 line 243.
MODIFICATION
“The physiochemical properties of all spent catalysts were evaluated by using TGA analysis and the results are presented in Figure 10. All spent catalysts exhibited the %weight loss in the range of 0.8 to 5% in the temperature range of 100 to 500°C. These weight losses could probably be due to the thermal decomposition or volatilization of chemical substance presented in the TiO2 structure [51, 52]. While, the weight loss occurred at higher temperature would be attributed the condensation reaction between two adjacent Ti-OH groups, which resulted in the formation of Ti-O-Ti bonds and the loss of water molecules [53]. This process was associated with crystal growth and rutile phase transformation process. The amount of %weight loss decreased as the calcination temperature increased, which was due to fact that the chemical substance and loss of water had already occurred after thermal treatment.”
Figure 10. TGA analysis of all spent catalysts; P25 (a), P25-600-air (b), P25-700-air (c), P25-700-N2 (d), P25-700-H2 (e), P25-800-air (f), P25-900-air (g)”
-in all the manuscript the authors discuss the topic of this research from an industrial point of view, but it is not clear the real application of the photocatalytic materials developed…..for example Sabatini and all in Catalysts, (2018), DOI: 10.3390/catal8110568, discuss the preparation of a floating hybrid device for the purification of waste water. In this case it is not clear the application of the photocatalytic layers prepared in a photocatalytic device. The authors should discuss this point adding some info about prospective applications.
The application of this research has been added in Introduction section on page 2.
MODIFICATION
“Presently, the photocatalytic reaction process has attracted considerable attention due to its various applications such as hydrogen production by water splitting, air purification, waste water treatment and selective synthesis of organic compound [11]. When UV-light was adsorbed by the photocatalysts, the electron in valence band jumps through the band gap to the conduction band, leaving a positive hole in valence band causing the reduction and oxidation, respectively. Among all photocatalysts, TiO2 is a common, cheap and non-toxic material and widely used in many applications as the photocatalysts for environmental protection; such as removal of air pollutants, removal of hazardous, disinfection, deodorization and removal of NOx; and energy field for example dye sensitized solar cell and hydrogen evaluation [12-15]. Synthesis of organic compound by photocatalytic hydrogenation process at room temperature has become more interesting alternative process due to its high safety, indispensable light source, and clean process [2, 6].
Production of aniline by photocatalytic hydrogenation of nitroaromatic had been reported by Inamura et al. [16-18]. This process can be operated in oxalic acid or formic acid or alcohol as a hole scavenger with the suspension of TiO2 at the atmospheric pressure and room temperature without the use of any reducing agent. Most research works showed very high aniline selectivity. Moreover, using alcohol as the solvent and the hole scavenger not only aniline was produced but ketone was also formed. The effect of reaction conditions such as the effects of the presence of O2 and type of TiO2 had been investigated. However, the effect of the TiO2 properties on the photocatalytic performance was not deeply studied. Therefore, in this work, we had investigated the effect of TiO2 properties obtained after treatment at various conditions on the catalytic performance in liquid phase photocatalytic hydrogenation of 3-NS to 3-VA in 2 propanol under UV light irradiation.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review for “Photocatalytic liquid-phase selective hydrogenation of 3-nitrostyrene to 3-vinylaniline of various treated-TiO2 without the use of reducing gas”
In the manuscript, the authors investigate how the calcination treatment affects the TiO2 performance on 3-NS hydrogenation reaction. The authors claim that a higher photocatalytic activity is observed and resulting from the lower radiative recombination, high crystallinity and synergistic effect from two phases of TiO2. The article is well written and organized. There are some minor points need to be addressed before published on Catalysts.
1. Page 5, line 116, the authors claim that the enhancement of the visible light absorption and sharpness of UV-vis indicate a higher degree of crystalline quality. The lowest bandgap from f and g is even below the reported Rutile band gap, i.e. 3 eV, while they are not fully converted to rutile. Could the authors discuss the possible effects of defects on the absorption spectra?
2. Figure 8d, the figure letter is overlapping with the notation. Please address.
3. In Page 10, line 197, for the “isopropanol and h+”, it is confusing of h+ as a hole or typo of H+. Please using consistent language for the hole.
Author Response
Overall Opinion
In the manuscript, the authors investigate how the calcination treatment affects the TiO2 performance on 3-NS hydrogenation reaction. The authors claim that a higher photocatalytic activity is observed and resulting from the lower radiative recombination, high crystallinity and synergistic effect from two phases of TiO2. The article is well written and organized. There are some minor points need to be addressed before published on Catalysts.
We thank reviewer for valuable comment. The correction has been made and reported as follow:
1. Page 5, line 116, the authors claim that the enhancement of the visible light absorption and sharpness of UV-vis indicate a higher degree of crystalline quality. The lowest bandgap from f and g is even below the reported Rutile band gap, i.e. 3 eV, while they are not fully converted to rutile. Could the authors discuss the possible effects of defects on the absorption spectra?
We agree with reviewer and we have added the discussion about the effect of defect on the adsorption spectra in Results and Discussion section on page 5 line 129.
MODIFICATION
“Moreover, the formation of defect by oxygen loss during the calcination process can lower band gap value of TiO2, which promote the electron transition from the valence to the conduction band.”
2. Figure 8d, the figure letter is overlapping with the notation. Please address.
Figure 8 has been fixed and shown in Results and Discussion section on page 9.
3. In Page 10, line 197, for the “isopropanol and h+”, it is confusing of h+ as a hole or typo of H+. Please using consistent language for the hole
H+ is not hole (h+). In order to make it clearer, we change the h+ to hole (h+) and shown in Results and Discussion section on page 10 line 203
MODIFICATION
“the substrate like conventional liquid phase selective hydrogenation but it need the H+, generated from reaction between isopropanol and hole (h+) and electron to form VA. Electron and hole (h+) required in this process were generated from the photoreaction. Therefore, the electron and hole separation process is directly affected the photocatalytic activity in selective hydrogenation of 3-NS.”
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper provides usefull information. I have a few minor comments as written below:
Optical reflectance of the prepared sample plays a key role in the performance of the sample. I think the optical reflection of the sample should be provided.
Impact of the Various Atmospheres on the Photocatalytic performance of the TiO2 was investigated in the following paper.
Photocatalytic activity of TiO2 nanoparticles: effect of thermal annealing under various gaseous atmospheres
Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO2 under Various Atmospheres
Solar Energy Materials and Solar Cells, Volume 88, Issue 3, 15 August 2005, Pages 269-280
3. Providing more explanation about the crystal quality of prepared sample under different condition would make the paper more interesting for a wider range of researcher.Author Response
Overall Opinion
This paper provides useful information. I have a few minor comments as written below:
Optical reflectance of the prepared sample plays a key role in the performance of the sample. I think the optical reflection of the sample should be provided.
Optical reflectance of the catalysts has been done and shown in Figure 3 and shown in Results and Discussion section on page 6.
MODIFICATION
Figure 3. UV-Vis absorption and UV-Vis-DR spectra of P25 (a), P25-600-air (b), P25-700-air (c), P25-700-N2 (d), P25-700-H2 (e), P25-800-air (f), P25-900-air (g)
Impact of the Various Atmospheres on the Photocatalytic performance of the TiO2 was investigated in the following paper.
Photocatalytic activity of TiO2 nanoparticles: effect of thermal annealing under various gaseous atmospheres
Evaluation of Solar-Driven Photocatalytic Activity of Thermal Treated TiO2 under Various Atmospheres
Solar Energy Materials and Solar Cells, Volume 88, Issue 3, 15 August 2005, Pages 269-280
3. Providing more explanation about the crystal quality of prepared sample under different condition would make the paper more interesting for a wider range of researcher.
We thanks reviewer for valuable comment. We have added the explanation about the crystal quality in Results and Discussion section on page 4-5.
MODIFICATION
“P25-TiO2 was the commercial titanium dioxide having 80% anatase and 20% rutile phase components. After calcination at 600°C, the peaks of anatase and rutile phases increased corresponding to the slightly increase of rutile phase content from 17 to 27%. However, calcination at higher temperature caused the rapid increase of rutile phase and crystallite size [20, 21]. For example, calcination at 700°C resulted in the rapid phase transformation and 77% of rutile phase was formed. Anatase phase was transformed completely after calcination temperature further increased to 800°C. Increasing of calcination temperature influenced the phase composition and crystallization. The calcination at high temperature leads to phase transformation of anatase to rutile and the crystal growth [20, 21]. Changing the calcination atmosphere from air to N2 did not altered the phase transformation and crystal growth, however, calcination in H2 gave higher rutile phase content. This probably due to the reduction reaction between H2 gas and TiO2 surface, which created the oxygen vacancy and promoted the rutile phase transformation. After the heat treatment process, the XRD peak intensity of TiO2 became higher, which indicates the increasing of crystallinity caused by a re-arrangement of TiO2 crystal structure. ”
“The UV-Vis absorption and UV-Vis-DR spectra are used to investigate the light adsorption of all treated TiO2 samples at UV and visible light range and the result is shown in Figure 3. The typical band of P25-TiO2 was found at 392 nm, which could be ascribed to the absorption of light caused the excitation of electrons transfer from valence band to conduction band [21]. Increasing of calcination temperature resulted in the enhancement of the visible light adsorption (l > 400 to 700nm) and the sharpness of UV-vis curve (steep slope), which indicated a higher degree of crystalline quality. This was in good agreement with XRD results. The band gap energy of various treated TiO2 catalysts can be determined from a plot of (hvα)1/2 versus photon energy (hv), which show in Figure 4, and the results are shown in Table 2. The redshift in band gap energy of TiO2 was observed by treating at higher temperature. This could be due to the increasing of rutile phase content in TiO2 photocatalysts [21, 23, 24]. The band gap energy of pure anatase and rutile phase were 3.2 and 3.0 eV, respectively [25, 26]. Therefore, the increase rutile content after calcination at high temperature would narrow the band gap. Moreover, the formation of defect by oxygen loss during the calcination process can lower band gap value of TiO2, which promote the electron transition from the valence to the conduction band. On the other hands, calcination under different atmosphere did not changed the main adsorption edge and band gap energy but the P25-700-H2 exhibited the addition adsorption spectra at visible light region due to the formation of oxygen vacancy.”
Author Response File: Author Response.pdf
Reviewer 4 Report
The following contribution discussed the ability of a variety of TiO2 P25 catalysts to facilitate nitrostyrene to vanillyl aniline using UV light. The catalysts were treated at various temperatures and in the presence of N2 and H2. Overall, I feel that this publication does not add much to the well understood photocatalytic activity of TiO2 P25 semiconductors. I do have a few suggestions that may strengthen the manuscript in the present form - however, I unfortunately, cannot , recommend for publication, as is.
1) The authors mention that conversion of the nitro to aniline derivative seemed to diminish when the 900 degC TiO2 P25 catalyst was used. From Figure 3 and 4, it is clear that the band gap has decreased in this material quite substantially (~418 nm). Have the authors examined a spectrum of their light source. How can they be confident that the decrease in conversion to the desired aniline product is not simply due to due reduced excitation energy at the band gap energy for these materials, given the use of a broad wavelength light source?
2) Perhaps my largest issue is that the authors have not shown catalyst versatility or recyclability. Both of these are at the forefront of heterogeneous catalysis. Can the TiO2-P25 catalytic systems examined in this work be extended to other nitroarenes? How does the catalyst perform in subsequent reuses? These issues need to be addressed in an effort to strengthen the present work.
Author Response
Reviewer: 4
Overall Opinion
The following contribution discussed the ability of a variety of TiO2 P25 catalysts to facilitate nitrostyrene to vanillyl aniline using UV light. The catalysts were treated at various temperatures and in the presence of N2 and H2. Overall, I feel that this publication does not add much to the well understood photocatalytic activity of TiO2 P25 semiconductors. I do have a few suggestions that may strengthen the manuscript in the present form - however, I unfortunately, cannot, recommend for publication, as is.
We thanks reviewer for the useful comment. We have tried our best to improve the quality of the manuscript as much as we can as follow:
1) The authors mention that conversion of the nitro to aniline derivative seemed to diminish when the 900 degC TiO2 P25 catalyst was used. From Figure 3 and 4, it is clear that the band gap has decreased in this material quite substantially (~418 nm). Have the authors examined a spectrum of their light source. How can they be confident that the decrease in conversion to the desired aniline product is not simply due to due reduced excitation energy at the band gap energy for these materials, given the use of a broad wavelength light source?
Yes, our light source is mercury mixed lamp Philips 500W E40, consisted with UV98.5% and visible1.5% measured by using IL 1700 Research Radiometer.
2) Perhaps my largest issue is that the authors have not shown catalyst versatility or recyclability. Both of these are at the forefront of heterogeneous catalysis. Can the TiO2-P25 catalytic systems examined in this work be extended to other nitroarenes? How does the catalyst perform in subsequent reuses? These issues need to be addressed in an effort to strengthen the present work.
We thanks for the valuable comments. Yes, this reaction can be extended to other nitroarenes as reported from many earlier works, for example, Imamura et al. [1-3] studied the photocatalytic chemoselective reduction of nitrobenzenes to aminobenzenes, m-nitrobenzenesulfonic acid to m-aminobenzenesulfonic acid and aminonitrobenzenes to diaminobenzenes. The recyclability of the catalysts has been tested and shown Figure 9 in Results and Discussion section on page 11.
MODIFICATION
2.3 Recyclability and properties of spent catalysts
In order to determine the stability and the recyclability of the catalysts, the photocatalytic selective hydrogenation performance of P25-700-air catalyst was determined repeatedly for five consecutive batches. The catalysts were recovered by using centrifugal and filtration from the obtained reaction mixture and then were re-used. As shown in Figure 9, it is clearly seen that only negligible loss (less than 13%) in %3-NS conversion was observed. This suggests that the prepared photocatalyst is still active and can be used for long-term applications.
Figure 9. The catalytic performance of P25-700-air under UV light irradiated for 6h at different cycles
Reference
1. Imamura, K.; Yoshikawa, T.; Hashimoto, K.; Kominami, H. Applied Catalysis B: Environmental. 2013, 134-135, 193-197.
2. Imamura, K.; Iwasaki, S.; Maeda, T.; Hashimoto, K.; Ohtani, B.; Kominami,H. Phys Chem Chem Phys. 2011, 13, 5114-5119.
3. Imamura, K.; Hashimoto, K.; Kominami, H. Chem Commun (Camb). 2012, 48, 4356-4358.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I suggest to publish this paper after the revision step
Author Response
Responses to the Reviewers’ comments
Re: Ms. Ref. No.: Catalysts-456267
Title: Photocatalytic liquid-phase selective hydrogenation of 3-nitrostyrene to 3-vinylaniline of various treated-TiO2 without use of reducing gas.
BY: Okorn Mekasuwandumrong, Saknarin Chaitaworn, Joongjai Panpranot and Piyasarn Praserthdam
Reviewer 1
I suggest to publish this paper after the revision step
We thank reviewer for the comment. English usage has been improved throughout the manuscript by English expert.
Reviewer 4 Report
I thank the authors for their response, however some of my questions still remain unanswered:
1) The mercury lamp is a common excitation source. The authors cite a 98.5% "UV", but what is the predominant wavelength of this region? UVA? UVB? I still believe this is necessary to address the following comment - Have the authors examined aspectrum of their light source. How can they be confident that the decrease in conversion to the desired aniline product is not simply due to due reduced excitation energy at the band gap energy for these materials, given the use of a broad wavelength light source?
If the "UV" is centred at 380 nm, it will likely not effectively excite the material with the 418 nm bandgap and this will translate into lower conversions to aniline products.
2) Thank you very much for the recyclability information. However, indicating that previous contributions have been able to extend the versatility of this reaction is not applicable to the current work. Even if they are the "same catalyst", they have been made by different hands and need to be quantified accordingly. I may be mistaken, but in the references given, none of the authors of the current paper are on these - meaning they were completed by completely different research groups? Can the authors clarify? If the work has been done within the same research group, then this should be explicitly stated. If not, then the authors should see if their batches of catalyst exhibit the same versatility.
Author Response
Dear Reviewer
In attachment, you will find our answer and some experimental details. Thanks for your comment
Best Regard
Okorn Mekasuwandumrong
Author Response File: Author Response.pdf
