Bismuth-Supported Mesostructured Silica: Ligand-Directed Growth of Nanosheets for Sustainable Catalysis and Iodine Scavenging
, Mohammed Majdoub 3, Nadia Katir 1, Khalil Anis 2, Abdelhak Kherbeche 2, Sébastien Royer 4 and Abdelkrim El Kadib 1,5,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article " Bismuth-Supported Mesostructured Silicas: Ligand-Directed Growth of Nanosheets for Sustainable Catalysis and Iodine Scavenging" the study reports on bismuth in mesoporous silicafor applications in catalysis. The results demonstrate the efficiency of iodine adsorption by the Bi-SBA samples. Some suggestions are recommended for publication in the Sustainability.
1 - Improve the quality of figures 1 and 3. In scheme 1, enlarge the image that focuses on the functional group located within the nanopores.
2 - In Figure 5, the growth of bismuth nanosheets occurs. How does the chemical bonding between SBA-15 or SBA-NNNH2 and the bismuth nanosheets occur?
3 - Add the absorbance spectra of the samples Bi-SBA-15, Bi-SBA-NH2, Bi-SBA-NNH2, and Bi-SBA-NNNH2. Does the pore size in Table 1 influence the UV-Vis spectra as well as the iodine adsorption?
4 - Based on the absorption spectra in Figure 6, do the Bi-SBA samples exhibit luminescent emission? Could these samples be used for photocatalysis?
5 - Do the toxicity levels of the Bi-SBA samples allow for their application in pharmacology? Add a table or figure showing the toxicity index of the samples.
Author Response
The article " Bismuth-Supported Mesostructured Silicas: Ligand-Directed Growth of Nanosheets for Sustainable Catalysis and Iodine Scavenging" the study reports on bismuth in mesoporous silica for applications in catalysis. The results demonstrate the efficiency of iodine adsorption by the Bi-SBA samples. Some suggestions are recommended for publication in the Sustainability.
We are very grateful to the reviewer for the time dedicated to the assessment of our manuscript and for her/his positive comments.
1 - Improve the quality of figures 1 and 3. In scheme 1, enlarge the image that focuses on the functional group located within the nanopores.
This has been done and Figure 1 and 3 and Scheme 1 were now improved.
2 - In Figure 5, the growth of bismuth nanosheets occurs. How does the chemical bonding between SBA-15 or SBA-NNNH2 and the bismuth nanosheets occur?
It is an interesting question and some suggestions were already provided in the manuscript. Pristine SBA-15 lacking amine groups interacts with Bismuth precursor through hydrogen bonding with its terminal silanol groups (Si-OH). Instead, each nitrogen (NH or NH2) groups belonging to SBA-NHNH2 interacts strongly with Bismuth through long pair base to acid (N: à Bi) donation, allowing to concentrate a substantial seed near to each other. This situation provides the driving force for forming elongated particles by fusing elementary particles one to each other. Bismuth particles grown on pristine SBA-15 experiences more freedom because of the lack of functional directing groups on the surface, which results in the formation of spherical particles.
3 - Add the absorbance spectra of the samples Bi-SBA-15, Bi-SBA-NH2, Bi-SBA-NNH2, and Bi-SBA-NNNH2. Does the pore size in Table 1 influence the UV-Vis spectra as well as the iodine adsorption?
The UV-Vis spectrum has been added. They exhibit an absorption band in the UV range (270–321 nm), which is assigned to oxidized bismuth species present in the materials.
Regarding the question, the pore size has little direct influence on the position of absorption bands, but it can affect the intensity due to differences in adsorption capacity (specifically in the case of silica thin films). In contrast, pore size significantly affects iodine adsorption. Larger and more accessible pores facilitate the diffusion and adsorption of iodine molecules. However, functional groups such as NH2 and its derivatives also play a key role by enhancing interactions with iodine. Therefore, iodine adsorption depends on both pore structure and surface chemistry
4 - Based on the absorption spectra in Figure 6, do the Bi-SBA samples exhibit luminescent emission? Could these samples be used for photocatalysis?
We thank the reviewer for this pertinent comment. the UV-Vis absorption spectra presented in Figure 6 corresponds to the liquid solution without silica powder, thereby reflecting exclusively the reduction of nitrophenol to aminophenol. Many Bi-based materials are already described in the literature as photo-sensitive and photo-active devices (BiVO4, BiPO4, Bi2WO6, Bi5O7I,…). In contrast, little is known regarding bismuth (oxide) supported on silica supports. Understanding such behaviour would require photoluminescence measurements, which were not included in the present study but belong to the roadmap of our future research.
5 - Do the toxicity levels of the Bi-SBA samples allow for their application in pharmacology? Add a table or figure showing the toxicity index of the samples.
We are not sure these materials could be used directly in pharmacology without further toxicity assessment, but, we are targeting their use as catalysts for the synthesis of drugs and bioactive molecules that have utility in pharmacology. The huge interest of these materials lies in their leaching resistant properties, where nitrogen-containing silica supports preclude bismuth from leaching out to the solution. Keeping in mind that bismuth is comparatively less toxic compared to the routinely used metal catalysts (Pt, Pd, Rh, Ru), we can enthusiastically conclude on the positive role they may play as sustainable catalysts for the synthesis of active pharmaceutical ingredients.
Having said that, these materials could present some potential for use in health related application, but this needs more time for exploration. Tightly connected to this point, we are using bismuth-based films as wound healing materials, among other metal containing films. The most important result gleaned from this ongoing study is the very lower toxicity of films containing bismuth, compared to the ones featuring silver and copper nanoparticles. Other literature reports have also claimed the use of bismuth derivatives to kill bacteria.
The use of bismuth as catalyst for the ring opening polymerisation of polycaprolactones and polylactides as polymeric materials intended for wound healing and packaging, has been justified by the lower toxicity of bismuth derivatives. All these results consolidate our hypothesis regarding the advantages expected from the use of bismuth in various fields.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper focuses on the systematic study of nitrogen ligand guided growth of bismuth nanosheets, which has certain application value in the fields of sustainable catalysis and iodine adsorption; At present, there are a few issues that are suitable for publication after modification.
- The article proposes amine based coordination guided bismuth nucleation growth, and suggests supplementing quantitative evidence of coordination effects (such as XPS N 1s peak fitting, infrared shift quantification, DFT brief calculation or binding energy comparison). The mechanism of decreased catalytic activity and increased adsorption after reduction needs to be explained more clearly: the effect of nitrate departure on substrate adsorption/iodine binding.
- Only the optimal data after SBA-NNH ₂ reduction is provided. It is recommended to supplement the complete adsorption capacity comparison of four materials before and after reduction to enhance the persuasiveness of the rules. Supplement adsorption kinetics/isotherms, clarify adsorption model.
- After 5 cycles, the conversion rate decreased to 75%. It is recommended to supplement the post cycle characterization (XRD/XPS/TEM) to indicate whether the decrease in activity is due to site poisoning or structural damage.
- Maintain consistent significant figures for rate constant kapp, adsorption capacity, and metal leaching amount.
- Maintain consistent significant figures for rate constant kapp, adsorption capacity, and metal leaching amount.
- There is an issue with the vertical axis in Figure 2a.
Author Response
This paper focuses on the systematic study of nitrogen ligand guided growth of bismuth nanosheets, which has certain application value in the fields of sustainable catalysis and iodine adsorption; At present, there are a few issues that are suitable for publication after modification.
We are very thankful to the reviewer for the time dedicated to the assessment of our manuscript and for her/his positive comments.
- The article proposes amine based coordination guided bismuth nucleation growth, and suggests supplementing quantitative evidence of coordination effects (such as XPS N 1s peak fitting, infrared shift quantification, DFT brief calculation or binding energy comparison). The mechanism of decreased catalytic activity and increased adsorption after reduction needs to be explained more clearly: the effect of nitrate departure on substrate adsorption/iodine binding.
Thank you for this comment. The reviewer is right regarding the use of XPS and infrared spectroscopy to ascertain the NH2 to bismuth coordination. We have previously used these tools to confirm the coordination of NH2 groups to Lewis acids (Ti, Al, Sn, V, Mo, W). See for example: Chem. Eur. J., 17 (2011) 7940-7946; J. Catal., 273 (2010) 147. In these reports, the shift of the vibration of NH2 groups in infrared spectroscopy (below 1590 cm-1) along with the deviation of the NH2 binding energy from 398 eV to 399-401 eV are often taken as indication for such coordination. In our case, infrared spectra did not reveal any significant difference in this zone, while XPS analysis shows the expected shift as already mentioned in the manuscript. The possible overlap of some of these signals with those of nitrate groups recall to precautions when interpreting these results. However, based on the literature, the interaction of nitrogen to bismuth could be hypothesized without hesitation.
We have accordingly enriched the manuscript by the sentences appearing below as follow:
The N(1s) spectrum of aminopropyl- functionalized silica displays a component at ~ 399.5 eV, and a second contribution emerging above ~400.6 eV. The former signal is assignable to free NH2 groups, and the later to either protonated amine (-NH3⁺) interacting with surface silanols or nitrogen lone pair coordinated to Lewis-acidic Bi3+ centres. The third signal observed at 406 eV is typical of nitrate groups, which agree well with DRIFT and XRD analysis.
- Only the optimal data after SBA-NNH₂ reduction is provided. It is recommended to supplement the complete adsorption capacity comparison of four materials before and after reduction to enhance the persuasiveness of the rules. Supplement adsorption kinetics/isotherms, clarify adsorption model.
Since Bi@SBA-NNH₂ exhibited the most favourable nitrophenol conversion kinetics among the studied materials, we chose to continue our investigation using this material, in comparison with pristine Bi@SBA-15 to elucidate the influence of the functionalization of the behaviour of the material (Figure 7a compare the reactivity of pristine SBA and Bi@SBA-15 both before and after reduction, while Figure 7b gathers the results of pristine SBA-NNH2 and Bi@SBA-NNH2 before and after reduction). It is indeed obvious that this has been done for the two materials both before and after reduction. We have indeed succeeded in demonstrating the bi-facetted reactivity of these materials, where before reduction, they perform as better nitroarene hydrogenation catalysts, while after reduction, they perform as better iodine scavengers. Please note that figure Furthermore, the iodine adsorption study was conducted only as a complementary assessment; the primary objective of this work was initially focused on the reduction of nitro compounds.
Please note that more details and deep study focusing on iodine adsorption is envisioned to further highlight the potential of these materials. Because of the limited space available for the present contribution, this will be reported elsewhere.
- After 5 cycles, the conversion rate decreased to 75%. It is recommended to supplement the post cycle characterization (XRD/XPS/TEM) to indicate whether the decrease in activity is due to site poisoning or structural damage.
XPS analysis after the first catalytic cycle has already been included in the supporting information (Figure S10) and the paragraph below comments on the observed pattern.
Nitrogen physisorption of the spent catalyst revealed similar profile as for the pristine catalyst, while XPS analysis showed similar binding energy for bismuth, oxygen, silicon and nitrogen as for the pristine catalysts (Figure S10). These findings reflect the intactness of the support and the chemical stability of bismuth phase attained through its strong interaction with amine-terminated linkers on the support, which effectively preserves the structural integrity and allows indeed for the catalyst recovery and its further recycling.
ICP analysis of Bismuth ruled out the leaching of the metal during catalysis. Besides, nitrogen physisorption of the spent catalyst confirms the retention of the mesostuctured network and ruled out the occurrence of structural degradation or significant collapse of the framework. This behaviour is quite expected considering that milder reaction conditions are applied herein. Consequently, we attribute the decrease in the catalytic activity to either partial blocking or adsorption of reaction intermediates on actives sites rather than to structural collapse of the support or loss of Bi active species.
Finally, as suggested, XRD and TEM analyses could complement these observations, but, unfortunately, they require an extended time that could severely delay the submission.
- Maintain consistent significant figures for rate constant kapp, adsorption capacity, and metal leaching amount.
We thank the reviewer for this comment. The values of the apparent rate constant (kapp), adsorption capacity and metal leaching have been revised and adjusted to ensure consistent use of significant figures throughout the manuscript.
kapp= 3.8 10- 3. s-1 line 498.
6.3*10-6 % line 534.
442 mg. g-1 line 567.
- There is an issue with the vertical axis in Figure 2a.
The vertical axis in Figure 2a has been corrected accordingly in the revised version of the manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this paper by El Kadib et al., the synthesis of bismuth catalysts supported on functionalized SBA-15 type silicas is described and their application for nitrocompounds reduction and iodine uptake is discussed. Although this is a well structured study with an extensive and accurate catalyst characterization there are several issue along the paper. In particular, there are serious flaws in the catalytic experiments section which must be addressed to allow the manuscript publication.
- The authors claim a scarce use of bismuth in heterogeneous catalysis and reduction of nitro compounds, this seems not true. Concerning the use of bismuth in heterogeneous catalysis, a Scifinder search gave more than 300 entries. Similarly, almost 400 entries were found for papers using bismuth in nitrophenol reduction, a significant amount of them employing supported Bi nanoparticles. I suggest the authors moderate their claims in lines 18-19 and 70-71.
- the authors claim in line 86-87 that their catalysts show excellent chemoselectivity in the reduction of nitrophenol. However, this is not proven by the data showed in the paper, as the sole UV analysis is not enough to exclude the presence of byproducts and apparently only the nitrophenol conversion was measured. The authors should either prove this chemoselectivity with other analysis (e.g. chromatographic or mass analyses) or claiming an excellent activity only.
- Figure 6 caption is very limited. It should explain in detail what each graph shows. Probably in Figure 6d the legend is not correct as it does not reflect what written in lines 491-493. Where a pseudo first-order was observed, the line obtained from a linear regression should be showed in the ln(A/A0) vs time graphs.
- in line 497 the authors say "tiny amount of bismuth in 0.5%Bi@SBA-NNH2". As I undestood, 0.5% is the bismuth loading on the solid, but the molar ratio of bismuth with respect to nitrophenol is always 10%mol ( as written in line 491). Can the authors clarify this? It seems sometimes there is some confusion between the bismuth loading on SBA-15 and the catalytic ratios.
- when expressing kinetic constants, the k should not be capital (that is for equilibrium constants).
- the kinetic constant comparison in lines 497-500 is superficial and approximate in my opinion. Apparently, the authors use the simplified kinetic equation (2) and directly compares the k value obtained with 10%mol of Bi and 30 eq of NaBH4 with data of other papers (without reference). It is impossible to verify wheter this comparison is appropriate (as we don't know the conditions and the equations used in the other papers) and therefore the outperformance claimed in lines 498-499 is not proved. Moreover, the calculation of the kinetic constant is not reported and the error associated to its calculation is missing.
- please report the conversions value for the nitrocompounds screening (Figure S11 shows only the UV spectra) to support the claims in lines 539-540
Author Response
In this paper by El Kadib et al., the synthesis of bismuth catalysts supported on functionalized SBA-15 type silicas is described and their application for nitrocompounds reduction and iodine uptake is discussed. Although this is a well-structured study with an extensive and accurate catalyst characterization there are several issue along the paper. In particular, there are serious flaws in the catalytic experiments section which must be addressed to allow the manuscript publication.
We are very thankful to the reviewer for the time dedicated to the assessment of our manuscript and for her/his positive comments.
- The authors claim a scarce use of bismuth in heterogeneous catalysis and reduction of nitro compounds; this seems not true. Concerning the use of bismuth in heterogeneous catalysis, a Scifinder search gave more than 300 entries. Similarly, almost 400 entries were found for papers using bismuth in nitrophenol reduction, a significant amount of them employing supported Bi nanoparticles. I suggest the authors moderate their claims in lines 18-19 and 70-71.
We agree for the necessity to moderate our claims regarding the use of bismuth in catalysis and we have accordingly fixed this in the revised manuscript.
We acknowledge that many precedents in the literature have explored photo- and thermal bismuth-based catalysis. Our statement derives from the comparison on the literature dealing with conventional palladium, platinum, ruthenium and rhodium-based catalysts on one hand and those dealing with bismuth-based catalyst. From this comparison, it is obvious that bismuth displayed little allure and motivated few communities. A key pillar to setup sustainability in organic synthesis lies in the exploration and discovery of new materials and active phase catalysts, based on abundant and cost-effective metal catalysts, thereby recalling to further explore the nucleation and growth of the corresponding metal oxides on porous supports.
- the authors claim in line 86-87 that their catalysts show excellent chemoselectivity in the reduction of nitrophenol. However, this is not proven by the data showed in the paper, as the sole UV analysis is not enough to exclude the presence of byproducts and apparently only the nitrophenol conversion was measured. The authors should either prove this chemoselectivity with other analysis (e.g. chromatographic or mass analyses) or claiming an excellent activity only.
The reviewer was right and we thank her/him for rising this point. We have accordingly modified the sentence in the revised version.
- Figure 6 caption is very limited. It should explain in detail what each graph shows. Probably in Figure 6d the legend is not correct as it does not reflect what written in lines 491-493. Where a pseudo first-order was observed, the line obtained from a linear regression should be showed in the ln(A/A0) vs time graphs.
The caption of Figure 6 has been revised and expanded to provide a clearer and more detailed description of each figure. The legend in figure 6d has been corrected to ensure consistency with discussion presented in line 491-493.
For the experiments exhibiting pseudo-first order kinetics the corresponding linear regression lines have been corrected to better illustrate the kinetic fitting and improve the clarity of the result.
- in line 497 the authors say "tiny amount of bismuth in 0.5%Bi@SBA-NNH2". As I understood, 0.5% is the bismuth loading on the solid, but the molar ratio of bismuth with respect to nitrophenol is always 10%mol (as written in line 491). Can the authors clarify this? It seems sometimes there is some confusion between the bismuth loading on SBA-15 and the catalytic ratios.
We would like to clarify that the value of 0.5%Bi@SBA-NNH2 refers to the weight loading of bismuth in the SBA-15 support (the amount of metal deposited on the material). In contrast, the 10 mol% ratio mentioned in line 491 corresponds to the amount of bismuth introduced into the reaction medium relative to the substrate (nitrophenol).
Furthermore, the expression “tiny amount of bismuth in 0.5%Bi@SBA-NNH₂ provides an interesting conversion kinetics, with a kapp = 3.8 10-3. s-1” refers to the reduced amount of bismuth used under the catalytic conditions relative to nitrophenol. In this context, additional experiments were performed using lower molar ratios of 5 mol% and 2.5 mol%. The results indicate that a 5 mol% ratio provides a satisfactory conversion rate, achieving significant conversion within 10 minutes.
- when expressing kinetic constants, the k should not be capital (that is for equilibrium constants).
This has been corrected consistently, please see line 466 of the manuscript.
- the kinetic constant comparison in lines 497-500 is superficial and approximate in my opinion. Apparently, the authors use the simplified kinetic equation (2) and directly compares the k value obtained with 10%mol of Bi and 30 eq of NaBH4 with data of other papers (without reference). It is impossible to verify whether this comparison is appropriate (as we don't know the conditions and the equations used in the other papers) and therefore the outperformance claimed in lines 498-499 is not proved. Moreover, the calculation of the kinetic constant is not reported and the error associated to its calculation is missing.
We thank the reviewer for this comment regarding the comparison of kinetic constats, in the revised manuscript, we have clarified the calculation method based on the simplified kinetic equation (2).
we clarify that was determined under the commonly used pseudo-first-order assumption, valid under excess NaBH₄ conditions. In this approach, the reaction rate depends only on the concentration of 4-nitrophenol, and the kinetic constant is obtained from the linear fitting of:
Where and correspond to the concentrations (or absorbance values) at time t and initial time, respectively. The kapp values were determined from the slope of the linear fitting of ln(At/A0) versus reaction time.
Furthermore, we acknowledge that the previous comparison with literature values was not sufficiently supported. Therefore, we have revised this section by adding the appropriate references and by discussing the differences in experimental conditions and kinetic models used in in supplementary information (Table S2).
Table S2. Table of the Efficiency of the Catalysts in hydrogenation of nitroarene.
|
Materials |
kapp (s-1) |
Conditions |
Conversion efficiency |
References |
|
Au@PMSiO2-500 |
2.42 * 10-4 |
4-NP (0.2 mmol), (3.6 10-2 mmol) NaBH4, and 2 mg/L of the catalyst for 60 min at RT. |
80% |
1 |
|
AuNPs |
1.28±5 - 8.2±3 |
1 mM of 4-NP ( 100 μL), 100 mM NaBH4 ( 100 μL), and 5 or 10 μL of the AuNP for 30 min at RT. |
complete reduction |
2 |
|
APSMNPs |
2.5 × 10⁻² |
0.5 mL of 1.0 mmol/L 4-NP, 2 mL of 0.1 M NaBH4, 0.5 mL of deionized water and (32.3 ) of catalyst at RT. |
100 |
3 |
|
AuNP_IL-SBA-15 PtNP_IL-SBA-15c PdNP_IL-SBA-15 RuNP_IL-SBA-15 CuNP_IL-SBA-15 |
13.4 ± 0.9* 10-3 3.8 ± 0.1* 10-3 47.4 ± 0.7* 10-3 3.7 ± 0.1* 10-3 1.6 ± 0.1* 10-3 |
4-NP / NaBH₄ = 1 / 50, 0.16 mg- 1mg pf catalyst, at RT |
100% 85% 100% 89% 90% |
4 |
|
BiNPs |
2.7* 10-2 |
4NP (2.5mL, 0.21g/L), NaBH4 (0.5mL, 33.4g/L), 0.5mL BiNPs (2g/L) for 2 min at RT. |
complete conversion |
5 |
|
Fe(OH)x/GO+ Bi(NO3)3 |
- |
1 mmol 4-NP, 2 mmol of hydrazine and 7 mg of catalyst for 40 min at 110°C. |
> 99 |
6 |
|
Bi NP |
- |
0.3 mL 4-NP aqueous solution (2 mM), 1.4 mL of water, NaBH4 (30 mM, 1 mL and (0.75 mg/mL) of catalyst at 25 °C. |
- |
7 |
|
CSp-Bi |
- |
500mL of 4-NP (1mmol), (10 to 30 eq) of NaBH4 and 5% mol of Bi at RT for 10 min. |
80-96 |
8 |
|
Bi NPs |
3.8* 10-3 |
2.5 mL of 4-NP 0.2 mM, 1 ml of NaBH4 0.05 M, and 0.5 mg/mL for 8-12 min at RT. |
- |
9 |
|
Bi-NC/γ-Al2O3 |
- |
1mmol NP, H₂ moléculaire, 50 mg of catalyst at 80°C for 8-12h. |
99 |
10 |
|
BiWO6@Csb |
6.1 *10-3 -1.2*10-2 |
6 mL of 4-NP (10 mg/L), 2 mL of NaBH4 solution (0.5, 1 or 2 M), and 0.74-16 mg of the Bi2WO6@CSb for 12 min at RT . |
≥ 98 |
11 |
|
0.5%Bi@SBA-NNH2 |
3,8 × 10⁻³ |
500mL of 4-NP (1mmol), (30 eq) of NaBH4 and 5% mol of Bi at RT for 10 min. |
100 |
This work |
- please report the conversions value for the nitrocompounds screening (Figure S11 shows only the UV spectra) to support the claims in lines 539-540
This has been added on the supplementary information Figures S11 and is explained in lines 539-540 as follow:
Next, the 0.5%Bi@SBA-NNH2 catalyst was tested for the reduction of three additional nitro-substituted aromatic under the following conditions: NaBH4 (30 equiv.) and catalyst (5 mol %) for 10 min. The catalyst achieves a conversion of 51% for 1-iodo-4-nitrobenzene, 44% for 1-bromo-4-nitrobenzene and moderate 27% conversion for 4-nitro-benzoic acid (Figure S12).
2
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors conducted the revisions and the article is recommended for publication in the journal Sustainability.
Author Response
We thank the reviewer for the time dedicated to the assessment of our manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author has provided detailed responses and corresponding revisions to the comments raised by the reviewer, and recommends accepting this version of the manuscript
Author Response
We thank the reviewer for the time dedicated to the assessment of our manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsI thank the authors for considering my comments
However, a few issues I raised in the previous review are still unsolved, please find my new comments in attachment
Comments for author File: Comments.pdf
Author Response
Please see the file attached for more clarety.
We are again very thankful for the third reviewer for his meticulous assessment of our work and her/his three raised comments. Please find our answers below with this same colour, each one appearing after the comment of the reviewer marked in red.
- Figure 6 caption is very limited. It should explain in detail what each graph shows. Probably in Figure 6d the legend is not correct as it does not reflect what written in lines 491-493. Where a pseudo first-order was observed, the line obtained from a linear regression should be showed in the ln(A/A0) vs time graphs.
(Authors) The caption of Figure 6 has been revised and expanded to provide a clearer and more detailed description of each figure. The legend in figure 6d has been corrected to ensure consistency with discussion presented in line 491-493. For the experiments exhibiting pseudo-first order kinetics the corresponding linear regression lines have been corrected to better illustrate the kinetic fitting and improve the clarity of the result.
(reviewer) I appreciate the scale change to ln(A/A0) vs. time. Actually, the linear regression is not showed in Fig 6, graphs 6c and 6d have broken lines instead of point dispersion with a regression curve.
(Our reply) Thank you for the comment. Figure 6 has been corrected and the linear regression lines are now clearly shown in figures 6c and 6d.
- in line 497 the authors say "tiny amount of bismuth in 0.5%Bi@SBA-NNH2". As I understood, 0.5% is the bismuth loading on the solid, but the molar ratio of bismuth with respect to nitrophenol is always 10%mol (as written in line 491). Can the authors clarify this? It seems sometimes there is some confusion between the bismuth loading on SBA-15 and the catalytic ratios.
--------------------------------------------------------------------------------------------------------------------
(Authors) We would like to clarify that the value of 0.5%Bi@SBA-NNH2 refers to the weight loading of bismuth in the SBA-15 support (the amount of metal deposited on the material). In contrast, the 10 mol% ratio mentioned in line 491 corresponds to the amount of bismuth introduced into the reaction medium relative to the substrate (nitrophenol).
Furthermore, the expression “tiny amount of bismuth in 0.5%Bi@SBA-NNH₂ provides an interesting conversion kinetics, with a kapp = 3.8 10-3. s-1” refers to the reduced amount of bismuth used under the catalytic conditions relative to nitrophenol. In this context, additional experiments were performed using lower molar ratios of 5 mol% and 2.5 mol%. The results indicate that a 5 mol% ratio provides a satisfactory conversion rate, achieving significant conversion within 10 minutes.
(reviewer) I thank the authors for the clarification in the catalyst loading on the solid vs. catalyst loading relative to 4-NP. However, their differentiation in the main text is still quite confused. Please distinguish clearly between Bi Loading on the solid and %mol of Bi in the catalytic reaction in the main text.
Also, I don’t see any mention in the text to the experiments with 0.5%Bi@SBA-NNH₂ performed at 5 mol% Bi and 2.5 mol% Bi. The only value of Bi mol% expressed in the text is the 10mol% in line 599.
(Our reply) That’s true. We agree that the distinction between the Bi loading on the solid support and the molar percentage of catalyst used in the catalytic reaction was not sufficiently clear in the previous version of the manuscript and we apologies for that. The revised manuscript now clearly distinguished between the bismuth loading on the support and catalyst amount used in the catalytic reaction (line 472). This appears in the manuscript as follow:
It should be noted that the 5% bismuth loaded on SBA-15-type materials (5%Bi@SBA-15, 5%Bi@SBA-NH2, 5%Bi@SBA-NNH2 and 5%Bi@SBA-NNNH2) refers to the weight loading of bismuth immobilized on the SBA supports, whereas the 10 mol% value correspond to the amount introduced into the reaction medium relative to the nitrophenol substrate.
We also agree that the discussion regarding the experiments performed with 0.5%Bi@SBA-NNH₂ at 5 mol% Bi and 2.5 mol% Bi was not sufficiently detailed in the previous version of the manuscript. The revised manuscript now explicitly includes the catalytic experiments carried out at 2.5 mol% and 5 mol% Bi in the main text. The corresponding discussion has been added (line 504) in order to clearly distinguish these catalytic conditions from the 10 mol% Bi experiment previously mentioned in line 499.
In order to further investigate the catalytic performance, we decreased the catalyst loading of 0.5%Bi@SBA-15 relative to the substrate and evaluated two catalyst amounts (2.5 mol% and 5 mol%). The obtained results showed that 5 mol% provides more favourable conversion kinetics, with an apparent rate constant kapp = 3.8 10-3. s-1.
--------------------------------------------------------------------------------------------------------------------
- the kinetic constant comparison in lines 497-500 is superficial and approximate in my opinion. Apparently, the authors use the simplified kinetic equation (2) and directly compares the k value obtained with 10%mol of Bi and 30 eq of NaBH4 with data of other papers (without reference). It is impossible to verify whether this comparison is appropriate (as we don't know the conditions and the equations used in the other papers) and therefore the outperformance claimed in lines 498-499 is not proved. Moreover, the calculation of the kinetic constant is not reported and the error associated to its calculation is missing.
(Authors) We thank the reviewer for this comment regarding the comparison of kinetic constats, in the revised manuscript, we have clarified the calculation method based on the simplified kinetic equation (2).
we clarify that was determined under the commonly used pseudo-first-order assumption, valid under excess NaBH₄ conditions. In this approach, the reaction rate depends only on the concentration of 4-nitrophenol, and the kinetic constant is obtained from the linear fitting of:
Where and correspond to the concentrations (or absorbance values) at time t and initial time, respectively. The kapp values were determined from the slope of the linear fitting of ln(At/A0) versus reaction time.
Furthermore, we acknowledge that the previous comparison with literature values was not sufficiently supported. Therefore, we have revised this section by adding the appropriate references and by discussing the differences in experimental conditions and kinetic models used in in supplementary information (Table S2).
(reviewer) I thank the authors for reporting the references. However, for a more accurate comparison between different systems, the kinetic constant value alone is not sufficient as the amount of catalyst employed in the reaction is not considered. I think comparing TOF (turn over frequency) values instead of kapp values would be more significant in the comparison of different catalytic systems.
(Our reply). We thank the reviewer for this comment and agree that greater accuracy is needed when comparing the activity of different catalysts. Typically, TON is used to assess the long-term stability of a catalyst, whereas TOF provides insight into how rapidly the active sites operate. In contrast, the apparent kinetic constant (Kapp) often reflects the mechanistic pathway and intrinsic reactivity of the system. This distinction is particularly important in the present case, as the reduction of nitrophenol may proceed via an alternative pathway leading to azoarene formation through an oxidative process.
It should also be emphasized that nitrophenol reduction is widely employed as a model reaction because it is experimentally straightforward, allows good control over key parameters, and serves as a convenient screening test for catalytic activity prior to more demanding evaluations. Under typical conditions, the catalyst is not driven to deactivation; therefore, TON is not a relevant metric in this context. While TOF could be used, we agree that caution is required when comparing catalysts with differing surface areas, accessibility, and dispersion. Moreover, TOF values are not consistently reported in the literature for this reaction, which further limits their usefulness for comparative purposes.
To address this issue, the available TOF values have now been added to Table S2 in the supporting information (see below). We have also added a small comment regarding this issue, recalling for a precaution when comparing different catalysts.
Table S2. Comparison of the Efficiency of the Catalysts in hydrogenation of nitroarene.
|
Materials |
TOF (h-1) |
Kapp (s-1) |
Conditions |
Conversion efficiency |
References |
|
Au@PMSiO2-500 |
NR |
2.42 * 10-4 |
4-NP (0.2 mmol), (3.6 10-2 mmol) NaBH4, and 2 mg/L of the catalyst for 60 min at RT. |
80% |
[1] |
|
AuNPs |
NR |
1.28±5 - 8.2±3 |
1 mM of 4-NP (100 μL), 100 mM NaBH4 (100 μL), and 5 or 10 μL of the AuNP for 30 min at RT. |
complete reduction |
[2] |
|
APSMNPs |
1428 |
2.5 × 10⁻² |
0.5 mL of 1.0 mmol/L 4-NP, 2 mL of 0.1 M NaBH4, 0.5 mL of deionized water and (32.3) of catalyst at RT. |
100 |
[3] |
|
AuNP_IL-SBA-15 PtNP_IL-SBA-15c PdNP_IL-SBA-15 RuNP_IL-SBA-15 CuNP_IL-SBA-15 |
1.2* 10-5 0.4* 10-5 3.5* 10-5 0.3* 10-5 0.1* 10-5 |
13.4 ± 0.9* 10-3 3.8 ± 0.1* 10-3 47.4 ± 0.7* 10-3 3.7 ± 0.1* 10-3 1.6 ± 0.1* 10-3 |
4-NP / NaBH₄ = 1 / 50, 0.16 mg- 1mg pf catalyst, at RT |
100% 85% 100% 89% 90% |
[4] |
|
BiNPs |
NR |
2.7* 10-2 |
4NP (2.5mL, 0.21g/L), NaBH4 (0.5mL, 33.4g/L), 0.5mL BiNPs (2g/L) for 2 min at RT. |
complete conversion |
[5] |
|
Fe(OH)x/GO+ Bi(NO3)3 |
NR |
- |
1 mmol 4-NP, 2 mmol of hydrazine and 7 mg of catalyst for 40 min at 110°C. |
> 99 |
[6] |
|
Bi NP |
NR |
- |
0.3 mL 4-NP aqueous solution (2 mM), 1.4 mL of water, NaBH4 (30 mM, 1 mL and (0.75 mg/mL) of catalyst at 25 °C. |
- |
[7] |
|
CSp-Bi |
NR |
- |
500mL of 4-NP (1mmol), (10 to 30 eq) of NaBH4 and 5% mol of Bi at RT for 10 min. |
80-96 |
[8] |
|
Bi NPs |
NR |
3.8* 10-3 |
2.5 mL of 4-NP 0.2 mM, 1 ml of NaBH4 0.05 M, and 0.5 mg/mL for 8-12 min at RT. |
- |
[9] |
|
Bi-NC/γ-Al2O3 |
NR |
- |
1mmol nitroarene, H₂ moléculaire, 50 mg of catalyst (0.012 mmol), temperature (100◦C to 150◦C) for 18h to 36h. |
99 |
[10] |
|
BiWO6@Csb |
NR |
6.1 *10-3 -1.2*10-2 |
6 mL of 4-NP (10 mg/L), 2 mL of NaBH4 solution (0.5, 1 or 2 M), and 0.74-16 mg of the Bi2WO6@CSb for 12 min at RT. |
≥ 98 |
[11] |
|
0.5%Bi@SBA-NNH2 |
120 |
3,8 × 10⁻³ |
500mL of 4-NP (1mmol), (30 eq) of NaBH4 and 5% mol of Bi at RT for 10 min. |
100 |
This work |
In the manuscript, we have added this passage:
In Table S2, we summarize the catalytic performance of selected literature catalysts for comparison, based on their kapp and TOF values. Nevertheless, these comparisons should be interpreted with caution, as more complex reaction scenarios may occur depending on the experimental conditions. Considering the cost of the ubiquitously used metal catalysts (ex. Platine and Ruthenium) [57], their toxicity and in many cases, the nontrivial synthesis of the support, our supported bismuth reported herein seems to be largely attractive.
Author Response File: Author Response.pdf
