Sulfonic Acid-Functionalized Inorganic Materials as Efficient Catalysts in Various Applications: A Minireview

Round 1

Reviewer 1 Report

In this manuscript, the authors describes a series of efficient sulfuric acid-functionalized inorganic solid materials catalysts used in various applications. Acid catalysts are very powerful systems used in chemical synthetic industrial processes. Generally, this catalyst are implicated in homogeneous catalysis and one of the most problem is it’s recovery and reuse from the reaction media. Heterogeneous catalyst permit to avoid the problem because, generally, the catalyst is present in solid phase and can be recovered through a simple filtration technique. In this context, solid catalyst represent the solution to the industrial grievous problem. In particular, many reactions are catalyzed with acidic catalyst and the use of heterogeneous acid catalysts in reaction systems allows an higher eco-compatibility of the process. In this perspective, sulfuric solid acid materials represent a valid alternative to the homogeneous acid catalysis in several reactions. For these reasons, this mini review is well suited to the scientific world to provide an overview of recent developments in the field of synthesis of new heterogeneous sulfuric acid-based catalysts.

The manuscript is well organized in: introduction, sulfonic acid-functionalized materials: synthesis and applications, sulfonic acid-functionalized materials: characterization, considerations on the stability of sulfonic solid acid catalysts, conclusion. All sections are nicely structured with good descriptions of the concepts. However, some minor modifications are required before the manuscript can be accepted.

1. I suggest the addition of references in sentence reported in 39-43 rows to improve the specificity of some concepts: “Due to their versatile use, they are involved in pharmaceutical chemistry for the synthesis of new molecules as potential drugs [ref.1], in environmental chemistry for the abatement of pollutants [ref.2], in biomass conversion for the production of sustainable added value products or for the achievement of new eco-friendly biofuels [ref.3, ref. 4]”.

• [Ref.1]: Li, R.; Ouda, R.; Kimura, C.; Narita, R.; Nishimura, H.; Fujita, T.; Watanabe, T. Conversion of Beech Wood into Antiviral Lignin–Carbohydrate Complexes by Microwave Acidolysis. ACS Sustainable Chem. Eng.2021, 9 (28), 9248–9256.
• [Ref. 2]: De Nino, A.; Tallarida, M. A.; Algieri, V.; Olivito, F.; Costanzo, P.; De Filpo, G.; Maiuolo, L. Sulfonated Cellulose-Based Magnetic Composite as Useful Media for Water Remediation from Amine Pollutants. Sci. 2020, 10, 8155.
• [Ref.3]: Jehadin, F.; Rabeya, T.; Asad, M. A.; Ayodele, O. O.;  Adekunle,  E.;  Islam, M. S. Effient conversion of cornstalk to bioethanol using dilute H₂SO₄ pretreatment. International Journal of Energy and Environmental Engineering 2021, 12, 203–211.
• [Ref. 4] Knoshaug, E. P.; Dong, T.; Spiller, R.; Nagle, N.; Pienkos, P. T. Pretreatment and fermentation of salt-water grown algal biomass as afeedstock for biofuels and high-value biochemicals. Algal Research 2018, 36, 239–248.

2. In the sentence reported in 66-69 rows, is necessary the introduction of a reference: “Due to the presence of several OH groups on its surface area, it can be easily chemically modified by using different functionalization procedures with various linkers, for the improvement of the stability and/or the chemical properties of the support [ref.]”.
3. Please, the authors must introduce the numbering for each molecule present in the mini review both in the text and in the reaction schemes, considering that if a molecule is reported several times in the text, it must have the same number.
4. The authors, must be introduce the reaction conditions in all schemes and figures presents in the manuscript.
5. In row 193 N-propylsulfamic must be replaced with N-propylsulfamic.
6. In the sentence reported in 238-240 rows, is necessary the introduction of a references: “In this context, Fe₃O₄ nanoparticles have attracted high interest due to their low toxicity [ref.], biocompatibility [ref.], high surface area [ref.], large-scale production with low cost [ref.], thermal and mechanical stability [ref.].
7. In row 258 “catayst” must be replaced with catalyst.
8. In rows 268 and 271 “S-sulfonic” can be replaced with S-sulfonic.
9. In the sentence reported in 295-298 rows, is necessary the introduction of a reference: “Different functionalizations of the surface of TiO₂ allow to produce materials with several application as active catalysts or catalyst supports in diverse catalytic processes[ref.], in the field of photovoltaics [ref.], heterocycles chemistry [ref.], chemical platform or biofuels [ref.].
10. In row 445 n-propylsulfonated must be replaced with n-propylsulfonated.
11. In Figure 14, another -CH₂- must be added in the alkyl chain of the product, so structure -S(CH₂)₂-SO₃H must be replaced with structure -S(CH₂)₃-SO₃
12. In row 523 “to asymmetric, stretching,” can be replaced with “to asymmetric stretching,”.
13. What is 5-HMF in row 621? Please revise all manuscript and introduce the name of compounds when for the first time are discussed, for example: 5-(hydroxymethyl)furfural (5-HMF).
14. Whenever possible, authors should indicate the range of reaction yields in which the heterogeneous acid catalyst has been applied.

Author Response

Dear Dr. Bonnie Luo

Thanks for your e-mail and the enclosed comments of the reviewers. Thanks also the reviewers for the valuable comments that improve the manuscript. We have revised the manuscript “Sulfonic acid-functionalized inorganic materials as efficient catalysts in various applications: a minireview” (catalysts-1384901) and the comment upon the interesting remarks pointed out by the reviewers are listed below. In the article, all the variations are highlighted in yellow, in order to better notice the changes.

Reviewer #1: 1. I suggest the addition of references in sentence reported in 39-43 rows to improve the specificity of some concepts: “Due to their versatile use, they are involved in pharmaceutical chemistry for the synthesis of new molecules as potential drugs [ref.1], in environmental chemistry for the abatement of pollutants [ref.2], in biomass conversion for the production of sustainable added value products or for the achievement of new eco-friendly biofuels [ref.3, ref. 4]”. 2. In the sentence reported in 66-69 rows, is necessary the introduction of a reference: “Due to the presence of several OH groups on its surface area, it can be easily chemically modified by using different functionalization procedures with various linkers, for the improvement of the stability and/or the chemical properties of the support [ref.]”.

As suggested by the reviewer, in order to improve the concepts we added some appropriate references, concerning the points 1-2.  

3. Please, the authors must introduce the numbering for each molecule present in the mini review both in the text and in the reaction schemes, considering that if a molecule is reported several times in the text, it must have the same number. 4. The authors, must be introduce the reaction conditions in all schemes and figures presents in the manuscript.

Schemes and figure were modified according to the referee suggestion.

5. In row 193 N-propylsulfamic must be replaced with N-propylsulfamic. 7. In row 258 “catayst” must be replaced with catalyst. 8. In rows 268 and 271 “S-sulfonic” can be replaced with S-sulfonic. 10. In row 445 n-propylsulfonated must be replaced with n-propylsulfonated. 12. In row 523 “to asymmetric, stretching,” can be replaced with “to asymmetric stretching,”.

The typos of the sentences specified in points 5, 7, 8, 10, 12 were changed.

6. In the sentence reported in 238-240 rows, is necessary the introduction of a references: “In this context, Fe₃O₄ nanoparticles have attracted high interest due to their low toxicity [ref.], biocompatibility [ref.], high surface area [ref.], large-scale production with low cost [ref.], thermal and mechanical stability [ref.]. 9. In the sentence reported in 295-298 rows, is necessary the introduction of a reference: “Different functionalizations of the surface of TiO₂ allow to produce materials with several application as active catalysts or catalyst supports in diverse catalytic processes[ref.], in the field of photovoltaics [ref.], heterocycles chemistry [ref.], chemical platform or biofuels [ref.]

The references related to Fe₃O₄ nanoparticles (point 6) and the application of TiO₂ (point 9) were properly added.

11. In Figure 14, another -CH₂- must be added in the alkyl chain of the product, so structure -S(CH₂)₂-SO₃H must be replaced with structure -S(CH₂)₃-SO₃H-

Thanks to the referee to notice the mistake. Figure 14 was corrected.

13. What is 5-HMF in row 621? Please revise all manuscript and introduce the name of compounds when for the first time are discussed, for example: 5-(hydroxymethyl)furfural (5-HMF).

According to the referee suggestion, the name of compounds were introduced when for the first time are discussed

14. Whenever possible, authors should indicate the range of reaction yields in which the heterogeneous acid catalyst has been applied.

During the discussion on the applications of sulfonic acid catalysts some more details were added.

Author Response File: Author Response.pdf

Reviewer 2 Report

All the comments and suggestions can be found in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear Dr. Bonnie Luo

Thanks for your e-mail and the enclosed comments of the reviewers. Thanks also the reviewers for the valuable comments that improve the manuscript. We have revised the manuscript “Sulfonic acid-functionalized inorganic materials as efficient catalysts in various applications: a minireview” (catalysts-1384901) and the comment upon the interesting remarks pointed out by the reviewers are listed below. In the article, all the variations are highlighted in yellow, in order to better notice the changes.

Reviewer #2: 2.1. Sulfonic-silica based materials. The Authors describe the use of ClSO3H and sultones in multistep modifications, but it would be good to add to this section publications in which direct sulfonation with ClSO3H or sultone are described, e.g.:MCM-41 anchored sulfonic acid (MCM-41-SO3H): An efficient heterogeneous catalyst for green organic synthesis - Vekariya et al. https://doi.org/10.1080/00397911.2016.1212380 The catalytic effect of Al-KIT-5 and KIT-5-SO3H on the conversion of fructose to 5- hydroxymethylfurfural - Chermahini et al. https://doi.org/10.1007/s11164-017-2991-7

According the referee‘s suggestion, a paragraph on the synthesis (ref. Vekariya et al.) and application (ref. Hasan et al.) of SiO₂-SO₃H  was added.  Chermahini’s study was discussed in the paragraph related to the use of sultone.

Also worth mentioning in this section are additional modifications to the silica supports. Examples below:

SiO₂ + zeolite: Propylsulfonic acid functionalized MCA cubic mesoporous and ZSM-5-MCA composite catalysts for anisole alkylation - Samutsri et al.  https://doi.org/10.1016/j.micromeso.2016.10.021

SiO₂ + carbon: Preparation of a Carbon-Silica Mesoporous Composite Functionalized with Sulfonic Acid Groups and Its Application to the Production of Biodiesel - Fang et al. https://doi.org/10.1016/S1872-2067(10)60282-3

SiO₂ + TiO₂: Arenesulfonic Acid-Functionalized Mesoporous Silica Decorated with Titania: A Heterogeneous Catalyst for the One-Pot Photocatalytic Synthesis of Quinolines from Nitroaromatic Compounds and Alcohols - Hakki et al. https://doi.org/10.1021/cs300736x

The modifications to the silica supports can improve some characteristics such as stability, acidity or catalytic properties. So agree with the reviewer, a paragraph including the cited references was added

In my opinion, a very important aspect for solid acid catalysts is to apply microwave radiation in the synthesis of -SO₃H-modified materials and in catalytic reactions. This topic should be described more extensively for SiO₂-based materials. Since the Authors declare that the key to this minireview was “an overview of the recent advances on the preparation, stability and application of these materials” and “The preparation procedures as well as the applications will be addressed with a special attention to those processes with higher sustainability.”, I believe that at least the publications listed below should be included as examples: Synthesis: Tuning the acid content of propylsulfonic acid-functionalized mesoporous benzene-silica by microwave-assisted synthesis - Domingues et al.  https://doi.org/10.1016/j.micromeso.2016.02.0182

Boosted selectivity toward high glycerol tertiary butyl ethers by microwave-assisted sulfonic acid-functionalization of SBA-15 and beta zeolite - Gonzalez et al. https://doi.org/10.1016/j.jcat.2012.03.019

We agree with the referee so these two studies were introduced and discussed in the synthesis of sulfonic silica carried out by the use of microwaves source.

Catalytic reactions: Jetti et al. applied catalysts which are already mentioned in this manuscript [16] (silica-bonded N-propyl sulfamic acid) in the synthesis of derivatives of pyrimidinones and thiones with microwave irradiation and in solvent-free condition (3,4-Hydropyrimidin-2-(1H)one derivatives: solid silica-based sulfonic acid catalyzed microwave-assisted synthesis and their biological evaluation as antihypertensive and calcium channel blocking agents - Jetti et al. (https://doi.org/10.1007/s00044- 014-0988-y)

Nanostructured KIT-6 materials functionalized with sulfonic groups for catalytic purposes – MW-assisted Friedel-Crafts alkylation, fatty acid esterification and Pechmann condensation - Wawrzynczak et al. https://doi.org/10.1016/j.cattod.2021.06.019

Esterification and acetylation reactions over in situ synthesized mesoporous sulfonated silica -Hasan et al. http://dx.doi.org/10.1016/j.cej.2014.12.025

Concerning the above-mentioned references, they were included in the text. In particular, Jetti et al was added in the paragraph concerning the synthesis and application of silica-bonded N-propyl sulfamic acid; Wawrzynczak et al. was included in section 4 where MW-assisted organic reactions were discussed; and finally, as already mentioned, Hasan et al.  was integrated in the paragraph concerning the synthesis and applications of SiO₂-SO₃H.

2.2. Sulfonic-titania based materials. In the line 306 the Authors claim that: “Specifically, TiO2 presents a very low SSA with respect to silica (about 10%).” In general this is true, but it would be nice to mention also mesoporous titania in which SSA could be far more developed, exceeding even 260 m2/g: Synthesis and characterization of trifluoromethanesulfonic acid supported on mesoporous titania – Pizzio et al. https://doi.org/10.1016/j.matlet.2006.07.190)

Thanks to the referee for this suggestion. The reference was added.

3. Sulfonic acid-functionalized materials: Characterization.

FT-IR allows to confirm the presence of functional groups containing sulfur atom (-SH or -SO₃H) only in case of relatively high concentrations. In other cases Raman spectroscopy can be definitely more convenient – it would be worth mentioning this in the paper, giving examples from the recent literature. The Authors mention acid-base titration method only in one sentence (lines 582-583) whereas it is a commonly used and well-established method for the determination of sulfonic groups content. This method can be also used in different variants, i.e. as direct titration with NaOH, but also as reverse titration, where the unreacted excess of NaOH is titrated with HCl. Besides the methods described by the Authors, also other techniques for qualitative and quantitative determination of sulfur introduced in the modification process seem to be worth mentioning, namely XRF and elemental analysis. Many relevant examples can be found in the literature, viz.:

Yang et al. https://doi.org/10.1016/j.micromeso.2005.05.037;

Wawrzynczak et al. https://doi.org/10.1016/j.cattod.2021.06.019

Li et al. https://doi.org/10.3390/catal8080297 and many other.

According to referee suggestion we enriched the characterization section adding Raman spectroscopy and techniques for elemental analysis of materials.

4. Considerations on the stability of sulfonic solid acid catalysts

The following papers are worth adding to the section on carrier stabilization by hydrophobization: Influence of Site Pairing in Hydrophobic Silica-Supported Sulfonic Acid Bifunctional Catalysts -hydrophobic decyl (−C10) chains - Kasinathan et al. https://doi.org/10.1021/acs.langmuir.0c01759

Hydrophobic modification of SO₃H-functionalized mesoporous silica and investigations on the enhanced catalytic performance - Kamegawa et al. https://doi.org/10.1016/j.cattod.2014.08.017

The references were added in the suggested paragraph.

5. Conclusions

In lines 659-660 the Authors state: “As inorganic supports, SiO₂ and TiO₂, were considered due to their economic, ecofriendly and good chemical and thermal stability properties” What about other supports which are described in the chapter 2.3?

According to the referee’s comment the sentence was changed to be clear.

In lines 665-668 the Authors claim: “The principal techniques for the characterization of the sulfonic groups, located both on the external and internal surface of the inorganic support, were also described. They included solid state NMR, XPS, FT-IR, TGA, XRD, Nitrogen physisorption, acid evaluation by FTIR of adsorbed pyridine/NH₃ and titration.”. However, nitrogen physisorption is not discussed in the manuscript.

We thank the referee for indicating this mistake. We corrected the sentence with the characterization actually discussed.

Some flows in the text that should also be corrected:

Conclusions chapter should be numbered as 5. The Authors should standardize the writing throughout the text: „sulphonation” or „sulfonation, sulphonic” or „sulfonic”, etc. The same for “FT-IR” or “FTIR”. There should always be a period in the notation "et al.".

When giving a reference in the text, it must be standardize everywhere to the form of writing with a period after the reference, not before it. No reference in the text to the posted figures 5, 15-18, and 20. Figure 20 is not very clear.

Note the subscripts and superscripts in the text (especially when describing NMR and FT-IR) and literature list.

All these notes were changed according to the referee’s suggestions.

Typos should be corrected – see the following lines:

193 – „Silica-bonded” starts with a capital letter

228 – hyphen is missing In the “cocondensation”

308 – two dots at the end of the sentence

327 – “efficient catalyst on in the multicomponent reaction” on or in?

363 – hyphen is missing In the “MCM41”

367 – corrisponding

406 – “grafting procedure with chlorosulfonic as a source” – the word “acid” should be added

511 – solphonic4

514 – 3-MPTS should be abbreviated as MPTMS, since this form was used in the previous parts of

the manuscript

539 – are foun at

545 – ter

583 – exhanger

671 – as e efficient

All the typos were corrected

In general, I have no objections to the quality of the language, but a few sentences seem to me

worth correcting for better understanding:

Line 534 – techniques is applicable

Lines 538-541 – it is too long and hard to follow

Lines 559-560 – is this sentence finished?

Lines 628-629 – is this sentence finished?

Lines 634-637 – it is not clear

The above mentioned sentences and paragraphs were better explained in order to be clearer to readers

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The manuscript has been revised and supplemented by numerous publications, thus gaining a broader perspective on the topic discussed. I believe that in its present form it deserves to be published. However, the Authors should pay attention to the formal side of the added fragments (typos, spelling, lack of spaces, etc.).