Applicability of Clay/Organic Clay to Environmental Pollutants: Green Way—An Overview
, Dhirpal D. Shah 3 and Zhaoyang You 1,*
Round 1
Reviewer 1 Report
In this manuscript, the authors comprehensively reviewed the classification of the clay family to identify its properties and examine applicability for pollution control applications. In addition, authors summarized the role of green chemistry in establishing global sustainability. The manuscript is interesting and well fit the aim and scope of the journal. Therefore, I will be glad to recommend the publication of this manuscript in the Applied Sciences (MDPI) after the following revisions are fully addressed:
Abstract: Abstract must include the novelty, objectives, and major outcome.
Introduction;
# The introduction is not sufficient enough to justify the novelty of the study. Update it with more focused points.
# Please add a graph showing the number of publications (research articles) on the topic of application/role of organic clay in environmental pollutant ion control or pollutants mitigation to highlight the apparently increased attention around this topic over the recent few years.
#This review provides a comprehensive update in view of the existing literature. Nevertheless, the authors need to mention previous similar reviews on this topic.
#The introduction should be extended to discuss the hypothesis and research questions in detail. The introduction needs more clarity with state of arts, and objectives of the study for the scientific novelties of the manuscript. Additionally, the introduction should cover the recent literature related to this subject.
#Pl. define and abbreviate while first appearance of the scientific terms, thereafter use abbreviated form throughout the text uniformly. Please correct line no. 47; page 2; SOx, NOx, COx, Line 344-347.
#Line 72, Page -2; Please expand, GDP.
#Line 79, Page-2; LPG?
#Line 132; Page 3; silicon tetrahedron (SiO42-) and aluminum octahedron [Al(OH)63-] should be corrected.
#Line 234; Page 7; Na+, Ca2+, please correct them as per standard.
#Line 284; Page 8, SEM and TEM???
#Append contemporary linked literature to all sections and improve the discussion in depth.
Conclusion and Recommendation;
Please split section 5 into two sections with a clear summary of the current status of the progress made in the field of the topic. In the second section (perspectives), the authors should specifically highlight the remaining challenges and the proposed solution for future research directions in the form of separate bullet points.
Tables and Figures;
#The legends and captions need improvement. They should have enough description for a reader to understand the figure without having to refer back to the main text of the manuscript.
References;
#Old references may be replaced with recent references.
#The list of references is not consistent; format it in accordance with the journal guidelines.
#The technical language of the manuscript is good. A few grammatical errors should be checked.
Comments for author File: 
Comments.pdf
Author Response
Reviewer #1
Reviewer #1: In this manuscript, the authors comprehensively reviewed the classification of the clay family to identify its properties and examine applicability for pollution control applications. In addition, authors summarized the role of green chemistry in establishing global sustainability. The manuscript is interesting and well fit the aim and scope of the journal. Therefore, I will be glad to recommend the publication of this manuscript in the Applied Sciences (MDPI) after the following revisions are fully addressed:
Response: Thank you for your diligence and positive comments. Thank you very much for your expertise which helps us to improve the quality of this work. The corrections have been made in red color in the revised file. Thank you again for your efforts in reviewing this manuscript.
- Abstract: Abstract must include the novelty, objectives, and major outcome.
Response: Thanks for your comment. Based on that, we have modified it with focusing more novelty, objective and outcomes.
Action: Natural clay mineral and its modifier called modified clay have been used in many environmental applications for a number of years. However, they are not enough to achieve a higher conversion rate and so-called ecological sustainability. This can be due to a lack of understanding of the selectivity of clay and its modifier, or a lack of compatibility between clay and pollutants. Recently, the development and implementation of green principles into practice is an emerging field that brings together green chemistry and engineering practices to achieve a pollutant-free environment (air, water and soil). This review summarized the role of clay/modified clay in pollution control and discussed the role of green chemistry in creating global sustainability. In this context, this review sheds light on the complete classification of the clay family to identify its properties and to critically examine the applicability of clay and modified clay for air, water and soil pollution control over the past decade. This is the unique point of this review, showing how the properties of clay/modified clay can be useful for removing any type of pollutants without focusing on a single type of pollutants or clay. Furthermore, the importance of green materials in clay research as well as the future area of ​​application was discussed. Overall, this review places value on multidisciplinary researchers to determine the role of the green pathway in the application of clay and modified clay in achieving environmental sustainability.
- Introduction: # The introduction is not sufficient enough to justify the novelty of the study. Update it with more focused points.
Response: Thanks for your comment. Based on that, we have addressed a paragraph explaining the difference between other reviews and this review. In addition, most of the most recent reviews have been cited in specific segments. This paper is unique in that it provides brief data on the applicability of clay to air and soil pollution.
Action:
In the latest study, the modified clay was most commonly used to remove water pollutants such as dyes, organic pollutants and heavy metals. However, this paper not only focuses on the adsorption of pollutants in organic clay water, but also pays attention to the adsorption effect of pollutants in soil and air. This is the unique selling point of this article, which shows the properties and classification of clay as beneficial for the adsorption of pollutants. In addition, this overview focuses on all keys and not just a single type.
- # Please add a graph showing the number of publications (research articles) on the topic of application/role of organic clay in environmental pollutant ion control or pollutants mitigation to highlight the apparently increased attention around this topic over the recent few years.
Response: Thank you for the reviewer's comment. Based on the comments, we added the number chart showing the number of research article published in the last 10 years.
Action:
Figure 1 shows the number of publications (research articles) on the application/role of organic clays in pollution control or pollution abatement in the last decade (from 2013 to August 2023). It can be seen that clay-based research for environmental applications is continuously growing exponentially, showing that the applicability of clay research has become a current hot topic. In addition, researchers from all over the world participate in this research area. Even in times of COVID-19, we can observe that the concern in this area is also increasing, which shows the great importance of this topic in recent times.
Figure 1. The number of publications (research articles) on the application/role of organic clay in the control or mitigation of pollutant ions in the environment
- #This review provides a comprehensive update in view of the existing literature. Nevertheless, the authors need to mention previous similar reviews on this topic.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer. In the revised manuscript, the areas have been marked in red highlight any changes of this time.
Action: Thus, the purpose of this article is to examine the role of clay in the field of pollution control without limiting the specific pollutants or clay. There are many clays used for many commercial and pollution control applications that have steadily increased over the last 10 years. However, they fail to catch on and achieve a wide range of removal rates and environmental credentials. Failure to achieve a high conversion rate may be due to a poor understanding of the properties and types of clay and their compatibility with modifiers. This problem can be solved by understanding the classification of clay and putting into practice the principle of green chemistry.
- #The introduction should be extended to discuss the hypothesis and research questions in detail. The introduction needs more clarity with state of arts, and objectives of the study for the scientific novelties of the manuscript. Additionally, the introduction should cover the recent literature related to this subject.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer. In the revised manuscript, the areas have been marked in red highlight any changes of this time.
First the trend: We've added Figure 1, which shows the current trend for clay-based research. Section 1.4 is where strategies for sustainability can be useful. Most of the review has been highlighted on either water based contaminants or specific clays such as Gemini based surfactant clay for contaminant removal, Ref #47; cationic clay Ref. No. 19; Bioreactive Clay for Environmental Remediation Ref. No. 153. Additionally, there is no report emphasizing soil and air pollution together. This is the first and most unique review that has combined all of the literature to justify clay as a source of pollution control and the role of green chemistry in practice.
Action:
In the latest study, the modified clay was most commonly used to remove water pollutants such as dyes, organic pollutants and heavy metals. However, this paper not only focuses on the adsorption of pollutants in organic clay water, but also pays attention to the adsorption effect of pollutants in soil and air. This is the unique selling point of this article, which shows the properties and classification of clay as beneficial for the adsorption of pollutants. In addition, this overview focuses on all keys and not just a single type.
- #Pl. define and abbreviate while first appearance of the scientific terms, thereafter use abbreviated form throughout the text uniformly. Please correct line no. 47; page 2; SOx, NOx, COx, Line 344-347.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
Meanwhile, the main air pollutants are SOx (sulfur oxides), NOx (oxides of nitrogen), COx (carbon oxides),
- #Line 72, Page -2; Please expand, GDP.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
Despite today's development of science and technology, the pursuit of a pollution-free world is still not enough, although a large part of Gross Domestic Product (GDP) is spent on sustainability, and the number of deaths from pollution is one in six deaths worldwide.
- #Line 79, Page-2; LPG?
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
There are many reports stating that introducing a new lifestyle, such as switching to electric and natural gas cooking from legacy fossil fuels and traditional Liquefied Petroleum Gas (LPG) -based cooking has reduced the pollution, but this is also fact that the more than half of the countries worldwide have had more deaths from outdoor air pollution than from indoors air and water pollution [12].
- #Line 132; Page 3; silicon tetrahedron (SiO42-) and aluminum octahedron [Al(OH)63-] should be corrected.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
The clay material that we most commonly refer to as phyllosilicate, a layered structure, are silicon tetrahedron (SiO42-) and aluminum octahedron [Al(OH)63-], which exist in various combinations [16, 17].
- #Line 234; Page 7; Na+, Ca2+, please correct them as per standard.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
In addition, Na+ has a higher affinity for CEC than K+ and Ca2+, so Na-rich clay gives a higher medication rate in most cases.
- 11. #Line 284; Page 8, SEM and TEM???
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
This roughness and changes are identified by Scanning electron microscope (SEM) and Transmission electron microscope (TEM) images.
- #Append contemporary linked literature to all sections and improve the discussion in depth.
Response: Thanks for your comment. Section 4 provides a summary of all three types of pollutants for use in pollution control. No special linkage is required at this point. This is the follow-up paper where detailed physicochemical properties must be discussed with their theoretical studies.
- Conclusion and Recommendation;
Please split section 5 into two sections with a clear summary of the current status of the progress made in the field of the topic. In the second section (perspectives), the authors should specifically highlight the remaining challenges and the proposed solution for future research directions in the form of separate bullet points.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer. In the revised manuscript, the areas have been marked in red highlight any changes of this time.
Action:
5.1 Current research status
The applicability of clay and modified clay is a very large field and has tremendous potential due to low cost, large surface area, easy availability and promising material. Table 2-4 summarizes the applicability of clay to air, water and soil pollution using different types of clay, their modifiers and adsorption capacity. From summarizing more than 100 major publications of the literature over the past 10 years, it is clear that clay and organoclay are heavily used in pollution control application, with bentonite or montmorillonite modified by cation exchange techniques for production and application being predominant in other clays and modifiers. Approximately 85% of the papers indicated the use of cation exchange methods. As can be seen from Table 1，2，3， apply the removal of heavy metals in soil, dyes, phenols and heavy metals in water, CO2 and CH4 in air, and the removal effect is good. From this review it is concluded that natural clay and its components are suitable for pollution control. In addition, in most cases it has been demonstrated that the applicability of clay and organoclay is better than or comparable to the existing commercially available adsorbents. In addition, it can be seen that the applicability of clay and organoclay to water pollution is higher than that of air and solid waste. However, recent developments with a trend towards these applications cannot be neglected.
This review also suggests the role of green chemistry in clay application and clay modification. It can be said that this release trend supports the applicability of natural clay to support the environment, playing the role of pollution prevention, atom economy, less hazardous synthesis, the development of a safer catalyst, solvent-free synthesis, energy efficiency, use of renewable/natural materials and less production plays of derivatives, natural catalyst, design material for decomposing pollutants, prevention of environmental pollution and prevention of accidents due to simple synthesis is preserved.
5.2 Future research directions
However, there are several gaps that should be considered as a potential research area for the future, such as:
- The applicability of clay and modified clay to improve efficiency in soil and air pollution removal. This gap is due to clay's ease of processing as a water absorber, which is difficult in the air and soil environment, but still not negligible.
- Further research is needed to use natural modifiers instead of surfactant molecules or to use bio surfactant as a modifier to aid in a less hazardous synthesis.
- More urgent research was needed to use clay material to remove micro plastics as COVID has increased the use of masks, which are potential water pollutants compared to other organic pollutants.
- In addition, there is high potential for the applicability of clay and organoclay materials to remove and treat emerging contaminants.
- It is also an interesting study to determine the role of microbes in breaking down pollutants or converting them to less harmful forms in the presence of clay or organic clay media.
The search for the above question is very important because clay is a naturally occurring, low-grade, easily treated, and economically viable adsorbent material that has the potential to be used as a large-scale material for environmental applications. At the same time, green chemistry development is also a promising emerging field in which key natural modifiers and modified technologies can be identified to develop environmental entrepreneurs that have less toxic effects on the ecosystem.
- Tables and Figures;
#The legends and captions need improvement. They should have enough description for a reader to understand the figure without having to refer back to the main text of the manuscript.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
Figure 2. The basic classification of silicates and clay minerals
Figure 3 Applicability of clay as a multi-element mineral additive in red soil to remove heavy metal contaminants (Cd2+, Pb2+, Cr3+ and Hg2+) [43] copyright 2019, Elsevier.
Figure 4. Applicability of (mono-; bi-; tetra-tails, and benzyl substituted) quaternary ammonium modified montmorillonite clay as a potential binding site provider for phenol removal in aqueous media [81] copyright 2018, Elsevier.
Figure 5. Applicability of cationic and anionic dendrimer-modified cationic and anionic clays as a potential binding site provider for CO2 and NH3 gas adsorption [27] copyright 2017, Elsevier.
- References;
#Old references may be replaced with recent references.
Response: Thank you for your comment. There are no old references. This paper includes references from 2013 to 2023 (80%) as part of the chronological references. Unlike other references, 2008 is the oldest that is part of the review. So there is no need to replace references.
- #The list of references is not consistent; format it in accordance with the journal guidelines.
Response: Thanks a lot for the reviewer’s comment. The author revised the manuscript based on the comments of the reviewer.
Action:
3.Pollution Causes 40 Percent Of Deaths Worldwide, Study Finds. Available online: https://www.sciencedaily.com/releases/2007/08/070813162438.htm (Accessed on 29 may 2023).
- Kasha Patel, Pollution caused 1 in 6 deaths globally for five years, study says Available online: https://www.washingtonpost.com/climate-environment/2022/05/17/pollution-caused-1-6-deaths-globally-five-straight-years-study-says/ (Accessed on 15 April, 2023).
- Mineral Classification. Available online: https://sternberg.fhsu.edu/research-collections/geology/mineral-classification-page.html (Accessed on 19 November 2022).
- Mineralogy, Available online: http://condor.wesleyan.edu/ethomas/ees123/sheet04.htm (Accessed on 12 December 2022).
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article raises a very important issue related to the prevention of pollution.
Theoretical introduction well describing the discussed issue. The overview of many works included in the table is very extensive.
Doesn't the mere mining of clay, adding additives to it, modifying it cause a lot of pollution? And if so, to what extent?
Author Response
The article raises a very important issue related to the prevention of pollution.
Theoretical introduction well describing the discussed issue. The overview of many works included in the table is very extensive.
Doesn't the mere mining of clay, adding additives to it, modifying it cause a lot of pollution? And if so, to what extent?
Response- Firstly, we greatly appreciate the reviewer find our manuscript is interesting and publishable in Applied Science.
Thank you for your question. Let me draw your attention to the first and most important aspect of the properties of clay. Original clay has less swelling, less adsorption and binding sites for pollutants. The modifier plays an important role as it is also not bound to clay platelets but is adsorbed due to the cation exchange property of the clay. This modifier added values ​​such as increase or decrease in surface charge, surface area, polarity, d-spacing, and new connections between clay geometries for pollutant exchange or adsorption. Data gleaned from most releases suggests that the modification adds value to the sound higher than that of the original.
Now the question arises about the selectivity of the modifier, whether the modifier is basic molecules or whether they follow the principles of green chemistry, e.g. as a natural or recycled material, the usefulness of this modifier for clay modifications is higher. Most often, modified clay can be reused or regenerated and applied for 5-8 cycles. Now when you consider the cost, this is really a very important result that can also offset the cost of modifications and the impact on the environment. Considering the 3E advantages, energy, economy and environment, there are no problems in the development of organoclay for pollution research; the only concern is the type of modifier
Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors
Based on my knowledge, this paper has been well written and supported by a detailed explanation. I state that this paper is very good and has a high potential to be cited in future studies. I recommend that the author describe the methodology employed during the review process. In addition, it is imperative to augment the annual publication output about the advancement of clay as a green chemistry medium. I propose including a spatial distribution visualization to depict the research site on clay, thereby enhancing the reader's comprehension and interpretation of the conveyed message.
Best regards
Author Response
Dear authors
Based on my knowledge, this paper has been well written and supported by a detailed explanation. I state that this paper is very good and has a high potential to be cited in future studies. I recommend that the author describe the methodology employed during the review process. In addition, it is imperative to augment the annual publication output about the advancement of clay as a green chemistry medium. I propose including a spatial distribution visualization to depict the research site on clay, thereby enhancing the reader's comprehension and interpretation of the conveyed message.
Best regards
Response- First, we are very pleased that the reviewer thinks our manuscript is interesting and worthy of publication in Applied Science. Your kind comment is really grateful for our research team. In fact, this review has the potential to get a high number of citations as it provides all the basic details from theory to application. We have added the trend of research of clay for pollution application in Figure 1.
We have added the trend of exploring clay for pollution applications in Figure 1. There is no specific methodology, we used the keywords “application/role of clay/organic clay in pollution control or reduction” for the search and then listed the data in tabular form with chronological order and we avoided the redundancy modifier to retain the meaning of the modifier.
Regarding modification sites and visualization, we have published a number of articles detailing molecular images at adsorption and binding sites. However, we have attempted to summarize this work to illustrate the pollutant removal application to give the reader an understanding of the importance of binding sites.
Figure 1 shows the number of publications (research articles) on the application/role of clay/organic clays in pollution control or pollution abatement in the last decade (from 2013 to August 2023). It can be seen that clay-based research for environmental applications is continuously growing exponentially, showing that the applicability of clay research has become a current hot topic. In addition, researchers from all over the world participate in this research area. Even in times of COVID-19, we can observe that the concern in this area is also increasing, which shows the great importance of this topic in recent times.
Figure 1. The number of publications (research articles) on the application/role of clay/organic clay in the control or mitigation of pollutant ions in the environment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have now addressed all the comments and suggestions given by me. I have reviewed all the changes in the text and these changes are in line with my suggestions. My decision is Accept the manuscript in its present form.
