Effective Heavy Metals Removal from Water Using Nanomaterials: A Review

Round 1

Reviewer 1 Report

1. Line 19: “The discharge of toxic heavy metals”?, enlist suitable examples of toxic heavy metals.
2. Line 21-Line 24: “were offered using the nanotechnology and nanomaterials …....various nanoadsorbent materials.. ” Examples of the used materials and techniques should be clarified in the abstract…
3. Line 26: “Also, the effect of various experimental factors…” I suggest adding “physicochemical factors”
4. Line 51: “atmospheric accumalation,” correct by “atmospheric accumulation,”
5. Line 68:…“… it has no limitations as reported for other techniques.. ” what type of limitations? Give examples…
6. Line 73:. ….. the abbreviation NPs? Should be indicated after the full word “Nanoparticules“
7. Line 92: ….“nanomaterials achieved”….. correct  “was achieved”
8. Line 97: add a sentence clarifying the interesting properties of carbon nanomaterials
9. Line 99: I suggest adding some chemical characteristics of grapheme
10. Line 107: add the number [34] of the reference “Zeng et al.”
11. Line 109 and Line 113:  add the word “adsorption” capacity. Also, Line 253, Go through the manuscript and correct adsorption capacity.
12. Line 118: correct   …“was designated” by several researchers..
13. Line 142: “138.9 mg.g^-1” standardize the writing of units (138.9 mg/g). The same remarks in page 5 line 199 (90.75 mg.g^-1), in page 10, line 455 (251.90 mg.g^-1), in page 10, line 465 (146.42 mg.g^-1), in page 11, line 510 (75.78 mg.g^-1)
14. Line 147: authors reported the use of polymers. Give examples of these polymers
15. Line 157: add the number [44] of the reference  “Abou-Zeid et al”
16. Line 197: change the word “workers” by “researchers”
17. Line 204: add the number [55] of the reference “ Sohail et al”
18. Line 212: authors reported the use of chitosan. What is the origin of chitosan?
19. Line 248: The application of non-magnetic nanomaterials in water treatment is lower than magnetic nanomaterials. Explain lower treatment?
20. Line 308 : Here the abbreviation EDTA was used for the first time, mention the full name.
21. Line 345: add the number [78] of the reference (Li et al.)
22. Line 411: correct “magnetic”
23. Line 508: add the number [116] of the reference (Dehghani et al)
24. Line 523: add the number [116] of the reference (Kumari et al.)
25. Line 563: corrected the sentence “of toxic metalsé This indicates)
26. Throughout the manuscript and the table, subscripts/superscripts need attention.
27. In the conclusions section, future recommendations should be added. Generally. All experiments are conducted at lab-scale for toxic metals in aqueous solutions and researches are needed to evaluate the process efficiency at pilot and large scale using real wastewater. This statement should be added in the conclusion.

Author Response

1. Line 19: “The discharge of toxic heavy metals”?, enlist suitable examples of toxic heavy metals.

Examples of heavy metals were added (Page 1, Line 19).

2. Line 21-Line 24: “were offered using the nanotechnology and nanomaterials …....various nanoadsorbent materials.. ” Examples of the used materials and techniques should be clarified in the abstract…

 

Examples of the used materials were added (Page 1, Line 24).

 

3. Line 26: “Also, the effect of various experimental factors…” I suggest adding “physicochemical factors”

 

The statement “physicochemical factors”  was added  (Page 1, Line 29).

4. Line 51: “atmospheric accumalation,” correct by “atmospheric accumulation,”

 

The word was corrected (Page 2, Line 53)

 

5. Line 68:…“… it has no limitations as reported for other techniques.. ” what type of limitations? Give examples

Statements concerning the limitation of the other techniques were added (Page 2, Line 72)

 

6. Line 73:. ….. the abbreviation NPs? Should be indicated after the full word “Nanoparticules“

The abbreviation was written after the full word (Page 2, Line 81)

 

7. Line 92: ….“nanomaterials achieved”….. correct “was achieved”

The word was corrected (Page 3 , Line 105)

 

8. Line 97: add a sentence clarifying the interesting properties of carbon nanomaterials

Statements concerning the properties of carbon nanomaterials were added (Page 3, Line 111-113)

 

9. Line 99: I suggest adding some chemical characteristics of grapheme

 

Statements concerning the chemical characteristics of grapheme were added (Page 3, Line 116-118)

 

10. Line 107: add the number [34] of the reference “Zeng et al.”

The reference number was added (Page 3, Line 125)

11. Line 109 and Line 113: add the word “adsorption” capacity. Also, Line 253, Go through the manuscript and correct adsorption capacity.

The word “adsorption” was added (Page 3, Line 127)

 

12. Line 118: correct …“was designated” by several researchers..

The word was corrected (Page 3, Line 136)

 

13. Line 142: “138.9 mg.g-1” standardize the writing of units (138.9 mg/g). The same remarks in page 5 line 199 (90.75 mg.g-1), in page 10, line 455 (251.90 mg.g-1), in page 10, line 465 (146.42 mg.g-1), in page 11, line 510 (75.78 mg.g-1)

All the units were written in mg/g

 

14. Line 147: authors reported the use of polymers. Give examples of these polymers

Examples were added (Page 4, Line 167)

 

15. Line 157: add the number [44] of the reference “Abou-Zeid et al”

The reference number was added (Page 4, Line 176)

 

16. Line 197: change the word “workers” by “researchers”

The word “workers” Was changed by “researchers” (Page 5, Line 216)

 

17. Line 204: add the number [55] of the reference “ Sohail et al”

The reference number was added (Page 5, Line 223)

 

18. Line 212: authors reported the use of chitosan. What is the origin of chitosan?

Statements concerning chitosan were added (Page 5, Line 231-234)

 

19. Line 248: The application of non-magnetic nanomaterials for water treatment is lower than magnetic nanomaterials. Explain lower treatment?

“The application” was replaced by “the efficiency” (Page 6, Line 269)

 

20. Line 308 : Here the abbreviation EDTA was used for the first time, mention the full name.

For the first time, the full name  of EDTA was added (Page 8, Line 360)

 

21. Line 345: add the number [78] of the reference (Li et al.)

The reference number was added

 

22. Line 411: correct “magnetic”

The word was corrected (Page 9, Line 442)

 

23. Line 508: add the number [116] of the reference (Dehghani et al)

The reference number was added

 

24. Line 523: add the number [116] of the reference (Kumari et al.)

The reference number was added

 

25. Line 563: corrected the sentence “of toxic metalsé This indicates)

The word was corrected (Page 15, Line 593)

 

26. Throughout the manuscript and the table, subscripts/superscripts need attention.

All the manuscript was revised and errors were corrected

 

27. In the conclusions section, future recommendations should be added. Generally. All experiments are conducted at lab-scale for toxic metals in aqueous solutions and researches are needed to evaluate the process efficiency at pilot and large scale using real wastewater. This statement should be added in the conclusion.

Statements were added (Page 18, Line 741)

 

Reviewer 2 Report

The paper provides a review on the nanomaterials for heavy metal removal, it can be published after addressing the following issues:

 

1. In terms of the pH effect on the adsorption, not all sorbents perform well at moderate pH. Exceptions like chromium should be taken into consideration. The adsorption of chromium prefers lower pH due to the pH dependent oxidation state.
2. Some general introduction to fundamental properties of nanomaterials and their impact on heavy metal removal should be addressed, for example, the particle size and morphology.
3. Page 2: It would be better to clarify how these sorbents are classified into different categories before move into the specific category. The classification basis should be clearly stated.
4. Page 2 line 68: The limitation of other techniques should be briefly introduced and the evidence of why adsorption is the most effective should be provided to prove the announcement.
5. Page 7: In 4.2 Inorganic Functionalized Magnetic Nanoparticles section, the examples including EDTA, dithiocarbamate groups and glutathione are organic species, so they are not suitable for this section which concentrates on the inorganic functionalization.
6. Page 6 line 258: The ‘hydrated ion radius’, instead of the ‘ion radius’ is more accurate for this example. Ion radius is ambiguous in this context since the ion radius of Pb is larger than Mn, Zn, Cu obviously. However, the hydrated ion radius of Pb is the smallest, and it is the hydrated ion radius that affects the electrostatic interaction between the adsorption sites and metal ions.
7. The content of part 4 ‘Nanoadsorbent Separation from Experiment Medium’ is not consistent with the title. The content focus on the desorption and recyclability of adsorbent, while the title emphasizes the how to separate adsorbent from medium, like centrifuge from my aspect.
8. Silica is not metal or metal oxides, so assigning 5.1. Silica Based Nanomaterials section in the 2.5 Metal Oxides and Metal Based Nanomaterials is inappropriate. It would better to combine 2.5. Metal Oxides and Metal Based Nanomaterials, 2.4 Magnetic Nanomaterials and 2.2 Zeolite Nanoparticles into a new section “inorganic nanomaterials”.

 

Minor comments:

1. Page 16 line 705: There is a typo ‘reoval’.

 

2. Page 4 line 146: The title ‘Polymer Based Nanomaterials’ should be 2.3 instead of 2.2. The subtitles under this part are assigned with wrong number as well.

 

3. It would be better to rearrange Table.1 according to the target ions or the classification of sorbent, then readers can retrieve the information more conveniently.

Author Response

 

1. In terms of the pH effect on the adsorption, not all sorbents perform well at moderate pH. Exceptions like chromium should be taken into consideration. The adsorption of chromium prefers lower pH due to the pH dependent oxidation state.

 

The authors thank the reviewer for this comment. Statements concerning chromium  was added in the section" 3.6. pH Effect". (Page 16, Line 672-675)

 

 

2. Some general introduction to fundamental properties of nanomaterials and their impact on heavy metal removal should be addressed, for example, the particle size and morphology.

 

Statement "concerning the importance of the nanomaterial properties for heavy metal removal "were added in the text (Page 2, Line 72-77)

 

 

3. Page 2: It would be better to clarify how these sorbents are classified into different categories before move into the specific category. The classification basis should be clearly stated.

 

Generally, these nanomaterials are classified based on their origins, their shape, their size, and chemical properties. In this review, we can not adopt this classification because we have listed and discussed many various prepared nonmaterial fabricated using mixtures of various materials (organic, inorganic, natural synthetic...). Consequently, the nanomaterials listed in this review are arranged based on their basic material used as absorbent independently of their organic or inorganic nature, and also based on their importance for heavy metal removal.   To clarify this, a statement was added (Page 3, Line 105-107)

 

4. Page 2 line 68: The limitation of other techniques should be briefly introduced and the evidence of why adsorption is the most effective should be provided to prove the announcement.

 

Statements were added in the text (Page 2, Line 68-77 )

 

5. Page 7: In 2 Inorganic Functionalized Magnetic Nanoparticlessection, the examples including EDTA, dithiocarbamate groups and glutathione are organic species, so they are not suitable for this section which concentrates on the inorganic functionalization.

 

This section was arranged. The unsuitable materials for this section were replaced (Page 7, line 329- 336)  and introduced in right section (Page 8, line 371-382)

 

 

6. Page 6 line 258: The ‘hydrated ion radius’, instead of the ‘ion radius’ is more accurate for this example. Ion radius is ambiguous in this context since the ion radius of Pb is larger than Mn, Zn, Cu obviously. However, the hydrated ion radius of Pb is the smallest, and it is the hydrated ion radius that affects the electrostatic interaction between the adsorption sites and metal ions.

 

The authors thank the reviewer for this comment. " ion radius " was changed by " hydrated ion radius "

 

 

7. The content of part 4 ‘Nanoadsorbent Separation from Experiment Medium’ is not consistent with the title. The content focus on the desorption and recyclability of adsorbent, while the title emphasizes the how to separate adsorbent from medium, like centrifuge from my aspect.

 

"Nanoadsorbent Separation from Experimental Medium" Was Changed by "desorption and recyclability of the nanoadsorbent"

 

8. Silica is not metal or metal oxides, so assigning 1. Silica Based Nanomaterialssection in the 2.5 Metal Oxides and Metal Based Nanomaterials is inappropriate. It would better to combine 2.5. Metal Oxides and Metal Based Nanomaterials, 2.4 Magnetic Nanomaterialsand 2.2 Zeolite Nanoparticles into a new section “inorganic nanomaterials”.

 "Alumina Based Nanomaterials" sub-section was integrated in the section "Metal Oxides and Metal Based Nanomaterials". (Page 11, Line 508)

"Silica Based Nanomaterials" was considered as a separate section. However, we can not combine the sections 2.5; 2.4 and 2.2 because the Magnetic Nanomaterials contain both organic and inorganic materials and also as indicated above, the natomaterials listed in this review are arranged based on their basic material used as absorbent independently of their organic or inorganic nature, and aslo based on their importance for heavy metal removal.

 

Minor comments:

1. Page 16 line 705: There is a typo ‘reoval’.

 The word was corrected

1. Page 4 line 146: The title ‘Polymer Based Nanomaterials’ should be 2.3 instead of 2.2. The subtitles under this part are assigned with wrong number as well.

 The wrong number for the section was corrected

1. It would be better to rearrange Table.1 according to the target ions or the classification of sorbent, then readers can retrieve the information more conveniently.

 

Table was arranged according to the target ions

Reviewer 3 Report

This review describes the adsorption of metals on nanomaterials is well written generally.

The following points were should be considered.

1. Section 3. Factors affecting adsorption process : General information on this topic is difficult to describe. Authors statement is not specilalized on the adsorption of metals on the nanomaterials. Sextion 3 should be omitted. 
2. Authors used term "eco-friendly". The meanings of this term should be defined.

Author Response

Comments and Suggestions for Authors

 

• Section 3. Factors affecting adsorption process: General information on this topic is difficult to describe. Authors statement is not specilalized on the adsorption of metals on the nanomaterials. Sextion 3 should be omitted.

I agree with the reviewer, the factors affecting adsorption process is difficult to describe. But, we think it is very important in this review to raise this question and all the discussed information is based on experimental data. This section is closely related to the data reported in Table 1 which makes its elimination difficult and disruptive the general plan of the paper.

 

• Authors used term "eco-friendly". The meanings of this term should be defined

The term "eco-friendly" means safe and non toxic for the environment. The word "eco-friendly" was replaced by environmentally-safe in the manuscript.

 

Round 2

Reviewer 2 Report

I think the revised version can be accepted.