Eco-Friendly Gelatin–Cerium–Copper Sulphide Nanoparticles for Enhanced Sunlight Photocatalytic Activity

Round 1

Reviewer 1 Report

I consider that the present paper deals with a topic of interest for the reader of the journal, the use of solar light for the degradation of organic dyes. However, this paper cannot be accepted in its present form for the following reasons:

 

In the abstract and along the MS the authors claim that they are preparing nanoparticles. If so, scanning electron microscopy is not the most suitable technique for their characterization. Moreover, x-ray diffraction and EDS are not the most suitable techniques for their characterization either. A more precise composition characterisation of the NPs is required (including thermogravimetric analysis, ICP, XPS and TEM).

 

In Line 139 and in Figure 5 I have a great concern about reproducibility. Can the authors comment how many times have the tests been reproduced and which are the error limits?

 

In-line 159 it is difficult for me to understand what do you mean with the cerium 4+ 111 plane. X-ray diffraction provides information about crystalline structures but not about ions. ¿¿??

 

A very important concern is related to the other catalysts tested that are highlighted in lines 185 and 186. There is not any kind of information/characterization about the properties of those catalysts, how they were prepared, their brand, their mean crystal sizes or some properties that let a reasonable comparison.

 

Also, in some cases the activity differences are not so important… see figures 5 series a and d. Error bars and reproducibility are very important!

 

Why the study presented in line 264 was not performed with the other photocatalysts?

 

In section 4 The mechanism seems to be proposed but not confirmed by any experiment.

 

The conclusions section is very vague. Some conclusions are incorrect as well. It is not possible to refer to dopant gelatine cerium. Which is the dopant? Both? Has doping been proved ?

 

Large part of the study has no relevant conclusions and the mechanism is supposed to be a conclusion (included in section 4.1) despite no experimental evidence was shown.

 

 In the abstracts, the sentence “deterioration process has been suggested” is not clear.

 

English should be revised all along the manuscript since there are many errors, for example in lines 28, 53, 65, 88-89, 102, 108, 145, and some others.

 

The sentence in lines 57-58 is not correct what does “Cerium copper sulfide (Ce-CuS) is an inorganic component that is used to create nanocomposite materials” mean? Inorganic component?

 

In line 62 and 63 it is not clear what is being doped with cerium.

 

In line 94 when the authors claim about adjusting pH of the solution it is not clear to which pH it is adjusted.

 

In lines 109 and 110 It is not explained how the gelatine content has been determined.

 

The sentences in lines 167-168 are not clear. Also, I would remark that TEM would be the most suitable for NPs characterisation.

 

 

 

Author Response

I consider that the present paper deals with a topic of interest for the reader of the journal, the use of solar light for the degradation of organic dyes. However, this paper cannot be accepted in its present form for the following reasons:

• Dear Reviewer, thank you for your useful comments. As suggested by you, we have revised the paper, and resubmitting it.

In the abstract and along the MS the authors claim that they are preparing nanoparticles. If so, scanning electron microscopy is not the most suitable technique for their characterization. Moreover, x-ray diffraction and EDS are not the most suitable techniques for their characterization either. A more precise composition characterisation of the NPs is required (including thermogravimetric analysis, ICP, XPS and TEM).

• As suggested XPS and HR-TEM are included. For our future work, we will include Thermogravimetric analysis.

In Line 139 and in Figure 5 I have a great concern about reproducibility. Can the authors comment how many times have the tests been reproduced and which are the error limits?

• The experiments (Figure 7) were carried out in triplicate. Now, the error bar (±4%) is provided in the figure. (Figure 5 converted into Figure 7)

 In-line 159 it is difficult for me to understand what do you mean with the cerium 4+ 111 plane. X-ray diffraction provides information about crystalline structures but not about ions. ¿¿??

• I agree with the reviewer. The representation of Ce⁴⁺ ions are nothing but CeO₂, and confirmed by using reference XRD (Ref No: 66).

A very important concern is related to the other catalysts tested that are highlighted in lines 185 and 186. There is not any kind of information/characterization about the properties of those catalysts, how they were prepared, their brand, their mean crystal sizes or some properties that let a reasonable comparison.

• We have used the different catalysts (CuS, ZnO, TiO₂, CuO, and ZnS) for comparison purpose only. Among those, except CuS, the other materials were obtained by different companies (commercially available, the details are given in section 2.1). The synthesis procedure for CuS was given in section 2.2, the characterization of the CuS was also discussed in the manuscript along with Ge-Ce-CuS.

Also, in some cases the activity differences are not so important… see figures 5 series a and d. Error bars and reproducibility are very important!

• As per your previous comments, the error bar is provided in Figure. 7. (Figure 5 converted to Figure 7)

 Why the study presented in line 264 was not performed with the other photocatalysts?

• In our research work we have reported COD values for our prepared nanocatalyst (Ge-Ce-CuS) only, we cannot measure other catalysts.

In section 4 The mechanism seems to be proposed but not confirmed by any experiment.

• As suggested by you, in our revised paper we have included the references (Ref No: 87,88)

The conclusions section is very vague. Some conclusions are incorrect as well. It is not possible to refer to dopant gelatine cerium. Which is the dopant? Both? Has doping been proved ?

• As suggested by you, the conclusion section have revised.

Large part of the study has no relevant conclusions and the mechanism is supposed to be a conclusion (included in section 4.1) despite no experimental evidence was shown.

• Degradation process is confirmed by chemical oxygen demand (COD) values. The values are given in Table 2. The COD removal values (71.4%) indicates the mineralization of dye. (section 4.1 converted to section 4.3).

 In the abstracts, the sentence “deterioration process has been suggested” is not clear.

• As suggested, abstract part have revised.

English should be revised all along the manuscript since there are many errors, for example in lines 28, 53, 65, 88-89, 102, 108, 145, and some others.

• The English corrections have been made throughout the revised manuscript.

The sentence in lines 57-58 is not correct what does “Cerium copper sulfide (Ce-CuS) is an inorganic component that is used to create nanocomposite materials” mean? Inorganic component?

• We have removed the line and modified it.

In line 62 and 63 it is not clear what is being doped with cerium.

• The sentence has been corrected as “Zhang and Liu suggest that cerium doping with TiO₂ may well prohibit the recombination of the photo-generated electron-hole pairs”.

In line 94 when the authors claim about adjusting pH of the solution it is not clear to which pH it is adjusted.

• The MGO dye solution with catalyst at different pH are prepared and dye degradation percentages are analysed.

In lines 109 and 110 It is not explained how the gelatine content has been determined.

• Thank you for pointing out this mistake. It is not 2% of gelatine (typographical error) Gelatin was used as a template. The dopant is Cerium (Ce). In our modified paper the synthesis procedure is given in pictorial form (Scheme 1).

.

The sentences in lines 167-168 are not clear. Also, I would remark that TEM would be the most suitable for NPs characterisation.

• We have modified the above lines. We also included HR-TEM images in our modified manuscript.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript looks interesting and could be a good addition for the readers of the Sustainability. 

I have some comments which could improve the manuscript.

1) What deterioration process was suggested? Elaborate in the conclusion of abstract.

2) Line 86: Write full name with address of the laboratory.

3) Line spacing is different in the manuscript. Use consistent formatting.

4) Provide reference for  Gelatin-Cerium loaded CuS preparation.

5) Line 122: What was the molar ration of dye solution? Write clearly.

6) What was the dose of photo catalysts used in this study?

7) Line 206: Correct units and describe how this dose was selected? Was there any preliminary study?

8) Line 224-225: Elaborate how much decrease at lower pH compared to higher pH 9

Author Response

Reviewer Comments:

1). What deterioration process was suggested? Elaborate in the conclusion of abstract.

• Malachite Green Oxalate (MGO) dye (it act as a water pollutant) deterioration process was studied.
• It is already given (line 326-328) in conclusion part. Under optimal reaction conditions, the Ge-Ce-CuS nanocatalyst has a high solar photocatalytic activity for the degradation (deterioration) of MGO dye.
• As suggested, abstract and conclusion part have revised

2) Line 86: Write full name with address of the laboratory.

• As suggested by you the full name and the address of the lab. Chemical manufacture address is given [Oxford lab fine chemical manufacturer, in Maharashtra].

      3) Line spacing is different in the manuscript. Use consistent formatting.

• As suggested the manuscript has been modified by using same line spacing.

     4) Provide reference for Gelatin-Cerium loaded CuS preparation.

• We have referred the journal for preparation of the catalyst (CuS, Ce-CuS) by using hydrothermal technique. Preparation of Co-doped CuS nanocrystals by hydrothermal method reference is already given (line 71, Ref – 57)
• There is no reference for the preparation of Gelatin Cerium CuS. So we have not provide the reference for Ge-Ce-CuS preparation.

     5) Line 122: What was the molar ration of dye solution? Write clearly.

• The dye solution (MGO dye) of desired molar ratio (1x10^-4 M, 2x10^-4 M, 3x10^-4 M, 4x10^-4 M, 5x10^-4 M) was freshly prepared from the stock solution (Higher concentration 1x10^-3 M) of the dye.
• As suggested by you, it is included in the revised manuscript.

     6) What was the dose of photo catalysts used in this study?

• The optimum catalyst weight for this photocatalytic degradation is 1.5 g/L. So 1.5 g L^-1 was the dose of photocatalyst (Ge-Ce-CuS) used in this study.

      7) Line 206: Correct units and describe how this dose was selected? Was there any preliminary study?

• Yes, the effect of different weight catalyst loading was studied using 0.5 g L^-1 to 2.5 g L^-1 of Ge-Ce-CuS catalyst. From this we have fixed the optimum concentration (1.5 g L^-1) of the catalyst for getting maximum degradation.
• This study is already given in line 201-216
• We have corrected the unit also 0.5 to 2.5 g/L^-1 changed to 0.5 to 2.5 g L^-1.

        8) Line 224-225: Elaborate how much decrease at lower pH compared to higher pH 9.

                  We have already given the elaborate degradation rate (lines 223-224) at lower pH 3, 5, 7.

• pH = 3 (43.0 % of degradation)
• pH = 5 (66.8 % of degradation)
• pH = 7 (71.7 % of degradation)
• pH = 9 (88.6 % of degradation)
• pH = 11 (60.1 % of degradation)

Open Review

               Extensive editing of English language and style required.

• The English corrections have been made throughout the revised manuscript

                 

Author Response File: Author Response.pdf

Reviewer 3 Report

This contribution entitled “Eco-friendly Gelatin–Cerium–Copper Sulfide nano-particles for enhanced sunlight photocatalytic activity” by Shanthi et al submitted to Sustainability/MDPI presents the physiochemical properties, toxicity, and photocatalytic activity of CeO2 NPs as an effective catalyst to deteriorate the dye under the sunlight. The authors have shown that light-activated CeO₂ nanocatalysts synthesized hydrothermally revealed superior photocatalytic performance on the degradation of MGO pollutants with an excellent removal rate. Ceria is well-known for its radical scavenging activity due to the redox switch of the Ce ions between +3 and +4 oxidation states, which makes this oxide particularly attractive for bioapplications/wastewater etc. The photocatalytic degradation of dyes, present in water using semiconductor materials depends on several parameters phase composition, crystallinity, morphology, and surface area of catalyst, which are well discussed. The area of research is significant and addresses the environmental problem. The manuscript itself is written OK but the main concern of this paper and the areas that require clarification are given below.

·         The most common way used to enhance the photocatalytic performance of semiconductors is the development of heterojunction structures, which can be briefly commented. A few of the representative heterojunctions such as copper sulfide/metal oxide, copper sulfide/metal sulfide, and copper sulfide/carbon-based materials which have been reported can be compared.

·         In the introduction lines 58 – 60; Cerium dopant has also been used in energy storage applications while utilizing the redox couple effectively (doi.org/10.1016/j.jallcom.2008.12.143). Please include.

·         Researchers have studied the light-assisted photodegradation of many organic dyes, such as Rhodamine (RhB), which need to be included while referring to the mineralization studies reported in the literature (DOI: 10.1002/slct.201600867).

·         Is the enhanced photocatalytic activity of the Ce hybrid catalyst mainly due to its high surface area or stronger electrostatic attraction between the Gelatin molecule and Ce NPs?

·         The planes/ (h k l) indices are missing in Figure 2b.

·         The authors are encouraged to use the scale bar within the SEM images in Figure 3.

·         Have you seen the elements related to Gelatine in the EDS composition?

·         Section 3.3 lines 184 – 186: the polymorphic phases of TiO2 can be referred to in the literature (doi.org/10.1007/s10800-005-9112-9).

·         Section 3.3; line 190 the data 3x10-4 is unclear, where does this come from?

·         Section 3.6 the last two lines need to be discussed effectively.

·         Section 3.7; line 264 what is “COD”?

·         Tables 1 and 2 requires a caption. (Similar to that of the figure caption)

·         The superoxide radicals and their equations shown in lines 301 – 302 can be referenced.

 

 

 

Author Response

Reviewer – 3

Dear Reviewer,

 We would like to thank for your valuable comments. We introduced several changes in the text, as suggested by you.

1). The most common way used to enhance the photocatalytic performance of semiconductors is the development of heterojunction structures, which can be briefly commented. A few of the representative heterojunctions such as copper sulfide/metal oxide, copper sulfide/metal sulfide, and copper sulfide/carbon-based materials which have been reported can be compared.

• We have referred so many heterojunction nanocatalyst development procedures, and some representative reference for nanocomposite CuS/metal ion is already given (line 71, Ref.57).
• As suggested, the efficiency of Ge-Ce-CuS is compared with other modified CuS based materials (Table 1)
• (comparison should be discussed in section 3.9 Stability of the catalyst and comparison with literature)

2). In the introduction lines 58 – 60; Cerium dopant has also been used in energy storage applications while utilizing the redox couple effectively (doi.org/10.1016/j.jallcom.2008.12.143). Please include.

• According to the reviewer - 2 instructions, we indexed some related papers. [doi.org/10.1016/j.jallcom.2008.12.143; Minakshi etal, J. of Alloys and compounds, 479 (2009) 87-90] and included in our revised manuscript – introduction section (Ref -no-32)

 3). Researchers have studied the light-assisted photodegradation of many organic dyes, such as Rhodamine (RhB), which need to be included while referring to the mineralization studies reported in the literature (DOI: 10.1002/slct.201600867).

• As suggested by you Rhodamine B dye (RhB), reference is included in our revised manuscript in introduction section (line 33, Ref – 6).
• [Ref – 6 :- Boral et al, chemistry select, 2016, 1, 4277-4285].

4). Is the enhanced photocatalytic activity of the Ce hybrid catalyst mainly due to its high surface area or stronger electrostatic attraction between the Gelatin molecule and Ce NPs?

• The enhanced photocatalytic activity of Ce- hybrid catalyst (Ge-Ce-CuS) is mainly due to its high surface area. It is confirmed by BET method.
• Ge-Ce-CuS nanocomposite have higher surface area (88.6 m² g^-1) than bare CuS (66.0 m² g^-1). So Ge-Ce-CuS have enhanced photocatalytic activity

5).The planes/ (h k l) indices are missing in Figure 2b.

• As suggested by you the (hkl) indices are included in Fig-2b.

6). The authors are encouraged to use the scale bar within the SEM images in Figure 3.

• The scale bar values for SEM images are given in our modified manuscript.

7). Have you seen the elements related to Gelatine in the EDS composition?

• The addition of gelatin (template) did not see in EDS composition. Since gelatin getting decomposed during calcinations, and did not observe in EDS.

 

8). Section 3.3 lines 184 – 186: the polymorphic phases of TiO2 can be referred to in the literature (doi.org/10.1007/s10800-005-9112-9).

• We have referred the TiO₂ paper and included in our revised manuscript introduction section (Ref- 19)
• [Minakshi et al, J. of applied electrochemistry 2006, 36, 599-602].

9). Section 3.3; line 190 the data 3x10-4 is unclear, where does this come from?

• In line 190, the data 3x10^-4 M, it is the optimum concentration of dye, which is undergoes the degradation by using the Ge-Ce-CuS catalyst.

10). Section 3.6 the last two lines need to be discussed effectively.

• As suggested by you, the last two lines (section 3.8) are modified and included in our revised manuscript. (Section 3.6 converted to 3.8).
• [The large amount of adsorbed dye is also have a competing effect on the adsorption of O₂ and OH^- onto the surface of the catalyst].

11). Section 3.7; line 264 what is “COD”?

• Section 4.0 (line 264) COD is called as Chemical Oxygen Demand analysis. From this method mineralization of dye content is confirmed.
• We have modified the heading. (Section 3.8 converted to 4.0)

 12). Tables 1 and 2 requires a caption. (Similar to that of the figure caption).

• We have included the captions in Table 2 and 3. In our revised paper.
• Table – 2: COD measurements. (Table 1 & 2 converted to Table 2 & 3).
• [MGO] = 3´10^–4 M, catalyst suspended = 1.5 g L^–1, pH = 9, airflow rate = 8.1 mL s^–1, I_solar = 1250´100 ± 100 lux.

 

• Table – III : Antibacterial zone of growth inhibition capacities owing the prepared bare CuS and Ge-Ce-CuS nanocomposite with the different bacterial strain

       13). The superoxide radicals and their equations shown in lines 301 – 302 can be referenced.

• We have so many references related to superoxide radicals (our research groups publications).
• In this modified paper we have included one reference manuscript. (Ref No: 88).

Reviewer 3 (open review)

English language and style:- Moderate English changes required.

• We have checked the whole manuscript carefully and tried to avoid any grammer and spelling mistakes.
• In addition we have asked several experts who are skilled authors of English language papers to check the English. We believe that the language is now acceptable for publication.

 

 

 

                   

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Accept

Reviewer 3 Report

I have read the author's responses and revised part of the manuscript. The authors have fairly addressed my queries concisely. The revised version is suitable for publication.