Magnetic and Hydrophobic Composite Polyurethane Sponge for Oil–Water Separation

Round 1

Reviewer 1 Report

The manuscript “Magnetic and Hydrophobic Composite Polyurethane Sponge for Oil-Water Separation” by Jiang et al. describes the synthesis and characterization of a composite material between iron oxide nanoparticles, stearic acid and poly urethane. The material is analyzed with infrared spectroscopy, with scanning electron microscopy and towards its adsorption capacity with a balance.

The authors introduce their topic and discussed their findings very well and I really enjoyed reading the manuscript.

However, there are some points, which should be addressed to even improve a well-written manuscript:

In the introduction, you should state more clearly, why you want/need to add magnetic nanoparticles to a sponge? What is the benefit? Add two sentences to clarify, why you put magnetic particles to your sponge.

 

There is an inconsistency with adsorption and absorption throughout the text. I think you should use adsorption in the whole manuscript.

 

You use the term Fe3O4, but do not really investigate the structure of your iron oxide nanoparticles. I would recommend using iron oxide nanoparticles (IONs) since it is quite difficult to differentiate between the phases Fe3O4 and γ-Fe2O3. However, your IR spectrum indicates mainly Fe3O4.

 

In the IR spectra you should use another unit for the y-axis since it is not the absolute percentage but the respective percentages of transmittance for each sample.

 

There are a few typos and the numbers and units are not always separated.

 

Major issues:

The time of the adsorption experiments is missing in the experimental details.

 

There is no magnetic measurement of either the particles or the final sponge. Can you do a magnetometry measurement in order to analyze the saturation magnetization?

Author Response

Thanks for your advice. I have revised the introduction of my manuscript. I used ‘adsorption’in the whole manuscript. Our FTIR spectra data of Fe3O4 nanoparticles is consist with that of reference, so we can say with certainty that the nanoparticle is Fe3O4. In addition, we can not find an appropriate unit for the y-axis of FTIR spectra. According to other references, the unit for the y-axis of FTIR spectra is percentage of transmittance. As for the major issues, we mainly investigated the oil adsorption capacity and reusability instead of the time of the adsorption experiments. Finally, as for the magnetic measurement, on the one hand, we tested the magnetism of Fe3O4 nanoparticles and composite sponge by magnet, which indicate that the Fe3O4 nanoparticles and composite sponge have excellent magnetism; on the other hand, affected by the Wuhan SARS-CoV virus epidemic, martial law was implemented throughout China and schools and enterprises were temporarily suspended, so we can not do a magnetometry measurement.

Author Response File: Author Response.docx

Reviewer 2 Report

After carefully, reviewing the manuscript titled “Magnetic and Hydrophobic Composite Polyurethane sponge for oil-water separation” it is advised to be accepted for published as is. In recent times, the oil-water separation has become very important hence has gained interest of the scientific community to find ways to clean water from the oil through various research and development advancement. On the similar lines the study presented by authors for the development of the composite polyurethane sponge here is of key importance. Study like the ones presented by author in this work add value to the scientific community and could be helpful for the general reference for the future work.  In general, the manuscript is sound with scientific quality.

Author Response

Response to Reviewer 2
Thanks for your approval and advice. I have made improvements to my manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper "Magnetic and Hydrophobic Composite Polyurethane Sponge for Oil-Water Separation" presents an experimental study of application of a magnetic porous materials for wather - oil separation. h The experimental investigation and analysis are well done and scientifically sound but some parts of paper need correction. Thus the paper is suitable for publication in App Sci after the following points have been carefully addressed (minor revisions and comments):

Line 76: "Magnetic Fe3O4...". Index in a chemical formula is missing. Line 110-111. What type of wather was used for measutements? Purified or tap? Paragraph 3. Did you chceck chemical composition of NPs by EDX? Fig. 2 and 6. Add more visible scale bar.  Did you calculate the average size of NPs? Fig. 8 and 9. How did you calculate uncertainty? There is not clear what is sampe 1 and sample 2. What are the differences between samples?

Author Response

Response to Reviewer 3
Thanks for your approval and advice. I have revised the introduction of my manuscript. Purified water was used for measutements. Our FTIR spectra data of Fe3O4 nanoparticles is consist with that of reference, so we can say with certainty that the nanoparticle is Fe3O4. Besides, affected by the Wuhan SARS-CoV virus epidemic, martial law was implemented throughout China and schools and enterprises were temporarily suspended, so we can not chceck chemical composition of NPs by EDX. We have added more visible scale bar in Fig 2 and 6. We did not calculate the average size of NPs, we have revised it to ‘The diameter of magnetic Fe3O4 nanoparticles is between 10-20 nm, and the particle size reaches nanoscale’. We calculated the uncertainty by doing multiple sets of repeated experiments. The difference between sample 1 and sample 2 is whether the skeleton surface of the sponge is covered with stearic acid.

Author Response File: Author Response.docx

Reviewer 4 Report

This paper reports on “Magnetic and Hydrophobic Composite Polyurethane Sponge for Oil-Water Separation”. The author use a facile and cheap approach to disperse expanded graphite (EG), stearic acid and Fe3O4 magnetic nanoparticles on the skeleton surface of polyurethane (PU) sponge to prepare the magnetic and hydrophobic composite polyurethane sponge for oil-water separation.  The results reported in this paper could be valuable for publication. However, there are several points which have to be reconsidered for major revision as mentioned below.

As shown in Figure 8, no enhancement on adsorption capacity of the sponge by the addition of stearic acid, thus, what was the goal of coating the sponge with this acid because it increases the costs of the materials but not the efficiency? As shown in Figure 7, the authors removed the sponge after absorption experiments using tweezers, so, what was the goal of using Fe3O4 magnetic particles to the sponge? The authors should remove the sponge after absorption by a magnet instead. The reaction mechanism and the chemical bonging between EG, stearic acid and Fe3O4 and polyurethane sponge should be explained and discussed based on FTIR results and XPS characterizations, if it is possible. Sponge should be also characterized after the absorption and desorption experiments to check whether the EG, stearic acid and Fe3O4 compounds still attached to the sponge and not removed. Table 2 should be updated as there are several other works reported the use of polyurethane sponge for oil absorptions. It is also necessary to compare the absorption capacity of the composite sponge with the mere polyurethane sponge without adding EG, stearic acid and Fe3O4. Therefore, the authors should make an absorption experiments on the mere polyurethane sponge and the results of this experiment should be added to the manuscript. More details should be given in the experimental part about how the authors prepared their samples for TEM, SEM, FTIR and contact angle measurements. The measurements parameters should be also given. More details should be given absorption tests such as how they prepared the oil/water emulsion, with which concentrations, etc. The preparation of Fe3O4 by co-precipitation is not new and it has been already reported. Thus, the reference should be given. Also the authors wrote “the FeCl2 and the FeCl3 were quickly weighed in a ratio of 1:2 to a four-neck flat-bottomed flask”, which ratio here, mole ratio or weight ratio? This should be clarified. Furthermore, the sentence “A measuring cylinder was used to measure ammonia water and added to a four-neck flat-bottomed flask” does not give any important information. Instead, the amount/volume and concentration of ammonia used in the synthesis should be specified precisely. They also wrote that they dissolved 0g of stearic acid in 20 ml ethanol, which it does not have any physical meaning. Generally, the experimental part should be written more carefully to be clear to the readers. In page 4, it is written that “the magnetic Fe3O4 nanoparticles are firmly adsorbed on the glass wall by magnets” and “the magnetic composite sponge can be easily sucked up by magnets”. The two verbs “adsorbed” and “sucked up” are incorrect here and the verb “attracted” should be used instead. The author sometimes describe the separation of the oil from water by the sponge by “adsorption process” and sometime by “absorption process”. Since both processes are different, the authors should find the right definition and use through the entire manuscript. They also used adsorption to describe the FTIR bands, which is not correct and they should use absorption band instead. Moreover, the references for values of FTIR absorption bands should be given in page 5. Also, why the FTIR spectrum of original polyurethane sponge in Fig. 5-iv did not start from 500 cm-1 like for other materials? The scale bar in Fig 6-b2 is missing. The authors quoted some sentences without rephrasing or citation. For example, page 8 line 215-217 “their absorbance capacities slightly decreased due to the loss of absorption capability as a result of the small amount of oil remaining on the sponge” see “Ind. Eng. Chem. Res. 2015, 54, 3657−3663”. Page 8, line 191-192 “The absorbed oils can be readily removed from the sponge through a simple mechanical extrusion method due to its excellent mechanical flexibility” see “Journal of Colloid and Interface Science 497 (2017) 57–65”. The English of the manuscript should be strongly improved.

Author Response

Response to Reviewer 4
Thanks for your advice. I have revised my manuscript. Actually, the oil absorption capacity of sample 2 was slightly higher than that of sample 1. Coating the sponge with stearic acid could enhance the hydrophobicity of sponge, and the cost of stearic acid is very low. We tested the magnetism of Fe3O4 nanoparticles and composite sponge by magnet, which indicate that the Fe3O4 nanoparticles and composite sponge have excellent magnetism. So we removed the sponge after adsorption experiments using tweezers. Our FTIR spectra data of EG, stearic acid and polyurethane sponge and Fe3O4 nanoparticles is consist with those of reference. This means that the expanded graphite, Fe3O4 magnetic nanoparticles and stearic acid were dispersed successfully into the original PU sponge and there is no new bond created on magnetic composite sponge surface. Because this experiment is to physically disperse EG and other substances into the sponge by ultrasonic dispersion, and make them adhere to the skeleton surface of sponge, so we did not make XPS characterizations. We updated the table 2 with other works reported the use of polyurethane sponge for oil absorptions. In addition, affected by the Wuhan SARS-CoV virus epidemic, martial law was implemented throughout China and schools and enterprises have been suspended for a long time, so we can not make an absorption experiments on the mere polyurethane sponge. We added the oil adsorption capacity of mere polyurethane sponge from reference in table 2. The measurements parameters of TEM, SEM, FTIR and contact angle measurements were added in the revised manuscript. Oil adsorption of sponge experiments were performed in pure oil, so no water / oil emulsion was prepared. The references of the preparation of Fe3O4 by co-precipitation were added in the revised manuscript. FeCl2 and FeCl3 were quickly weighed in a mole ratio of 1: 2. The amount/volume and concentration of ammonia used in the synthesis was added in the revised manuscript. The experimental part has been extensively modified. We used ‘adsorption’for adsorption process and ‘absorption’for FTIR spectra in the whole manuscript. The incomplete FTIR spectrum due to negligence has been corrected. We added references for the quoted sentences.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript has been improved.

I can understand, that magnetic measurements might be difficult to conduct, even though they are really interesting for this application.

 

However, my main request is still that you add the time for your adsorption experiment.

 

 

Author Response

Response to Reviewer 1

Thanks for your and advice and understanding. I have added the time for adsorption experiment. Best regards to you！

Author Response File: Author Response.docx

Reviewer 4 Report

Unfortunately, the authors couldn’t revise the manuscript according to all my suggestions because of the Wuhan SARS-CoVvirus epidemic as China and schools and enterprises have been suspended for a long time, as they claimed. However, they tried to improve the manuscript as much as possible. Therefore, I recommended the acceptance of this manuscript in its present form.

Author Response

Response to Reviewer 4

Thanks for your and advice and understanding. Best regards to you！

Author Response File: Author Response.docx