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Peer-Review Record

Diethylene Glycol-Assisted Organized TiO2 Nanostructures for Photocatalytic Wastewater Treatment Ceramic Membranes

Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Water 2019, 11(4), 750; https://doi.org/10.3390/w11040750
Received: 16 March 2019 / Revised: 5 April 2019 / Accepted: 6 April 2019 / Published: 10 April 2019

Round 1

Reviewer 1 Report

The manuscript could be accepted after addressing these following questions. 

1. The scale bar and markings in AFM images are not visible.  Need clear and prominent dimensions.

2. In xrd some peaks are not identified.  32, 38, 54 and 75 degrees.  Need explanation. 

3. Need a comparison table where author should compare the degradation with reported literature values.

4. There are only few reference present for TiO2 or composite TiO2 catalytic films and those are old. Some upto date citation needed. Following literature may be cited.

[doi.org/10.1680/nme.12.00034], [

10.1016/j.cej.2015.07.080], [10.1515/ijcre-2016-0153], [doi: 10.3390/ma11040488

]

5.Table 1 shows porosity but there is no unit. Unit should be '%' porosity

Author Response

Reviewer 1:

The manuscript could be accepted after addressing these following questions. 

1. The scale bar and markings in AFM images are not visible. Need clear and prominent dimensions.

Response: Thank you for your comments. AFM images in Figure 7 was modified in manuscript to show clear dimensions.

2. In xrd some peaks are not identified.  32, 38, 54 and 75 degrees. Need explanation. 

Response: Those peaks don’t correspond to the diffraction patterns of Al2O3 and TiO2. The peaks also have very low intensity in comparison to the major peaks of Al2O3 and TiO2 with high intensity. As these were observed even in pristine Al2O3 membrane, it is thought that the existence of the weak diffraction patterns resulted from small amount of impurities in pristine Al2O3 membrane, which was purchased from Korean company.

3. Need a comparison table where author should compare the degradation with reported literature values.

Response: Comparison of dye degradation of various organic dye compounds using photocatalytic membrane reactor with reported literature values was made in Table 2 on Page 12.

4. There are only few reference present for TiO2 or composite TiO2 catalytic films and those are old. Some upto date citation needed. Following literature may be cited.

[doi.org/10.1680/nme.12.00034],[10.1016/j.cej.2015.07.080],[10.1515/ijcre-2016-0153], [doi: 10.3390/ma11040488]

Response: Thank you for your suggestions. New references from reference number 19 to 22 were cited in the Introduction part.  

5.Table 1 shows porosity but there is no unit. Unit should be '%' porosity

Response: The unit of porosity was changed into “%” in Table 1.

 

Reviewer 2 Report

Presented by Ahmad et al. manuscript titled: "Diethylene glycol-assisted organized TiOnanostructures for photocatalytic wastewater 4 treatment ceramic membranes" is very interesting and well written. Bothe the subject of the studies, and the quality of results presentation is good enough to be published without revision. My only comments are: 

1. What was the role of DEG? This must be explained in Introduction.

2. Why 3 hour were used for the studies?


Author Response

Reviewer 2:

Presented by Ahmad et al. manuscript titled: "Diethylene glycol-assisted organized TiOnanostructures for photocatalytic wastewater 4 treatment ceramic membranes" is very interesting and well written. Bothe the subject of the studies, and the quality of results presentation is good enough to be published without revision. My only comments are: 

1. What was the role of DEG? This must be explained in Introduction.

Response: Thank you for your comments. As mentioned in the beginning of results, DEG promoted directional growth of TiO
2 to one dimensional structures by retarding the hydrolysis of TiO2 precursor during hydrothermal synthesis of TiO2. According to your advice, clear explanation for the role of DEG was additionally incorporated in the Introduction part.

2. Why 3 hour were used for the studies?

Response: In this study, operational time of 3 h was needed to obtain more than 90% of degradation efficiency of Congo Red dye in photocatalytic membrane reactor. Statement was added in the Materials and Methods part on Page 3.

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscripts deals with the development of a ceramic membrane based on an alumina support and titania nanostructures growth on it by means of a hydrothermal method in the presence of diethylene glycol as capping agent. The authors concluded that these composites are promising as photocatalytic membranes for wastewater treatments.

 

In my opinion the paper is well written and organized and provides some interesting results on the subject. The techniques used to characterize the composites are appropriate and up to date. There are only some minor points to be clarified. Specifically:

 

- A deeper discussion on the role of different properties (phases, amount, thickness, distribution, etc.) is necessary. Moreover I think that it is difficult to state with certainty that anatase is the best phase. For instance, it is widely reported that the co-presence of anatase and rutile is more effective for photocatalytic oxidation reactions. Therefore the statement in lines 22-24 of the abstract appears debatable, being also highly important other factors as the homogeneous distribution of TiO2 and the porosity/permeability of the membrane.

- Fig. 2: the image of the intermediate sample (2e) appears completely different from 2c and 2g ones. Why?

- Table 1: the permeability value for T3 is really very low compared to T1 and T2 (this latter sample has the same photoactivity), also considering other parameters (porosity and thickness). Please comment on this.

- Experimental: it is not fully clear where the membrane is located in the batch reactor of Fig. 1(a). In fact, in case of the setup shown in the figure, it seems highly probable that the stirrer can damage the membrane.


Therefore my suggestion is: accept after minor revision.

Author Response

Reviewer 3:

The manuscripts deals with the development of a ceramic membrane based on an alumina support and titania nanostructures growth on it by means of a hydrothermal method in the presence of diethylene glycol as capping agent. The authors concluded that these composites are promising as photocatalytic membranes for wastewater treatments

In my opinion the paper is well written and organized and provides some interesting results on the subject. The techniques used to characterize the composites are appropriate and up to date. There are only some minor points to be clarified. Specifically:

1.A deeper discussion on the role of different properties (phases, amount, thickness, distribution, etc.) is necessary. Moreover I think that it is difficult to state with certainty that anatase is the best phase. For instance, it is widely reported that the co-presence of anatase and rutile is more effective for photocatalytic oxidation reactions. Therefore, the statement in lines 22-24 of the abstract appears debatable, being also highly important other factors as the homogeneous distribution of TiO2 and the porosity/permeability of the membrane.

Response: Thank you for your comment. Although co-existence of anatase and rutile phase of TiO
2 can improve photocatalytic activity for removal of organic materials, it is also known that combination between them such as composition and morphology is of great importance for enhancement of photocatalysis. In other words, the mere co-existence does not necessarily improve photocatalysis, but rather can deteriorate it. In XRD result, rutile phase with very low intensity was observed in comparison to anatase phase with high intensity, indicating formation of very small amount of rutile phase. Therefore, it is regarded that the presence of small amount of rutile phase did not enhance the photocatalysis, but rather deteriorated it in our works. Statements were made in the Discussion part.

2.Fig. 2: the image of the intermediate sample (2e) appears completely different from 2c and 2g ones. Why?

Response: Thank you for your comments. Figure 2e shows T2 membrane surface densely packed with nanorods, which was ascribed to the synthesis of a large number of TiO
2 nanorods on Al2O3 membrane. As the DEG amount decreased in the synthesis of T3 membrane, the directional growth of TiO2 to one-dimensional nanorods was suppressed. Thus, short and thick nanorods with layered structures formed on the surface of T3 membrane. The observed difference between them is attributable to incorporation of different amount of DEG for the synthesis of TiO2 on the membrane.

3.Table 1: the permeability value for T3 is really very low compared to T1 and T2 (this latter sample has the same photoactivity), also considering other parameters (porosity and thickness). Please comment on this.

Response: Thank you for your comment. For the T3 membrane, our SEM observations (Figure 2) showed that the TiO2 layer grown on the support had aggregated structure with shorter and thicker layered clusters compared with those observed for T1 and T2 membrane. In addition, the cross-sectional SEM images T3 membrane, as shown in Figure 4d, clearly showed that a larger amount of TiO2 was deposited on the cross-section as well as the surface of the membrane. Although the photocatalytic degradation of T2 and T3 membrane was not significantly different as observed during batch study as shown in Figure 8, the layered morphology of T3 membrane not only posed detrimental effect on membrane antifouling property but also least permeability. Statements were made in 3.1 and 3.4 in manuscript on Page 7 and Page 13, respectively.  

4.Experimental: it is not fully clear where the membrane is located in the batch reactor of Fig. 1(a). In fact, in case of the setup shown in the figure, it seems highly probable that the stirrer can damage the membrane

Response: In batch photocatalytic reactor, both stirrer and membrane were placed at the corners of jacket beaker and kept at sufficient distance to avoid any physical contact. Statement was made in 2.4 in manuscript on Page 3.

Author Response File: Author Response.docx

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