Exploitation of Lignocellulose Fiber-Based Biotemplates to Improve the Performance of an Immobilized TiO₂ Photocatalyst

Round 1

Reviewer 1 Report

The manuscript contributes a new idea; the addition of Lignocellulose Nanofibers to TiO₂-branched poly(ethyleneimine) colloids and also describes the improvement of the photocatalytic performance of the composites. Many of the conclusions of the authors though are not supported adequately by the presented data. See comments 7, 8, 10 and 12. A major revision is required thus before publication.  

 

1) There are several grammatical errors for example page 3 line 106 “Colloids systems enables materials delivery”. A recheck is required.

 

 2) The quantity (ies) of TiO₂ dispersed into the initial aqueous solutions must be included in the manuscript.

 

3) Page 5 line 208 the authors are discussing contents (wt.%) whereas in Figure 1 and in line 204 contents (vol.%.).

 

4) Page 5 line 212 “The results plotted in Figure 3b” I suppose it is Figure 1b.

 

5) The x axis legend of Figure 1b is wrong. It should be “volume fraction” and somewhat confusing to the reader. It would be better if it matched Figure 1a legend and the contents were in vol.%.

 

6) Page 5 lines 217-218. “The volume fraction of solids of 0.10-0.12 corresponds to a point where viscosity steeply increases.” From the diagram it seems that steep increase is rather observed at 0.14.

 

7) Page 8 lines 301-303 “However, the tendency of the curves in figure 5a was not completely linear in all cases. The dispersion and deviation of mass values was larger for the coatings built with 9 layers and even for 6 layers coating.“ In my opinion these conclusions are premature. More intermediate data from layers are needed particularly in the area 1 to 5 layers.

 

8)   Page 9 lines 339-340 “All coatings maintain firmly joined to the glass substrate, without releasing when pulling out with scotch tape.” They authors do not describe how they examined scotch tapes and excluded the presence of small amounts of coatings. This method is not recommended. A simple immersion into an aqueous solution for 24 in the same conditions as the catalysis experiment with subsequent weighing of the dried sample is proposed insted.

 

9) The legend of figures 7a and 7b is also confusing. It should be rather MO % remaining or better the author could indeed plot the actual degradation percentages (100-y axis values).

 

10) Page 11 lines 381-383 “Some additional tests were made to study the reusing capability of coatings. In this sense the layers showed no significant deterioration in photocatalytic performance, which is very important from the application point of view” This is very interesting and very important but where are the kinetics experiments results?   

 

11) Page 11 lines 385-388 “the results obtained under our approach are in concordance with others similar materials reported previously in literature, which were prepared through more complex methodologies [24–26,28].” A Table here comparing k values from each reference would be very helpful.

 

12) Page 11 lines 394-396. “The addition of 4 % wt. of LCNF over the TiO₂ suspension was the optimal amount of biotemplate to avoid microstructural defects such as cracks or delamination.” How do the authors know? Did they perform experiments with higher LCNF percentages? Where are the results? In fact since the 4% in LCNF samples exhibited the best results a solid justification why not testing higher contents is needed.  

Author Response

Dear reviewer,

Thank you very much for all your comments and corrections. The manuscript “catalysts-1077174”, has been substantially revised and improved. We provide our replies below. Modifications as well as new text have been highlighted in yellow throughout the manuscript.

We hope to have satisfactorily fulfilled all the requirements

1) There are several grammatical errors for example page 3 line 106 “Colloids systems enables materials delivery”. A recheck is required.

We acknowledge the reviewer’s revision. The paragraph has been modified and highlighted in text. In addition, we have completely checked the manuscript.

2) The quantity (ies) of TiO₂ dispersed into the initial aqueous solutions must be included in the manuscript.

This info has been included in experimental section. The paragraph has been clarified and rewritten as follow:

“The mass of nanoparticles was adjusted to achieve solid contents ranging from 2 vol% to 16 vol%. All TiO₂ suspensions were ball-milled for 120 min using Al₂O₃ balls of 1 cm in diameter in order to break the possible agglomerates from the commercial powder.………………………. After the surface modification of TiO₂ nanoparticles, the aqueous solvent of suspensions was removed by centrifugation and changed by an organic one (ethanol) in order to favor the drying process of the future coatings avoiding possible microstructural defects”  

3) Page 5 line 208 the authors are discussing contents (wt.%) whereas in Figure 1 and in line 204 contents (vol.%.).

We thank the reviewer’s comment. The mistake has been corrected

4) Page 5 line 212 “The results plotted in Figure 3b” I suppose it is Figure 1b.

Yes, the mistake has been modified in text

5) The x axis legend of Figure 1b is wrong. It should be “volume fraction” and somewhat confusing to the reader. It would be better if it matched Figure 1a legend and the contents were in vol.%.

We acknowledge the reviewer’s suggestion. The x axis legend of figure 1b has been modified.

The Krieger- Dougherty fit has been calculated from the viscosity values of suspensions and the volume fraction of the dispersed solids. Therefore, the X-axis should be named in figure b as the volume fraction of the dispersed solid, not as vol.%

6) Page 5 lines 217-218. “The volume fraction of solids of 0.10-0.12 corresponds to a point where viscosity steeply increases.” From the diagram it seems that steep increase is rather observed at 0.14.

The paragraph has been modified according to the referee’s comment. The text is now as follow:

“The volume fraction of solids of 0.10-0.12 corresponds to a range where viscosity start to increase. Above 0.14, the viscosity increases steeply.”

7) Page 8 lines 301-303 “However, the tendency of the curves in figure 5a was not completely linear in all cases. The dispersion and deviation of mass values was larger for the coatings built with 9 layers and even for 6 layers coating. “In my opinion these conclusions are premature. More intermediate data from layers are needed particularly in the area 1 to 5 layers.

We acknowledge the reviewer’s suggestion and we agree that a higher number of intermediate layers could clarify this affirmation. Taking account into that the mass were only measured for coatings made with 3, 6 and 9 layers, we have removed the part of the sentence that could be misunderstood, i.e. “the tendency of the curves in figure 5a was not completely linear in all cases”. In this way we are assuming the non-linearity and the number of points are acceptable to confirm it and assume that the dispersion and deviation of mass values is larger for the coatings built with 9 layers. The sentence is now as follow:

“As expected, the deposited mass values are higher as the number of layers increase. The dispersion and deviation of mass values was larger for the coatings built with 9 layers and even for 6 layers coating.”

8)   Page 9 lines 339-340 “All coatings maintain firmly joined to the glass substrate, without releasing when pulling out with scotch tape.” The authors do not describe how they examined scotch tapes and excluded the presence of small amounts of coatings. This method is not recommended. A simple immersion into an aqueous solution for 24 in the same conditions as the catalysis experiment with subsequent weighing of the dried sample is proposed instead.

Although the scotch tape was visually analyzed after pulling out and any appreciable evidence was not found, the mass of some samples has been measured again after their corresponding photocatalytic tests (in which the sample was effectively immersed in aqueous solution during 24h). The results did not change significantly respect to the previous ones. According to the referee's comment, this information has been also included to the manuscript. The text is now as follow:

“All coatings maintain firmly joined to the glass substrate, without releasing when pulling out with scotch tape. Furthermore, the mass of the dried samples was measured before and after the photocatalytic tests, proving film preservation, and confirming the adhesion of the film to the substrate and cohesion of the layer-by-layer processed films.”

9) The legend of figures 7a and 7b is also confusing. It should be rather MO % remaining or better the author could indeed plot the actual degradation percentages (100-y axis values).

We thank the reviewer’s suggestion. The legend has been modified in order to show better understanding.

10) Page 11 lines 381-383 “Some additional tests were made to study the reusing capability of coatings. In this sense the layers showed no significant deterioration in photocatalytic performance, which is very important from the application point of view” This is very interesting and very important but where are the kinetics experiments results?   

We thank the reviewer’ comment. Only the T4C-6layers coating was measured twice and no significant differences were observed, so any additional curve was added to the graphs. Considering that more than two photocatalytic tests should be made to confirm the total reusing capability, the text has been modified to inform about this second photocatalytic assay. We have included this info in text in order to provide a first idea about the no deterioration as well as to remark their importance from the application point of view. The text is now as follow:

“On the other hand, a second photocatalytic test of the T4C-6 layers coating was made to prove the capability of films reuse. No significant differences were observed in terms of photoactivity and mass preservation, which is very important from the application point of view.”

11) Page 11 lines 385-388 “the results obtained under our approach are in concordance with others similar materials reported previously in literature, which were prepared through more complex methodologies [24–26,28].” A Table here comparing k values from each reference would be very helpful.

The required table has been included in the manuscript together with the following paragraph:

“Keeping this in mind it is possible to say that the results obtained under our approach (using commercial particles and templates obtained from natural-derived resources) are competitive with others pure TiO2 materials (no composites) reported previously in literature, which were prepared through more complex methodologies like sol gel. Table 1 show an overview of some works”.

 

Table 1. Overview of the Photocatalytic Performance of others similar pure TiO2 materials

Material	Preparation method	Degraded component	1st rate constant (h-1)		Ref.
Ordered mesoporous TiO2	Sol gel	(AO7)	0.18	[37]
Dual Source TiO2 Films templated by NCC	Sol gel + hydrothermal	4-chlorophenol	0.19-0.53	[28]
Mesoporous TiO2	Sol gel	MB, RhB, MO and Phenol	0.24-0.36	[38]
Immobilized TiO2 films	Electrophoretic deposition of TiO2	4-chlorophenol	0.19	[5]
Our coatings	Dip Coating of colloidal mixture + Sintering	MO	0.29-0.45	This work

* Acid orange 7(AO7), Methylene Blue(MB), Rhodamine B (RhB)

 

12) Page 11 lines 394-396. “The addition of 4 % wt. of LCNF over the TiO₂ suspension was the optimal amount of biotemplate to avoid microstructural defects such as cracks or delamination.” How do the authors know? Did they perform experiments with higher LCNF percentages? Where are the results? In fact, since the 4% in LCNF samples exhibited the best results a solid justification why not testing higher contents is needed.

In order to study this effect, a suspension with higher content of LCNF (>6%wt.) was formulated with the same total solid content that other samples. The increase of viscosity difficult suspension handling and dipping, and relevant cracks and defects were observed in the films surface. Related sentences have also included in the manuscript, at the result section:

“A suspension with higher content of LCNF (T-6C) was also formulated maintaining the 2 vol.% solid content. The increase of viscosity limits the suspension handling and the dipping process. It is noteworthy that although the increase of viscosity produced by the addition of more amount of LCNF in suspension, favors the time consumption for manufacturing, an excess of LCNF provokes heterogeneities and non-desirable defects. For this reason, 4 wt.% of LCNF was considered optimum for a reliable process”

And at the conclusion section:

“Increasing the addition of LCNF provokes boost the suspension viscosity limiting its handling and the dipping process, and leading to surface macroscopic cracks at the prepared coatings”

Author Response File: Author Response.pdf

Reviewer 2 Report

The topic of the paper is within the scope of the journal. The mansucript is well-written, the obtained results are interesting and correctly presented and discussed.
Therefore it is my pleasure to recommend it for publication in Catalysts after adressing the following issues.

- lines 91-93 - the sentence seems to be doubled
- figure 3 - the scale bar on the SEM image is not clear enough
- lines 381-383: It would be beneficial to show or discuss more detailed the results showing the stability of the catalysts (e.g., prove the evidence for the statement "the layers showed no significant deterioration in photocatalytic performance")
- the last paragraph of the Results section. It would be beneficial to compare the obtained results with those previously reported in the literature i.e. in the form of table.

Author Response

Dear reviewer,

Thank you very much for all your comments and corrections. The manuscript “catalysts-1077174”, has been substantially revised and improved. We provide our replies below. Modifications as well as new text have been highlighted in yellow throughout the manuscript.

We hope to have satisfactorily fulfilled all the requirements

- lines 91-93 - the sentence seems to be doubled.

We thank the reviewer’ comment. The mistake has been corrected.

- figure 3: the scale bar on the SEM image is not clear enough.

The scale bar of this micrograph has been modified.

- lines 381-383: It would be beneficial to show or discuss more detailed the results showing the stability of the catalysts (e.g., prove the evidence for the statement "the layers showed no significant deterioration in photocatalytic performance").

(Similar comment of the reviewer 1) We thank again the reviewer’s comment. Only the T4C-6layers coating was measured twice and no significant differences were observed, so any additional curve was added to the graphs. Considering that more than two photocatalytic tests should be made to confirm the total reusing capability, the text has been modified to inform about this second photocatalytic assay. We have included this info in text in order to provide a first idea about the no deterioration as well as to remark their importance from the application point of view. The text is now as follow:

“On the other hand, a second photocatalytic test of the T4C-6 layers coating was made to prove the capability of films reuse. No significant differences were observed in terms of photoactivity and mass preservation, which is very important from the application point of view.”

- the last paragraph of the Results section. It would be beneficial to compare the obtained results with those previously reported in the literature i.e. in the form of table.

The required table has been included in the manuscript together with the following paragraph:

“Keeping this in mind it is possible to say that the results obtained under our approach (using commercial particles and templates obtained from natural-derived resources) are competitive with others pure TiO2 materials (no composites) reported previously in literature, which were prepared through more complex methodologies like sol gel. Table 1 show an overview of some works”.

 

Table 1. Overview of the Photocatalytic Performance of others similar pure TiO2 materials

Material	Preparation method	Degraded component	1st rate constant (h-1)		Ref.
Ordered mesoporous TiO2	Sol gel	(AO7)	0.18	[37]
Dual Source TiO2 Films templated by NCC	Sol gel + hydrothermal	4-chlorophenol	0.19-0.53	[28]
Mesoporous TiO2	Sol gel	MB, RhB, MO and Phenol	0.24-0.36	[38]
Immobilized TiO2 films	Electrophoretic deposition of TiO2	4-chlorophenol	0.19	[5]
Our coatings	Dip Coating of colloidal mixture + Sintering	MO	0.29-0.45	This work

* Acid orange 7(AO7), Methylene Blue(MB), Rhodamine B (RhB)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors made substantial efforts to improve the quality of the manuscript. In this context I recommend acceptance.