Adsorption and Photocatalytic Decomposition of Gaseous 2-Propanol Using TiO2-Coated Porous Glass Fiber Cloth
Round 1
Reviewer 1 Report
In the present work the authors address the photocatalytic decomposition of a volatile organic compound as 2-propanol by using a porous glass fiber cloth coated with TiO2.
The authors demostrate the importance of several factors as the porosity of the substrate, the temperature or the water content in the photocatalytic decomposition of 2-propanlol, acetone and the subsequent generation of CO2.
The manuscript is well writen, and interesting for the Catalysts community. However, some points have to be clarified before publication:
In figure 3, the TiO2 content in the composite is reduce between 3-12h leaching time. Can the author explain this phenomenon? I would expect a saturation behavior instead of a decrease.
The authors did not mention nor characterize the employed TiO2. The deposited TiO2 seems to present particle shape, however no comment nor SEM image is shown in the manuscript.
As it is well known, anatase polymorph is more photocatalytically active than rutile TiO2. Maybe a comment and some XRD results could be included to give information about the employed TiO2.
The previous point is crucial in terms of light absorption in the TiO2, since anatase and rutile polymorphs have different bandgaps, even it is true that the employed UV light presents higher energy (365 nm) that any of those polymorphs, this point has to be more clear.
The quality of figures 6a and 7a shoul be increased. A color code is recommended.
Author Response
In figure 3, the TiO2 content in the composite is reduce between 3-12h leaching time. Can the author explain this phenomenon? I would expect a saturation behavior instead of a decrease.
Thank you for your advice. Acid treatment during 3-12h did not increase the weight loss, and the number of cracks on the fibers. Therefore, there are no clear causes of the amount of TiO2 decreasing. We also think this phenomenon was saturation and added an explanation to the manuscript.
“In contrast, the increase in leaching time from 3 to 12 h decreases the TiO2 amount. However, the factors that can affect the TiO2 loading, weight loss, cracking, and surface conditions were not significantly altered in this time range. Therefore, the loading amount of TiO2 was observed to be saturated rather than decreased.”
The authors did not mention nor characterize the employed TiO2. The deposited TiO2 seems to present particle shape, however no comment nor SEM image is shown in the manuscript.
Thank you for your variable comment. We used TiO2 nanoparticle suspension for coating, and the TiO2 particles formed particle layer on the cloth. However, homogeneous coating of each fiber by dip-coating of cloth sample would be difficult. In addition, the sampling process for FE-SEM may give some damage to the TiO2 coating. As the results, only aggregated TiO2 particles observed on fibers. We added an explanation to the manuscript, and new SEM images of the TiO2 coating as a supporting information.
“Panels (g), (h), and (i) of Figure 1 denote the side views of the TiO2-coated fibers. Agglomerates of the TiO2 nanoparticles are observed on the surfaces, and the coating is observed to be inhomogeneous. Because the glass cloth samples have high fiber density, homogeneous coating of each fiber by dip-coating the cloth sample would be difficult. Further, the sampling process before FE–SEM observation can cause some damage to the TiO2 coating. Fig. S1 depicts the surface and fracture cross section of TiO2 coating on the porous glass cloth at a position where plenty of TiO2 is loaded and where only little sample damage is observed. The TiO2 coating exhibited a porous structure, and VOCs can penetrate the coating.
As it is well known, anatase polymorph is more photocatalytically active than rutile TiO2. Maybe a comment and some XRD results could be included to give information about the employed TiO2.
I entirely agree with you. I grinded the TiO2 coated porous glass cloth and measured XRD. Although the strongest 101 peak of anatase was overwrapped with glass halo, the other peaks of anatase were detected. In addition, The TiO2 suspension used for TiO2 coating shows only anatase peaks. From these results, the possibility of rutile and brookite existence was very low and TiO2 on the cloth was mainly anatase. We add the new figure of XRD patterns as Figure 2.
The previous point is crucial in terms of light absorption in the TiO2, since anatase and rutile polymorphs have different bandgaps, even it is true that the employed UV light presents higher energy (365 nm) that any of those polymorphs, this point has to be more clear.
From above discussions, TiO2 on the cloth samples was anatase. The center wavelength of black light lump was 365 nm, it was enough for anatase excitation. I add some explanation to XRD results.
“It indicates that the usage of black light lump (center wavelength: 365 nm) in the following photocatalytic decomposition experiments is suitable for the photoexcitation of this composite because anatase exhibits a bandgap of 3.2 eV (388 nm) “
The quality of figures 6a and 7a should be increased. A color code is recommended.
Thank you for your kindly comment. Colors were introduced to the Figure.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This paper reports adsorption and photocatalytic decomposition of gaseous 2-propanol by TiO2-coated porous glass fiber cloth. The photocatalytic degradation based on glass fiber supported TiO2 nanoparticles is interesting as photocatalytic decomposition of VOC is important in industry. However, some issues should be addressed before the paper can be accepted in Catalysts.
1. How did the mechanical properties change after acid leaching?
2. Please check the time unit of Figures 7a and 8a.
3. Please check the “nonporous” in the legend of Figure 7.
4. The physical parameters of glass fiber cloth may be given instead of an optical image, such as warp and weft thread, thickness and gram weight.
5. Can SEM show the porous structures of glass fibers except for cracks?
Author Response
1. How did the mechanical properties change after acid leaching?
Elasticity of the fibers was decreased by the acid leaching, but flexibility maintained at a high level. When the curvature radius was 3 mm, the porous glass cloth was not broken and recovers without deformation. We added the explanation to the microstructure section.
“Despite the generation of clacking by acid leaching, the flexibility of the porous glass cloth was maintained at a high level. When the 3-h leached glass cloth was curved with a curvature radius of 3 mm, the glass cloth was not broken; further, its form was recovered without any deformation.”
2. Please check the time unit of Figures 7a and 8a.
Thank you for your important pointing out. I corrected “hour” to “min”.
3. Please check the “nonporous” in the legend of Figure 7.
Thank you for your kindness. I corrected “nonporous” to “non-porous”
4. The physical parameters of glass fiber cloth may be given instead of an optical image, such as warp and weft thread, thickness and gram weight.
Thank you for your variable comment. I checked characteristic value of the glass cloth and added the information of E-glass cloth in the manuscript.
“It has a plain weave structure, and approximately 400 E-glass fibers of 9.1-μm diameters form the warp and weft thread; further, the thread density, the number of warp and weft thread per certain area of woven fabric, was 44 × 32 in 25 × 25 mm2. The thickness of the cloth was 180 μm, and the weight per unit area was 203.5 g/m2.”
5. Can SEM show the porous structures of glass fibers except for cracks?
The size of the pores estimated from N2 adsorption was less than 1nm. This is out of observation range of FE-SEM. STEM and TEM can take more magnified image, but the energy of electron beam is too high to maintain the porous structure. We cannot observe the porous silica structure because the electron beam of STEM/TEM sintered the silica gel. Gas adsorption is only the method of estimate the porous size.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed all the comments and recommendations made by the reviewers, and the manuscript is now clearer and more understandable. In my opinion, this work is ready for publication in Catalysts in its present form.
Reviewer 2 Report
I am happy with this version. The paper could be accepted as is.
