Investigation of the Self-Cleaning Property of Photocatalytic Coatings at a Laboratory Scale

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this work, based on semiconductor oxides, mostly titanium dioxide (TiO2), which induce photocatalytic oxidation activity and superhydrophilicity. Therefore, the authors present an experimental procedure at labscale to assess the self-cleaning ability of various photocatalytic coatings (five TiO2-based commercial products and one lab-grade zinc oxide (ZnO) product) applied to mortar surfaces. The samples were artificially stained with three types of soiling: Congo red dye, diesel soot, and motor oil. This work is interesting with certain novelty, and the main conclusions are convincible. Therefore, I think this work is publishable after moderate revision as noted:

1. To increase the authenticity of your experimental results, please add error bars to your performance tests

2. For most of all figures, it is necessary to improve the quality.

3. The author briefly describes the photocatalytic process in the third paragraph of the introduction. However, the introduction is not specific and contains errors. Please refer to the literature and correct it.

4. In the abstract, the authors propose “However, the self-cleaning potential of the coatings was difficult to identify because of the positive action of light and water run-off on the attenuation of the stains.” Is there a good solution to this problem?

5. In the photocatalytic process, which active substance is produced by each Product to degrade pollutants?

6. Some new advances of photocatalysts are suggested to be included, such as Chem. Eng. J., 2020, 384, 123275; J. Alloys Compd., 2023, 968, 172127; Appl. Catal. B, 2020, 277, 119254; Chem. Eng. J., 2018, 350, 335; et al,

Comments on the Quality of English Language

Quality of English Language can be improved to some extent.

Author Response

Please see the attachments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The work by Hot et al. describes the use of an experimental test bench for the evaluation of the self-cleaning capabilities of different photocatalytic materials. An interesting combination of target compounds is tested (dye, soot and motor oil). It is interesting to combine several methodologies for the evaluation of the self-cleaning behavior, ranging from digital image techniques to wettability measurements. The results are well supported by the data, and some shortcomings of the employed methodologies, are explicitly addressed, but could be further elaborated. The work is also clearly written. I therefor support publication of this manuscript pending (very) minor revisions.

- Seeing the construction of the test bench in Figure 2, I wonder if the authors could add a comment on the homogeneity of the UV irradiance at the location of the different samples and test spots. This is important for an accurate and fair comparison amongst samples.

- The authors mention a critical problem with respect to the digital image analysis method: the color of the test spot (and potentially even the substrate itself) also changes due to other factors than just the self-cleaning activity. A similar problem has very recently been addressed by Van Hal et al. (Environ Sci Pollut Res 30, 22262–22272 (2023)), in the context of self-cleaning surfaces for soot degradation, as in the present work, using substrates that intrinsically change color over time. The authors are therefore encouraged to use, or at least discuss, this technique as a potential improvement over the current method.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf