Thermal Transformation of Caffeic Acid on the Nanoceria Surface Studied by Temperature Programmed Desorption Mass-Spectrometry, Thermogravimetric Analysis and FT–IR Spectroscopy
Round 1
Reviewer 1 Report
Authors study the interaction of caffeic acid with the surface of cerium oxide by FTIR. Thereby, different amounts are impregnated on the solid and the FTIR spectrum recorded. FTIR measurements were carried out under ambient conditions. Water adsorption was not prevented by vacuum or protection atmosphere. Measurements were only done at room temperature without the possibility of any further treatment of the sample (e.g. desorption at higher temperature.) One sample was extracted again with ethanol for “desorption” of caffeic acid. In principle, this should generate a material that would also be obtained by adsorbing a lower amount?
The State of Art treatment would be at least to apply vacuum to desorb ambient water. From the TG-MS it can be seen that water is present on the surface. The interpretation of the data is not based on experimental proofs, it seems to be a more lengthy discussion. The series of increasing the amounts does not provide a clear trend. Perhaps intermediate points may improve this.
The overall merit of the paper is low. Publication is not recommended. No real advances are reported apart from several FTIR spectra with a limited benefit.
Minor points:
In the Materials and Methods part Authors state that Nanoceria was dried at 500 °C. In air, this would be a classical calcination. In which atmosphere has this been carried out, in aire or in nitrogen?
Figure 1a displays different spectra for the adsorption of increasing amounts of caffeic acid. The visualization could be improved by expanding the figure vertically and avoid overlays to a big extend. All major bands of caffeic acid can be detected at higher load (0.9 mmol/g and higher).
Line 203, the reference should be to Figure 2, not to Figure 3.
Authors state that different products might be formed from caffeic acid over cerium oxide, such as 3,4-dihydroxyphenylethylene, acetylene carboxylic acid, pyrocatechol and phenol. Authors should facilitate the understanding and provide a complete reaction network as graphic.
Authors describe the usefulness of caffeic acid itself. This is not strongly related to the topic of the manuscript and, therefore, it might be skipped.
Author Response
Dear Reviewer! We greatly appreciate that we have been given the opportunity to revise our manuscript entitled “Thermal transformation of caffeic acid on the nanosized cerium dioxide studied by temperature programmed desorption mass-spectrometry and FTIR-spectroscopy”. We carefully considered the comments and the criticism offered by the reviewers. We think that the raised issues are valid and important. A revision was prepared along the lines proposed. We are sending to you revised manuscript and highlighted version of the manuscript with all our changes (please see the attached files). We prepared the responses to Reviewers with detailed explanation (please see the attached files). Best regards, Dr. Nastasiienko
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This manuscript studies the thermal transformation of coffee acid on the surface of nano cerium through temperature-program desorption mass spectrum and FTIR spectrum. This is an interesting research, but needs major revision. (1) This research investigated a pyrolysis process of CA Surface Complexes by using temperature-programmed desorption mass spectrometry (TPD-MS). This was not enough for the thermal degradation mechanism. I recommend the authors to do some extra experiments by using Py-GC/MS for the pyrolysis mechanism of CA, because Py-GC/MS is more powerful instrument than TPD-MS used in the field of pyrolysis. The testing method could be found in the following literatures: Ma ZQ, et al. Fuel Processing Technology, 2018, 181: 142-156. Ma ZQ et al. Journal of Analytical and Applied Pyrolysis. 2018, 2018, 134: 12-24. (2) In Fig. 1 of FTIR analysis of CA Surface Complexes, please keep Fig (a), (b), and (c) in a line. More importantly, if possible, please calculated the relative content of each functional group by using relative peak area, for a more clear comparison of the evolution of functional group. Please see the reference of Dai et al. Energy & Fuels, 2018, 32: 4160-4166. (3) The title of Fig. 3, “(a)” was missed. (4) In the part of the thermal degradation mechanism analysis, the authors stated some gaseous components with small molecular weight, such as CO2, CO, and CH4, was produced. I recommend the authors to do some pyrolysis experiment by using TGA-FTIR, because these components could be directly detected by TGA-FTIR.Author Response
Dear Reviewer! We greatly appreciate that we have been given the opportunity to revise our manuscript entitled “Thermal transformation of caffeic acid on the nanosized cerium dioxide studied by temperature programmed desorption mass-spectrometry and FTIR-spectroscopy”. We carefully considered the comments and the criticism offered by the reviewers. We think that the raised issues are valid and important. A revision was prepared along the lines proposed. We are sending to you revised manuscript and highlighted version of the manuscript with all our changes (please see the attached files). We prepared the responses to Reviewers with detailed explanation (please see the attached files). Best regards, Dr. Nastasiienko
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Accept.
