Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors and Future Research Prospects
Round 1
Reviewer 1 Report
The objective of the presented review is to examine the feasibility of photocatalysis-involved treatment for removal of contaminants in produced water. From many studies revealed that photocatalysis was effective to decompose recalcitrant organic compounds. The factors affecting decontamination and strategies to improve efficiency of photocatalysis are discussed. The review is comprehensive and contains several experimental data and important relationship between acitivity and several preparation and modification factors. The review could be published after minor correction.
- The hydrothermaly prepared catalysts often contains phisisorbed and lattice water which may contribute to the efficiency of photocatalysts. Typical examples are the differen titanates. Please mention them in the Reviw (Bavykin DV, Friedrich JM, Walsh FC (2006) Adv Mater 18:2807–2824; Kukovecz .... (2016) Surf. Sci Rep. 71:473-546. Latice water similar to carbonates may help in separation of the electron-hole pair.
- OH radicals formed in UV radiaion could significantly oxidize the methane catalysed by metals supported on nanotitanates. Supplementation of present review with these observations could probably increase the number of useful examples.
- Surface water molecules can catch the hole and produce a reactive OH radical and H+ that delocalizes ont he nearby water molecules as was described in Catal. Lett 2019, 149:1441:1454. The generated hydroxyl radicals are very aggressive oxidant and start to oxidize organic compounds in a radical type reaction. Probably this picture can help in considering of affecting factors in treatment of produced water with photocatalysis.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript entitled “Treatment of Produced Water with Photocatalysis: Recent Advances, Affecting Factors, Future Research Prospects” reviews already published papers dealing with removal of contaminants in water by photocatalysis.
The authors of this manuscript, in the abstract state that “The objective of this review is to examine the feasibility of photocatalysis-involved treatment for removal of contaminants in produced water”.
I understand that a review cannot be comprehensive but I see that many important results on this field, appeared on high IF journals, are missing in the discussion as well as in the References.
Also a chapter concerning the removal of metal ions and other compounds that cannot be eliminated by the photocatalytic treatment should be added. For example, some papers related to the removal of chromium (VI) appeared on JACS and many others of this relevance are not mentioned at all in this review. In contrast, there are many redundancies (refs 64, 73, 81 to name a few).
Also the removal of many widely used organic compounds was not taken into account in this review. As a consequence, I cannot suggest to publish this paper in this form.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
Table 1 - The photolysis couldn’t be an example of catalyst as we can find in the first column. I propose to add e.g. without catalyst.
The part of the article: Photocatalytic treatment of produced water should be improved, the reaction of formation of free radicals should be included. With the irradiation of UV or visible light, semiconductor (e.g. TiO2) can generate hydroxyl and superoxide anion radicals,then these radicals can mineralize a wide range of organic compounds. – it is too little information about photocatalysts and the photocatalytic degradation mechanisms. When semiconductor such as TiO2 or ZnO are illuminated with light energy equal to or higher than its bandgap (λ<380 nm) an electron in conductive band and positive hole in the valence band are generated. The holes in the valence band may generate strong oxidizing hydroxyl radicals (OH•). Further reaction can lead to the creation of hydrogen peroxide which also promote the formation of OH•. The hydroxyl radical and superoxide radical anions are probably the primary oxidizing species that can lead to oxidation of the organic compounds.
Author Response
Please find the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The manuscript was improved
