TiO2 and TiO2-Carbon Hybrid Photocatalysts for Diuron Removal from Water
, María del Carmen Román-Martínez 1, Patricia García-Muñoz 2 and Nicolas Keller 2Round 1
Reviewer 1 Report
The authors have prepared TiO2 and TiO2/carbon-based photocatalysts, characterized their physico-chemical properties and critically compared their efficiency for diuron removal from water. The study contains detailed, meaningful results and the manuscript is well written. A few remarks can be made to improve the discussion of the results:
- The link made by the authors between the specific surface area and the crystallite size is too straightforward and, as it is (Lines 211, 239, 245), not correct. If a phenomenon of grain coarsening (here due to thermal treatment) can lead to a reduction of porosity and specific surface area, it is not always the case. Crystal size can be improved without affecting the morphology (best example is the mesoporous single crystals), and loss of s.s.a. can simply arise from agglomeration. So, the crystallite size growth doesn't imply a reduction of specific surface area, even if they can go together in some cases.
- BET analysis could be deepened by determining the pore size distribution. Especially because the photocatalysis of diuron implies diffusion through the (meso,micro)structure and the pore size distribution affects the access of diuron to the reaction sites, and so the kinetics. Discussing the kinetic constants taking this parameter into account in addition to s.s.a. can bring a better understanding of the results.
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Reviewer 2 Report
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Reviewer 3 Report
The manuscript describes the diuron photodegradation with titania and titania functionalized with carbon. The manuscript is well organized, although some insights are need in order to be published.
In particular, looking at Figure 2b, the behavior of TiO2, TiO2-AC0.5 and TiO2 –AC1 is very similar, as evidenced also by the similar values of kapp.
kapp is calculated after t=0, so looking at the figure I do not understand how the kapp for TiO2-AC10 and AC5 is so high compared to the others three samples (it’s counterintuitive, looking at the slope of the curve it is in my opinion lower). Same type of consideration on the curves of Figure 3.
The results in terms of kapp need to be critically compared with the values found in the literature for similar systems; this comparison is important for the reader in order to understand the real improvement and novelty of this system.
In the last paragraph of the manuscript, the authors have verified the degradation of absorbed diuron; in my opinion for one or tweo systems, a couple of recycles of the TiO2-AC catalyst should be present and compared with the first original experiment, in order to understand if the system con be reused with the same efficiency.
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Round 2
Reviewer 2 Report
The authors did a good job in terms of addressing the reviewer's comments. However a few minor changes are necessary as shown below. The manuscript can be considered for acceptance with the following corrections -
L232: "..between 3 and 18 nm (comprising both micro and mesopores),.." Micro pore traditionally refers to pore size below 2 nm. Here the pore sizes range b/w 3- 18 nm, which are in the Mesopore range.
L270: Average size should include the std. deviation. Else provide the size range of the mesospheres reported here.
L302: "....the photocatalysts (with mean pore diameters around 8-9 nm and pore sizes ranging 3-18) allow to consider ..." - Check it out.
L430: A micrograph of the TiO2-AC (before & after different processes) would be ideal to support the statement.
- Change the word "issue" in that statement too.
L459: "..the surface area decreases and the anatase content and crystallite size increase......." Increase in Anatase content in relative to temp. increase from 350 (76%) to 500 (78%) deg C is not significantly high. Considering inherent experimental error, it would be safe to say that the anatase % remains almost same in that temp. range. Authors could rephrase their conclusion.
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Reviewer 3 Report
The manuscript has been improved according to the suggestions of the Referees. The comparison with literature data in the diuron photodegradation with titania is still limited (results compared with only one manuscript) and in my opinion should be expanded. I understand that conditions are different and a comparison is difficult, but it will be important for understanding the novelty and improvements of the system described in the present manuscript. As a whole, if this point is addressed, the manuscript can be accepted for publication.
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