Thin-Film Nanocrystalline Zinc Oxide Photoanode Modified with CdO in Photoelectrocatalytic Degradation of Alcohols
, Victor V. Emets, Alexander D. Modestov *, Aleksey A. Averin and Andrei A. Shiryaev
Round 1
Reviewer 1 Report
ZnO photoanode is not a very new topic. The doping of CdO in ZnO is seldom reported. However, the author didn;t state the importance of his work, neither the novelty. Cd is a toxic element. What is the specific reason for usage of Cd as doping elements? In the introduction, the scientific question to be addressed by this work should be clearly stated. This work needs major revision before acceptance.
1. Line 45, Page 1, the grammar needs revision.
2. Equation 1 in page 2, should be double checked. Whether this reaction occurs or the completive hydrogen reduction reaction?
3. Figure 2, the label in x axis is too rough to tell the peaks at 233cm-1 , 264 cm-1and 364 cm-1 c, which should be marked in the figure.
4. Line 214-217, there are some extra space in the sentence.
5. Figure 4, the number labels should be 0.4 instead of 0,4.
6. In figure caption of Line 242 and 262, the <dark> should be dark.
7. Line 300, the PEC current for hematite should be much higher than 0.25 mA/cm2. There are many refs for hematite photoanodes.
8. The i-t curve is suggested.
Some grammar should be improved.
Author Response
Response to the Reviewers’ comments
Reviewer 1.
Recommendation: This work needs major revision before acceptance.
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks.
ZnO photoanode is not a very new topic. The doping of CdO in ZnO is seldom reported. However, the author didn’t state the importance of his work, neither the novelty. Cd is a toxic element. What is the specific reason for usage of Cd as doping elements? In the introduction, the scientific question to be addressed by this work should be clearly stated. This work needs major revision before acceptance.
Response. We changed the Introduction section. The known works on photoelectrolysis with ZnO/CdO system deal with water splitting accompanied by oxygen evolution. The novelty of our work consists in modification of ZnO thin film photoelectrode by incorporation of CdO as a solid solution in ZnO lattice. The produced photoanodes were used for photoassisted electrochemical degradation of model organic pollutants.
Minor addition of CdO to ZnO does not contaminate aqueous electrolyte. It is proved by chronoamperometric curves of ZnO/(0.05C)CdO/FTO which show no decrease of photocurrent with time at constant potentials. The curves were measured in the presence of glycerin in 0.5M Na2SO4 electrolyte. The curves are shown in S.5 (supplementary materials). Stability in time of photocurrent is evidence of chemical stability of ZnO/(0.05C)CdO/FTO photoanode.
Amendments were made in page 11 of the corrected manuscript.
We agree with the Reviewer that cadmium salts are very toxic and should be handled with great care. However, CdO is not toxic because it does not dissolve in water and is chemically stable in the environment. To prove it we cite the opening sentence of the article published in Nature [R. P.Lefojane, B. T. Sone, N. Matinise, K. Saleh, P. Direko, P. Mfengwana, S. Mashele, M. Maaza, M.P. Sekhoacha, CdO/CdCO3 nanocomposite physical properties and cytotoxicity against selected breast cancer cell lines. Scientific Reports (2021) 11, 30]:
“Cadmium Oxide nanoparticles have the lowest toxicity when compared to nanoparticles of other semiconductors and they are not detrimental to human and mammalian cells, thereby making them candidates for targeting cancer cells”.
Remark 1. Line 45, Page 1, the grammar needs revision.
Response. Grammar mistakes were corrected.
Remark 2. Equation 1 in page 2, should be double checked. Whether this reaction occurs or the completive hydrogen reduction reaction?
Response. The equations were checked. This reaction path was proposed in ref. [26]. However, we agree that hydrogen evolution at the electrode will cause similar results.
Remark 3. Figure 2, the label in x axis is too rough to tell the peaks at 233 cm-1, 264 cm-1, and 364 cm-1 c, which should be marked in the figure.
Response. In the corrected manuscript this figure is Fig. 3. The peaks, which are characteristic to ZnO, are marked in the corrected manuscript. The peaks indicated by the Reviewer are hardly discernible in Fig.3. The most prominent of ZnO peaks is at 438 cm-1. The are no peaks corresponding to pure CdO in Ramman spectrum. Ideal stoichiometric cubic CdO does not possess Raman-active vibrations, however, deviations from stoichiometry (e.g., oxygen vacancies) may lead to appearance of Raman peaks at 233cm-1, 264 cm-1and 364 cm-1 [31]. Even if present, these peaks are very weak and may be very difficult to observe on strong background from ZnO and glass substrate. The absence of CdO in Raman spectra was also observed in ref. [32] Senthil, Y.T. K.; Seol, M.; Yong, K. Synthesis and Characterization of ZnO Nanowire–CdO Composite Nanostructures. Nanoscale 488 Res. Lett. 2009,4, 1329-1334. Explanations were placed in pages 6 and 7.
Remark 4. Line 214-217, there are some extra space in the sentence.
Response. Correction was made.
Remark 5. Figure 4, the number labels should be 0.4 instead of 0,4.
Response. Correction was made in Fig. 5 (former fig. 4)
Remark 6. In figure caption of Line 242 and 262, the <dark> should be dark.
Response. Correction was made in Fig. 5
Remark 7. Line 300, the PEC current for hematite should be much higher than 0.25 mA/cm2.
There are many refs for hematite photoanodes.
Response. This point is discussed in lines 319-325 (amended version). The difference in photocurrent values cited in our work and given in refs. [1, 39, 40] originates from difference of total measured photocurrent, which includes photocurrent of water oxidation and oxidation of organic species, and partial photocurrent of oxidation of organic species. In [1, 39, 40] total photocurrent values are given. Apparently, partial photocurrent of oxidation of organic species is lower than total photocurrent.
Remark 8. The i-t curve is suggested.
Response. We added curves in Supplementary materials Figure S5. I-t curves of film photoanode ZnO/(0.05)CdO/FTO at various bias potentials (1) 0.4 V and (2) 0.62 V vs. Ag/AgCl in 0.5 M Na2SO4 + 20% C3H5(OH)3 under visible light illumination with a power density of 100 mW cm‑‑2.
Reviewer 2 Report
In this manuscript, the authors prepared the ZnO/CdO/FTO photoanode for photoelectrocatalytic degradation of alcohols. Although the author claimed the coating of CdO on the ZnO could effectively improve the electron-hole pairs recombination and enhance the rate of photo-induced charge transfer. Therefore, the manuscript still lacks the necessary data supports overall. I do not recommend that the manuscript could be accepted as it is.
1.First of all, in the XRD patterns, there is no evident diffraction peaks for the coating layer of CdO. The authors claimed that the CdO is doped in the ZnO. Not Convincing!
2.Necessary TEM and SEM images is strongly recommended, as well as the EDS mapping.
3.Using the Normalized IMPS dependences to investigated the photoelectrocatalytic degradation of alcohols is insufficient.
4.The band alignment figure should be provided.
5.The reason for choosing the 0.8, 0.1 and 0.05 C cm-2 in electric units should be explained. The gap is too big.
I have no comment in the Quality of English Language.
Author Response
Response to the Reviewers’ comments
Reviewer 2.
Recommendation: I do not recommend that the manuscript could be accepted as it is.
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks
In this manuscript, the authors prepared the ZnO/CdO/FTO photoanode for photoelectrocatalyticdegradation of alcohols. Although the author claimed the coating of CdO on the ZnO could effectively improve the electron-hole pairs recombination and enhance the rate of photo-inducedcharge transfer. Therefore, the manuscript still lacks the necessary data supports overall. I do not recommend that the manuscript could be accepted as it is.
Remark 1. First of all, in the XRD patterns, there is no evident diffraction peaks for the coating layer of CdO. The authors claimed that the CdO is doped in the ZnO. Not Convincing!
Response. Indeed, there are no peaks of CdO as a separate phase in XRD patterns. This is explained by formation of a solid solution of CdO in ZnO. Discussion about the absence of CdO in XRD as a separate phase is given in lines 186-240 (amended version)
Remark 2. Necessary TEM and SEM images is strongly recommended, as well as the EDS mapping.
Response. In a short time given by the Editors we are unable to repair SEM/TEM instruments of our institution. We are also unable to arrange for measurements outside. To compensate partially for this, we conducted X-ray fluorescence mapping of distribution of Cd and Zn over the surface of the photoanode. Results and discussion are given in lines 210-215 and Fig. 2
Results of the XRF mapping confirm uniform deposition of both Zn and Cd.
Remark 3. Using the Normalized IMPS dependences to investigated the photoelectrocatalytic degradation of alcohols is insufficient.
Response. Example of experimental IMPS curve is shown in Supplementary materials, fig. S6. It was measured using ZnO/(0.05C)CdO/FTO film photoanode illuminated with monochromatic light 407 nm wavelength in 0.5 M Na2SO4. This curve was not normalized. Similar IMPS measurements were performed using для ZnO/(0.05) CdO/FTO photoanode in the presence of methanol, ethylene glycol, and glycerol. In this case the curves were normalized to determine rate constants of hole recombination and charge transfer to the adsorbed species. The dependences of photocurrent under illumination by light of constant intensity are shown in figs. 5, 7, and S.5 (supplementary materials).
Remark 4. The band alignment figure should be provided.
Response. Band alignment for ZnO/CgO heterojunction was reported in a number of works, e.g. [A. Bera, R. Thapa, K.K. Chattopadhyay, B. Saha, In plane conducting channel at the interface of CdO–ZnO isotype thin film heterostructure, Journal of Alloys and Compounds 632 (2015) 343–347] shown below.
In plane
However, we could not find evidence of formation distinct layer of CdO on top of ZnO. Therefore, we assume that solid solution of CdO in ZnO was formed at the surface with gradient of CdO concentration. In this case energy band diagram is not obvious for us. Most probably CdO will form impurity levels within the band gap of ZnO.
Remark 5. The reason for choosing the 0.8, 0.1 and 0.05 C cm-2 in electric units should be explained. The gap is too big.
Response. Indeed, our choice of CdO doping level is partly arbitrary. According to our measurements addition of CdO to ZnO extends light absorption of ZnO based oxide into visible range. It is a positive influence of CdO. On the other hand, addition of excessive amount of CdO to ZnO reduces photocurrent generation, apparently due to increased rate of recombination. It is a negative influence. We did not try to find optimal level of doping because we believe that there are too many parameters which could be optimized. Since the system is very far from real pilot plant stage.
Reviewer 3 Report
This work investigated the preparation of CdO modified ZnO photoanode, and its photoelectrocatalytic degradation performance for alcohols. Some results are positive. However, the following issues should be considered before I recommend it be published.
1. The Raman peaks related to ZnO and CdO could be marked In Figure 2, which will be convenient for the readers to grasp the important information from Figure 2.
2. In Figure 4, it seems that with decreasing from 0.8 C cm-2 to 0.05 C cm-2, the current increased from ZnO/(0.8)CdO/FTO to ZnO/(0.05)CdO/FTO. Why not continue to decrease CdO content?
3. How was the stability of ZnO/(0.05)CdO/FTO for the photoelectrocatalytic degradation of alcohols ?
4. More characterization such as SEM, TEM and active species capture experiment could be conducted to enrich the work.
Only minor editing of English language is required.
Author Response
Response to the Reviewers’ comments
Referee 3. Recommendation: However, the following issues should be considered before I recommend it be published.
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments, which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks
This work investigated the preparation of CdO modified ZnO photoanode, and its
photoelectrocatalytic degradation performance for alcohols. Some results are positive. However,
the following issues should be considered before I recommend it be published.
Remark 1. Raman peaks related to ZnO and CdO could be marked In Figure 2, which will be convenient for the readers to grasp the important information from Figure 2.
Response. In the corrected manuscript this figure is Fig. 3. The peaks, which are characteristic to ZnO, are marked in the corrected manuscript. The are no peaks corresponding to pure CdO in Ramman spectrum. Ideal stoichiometric cubic CdO does not possess Raman-active vibrations, however, deviations from stoichiometry (e.g., oxygen vacancies) may lead to appearance of Raman peaks at 233cm-1, 264 cm-1and 364 cm-1 [31]. Even if present, these peaks are very weak and may be very difficult to observe on strong background from ZnO and glass substrate. The absence of CdO in Raman spectra was also observed in ref. [32] Senthil, Y.T. K.; Seol, M.; Yong, K. Synthesis and Characterization of ZnO Nanowire–CdO Composite Nanostructures. Nanoscale 488 Res. Lett. 2009,4, 1329-1334. Explanations were placed in pages 6 and 7.
Remark 2. In Figure 4, it seems that with decreasing from 0.8 C cm-2 to 0.05 C cm-2, the current
increased from ZnO/(0.8)CdO/FTO to ZnO/(0.05)CdO/FTO. Why not continue to decrease CdO content?
Response. Response. Indeed, our choice of CdO doping level is partly arbitrary. According to our measurements addition of CdO to ZnO extends light absorption of ZnO based oxide into visible range. It is a positive influence of CdO. On the other hand, addition of excessive amount of CdO to ZnO reduces photocurrent generation, apparently due to increased rate of recombination. It is a negative influence. We did not try to find optimal level of doping because we believe that there are too many parameters which could be optimized. The system is very far from pilot plant stage.
Remark 3. How was the stability of ZnO/(0.05)CdO/FTO for the photoelectrocatalytic degradation of alcohols ?
Response. According to published works stability of ZnO/CdO photoanode is quite high.
We proved the stability of ZnO/(0.05)CdO/FTO photoanode by chronoamperometric measurements. Figure S5 shows I-t curves of film photoanode ZnO/(0.05)CdO/FTO at potentials 0.4 V and 0.62 V vs. Ag/AgCl in 0.5 M Na2SO4 in the presence of 20% C3H5(OH)3. Curves were measured under visible light illumination with a power density of 100 mW cm-2. There are no visible changes of photocurrent in 30-minute experiment. This diagram is added to the revised Supplementary Materials.
Reviewer 4 Report
In this paper, a method of preparing thin-film ZnO/CdO/FTO composite photoanodes by electrochemical deposition of oxides on FTO glass substrate is proposed, which provides a new idea for improving the characteristics of zinc oxide based photochemical devices, and the photochemical degradation ability and promoting mechanism of the composite electrode are studied in detail. However, some modifications should be done. Therefore, this manuscript could be accepted after minor revision
1.The author should add more explanations for the phenomenon that excessive modification of ZnO by CdO leads to a decrease in the photocurrent density of water oxidation
2. Some picture numbers appear in italics, for example figure 1. (1) and figure 3. (1) and (2).
3.The font size and thickness of horizontal and vertical coordinates in figure 3. (a) are different from those in other figures
4. Line 255, figure 6 should be figure 5.
Minor editing of English language required
Author Response
Response to the Reviewers’ comments
Referee 4. Recommendation: This manuscript could be accepted after minor revision
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks
In this paper, a method of preparing thin-film ZnO/CdO/FTO composite photoanodes by electrochemical deposition of oxides on FTO glass substrate is proposed, which provides a new idea for improving the characteristics of zinc oxide based photochemical devices, and the photochemical degradation ability and promoting mechanism of the composite electrode are studied in detail. However, some modifications should be done. Therefore, this manuscript could be accepted after minor revision.
Remark 1. The author should add more explanations for the phenomenon that excessive modification of ZnO by CdO leads to a decrease in the photocurrent density of water oxidation.
Response. Response. According to our measurements addition of CdO to ZnO extends light absorption of ZnO based oxide into visible range. It is a positive influence of CdO. On the other hand, addition of excessive amount of CdO to ZnO reduces photocurrent generation, apparently due to increased rate of recombination of photogenerated holes. It is a negative influence. We did not try to find optimal level of doping because we believe that there are too many parameters which could be optimized. The system is too far from pilot plant stage.
Remark 2. Some picture numbers appear in italics, for example figure 1. (1) and figure 3. (1) and (2).
Response. Corrected.
Remark 3. The font size and thickness of horizontal and vertical coordinates in figure 3. (a) are different from those in other figures.
Response. Corrected.
Remark 4. Line 255, figure 6 should be figure 5.
Response. Corrected.
Reviewer 5 Report
In the present work, the authors reported the fabrication of the ZnO electrode coated with CdO through electrochemical deposition. The as-prepared electrode exhibited high efficiencies in the photodegradation of different alcohols, such as methanol, ethylene glycol and glycerol, under sunlight. This resulted from the suppression of charge recombination and increased charge transfer. Some revision is needed before processing the next steps.
1. In Section 2, a schematic illustration of the system employed for the electrochemical deposition should be provided for the readers to understand the current work better.
2. SEM coupled with EDX (or elemental mapping) analysis should be performed to observe the morphological structure and identify the composition of prepared electrodes. As CdO was formed as a layer on the surface of ZnO, a side-view via SEM analysis of the prepared electrode may provide the observation of the CdO-ZnO interface.
3. In addition to XRD and Raman, XPS analysis should be performed to verify the oxidation states of Cd, which provides valuable information to confirm the formation of CdO.
4. In line 315, "Results are shown in Fig.7" instead of Fig. 6.
5. The photodegradation mechanism should be discussed along with a schematic illustration in the manuscript.
There are some gramatical errors in the text, which need to be corrected.
Author Response
Response to the Reviewers’ comments
Referee 5. Recommendation: Some revision is needed before processing the next steps.
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments, which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks.
In the present work, the authors reported the fabrication of the ZnO electrode coated with CdO through electrochemical deposition. The as prepared electrode exhibited high efficiencies in the photodegradation of different alcohols, such as methanol, ethylene glycol and glycerol, under sunlight. This resulted from the suppression of charge recombination and increased charge transfer. Some revision is needed before processing the next steps.
Remark 1. In Section 2, a schematic illustration of the system employed for the electrochemical deposition should be provided for the readers to understand the current work better.
Response. A photo of the three-electrode cell which was used for electrodeposition of of ZnO and CdO on FTO-coated glass slide is shown in Supplementary materials as S.1. Part of the FTO slide, which is not intended for oxide deposition, is isolated by a Teflon frame.
Remark 2. SEM coupled with EDX (or elemental mapping) analysis should be performed to observe the morphological structure and identify the composition of prepared electrodes. As CdO was formed as a layer on the surface of ZnO, a side-view via SEM analysis of the prepared electrode may provide the observation of the CdO-ZnO interface.
Response. In a short time given by the Editors we are unable to repair SEM instruments of our institution. We are also unable to arrange for measurements outside. To compensate partially for this, we conducted X-ray fluorescence mapping of distribution of Cd and Zn over the surface of the photoanode. Results and discussion are given in lines 210-215 and Fig. 2. Results of the XRF mapping confirm uniform deposition of both Zn and Cd. Results of the EDS mapping confirming deposition of both Zn and Cd are added.
Remark 3. In addition to XRD and Raman, XPS analysis should be performed to verify the oxidation states of Cd, which provides valuable information to confirm the formation of CdO.
Response. Indeed, XPS may provide information about valence of Cd. In our work, we do not claim that CdO was formed as an individual phase. Most likely, it is present as a solid solution in ZnO. Results and discussion are given in lines 210-215 and Fig. 2. Results of the XRF mapping confirm uniform deposition of both Zn and Cd. Results of the EDS mapping confirming deposition of both Zn and Cd are added.
Remark 4. In line 315, "Results are shown in Fig.7" instead of Fig. 6.
Response. Corrected.
Remark 5. The photodegradation mechanism should be discussed along with a schematic illustration in the manuscript.
Response. We agree with Reviewer. However, to sketch even primitive mechanism of alcohol degradation one needs analysis of products. Knowledge of stable products can give only vague clue to that problem. We are currently not in position to speculate about particular oxidation paths and oxidation products. Nonetheless, analysis of products is a subject of our future work.
Reviewer 6 Report
This work examines the modification of ZnO with CdO to enhance the photoelectrochemical efficiency for decomposing various alcohols. The topic pertains to coatings; however, it requires substantial revisions before publication.
Specific points:
Photoelectrochemical experiments: The authors should perform actinometry to determine the actual power inside the reactor, expressed as Einstein/sec.
Considering the various materials available in the literature for modifying ZnO, it would be beneficial for the authors to explain why they specifically chose Cd, despite its well-known toxicity.
Another crucial aspect missing from the study is the stability of the prepared material, both in terms of mechanical properties of the film and the observed efficiency or current relationship. This information is vital for a comprehensive understanding.
Including SEM images would provide valuable additional information and engage the reader, as the surface characteristics and morphology of the material are currently unknown.
minor
Author Response
Referee 6. Recommendation: it requires substantial revisions before publication.
We are grateful to the Reviewer for careful reading of the manuscript, valuable comments, which were made, and high evaluation of our work. We agree with all the comments and respond by corrections of the manuscript. The amendments which were made undoubtedly improved readability and quality of the manuscript. The amendments are highlighted by red color.
General remarks.
This work examines the modification of ZnO with CdO to enhance the photoelectrochemical efficiency for decomposing various alcohols. The topic pertains to coatings; however, it requires substantial revisions before publication.
Remark 1. Photoelectrochemical experiments: The authors should perform actinometry to determine the actual power inside the reactor, expressed as Einstein/sec.
Response. There are few points here.
- The actual power of light that hits the ZnO/CdO layer was measured by placing Nova instrument (OPHIR-SPIRICON Inc., Israel) just behind the uncoated FTO slide. The difference between powers of incident light and of light that passed through the FTO slide is mostly due to reflectance. It is of the order of only few percent. This correction was made in all experiments.
- In some experiments, namely shown in Figure 7, 8, S.6, monochromatic light source was used.
In this case photon flux was easily calculated dividing light power (measured by OPHIR-SPIRICON instrument) by photon energy. It was done.
- In experiments with simulated sun irradiation calculation of photon flux is nearly useless because only small fraction of light causes excitation of holes in the valence band.
Remark 2. Considering the various materials available in the literature for modifying ZnO, it would be beneficial for the authors to explain why they specifically chose Cd, despite its well-known toxicity.
Response. We selected CdO for modification of ZnO because it enables to extend light absorption of ZnO into visible range light spectrum. We agree with the Reviewer that cadmium salts are very toxic and should be handled with great care. However, CdO is not toxic because it does not dissolve in water and is chemically stable in the environment. To prove it we cite the opening sentence of the article published in Nature [R. P. Lefojane, B. T. Sone, N. Matinise, K. Saleh, P. Direko, P. Mfengwana, S. Mashele, M. Maaza, M. P. Sekhoacha, CdO/CdCO3 nanocomposite physical properties and cytotoxicity against selected breast cancer cell lines. Scientific Reports (2021) 11, 30]:
“Cadmium Oxide nanoparticles have the lowest toxicity when compared to nanoparticles of other semiconductors and they are not detrimental to human and mammalian cells, thereby making them candidates for targeting cancer cells”.
Remark 3. Another crucial aspect missing from the study is the stability of the prepared material, both in terms of mechanical properties of the film and the observed efficiency or current relationship.
Response. According to published works stability of ZnO/CdO photoanode is quite high. We proved stability of ZnO/(0.05)CdO/FTO photoanode by chronoamperometric measurements. Figure S5 (revised Supplementary Materials) shows I-t curves of film photoanode ZnO/(0.05)CdO/FTO at potentials 0.4 V and 0.62 V vs. Ag/AgCl in 0.5 M Na2SO4 in the presence of 20% C3H5(OH)3. Curves were measured under visible light illumination with a power density of 100 mW cm-2. There are no visible changes of photocurrent in 30-minute experiment.
We did not conduct measurements of mechanical properties of oxide films and have no instruments for this. We can only state that we did not observe peeling off of oxide layers from the FTO glass slides or even minor changes of shape of photoanodes in experiments.
Remark 4. This information is vital for a comprehensive understanding. Including SEM images would provide valuable additional information and engage the reader, as the surface characteristics and morphology of the material are currently unknown.
Response. In a short time given by the Editors we are unable to repair SEM/TEM instruments of our institution. We are also unable to arrange for measurements outside. To compensate partially for this, we conducted X-ray fluorescence mapping of distribution of Cd and Zn over the surface of the photoanode. Results and discussion are given in lines 210-215 and Fig. 2 (revised manuscript). Results of the XRF mapping confirm uniform deposition of both Zn and Cd.
Round 2
Reviewer 1 Report
The questions have been addressed and can be accepted for publication.
Reviewer 2 Report
The authors made some revisions with the manuscript. It could be acceptable.
Reviewer 3 Report
It is OK to me.
Reviewer 5 Report
The authors have revised the manuscript with appropriate corrections. I recommend publication of this work in its present form.
Reviewer 6 Report
The authors improved their work according to the suggestions
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