Photoelectrocatalytic Reduction of Cr(VI) in Wastewater with a CuBi₂O₄ Thin Film Photocathode

Round 1

Reviewer 1 Report

In this work, the authors used CuBi2O4 photocathodes for the photoreduction of Cr(IV) in wastewater. However, there are some other recent studies on CuBi2O4 where the material showed appreciable efficiency in dye degradation, pharma waste management, and Cr(IV) reduction (https://0-doi-org.brum.beds.ac.uk/10.1016/j.jwpe.2024.105074, https://0-doi-org.brum.beds.ac.uk/10.1016/j.colsurfa.2023.131389). The manuscript can be accepted after major changes. However, some of the specific comments for improvement are appended below.

Recommendation: Major Revision

1.     In the abstract, the line should be corrected as "Photoelectrocatalytic approaches show promise for contaminant removal in wastewater through redox reactions."

2.     The abstract lacks discussion about the material used for reduction, hindering a succinct overview of the research. Refer to the articles tagged  below

https://0-doi-org.brum.beds.ac.uk/10.1002/smll.202302692

3.     In the last paragraph of the introductory section the authors are suggested to justify the novelty of the present work by comparing the efficiencies to other reported works (recent works).

4.     Authors suggested conducting pH studies to determine the optimal conditions for photoreduction of Cr(IV) and photocurrent density studies aiding in understanding the material's performance.

5.     The work lacks the analysis of various factors that influence the photodegradation process mainly time and temperature.

6.     XPS data explanation is not sufficient.

7.     Include FTIR analysis which will help to understand the surface chemistry of the material.

8.     Enhance the schematic to vividly depict the innovative approach and its pivotal role in elucidating the optimal conditions for Cr(IV) reduction (Figure. 7).

9.     The authors are suggested to compare the performances (Include a table) of various photodegradation catalysts reported on the photocatalytic reduction efficiency of Cr(VI) in water.

10.  The manuscript exhibits a degree of repetition, with certain information reiterated multiple times.

11.  Efficiency of the material requires more clarity in conclusion, reframe the sentences in a more understandable way.

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this work, copper bismuth oxide photoelectrodes were synthesized and used in the photoelectrocatalytic reduction of Cr(VI). An important problem with this work is the lack of clarity regarding its novelty. According to the following comments, I believe it requires major revision before it can be considered for publication:

• Lines 19-20: There is no specific value for 97% since it is dependent upon the experimental conditions. The drinking standards are based on the concentrations, on the other hand.

The novelty of the work is unclear. Based on the literature review, it must be highlighted and strongly improved.

Lines 78-80: "However, these preparation methods can’t meet the requirements for designing photoelectrode structures to address low-concentration environmental pollutant scenarios". This statement must be clarified.

Line 82: "more suitable" indicates that literature reports are suitable, but that this work shows more suitable photoelectrodes!

Please provide the source of the used chemicals

Line 116: "we hypothesize ..." is there any evidence for this hypothesis?

How does adsorption affect the removal of Cr ions?

The mechanism illustration should be improved

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

I propose some additional experiments to improve the quality of presented results. My comments are as follow:

1.      This material was used for photoelectrocatalytic performance elsewhere:

https://0-pubs-rsc-org.brum.beds.ac.uk/en/content/articlelanding/2019/ta/c9ta07892d

https://0-www-ncbi-nlm-nih-gov.brum.beds.ac.uk/pmc/articles/PMC8001249/

https://0-www-mdpi-com.brum.beds.ac.uk/2304-6740/11/4/147

2.      Please provide some examples of recent applications of this material in the introduction section.

3.      Please indicate if there is something new in the procedure of CuBi2O4 synthesis.

4.      L 116 – you should compare the efficiency in reducing low concentrations of Cr(VI) with nanoporous and microporous material, then you could prove this hypothesis.

5.      Please calculate band gap of this material from Mott-schottky equation

6.      Fig 4. Please indicate conditions of the experiment of Cr (VI) reduction

7.      Fig 4a – this description could be misleading, you present the solution after reaction with DPD, not the solution which was used for reaction.

8.      L 274 – you observed that: the reduction efficiency gradually decreased, could you propose some way to eliminate this fact, eg. some washing step of electrode?

9.      Did you do some experiments of only photocatalytic or only electrocatalytic processes (in dark)? These experiments are needed to confirm the photoelectrocatalytic process accelerating the overall efficiency of Cr(VI) reduction.

Author Response

Please refer to the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revision has been done very extensively, so I recommend for the acceptance now.

Reviewer 2 Report

Can be accepted in the current version