Comments on title, abstract and references

The title is informative and relevant. The abstract was written in simple and understandable sentences. The aim and the result of the study are clear. However, there are some things that need further clarifications or be addressed: 1. The author mentioned that the oxalate complex was analyzed by thermal gravimetric analysis and FTIR. There was no FTIR spectrum and DTA curve for the oxalate complex provided in the manuscript. Those data were only prepared for the synthesized complex. What purpose would this analyze served if they were actually performed on the staring oxalate complex? Verify the integrity of the oxalate starting material? The author needs to address or correct this deficiency. 2. The statement about the reduction progress being controlled by Uv-vis absorption should have been the reduction progress was monitored by Uv-vis because based on the supplied experimental data, there is no stipulation that the reduction reaction was controlled by Uv-vis absorption. There are some irregularities in the reference formatting. Some of the publication years are bolded and the others are not. The citation format needs to be made uniform.

Comments on introduction/background

There is no research question. What was already known about the applications of NiMoO4 was highlighted but information about other catalysts that were used in the reduction of nitrophenols and their limitations that warrants the need for a better catalyst (the proposed NiMoO4) was/were not mentioned. Making this correction will create a logical flow in the introduction.

Comments on methodology

The methods employed in this research is reasonable. However, the following points need to be put into consideration and attended to improve the content of the manuscript: 1. There is no information about the sources of the chemicals used in this research in terms of the vendor, the grade and if any further purifications were performed before usage. 2. Was the NaBH4 tried at different concentration to see the effect of this reductant at different concentrations on the reactions?
3. There is no information about the amount of NiMoO4 used in the catalytic reaction. Was there any optimization performed to determine the optimum amount of NiMoO4 that should be used for each reaction? This needs to be mentioned in the manuscript. 4. Also, were the obtained reduced products characterized? They need to be confirmed by techniques such as mass spectrometry and FTIR and the data needs to be provided in the manuscript. 5. I will also recommend performing kinetic experiments. This will boost the relevancy of this scientific research and make it more insightful. 6. It is obvious that the NiMoO4 is a solid catalyst. Can it be recovered and reused after a reaction cycle. If so, how many times can it be recycled before the activity drop significantly? 7. Can information be provided on the % conversion? I believe if these points are attended to, it will improve the method/content of this manuscript. 8. There are some typos in the paper: a. The chemical equation on line 47 showing the water of crystallization should be '.' instead of ',' b. The degree sign is missing from the temperature value of 160 degree Celsius on line 52 c. Table 1 caption on line 154 should have 4-Np as 4-NP to keep the consistency in the abbreviation.

Comments on data and results

The Figures need to be relabelled and captioned properly. 1." Fig. 2. Fourier transform infrared spectrum of the synthesized complex". should be FTIR spectrum of the synthesized precursor complex from nickel nitrate, ammonium molybdate, and oxalic acid in the molar ratio 1 /0.143 /10. Or the author can label the precursor complex and keep using that label to refer to the precursor complex. The same correction applies to Fig. 3. 2. Fig. 3. The two arrows should be removed because they are confusing. They look like they are pointing to values on each of the y-axes whereas they are pointing the attention of the reader to the corresponding axes for each of the curves. A better way to do this is to change the axes line to the colors of the corresponding curves. 3. Fig 6. caption needs to be relabelled to show that it includes the catalyst. 4. Fig 7. caption needs to be relabelled to show that it does not include the catalyst.

Comments on discussion and conclusions

1. The conclusion at the molecular formula (NH4)NiMoO(C2O4)2(OH).H2O based on the information obtained from only FTIR and thermogravimetric analysis is ambiguous. This information is not enough to suggest a molecular formula because the compound might be non-stoichiometric. Elemental CHN analysis and atomic absorption or emission spectroscopy would be useful to confirm the formula suggested.
2. There is no information about the bands at ca. 260 nm in Fig.6b-c. what could be responsible for that band and why is it absent in Fig. 6a?
3. The weight losses mentioned in the discussion needs to be shown through labelling in Fig. 3 to guide readers through the understanding of the thermogravimetric curve.