Uncovering the Use of Fucoxanthin and Phycobiliproteins into Solid Matrices to Increase Their Emission Quantum Yield and Photostability

Round 1

Reviewer 1 Report

The manuscript titled “Uncovering the use of natural luminescent colorants into solid matrices to retain the long-term viability for solar energy harvesting and conversion” The authors fabricated R-phycoerythrin (R-PE), C-phycocyanin (C-PC), and fucoxanthin (FX) into poly (vinyl 24 alcohol) (PVA) and studied their optical properties before and after incorporation

I have some note regarding this manuscript:

1. the title is needed to be more informative; including the sample, condition (variable), and the outcome.
2. figures in the appendix should be within the text to be more interesting to the reader.

3. write the equation for emission quantum yield calculations.

4. Compare your results with others as in (1).

5. there are some long sentences which are not clear such as page 5 line 222-225.

6. there is no clear application for solar cell harvesting as mentioned in the title?

1. Hernández-Rodríguez MA, Correia SFH, Ferreira RAS, Carlos LD. A perspective on sustainable luminescent solar concentrators. J Appl Phys. 2022;131(14):140901.

Author Response

(variable), and the outcome.

Answer. The manuscript title was rewritten considering the referee’s suggestions.

Question 1.2. Figures in the appendix should be within the text to be more interesting to the reader.

Answer. Part of the figures in the appendix were included in the revised manuscript.

Question 1.3. Write the equation for emission quantum yield calculations.

Answer. The equation was included in the experimental section of the revised manuscript.

Question 1.4. Compare your results with others as in Hernández-Rodríguez MA, Correia SFH, Ferreira RAS, Carlos LD. A perspective on sustainable luminescent solar concentrators. J Appl Phys. 2022;131(14):140901.

Answer. We followed the suggestion, and the comparison was added.

Question 1.5. There are some long sentences which are not clear such as page 5 line 222-225.

Answer. The sentences were rephrased.

Question 1.6. There is no clear application for solar cell harvesting as mentioned in the title?

Answer. We apologize for the misleading title. Please see answer to question 1.1.

Reviewer 2 Report

This paper describes using natural fluorescent biomolecules in a organic host (PVA) as a luminescent solar concentrator (LSC) construction.  The goals of the paper are adequately stated and the results are honest and mostly clearly presented.  However, I have a few comments and points of concern I feel need to be addressed:

• I was surprised that for an LSC paper that no edge emission measurements have been taken.  This would seem a natural experiment, following the protocols suggested in the paper Energ. Environ. Sci. 2021, 14, 293-301, cited in the work.  This would make the potential of the device much more apparent, as comparison with the many devices described in the literature using internal and external efficiencies would become possible.  Care should be taken to use the appropriate sample sizes and conditions as described in the cited paper.
• p1, ln 38: "which are often non-recyclable thus becoming environmental  contaminants when disposed"  I guess this is true, but at the quantities included in LSCs (in the 30-100 ppm scale) is there really enough to be a major concern and selling point for the paper, especially as most LSCs use polymers, which are seemingly a much greater problem.
• p2, ln45: "whose performance under diffuse light conditions is an advantage."  I suggest adding a reference for this statement.
• p2, ln72: The sentence beginning "Other works using the encapsulation..." is incomplete.
• The efficiencies cause me to worry a bit, especially given the limited Stokes shift.  I think some comparison to existing dyes used in LSCs should be made for a realistic vision of the biodye's capabilities. 
• p7, ln291:  The 6 months in ambient were stored in a dark drawer or were they light-exposed during this time?
• p7, ln303: ..."exposure, pointing out the need to find new methodologies to avoid aggregation when incorporating the phycobiliproteins in solid matrices."  Is the loss of performance really continued aggregation, or is it oxidative/UV/other damage breaking down the dyes?  This possibility seems to be discounted without a reason.
• The decrease of performance of 40% after only 216 hours exposure is quite rapid: I think it fair to put this in context with other dyes described in the literature for transparency.
• How thick were are the samples?  What were their absorbances?  We only have the normalized values.
• p6, ln242: Wavelengths, therefore they are not 'larger' and 'smaller', but 'longer' and 'shorter'.

Author Response

General comment. This paper describes using natural fluorescent biomolecules in a organic host (PVA) as a luminescent solar concentrator (LSC) construction.  The goals of the paper are adequately stated and the results are honest and mostly clearly presented.

Answer. We thank the reviewer for the positive comment.

Question 2.1. I was surprised that for an LSC paper that no edge emission measurements have been taken. This would seem a natural experiment, following the protocols suggested in the paper Energ. Environ. Sci. 2021, 14, 293-301, cited in the work.  This would make the potential of the device much more apparent, as comparison with the many devices described in the literature using internal and external efficiencies would become possible.  Care should be taken to use the appropriate sample sizes and conditions as described in the cited paper.

Answer. We thank the reviewer for the pertinent comment. This manuscript focuses on the improvement of the processing and photostability of natural-based biomolecules and the optimization of a prototype was not addressed. Nonetheless, the dimensions were included in the revised manuscript.

Question 2.2. p1, ln 38: "which are often non-recyclable thus becoming environmental  contaminants when disposed"  I guess this is true, but at the quantities included in LSCs (in the 30-100 ppm scale) is there really enough to be a major concern and selling point for the paper, especially as most LSCs use polymers, which are seemingly a much greater problem.

Answer. The authors thank the referee comment. It seems reasonable to think that for example, the danger of synthetic dyes being applied in the textile industry is much higher that the impact that the ones applied in LSCs can have, which is true. However, for the compounds to have toxic effects the amount required for certain organisms, namely those in the aquatic compartment is certainly very low and sometimes even residual.  Indeed, the presence of synthetic dyes even at very low amounts can cause significant alterations in the ecological conditions of the aquatic fauna and flora because their non-biodegradable nature, which means a negative impact on the equilibrium of the aquatic environment. We can identify serious dangers, namely eutrophication, under-oxygenation, or turbidity, but also long-term problems such as persistence, bioaccumulation of carcinogenic aromatic products and the formation of by-products of chlorination), mutagenicity and carcinogenicity. We re-wrote the introduction of the manuscript to include this aspect.

Question 2.3. p2, ln45: "whose performance under diffuse light conditions is an advantage."  I suggest adding a reference for this statement.

Answer. A reference was added in the revised version of the manuscript.

Question 2.4. p2, ln72: The sentence beginning "Other works using the encapsulation..." is incomplete.

Answer. The sentence was rephrased in the revised version of the manuscript.

Question 2.5. The efficiencies cause me to worry a bit, especially given the limited Stokes shift.  I think some comparison to existing dyes used in LSCs should be made for a realistic vision of the biodye's capabilities. 

Answer. We thank the reviewer for the pertinent comment. Limited stokes shifts is a well-known disadvantage of organic dyes (synthetic and bio) compared with inorganic materials. We note that one of the proposed biodyes (FX) here reported displays a strong relative intensity absorption in the UV and emission in the red-spectral region, ensuring a large Stokes shift, enabling to predict larger efficiency for UV-excited LSCs. The manuscript was revised to include this discussion.

Question 2.6. p7, ln291:  The 6 months in ambient were stored in a dark drawer or were they light-exposed during this time?

Answer. This information was added in the revised version of the manuscript.

Question 2.7. p7, ln303: ..."exposure, pointing out the need to find new methodologies to avoid aggregation when incorporating the phycobiliproteins in solid matrices."  Is the loss of performance really continued aggregation, or is it oxidative/UV/other damage breaking down the dyes?  This possibility seems to be discounted without a reason.

Answer. This point was included in the revised version of the manuscript.

Question 2.8. The decrease of performance of 40% after only 216 hours exposure is quite rapid: I think it fair to put this in context with other dyes described in the literature for transparency.

Answer. Please see answer to question 1.4.

Question 2.9. How thick were are the samples?  What were their absorbances?  We only have the normalized values.

Answer. The absorption spectra of the solutions were included in the new Figure 2 of the revised manuscript and the absorption coefficient was estimated. For the polymeric samples, the excitation spectra were included, new Figure 3b.

Question 2.10. p6, ln242: Wavelengths, therefore they are not 'larger' and 'smaller', but 'longer' and 'shorter'.

Answer. This was corrected in the revised version of the manuscript.

Round 2

Reviewer 2 Report

The authors have responded to all my comments to my satisfaction.  I do note an error they may wish to repair: in the SI table S1, instead of an 'eta' there is an 'H' as header for quantum yield.