Dynamic Light Scattering: A Powerful Tool for In Situ Nanoparticle Sizing

Round 1

Reviewer 1 Report

The review on Dynamic light scattering for in-situ nanoparticle sizing is very well written. However it requires some improvements in the discussion. Please see my comments below,

1.       The authors need to check carefully all the sentences, for example in line 65, 109-115, 133, 135-136, 141…

2.       Line 124 ACF need to be defined prior to using the short notation.

3.       If there are any disadvantages to DLS, the authors may discuss about them.

4.       Does DLS measurement depends on the wavelength of the input laser. Also, how the laser fluctuations and particle shape influence DLS measurements.

5.       The influence of double and multiple light scattering events in the estimation of particle size need to be discussed.

6.        Does the refractive index of the solvent effect the DLS measurement, i.e. would measuring the particle size in different solvents produce the same result?

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper  “Dynamic light scattering: a powerful tool for in-situ nanoparticle sizing” was submitted to Colloids and Interfaces for review.

General observations:

In this manuscript, the authors focus on in-situ size characterization of metal oxide nanoparticles (MONs). They detail the measurement principle and the instrument design of DLS, as its advantages and limitations. Ex-situ and in-situ configuration of DLS, sample preparations, measurement conditions and reaction cell design for in-situ configuration were addressed.

The English language and style are correct, only minor spelling are required.

The manuscript is of quality, clear, well documented with many relevant references. However, some details about the theory and the results obtained by DLS are missing. For example, although the authors introduce the hydrodynamic radius, they do not discuss the Z-average (Zav), the intensity-weighted average diameter calculated from the cumulant analysis, that is often used as the hydrodynamic radius. Therefore, for all of the above reasons and my suggestions that follow, I cannot recommend publication of this work in Colloids and Interfaces before a minor revision.

Observations and comments:

Title:

The title chosen by the authors is too general as confirmed by what is written in lines 81-82 p.2 “In this review, we focus on in-situ measurement of 80 MONs’ size in the sol-gel process”. In order for the readers to have a better idea of what the review is about, and also to differentiate from other reviews I suggest to add the notion of “sol-gel process”. For example, the tittle could be “Dynamic light scattering: a powerful tool for in-situ nanoparticle sizing of sol-gel process”.

Introduction:

Line 31 p.1 : “great” is better than “enormous”.

Lines 61-62 p.2 :  “The energy of the photogenerated charges increases with the decrease of the size of the particles” is better.

Lines 62-63 p.2 : last sentence of the paragraph can be removed.

Lines 64-65 : the first sentence of the paragraph is confusing, please rephrase it.

Line 70 p.2 : Damkohler numbers are not obvious to all DLS users, please add a short definition to know what we are talking about here.

Line 79 p.2 : others references should be added as https://doi.org/10.1016/j.jconrel.2016.06.017 and 10.5281/zenodo.6484683.

Measuring principle:

Lines 102-107 p.3 : Other limitations can be encountered with DLS as “ghost peaks” from bubbles, opalescent and reflective particles, optical model … See chapter 3 in Size analysis of dispersion in liquid phase (10.5281/zenodo.6484683).

Lines 109-115 p.3 : it would be better to focus on DLS and not mention SLS to avoid confusion.

Lines 116-121 and fig.1 p. 3 : the description of the DLS can be improved just like Fig.1, with for example the intensity versus time curve at different times to better understand how the correlation versus time is constructed (see the references suggested above).

Line 133 p. 4 : “autocorrelation”.

Line 136 p.4 : add at least another reference.

Instrument design:

Line 153 p. 4 : it would be better to indicate the volume in microliter or nanoliter.

Lines 152-157 p.4 : The authors should also comment about the problem of low concentration to evaluate correctly the size distribution.

Line 177 p.5 : since the Tyndall effect is not as well-known as Rayleigh scattering, a brief description of this effect should be included.

Table 2 : In reference 41, the cell is designed to allow experiments up to 450°C but the results presented in the article are for temperature up to 275°C. As it is very rare to perform tests at such a high temperature, it would be more appropriate to indicate the temperature limit of the results rather than that of the cell, unless the authors know of a reference that presents results up to 450°C.

Catalysts preparation monitored by DLS

Line 224 p.7 : “The DLS measurement often overestimate the particle size compared to TEM”, the results of DLS and TEM are simply different as the same parameter is not being measured. It's quite ordinary to have discrepancies between techniques. Conventionally, the number-based core size average is measured using TEM as opposed to the intensity-based hydrodynamic size estimated from DLS. So, it is complicated to compare number-based and intensity-based diameter. Although the authors explain the reason for the differences between these 2 technics, they must specify that it is not the same parameters that are measured .

Also, the authors do not comment on how the hydrodynamic diameter is obtained. It is very important to specify if in the different articles it is the Z-average number that is reported. Moreover, an explanation should be given earlier  in the manuscript to explain this number and what is the difference with the obtained size distribution (see chapter IV in 10.5281/zenodo.6484683).

Line 229 p.7 : “ a large number of particles”.

Line 312 p.19 : please define “at.%”.

Line 414 p.12 : “nanorods”.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Attached.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has undergone a major improvement with the inclusion of all relevant information about the demonstration of the experiment and the application of DLS in various catalysts. However, I would suggest enhancing the quality of the figures. For example, in Figure 1, it would be helpful to include units for the x and y-axes.

Reviewer 3 Report

A great work was done by the authors, and the reviewers' comments were properly taken into account.