Use of Ethylamine, Diethylamine and Triethylamine in the Synthesis of Zn,Al Layered Double Hydroxides
Round 1
Reviewer 1 Report
Dear Authors,
In my personal opinion, the work is of great interest for the synthesis of ionic solids. The synthesis process of the compounds is described sufficiently for a repeatable synthesis. A comprehensive analysis of the obtained LDH demonstrates the effectiveness of the selected agents (EA, DEA, TEA). The resulting Zn-Al-NO3 compounds may find use as a drug delivery system.
Author Response
Thank you very much for your comments.
Reviewer 2 Report
The work deals with the synthesis of Zn2Al-LDHs using various organic amines as precipitant agents. The authors applied several characterization techniques (XRD, ICP-OES, PSD, FT-IR and surface/textural analysis), some part of the work is maybe of interest, especially the application of microwave radiation as help for the crystallization of the LDHs, but the manuscript in its present form requires revision.
1. There are some missing important technical information; the volume of the applied aqueous solutions of the nitrate metal salts and the amines, the atmosphere of the drying of the LDHs, the type of the used accessory for the FT-IR analysis (DRS or transmission), for the PSD measurements the temperature of the analysis and the concentration of the dispersions obtained.
2. Some small typing errors found: H2O in line 102, ¿LDH? in Table 1, ν3 and ν2 in line 325, ν1 and ν4 in line 327, precipitatn in line 335.
3. For the assignation of the reflections on the X-ray diffraction patterns (Figure 1, 2, 3), the reviewer would like to see the used references or crystal database cards.
4. For the interpretation of the thermal behaviours (Fig. 5, 6), the atmosphere used is not signed, N2 or O2?
5. It is not clear why the use of ethylamine did not result in LDH formation in conventional hydrothermal treatments, but did in microwave hydrothermal treatments. It should be discussed.
Author Response
The authors give thahks to reviewer for the coments. In our oppinion the manuscript will be improve after this considerations.
The answers and comentaries to the questions are incluided bellow, after the original question.
- There are some missing important technical information; the volume of the applied aqueous solutions of the nitrate metal salts and the amines, the atmosphere of the drying of the LDHs, the type of the used accessory for the FT-IR analysis (DRS or transmission), for the PSD measurements the temperature of the analysis and the concentration of the dispersions obtained.
The required technical information has been incorporated in the reviewed manuscript.
With respect to the required specifications for PSD measurements, the concentration is not a key factor since the equipment adjusts the measurement according to the transmittance, so it is not usual to determine the concentration prior to the measurements. An approximate value, automatically calculated by the equipment, of the volume percentage occupied by the particles is included in the manuscript.
- Some small typing errors found: H2O in line 102, ¿LDH? in Table 1, ν3 and ν2 in line 325, ν1 and ν4 in line 327, precipitatn in line 335.
Thank you for pointing out the mistakes in the lines 102 and 335.
With regard to the expression ¿LDH?, we have removed the question marks and put it as LDH*. In this case we indicate only LDH, where the * indicates at the bottom of the table that it was not possible to determine the chemical formula. This is also discussed in more detail in the text.
In lines 325 and 327, we refer to the Greek letter “nu” to indicate the vibration modes of the molecules.
- For the assignation of the reflections on the X-ray diffraction patterns (Figure 1, 2, 3), the reviewer would like to see the used references or crystal database cards.
The crystal database cards JCPDS for the Zn-AL-NO3 LDH (JCPDS: 22-0700) and ZnO (JCPDS: 00-036-1451) phases have been included in the text, according to the reported by De la Rosa et al. [29]. Also, this reference has been included in the manuscript.
- For the interpretation of the thermal behaviours (Fig. 5, 6), the atmosphere used is not signed, N2or O2?
The thermal behaviours were studied under O2 atmosphere. In the reviewed manuscript, the atmosphere used have been signed in the figure caption. Furthermore, in the characterization section, the possibility of carrying out the thermal study in a nitrogen atmosphere has been eliminated.
- It is not clear why the use of ethylamine did not result in LDH formation in conventional hydrothermal treatments, but did in microwave hydrothermal treatments. It should be discussed.
This is certainly a reasonable doubt presented by the reviewer and one that we also share. As we do not have a clear justification to explain this behaviour, we limit ourselves to describing the empirically observed fact. We hope to address this question in subsequent studies, as we believe that conventional hydrothermal treatment versus microwave, due to its greater aggressiveness, favours the segregation of undesired oxide phases when amines with alkyl chains that increase the nucleophilic character of the amine are used in the medium.
Reviewer 3 Report
The manuscript,“ Use of ethylamine, diethylamine, and triethylamine in the synthesis of Zn, Al Layered Double Hydroxides” presents the use of organic as a precipitating agent for LDH synthesis. This is the type of science that should be published in ChemEngineering. Overall, I think this manuscript should be published after addressing one small but important concern: is it the role of organics in the synthesis of LDHs?
1. A synthesis condition plays a major role in the formation of phase pure/single phase LDHs, comment on why pH 10 was chosen despite in the literature the synthesis of Zn-Al-NO3 LDH was attempted at pH 8. I agree in the procedures reported at pH 8 don’t involve any organics in their synthesis. Was the use of organics in the current synthesis determines the pH at precipitation?? Or was the synthesis attempted at pH 8? Comment on it.
2. Looks like the synthesis was attempted at room temperature, why was the synthesis not done at 60 deg as reported in the previous reports for Zn-Al-NO3 LDH. In this case, the as-synthesized sample without hydrothermal treatment would have had better crystallinity.
3. When singe phase, highly crystalline LDHs are formed just by using mixed metal nitrates solution, at the desired pH, temperature, and post-synthesis modifications which eliminate turbostratic disorder and stacking faults. I am still left with great curiosity as to why organics were used?? Have you compared the crystallinity and BET surface area for the LDH synthesized without using organics as precipitating agents? Authors claim high crystallite size but it's not compared with non-organic assisted LDH synthesis.
Author Response
The authors give thahks to reviewer for the coments. In our oppinion the manuscript will be improve after this considerations.
The answers and comentaries to the questions are incluided bellow, after the original question.
- A synthesis condition plays a major role in the formation of phase pure/single phase LDHs, comment on why pH 10 was chosen despite in the literature the synthesis of Zn-Al-NO3 LDH was attempted at pH 8. I agree in the procedures reported at pH 8 don’t involve any organics in their synthesis. Was the use of organics in the current synthesis determines the pH at precipitation?? Or was the synthesis attempted at pH 8? Comment on it.
As reported by Koplogre et al., at pH 8 a lower crystallinity of the hydrotalcite-like phase is achieved than when it is synthesising at pH 10. Furthermore, at pH 10, the segregation of the ZnO phase is not yet observed. For these reason the synthesis has been carried out at pH 10. (Kloprogge, J.T.; Hickey, L.; Frost, R.L. The Effects of Synthesis PH and Hydrothermal Treatment on the Formation of Zinc Aluminum Hydrotalcites. J. Solid State Chem. 2004, 177, 4047–4057, doi:10.1016/j.jssc.2004.07.010.)
Furthermore, studies carried out by our research group have revealed the suitability for obtaining homogeneous phases of Zn-containing hydrotalcite-type compounds when the synthesis is carried out at pH 10. (Benito Martín, P. Influencia de La Radiación Microondas En El Proceso de Síntesis de Compuestos Tipo Hidrotalcita y Óxidos Relacionados, Universidad de Salamanca, 2007).
- Looks like the synthesis was attempted at room temperature, why was the synthesis not done at 60 deg as reported in the previous reports for Zn-Al-NO3 LDH. In this case, the as-synthesized sample without hydrothermal treatment would have had better crystallinity.
The extended objective of this work (only a very important part of our general objective is addressed in this paper) is to obtain particles that can be used in processes to obtain composites for industrial applications. Therefore, the use of ambient conditions facilitates the incorporation of the process to the manufacture of plastics at an industrial level.
- When singe phase, highly crystalline LDHs are formed just by using mixed metal nitrates solution, at the desired pH, temperature, and post-synthesis modifications which eliminate turbostratic disorder and stacking faults. I am still left with great curiosity as to why organics were used?? Have you compared the crystallinity and BET surface area for the LDH synthesized without using organics as precipitating agents? Authors claim high crystallite size but it's not compared with non-organic assisted LDH synthesis.
The use of organic nitrogen compounds, considered as weak bases, as opposed to the common use of strong inorganic bases (such as NaOH) seeks to know the influence on the nucleation rate of the crystallisation process in order to know the influence this may have on the crystal sizes and particle size. In a previous work referenced in the manuscript (ref 27), the synthesis has been carried out in the absence of amines using NaOH as precipitating agent, as well as the comparative study of the crystal size and particle size between the solids obtained in an organic medium versus those obtained in an inorganic medium.
Round 2
Reviewer 3 Report
The authors have addressed all my queries and the manuscript can be accepted in its present form.
Author Response
Thanks for your comments
