Immersion Enthalpy of Activated Carbon–Cyclohexane and Activated Carbon–Hexane. Difference in the Solid–Liquid Interaction Enthalpy Due to the Structure of the Solvent
Round 1
Reviewer 1 Report
This paper discussed the measurement of the enthalpy of adsorption of cyclohexane and hexane to various activated carbons. The MS could do with a number of additions to make the results easier to understand.
Title should be solid-liquid interaction
Line 17 - it is not necessary to put experimental details in the abstract
Line 22 - ensure you're putting spaces in units
Line 49 - Here you talk about the isotherm of adsorption, but this is not done anywhere in the paper, thus it is not relevant to this work. It should be explained that although this is a good method it was not carried out and give reasons why.
The introduction has good content, but needs thorough proof reading. Also, please explain why you studied a liquid phase process for a gas phase application.
Line 81 - please give supplier for coconut shell. The acronym GAC is sometimes used and sometime you use CAG please be consistent. Acronyms should be given in brackets.
Line 93 - give reference for Boehm
Section 2.4 - I think it would be beneficial to give a diagram of the apparatus to better explain the process for enthalpy measurements
Line 114 - BET should have been defined earlier.
Table 1 - I think this would be better understood if the table was ordered in order of treatment, with CAG first and then CAN and then the heat treatments.
Line 129 - provide references for the removal of heteroatoms increasing the surface area.
Line 140 - why is the basicity higher for the thermally treated samples and the acidity higher for the non-thermally treated samples?
Figure 1 - format of this figure is different from others
Figure 2 - can you explain why the peak has shifted to longer time scales for 1173 and 1023 samples.
Figure 3 - can you explain why the blue curve has a broader peak
Line 156 - please reference which figure you mean by graph
Line 160 - can you give some values for the immersion enthalpies
Figure 4 - it would be beneficial to note which point refers to which sample
Line 175 - why did the interaction become similar for small pores?
Line 181 - please explain how you calculated this difference.
Line 187 - why does the shape of the molecule influence the adsorption?
Line 193 - why did you calculate the average enthalpy per unit volume from figure 5. Wouldn't it be better to calculate this for each solvent.
Line 198 - why does the removal of oxygen groups increase basicity? Most basic groups, eg. hydroxide, include oxygen.
Figure 8 - hexane is spelled incorrectly
Figure 9 - labelled as figure 8
Figure 9 - why are you plotting the difference on the x-axis but then giving the results for both solvents. This plot makes little sense to me.
I think the results of your paper are good. You've clearly shown that surface area, pore volume, and basicity influence the adsorption enthalpy of hexane and cyclohexane. And you've shown the difference between a linear and a cyclic solvent molecule. However I have no idea why you've plotted the difference graphs. I don't see how these add anything to the paper, and they confuse your results. I think you're better to just plot the data and explain that there is a difference between the two solvents, as can be clearly seen by the gradients.
Author Response
March 18, 2019.
Editorial board
PROCESSES
Ref.: processes-470135 Type of manuscript: Article
Title: Immersion enthalpy of activated carbon – cyclohexane and activated
carbon – hexane. The difference in the enthalpy of interaction solid-liquid
due to the structure of the solvent.
Authors: Diana Hernández-Monje, Liliana Giraldo, Juan Carlos Moreno-Piraján
Dear Reviewer,
Thank you very much for reviewing our manuscript, we also greatly appreciate the comments and suggestions. We have revised and corrected the manuscript according to the points described:
•Title should be solid-liquid interaction
Response: The title has been changed according to your suggestion: “Immersion enthalpy of activated carbon – cyclohexane and activated carbon – hexane. Difference in the solid-liquid interaction enthalpy due to the structure of the solvent”
•Line 17 - it is not necessary to put experimental details in the abstract
Response: The experimental details were omitted in the abstract.
•Line 22 - ensure you're putting spaces in units
Response: The spaces were put in units
•Line 49 - Here you talk about the isotherm of adsorption, but this is not done anywhere in the paper, thus it is not relevant to this work. It should be explained that although this is a good method it was not carried out and give reasons why.
Response: This paragraph was added: “Although the study of isotherms of adsorption is interesting, it is not discussed in this document, because it is intended to describe how the other technique, the immersion calorimetry, can generate information regarding the interaction between the solvent and the porous solid and relate the intensity of that interaction with the characteristics of the adsorbent and the adsorbate”.
•The introduction has good content, but needs thorough proof reading. Also, please explain why you studied a liquid phase process for a gas phase application.
Response: The manuscript was proofread after incorporating the reviewers' suggestions.
•Line 81 - please give supplier for coconut shell. The acronym GAC is sometimes used and sometime you use CAG please be consistent. Acronyms should be given in brackets.
Response: It was corrected according to your suggestions.
•Line 93 - give reference for Boehm
Response: Boehm is mentioned in reference 18:
18.Boehm, H.P. Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon. 1994, 32, 759-769
•Section 2.4 - I think it would be beneficial to give a diagram of the apparatus to better explain the process for enthalpy measurements
Response: The scheme of the calorimeter used for this work is shown in: Vargas, D. P.; Giraldo, L.; Moreno-Piraján, J. C. Calorimetric study of the CO2 adsorption on carbon materials. J Therm Anal Calorim. 2014, 117(3), 1299–1309 (Figure 1). The reference was added to section 2.4.
•Line 114 - BET should have been defined earlier.
Response: BET is defined in section 2.2.
•Table 1 - I think this would be better understood if the table was ordered in order of treatment, with CAG first and then CAN and then the heat treatments.
Response: The table was ordered according to your suggestion.
•Line 129 - provide references for the removal of heteroatoms increasing the surface area.
Response: These references were added to the manuscript [27-29]:
27. Belhachemi, M.; Addoun, F. Effect of Heat Treatment on the Surface Properties of Activated Carbons. E- J. Chem. 2011, 8(3), 992-999
28. Wang, R.; Lang, J.; Yan, X. Effect of surface area and heteroatom of porous carbon materials on electrochemical capacitance in aqueous and organic electrolytes. Sci China Chem. 2014, 57(11), 1570–1578
29. Yin, C.; Aroua, M.; Daud, W. Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions. Sep. Purif. Technol., 2007, 52(3), 403–415
•Line 140 - why is the basicity higher for the thermally treated samples and the acidity higher for the non-thermally treated samples?
Response:
Thermal treatments at high temperature generate materials with low amount of oxygen containing groups and high basicity, it results from the decrease of acidic groups, the ketonic groups remaining on the surface, and mainly from the delocalized π electrons of the solid basal planes.
On the other hand, the acidity is higher for the non-thermally treated samples due to carboxylic groups decompose between 523 and 673 K, besides it is considered that nitric acid increases the amount of superficial oxygenated groups. This favors electrostatic interactions and therefore increases the hydrophilicity of the sample.
References:
Y. Gokce, Z. Aktas, Appl. Surf. Sci. 313 (2014) 352-359.
N. Soudani, S. Souissi-najar, A. Ouederni, Chin. J. Chem. Eng. 21 (2013) 1425-1430.
L. Pereira, R. Pereira, M.F.R. Pereira, F.P. van der Zee, F.J. Cervantes, M.M. Alves, J Hazard Mater. 183 (2010) 931-939.
J. Jaramillo, P. Álvarez, V. Gómez-Serrano, Appl. Surf. Sci. 256 (2010) 5232–5236.
J. Rivera-Utrilla, M. Sánchez-Polo, Water Research. 37 (2003) 3335-3340.
•Figure 1 - format of this figure is different from others
Response: The format of the figure was changed according to your suggestions.
•Figure 2 - can you explain why the peak has shifted to longer time scales for 1173 and 1023 samples.
Figure 3 - can you explain why the blue curve has a broader peak
Response: The area under the curve of these peaks is proportional to the interaction between the activated carbon and the solvent and, in turn, to the value of the enthalpy of immersion product of the contact between the solid and the adsorbate, so that if the peak is broader, it implies that the enthalpy of immersion is greater, just what happens, since the corresponding value for this sample is -66.10 J g-1, the highest value for the series of samples.
•Line 156 - please reference which figures you mean by graphs
Response: The figures 2 and 3 are related to the expression “graphs”, this information was also added to the manuscript.
•Line 160 - can you give some values for the immersion enthalpies
Response: The values for the immersion enthalpies for the two solvents in the five samples were added to the manuscript.
•Figure 4 - it would be beneficial to note which point refers to which sample
Response: Each sample in the Figure was labeled.
•Line 175 - why did the interaction become similar for small pores?
Response: This may occur because the presence of more oxygenated groups on the surface interferes with the solid-liquid interaction and in turn; these groups decrease the hydrophobicity of the activated carbon and therefore the interaction with the solvents because they are non-polar molecules.
•Line 181 - please explain how you calculated this difference.
Response: This difference is calculated from the subtraction between the immersion enthalpies of cyclohexane and hexane in order to obtain the contribution of the structure of the solvent had in the solid-liquid interaction.
•Line 187 - why does the shape of the molecule influence the adsorption?
Response: The shape of the molecule influences the adsorption process because the way in which it is available can allow or restrict its entry into the porous structure. On the other hand, also the way in which the adsorbate is accommodated can increase or decrease the interaction with the pore and therefore, increase or decrease the adsorption energy.
•Line 193 - why did you calculate the average enthalpy per unit volume from figure 5. Wouldn't it be better to calculate this for each solvent.
Response: The observation is not clear since Figure 5 relates the change in the enthalpy of immersion of activated carbons in each solvent based on the content of basic groups of the surface of the solid, with the purpose of observing the interaction of the solvent with the decrease in the content of oxygenated groups.
•Line 198 - why does the removal of oxygen groups increase basicity? Most basic groups, eg. hydroxide, include oxygen.
Response: The removal of these surface groups occurs because it is considered that carboxylic groups decompose between 523 and 673 K, lactones between 673 and 923 K and phenols between 873 and 1073 K and temperatures higher than 1173 K decompose the quinone and pyrone groups. Then, the basicity possibility increased by the presence of chromene and pyrone groups that only decompose at high temperatures, or by the electronic density on the graphene layers, specifically the delocalized π electrons.
References:
J. Jaramillo, P. Álvarez, V. Gómez-Serrano, Appl. Surf. Sci. 256 (2010) 5232–5236.
J. Rivera-Utrilla, M. Sánchez-Polo, Water Research. 37 (2003) 3335-3340.
•Figure 8 - hexane is spelled incorrectly
Response: The spelling was corrected
•Figure 9 - labelled as figure 8
Response: The labelled was corrected to “Figure 9”
•Figure 9 - why are you plotting the difference on the x-axis but then giving the results for both solvents. This plot makes little sense to me.
Response: In Figure 9, the x-axis corresponds to the immersion enthalpy of the two solvents, not the difference. This inaccuracy is corrected in the graph and its label.
•I think the results of your paper are good. You've clearly shown that surface area, pore volume, and basicity influence the adsorption enthalpy of hexane and cyclohexane. And you've shown the difference between a linear and a cyclic solvent molecule. However, I have no idea why you've plotted the different graphs. I don't see how these add anything to the paper, and they confuse your results. I think you're better to just plot the data and explain that there is a difference between the two solvents, as can be clearly seen by the gradients.
Response: What we want to show is that the difference in the immersion enthalpy ΔHimciclohexane - ΔHimhexane represents the enthalpic contribution by the change in the structure of the solvent and it is related to the characteristics of the activated carbons, in order to establish the behavior with a thermodynamic property that quantifies this change of structure.
The information that was added to the manuscript is in blue.
Best regards,
Dr. Juan Carlos Moreno Piraján
Full Profesor
Universidad de los Andes
Science Faculty
Chemistry Department
Group of Porous Solids and Calorimetry
Author Response File: 
Author Response.doc
Reviewer 2 Report
In this manuscript, the authors measured the immersion enthalpy of two different solvents on 6 different carbon supports. The authors also discussed about the relationship between the enthalpy and the physical properties of carbon materials. These results could be useful for researchers dosing similar research. However, there are several parts in the manuscript not clear. This manuscript can be published after the authors address the comments below:
Page 1 line 37: Before introducing the adsorption as an alternative for purification, need a sentence to introduce and discuss different ways of VOCs removal: adsorption, absorption, biofiltration, pyrolysis, catalytic combustion, and photocatalytic degradation have been developed for the elimination of VOCs. See these articles (J. Loss Prevent. Proc., 2000,13, 527-545; Chemical Engineering Journal, 2014, 245, 80-88; Chemosphere, 2003, 53(1) 17-27; Appl. Catal., B, 2003, 44, 325–331; RSC Advances 2013, 3 (4), 1103-1111)
Page 1line 41: The importance of this work has to be highlighted. There are more studies to show the importance of solid vapor interaction, which have been shown in catalysis and other fields. Seeexamples:(Surface Science Reports, 2002 46, 1-308;Journal of Analytical and Applied Pyrolysis, 2009 86(1-2), 237-246)
Page 2 line 58: Explain what is theta.
Page 3 line 87: Specify how long was the thermal treatment
Page 3 line 96: Cite the original paper by Boehm
Page 3 line 127: Are there any other studies to support this pore volume increase due to the thermal stability of the oxygenated group?
Page 4 line 146: x-axis in figure 1 width instead of with. Typo. Also, please label the inside figure.
Page 5 line 161: Explain what is the y-axis potential (V) and why the area under the curve will give the enthalpy of immersion.
Page 5 line 174: as a function, instead of in function
Page 5 line 178: How could the slope related to the value of enthalpy. Need explation.
Page 6 line 185: Specify the ‘difference’. Which one minus which.
Page 6 line 195: Can you give some possible explanation on why the difference is linear. In other words, why will be the difference in immersion enthalpy bigger between cyclohexane and hexane at higher volume?
Page 8 line 217: Fix figure 7. One point is out of the boundary.
Page 9 line 229 Isn’t the surface area and pore volume also related? Should have some discussion about this.
Author Response
March 18, 2019.
Editorial board
PROCESSES
Ref.: processes-470135 Type of manuscript: Article
Title: Immersion enthalpy of activated carbon – cyclohexane and activated
carbon – hexane. The difference in the enthalpy of interaction solid-liquid
due to the structure of the solvent.
Authors: Diana Hernández-Monje, Liliana Giraldo, Juan Carlos Moreno-Piraján
Dear Reviewer,
Thank you very much for reviewing our manuscript, we also greatly appreciate the comments and suggestions. We have revised and corrected the manuscript according to the points described:
•Page 1 line 37: Before introducing the adsorption as an alternative for purification, need a sentence to introduce and discuss different ways of VOCs removal: adsorption, absorption, biofiltration, pyrolysis, catalytic combustion, and photocatalytic degradation have been developed for the elimination of VOCs. See these articles (J. Loss Prevent. Proc., 2000,13, 527-545; Chemical Engineering Journal, 2014, 245, 80-88; Chemosphere, 2003, 53(1) 17-27; Appl. Catal., B, 2003, 44, 325–331; RSC Advances 2013, 3 (4), 1103-1111)
Response: This paragraph was added to the manuscript:
With the persistent increase of volatile organic compounds and their harmful effects on human health and the environment, the development of effective techniques that allow the removal of these is of great importance. Control mechanisms have emerged and they can generally be divided into methods of recovery and methods of destruction. Recovery methods include adsorption, condensation, absorption and separation by membranes, while destruction techniques include incineration, catalytic oxidation, biological degradation, etc. In comparison with destruction methods, which convert mainly VOCs into CO2 and H2O, recovery methods are more economical; In addition, incineration and most other methods of destruction, expend enormous amounts of energy to produce high temperatures that allow carrying out the reactions, and in turn, generate some toxic products such as NOx, O3, OH radicals, organic aerosols secondary, etc. Among the methods of recovery, adsorption is considered one of the favorable methods due to its low cost and high efficiency, for which, carbonaceous materials have been widely used due to its versatility, selectivity, surface area, variety of porous structure, high capacity and rapid adsorption kinetics [3-9].
•Page 1line 41: The importance of this work has to be highlighted. There are more studies to show the importance of solid vapor interaction, which have been shown in catalysis and other fields. See examples:(Surface Science Reports, 2002 46, 1-308; Journal of Analytical and Applied Pyrolysis, 2009 86(1-2), 237-246)
Response: This paragraph was added to the manuscript:
This manuscript not only describes the interaction between two organic molecules (cyclohexane and hexane) and activated carbons modified in their chemical and textural properties, but also how the system is affected according to the properties of its components: as for adsorbates, one is a closed chain aliphatic compound (cyclohexane), while the other is an open chain aliphatic compound (hexane); With respect to the adsorbents, they have different textural properties and content of surface groups (lactonic, carboxylic and phenolic) that, in turn, modify the dispersive type interactions that may exist between this type of molecules and activated carbon; besides, the difference between the immersion enthalpy cyclohexane and hexane was calculated to indicate the contribution of the chemical structure of the two solvents in the solid-liquid interaction; In turn, a correlation between the immersion enthalpy, the adsorption energy and the microporous structure of the solid was established.
•Page 2 line 58: Explain what is theta.
Response: Ɵ is the degree of micropore filling, W/Wo (this information was added to the manuscript)
•Page 3 line 87: Specify how long was the thermal treatment
Response: The paragraph was modified to add the information:
The starting sample was granular activated carbon prepared from coconut shell, GAC. A fraction of GAC was subjected to an oxidation process with a solution of nitric acid 6 M to obtain an oxidized activated carbon, CAN; two fractions of CAN were exposed to thermal treatment at 723 K (5 hours at a rate of 1.5 °C min-1, and then one hour at 723 K) and 1023 K (8 hours at a rate of 1.5 °C min-1, and then one hour at 1023 K) under nitrogen atmosphere: CAN723 and CAN1023. A final sample was obtained by subjecting activated carbon GAC to a thermal treatment in N2 atmosphere, at 1173 K (10 hours at a rate of 1.5 °C min-1, and then one hour at 1173 K), CAG1173 [17].
•Page 3 line 96: Cite the original paper by Boehm
Response: The paper is cited according to your suggestion.
•Page 3 line 127: Are there any other studies to support this pore volume increase due to the thermal stability of the oxygenated group?
Response: These references were added to the manuscript [28,31]:
28. Belhachemi, M.; Addoun, F. Effect of Heat Treatment on the Surface Properties of Activated Carbons. E- J. Chem. 2011, 8(3), 992-999
31. Mangun, C. L.; Benak, K. R.; Daley, M. A.; Economy, J. Oxidation of Activated Carbon Fibers: Effect on Pore Size, Surface Chemistry, and Adsorption Properties. Chem. Mater. 1999, 11(12), 3476–3483.
•Page 4 line 146: x-axis in figure 1 width instead of with. Typo. Also, please label the inside figure.
Response: The x-axis label was corrected and the figure inside was labeled too.
•Page 5 line 161: Explain what is the y-axis potential (V) and why the area under the curve will give the enthalpy of immersion.
Response: The plot of the potential (V) as a function of time contains two peaks: the first corresponds to the immersion process, breaking the cell and wet sample, and the second to electrical calibration of the calorimeter. In this manuscript only the peak for the immersion process is shown due to the second is used to determine the calorimeter constant, not the interaction between the solid and the adsorbate.
The electrical calibration of the equipment is carried out by heating the system with a resistance of 100Ω that allows to calculate the electrical work dissipated in the system, taking into account that:
(1) When obtaining Welec, the calorimeter constant (K) is calculated, which corresponds to:
(2) Once the calorimeter constant is determined, the energy of immersion (J) is calculated:
(3) And then, the immersion enthalpy (J g-1) in function of the mass of solid is obtained:
(4) Page 5 line 174: as a function, instead of in function
Response: The expression was corrected according to your suggestion
•Page 5 line 178: How could the slope related to the value of enthalpy. Need explanation.
Response: This may mean that for the case of cyclohexane, the interaction is much more sensitive to the microporous structure of the activated carbon, since the adsorption in the micropores is associated with the adsorption potential present in the walls thereof. Thus, the increase of the available micropores, which have a quite high adsorption potential from the superposition of the existing fields in said pores, increases the contribution of the interaction between the liquid and the porous solid.
•Page 6 line 185: Specify the ‘difference’. Which one minus which.
Response: This difference is calculated from the subtraction between the immersion enthalpies of cyclohexane and hexane in order to obtain the contribution of the structure of the solvent had in the solid-liquid interaction.
•Page 6 line 195: Can you give some possible explanation on why the difference is linear. In other words, why will be the difference in immersion enthalpy bigger between cyclohexane and hexane at higher volume?
Response: As said above, probably, the interaction is much more sensitive to the microporous structure of the activated carbon for cyclohexane than for hexane, since the adsorption in the micropores is associated with the adsorption potential present in the walls thereof. Thus, the increase of the available micropores, which have a quite high adsorption potential from the superposition of the existing fields in said pores, increases the contribution of the interaction between the liquid and the porous solid.
•Page 8 line 217: Fix figure 7. One point is out of the boundary.
Response: What happens in this Figure is that there are two tendencies, one corresponds to the behavior when the basicity presents low values and another when the functional groups of basic type increase. It shows that the two solvents presented a total effect which included the interactions with the functional groups and with the surface.
•Page 9 line 229 Isn’t the surface area and pore volume also related? Should have some discussion about this.
Response: As it is a mainly microporous material, there is a close relationship between the volume of micropore and the surface area, so that they increase proportionally. When the available area of the adsorbate increases, the possibility of the solid-liquid interaction increases too, causing that the enthalpy of immersion gets higher values.
The information that was added to the manuscript is in blue.
Best regards,
Dr. Juan Carlos Moreno Piraján
Full Profesor
Universidad de los Andes
Science Faculty
Chemistry Department
Group of Porous Solids and Calorimetry
Author Response File: Author Response.doc
