Hydrogen Gas Adsorption of the Triassic Chang 7 Shale Member in the Ordos Basin, China
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. Authors claimed the existence of clay minerals which is predominantly illite/smectite mixed layer (S%=15%) is the main reason why H2 adsorption capacity is high. But in the other literature published by same authors titled with “High-pressure hydrogen adsorption in clay minerals: Insights on natural hydrogen exploration”, the adsorption of hydrogen on montmorillonite/chlorite/illite/kaolinite is minimal. Please explain the contradict results.
2. Author presented weight percentage of organic matter in table 3 but no percentage for the total minerals reported in table 1: is it equal to 1-organic matter%?
3. Most of the information in this literature is known in other published literature such as mineral/organic composition (Fan et al., Processes 2023, 11(11), 3090 etc.), pore types of the shale sample, nitrogen adsorption isotherm (Gao et al., Energy Exploration & Exploitation 39(2). It seems only hydrogen adsorption isotherm on the shale is not easily found in other literature. But as author claimed in section 4.5 that organic matter (line 304-307) and clay minerals (314-315) are main contributions for hydrogen adsorption and have been reported before. Therefore, it looks like the novelty of this literature is weak.
4. No reference or data is supporting line 308-311. No reference or data is supporting line 287-288.
5. More evidence is needed to support authors claim in line 343-345. The reference listed in section 4.5 about clay minerals affect the development of pores in the range of <5nm/10-50nm/ 2-5nm/20-100nm/2-50 nm is not supporting line 343-345. Authors should report pore sizes and surface areas of tested samples to prove the formation of larger size pores.
6. Langmuir adsorption parameters have physical meanings. It is confusing VL sometimes increases with temperature.
7. What are S1-S11 in Figure 6d.
8. Since authors are comparing hydrogen adsorption isotherm of tested samples with SK2 sample in Figure 6d, properties of SK2 need to be more clearly listed besides information in line 298-300, i.e., complete mineral composition, shale structure as shown in Figure 4. If authors want to claim the factors of pore size/SSA influence hydrogen adsorption, then the pore size/SSA of both samples need to be reported.
8. Reference is needed for line 283. 39 out of 44 reference is listed before results and discussion. Authors need to check reference is not missing in the result discussion section.
9. Typo “mectite” in ine 194.
Author Response
Thank you very much for your valuable suggestions. We have revised them one by one. Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript aims to determine the adsorption of hydrogen gas by the Triassic Chang 7 Member 8 shale in the Ordos Basin, China. The following comments must be addressed:
- Some important conditions for hydrogen adsorption study are not reported such as the amount of the adsorbent used and contact time?
- Was the hydrogen volume adsorbed in Fig. 6 taken from the equilibrium state? If it was, how did authors make sure that the equilibrium was reached?
- The units of composition in Table 1 are by mass? Authors concluded that “Quartz and feldspar are the next-most abundant minerals.”However, the data reported in Table 1 did not correspond to this claim?
- A scale and magnification used in Fig 3 must be reported along with the figure. Authors claim that the Chang 7 shale is rich in organic matter based on the microscopic images. However, TOC in Table 3 is low (<15%) which is contrast to the claim. Please clarify this.
- Data in Fig 6 should be plotted against Freundlich and Langmuir models to show the fit, apart from Table 4.
- The last paragraph in section 4.4 discuss the methane adsorption which is not relevant to the study. It should be removed.
- On lines 315, why authors claimed 60% of the hydrogen adsorption was attributed to clay minerals. How this amount came from?
- On lines 343-345, authors related the higher adsorption capacity with higher micropore and mesopore volumes. However these data was not reported or determined from nitrogen adsorption isotherm to support this claim.
Author Response
Thank you very much for your valuable suggestions. We have revised them one by one. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this study, the authors investigated the adsorption of hydrogen gas by the Triassic Chang 7 Member 8 shale. The mineral composition, microscopic morphology, pore characteristics, hydrogen adsorption capacity, and factors influencing hydrogen adsorption were explored by different techniques. However, the organic matter content was not quantified; it was observed and analyzed qualitatively by microscopy. The data on the effect of organic matter on H2 adsorption was not presented. I recommend publishing this study in the Sustainability journal after major revisions:
Page 2, paragraph 4, line 5: Correct in “...II kerogen kerogen”
The scale in Figure 3 a-d is not clear; the authors need to revise and correct it.
In Figure 4, the authors need to add what kind of electron is used for the images, ¿secondary electrons or backscattered electrons? Also, the authors must add EDS analysis for chemical analysis and discussion of the different regions. How can the authors be sure the regions in the images correspond to organic, clays, etc.?
Page 7, last paragraph, last line: Add reference for this statement “Intragranular (intracrystalline) pores are one of the most common pore types and 232 play a crucial role as gas storage spaces.”
Page 9, first paragraph, first line: Authors need to show evidence or references about this statement “... Some pores exhibit good internal connectivity”
The authors need to revise and correct the caption of Figure 5.
Page 11, first paragraph, first line: Authors need to show evidence or references about this statement “The hydrogen adsorption capacity of shale is lower than its methane adsorption capacity as methane exhibits stronger van der Waals interactions with shale.”
Authors must add the study with and without organic matter or the corresponding reference.
The authors mentioned in the conclusion that they investigated organic carbon content; however, no related analysis was observed in this study. Authors need to add such information or correct the text. What is the percentage of kerogen in the sample?
The authors concluded, "This study provides valuable insights into the complex interplay of mineralogical, organic, and structural factors that affect the capacity of shale to adsorb hydrogen gas.” However, analysis concerning organic matter is not observed in this study. Authors need to add such information or correct the text. Where are the figures for H2 adsorption with organic matter and clays?
Author Response
Thank you very much for your valuable suggestions. We have revised them one by one. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsLines 2-3: I recommend you change this into: "Chang 7 Shale Member" instead of "Chang 7 Member Shale". Please apply all over the text.
Lines 8-20, Abstract: Some minor modifications are needed as shown in the annotated pdf.
Line 21, Keywords: The keywords can be improved by including additional words such as exploration. These keywords need re-arrangement so that the authors should start with lithology (Chang 7; shale member), then target of study (hydrogen adsorption; natural hydrogen; exploration) and finally the locality (Ordos Basin). Preferably China would be also added as the last keyword.
Line 31, Introduction: Density unit for the hydrogen gas needs correction to be g/l instead of g/L.
Line23-95: Introduction is ok but needs fixation of minor typographic errors.
Line 113, Geological Background: Figure 1 needs some minor editing, e.g. Formation is abbreviated as "Fm" and not "Fr.". Also, in the legend, grit sandstone should be in yellow colour same as in the lithostratigraphic section. In addition, geographic north (N) is needed for the two maps and preferably geographic coordinates for the China location map (a).
Line 115: You need to delete "era" because it is used for high-ranked geological time than the Jurassic, e.g. the Mesozoic Era.
Line 138: Replace the title "Samples and Experimental Methods" by either "Materials and Methods" or "Samples and Experimental Work".
Line 158: TOC is abbreviated form of total organic carbon content and should be written as “total organic carbon content (TOC)” when it is mentioned for the first tem. Then, feel free to use TOC only n the rest of text.
Line 178: The authors should divide this into two separate sections, one for results and the other for discussion.
Lines 187-188, Results: As to kaolinite percentage from the XRD runs, the authors mentioned it is relative, so relative to what and how much?, even it is trace or very minor.
Line 189, Table 1: Ammonium should not be counted among the mineral composition because it is not a mineral like the others in the table. Also, the authors should explain why it is inserted in that site. Also, the caption should be re-phrased.
Line 191, Table 1: If chlorite/smectite is absent in the three analysed mudstone samples, them delete it. Also, for kaolinite if not detected as in sample #427, use n.d. instead of slash “/”.
Line 202, Table 2: No need for dot before weight percent "wt%" for TOC and TS. Also, Why do you write sample id as Y-412 for example?. Please unify either with Y- or without for all tables and the text as well.
Line 210, Microscopic Indentification: All minerals in the photomicrographs (Figure 3) should be shown on each photo in the abbreviated form, e.g. quartz (Qz) and include this in the figure caption too. You can follow the international scheme of mineral abbreviations, e.g. Whitney and White (2010) or the updated version Warr (2023) that published in the Mineralogical Magazine recently.
Line 218: All photomicrographs shown in Figure 3 do not possess bar scale. Please insert it for all.
Line 235: The SEM images shown in Figure 4 are ok and have bar scale, but the authors need to use mineral abbreviations same as Figure 3.
In Figure 4c, strawberry-shaped pyrite is a strange and incorrect. Please use an alternative/suitable adjective to describe the morphology of the shown framboidal pyrite.
Lines 256-258: What are your evidence?. Please insert 1-2 reference to support the origin of the pore fissures.
Lines 311-312: The authors mentioned that there are XRD measurements in the form of a supplementary file S1, which is not found with the text. Probably something wrong happened during the electronic submission and the file was not uploaded.
Line 347: Table 4 needs some re-editing. Also, I wonder about the use of sample id Y412, Y-412 or 412?. Please unify in Table 4 to be compatible with Tables 1-3.
Line 350: Conclusions are good and based on reasonable interpretation of the experimental work and its results. Nevertheless, the conclusions are presented in the form of three-numbered paragraphs that are length. The authors are advised to shorten them and fragment into 4-bullets.
Line 385: Please re-edit the reference list careful y and consider punctuation as in reference No. 40. Also, check for odd sentences that should be removed from reference No. 37. Please use "and" instead of its symbol "&" for journal names as in the last reference No. 47.
Comments for author File: Comments.pdf
Just fine English polishing
Author Response
Thank you very much for your valuable suggestions. We have revised them one by one. Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThanks for the revision. I don't have further comments.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript has been corrected according to my comments.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors made proper corrections. I suggest publishing this paper in its present form.
Reviewer 4 Report
Comments and Suggestions for AuthorsThank you for the improvement of the manuscript.
Comments on the Quality of English Language
Just fine English polishing is needed upon acceptance.
