Heterostructure particles enable omnidispersible in water and oil towards organic dye recycle

Dispersion of colloidal particles in water or oil is extensively desired for industrial and environmental applications. However, it often strongly depends on indispensable assistance of chemical surfactants or introduction of nanoprotrusions onto the particle surface. Here we demonstrate the omnidispersity of hydrophilic-hydrophobic heterostructure particles (HL-HBPs), synthesized by a surface heterogeneous nanostructuring strategy. Photo-induced force microscopy (PiFM) and adhesion force images both indicate the heterogeneous distribution of hydrophilic domains and hydrophobic domains on the particle surface. These alternating domains allow HL-HBPs to be dispersed in various solvents with different polarity and boiling point. The HL-HBPs can efficiently adsorb organic dyes from water and release them into organic solvents within several seconds. The surface heterogeneous nanostructuring strategy provides an unconventional approach to achieve omnidispersion of colloidal particles beyond surface modification, and the omnidispersible HL-HBPs demonstrate superior capability for dye recycle merely by solvent exchange. These omnidispersible HL-HBPs show great potentials in industrial process and environmental protection.


Point-by-point Response
We greatly appreciate the reviewers' important comments and helpful suggestions that significantly improved the quality of our revised manuscript.

Response to Reviewer #1:
Reviewer #1 (Remarks to the Author): This study demonstrates the omnidispersity of hydrophilic-hydrophobic heterostructured particles (HL-HBPs), which are synthesized using a surface heterogeneous nano-structuring strategy. The as-synthesized HBPs were then applied for the adsorption and recycling of organic dyes. There is no doubt that the authors are experienced in synthesizing materials containing both hydrophobic and hydrophilic domains and have published excellent work previously. Therefore, the application needed to stand out with exceptional performance. Firstly, the dispersibility of HBPs should be backed up using theoretical models to explain the interaction and their ability to not aggregate in aqueous media. Secondly, the reasoning for achieved performance is not sound and the mechanism of adsorption requires to be supported with experimental/theoretical results, especially the fast equilibrium. Thirdly, given the low surface area, HBPs may not be suitable for dye adsorption, because their adsorption capacity of less than 15 mg/g is many folds lower than the materials reported in the literature. Finally, the claim that HBPs show promise for sustainable organic dye separation and recycling in an energy-saving and chemical-saving way is not substantiated, especially when membrane filtration (twice) and distillation steps are required for dye recycling. Therefore, this study is not recommended for publication.

Response:
We greatly appreciate the reviewer's important comments that help us to understand our work deeply. These helpful suggestions have significantly improved the quality of our revised manuscript. We are grateful that the reviewer recognized our previously published works on synthesizing materials containing both hydrophobic and hydrophilic domains. Those works have explored applications for biological separation, ). The novelty of present work is that unique omnidispersity of the synthesized particles can be achieved by the surface heterogeneous nanostructuring strategy, which was not revealed in our previous works.
Furthermore, the unique omnidispersity of HL-HBPs enables maximal contact with, rapid adsorption and recovery of organic dyes in synthetic wastewater. Therefore, both omnidispersity and recyclability for organic dyes indicate their exceptional performance, and represent significant advances compared with our previous works. To address the reviewer's comments, we have carefully revised the manuscript after performing many additional experiments and theoretical calculations, and made comparisons to existing materials reported in the literatures. We believe the revised manuscript is suitable for publication in Nature Communications.
Firstly, according to the reviewer's suggestion, we have used Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to calculate the interactions between HL-HBPs and to explain their ability to disperse in different solvents. The calculated total potential values in aqueous medium and oily medium both indicate a repulsive force between HL-HBPs to maintain dispersible. Calculation details are illustrated in the Response to Comment 5. Secondly, it is a difficult task to clearly and quantitatively explain the adsorption mechanism based on the current adsorption theories. We have tried our best to understand what is behind this unique performance from the viewpoint of intense local electrostatic interactions. For fast equilibrium, we attributed the fast dye adsorption performance to the unique heterostructure of HL-HBPs. The outer hydrophilic domains are composed of negatively charged PSS with thickness of tens of nanometers, which provides intense electrostatic field for strong electrostatic interaction. Positively charged organic dyes in a long range (~1 μm) can be attracted immediately to neutralize the charge of hydrophilic domains. Upon attracted towards the HL-HBPs, the hydrophobic domains on HL-HBPs provide short-range hydrophobic/π-π bonding 3 interaction. HL-HBPs allow rapid diffusion and adsorption of organic dye molecules due to their wide pore size distribution from 10 nanometers to 100 nanometers ( Supplementary Fig. 4c,d), which surpasses the microporous materials including MOFs and activated carbons (Supplementary Table 4). When the surface charge of HL-HBPs is neutralized, the diffusion of organic dyes towards the particles is almost halted, and adsorption equilibrium is achieved.
Thirdly, the surface area of our HL-HBPs is not high compared with most existing materials reported in the literatures. A large surface area certainly indicates a high adsorption capacity. However, a high surface area always suggests a small pore size, which is not beneficial for rapid diffusion and adsorption. For example, MOFs are microporous adsorbents exhibiting high surface area, but the adsorption equilibrium is always achieved in tens of hours. In our manuscript, we would not like to highlight the adsorption amount, but we want to show our HL-HBPs exhibit advantages in rapid adsorption. Dye adsorption equilibrium can be achieved in 5 s. Details are illustrated in the Response to Comments 1, 3, 4, and 8.
Fourthly, to avoid misleading the readers, we have revised our statements about sustainable organic dye separation. Some energy and chemicals are certainly required in all the steps, so we have deleted the statements, such as "sustainable organic dye separation", "energy-saving", and "chemical-saving" in the revised manuscript. Details are illustrated in the Response to Comment 10.
Major Comments: 1. The premise of this work is sound and shows good promise. Well-dispersed colloidal particles could be applied in various fields as building blocks for self-assembly, as catalysts for energy conversion, and as therapeutic agents for tumor management. The buildup is interesting, especially the suitability of the surface heterogeneous nanostructuring strategy over the conventional surface modification strategy. However, the claimed application of HL-HBPs for sustainable water purification and organic dye recycling is not innovative or novel, particularly when adsorbents with exceptional dye 4 separation and recycling have been reported in the literature. Additionally, it is not recommended to provide speculative statements without any comparison of the results achieved in this study vs. the literature.

Response:
We greatly appreciate the reviewer's positive comments on the dispersity of particles and helpful suggestions on dye recycle. After comparison with adsorbent materials reported in the literature according to the reviewer's suggestions, the novelty of our particles is made more clearly, including rapid dye adsorption (Supplementary Table 4) and simultaneous regeneration of adsorbent materials and recycle of organic dyes (Supplementary Table 6). Firstly, the HL-HBPs demonstrate unique advantages in rapid adsorption, as dye adsorption equilibrium can be achieved in several seconds. In contrast, the adsorption equilibrium time of most existing adsorbent materials ranges from 5 min to tens of hours. Secondly, we propose an alternative and facile approach to desorb organic dyes from adsorbent materials. Conventional approaches mostly desorb dyes to regenerate adsorbent materials. In comparison, our strategy can simultaneously realize regeneration of adsorbent materials and recycle of organic dyes. To desorb organic dyes from materials reported in literatures, eluents containing inorganic acid, alkaline, or salt, are often added into the aqueous solution to weaken the interactions between materials and dyes. Such eluents make the dye recycle more complicated and require multiple steps. In comparison, organic solvent is used for dye desorption in our approach, and dyes can be recycled under a simple distillation process. Thus, adsorbent materials and organic dyes can be simultaneously recycled. Supplementary Tables 4   and 6 were added in the Supplementary Information to compare the difference. In addition, we added some perspectives discussing the future challenges and developments in the part of Conclusions.
Page 15, Line 283-287 in revised manuscript: "The rapid dye adsorption equilibrium of HL-HBPs indicates their outstanding capability of dye adsorption, which is difficult to achieve with existing adsorbent materials, such as LDHs (from 5 minutes to tens of minutes) 58-60 , activated carbons (at least tens of minutes) 53-55 , and MOFs (tens of hours) 51, 57 (Supplementary Table 4)." 5 Page 21, Line 405-411 in revised manuscript: "The HL-HBPs provide a promising candidate for organic dye recycle compared with existing materials. To desorb organic dyes from materials reported in literatures, eluents containing inorganic acid, alkaline, or salt, are often added into the aqueous solution to weaken the interactions between materials and dyes (Supplementary Table 6). Such eluents make the dye recycle more complicated. In this study, organic solvent is used for dye desorption, and dyes can be recycled under a simple distillation process." Page 22, Line 422-425 in revised manuscript: "Although the dye adsorption amount of HL-HBPs is lower than those existing materials with high surface area like MOFs, their adsorption rate is rapid. The next challenge is to create adsorbent materials with high adsorption capacity while maintaining the rapid adsorption performance."   for all particles, probably due to the low interfacial tension of the oil (octane). Contact angle measurement process is described as follows. The particle powders were adhered to a tape on a glass slide. Powders that were not tightly adhered were blew away. A drop (2 μL) of water or oil (octane) was dropped on the particles. A surface analyzer (LSA 100, LAUDA Scientific, GmbH) was used to determine the contact angles. For water contact angle in air, the data were automatically calculated and recorded by the software.

Supplementary
For oil contact angle in air, the oil droplets can spread rapidly with a contact angle of ~0 o . 12 4. HL-HBPs with varied BET surface areas are synthesized ( Figure S4). The overall surface area of HL-HBPs remains less than 15 m 2 /g, which should not be considered suitable for application in an adsorption process. Additionally, the adsorption/desorption curves of different HL-HBPs should be provided, and discuss the reasoning/hypothesis why the authors believe that HL-HBPs could be a good adsorbent.
Response: Thanks for the reviewer's suggestion. We measured the N2 adsorptiondesorption isotherms of the HL-HBPs with various BET surface area (Supplementary HBPs (ζ = +7.1 mV). These results indicate that the dispersion of HL-HBPs in oil is stable (Fig. 3f). Therefore, the unique HL-HBPs can be dispersed and maintain stable in both water and oil. Theoretical calculations were added in the revised manuscript.
Page 9, Line 153-Page 10, Line 181 in revised manuscript: Theoretical calculations for the dispersion mechanism of the HL-HBPs.
To elucidate the unconventional dispersion property of the HL-HBPs, we calculated the interaction potential between two HL-HBPs using classical Derjaguin-Landau-Verwey- Overbeek (DLVO) theory ( Fig. 3d-f). In typical cases of water and oil (octane), two HL-HBPs are separated by a distance d (Fig. 2d). First, the hydrophilic domains are favorable for the wetting of water, and the hydrophobic domains are favorable for the wetting of oil, making it easy for both water and oil to fill the gaps between particles. Second, introduction of charge on hydrophilic domains offers interparticle repulsive force, preventing the particles from aggregating.
Therefore, the unique HL-HBPs are dispersible in both water and oil. respectively. To simplify calculation, the HL-HBPs are treated as core-shell particles.
Two HL-HBPs of radius R and shell thickness of δ are separated by a distance d. The Hamaker constants of the core, the shell and the medium solvent are Ac, As, and Am, respectively. We assume the pores of HL-HBPs are filled with air when they are dispersed in water, while filled with oil when they are dispersed in oil ( Supplementary   Fig. 7), and the corresponding Hamaker constants are given by 37 where p represents the particle porosity, which is obtained from the pore volume when the particle density is assumed to be 1 g cm -3 . Here the Hamaker constant of pure substance 1 is calculated by 8  where ε0 = 8.85 × 10 -12 Farad m -1 , εr is the dielectric constant of the solvent, ζ is the zeta potential of the particles in the solvent, κ -1 is the Debye length.
For HL-HBPs dispersed in water, we used εr = 80.2, κ -1 = 100 nm. In addition, ζ   Firstly, it is an oversimplification that water pollution is a direct reason for water scarcity. Secondly, obviously, Dye is discharged in the form of wastewater, so the research would obviously be focused on dye removal from water. Thirdly, the sludge issue in biological treatment is not related to dye sludge but biomass sludge, and it is to be noted that biological treatment should not be referred to as 'unsustainable' and 'not eco-friendly'. Fourthly, there are studies that focus on the recycling of the dyes and, with little effort, the authors will find suitable literature on this. Finally, all listed materials are not nano-porous (Line 166) and could just be called porous materials.
Response: Thanks for the reviewer's suggestions. We have carefully revised related statements in the revised manuscript.
Firstly, according to the reviewer's suggestion, we have revised the statement that "The global production of organic dyes approaches 700,000 tons annually, however, 20 nearly 10-15% of them is discharged into industrial and household wastewater, raising the risks of ecology pollution, water scarcity, and public health." to "The global production of organic dyes approaches 700,000 tons annually, however, nearly 10-15% of them is discharged into industrial and household wastewater, which has become an important source of water pollution and a non-negligible threat for public health 41-44 ." (Page 11, Line 191-194 in revised manuscript).
Secondly, we certainly agree with the reviewer that the research should be mainly focused on the dye removal from water. Nevertheless, in addition to address the water pollution issue caused by the organic dyes, we also attempt to recycle organic dyes from the wastewater. According to our results, the recovered dyes have rarely changed after the adsorption-desorption process, implying their successful recycle. Therefore, our research provides a green approach to achieve repeated use of organic dyes, which is beneficial for reducing organic dye pollution in printing and dyeing industry.  "Quantificationally, the dye adsorption efficiency was tested for kinetics study when the concentration of HL-HBPs varied from 1.33 mg mL -1 to 3.33 mg mL -1 , 6.67 mg mL -1 , 10 mg mL -1 , and 13.33 mg mL -1 . The adsorption equilibrium was almost achieved at adsorption time of 5 s, and adsorption efficiency rarely increased in 5 min (Fig. 5b)." Response: Thanks for the reviewer's kind suggestions. Some energy and chemicals are certainly required in all the steps, so we have deleted the statements, such as "sustainable organic dye separation", "energy-saving", and "chemical-saving" in the revised manuscript.
According to the reviewer's suggestions, we also investigated the property changes of the membrane (Supplementary Fig. 14). 11. How about the changes in the properties of HBPs after 10 rounds and the purity of the organic dye? A simple NMR before and after the dye adsorption/desorption process should be able to show the purity levels.
Response: Thanks for the reviewer's helpful suggestions. We used UV-vis absorption spectra to characterize the HL-HBPs before and after 10 rounds of dye adsorptiondesorption. In addition, NMR spectra were used to characterize the dyes before and 29 after dye adsorption-desorption. UV-vis absorption spectra (Wave length: 300-700 nm) of the HL-HBPs have rarely changed after 10 rounds of adsorption-desorption process, including the characteristic absorption peak of the dyes (λmax,RB = 553.5 nm), indicating that dyes are rarely retained on the HL-HBPs (Supplementary Fig. 12). 1 H NMR spectra show that the chemical shift positions have rarely changed after the adsorptiondesorption process, indicating that there are rare additional impurities in the recycled dyes ( Supplementary Fig. 13).

Response:
Thanks for the reviewer's helpful comments and valuable suggestions. It is speculated that the decrement of dye adsorption efficiency in initial rounds can be attributed to the retainment of minority of the dyes on HL-HBPs, probably caused by the existence of dead pores in HL-HBPs. To reduce the retainment of organic dyes and further enhance the recycle efficiency, we added a post-treatment process for HL-HBPs to improve their pore interconnectivity by eliminating dead pores. In a typical posttreatment process, HL-HBPs were dispersed in DCM to dissolve and remove the linear PS, which was introduced as template particles during the synthesis process of HL-HBPs. Resultantly, the dye adsorption efficiency and desorption efficiency maintain 93~96% and 94~98%, respectively, in 10 dye recycle rounds (Fig. 6c). We greatly appreciate that the reviewer has proposed the concern, which helps us to recognize the important issue of recycle efficiency. We believe the quality of our work has improved significantly after a careful revision according to the reviewer's valuable suggestions. Page 20, Line 396-Page 21, Line 397, in revised manuscript: "In 10 dye recycle rounds, the dye adsorption efficiency and desorption efficiency maintain 93~96% and 94~98%, respectively (Fig. 6c)."  Response: Thanks for the reviewer's suggestion. We tested the dye adsorption performance at different concentration of HL-HBPs (from 1.33 mg mL -1 to 3.33 mg 40 mL -1 , 6.67 mg mL -1 , 10 mg mL -1 , and 13.33 mg mL -1 ) to analyze the adsorption kinetics.
The adsorption equilibrium was almost achieved at adsorption time of 5 s, and adsorption efficiency rarely increased in 5 minutes (Fig. 5b in  "Quantificationally, the dye adsorption efficiency was tested for kinetics study when the concentration of HL-HBPs varied from 1.33 mg mL -1 to 3.33 mg mL -1 , 6.67 mg mL -1 , 10 mg mL -1 , and 13.33 mg mL -1 . The adsorption equilibrium was almost achieved at adsorption time of 5 s, and adsorption efficiency rarely increased in 5 min (Fig. 5b)."  9. The adsorption mechanism should be added.

Response:
Thanks for the reviewer's kind suggestion. The dye adsorption can be attributed to the synergy of electrostatic interaction, hydrogen bonding interaction, hydrophobic/π-π bonding interaction. Detailed adsorption mechanism has been added in the revised manuscript, and the role of hydrophilic domains has been further clarified in Supplementary Fig. 11. HBPs. Resultantly, the dye adsorption efficiency and desorption efficiency maintain 93~96% and 94~98%, respectively, in 10 dye recycle rounds (Fig. 6c). We greatly appreciate that the reviewer has proposed the concern, which allows us to recognize the important issue of recycle efficiency. We believe the quality of our work has improved significantly after a careful revision according to the reviewer's valuable suggestions. Page 20, Line 396-Page 21, Line 397, in revised manuscript: "In 10 dye recycle rounds, the dye adsorption efficiency and desorption efficiency maintain 93~96% and 94~98%, respectively (Fig. 6c)."   "It should also be noted that the interaction energy of electrostatic interaction (~100 kT) is much higher than that of other interactions, including hydrogen bonding interaction (5~10 kT) and hydrophobic/π-π bonding interaction (~1 kT) 8 . Nevertheless, it remains a difficult task to clearly and quantitatively define the contribution factor of different types of interactions for dye adsorption due to the unique heterostructure. The adsorption index is an immature attempt to explain the difference of dye adsorption amounts. Further modification is expected for more accurate explanation and prediction as the development of experimental techniques and fundamental theories." Reviewers' Comments: Reviewer #1: Remarks to the Author: This is a revised version of the manuscript previously reviewed by this reviewer. Although the authors have made significant efforts to revise the manuscript, this reviewer finds that the underlying reasons for the original recommendation (i.e., reject) still hold. The decision that this reviewer has to make is that is the heterogeneous nanostructuring strategy to obtain omnidispersity novel or an extension (i.e., incremental) of authors' previous work? This reviewer believes that the novelty and application of this incremental work do not rise to the level warranting publication in Nature Communication. In addition, the claims made in the study about the significance of using organic solvents instead of inorganic solvent during dye recycling is weak and does not provide solid ground for the publication of this article. Finally, as pointed out in previous review comments, the material adsorption capacity is very poor and would be a major hurdle in their practical/industrial application. There are many issues that have not been adequately addressed. Some of them are outlined below: Is a BET surface area of less than 15 m2/g considered good? It remains a challenge to estimate the pore size of materials with a surface area of less than 50 m2/g. This is the reason why it is important to explain why a certain model is used for pore size estimation.
The contact angle data clearly shows that HL-HBPs are clearly hydrophobic, which raises the question about the electrostatic interaction (dye removal mechanism claimed by the author). There is a need to discuss the implications of the achieved results. The authors claimed that the adsorption rate is rapid. The standard is to compare adsorption performance based on adsorption capacity data (mg/g) rather than adsorption rate. This is because experimental conditions (adsorbent concentration, dye concentration, stirring speed, contact time) affect the adsorption rate. Hence, the reasoning provided by the authors is weak. "According to our results, the recovered dyes have rarely changed after the adsorption-desorption process, implying their successful recycling. Therefore, our research provides a green approach to achieve repeated use of organic dyes, which is beneficial for reducing organic dye pollution in the printing and dyeing industry." -Mechanisms remain still unclear, especially how to disperse a hydrophobic material (contact angle around 120 degrees).
Without going back and forth (as it is not scientific brainstorming), this reviewer does not recommend the publication of this work.
Reviewer #2: Remarks to the Author: The authors have revised based on the suggestions.
Reviewer #3: Remarks to the Author: In the revised manuscript, the authors have put additional efforts to address my major concerns. The overall recycling performance has been largely improved. On this basis, I would recommend the publication of this work as it is. 1

Point-by-point Response
We greatly appreciate the reviewers' important comments and helpful suggestions that significantly improved the quality of our revised manuscript.

Response to Reviewer #1:
Reviewer #1 (Remarks to the Author): This is a revised version of the manuscript previously reviewed by this reviewer.
Although the authors have made significant efforts to revise the manuscript, this reviewer finds that the underlying reasons for the original recommendation (i.e., reject) still hold. The decision that this reviewer has to make is that is the heterogeneous nanostructuring strategy to obtain omnidispersity novel or an extension (i.e., incremental) of authors' previous work? This reviewer believes that the novelty and application of this incremental work do not rise to the level warranting publication in Nature Communication. In addition, the claims made in the study about the significance of using organic solvents instead of inorganic solvent during dye recycling is weak and does not provide solid ground for the publication of this article. Finally, as pointed out in previous review comments, the material adsorption capacity is very poor and would be a major hurdle in their practical/industrial application. There are many issues that have not been adequately addressed. Some of them are outlined below.

Response:
We greatly appreciate the reviewer's important comments that further deepen our understanding on our study. We would like to response the main concerns raised by the reviewer.
Firstly, we believe that the present work has significant novelty compared with our previous works. It is a great challenge to prepare omnidispersible colloidal particles, although several examples have been demonstrated by introduction of nanoprotrusions.
In present work, we have proposed a surface heterogeneous nanostructuring strategy to realize the omnidispersion of particles. This strategy can be realized by the heterostructure particles synthesized by emulsion interfacial polymerization proposed 2 in our previous works. As the reviewer pointed out, the previous works have mainly concentrated on the separation of trace biomolecules from complex samples. The unique omnidispersity of heterostructure particles enables an unprecedent simultaneous recycle of organic dyes and regeneration of HL-HBPs from the synthetic wastewater merely through solvent exchange. Therefore, we believe this work is not an extension (or increment) of our previous works, and its novelty can meet the high standard and high quality of Nature Communications.
Secondly, there is unique significance to use organic solvents instead of inorganic solvent for organic dye recycle. In previous revision, we have systematically summarized and compared the recyclability of adsorbent materials and organic dyes with existing material and our particles (Supplementary Table 6). Organic solvents are easy to be removed from dyes by simple distillation. In contrast, additional steps are required to remove inorganic acid, alkaline, and salt from water. We have added the significance in the revised manuscript.
Page 21, Line 409-412: "There is unique significance to use organic solvents instead of inorganic solvent for organic dye recycle. Organic solvents are easy to be removed from dyes by simple distillation. In contrast, additional steps are required to remove inorganic acid, alkaline, and salt from aqueous solution of recycled dyes." Thirdly, we have underlined the necessity of improving dye adsorption capacity in the revised manuscript. Although the dye adsorption amount of HL-HBPs is lower than those existing materials with high surface area like MOFs, their adsorption rate is rapid (Supplementary Table 4). The next and great challenge is to create adsorbent materials with high adsorption capacity while maintaining the rapid adsorption performance. In our lab, several projects are ongoing from different aspects for this supreme goal.
Major Comments: 1. Is a BET surface area of less than 15 m 2 /g considered good? It remains a challenge to estimate the pore size of materials with a surface area of less than 50 m 2 /g. This is 3 the reason why it is important to explain why a certain model is used for pore size estimation. (Springer Science+Business Media New York, 2004)). In this book, we have learned that "Using highly accurate volumetric adsorption equipment, it is possible to measure absolute surface areas as low as approximately 0.5-1 m 2 with nitrogen as the adsorptive."

Response
(Page 79), and that "Among these different approaches, the Barrett-Joyner-Halenda method can be considered as the most popular method for mesopores size analysis." (Page 104). The total surface area of HL-HBPs used for nitrogen adsorption-desorption (2.9-3.9 m 2 ) is higher than that is required (as low as approximately 0.5-1 m 2 ). In addition, the adsorption-desorption isotherms of HL-HBPs indicate a type Ⅳ adsorption model, and most of the pores exhibit pore diameter from 10 nanometers to 100 nanometers ( Supplementary Fig. 4b, c). Therefore, the pore size estimation results based on BJH model are reliable.
2. The contact angle data clearly shows that HL-HBPs are clearly hydrophobic, which raises the question about the electrostatic interaction (dye removal mechanism claimed by the author). There is a need to discuss the implications of the achieved results.

Response:
We appreciate the reviewer's comments and helpful suggestions. We would like to clarify that the contact angle for HL-HBPs adhered tape (122.6 ± 1.6 o ) does not certainly imply the absence of electrostatic interaction on HL-HBPs. The hydrophilicity-hydrophobicity of the particles was evaluated by a commonly-used approach. Typically, the particles were adhered to a glass microscope slide by doublesided adhesive tape, and three-phase contact angle was measured by the sessile drop method (Powder Technol. 233, 52-64 (2013)). The contact angle can be affected by the coverage of the particles on the tape, the interfacial tension of the particles, and the