Evaluation of the Inactivating Ability of Carbon-Nanotube Coated Plasma Treatment on Bioaerosols for Indoor Air Cleaning

Round 1

Reviewer 1 Report

Dear Author,

The work submitted by the Chuang et al is discussing about the Carbon-nanotube Coated Plasma based system for air cleaning. This work needs several rectification/modification(s) for publication.

Please consider carefully the following points:

1) the synthetic methods of the Carbon nanotube should be written descriptively and submit a scheme for that. Give the TEM image of the synthesized Carbon nanotube.

2) Give the antipathogenic action of the material used for the air cleaning purposes.

3) Cite some very significant references https://doi.org/10.1016/j.molliq.2019.03.010,

DOI https://doi.org/10.1039/C5RA27886D, https://doi.org/10.1016/j.molliq.2021.117482 in the introduction section of the paper.

4) The conclusion part should be more concise.

5) The discussion regarding the effect of operating flow rate of inactivation efficiency on bioaerosols is inappropriate. Explore it properly.

6) Give the statistical accounts of the biological experimental outcomes.

7) Give the precautionary measures regarding the work of l virus.

8) Explain the Mechanical ventilation of E. coli in details.

Author Response

The manuscript has processed with English editing (as certificate).

 

Please consider carefully the following points:

1. the synthetic methods of the Carbon nanotube should be written descriptively and submit a scheme for that. Give the TEM image of the synthesized Carbon nanotube.

Reply:

Thanks for the comments. For the carbon-nanotube electrode coating procedure, this study used silver glue adhesion over the stainless steel electrode and releasing discharge voltage by a power supply as the carbon-nanotube powder. As for the carbon-nanotube, arc-discharge produced multi-wall carbon nanotube (MWCNT, purchased from TECO Nanotech Inc., Taiwan) product was utilized. The scanning and transmission electron microscopes observed structure and dimensions of MWCNT (provided by TECO Nanotech Inc., Taiwan) is shown in Fig.1. The outside and inside diameter range of MWCNT is 15~20 nm and 3~5 nm, respectively. The length of MWCNT is ≦5 nm. The description was added in Lines 152-159. The TEM image was add in Figure 1 (Line 170 ).

 

2. Give the antipathogenic action of the material used for the air cleaning purposes.

 

Reply:

Thanks for the comments. This work used the CNT-coated plasma as non-thermal plasma systems. Recently, non-thermal plasma had been applied to inactivate indoor bioaerosols. Gallagher et al. [25] have used it to eliminate 99.999% of indoor E.coli bioaerosol during a 2-minute testing time. The most common way to induce plasma inactivation mechanisms for eliminating microorganisms are UV-C and VUV(vacuum ultraviolet) irradiation in a wavelength range below 300 nm, which produce diffusion of oxidative species (O, O3, and O2*) or oxygen-containing radicals (e.g. OH and NO), a bombardment of the cell wall by charged particles (electrons and ions), and localized, periodical, and short-term heating of microorganisms. All of the various plasma active components can synergistically interact. Furthermore, this work identified OH radical as the main component of the inactivation mechanism during microbial inhibition. The description was revised in Lines 81-90.

 

3. Cite some very significant references 

https://doi.org/10.1016/j.molliq.2019.03.010,

DOI https://doi.org/10.1039/C5RA27886D, https://doi.org/10.1016/j.molliq.2021.117482 in the introduction section of the paper.

 

Reply:

Thanks for the comments. These researches had been added in Lines 59-64. Gosh et al. [12] utilized Ag-nanoparticle capped graphene oxide (GO) nano-sheet based supramolecular hydrogel to inactivate E. coli and Bacillus subtilis in broth. The result show that GO dispersed supramolecular hydrogel capped silver nanoparticles are extremely potent for inducing lethality in pathogenic bacteria. In addition, supramolecular hydrogel capped were reported to yield various bioactivities which is related to microorganism inactivation [13-14].

 

4. The conclusion part should be more concise.

 

Reply:

Thanks for the comments. This part had been reworded in Lines 485-495. In this study, three essential operating parameters influencing CNT-coated plasma inactivating ability were evaluated in environmental-controlled chamber. Under the higher ACH condition, the CNT-coated plasma performed higher bioaerosol purifying efficiency even accompanied with the mechanical dilution of clean air exchange. Increasing flowrate and operating voltage could increase the inactivating ability of CNT-coated plasma apparatus. Also, this apparatus demonstrated its satisfied cleaning performance to suppress the airborne bacteria concentration in field medical environment. The approaches of preparing a CNT-coated plasma will be improved and targeted on energy-saving and cost-down. Investigation of the inactivating effects of the CNT-coated plasma to various microorganisms will also be conducted to expand the applicability of the emerging technology.

 

 

5. The discussion regarding the effect of operating flow rate of inactivation efficiency on bioaerosols is inappropriate. Explore it properly.

 

Reply:

Thanks for the comments. In the experimental results on airborne bacteria inactivation conducted by Perhn et al. [36] and Timmeran et al. [37], plasma-generated reactive species, e.g., ions and hydroxyl radical, is the major antimicrobial agent. Lower airflow velocity may increase the opportunity for bioaerosols to exposed under antimicrobial agent. This part had been revised and added literature for illustrating in Lines 396-416.

 

6. Give the statistical accounts of the biological experimental outcomes.

 

Reply:

Thanks for the comments. The statistical accounts, R² and p vaule, of all k_n and k_CNT had been added in this article.

 

7. Give the precautionary measures regarding the work of l

 

Reply:

Thanks for the comments. The l virus is a non-infectious virus. It was utilized as the surrogates for studying airborne dispersion of SARS-CoV-2 in previous study [32]. Therefore, no special precautions have been taken. The description was revised in Lines 117-121.

 

8. Explain the Mechanical ventilation of E. coli in detail.

 

Reply:

Thanks for the comments. This part had been added in Lines 301-313. When the fresh air make-up in the environment-controlled chamber set at ACH = 0.5 (medium rate) and 1.0 (high rate) hr^-1, the kn value of the E. coli bioaerosol were 0.091 and 0.145 min^-1, respectively(R² = 0.99, p < 0.0001). These results indicated the kn value increased obviously with ACH. In these operating conditions, the mechanical bioaerosols was ventilation dilution. The increasing fresh intake air resulted in an obvious dilution effect on airborne bacterial bioaerosols inside the environment-controlled chamber. Also, for the l virus bioaerosol, the kn values were 0.081, and 0.138 min^-1 with the ACH set at 0.5 and 1.0 hr^-1, respectively (R²=0.99, p < 0.0001, shown in Fig. 6). These l virus bioaerosol data also revealed similar trends of ventilation dilution as the E. coli bacterial bioaerosol presented in the environment-controlled chamber. This meant that ventilation dilution (ACH) is a non-negligible mechanical removal mechanism in natural decay’s affecting parameters. Therefore, under the next CNT-coated plasma tests, the bioaerosol removal ability should deduct ventilation dilution effect.

Reviewer 2 Report

Manuscript Number; coatings-1950448

Title; Inactivating Ability Evaluation on Bioaerosols by Carbon-nanotube Coated Plasma Treatment for Indoor Air Cleaning

Although the topic is of interest to the Scientific community, before considering it for publication, this paper should be improved. Authors should reconsider the main objective of the paper according to the content. They should try to synthesize and emphasize the study's main findings and avoid long sentences. Furthermore, authors should avoid drawing risky conclusions.

Evaluation; Minor Revision.

                      

1.             Line 33-34;  The study showed that modern people spend an average of 87.2% of their time indoors. Therefore, indoor air quality is a significant environmental and health issue [1].

Reference;  Lance, W. Indoor Particles: A Review. J. Air Waste Manag. Assoc. 1996, 46, 98–126 is very old data (more than 25 years old).  Could you please up-to-date the data?

2.             Line 38-40; Please add the references.

3.             Line 66; 99.999% and further within the manuscript and tables: Many numeric data are given with too many significant figures; 2 significant figures suffice, and 3 suffice in case the first significant figure is "1".

 

4.             Conclusion; The conclusions could be further developed, there is a lot of interesting data in the article.

Comments for author File: Comments.pdf

Author Response

comments

1. Line 33-34; The study showed that modern people spend an average of 87.2% of their time indoors. Therefore, indoor air quality is a significant environmental and health issue [1]. Reference; Lance, W. Indoor Particles: A Review. J. Air Waste Manag. Assoc. 1996, 46, 98–126 is very old data (more than 25 years old). Could you please up-to-date the data?

 

Reply:

Thanks for the comments. This part had been reworded and added new references. Bioaerosols, as the major indoor contamination sources, can cause lots of respiratory system problems, like allergic syndromes, toxic reaction and infectious diseases, and also obviously affect indoor air quality in modern society [1]. Among these bioaerosols, bacteria and virus, as the major pathogenic components, cause serious health damage and cost consumption in health-care facilities. SARS-CoV-2 nosocomial infection, for example, has been discovered in numerous health-care facilities on a global scale [2-4]. This part had been reworded in Lines 31-36.

 

 

2. Line 38-40; Please add the references.

 

Reply:

Thanks for the comments. This part had been revised as the following. For protecting patients and workers in health-care facilities, plenty of physical and chemical air-cleaning techniques such as negative ion releasing, electrostatic precipitation, particle filtration, ozone generation, nano-particle, photocatalytic oxidation, ultraviolet germicidal irradiation, and disinfectant spraying, have been developed and evaluated to inactivate indoor bioaerosols contamination [8].

[8] Noorimotlagh, Z.; Mirzaee, S.A.; Jaafarzadeh, N.; Maleki, M.; Kalvandi, G.; Karami, C. A systematic review of emerging human coronavirus (SARS-CoV-2) outbreak: focus on disinfection methods, environmental survival, and control and prevention strategies. Environmental science and pollution research international 2021, 28, 1-15.

 

 

3. Line 66; 99.999% and further within the manuscript and tables: Many numeric data are given with too many significant figures; 2 significant figures suffice, and 3 suffice in case the first significant figure is "1".

 

Reply:

Thanks for the comments. The description of Line 66 had been reworded as the following sentences. Gallagher et al. [25] have used it to achieve 5-log reduction of indoor E.coli bioaerosol during a 2-minute testing time. Another, the significant figures of the results in this work had been set on 2 significant figures.

 

 

4. Conclusion; The conclusions could be further developed, there is a lot of interesting data in the article.

 

Reply:

Thanks for the comments. This part had been reworded in Lines 485-495. In this study, three essential operating parameters influencing CNT-coated plasma inactivating ability were evaluated in environmental-controlled chamber. Under the higher ACH condition, the CNT-coated plasma performed higher bioaerosol purifying efficiency even accompanied with the mechanical dilution of clean air exchange. Increasing flowrate and operating voltage could increase the inactivating ability of CNT-coated plasma apparatus. Also, this apparatus demonstrated its satisfied cleaning performance to suppress the airborne bacteria concentration in field medical environment. The approaches of preparing a CNT-coated plasma will be improved and targeted on energy-saving and cost-down. Investigation of the inactivating effects of the CNT-coated plasma to various microorganisms will also be conducted to expand the applicability of the emerging technology.

Round 2

Reviewer 1 Report

In the introduction part author should change as mentioned below:   "hydrogel capped were reported to yield various bioactivities which is related to mi-63 croorganism inactivation [13-14]."  should be  "hydrogel capped nano systems were reported to yield various bioactivities which is related to mi-63 croorganism inactivation [13-14].".

 

Author Response

Thank you for your comments.  This section has been revised on lines 63-65. 

Author Response File: Author Response.pdf