The graphene nanoribbons based filter membrane for antibacterial application using low applied voltage

ABSTRACT:

Graphene nanoribbons (GNRs) fabricating from multiwalled carbon nanotubes (CNTs) were used to synthesize the filter membrane by the vacuum filtration method. One of the important factors affecting the membrane’s stability was GNRs dispersion time and that was investigated from 5 to 20 minutes. Then, the GNRs based filter membrane was utilized to define the antibacterial ability by applying in low voltage range of 1-5V in 5 seconds. Both raw CNTs and GNRs were characterized by transmission electron microscopy (TEM) while filter membrane was characterized by scanning electron microscopy (SEM and evaluated the antibacterial ability by a power supply equipment. The results showed that GRNs dispersion in 15 minutes was optimized to fabricated the filter membrane and the bacterial destruction effect was extraordinary when applying the low voltage in short time.  Therefore, the GRNs based membrane filter is promising material to be utilized in the antibacterial field.

Keywords: graphene, graphene nanoribbons, carbon nanotubes, filter membrane, antibacteria.

1. Introduction

In the serious situation of Covid-19 pandemic, the field of antibacterial materials research is a leading trend and intense discovery. Composite materials capable of destroying bacteria are widely used in human life and are highly commercialized. Most applications are aimed at commonly used equipment such as masks, protective gear, or air purifiers. Most materials must be durable, user-friendly, environmentally friendly, and especially excellent antibacterial performance [1,2].

Graphene material was being used a lot in the research of germicidal materials because of its superior properties such as mechanical strength, large surface area, good electrical conductivity, and especially effective bactericidal ability [3-5]. Among the types of Graphene, nanoribbon structure was an outstanding shape and properties suitable for making gas filter membranes. On the side of the shape, the Graphene Nanoribbons were a good ability to intertwine, leading to narrowing of the pore size when fabricating the membrane. Therefore, the air would pass through easily but PM 2.5 dust particles and the bacterial would be trapped. On the side of properties, the Graphene Nanoribbons’ electrical conductivity is outstanding property for destroying bacterial using a low applied potential.     

Many scientists have researched Graphene composites for antibacterial applications. In 2021, Biagiotti et al [6] covered reduction Graphene oxide from commercial Graphene oxide onto the surface of cotton fabric. The result was effectively protected against bacterial on the cotton surface. Zhang et al [7] fabricated reduction Graphene oxide/ polyacrylonitrile composite to enhance ability air filtration and the filtration efficiency was increased above 99.9%. In 2019, the air filter membrane fabricating by laser indued Graphene method was researched by Stanford et al [8]. The high temperature of 250⁰C was created after charging with a voltage of 15 V and that was shown effective antibacterial mechanism.

In this study, Graphene Nanoribbons (GNRs), after synthesizing from CNTs, were fabricated antibacterial membrane. The dispersion ability of GNRs in isopropyl alcohol solvent was investigated to improve the fabrication membrane process. The sample was analyzed and evaluated antibacterial affordability by low applied voltage.

2. Material and method

2.1. Material

Carbon nanotubes (CNTs) was supplied by Ntherma Corp, USA. Potassium permanganate (KMnO₄, Sigma-Aldrich, ≥ 99%), Sulfuric acid (H₂SO₄ 99.999%, Sigma-Aldrich), Hydrogen peroxide (H₂O₂, 50%, Solvay, Thailand), Isopropanol (IPA, (CH₃)₂CHOH, 99.5%, Sigma-Aldrich) and Whatman Grade 589 Cellulose paper (Sigma-Aldrich) were used.

2.2. Method

2.2.1. Fabrication Graphene Nanoribbons

Graphene Nanoribbons were fabricated from delaminating of multiwall CNTs by chemical methods due to strong oxidation agent in the acid environment. This method was known as the effective synthesis for high quality GNRs [9]. Briefly, 1.75g multiwall CNTs and 8.75g KMnO₄ were stirred with 300 ml H₂SO₄ solvent at room temperature for 30 minutes before being increased the temperature to 100⁰C for 60 minutes. This composition was added 5 ml H₂O₂ after cooling in the ice bath. Then, the solution was dissolved about 3 liters of deionized water to filter in the vacuum filtration system and dried at 100^oC in oven [10].

Fabrication Graphene Nanoribbons based filter membrane

Graphene Nanoribbons 0.05% concentration was slowly poured into isopropyl alcohol (IPA) solution. Then, the GNRs in IPA solution were put into an ice bath before taking on probe sonication which decreased a high temperature in the dispersion process.  The dispersion ability of GNRs depends on setting up the time from 5 to 20 mins with 70% amplitude of the probe sonication equipment. After that, the uniform solution was slowly poured into vacuum filtration system. Finally, the sample was put in oven at 80⁰C temperature in 30 minutes and easily peel off Graphene Nanoribbons based filter membrane from Whatman paper.

2.2.2. Evaluating antibacterial ability using low applied voltage

Figure 1. The diagram of evaluating antibacterial process

The testing process was shown distinctly in this diagram in Figure 1. The Graphene Nanoribbons based filter membrane was prepared into the standard sample with the dimension of 2cm x 2cm. Then, the definite volume 5 µl E. coli solution of concentration 10⁶ M was slowly dropped onto the surface and dried naturally about 10 minutes. Next, the sample was connected with a power supply equipment which set up the different voltages from 1V to 5V on a definite period. Finally, the evaluation was analyzed due to comparing SEM images between applied and non-applied voltage.

2.3. Characterization

In this study, the structure of raw CNTs materials and Graphene Nanoribbons were obtained by scanning electron microscopy (FESEM S4800, Hitachi, Japan), and transmission electron microscopy (TEM J1400, Jeol, Japan) and surface and cross section of the Graphene Nanoribbons based membrane was obtained by SEM. The evaluating antibacterial test by low applied voltage was analyzed by YIHUA PS 3010D power supply equipment.

3. Result and discussion

The Nanoribbon shape of Graphene after synthesizing from multiwall Carbon Nanotubes by the oxidation method was changed and which was proved distinctly in Figure 2.

Firuge 2. The TEM images of a) Carbon Nanotubes and b) Graphene Nanoribbons

The result of TEM (Figure 2) indicated clearly a different structure between one-dimension of CNTs and two-dimension GRNs. The structure of CNTs (Figure 2a) was a homogenous tube form include the diameter inside under 10 nm and diameter outside approximately 30 nm and that was proved that CNTs was multiwall shape through its thickness of wall about 20 nm. Oppositely, Graphene Nanoribbons were shown only one boundary in the plane instead of two lines of CNTs and the diameter of the ribbon was larger than CNTs about 50 nm in Figure 2b. The result of GNRs was completely consistent with the previous investigation and the fabrication mechanism was reported [11]. The Graphene with the nanoribbon shape was exfoliated from the nanotube perfectly due to the strong oxidation agent (KMnO₄) in the intense acid environment (H₂SO₄). Therefore, the GNRs were fabricated successfully from CNTs and used to fabricate the Graphene Nanoribbons based filter membrane.

The structure of the Graphene Nanoribbons based filter membrane was shown distinctly via various scales in Figure 3. The shape of the membrane in the macroscopic scale which was captured by digital image (Figure 3a) while SEM image (Figure 3b) shown that nanoribbon of Graphene tightly intertwined each other like a net structure with many tiny holes. Especially, Figure 3c showed that the pore sizes are extremely small about 50 nm which fresh air can go through the membrane easily but the bacterial will be trapped. Moreover, the thickness of filter is approximately 60 nm shown in Figure 3d.

Figure 3. The structure of Graphene based membrane a) the digital image,

b) the SEM image of 1  scale, c) the SEM image of 200 nm scale,

d) the cross-section SEM

The Graphene Nanoribbons were able to combine tightly with high density due to dispersion ability in solution and that was an outstanding point when comparing with other structures of Graphene. Patra et al [12] fabricated the Graphene oxide-based membrane by the same vacuum filtration method and the results were obtained an ununiform structure including many holes and cracks. The problem was caused by the discrete bonding of the Graphene oxide larger film under the influence of the Van der Waal forces. Therefore, the important factor affecting the uniform membrane was the ability to disperse Graphene Nanoribbons in the solvent and this was investigated in Table 1.

Table 1. The dispersion process of Graphene Nanoribbons in the solution with different sonication time

The investigation and evaluation of the quality of the Graphene Nanoribbons based filter membrane depend on sonication time are shown distinctly in Figure 4.

Figure 4. The cross-section SEM of the membrane with different sonication time a) 5 minutes, b) 10 minutes, c)15 minutes, d) 20 minutes.

The cross-section SEM result in Figure 4 was shown the structure and analyzed the quality of the membrane. Figure 4a was obtained that the structure was many defects including the cracks and large gaps in a short sonication time of 5 minutes. When the period was increased to 10 minutes in Figure 4b, the membrane structure was improved due to narrow gaps. The structure of the membrane was highly effective when the dispersion time was longer than 15 minutes (Figure 4c) and that was not significantly changed for 20 minutes (Figure 4d). The structure of the membrane depends on the dispersibility of Graphene Nanoribbons in sonication time. When the sonication time under 10 minutes was not enough for the Graphene Nanoribbons to completely disperse in the solvent leading to the formation defects. In contrast, Graphene Nanoribbons were homogeneously dispersed in the solvent for a longer time as 15 minutes and that result was a uniform structure and high density. However, the sonication time is long as 20 minutes resulting in defects at edges of the ribbons due to the high generated temperature. Therefore, the sonication time of Graphene Nanoribbons solution is 15 minutes evaluating to be an optimal factor in the fabrication process.

Moreover, the thickness of the membrane measuring relatively via cross-section SEM (Figure 4) and the resistance investigating by the multimeter equipment were shown in the graph (Figure 5).

Figure 5. the Graph of the relation between the thickness

and the resistance

The graph showed the relationship between the thickness and the resistance of the membrane. When the sonication time was increased 5 minutes, 10 minutes, 15 minutes, 20 minutes while the thickness was decreased 104.0 m, 98.8  m, 88.7  m, 87.3 m, respectively. The resistance result was simultaneously decreased 15.1Ω, 9.9 Ω, 6.5 Ω, 5.3 Ω when the sonication process was longer. The result was obtained that the membrane’s thickness was reduced gradually over time demonstrating the narrow of the crack. The reduced defects with increasing density of the structure led to enhance electrical conductivity for the membrane. Besides that, both the thickness and the resistance were not significantly different values when the sonication period was longer from 15 minutes to 20 minutes. Based on the uniform structure (Figure 4) and the low resistance (Figure 5), the dispersion time of 15 minutes was chosen as an optimized factor for the antibacterial test. Moreover, the resistance of the membrane was obtained a low value and which was an outstanding factor for destroying bacterial by applying a small voltage.

After investigating the structure and resistance of the membrane, the dimension of 2cm x 2cm of GR15 sample containing bacteria was prepared to investigate the ability to destroy bacteria by the charging method and their results were shown in Figure 6.

Figure 6. The SEM of the E.coly bacterial when charging various potential of a) 0V, b)  1V, c) 3V, and d) 5V

 th The applied voltages were 1V (Figure 6b), 3V (Figure 6c) and 5V (Figure 6d) in 5 seconds. Figure 6a showed the ellipse shape of the E.coli bacteria without electrical stimulation and the structure of bacterial was not changed with applied voltage 1V. When the sample was applied with a higher voltage of 3V, the cell membrane was broken leading to a transformation shape. The significant change was obtained from the vestige of the residue of the cell membrane after stimulating with a voltage of 5V. The destroying bacterial mechanism by low applied voltage was demonstrated distinctly [8]. The generating temperature was caused by the carbonization process led to thermally eliminating not only all biological molecules but also the essential nutrients for supporting microorganisms. Based on the excellent conductive properties of Graphene Nanoribbon, the filter membrane was an outstanding performance and a potential material for the antibacterial field by charging a low potential.

4. Conclusion

In this research, Graphene Nanoribbons synthesizing from Carbon Nanotubes were used to fabricate the filter membrane. Both the uniform structure and the low resistance were obtained with the sonication time of 15 minutes. The Graphene-based membrane was destroyed bacterial when charging a low potential of 5V in a short time 5 seconds. Therefore, Graphene Nanoribbons and their filter membrane were promising and potential material in the antibacterial field.                                                           

ACKNOWLEDGEMENTS:

This research is funded by the Saigon Hitech Park Labs, under grant number NVTXTCN 6/2021.

REFERENCES:

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MÀNG LỌC GRAPHENE NANORIBBONS ỨNG DỤNG KHÁNG KHUẨN NHỜ SỬ DỤNG ĐIỆN THẾ THẤP

ThS. THÁI DƯƠNG¹

 ThS. NGUYỄN CÔNG DANH¹

 ThS. ĐỖ THANH SINH¹

ThS. TIÊU TƯ DOANH¹

¹Trung tâm Nghiên cứu Triển khai - Khu Công nghệ cao,

Thành phố Hồ Chí Minh

TÓM TẮT:

Graphene nanoribbon (GNRs) chế tạo từ than ống nano đa thành (CNTs) được sử dụng để làm màng lọc bằng phương pháp lọc hút chân không. Một trong những yếu tố quan trọng ảnh hưởng đến độ bền của màng là thời gian phân tán GNRs và thời gian khảo sát từ 5 phút đến 20 phút. Sau đó, màng lọc từ Graphene Nanoribbons được dùng để đánh giá khả năng kháng khuẩn bằng cách sử dụng nguồn điện thế nhỏ từ  1V đến 5V trong vòng 5 giây. Cả 2 vật liệu CNTs và GNRs đều được phân tích bởi kính hiển vi điện tử truyền qua (TEM) trong khi màng lọc được phân tích bởi kính hiển vi điện tử quét (SEM) và đánh giá khả năng kháng khuẩn bằng thiết bị cung cấp nguồn điện. Kết quả nghiên cứu cho thấy điều kiện phân tán Graphene Nanoribbons trong thời gian 15 phút là tối ưu trong việc chế tạo màng lọc và hiệu quả tiêu diệt vi khuẩn là nổi trội khi sử dụng một điện áp nhỏ trong khoảng thời gian ngắn. Do đó, màng lọc dựa trên Graphene Nanoribbons là vật liệu đầy hứa hẹn để ứng dụng trong lĩnh vực kháng khuẩn.

Từ khóa: Graphene, Graphene Nanobibbons, than ống nano, màng lọc, kháng khuẩn.

[Tạp chí Công Thương - Các kết quả nghiên cứu khoa học và ứng dụng công nghệ, 

Số 20, tháng 8 năm 2021]