Nano silver was investigated for antibacterial activity on cotton fabric
The application of nanoparticles to textiles has attracted considerable interest due to their novel physicochemical properties and potential applications. However, some of these particles are toxic or poorly effective, which makes them unsuitable for applications in medicine, filtration, textiles, and pollution exclusion. For example, nano-TiO2 for crack cleaning properties and applications in sanitary textiles [1-3] and ZnO nanoparticles for UV blocking properties, antibacterial and applications in medical and protective clothing [4, 5]. Nano silver have long been non-toxic, intolerant of disinfectants, able to eliminate more than 650 species of bacteria, viruses and fungi. Therefore, silver nanoparticles attract more and more attention from scientific and industrial circles from fields such as textile science [5, 6], medicine [7], agriculture [8], sensing transformers and detectors [7], and catalysts [9].
The antibacterial activity of Nano silver containing materials as diverse as polyurethane foam can be used for water treatment [10].
Cotton is a popular material for the production of sports and leisure textiles. It has excellent hygroscopicity. However, damp cotton can be easily attacked by bacteria.
The body’s decomposition products have a characteristic odor [11]. A recent study showed good antibacterial effect of nanoscale colloidal silver solution on polymer and textile fabrics [6, 12].
The objective of this study is not only to synthesize silver nanoparticles using microwave radiation as a heating source, but also to investigate the surface morphology of antibacterial cotton fabrics and the relationship between antibacterial properties and content Nano silver on cotton fabric was discussed. . Furthermore, the washing resistance to bacteria of cotton fabrics treated with nano silver was also examined.
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Experiment
Vật liệu
Used plain cotton fabric (107 g/m2) produced by Phuoc Thinh Textile Company, Ho Chi Minh City, Vietnam. AgNO3, Polyvinylpyrolidone (PVA) and Ethylenelycol (C2H4(OH)2) obtained from MERCH-Germany were purchased from Hoa Nam-Vietnam Company. Escherichia coli (E. coli) (ATTC 25922) and Staphylococcus aureus (S. aureus) (ATCC 290408) provided by Pasteur Institute-Ho Chi Minh City, Vietnam. Nutritional agar was provided by Microbiology Laboratory – University of Natural Sciences, Ho Chi Minh City, Vietnam.
Synthesis of nanoscale nano silver solution
A small amount of 0.70 g of PVP and 50 ml of C2H4(OH)2 were mixed with a magnetic stirrer at 80 – 900C for 1 h.
Then, 0.05g AgNO3 was added to the PVP solution. The solution was placed in the microwave chamber for 4 min at 160 W (figure 1). Finally, a yellow nanoscale colloidal silver solution was obtained.
Visible UV absorption behaviors for silver nanoparticle suspensions were recorded using a UV-VIS spectrometer (Varian, model 100, Australia). The size and shape of the silver nanoparticles were measured using a transmission electron microscope (TEM) JEM model 1400, 100 kV. The size distribution of the particles was determined using the UTHSCSA Image Tool 3.00 software.
Prepare antibacterial cotton fabric
The concentrations of colloidal silver solutions varied widely – 20, 50, 80 and 100 ppm – by diluting each nano-sized colloidal silver solution with distilled water. Cotton fabric (d = 9 cm) was padded with each concentration of colloid for about 5 min and wrung 100% wet using the test pad at constant pressure. Samples were dried immediately at 800 C for 15 min. Then, the samples were washed in water for 15 min and dried at 800 C. The dispersibility of silver nanoparticles on the cotton fabric surface was estimated using field emission scanning electron microscopy ( FESEM, S-4800) was operated at 5kV and used at 20000 magnification.
Inductively coupled plasma atomic absorption spectroscopy (ICP-AAS) was used to measure the residual amount of silver particles on the cotton fabric surface. We compared the concentrations of silver particles on the fabrics before washing with those on them after 5, 10 and 15 washes.
Silver nano antibacterial test
We used the Colony Count Method to study the antibacterial properties of fabrics finished with a nanoscale colloidal silver solution. The effect of bacterial strains was determined by the relationship
= (N1-N2)/N1*100%
where η is the percentage of bacteria removal, N1 is the number of viable colonies from the control sample, and N2 is the number of viable colonies from the test sample.
Results and Discussion
Characteristics of nano silver solution
The reduction of silver nanoparticles is clearly visible from the color change associated with it (from white to yellow). Figure 2 shows the UV-VIS absorption spectrum and the image of the nanoscale colloidal silver after the reduction process. As shown in Figure 2, the absorbance of nanosilver synthesized by microwave heating is very high. According to Bee’s law, the visible UV absorbance is proportional to the path length and the concentration of the suspension
Figure 1. Nano Silver solution in the microwave chamber.
Therefore, it can be concluded that the suspension of microwave heating has a high concentration of Ag nanoparticles. The sharp peak at 407 nm can be demonstrated to be the narrow size distribution of the silver nanoparticles formed in solution, because the peak absorption peaks shift to longer wavelengths as the particles become large. [13] and more uniform microwave heating [14]. As shown in figure 3, the visible UV spectrum of the silver nanoparticles did not change after a one-month aging period. It can be concluded that the stability property of silver nanoscale in solution is very high. The TEM image and the Ag nanoparticle size distribution results showed that the silver nanoparticles were found to have a spherical shape, with an average size of about 7-11 nm (Figure 4).
Figure 4. Transmission electron microscopy image and particle size distribution of nano silver.
Morphology of antibacterial cotton fabric
Figure 5. SEM image of antibacterial cotton fabric treated by immersion in colloidal silver solution: a) control; b) 20 ppm; c) 50 ppm; d) 80 ppm; e) 100 ppm.
Figure 5 is the FESEM image of antibacterial cotton fabrics with different Ag nano-adhesive content. As expected, silver nanoparticles are usually well dispersed on the fiber surface in each fabric.
On the other hand, the surface morphology and the Ag nanoparticle content on the cotton fabric (table 1) changed with the concentration of the nanoscale colloidal silver solution.
In Figure 5b, the suspension concentration of colloidal nano silver solution was low, silver nanoparticles were observed only at the cotton fiber surface, indicating low grafting content. As the concentration increased, the Ag nanoparticles were well dispersed on the cotton surface (Figures 5c and 5d) with a few particles agglomerating, and the nanosilver content on the cotton fabric also increased.
With the suspension concentration further increased, more Ag nanoparticles were clustered together on the fiber because of their high surface free energy, thus, larger agglomerates were observed on the cotton fiber surface. (Figure 5e).
However, Hoon Joo Lee and Sung Hoon Jeong [6] concluded that the agglomerated silver particles did not seem to have any adverse effect on the antibacterial activity of nanoscale colloidal silver on cotton samples.
Antibacterial properties of antibacterial cotton fabric
Effect of nanoscale colloidal silver concentration on the percentage of bacteria reduction
The antibacterial activity of cotton fabrics is a result of the presence of Ag nanoparticles grafted on their surface. The influence of the suspension concentration of nano silver colloid on the antibacterial activity of cotton fabric is presented in Table 2.
It was also found that the percentage of bacteria decreased with increasing concentration of nano-silver colloidal size and corresponded with the nano-silver content on cotton fabrics. When the concentration was lower than 50 ppm, the percentage reduction was higher for E. coli bacteria and S. aureus.
It is known that the structure of gram-positive and negative cell walls has different components. The peptidoglycan layer (about 20-30 nm) in gram-positive bacteria is thicker than in gram-negative bacteria [7]. However, when the concentration was above 50 ppm, the percentage of bacteria decreased, indicating that the increase slowed down.
The above results show that the silver nanoparticles on the cotton surface are necessary to inhibit the growth of bacteria.
Effect of exposure time on bacterial reduction
The effect of contact time on bacterial rate reduction with antibacterial cotton (cotton fabric buffered with 100 ppm nanoscale colloidal silver concentration) against E. coli and S. aureus is shown in Fig. 6.
It can be seen that the reduction of bacteria on cotton fabric increased to 65% after 10 h of exposure to E. coli or S. aureus. It can be clearly seen that the reduction percentage of S. aureus is lower than that of E. coli at 10 h, because the cell wall for gram-positive is composed of linear polysaccharide chains cross-linked by short peptides to form a rigid three-dimensional space. structure [15].
From Figure 6, it can be seen that the percentage reduction of nanosilver on cotton fabric was 99.99% and 99.96% after 15 h exposure to E. coli and S. aureus. Therefore, it can be suggested that the antibacterial activity of cotton cloth soaked in nanosilver colloidal solution is excellent.
Affect washing time to reduce bacteria
Silver nanoparticles on the cotton surface can be washed away when immersed in water. Therefore, the adhesion of silver nanoparticles on cotton fabric was evaluated by dipping the sample (sample buffered with a concentration of 100 ppm nano silver colloid) in water and stirring it for a certain time.
The antibacterial activity was examined after immersion. Table 3 shows the results for 5, 10, and 15 washes. It can be seen that the antibacterial rate of the sample washed for 15 times is lower than that of the sample washed for 5 times, and the content of silver nanoparticles on cotton fabrics decreases with increasing number of washings.
This phenomenon is related to the weak physical bond between the silver nanoparticles and the cotton surface. However, even after washing 10 times, the content of silver nanoparticles on cotton fabric is about 370 mg/kg giving an antibacterial rate of about 50%. So the durability of antibacterial cotton fabric has been satisfied.
Conclusion of the effectiveness of nano silver on cotton fabric
Silver nanoparticles are synthesized by a reduction method in which microwave radiation is used as a heating source, the prepared silver nanoparticles are quasi-spherical with a particle size distribution of about 7-11 nm .
The structure of nano Ag did not change after bonding the cotton surface. The silver nanoparticles are coupled and well dispersed on the cotton fabric surface. With the increase of nanoscale colloidal silver concentration during soaking, especially for concentrations above 80ppm, Ag nanoparticles became agglomerated on the cotton surface.
The antibacterial rate of cotton fabric shows excellent antibacterial activity against the tested germs. Nano silver content on cotton fabric and antibacterial rate were adjusted by controlling the concentration of sized colloidal nano silver during soaking.
When the concentration was 80 ppm, the antibacterial rate was 99.91% for E. coli and 99.31% for S. aureus. In addition, antibacterial cotton fabric has good washing fastness achieved after 10 washes.
Source: Investigation of antibacterial activity of cotton fabric incorporating nano silver colloid
Ngo Vo Ke Thanh and Nguyen Thi Phuong Phong Laboratory for Nanotechnology, Vietnam National University Ho Chi Minh City, Community 6, Linh Trung Award, Thu Duc District, Ho Chi Minh City, Vietnam