2.1 Materials

2.1.2 Chemicals

The chemicals required for the purpose of nanoparticle synthesis are silver nitrate (AgNO₃), sodium hydroxide pallets (NaOH), ascorbic acid (C₆H₈O₆), and acetic acid (CH₃COOH). These are purchased from Merck, Germany. Additionally, for dying, CI Direct Red 89 (Megadirect Scarlet BNLE), leveling agent, and Glauber’s salt (Na₂SO₄×10H₂O) of analytical grade are collected from Orient Chem., Bangladesh. The chemical structure of CI Direct Red 89 is shown in Figure 1. It shows the anionic nature in dye solution, which participates in bonding with nanoparticles.

Figure 1

CI Direct Red 89.

2.2 Methods

2.2.1 Preparation of nanosilver-deposited fabric

Nanoparticles are deposited on the fabric surface directly by the in situ process. Silver nanoparticles are synthesized by reduction of AgNO₃ salt with ascorbic acid (C₆H₈O₆) as shown in Figure 2. Initially, the fabric is subjected to alkali treatment in slack condition for surface activation. This enables the cotton fabric to absorb and formation of silver nanoparticles. This treatment is done on 3.0 g fabric dipping in 100 ml of 1.0M aqueous solutions of NaOH for 5 min at room temperature. The fabric is then taken away from bath and washed extensively. The alkali-treated fabric is instantly immersed into the 0.01M AgNO₃ aqueous solution for 1.0 h. Then, it is rinsed well with water. Silver nanoparticles are then synthesized by immersing fabrics into the 150 ml aqueous solution of C₆H₈O₆ (0.01M) for 45 min. The sample is afterward removed from the bath, rinsed with water, and then immersed in aqueous acetic acid at room temperature and dried at 60°C.

Figure 2

In situ synthesis and deposition process of Ag nanoparticles on cotton fabric.

2.3 Analysis and measurement

3.1 Surface morphology by SEM analysis

The existence and intensity of nanodeposition on the treated fabric are investigated by taking the SEM images in different magnifications and placed in Figure 3(b)–(d). The SEM image of the untreated fabric is also taken and placed in Figure 3(a) for better understanding and comparison. These images represent the larger view of the fiber and enable to show the deposition of nanoparticles. The images show that nanoparticles are distributed evenly through the whole surface area and no agglomeration of silver nanoparticles is found.

Figure 3

FE SEM image of (a) untreated and (b–d) Ag°-deposited fabric on x1000, x3000, and x5000 magnifications. FE, field emission; SEM, scanning electron microscopy.

3.2 Energy dispersive spectroscopy

The EDS results of untreated and treated samples are shown in Figure 4. The untreated fabric shows C (carbon) and O (oxygen) as characteristics peaks of cellulose as found in Figure 4(a). After nanosilver deposition, a new peak appears at 3 keV, which attributes to the signal of silver as shown in Figure 4(b). Both EDS and the SEM images have strong evidence of the formation and deposition of Ag° on the surface of cotton fabric. The elemental mass percentage of silver obtained from EDS is represented in Table 1. The table shows that the elements for untreated fabric are carbon and oxygen, which are the basic elements of cellulose. The treated fabric shows carbon, oxygen, and silver as its elements. The elemental mass of Ag in the treated fabric is obtained as 1.58%. The effect of this nanodeposition is analyzed in the subsequent section.

Figure 4

EDS spectrum of (a) untreated and (b) Ag°-treated fabric. EDS, energy dispersive spectroscopy.

3.3 X-ray diffraction analysis

The XRD pattern of Ag°-deposited fabric is shown in Figure 5. The figure shows that there are four diffraction peaks of Ag° deposition exhibited at 38°, 44.32°, 64.8°, and 78°. These sharp peaks confirm the formation of Ag° crystal on the fabric surface. It also confirms that silver ions have been reduced to nanometallic state inside the fabrics network. From the XRD data, the average crystalline sizes are determined by the Debye–Scherrer Equation (3) as follows:

where D is the average crystalline size, K is the crystalline shape factor (0.94), λ is the wave length of X-ray (0.15406 nm), β is the full width half maximum (FWHM), and θ is the Bragg angle in degree. The average crystalline size of Ag° in the fabric is about 26 nm, which is obtained from the peak analysis of Figure 5 using Equation (3).

Figure 5

XRD pattern of Ag°-deposited fabric. XRD, X-ray diffraction.

3.4 Dyeing performance evaluation

The color strength (K/S) and the reflectance (R%) curve of untreated and nano-Ag-treated fabric obtained from the spectrophotometer are shown in Figure 6(a) and (b). The K/S value of the untreated fabric is 14.38, which lies in between wavelengths 450 and 550 nm as found in Figure 6(a), where as for the Ag°-treated fabric, the value of color strength rises to 22.13 and lies at the same wavelength as for the untreated fabric. The obtained results of color (K/S) strength and dye exhaustion are given in Table 2. The improvement of color strength and dye exhaustion of Ag°-treated fabric are determined by taking the value of untreated and treated fabrics. The Ag°-deposited fabric shows 54% increment in color strength. The dye exhaustion percentage of the treated fabric increases about 11%. The color fastness property of untreated and treated fabrics is given in Table 3. The table indicates that the Ag nanodeposition causes improvement in the fastness property. The treated fabric shows better fastness rating as found in washing fastness (shade change), dry rubbing, and light fastness. The other fastness grades and color staining are quite same with the untreated fabric.

Figure 6

(a) Color strength (K/S) and (b) reflectance (%) curve of untreated and Ag°-treated fabric.

In the present investigation for the improvement of dyeing performance, it can be pointed out that the direct dye is an anionic dyestuff with low fastness property. Metallic salt is used for the improvement of the fastness property of the direct dye where the metallic molecules make a complex bond with the dyestuff and improve color fastness quality [21]. In case of Direct Red 89, several anionic sulfonate groups (SO3^-) are presented as shown in Figure 1. The negatively charged dye anions get attracted toward the fiber due to the polarity formed by the Ag⁺ on the fabric surface [22]. As a result, the dyestuff makes a strong bond with nanoparticles and causes the improvement of color strength, better fastness, and higher exhaustion for Ag°-immobilized fabric. The higher dye exhaustion indicates that Ag° has a significant role to reduce the dye wastage.

3.5 FTIR analysis of fabric

Internal bondings of untreated, nano-Ag-treated, and dyed both fabrics are investigated by taking the FTIR pattern as shown in Figure 7. This study reflects the bonding phenomenon of nano-Ag with cotton fiber and dyestuff. The wavelength 3000 – 4000 cm⁻¹ is magnified for showing clearly the newly formed small peak on the dyed fabric. The graph indicates mainly the general characteristic peaks of cellulose fibers 1036 cm⁻¹ (C–O–C stretching), 1317 cm⁻¹ (C–O stretching), 1656 cm⁻¹ (C=O stretching), 2906 cm⁻¹ (–CH stretching), and 3338 cm⁻¹ (O–H stretching). So nanodeposition does not change the chemical structure of the cellulose fiber. It only causes the physical deposition of nano-Ag on the fabric surface. On the other hand, the pattern of untreated dyed fabric is quite different where a new dyestuff is added with the cellulose fiber. The pattern of nano-Ag-treated and dyed fabric shows some new shapes of wave and the peak intensity of curve is also different. A clear peak is found at 1646 cm⁻¹, which is for the C=C stretching, and 2200 cm⁻¹, which is for the C≡N stretching. The dyed and Ag°-treated fabrics show many small packs from 3500 to 4000 cm⁻¹ that is visible after magnification in Figure 7(b). This is assigned for S=O bond from SO⁻³ function of Direct Red [23]. The displacement of peaks is observed in the dyed fabric for precipitation of the dyestuff.

Figure 7

FTIR spectra of untreated fabric, Ag°-immobilized fabric, untreated and dyed fabric, dyed fabric with nano-Ag. (a) Wave number 1000–4000 cm⁻¹ and (b) wave number 3000–4000 cm⁻¹ after magnification. FTIR, Fourier transform infrared spectroscopy.

3.6 Antibacterial properties

The silver nanoparticle is a potential and popular antimicrobial agent. The activity of nanoparticles depends on the size, shape, form, and application methods. In this study, the nanosilver is deposited by the in situ method and the Ag°-deposited fabric shows excellent bacterial reduction against both Gram-positive and Gram-negative bacteria as shown in Figure 8. The bacterial reduction is given with laundering durability, where the treated sample is subjected to 15 homes laundering for the longevity test of modified fabric. The performance of cotton woven fabric against both bacteria is excellent on washing and shows 88% reduction of bacteria for Staphylococcus aureus and 80% for Escherichia coli. The activity reduces gradually after washing with the increase in the washing cycle. The results of antimicrobial tests shown in Figure 8 indicate that the silver nanodeposited fabric is more effective against Gram-positive bacteria compared with Gram-negative bacteria. Additionally, it can be found that the antibacterial activity of present Ag°−deposited fabric is better compared with the results of our previous work on mechanical deposition of Ag° in fabric by the pad–dry–cure method [24].

Figure 8

Bacterial reduction (R%) with wash durability of Ag°-deposited fabric.