Nanotechnology has been one of the most emerging and active areas of research in the last two decades [1]. It is a science that deals with materials in the range of 1 to 100 nm [2, 3]. Nanoscience is adding new dimensions to research everyday [4]. Moreover, the synthesis of nanoparticles is increasing exponentially because of its wide range of applications in the field of optoelectronics [5, 6], biosensors [7], bio-nanotechnology [8] and bio-medicine [9].
The biosynthesis of nanoparticles employing biological microorganisms, such as fungi [10] and bacteria [11] or plant extracts [12-14], has been developed as a simple and viable method in comparison to more complex chemical methods. Different nanomaterials such as copper, zinc, titanium [15], alginate [16], magnesium, gold [17] and silver have been developed for different textile applications. Silver nanoparticles have been recognized as the most effective antimicrobial agent against various microbes, such as bacteria, viruses, and fungi [18]. Silver NPs play a vital role in nanomedicine and nanotechnology [19]. The impact of silver nanoparticles on the colour depth and tensile properties of wool and silk fabrics was critically discussed by Chattopadhyaya and Patel [20].
Previous studies also used typical chemicals to synthesize Zn, Au, Ag, Pd, and Pt nanoparticles. The application of toxic chemicals and their drainage after the application is a significant hurdle to establish an environment of sustainable development. Therefore, to achieve the long-term goal of sustainable development, this research work was planned to explore the potential of natural plant sources to produce herbal synthesized nanoparticles in place of toxic chemicals. Eucalyptus corymbia leaf extract was used to bio-reduce silver into nanoparticles. The bio-reduced silver nanoparticles were also applied by the pad-dry-cure method on cotton textile material to enhance the sustainability of the process in the future. The efficacy of eucalyptus corymbia as a reducing agent of silver was characterized. The antimicrobial potential of treated cotton fabric was assessed against
Silver nitrate crystal [Mw. 169.87] was obtained from S.D. Fine Chemicals ltd. Bacterial cultures of E. coli and S. aureus were procured from NCIM Pune. Chitosan was procured from SRL chemicals in Kanpur. Eucalyptus corymbia leaves were collected locally.
Twenty grams of dried leaves of eucalyptus corymbia were soaked in 200 ml of distilled water, followed by boiling for 30 minutes, and finally filtered twice to get the desired extract. 0.16987 g of AgNO3 salt was dissolved in 1000 ml distilled water to get a 1mM solution. The herbal extract was added to AgNO3 solution at pH 9 to get a 1:4 ratio (herbal extract: Ag salt solution) followed by continuous stirring for 24 hrs at 120 rpm. Then the solution was centrifuged at 12000 rpm in a REMI PR-24 centrifuge. The sediment was washed two times with distilled water and again centrifuged each time. The nanoparticles obtained were dried in an oven at 60°C, from which we got dried nanopowder, which was further characterized.
The nanoparticles [H-AgNPs] were applied to scoured cotton fabric. Before applying H-AgNPs on the cotton fabric, the fabric was scoured again. These biosynthesized nanoparticles were applied to the cotton fabric by the pad-dry-cure technique, followed by curing at 120°C for 3 minutes.
A Horiba Particle Size analyzer (ZX100) was used to analyse the particle size distribution, where distilled and deionized water was used as a dispersing agent working on the principle of dynamic light scattering. UV-visible spectra of H-AgNPs were recorded using Motras Scientific Instruments-UV plus UV Visible spectroscopy. An FTIR instrument was used to characterize the functional group in the nanoparticle solution in the transmittance mode. The spectra of FTIR were recorded at a wavenumber from 500 to 4000 (cm-1). Surface characterization of the nanoparticles was carried out by means of a Field Emission Scanning Electron Microscope NOVA NANOSEM 450 at 10 KV electron voltage. An Energy Dispersive X-ray (EDX) detector was integrated with the X-ray to obtain the chemical composition. A crystallographic study was performed by means of Panalytical Xpert XRD.
The antibacterial efficiency of the treated samples was quantitatively estimated as per the AATCC100 -2004 method. And this was calculated using the following equation:
The test results of various characterization techniques are summarized as follows.
Dynamic Light Scattering (DLS) is the most versatile technique used to identify the size of nanoparticles, which is obtained using a Horiba particle size analyzer (nanoParticaSZ-100V2). The nanoparticle analysis suggests that the Z-average value of nanoparticles is 62.7 nm. The particle size distribution follows a Gaussian distribution, as shown in Fig.1. The narrow distribution of AgNPs shows less variability and a uniform size. It also validated the effective reduction potential of Eucalyptus plant leaf extract.
UV-visible spectral analysis is an intense absorption analysis because of the surface plasmon excitation of conduction electrons in metals; silver as metal was used here. In Fig. 2, herbal extract containing Ag-NPs was analyzed in the 290-800 nm range. Silver nanoparticles show a maximum absorption band in the 390-430 nm range due to surface plasmon vibrations of conducting electrons on the silver metal [21, 22].
FTIR analysis of silver nanoparticles containing herbal extract was conducted to prove its role as a reducing agent and capping agent, as well as the presence of several functional groups. In Fig.3, FTIR results are used to establish the presence of functional groups of Eucalyptus corymbia leaf extract responsible for silver particle reduction to Nanoparticles (Ag+ to Ag0). The stretching of a bonded hydroxyl group from the phenol and or alcohol group is shown by a band between 3257 and 3382 cm-1, while the stretching of –C=C- stretch from alkenes is confirmed by the absorbance peak at 1652 cm-1, which verifies the presence of alkanols in alkaloids, flavones, and tannins in Eucalyptus corymbia leaf extract [23]. The absorbance at 2123 cm-1 confirms the presence of the alkyne group, which has a phyto nature. The FTIR results of this study suggest that the reduction of silver into nanoparticles is guided by (-C=C) and (-OH) hydroxyl groups of Eucalyptus corymbia leaf extract [24, 25].
The aqueous suspension of silver nanoparticles was placed onto clean aluminium foil, allowing the water to evaporate entirely in an oven. Thus, SEM samples of the solution were created.
After that, a specific sample was placed on electrical stubs. Before scanning, all of the samples were gold-coated. FESEM images are shown in Fig 4. The silver nanoparticles are visible, and the particle size distribution is also relatively narrow, which indicates the effective reduction potential of eucalyptus plant extract as an Ag-reducing agent.
It is clear from Fig 4, that the uniformity of Ag-NPs is significantly high. A 62 nm particle size of very high activity was achieved. The particle agglomeration is also visible, confirming these nanoparticles’ high reactivity. Maximum particles are found in a dumbbell shape, which again verifies the reduction potential of leaf extract.
An energy-dispersive X-ray spectrophotometer exploits the photon nature of light. Because a single photon’s energy is only enough to create a quantifiable voltage pulse X-ray in the X-ray range, the output of an ultralow noise preamplifier coupled to the low noise is a statistical estimate of the corresponding quantum energy. A comprehensive representation of the X-ray spectrum is built up practically simultaneously by digitally recording and counting many such pulses in a so-called Multi-Channel Analyzer. The digital quantum counting technique makes the energy dispersive spectrometry technique possible. The EDS approach is quite dependable. The EDX technique can examine microstructures in SEM for their elemental composition in greater depth. The elements and their concentrations are calculated reasonably and accurately because this is a non-destructive study. In an SEM, EDS (EDX) determines the material’s elemental composition.
In Fig. 5 the EDX data indicate the presence of silver nanoparticles. The nanoparticles were kept on aluminium foil during characterization by EDX. The weight % of silver nanoparticles (AgL) was found to be 63.54% with an atomic share of 30.36%, as shown in Table 1.
eZAF Smart Quant Results | ||||||||
---|---|---|---|---|---|---|---|---|
Element | Weight % | Atomic % | Net Int. | Error % | K ratio | Z | A | F |
AlK | 36.46 | 69.64 | 762.37 | 4.12 | 0.2184 | 0.7175 | 0.8302 | 1.0054 |
AgL | 63.54 | 30.36 | 419.26 | 3.71 | 0.3753 | 0.5538 | 1.0672 | 0.9995 |
The X-ray diffraction data ignored the presence of any impurity among the silver nanoparticles, which proves the reduction potential of natural plant Eucalyptus extract.
The full width at half-maximum (FWHM) data was used in Debye-Scherrer’s equation (2) to estimate the crystalline dimension of the silver nanoparticles.
These peaks indicate the (111), (200), (220), and (311) planes of silver nanoparticles. The XRD pattern of the nanoparticles fits the face-centred cubic (FCC) crystal structure as given in the X-pert X-ray library file JCPDS no. 89-3722. It is mentioned in Table 2 that various planes of silver nanoparticles have different sizes, indicating that the particles do not have a spherical shape. Various planes have different sizes in nanometers. Plane 111 has an average crystalline size (diameter equivalent) of 11.42 nm, plane 200 - 6.82 nm, 220 - 10.65 nm, and plane 311 - 10.53 nm. These planes showed a lattice constant of 4.10 Å and a cell volume of 68.92 Å, as similarly observed by some other researchers [26,27, 28].
‘2θ’ of Intense peak | Plane (h, k, l) | Crystalline size (D) nm | Lattice constant (Å) | Cell volume (Å3) |
---|---|---|---|---|
38.12 | 111 | 11.42 | 4.10 | 68.57 |
44.26 | 200 | 6.82 | 4.10 | 69.42 |
64.42 | 220 | 10.65 | 4.10 | 68.92 |
77.39 | 311 | 10.53 | 4.10 | 68.76 |
The antimicrobial efficiency of all samples was evaluated using the AATCC 100-2004 standard against
S. No. | Sample Code | Samples | Bacterial reduction in % (E. coli) | Antibacterial efficiency after 10th laundry | Bacterial reduction in % (S. aureus) | Antibacterial efficiency after 10th laundry in % |
---|---|---|---|---|---|---|
1. | S1 | Blank sample/untreated fabric | -Nil- | -Nil - | -Nil- | -Nil - |
2. | S2 | Sample treated only with AgNPs-100 ppm | 67.0% | 38.5% | 64.2 | 35.0 |
3. | S3 | Sample treated only with AgNPs-200 ppm | 76.2% | 42.3% | 72.4 | 38.2 |
4. | S4 | Sample treated only with AgNPs-300 ppm | 84.0% | 45.2% | 79.6 | 42.6 |
5. | S5 | Sample treated with-[chitosan 0.5% + AgNPs-100 ppm] | 82.5% | 71.2% | 78.0 | 70.8 |
6. | S6 | Sample treated with-[chitosan 0.5% + AgNPs-200 ppm] | 87.2% | 76.5% | 81.3 | 75.4 |
7. | S7 | Sample treated with-[chitosan 0.5% + AgNPs-300 ppm] | 93.2% | 82.4% | 87.0 | 81.3 |
8. | S8 | Sample treated with-[chitosan 1% + AgNPs-100 ppm] | 91.8% | 80.1% | 88.1 | 80.0 |
9. | S9 | Sample treated with-[chitosan 1%+ AgNPs-200 ppm] | 94.6% | 84.2% | 91.2 | 83.7 |
10. | S10 | Sample treated with-[chitosan 1% + AgNPs-300 ppm] | 97.8% | 90.6% | 94.8 | 89.5 |
Antimicrobial reduction against
It can safely be said that chitosan works as a coupling agent between cotton cellulose and silver nanoparticles, as shown in Fig.8.
The cotton fabric was first treated with chitosan to provide an active site for the adsorption of silver nanoparticles to be coupled with the cotton fabric surface, which has plenty of hydroxyl groups due to the availability of cellulose in cotton fibre as similarly explained by Xu et al., (2019). The herbal extract-capped silver nanoparticles are coupled with the hydroxyl group present in the cellobiose unit of the cotton fibre, as shown in Fig. 8.
As the chitosan content increased from 0.5% to 1%, the antimicrobial potential of silver nanoparticle treated cotton fabrics was further enhanced by 91.8, 94.6, and 97.8% in the case of 100, 200, and 300 ppm silver nanoparticles.
Figure 9 shows that as the antimicrobial efficacy was measured against
This study concludes that green synthesis of the silver nanoparticle is the safer way of silver reduction.
Protocol for a cost-effective, efficient and eco-friendly reduction of silver has been developed here.
The synthesis process is rapid, and the stability of the synthesized nanoparticles is also excellent.
No stabilizer was used here for the capping of the nanoparticles.
Eucalyptus leaf extract proved its silver reduction potential up to a nanometre level: of 62 nm, confirmed by a particle size analyzer and FESEM.
Crystallinity was confirmed by X-ray diffraction analysis and the presence of silver nanoparticles in the sample by EDX analysis.
The antimicrobial efficacy of 300 ppm AgNPs treated cotton fabric reached 84 % bacterial growth reduction, which was further enhanced to 97.9 % with a 1% addition of chitosan with 300 ppm AgNPs. The antimicrobial potential of green synthesized nanoparticle-treated fabric samples was found entirely satisfactory.
The durability of fabric treated with AgNPs alone is not so good, but when applied along with chitosan, its durability is satisfactory. This may be attributed to the adhesive nature of chitosan.
Green synthesis of nanoparticles is a very economical, eco-friendly, time-saving and sustainable method. Hence, there is good scope to explore new natural resources to synthesize the metal nanoparticles.
There is also sufficient future scope to improve the durability of antimicrobial potential and to enlarge the retention of nano finish on fabric.
This is original research work and has not been submitted to any other journal for publication in part or as a whole.
Authors have no conflict of interest with this research work.