Chitosan/AgVO3 nanocomposite thin films were synthesized via solution casting method using water as solvent. Silver vanadate (AgVO3) nanoparticles were prepared separately using a chemical precipitation technique. The structure and properties of the nanocomposite films were investigated using Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), swelling ratio tests, and antimicrobial assays. FTIR analysis confirmed the interaction between the amide I group of chitosan and AgVO3 nanoparticles. Increasing AgVO3 content resulted in decreased optical bandgap of the nanocomposite films. XRD patterns showed the amorphous nature of the nanocomposites. SEM images revealed evenly distributed AgVO3 nanoparticles within the chitosan matrix. The swelling ratio decreased with higher AgVO3 loading, suggesting improved hydrolytic stability. The nanocomposite films demonstrated potent antimicrobial activity against gram-positive and gram-negative bacteria as well as Candida fungus. The tunable optical properties, swelling behavior, and antibacterial effects spotlight the potential of chitosan/AgVO3 nanocomposites for versatile biomedical applications.
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1 Introduction
In many advanced sciences such as energy, environmental science, medicine, biotechnology, and other branches, nanotechnology has become an effective and critical tool that involves the design and synthesis of materials at nanoscale levels, creating new materials with enhanced properties (Paul et al. 2008). Polymer-based nanocomposites consist of polymer blended with nanoparticles which have attracted considerable attention recently due to their unique physical and chemical properties, which make them promising candidates for various applications besides their antibacterial effect (Abdelghany et al. 2021, Keller 2001, Ajayan et al 2000).
Nanocomposites are engineered materials designed to exhibit specific properties or characteristics due to the presence of nanoscale components. The nanoscale components may include nanoparticles, nanotubes, nanowires, or another nanostructure (Hameed et al. 2023). Natural polymers are utilized frequently in biomedical applications because they are abundant, chemically stable, and biocompatible, as opposed to synthetic polymers that lack biocompatibility and must therefore be mixed with another element to improve their qualities (Caillol 2021). Chitosan is a natural abundant biopolymer derived from chitin, it is found in the exoskeleton of crustaceans such as shrimp and crabs (Gu et al. 2003), It is a linear polysaccharide composed of N-acetylglucosamine and glucosamine units with a high level of biocompatibility, biodegradability, and low toxicity which intrinsic antibacterial characteristics that is produced via the N-deacetylation of chitin. The linear structure of the chitosan chain (poly [-(14)-2-amino-2-deoxy-Dgluco (Affonso et al 2020, Vanden Braber 2018). Chitosan (CS) can be considered a cationic linear polysaccharide containing –NH2 functional groups within its structure (Bashir et al. 2022). Such structure makes Chitosan soluble in acidic media (Abdelghany et al. 2019, Kalaivani et al. 2018, Liang et al. 2019, Qin et al. 2019). Because of its unique features, chitosan has been intensively researched as a biomaterial, such as its ability to form films, gels, and fibers, as well as its ability to bind to metal ions and form films. because of the presence of polysaccharides (Cao et al. 2018, Hu et al 2016).
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Chitosan can inhibit the growth of bacteria and fungi. It has been investigated as a wound dressing material, as it can help promote healing and prevent infections (Kumar et al.2010, Li et al. 2015). besides it maintains a moist environment which can promote re-epithelialization and can control necrotic or infected wounds due to its antibacterial qualities (Morgado et al. 2017, Ramasamy et al. 2015).
Silver vanadium oxides have attracted much interest in recent years. Due to their wide variety of crystalline forms, which have shown promise in various applications due to their significant physical and chemical properties (Gonzalez-Zavala et al. 2018, Ayaad et al. 2019). Silver vanadate nanoparticles are a type of nanomaterial that has a high surface area-to-volume ratio, which makes them highly reactive, and their small size allows them to easily penetrate bacterial cells. Silver vanadate nanoparticles have been found to exhibit excellent antibacterial activity against a wide range of bacterial strains. Due to the effectiveness in which it kills bacteria, silver-based compounds are frequently utilized as antibacterial components. The produced antibacterial thin films used in this investigation have the promising potential to stop microorganisms from endangering human health (Abdelghany et al. 2019, Jun et al. 2020, Ayello et al. 2004).
Previous studies have extensively explored the behavior of silver vanadate nanorods as filler with chitosan but with different concentrations enhancing the antimicrobial effect, (Abdelghany et al. 2018) studied the effect of variable filler concentrations for different optical and industrial applications but with higher concentrations (Ayaad et al. 2019), while in this presented work the focused study was using lower range concentrations of silver vanadate nanoparticles. Other previous research delved into determining the effect of variable filler concentrations for different optical and industrial applications and investigated the physical and biological characteristics of low-level doped nanocomposite consisting of natural biodegradable polymer with low content of inorganic nano silver vanadate. The work extended to the application of such matrix in versatile medical applications including swelling rate and antibacterial effects against pathogenic grams in addition to studying a correlation between the activity index against various pathogenic grams and the optical energy gap or nanoparticle dopant concentration.
2 Materials and method
2.1 Materials and sample preparation
The material used during the study includes silver nitrate (AgNO3) of molecular weight 169.87, Ammonium metavanadate (NH4VO3) of molecular weight 116.98 supplied by Sigma Aldrich Co., Chitosan supplied by Alpha Acer Co. A chemical precipitation method was used for the preparation of silver vanadate nanorods at room temperature and a constant pH, 200 ml of a 0.01M silver nitrate (AgNO3) aqueous solution was added drop by drop to 200 ml of a 0.01M ammonium metavanadate (NH4VO3) solution. The mixture was vigorously stirred, and the formation of a yellow precipitate indicated the synthesis of silver vanadate nanorods. The obtained precipitate was washed several times with distilled water and ethanol to remove residual ions before being dried at 50 °C. During the preparation process and for the precipitation reaction between Ag+ and VO3− ions to occur efficiently, the pH needs to be acidic enough to prevent the formation of insoluble hydroxides. Typical pH values used fall in the range of 2–4. Strongly acidic pH (< 2) is usually avoided to prevent protonation of the VO3− ions, which can inhibit the precipitation. Based on these points, a reasonable estimate for the pH during the AgVO3 synthesis would be 2–4, with an optimal value around 3.
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A precalculated amount of chitosan powder was emersed in distilled water which contained 2% Acetic acid to completely dissolve and vigorously stirred until a viscous bubble-free solution was formed. The viscous solution was then mixed with different mass fractions of synthesized silver vanadate (0.005, 0.01, 0.02, 0.03, 0.04 Wt.%). The mixture was then poured into Petri dishes and kept in an incubator regulated at 50°C for 24h to remove water traces and to obtain completely dry thin sheets. Sample nomination and composition were summarized as shown in Table 1.
Table 1
Sample Nomination and composition
Sample
Cs
Cs1
Cs2
Cs3
Cs4
Cs5
AgVO3 content wt. %
0.00
0.005
0.01
0.02
0.03
0.04
2.2 Sample characterization
Characterization was conducted for both the synthesized nanomaterial and the prepared pristine polymer thin films, as well as their nanocomposites containing varying amounts of silver vanadate. X-ray diffraction (XRD) spectral patterns were analyzed using (Malvern PANalytical Empyrean 3 NTRC-BUE) equipped with anode material Cu-Kα radiation enclosed by the Bragg’s angle (2θ) within the range extended from 5 to 80° with a step size 0.02°. FT-IR experimental data were measured directly for the thin sheets within the range 4000–400 cm−1 with resolution 2 cm−1 in transmittance modes via Nicolet is10 single-beam spectrometer. UV/Visible absorbance spectral data was collected via (V-570 UVVis–NIR, JASCO, Japan) double-beam spectrophotometer within the wavelength region of 190–1100 nm. A scanning electron microscope was used to utilize the morphology structure characterization of the samples (FEG-ESEM-Thermo Scientific USA, Model Quattro S- NTRC BUE 6510 LV).
The swelling behavior of the synthesized samples was calculated by using an immersion method. In which weighed dry amount of each sample was immersed in six different buffer solutions of pHs 4, 5, 6, 7, 8, and 9 till equilibrium (2h). After that, the swollen samples were weighed after removing the excess fluid from the surface gently by using dry filter paper. The swelling ratio of the studied samples was calculated according to the following equation.
Swelling Ratio% = \(\frac{Wt-W0}{W0}x100\) Where, W0 and Wt. are the dry initial sample weight and the swollen sample final weight at time t.
The antibacterial behavior of prepared samples was tested against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeuroginosa). In addition to pathogenic fungus (Candida albicans). The agar diffusion method was employed in which samples were placed in Petri plates containing agar media and incubated at 37 ℃ for about 24 h (Meikhail et al.2018). The inhibition zones were measured and the activity index was summarized and recorded in Table @6 from the equation:
$$Activity index\%=\frac{Zone of inhibition by test compound (diametre)}{\mathrm{Zone of inhibition by standard }({\text{diametre}})} \times 100$$
3 Results and discussion
3.1 Characterization of silver nanoparticles
Figure 1 shows the X-ray diffraction pattern of the synthesized nanostructured silver vanadate via the chemical precipitation route. The synthesized sample exhibited diffraction peaks assigned to the monoclinic β-AgVO3, cubic silver oxide phases, and metallic silver when compared to the card no (JCPDS 29–1154), (JCPDS 01–072-0607), (JCPDS 01–076-1489), and (JCPDS 81–1740) respectively (de Menezes et al. 2019, Holtz et al. 2010, Gao et al 2017).
Fig. 1
X-ray diffraction patterns of silver vanadate nanorods
×
Metallic silver (Ag) is a fascinating metal for biomedical applications, since it may enhance antimicrobial activity. The sample appears to be semi-crystalline, and the degree of crystallinity (DC) can be calculated using the following equation (Gao et al. 2017).
where AC and AT are the crystalline and total area of the peaks. The CD was found to be about 72%.
The synthesized sample was then characterized using transmission electron microscopy, Fig. 2 revealed that synthesized nanomaterial is mostly rod-like structure with varying micrometers lengths and diameters ranging between 30 and 62nm covered with some spherical metallic silver nanoparticles (Ag).
Fig. 2
Transmission Electron Microscope micrograph of synthesized silver vanadate
×
Synthesized nanorods are characterized by their surface area to volume ratio that provides more active sites for surface reactions like catalysis and sensing. In addition, the elongated shape of nanorods results in anisotropic optical, electrical, and mechanical properties, which may be useful for applications like polarizers, nanogenerators, etc. One-dimensional nanorods provide efficient charge transport along the length direction due to fewer grain boundaries. This benefits applications like batteries, and electronics (Singh et al. 2010). Nanorods show light scattering and antenna effects that can improve the absorption of incident light.
Figure 3 shows the Fourier transform infrared (FTIR) spectrum of the synthesized sample which is very similar to that previously reported for silver vanadate nano-rods. The obtained spectrum appears to consist of about 5 principal bands within the wavenumber extended from 1000 to 400 cm−1 without any further peaks till the end of the measurement. The band at 891 cm−1 corresponds to the bridging of the silver with oxygen (Ag–O–V) vibration mode or the (O–V–O) vibrations, while the symmetric stretching vibrations of VO3 and the vibration of the (V=O) double band appear at 924 cm−1. The band at 775 cm−1 may be assigned to the antisymmetric stretching vibrations of VO3. A band at 616 cm−1 may be associated with the symmetric and asymmetric stretching mode of (V–O–V). It can be concluded that the bands of ammonium vanadate shifted because of the changes in the vibration mode of V=O bonds due to the presence of silver molecules in the water system (Liang et al. 2013, Ayaad et al. 2019).
Fig. 3
FTIR of the synthesized silver Vanadate Nanorods
×
3.2 Characterization of synthesized nanocomposite
3.2.1 X-ray diffraction (XRD)
Figure 4 shows the x-ray diffraction pattern of the pristine chitosan sample and other nanocomposite samples containing variable mass fractions of dopant silver vanadate nanoparticles. The whole samples show an amorphous nature even with increasing content of silver vanadate this may attributed to the low doping level and the interstitial position taken by the nanorods within the polymeric matrices resulting in crosslinking and reduction of crystallinity. In addition, spectral data confirmed the relative homogeneity of the nanocomposite structural nature without any tendency for crystallization or the appearance of separated phases.
Fig. 4
X-ray diffraction pattern of (Cs/AgVO3) nanocomposites
×
3.3 Fourier transform Infrared FTIR analysis
Thin films of pure chitosan and other samples of mixed chitosan with varied mass fractions of silver vanadate were evaluated in the spectrum range of 400 to 4000 cm−1. The following functional group studies were done using chitosan fingerprints drawn from Fig. 5: Wavenumbers between 3311 and 3400 cm−1 were the range in which the stretching vibration of the hydroxyl group O–H took place. Symmetric or asymmetric stretching vibration CH2, which is related to the pyranose ring, is responsible for the band at 2883 cm−1. The bending vibration of the aliphatic (-CH) and (-CH2) vibration was responsible for the peak at 2850 and 2900 cm−1, respectively. The stretching of the carbonyl (C=O Stretching Vibration) and amine groups are responsible for the spectral bands at 1650 cm−1 and 1590 cm−1, respectively. The interaction of amide I (–NH2) (Singh 1999, Meikhail et al. 2018) groups in chitosan with silver vanadate was shown by the peak at 1370 cm−1. Asymmetric C–O–C in glycosidic linkage vibrates at 1153 cm−1, and the distinctive bands of skeletal polysaccharides have vibrational frequencies of 1081 and 1034 cm−1. V–O-Ag or O-V–O vibrations may be observed at the apex at 890 cm−1. With increasing silver vanadate content, an increase in band intensity at 600 cm−1 was observed. Table 2 summarizes the obtained data.
Fig. 5
FTIR spectra of the Cs and (Cs/β–AgVO3) Nanocomposite
Table 2
FTIR peak assignment
Peak position (cm−1)
Assignment
3311–3400
stretching vibration of the hydroxyl group O–H
2883
Symmetric or asymmetric stretching vibration CH2, related to the pyranose ring
2850–2900
bending vibration of the aliphatic (-CH) and (-CH2)
1650–1590
stretching of the carbonyl (C = O)
1370
interaction of amide I (-NH2) groups with silver vanadate
1153
Asymmetric C–O–C in glycosidic linkage
1081–1034
skeletal polysaccharides
890
V–O–Ag or O–V–O vibrations
×
3.4 UV–Vis spectra
Figure 6 shows the UV–Vis absorption spectra obtained for nanocomposite films containing varying amounts of silver vanadate (AgVO3) nanoparticles dispersed in a cesium polymer matrix. The spectra of the nanocomposite films are compared to that of the pure AgVO3 nanofiller material. Analysis of the absorption edges indicates that the electronic structure and optical bandgap of the nanocomposite films exhibit a dependence on the AgVO3 content. Increasing the nanoparticle concentration results in measurable changes in the absorption characteristics and bandgap energies. The optical bandgaps for each nanocomposite sample were estimated from the fundamental absorption edges using the Tauc relation. The sample designations, correlating AgVO3 concentrations, and calculated Eg values are provided in Table 3. The Tauc analysis involves plotting quantity (αhν)n as a function of photon energy (hν), where α is the absorption coefficient, h is Planck's constant, and ν is frequency. The exponent n depends on the nature of the optical transition. Extrapolating the linear part of the (αhν)n vs hν curve to the x-axis yields the optical bandgap energy Eg for the transition between occupied and unoccupied electronic states (El-Mallah et al 2020, Atwee et al. 2018). The results demonstrate the ability to systematically vary the optical properties of the cesium polymer films by controlling the concentration of embedded AgVO3 nanoparticles. The UV–Vis spectroscopy analysis provides insights into the electronic structure and interaction effects in the nanocomposite system.
Fig. 6
UV–Vis absorption spectrum of the Cs and (Cs/AgVO3) Nanocomposite
Table 3
The optical band gap and absorption edge
Sample
λedge (nm)
Optical band gap (eV)
Cs
234
5.29
Cs1
279
4.44
Cs2
344
3.60
Cs3
437
2.84
Cs4
465
2.67
Cs5
535
2.32
×
The relationship between the absorption edge and optical band gap is plotted in graph Fig. 7, revealing that the concentration of silver vanadate nanorods in the thin films increases, and the optical energy gap values decrease, inferring that the thin films' sensitivity is improved (AbuShanab et al. 2020). E = hc/ λedge.
Fig. 7
effect of increasing silver vanadate concentration on the optical energy gap
×
3.5 Scanning electron microscope
The morphology and size of thin films were examined by Scanning electron microscope on the surface of the thin films. SEM images in Fig. 8 show well-dispersed and not aggregated round-shaped nanoparticles that have a diameter ranging between 7.9:8 mm. The SEM images of all samples were taken at magnification 60 000x, at 1000kV. The roughness parameter was also calculated using Gwyddion 2.32 shareware program that converts SEM 2D micrograph to 3D micrograph. The obtained data was tabulated in Table 4
Fig. 8
Scanning electron microscopy images for Nanocomposites samples
Table 4
calculated roughness obtained from the 3D SEM image
Sample
Cs1
Cs2
Cs3
Cs4
Cs5
Average Roughness (nm)
31.0056
24.8955
28.8331
42.3377
48.5167
×
3.6 The swelling rate test
The obtained data indicates the relation between the Swelling ratio and the concentration of chitosan thin film at different fractions of silver vanadate concentration shown in Figs. 9 and 10. From the obtained results in Table 5, Swelling ratios recorded a noticeable decrease as the concentration of the thin films filled with silver vanadate increased, this is due to the compatibility of the chitosan polymer with the buffer solutions leading to a reduction in the free volume for swelling, at higher silver nanoparticle concentrations, there is an increased likelihood of particle aggregation. Aggregated nanoparticles can create physical barriers within the film, restricting the movement of the polymer chains and reducing swelling (Zhang et al 2004). With different pHs from acidic to alkaline increasing the pH, the swelling ratio has been decreased for the same concentration of thin film, Due to the amine groups in chitosan (–NH2), it could be protonated or deprotonated depending on the pH of the solution, in the acidic pH buffer chitosan is primarily protonated (lower pH), resulting in a positively charged polymer. As the pH increases (approaching alkaline conditions), chitosan becomes progressively deprotonated and begins to have a negative charge as amino groups (–NH3+) are changed to amino groups (–NH2). The electrostatic interactions within the chitosan matrix and between the chitosan and silver nanoparticles can be altered by this charge change, resulting in a decrease in swelling ratio (Qin et al. 2019).
Fig. 9
Swelling ratio as a function of dopant concentration
Fig. 10
Swelling ratio as a function of pH
Table 5
Swelling ratio of the tested sample as a function of concentration and pH
AgVO3
pH4
pH5
pH6
pH7
pH8
pH9
0
745
725
703
677
656
633
0.005
715
695
673
645
623
599
0.01
690
672
652
626
603
580
0.02
665
638
619
596
578
558
0.03
657
630
601
570
555
525
0.04
650
627
602
571
549
523
×
×
In summary, we distinguish two different functions for swelling ratio for the thin films first one is concentration and the second is pH and that reveals a notable inverse relationship between the concentration of silver nanoparticles in the thin film material and its swelling ratio. Specifically, as the concentration of silver nanoparticles increases, the swelling ratio of the thin film decreases. This observation suggests that a higher concentration of silver nanoparticles is associated with improved resistance to swelling.
3.7 Antibacterial activity
The antibacterial behavior of the studied sample against a panel of Gram-positive, Gram-negative bacteria, and pathogenic fungi was summarized in Table 6. Antibacterial behavior estimated from clear inhibition zone, and filler concentration influence antibacterial activity, whereas oxidation–reduction of vanadium between V4+ and V5+ improves antibacterial activity (Seda et al. 2007). Antibacterial activities index was found against all test cultures for the gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) to be 50.0 and 52.17 respectively, While the activity index for the gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) were 30.76 and 39.13 respectively at concentration 0.03%. Moreover, the activity index of Candida Fungi was 62.96 at the same concentration as the prepared sample. No antibacterial activity for Escherichia coli was found at 0.04 wt%.
Table 6
Antibacterial activity of the studied nanocomposites
Sample
E-Coli
Pseudomonas aeuroginosa
S. aureus
Bacillus subtilis
C. Albicans
D
A
D
A
D
A
D
A
D
A
Cs1
5
19.23
6
26.08
7
29.16
7
30.43
6
22.22
Cs2
7
26.92
7
30.43
6
25.0
8
34.78
13
48.14
Cs3
8
30.76
8
34.78
9
37.5
10
43.47
15
55.55
Cs4
8
30.76
9
39.13
12
50.0
12
52.17
17
62.96
Cs5
NA
0
9
39.13
11
45.83
9
39.13
12
44.44
Ampicillin
26
100
23
100
24
100
23
100
–
–
Clotrimazole
–
–
–
–
–
–
–
–
27
100
Based on the results and the diameter of the inhibition zone for different bacteria, it can be determined that Staphylococcus aureus and Bacillus subtilis have the highest inhibition activity.
A direct proportionality between activity index and filler concentration was detected, which was opposed to the relationship between the energy gap and activity of different grams, leading to a conclusion concerning the inverse relationship between optical energy gap and activity for different grams (Keller 2001). Chitosan itself possesses inherent antibacterial properties due to its polycationic nature which can disrupt bacterial cell walls and membranes. The positively charged chitosan chains can bind to negatively charged bacterial cell surfaces, causing leakage of intracellular components and cell death. However, the incorporation of silver vanadate nanoparticles provides additional antibacterial mechanisms that act synergistically with chitosan's effects. The nanoparticles have a high specific surface area and can release Ag + ions that penetrate bacterial cells. Inside the cells, Ag + ions bind to thiol groups of vital enzymes and proteins, inactivating them and disrupting metabolic processes. The nanoparticles may also generate reactive oxygen species that can damage bacterial cell membranes and DNA. The combination of cell wall/membrane disruption, enzyme inactivation, and oxidative damage provides multiple mechanisms for the nanocomposite films to inhibit bacterial growth.
4 Conclusion
Chitosan/AgVO3 nanocomposite thin films were successfully fabricated using a facile solution casting approach. Systematic characterization using FTIR, UV–vis spectroscopy, XRD, SEM, swelling tests, and antimicrobial assays provided valuable insights into the structure–property relationships in this nanocomposite system. Interaction between chitosan and AgVO3 nanoparticles was evidenced by FTIR analysis. The optical bandgap was tuned by controlling the AgVO3 nanoparticle content within the chitosan matrix. The nanocomposite films exhibited excellent antibacterial activity against both gram-positive and gram-negative bacteria as well as the Candida fungus. The hydrolytic stability was also enhanced at higher nanoparticle loadings, as indicated by reduced swelling ratios. Overall, this work demonstrates the potential of chitosan/AgVO3 nanocomposites for biomedical applications requiring antimicrobial behavior and tailorable optical properties. The facile synthesis and promising performance highlight future opportunities for more in-depth research and optimization of this nanomaterial system.
Declarations
Conflict of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Ethical approval
This work is not applicable to both human and/ or animal studies.
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