Viscose fibers decorated with silver nanoparticles via an in-situ green route: UV protection, antioxidant activities, antimicrobial properties, and sensing response

Abstract

Multifunctional cellulosic fibers are in high demand for use in a variety of applications. Functional cellulosic fibers obtained through green and sustainable approaches are getting special attention because of the need to limit the environmental impact of hazardous chemicals. Herein, a novel facile, efficient, and eco-friendly approach for multifunctional viscose fibers@Ag NPs (VF-Ag) was designed by a rapid, facile, and one-pot biosynthesis green route using guava leaf extract as a reducing and stabilizing agent. UV–Vis, TEM, SEM, EDX, FTIR, and XPS were used to analyze the formation of silver nanoparticles and their subsequent deposition on the surface of viscose fibers. The silver nanoparticles immobilized on the surface of viscose fibers endowed a yellow/brownish color to the fibers as well as improving the dyeing with reactive dye. The VF-Ag samples have multifunctional properties like protective activities against UV radiation and microorganisms, antioxidant activity, and sensor ability toward Hg²⁺. The results demonstrated that the UPF values of VF-Ag samples ranged from 280 to 355 compared to 103 for VF. The antioxidant activities of VF-Ag ranged from 79 to 85% compared to 9% for VF. VF-Ag samples exhibited excellent antimicrobial activities against Gram-positive and Gram-negative bacteria, very good activities against yeast, and low activities against fungus.

VF and VF-Ag were dyed using reactive dye (CI-reactive blue-19) at two color intensities (2.5, and 5%). The results show that the color of VF turned blue, while the color of VF-Ag turned greenish. The color strength of VF-Ag significantly increased with increasing silver content. Furthermore, VF-Ag showed high sensitivity to naked-eye colorimetric sensing for the detection of Hg²⁺. In straightforward, this innovative approach provides an easy, quick, and low-cost that will open the door for a range of versatile applications for modified viscose fibers in the fields of medical and analytical applications.

Introduction

Cellulosic fiber modification to create a surface with multifunctional properties is a significant means in several industries (Abdelhamid and Mathew 2022; Emam 2019). Viscose fibers, a form of regenerated cellulosic fiber, have sparked extensive interest in textile sectors especially technical and medical textiles due to their flexibility, excellent moisture absorption, excellent comfort, Ion exchange capacity, low cost, non-toxicity, and biodegradability. Viscose fibers are created using natural cellulose as the raw material, such as cotton and wood pulps, and are processed using either derived cellulose or direct dissolution (Xu et al. 2023). As a result, multifunctional viscose fibers are viewed as a technologically and economically viable alternative that may be used in a variety of applications. The advancement of research on viscose fiber modification utilizing nanoparticles is a result of the increased market demand for functional viscose fiber products. Different nanoparticles to modify viscose fiber surfaces were used to impart coloration (Emam et al. 2017, 2014; Rehan et al. 2017b), antimicrobial activities (Krkobabić et al. 2023; Rehan et al. 2019b, 2020a, 2018b; Sirotkin et al. 2022; Zheng et al. 2014), self-cleaning properties (Rehan et al. 2018a, 2019b, 2018b), UV protection (Rehan et al. 2019b, 2020a, 2018b), and photoluminescent (Emam et al. 2018a) to viscose fibers. Because of their unique physical and chemical properties, silver nanoparticles (Ag NPs) have gained substantial attention for use in several industries such as textiles, food, medical, health care, and sensors (Istiqola and Syafiuddin 2020; Kaushal et al. 2023; Radetić 2013; Vilela et al. 2012; Zhang et al. 2016). Silver nanoparticle-based fibers can transfer multifunctional properties to the resulting fiber products. Silver nanoparticles can be used as a colorant to impart the surface of fibers with color due to their surface Plasmon resonance (Butola and Mohammad 2016). Silver nanoparticles have some advantages over traditional colorants that could open up new opportunities for the dyeing industry. Furthermore, unlike traditional manufactured or natural dyestuffs, nano-colorants do not require any accountable color-bearing groups (such as hazardous azo) for dyeing. Besides the coloration properties, the functionalization of fibers with silver nanoparticles can transfer multifunctional properties such as antimicrobials (Barani and Mahltig 2020; Rehan et al. 2017a, 2015), UV protection (Čuk et al. 2021; Rehan et al. 2017a), catalytic (Qi et al. 2020; Rehan et al. 2017b), or conductive properties (Nateghi and Shateri-Khalilabad 2015; Rehan et al. 2020b; Xing et al. 2023). For the incorporation of silver nanoparticles into textiles, several ways have been devised, including synthetic polymer-nanoparticle composite (Gao et al. 2014; Sreekumar et al. 2009), ex-situ (Tang et al. 2011; Wu et al. 2016), and in-situ (Kelly and Johnston 2011; Rehan et al. 2023) strategies. The majority of the above synthesis techniques utilized hazardous chemicals or consumed more water and energy. To create non-toxic, environmentally friendly silver nanoparticles, it is necessary to avoid toxicity and manage environmental effects. Thus, green synthesis pathways for Ag NPs provide advantages such as environmental friendliness, economic effectiveness, being affordable, safer, and faster, and providing natural capping and stabilizing agents as well as improving their properties leading eventually to applications with greater effectiveness (Hebbalalu et al. 2013; Sharma et al. 2022a, 2022b; Vishwanath and Negi 2021). Plant extracts are considered the main source in the green synthesis of Ag NPs, owing to the existence of natural compounds like terpenoids, flavonoids, and polyphenolic compounds (Ahmed et al. 2016; Akhtar et al. 2013; Kuppusamy et al. 2016). These compounds act as reducing agents as well as stabilizing agents, assisting in the conversion of silver ions (Ag⁺) to silver metallic (Ag⁰) and aidingin their subsequent aggregation into clusters (Ag⁰)_n. The inclusion of several hydroxyl (-OH), carboxyl (-COOH), amino (-NH₂), or thiol (-SH) functional groups in their structure is attributed to their ability to reduce and stabilize silver nanoparticles in a complex redox-mediated process (Islam and Sun 2022).

Moreover, the polyphenolic compounds extracted from plant extract provide favorable antioxidant properties and enhance the sensor ability of silver (Dhaka et al. 2023; Maitra et al. 2023). The key benefits of employing plant resources are that they are readily available, affordable, and safe to handle (Ahmed et al. 2016; Rajeshkumar and Bharath 2017). Psidium Guajava Linn., a widespread plant known as guava and a member of the Myrtaceae family, is grown all over the world. Their leaves are considered byproducts and have been identified as sustainable and rich in polyphenolic compounds despite their low economic value (Kumar et al. 2021). Thus, polyphenolic compounds extracted from guava leaf can be used to reduce silver ions (Ag⁺) to silver nanoparticles (Ag NPs) (Akhtar et al. 2013; Patil and Rane 2020; Wang et al. 2018; Zayed et al. 2022). Moreover, guava leaf extract showed excellent properties, such as antimicrobial, anti-inflammatory, UV protection, antioxidant activity as well as wound healing properties (Naseer et al. 2018; Rehan et al. 2019a). Thus, the biosynthesis of silver nanoparticles using guava leaf extract could enhance the antimicrobial activities, UV protection, and antioxidant activities of formed nanoparticles.

Time is money; this was emphasized in all everyday operations, particularly in the chemistry field where a lot of time and energy was expended. As a result, the “one-pot process " was regarded as an ecological and economic breakthrough in chemistry. The one-pot process is a simple and successful approach for producing nanoscale organic/inorganic hybrid functional materials. To reduce the chemicals used in the chemistry field, reduce pollution, and save time, water, and energy, the inorganic components are synthesized in one step via a direct reaction.

Despite a high level of scholarly interest in the biosynthesis and deposition of silver nanoparticles on various textiles, the biosynthesis and deposition of silver nanoparticles on viscose fibers have been overlooked. A few papers have been published on the biosynthesis of silver nanoparticles on viscose fibers to acquire multifunctional characteristics (Krkobabić et al. 2023; Rehan et al. 2020a). Thus, more research is needed to propose novel designs to impart multifunctional properties of viscose fiber through a green approach for their use in different applications like protective textiles, medical textiles, and environmental applications. Silver nanoparticles can be used as sensors for heavy metals and bio-compounds (Ghosh et al. 2023). There are some problems with the applications of silver nanoparticles as a sensor such as separating, and recovering, thus the immobilization of silver nanoparticles on viscose fibers can play an important role in minimizing these risks and problems.

Based on the aforementioned and to address the above issues, a cost-effective green route was designed for the decoration of the surface of viscose fibers to provide and improve the effectiveness of the various properties and applications of viscose fibers. The current work offers for the first time evidence to support the viability of using an eco-friendly one-pot approach for the simultaneous preparation and application of silver nanoparticles on the viscose fiber surface using the extract of guava leaf to impart multifunctional properties to the viscose fiber surface, including coloration, antimicrobial activities, UV protection, antioxidant properties, and sensor ability as well as improvement of the dyeing process of viscose fibers. The biologically active compounds of guava leaf extract can be used as reducing and stabilizing agents for in situ biosynthesis Ag NPs as well as additively contribute to the multifunctional properties of viscose fibers. The simultaneous biosynthesis and deposition of Ag NPs on the surface of viscose fibers allows Ag NPs to grow on both the surface and inside the fibers, which also improves the homogeneity and uniformity of Ag NP distribution and decreases agglomeration.

Decorated viscose fibers with silver nanoparticles can be used in different applications, like protective and medical textiles, as well as in analytical applications.

Experimental

Materials and chemicals

Guava leaves (Psidium Guajava L.) were obtained from the local Egyptian market. Viscose fibers (VF) were obtained from Lenzing, Austria. Silver nitrate (Ag NO₃) was obtained from Panreac, Barcelona – Spain.

Natural compounds extraction from Guava leaf

Before being divided into tiny pieces and dried in a lyophilizer, the guava leaves were collected and thoroughly cleaned many times with distilled water. The dried leaves were crushed to facilitate the extraction of active compounds. Thereafter, employing ethanol/water (70:30) as a solvent, an ultrasound-assisted extraction approach was used. An ultrasonic bath was used to extract the bioactive components from guava leaf (38.50 kHz and 500 W), at 60 °C for 60 min, with a liquor ratio of 1:10. After filtering, the extract was given time to cool before being used for additional research and application (Rehan et al. 2019a).

Simultaneous synthesis and incorporation of silver nanoparticles (Ag NPs) on the surface of viscose fibers surface (VF) using guava leaf extract

Silver nanoparticles (Ag) are generated at the viscose fiber surface (VF) by the direct reduction of silver nitrate with guava leaf extract. 5 g of VF were submerged in a solution of silver nitrate of different concentrations (100, 300, and 500 ppm) using a liquor ratio of 1:50, After that, the guava leaf extract (2.5, 5, and 10 mL) was added dropwise to the solution to act as a reducing agent and the pH value of the solution was adjusted to 6. The VF-Ag⁺/ guava leaf extract was stirred for 30 min at room temperature which allowed the Ag⁺ and guava leaf extract to be well dispersed and adsorbed onto the VF surface. After that, the immersed VF-Ag⁺/ guava leaf extract was heated in a water bath with vigorous shaking at different temperatures (30 ⁰C, 50 ⁰C, and 80 ⁰C) for different interval times (15, 39, and 60 min). Subsequently, the fiber was removed, squeezed, and rinsed by running tap water and left to dry at ambient temperature before analysis and applications. The remaining solutions' absorbance was measured. The VF surface was modified with 10 mL of guava leaf extract without silver nitrate solution (VF-guava leaf extract) using a liquor ratio of 1:50, pH 6, at 80 ⁰C for 60 min.

Dyeing of VF and VF-Ag with traditional reactive

VF and VF-Ag samples were dyed with reactive dye (CI-reactive blue-19). Dye (2.5% and 5% o.w.f) was dissolved in distilled water, and then 5 g of VF or VF-Ag samples were added to the dye solution at a material-to-liquid ratio of 1:50. At 40 °C, 30 g/L sodium sulfate was added to this dye bath, and after 30 min, 20 g/L sodium carbonate was carefully added. The temperature was then increased to 60 °C, and the dyeing procedure was repeated for another 60 min. After dyeing, the dyed VF and VF-Ag samples were rinsed with hot and cold water and then dried at room temperature.

Characterization and measurement

To determine the total phenolic content (TPC) and total flavonoid content (TFC) of guava leaf extract, the Folin-Ciocalteu method and the aluminum chloride (AlCl₃) method were employed. The formation of Ag NPs, was characterized by UV–visible spectroscopy, transmission electron microscopy (TEM), VF, and VF-Ag, surfaces were evaluated by scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDX), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The silver content (mg/kg) was evaluated using a flame atomic absorption spectrophotometer (Rehan et al. 2017a). Mechanical properties were evaluated via evaluation of tenacity at break (g/den) and elongation % (Rehan et al. 2023).

Evaluation of colorimetric properties and fastness properties

The colorimetric analysis of the dyed samples was performed with a spectrophotometer equipped with pulsed xenon lamps as a light source (Ultra Scan Pro, Hunter Lab, USA) and 10 observers with D65 illuminant, d/2 viewing geometry, and a measurement area of 2 mm. The Kubelka Munk was used to calculate the corresponding color strength value (K/S).

$$\mathbf{K}/\mathbf{S}=(\mathbf1-\mathbf{R})^\mathbf2/\mathbf2\mathbf{R}$$

where R is the decimal fraction of the reflection of the colored textile fibers, K is the absorption coefficient, and S is the scattering coefficient.

The color space (L^*, a^*, b^*) of colored textile fiber samples was measured by the same spectrophotometer used for measuring of color strength at the same setup, and then the color difference was calculated using.

$$\mathbf\Delta\mathbf E=\mathbf L^{\mathbf2}+(\mathbf a^{\mathbf2}+\mathbf b^{\mathbf2})^{\mathbf1/\mathbf2}$$

where ΔE is the total difference between the sample and the standard, L^* is the lightness from black (0) to white (100), a^* is a red ( +)/green ( −) ratio, and b^* is yellow ( +)/blue ( −) ratio. The hue angle is reported as a degree from 0° (red) through 90° (yellow), 180° (green), 270° (blue) and back to 0° (Rehan et al. 2022). The colorfastness properties of washing (ISO 105-C02 technique), rubbing (ISO 105-X12 test method), and light (ISO 105-B02) were evaluated (Emam et al. 2014).

Evaluation of colorimetric properties, UV protection, and antioxidant properties of VF and VF-Ag

A spectrophotometer with pulsed xenon lighting (Ultra Scan Pro, Hunter Lab, and USA) was used to evaluate the colorimetric properties of VF and VF-Ag. The UV protection of VF-Ag was evaluated by the ultraviolet protection factor (UPF) by using the AATCC Test Method 183:2010-UVA Transmittance (Rehan et al. 2020a). The antioxidant activities of VF and VF-Ag were evaluated by using the 2, 2-diphenylpicrylhydrazyl (DPPH) assay (Rather et al. 2017) and 2, 2-azinobis-(3-ethylbenzothiazoline-6- sulfonic acid) (ABTS) assay (Shabbir et al. 2018).

Evaluation of antimicrobial activities of VF and VF-Ag

The antimicrobial activities of the VF and VF-Ag samples were evaluated qualitatively by using the agar disc diffusion method. The antimicrobial activities were evaluated against four microorganisms include staphylococcus aureus (a Gram-positive bacterium), Escherichia coli (a Gram-negative bacterium), Candida albicans (yeast), and Aspergillus niger (a fungus). Nutrient agar plates for bacteria and yeast were equally and extensively planted with 0.1 ml of 10⁵⁻ cells/ml. A Czapek-Dox agar plate seeded with 0.1 ml of the fungus inoculum was used to measure the antifungal activity. The surface of the inoculated agar plates was covered with VF-Ag, and the sample-saturated filter paper was also placed there. Plates were then kept at a low temperature (4 °C) for 2–4 h to allow for maximum diffusion. Following that, the bacteria were incubated at 37 °C for 24 h and the organisms at 30 °C for 48 h in an upright position. The antimicrobial activity was determined by measuring the diameter of the zone of inhibition in millimeters (mm) (Abdel-Wareth et al. 2019).

Evaluation of the antibacterial activity of VF-Ag by measuring colony forming unit (CFU)

The antibacterial activities of the VF and VF-Ag samples were evaluated quantitatively by using the colony-forming unit (CFU) method. The antimicrobial activities were evaluated against Staphylococcus aureus and Escherichia coli. 0.05 g of VF or VF-Ag was applied to a 100-conical flask each containing 10 ml nutrient broth. Bacterial stocks (100 µl of stock with an approximate CFU value of 10⁸) were inoculated using a 10 ml volume of freshly prepared liquid nutrient broth that contained 5 g/l peptone and 3 g/l beef extract at pH 6.8. The stocks were then cultured for 24 h. A control sample has been done (untreated S. aureus and E. coli). A serial dilution (10^–4. 10^–5, and 10^–6) was prepared from each culture containing a sample and the controls after 24 h of incubation at 37 °C. By inoculating Petri dishes containing solidified nutrient agar medium with 100 µl of each dilution, colony forming units (CFU) were used to measure the degree of microbial inhibition. The reduced growth rate (R) for treated samples compared to control (untreated) samples was determined using the following equation;

$$\mathbf R(\boldsymbol\%)=\mathbf B-\mathbf A/\mathbf B\times\mathbf{100}$$

where A is the treated sample's CFU/ml after 24 h of incubation and B is the untreated sample's CFU/ml after the same period of incubation time (Abdelraof et al. 2019).

Durability test

To investigate the durability of the functionalized viscose fibers, five repeated washing cycles were performed. The washing durability test technique was evaluated using the AATCC test method 61–1989. At 60 °C, 1 g of the sample is soaked in a 40 ml solution containing 2 g/l Egyptol®PLM for 30 min. After washing cycles, the samples were rinsed with water and dried at room temperature.

Release of silver

To investigate the release of silver from the VF-Ag samples, 100 mg of each sample at different stirring reaction times was immersed in 50 ml of deionized water at 37 °C. At time intervals, 10 mL of solution was withdrawn from the release media and replaced with 10 mL of fresh deionized water. The amount of released Ag⁺ ions was measured using ICP-OES (Wan Mat Khalir et al. 2020)..

Cytotoxicity test

The potential cytotoxicity of VF and VF-Ag samples was evaluated against normal human epidermal keratinocytes (NHEK) and normal human dermal fibroblasts (NHDF) via the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) assay (Maráková et al. 2017).

Evaluation of sensor properties of VF-Ag 5

VF-Ag 5 was evaluated for the naked-eye colorimetric sensing of eight metal ions (Co²⁺, Pb²⁺, Ni²⁺, Fe²⁺, Hg²⁺, Cd²⁺, Cu²⁺, and Zn²⁺). 100 ppm aqueous solutions of these metals were prepared. At room temperature, 0.5 g of VF-Ag 5 was dipped into a 50 mL solution of these metals for 5 min. The change in the color of VF-Ag is constantly noted by the naked eye.

Statistical analysis

The measurements were performed in triplicate and the net averages were measured and expressed by Mean ± SD.

Results and Discussion

The primary goal of this research was to improve the functional properties of viscose fiber surfaces by incorporating Ag NPs through a green route. Even though many researchers have worked on the in-situ deposition of cellulosic surfaces with Ag NPs, no publications have been published on the in-situ biosynthesis of Ag NPs to improve the multifunctional properties of viscose fibers using guava leaf extract. In-situ biosynthesis by immersing the viscose fibers in a solution containing silver nitrate and guava leaf extract allows silver ions as well as guava leaf extract to reach the interior of the viscose fibers, and then reduce them to silver nanoparticles. As a result, silver nanoparticles can be generated in situ inside the fiber to change it.

Coloration, dyeing process improvement, UV protection, antioxidant activity, antimicrobial activity, and sensor ability of viscose fibers were successfully obtained after in-situ biosynthesis of silver nanoparticles by using guava leaf extract as a reducing and stabilizing agent. UV–vis spectroscopy was used to assess the silver nanoparticles in the residual solutions at different reaction parameters. SEM, EDX, XRD, FTIR, and XPS investigations were used to confirm the presence and effect of Ag NPs on the viscose fibers (VF) and treated viscose fiber surfaces (VF-Ag 5) at 500 ppm Ag⁺ and 10 mL of guava leaf extract for 60 min at 80 °C. The mechanism of in-situ biosynthesis of Ag NPs and their incorporation into the VF matrix will be discussed. Finally, the multifunctional properties of modified viscose fibers will be evaluated and discussed. The modified VF-Ag is hereafter referred to as VF-Ag 1. VF-Ag 3 and VF-Ag 5 according to the concentrations of silver nitrate (100, 300, and 500, respectively).

Extraction of bioactive compounds from Guava leaf

The bioactive compounds from guava leaf were extracted to use these bioactive compounds as reducing agents in the conversion of metallic silver ions (Ag⁺) to zero-valent atoms (Ag⁰ NPs). A binary solvent containing ethanol/water (70:30) was used to extract the bioactive compounds. The phytochemical screening of the extract revealed the presence of bioactive compounds including carbohydrates, tannins, flavonoids, alkaloids, anthocyanins, and glycosides (Rehan et al. 2019a). The yield extraction percentage was 82%. TPC and TFC were 141.7 ± 1.2 mg GAE/g and 94.10 ± 1.3 mg QE/g. The extract exhibited a pale green color with a pH of 3.5 and high antioxidant activity (98 ± 0.4%).

TPC and TFC decreased to 78.7 ± 2.2 mg GAE/g and 44.10 ± 1.1 mg QE/g after the formation of silver nanoparticles. The decrease in TPC and TFC concentrations is directly associated with their roles as reducing agents to reduce Ag⁺ to Ag⁰ as well as stabilizers on the surface of the formed Ag NPs. Furthermore, as a result of its adsorption on the viscose fiber surface (Salgado et al. 2023).

Bioactive compounds in the guava leaf extract were identified using HPLC. Table 1S shows the result of the high-performance liquid chromatography (HPLC) analysis of guava leaf extract. This table shows that HPLC analysis confirmed the presence of 12 bioactive compounds identified in the extract. The bioactive compounds present in the extract include flavonoids, phenolic acids, and vitamins. The major bioactive compounds of the extract were flavonoids, which are represented by the compounds catechin, quercitrin, epicatechin, and rutin, Furthermore, the phenolic acids were identified in high proportions and are represented by compounds: caffeic acid, chlorogenic acid, and Gallic acid. Flavonoids and phenolic acid compounds are well known for their ability to function as natural reducing and stabilizing agents, initiating the reduction of Ag⁺ to Ag⁰ atoms and contributing to their subsequent aggregation into clusters (Ag⁰) n. The presence of multiple hydroxyl (-OH) and carboxyl (-COOH) functional groups in their structure is linked to their ability to decrease and stabilize nanoparticles in a complex redox-mediated process (Rehan et al. 2019a).

Effect of reaction parameters on the in-situ biosynthesis of Ag NPs on the VF surface

Because of their localized surface Plasmon resonance (LSPR) properties, Ag NPs show vivid and interesting colors. The color change in the treatment solution and the viscose fiber surface from white to yellow/brownish indicates the formation of Ag NPs. UV–vis spectroscopy is a straightforward and sensitive tool for assessing the formation of Ag NPs. Figure 1 displays the UV–Vis spectroscopy of guava leaf extract as well as the absorbance of supernatant silver solutions.

Fig. 1

UV–Vis absorbance spectra for residual Ag NPs solution after treatment by different volumes of guava leaf extract (a) different concentrations of Ag.⁺ ion (b) different treatment time (c) different temperature (d) TEM for the residual solution of VF-Ag 5

The UV–Vis spectrum of the guava leaf extract showed three peaks. The autochrome and chromophore substituent n → π^* transitions caused the first peak to form at 320 nm. The second peak, which appeared at 375 nm, is attributed to the phenolic groups' distinctive absorption. Around 675 nm, there was a third signal that was attributed to a flavonoid combination (Somchaidee and Tedsree 2018). The UV–Vis spectra of guava leaf extract and Ag + ion solutions showed a significant bathochromic shift, indicating an intermediate complex between the OH groups of the flavonoids or phenolic compounds and the Ag⁺ ions (Fig. 1S). After reduction, all the residual solutions display an absorption peak in the 410–490 nm range that is connected to the LSPR of Ag⁰, indicating the production of Ag NPs. Additionally, at 330 nm, the LSPR of bulk Ag⁺ was noticed. The disappearance of two peaks that appeared at 375 and 675 nm in the UV–Vis spectrum of extract after the reduction process was attributed to the roles of phenolic groups and flavonoids through the in-situ reduction of silver ions.

Figure 1a shows the UV–vis spectra of the Ag NPs obtained by using different volumes of guava leaf extract in the presence of 300 ppm Ag⁺, a liquor ratio of 1:50, and pH of 6 at 80 °C for 60 min. The figure illustrates the following findings: (i) there is a progressive enhancement in the intensity of LSPR with the increasing volume of guava leaf extract from 2.5 mL to 10 mL. At a high volume of extract, higher contents of the biomolecules involved in the silver reductive process are available, resulting in more Ag⁺ atoms being converted to Ag⁰. (ii) The peak intensity retained its position showing that the amount of guava leaf extract used did not affect the shape of the formed Ag NPs.

Figure 1b depicts the UV–vis spectra of the Ag NPs obtained by using different concentrations of Ag⁺ in the presence of 10 mL of guava leaf extract, a liquor ratio of 1:50, and pH of 6 at 80 °C for 60 min. The figure reveals several findings as follows: (i) the intensity of LSPR increases gradually as the Ag⁺ ion concentration rises from 100 to 500 ppm. The formation of more Ag NPs could explain the increase in SPR intensity. At high Ag⁺ concentrations, more Ag⁺ ions can be absorbed on the VF surface, facilitating complexation between the absorbed Ag + ions and the carboxyl and hydroxyl groups in the VF matrix; meanwhile, more Ag⁺ atoms benefit from a reduction to Ag⁰. (ii) The peak intensity increased while retaining its position indicating that the precursor concentration did not affect the morphology of the formed Ag NPs.

Figure 1c displays the UV–vis spectra of the Ag NPs obtained by using different times of reaction in the presence of 500 ppm Ag⁺, 10 mL of guava leaf extract, a liquor ratio of 1:50, and a pH of 6 at 80 °C. This figure clarifies that there was a progressive enhancement in the intensity of LSPR as the duration of the reaction increased from 15 to 60 min. This increase is attributed to the formation of more Ag NPs by increasing the duration of the reaction.

Figure 1d demonstrates the UV–vis spectra of the Ag NPs obtained by using different temperatures in the presence of 500 ppm Ag⁺, 10 mL of guava leaf extract, a liquor ratio of 1:50, and pH of 6 for 60 min. Several findings are revealed in the figure, as follows: (i) at 30 °C, there is no observable peak in the range of silver LSPR. (ii) There is a progressive improvement in the intensity of LSPR as the temperature increases from 30 °C to 50 °C. (iii) The intensity of LSPR increases rapidly as the temperature increases from 50 °C to 80 °C. Temperature plays a promising role in controlling guava leaf extract absorption and Ag + ion movement. Thus, temperature can facilitate the absorption of guava leaf extract as well as silver ion uptake from the solution to the surface of VF. Also, the temperature increases the kinetics of the reaction, resulting in the reduction rate of silver ions being accelerated, and the remarkable enhancement in the formation of Ag⁰.

Transmission electron microscopy (TEM) investigation was carried out to obtain insight into the precise form of the formed Ag nanoparticles. Figure 1e shows the TEM of Ag NPs obtained by using 500 ppm Ag⁺, 10 mL of guava leaf extract, a liquor ratio of 1:50, and a pH of 6 at 80 °C for 60 min. The TEM image demonstrates that the nanoparticles formed were mainly spherical or quasi-spherical in shape and monodispersed with an average particle size of approximately 57 ± 1 nm. The particle size distribution of Ag in solution was evaluated by the dynamic light scattering (DLS) technique. The silver nanoparticles' particle size distribution was 61 ± 3 nm (Fig. 2S). The majority of particle size distribution was located between 10 and 75 nm (91%), showing that the silver particles were adequately homogenous and well-dispersed. This result confirms the role of guava leaf extract in stabilizing and capping the formed nanosilver. The particle size distribution measured with DLS showed a large particle size distribution compared to TEM. This result may be attributed to the particle size measured by TEM being the size of bare silver nanoparticles, while the particle size measured by DLS is the size of silver nanoparticles containing the remaining guava leaf extract adopted on the surface of silver nanoparticles (Butola and Kumar 2020). The distinction between TEM and DLS measurements is that TEM only detects electron-rich metal particles, while DLS detects particle size as a whole (Zhou et al. 2018). This result confirms that the formed silver nanoparticles are successfully coated by the remaining guava leaf extract as a stabilizer.

Characterization of the VF and VF-Ag 5

The presence of Ag NPs on the functionalized viscose fibers was confirmed by UV–Vis spectroscopy (Fig. 3S). This figure shows that the VF did not show any absorption peak in the 400–420 nm range, while the VF-Ag samples exhibited strong absorption in the 400–420 nm range, which is attributed to the LSPR of Ag NPs. This absorption peak confirms the presence of spherical silver nanoparticles on the surface of viscose fibers, indicating the successful preparation of silver nanoparticles through this approach. The intensity of absorption peaks increases as the Ag + ion concentration increases, indicating that the silver content on the surface of viscose fiber increases in turn.

To investigate the morphology, chemical composition, formation, and distribution of Ag NPs on VF, the VF-Ag 5 was examined and compared with VF via SEM, EDX, and elemental mapping (Fig. 2). The SEM image of the VF (Fig. 2a) displays the smooth surface with the longitudinal fibril structure of the fibers, while the VF-Ag 5 demonstrates that the surface of the VF was coated with uniformly dispersed spherical silver nanoparticles (Fig. 2b), confirming their successful formation on the VF surface (Zhou et al. 2017). The distribution of Ag NPs on the surface of VF was determined by a software program through an SEM image. The silver nanoparticles' particle size distribution was 55 ± 4 nm (Fig. 2S). The majority of particle size distribution was located between 10 and 75 nm (95%), indicating that the silver particles were sufficiently homogeneous and well-dispersed. Ag NPs on the surface of VF showed better homogeneity and dispersibility compared to Ag NPs in the solution. This result confirms the role of guava leaf extract as well as cellulosic fiber in stabilizing the formed nanosilver.

Fig. 2

SEM image of VF (a), VF-Ag 5 (b) EDX of VF (c), VF-Ag 5 (d), and images of elemental mapping of VF-Ag 5 (e)

The EDX spectrum of VF (Fig. 2c) revealed two peaks related to carbon and oxygen which are the main characteristic elements of cellulosic fibers. The EDX spectrum of VF-Ag 5 (Fig. 2d) revealed a peak at 3 eV caused by Ag L, in addition to the two VF peaks, indicating the existence of silver nanoparticles on the surface of VF. Furthermore, elemental mapping was investigated for further confirmation of the Ag presence on the surface of VF. The elemental mapping image (Fig. 2e) of VT-Ag 5 showed differences in color representing different element components (C, O, and Ag) present in the VF-Ag 5. SEM, EDX, and elemental mapping results show the presence of Ag on the surface of VF, confirming the formation of nanoparticles through the in situ biosynthesis protocol.

To show crystal structure, and the presence of silver nanoparticles deposited in situ on the VF surface, X-ray diffraction (XRD) analysis was used (Fig. 3a). Peaks with 2θ angles of 12.1°, 21.5°, and 23.3° are visible in the VF's XRD pattern and are associated with the cellulose-II crystalline structure. The XRD pattern of VF-Ag 5 shows the cellulose-II crystalline structure. Furthermore, at 2θ angles of 38.6°, 44.5°, and 64.5°, three further diffraction peaks appeared. These were attributed to the (111), (200), and (220) planes of face-centered-cubic Ag (Deeksha et al. 2021). To investigate the detailed chemical composition, FTIR and XPS were used to further characterize the effects of in situ biosynthesis of silver nanoparticles on the surface of VF (Fig. 3).

Fig. 3

XRD of VF and VF-Ag 5 (a), FTIR of VF and VF-Ag 5 (b), XPS survey spectra of VF (c), XPS survey spectra of VF-Ag 5 (d), high-resolution C1s spectra of VF (e), high-resolution C1s spectra of VF-Ag 5 (f), O 1 s spectra of VF and VF-Ag 5 (g), and Ag 3d spectra of VF-Ag 5 (h)

Figure 3b shows the FTIR of VF and VF-Ag 5. The cellulose macromolecule is responsible for the characteristic peaks of VF, which are located at 3480 cm⁻¹ attributed to the stretching of O–H, 2910 cm⁻¹ attributed to the stretching of C-H, 1660 cm⁻¹ attributed to the stretching of C = O, 1515 cm⁻¹ attributed to the wagging of C-H, 1405 cm⁻¹ attributed to the bending of C-H, and 1210 cm⁻¹ attributed to the stretching of C–O. The FTIR spectra of the VF-Ag 5 revealed new distinctive peaks in addition to the conventional cellulose peaks with a little change in intensity and a hypochromic shift. The additional peaks appeared in 1690, 1550. 13,400, and 1030 cm⁻¹ which are attributed to the carbonyl group (C = O) of quinone or quinoid, C = C (aromatic) stretching, the hydroxyl (C–OH) group of the phenolic compounds, and the existence of the C-O group of the phenolic compounds (Rehan et al. 2018a, 2020a).

To investigate the role of guava leaf extract in the reduction and stabilization of generated silver nanoparticles, the XPS was evaluated to gain better insight into the oxidation state of generated silver nanoparticles and the chemical analysis of the surface of VF-Ag. The chemical structure of the surface of VF and VF-Ag 5 was analyzed by XPS, and the results are shown in Figs. 3c to h. The survey spectra of VF (Fig. 3c) showed the presence of peaks at a binding energy of 533 (O 1 s) and 285 (C 1 s) eV as expected in a spectrum of cellulosic materials, The survey spectra of VF-Ag 5 (Fig. 3d) showed the presence of a peak at a binding energy of 368 eV (Ag 3d) together with two peaks O 1 s and C 1 s which are related to VF. The appearance of an Ag 3d peak in the XPS spectrum confirmed that Ag NPs successfully in situ deposited on the surface of the VF via the reduction by guava leaf extract. Figures 3e and f show C1s high-resolution spectra of VF and VF-Ag 5, respectively Fig. 3e shows that the C1s spectrum of the VF showed three peaks at 284.5 eV, 286.7 eV, and 289 eV corresponding to the energies C–C, C-O, and COO, respectively. The intensity and area of the C-O peak are higher than those of the COO peak, which was expected due to the VF being produced from cellulose. Figure 3f shows that the C1s spectrum of the VF-Ag 5 showed three peaks also. The intensity of the three peaks increased in the VF-Ag 5 compared to the VF. Moreover, the peak that appeared at 289 eV (COO) was shifted to 289, 5 eV, and the peak area was much larger, which indicated that C = O groups were introduced on the surface of VF. The C = O double bond increases the peak area and binding energy. Figure 3g shows the O1s spectra of VF and VF-Ag 5. This figure reveals that the binding energy of O1s in VF-Ag 5 increased by 0.3 eV compared to the VF as well and the intensity of O1s increased in the VF-Ag 5. The increasing intensity of the C1s and O1s peaks in the VF-Ag 5 indicates the introduction of more oxygen-containing groups onto the VF surface. This increment of oxygen-containing groups shows the role of phenolic compounds present in the guava leaf extract in the reduction of silver ions to silver nanoparticles. The Ag 3d peak spectra (Fig. 3h) show two peaks at 368.9 eV (Ag 3d5/2) and 374.8 eV (Ag 3d3/2). The spin energy separation of Ag 3d was 5.9 eV, indicating that zero-valent metallic silver (Ag⁰) was successfully formed on the surface of VF. All of the XPS results provided additional insights into the chemistry and composition of the VF-Ag as well as the role of guava leaf extract in the reduction process.

Thus, the FTIR and XPS results show that silver nanoparticles were successfully formed on the VF through the biosynthesis route, which is stabilized by the function groups present on the VF surface. Also, the results show the role of bioactive compounds present in guava leaf extract in the reduction process and prove the formation of keto-forms of phenolic compounds after the reduction process and their role in stabilizing the formed nanoparticles.

Mechanism of decoration of VF with Ag NPs

The standard reduction potentials, (E⁰), determine the pair of reactants required for effective chemical reactions in the redox reaction system. This means that the free energy change in the reaction, G0, must be negative or equal to E⁰ > 0. The rather large electropositive reduction potential of Ag⁺ to Ag⁰ in water (E⁰ =  + 0.799 V) encourages the employment of many reducing agents. The reduction potential values for flavonoids and phenolic compounds in plant extracts (E⁰ [Ar-OH_(I)/Ar–O-], where Ar stands for phenyl group, vary from 0.3 to 0.8 V, implying that polyphenol-assisted reduction of Ag + -ions (E⁰ [Ag⁺/Ag⁰] = 0.799 V) is achievable (El-Seedi et al. 2019). It has been proposed that keto–enol tautomeric transformation of flavonoids and phenolic compounds may allow the release of reactive hydrogen atoms, which drive metal ion reduction. As previously mentioned in HPLC results, the extract of the guava leaf is rich in flavonoid and phenolic compounds. The flavonoids or phenolic compounds of the guava leaf extract are consumed in two reactions, one is silver nanoparticle formation, and the other is adsorption on the surface of VF (Patil and Rane 2020). According to the HPLC analysis (Table 1S), Catching, caffeic acid, chlorogenic acid, and Gallic acid were identified as the main compounds in the guava leaf extract, and assumed to be the major reducing and stabilizing agents in the in situ biosynthesis of Ag NPs on the viscose fiber surface. The bioreduction of Ag⁺ ions may occur by the synergistic action of one or more of these compounds. In the biosynthesis reduction process, two hydroxyl groups presented at the ortho position of the phenyl ring of the flavonoids or phenolic compounds can act as a reducing agent by losing electrons followed by oxidation to quinone or quinonoid form.

The FTIR of VF-Ag indicates the formation of quinone or quinonoid. Also, the XPS results confirm the incorporation of more oxygen-containing groups onto the surface of VF. The mechanism of decoration of VF with Ag NPs is adapted from the above-mentioned results as follows and schemes 1 and 2 demonstrate the proposed mechanism of decoration of VF with Ag NPs. The three steps of in situ synthesis of Ag NPs on the VF surface using guava leaf extract are pre-nucleation, nucleation, and growth. During the pre-nucleation step, when VF is dipped in an Ag⁺ ion solution, the Ag⁺ ions are adsorbed and diffused throughout the surface of the VF due to electrostatic interaction with the OH and/or COOH groups. Electrostatic interaction takes place through substituting hydrogen of a hydroxyl (-OH) group in VF with Ag⁺, resulting in the formation of a VF-O-Ag complex (Emam et al. 2014; Rehan et al. 2017b), Electrostatic interaction forces may decrease the mobility of silver ions, enhance the creation of metal nuclei, and control their growth (Scheme 1). The introduction of additional –OH and –COOH groups from flavonoids and phenolic compounds of guava leaf extract enhances the synthesis of silver nanoparticles. In the nucleation stage, the silver ions adsorbed on the surface of VF are reduced by the many -OH groups present in the flavonoids or phenolic compounds of guava leaf extract. First, the -OH groups of the flavonoids or phenolic compounds formed an intermediate complex with the Ag⁺ ions as confirmed by UV–vis spectra (Fig. 1S). Then flavonoids and phenolic compounds donated electrons through the OH hydroxyl groups to reduce the Ag⁺ ions to Ag⁰ allowing for the in situ biosynthesis and deposition of Ag NPs on the viscose fiber surface and leaving the flavonoids or phenolic molecules in their oxidized form (quinone or quinonoid). Once the silver atoms reach supersaturation, they combine to generate nuclei and seed crystals. During this step, silver nuclei formed, the solution and VF changed color, and seed crystals began to form. In the growth, silver nanoparticles are stabilized by the protection of quinone or quinonoid, which are adsorbed on their surface (Scheme 2).

Scheme 1

Decoration of the surface of VF with the in situ biosynthesis Ag

Scheme 2

Proposed hypothetical reduction and stabilization mechanism of Ag⁺ to Ag.⁰ in the presence of phenolic compounds (Caffeic acid) or flavonoid compounds (Catechin)

The mechanism of Ag NP attachment on the surface of viscose fibers can be clarified from many perspectives. The silver nanoparticles are ultimately attached to the VF surface as a result of a strong contact between their surface and the oxygen atoms of OH and –COOH (Rehan et al. 2018a, 2020a). The larger silver nanoparticles are generally entrapped inside the cellulosic matrix network. The smaller silver nanoparticles easily enter the porous viscose fibers structures and are then entrapped by developing a possible network from the remaining guava leaf extract (Mahmud et al. 2020; Mia et al. 2021).

Silver content, mechanical properties, water absorption %, and moisture sorption

The silver nanoparticle contents that are deposited onto the VF surface are greatly influenced by the concentration of silver ions and consequently, they affect the coloring, UV protection, and antimicrobial activities of the VF surface. The amount of Ag NPs deposited onto the VF surface was investigated using the ICP-OES technique. The silver content (mg/Kg) on the VF surface is displayed in Table 1. The findings demonstrated that during the in situ biosynthesis, the silver nanoparticles were deposited on the VF with silver contents of 798 mg/kg. Increasing the concentration of Ag⁺ ion from 100 to 500 ppm resulted in an increased silver content of Ag NPs deposited on the VF Ag NPs to 1543 mg/kg. As the concentration of silver ions increased, more silver ions were adsorbed onto the VF surface, allowing additional silver atoms to be transformed into silver nanoparticles for incorporation onto the VF surface. The results of silver content agree with the UV–Vis spectra data of VF-Ag samples (Figure S3).

Table 1 Silver content, mechanical properties, water absorption, and moisture sorption of VF and VF-Ag samples

Silver content deposited onto the VF surface was slightly decreased after five washing cycles (Table 1). The decrease in silver content increased as the concentration of silver ions increased. After 5 washing cycles, the decreased % of the silver content was 10.9, 12.7, and 14% for VF-Ag 1, VF-Ag 3, and VF-Ag 5 respectively. This means that more than 85% of the silver remained on the VF surface. A slight decrease in silver content was attributed to the release of Ag NPs in the washing liquor during the washing process. The high silver content that remained on the VF surface after washing is attributed to the role of quinone or quinonoid formed from phenolic compounds after the reduction process in the stabilization of the formed silver nanoparticles, as well as a strong contact between the silver nanoparticles and the oxygen atoms of the OH and COOH function groups present on the VF surface..

The mechanical properties of VF and VF-Ag samples were analyzed in terms of the tenacity at break (g/den) and elongation % (Table 1). This table reveals that the mechanical properties of the VF-Ag improved. The tenacity and elongation % of VF-Ag samples are higher than those of VF. The tenacity and elongation % increased as the silver ions increased. The tenacity at break (g/den) of VF was increased from 2.8 to 3.6 (VF-Ag 5) after successful in situ deposition of Ag on the VF surface. Also, the elongation % was increased from 13% to 14.8% (VF-Ag 5). The improvement in the mechanical properties of the VF-Ag samples could be attributed to the VF being coated in silver nanoparticles which form connections with one another and with the VF surface. Furthermore, due to their small size, silver nanoparticles have the potential to act as fillers or crosslinking agents, which contributes to the load-sharing effect when a load is applied to the VF. As a result, applied stress will be distributed more consistently along VF chains, avoiding stress concentration. As a result, the silver nanoparticles can cross-link the VF, enhancing their toughness as a result of load-sharing when the load is applied to the fibers. As a result, the VF chains will distribute the applied load more equally, reducing stress concentration. Also, this improvement is attributed to the role of quinone or quinonoid formed from phenolic compounds after the reduction process that assists in stabilizing and intercalating the silver nanoparticles into the VF matrix, which can avoid slippage during stress application.

Fibers with a high water absorption capacity are important in medical applications, especially in the area of antimicrobial activities as well as wound healing where fibers are required to uptake and retain biological liquids. The water absorption percentages of the VF and VF-Ag samples are shown in Table 1. This table shows that VF exhibited a relatively high capacity for water absorption (33 ± 4%). This high capacity is attributed to the presence of hydroxyl and carboxylic acid groups on the surface of VF, which results in a hydrophilic character capable of promoting water absorption. The VF-Ag samples displayed enhancement in water absorbance %. The water absorbance % increases as silver content increases. This could be attributed to coupling silver nanoparticles, as well as flavonoids and phenolic compounds present in guava leaf extract, onto the surface of VF, resulting in additional hydrophilic groups (OH and COOH) and more active site groups (Rehan et al. 2019a). The moisture sorption percentages of the VF and VF-Ag samples are shown in Table 1. This table shows that the silver nanoparticles and guava leaf extract showed a slight improvement in moisture sorption %. These results revealed that VF-Ag samples have significant capability for water, wound exudates and liquid drug absorption and can be presented as a viable candidate for medical applications. Furthermore, the high water absorption of the VF-Ag samples is required for other post-treatment processes, including finishing or dyeing processes.

Colorimetric properties

The biosynthesis of Ag on VF was demonstrated by a change in the color of the VF from white to yellow/brownish as shown in Fig. 4a. The appearance of the color on the surface of VF is attributed to the surface Plasmon absorption of Ag NPs.

Fig. 4

Photograph of VF and VF-Ag samples (a), VF and dyed VF with reactive dye (b), and VF-Ag 5 and dyed VF-Ag 5 with reactive dye (c)

A distinct color unevenness of the obtained samples indicated the effect of silver ions concentration on the final color of VF indicated the effect of silver ions concentration on the final color of VF. VF-Ag 1 showed a light yellow. The color of VF-Ag 3 and VF-Ag 5 changed to dark yellow and brownish respectively. The yellow/brownish obtained confirmed the presence of spherical silver nanoparticles as mentioned above in the results of UV–vis spectra and TEM.

This part examines the role that nanosilver incorporation plays in the dyeing of VF using blue reactive dye

A blue color was imparted onto VF after the dyeing of VF with CI-reactive blue-19 in the absence of silver nanoparticles (Fig. 4b). The green color was obtained after the dyeing of VF-Ag with CI-reactive blue-19. The green color was attributed to the combination of the blue color of the reactive dye and the yellow/brownish of VF-Ag. The dye concentrations did not significantly change the green hue but at high concentrations of dye (5%) the color of VF-Ag was dark green as shown in Fig. 4c.

The colorimetric data of the VF, VF-Ag samples, and the influence of silver nanoparticles immobilized on viscose fibers on the colorimetric data of dyed viscose fibers with CI-reactive blue-19 dye are presented in Table 2.

Table 2 Colorimetric data of VF-Ag, dyed VF, and dyed VF-Ag samples

The results showed that VF-Ag samples displayed higher K/S values compared to VF. The K/S values were increased with the increase in Ag⁺ ions concentrations; owing to the higher quantity of Ag NPs deposited onto the surface of VF. Evident K/S values are in line with silver content results as mentioned above (Table 1), which shows that a higher concentration of silver nitrate solution causes larger Ag⁺ ions uptake and higher total content of silver in the surface of VF. The (L^*, a^*, b^*) values for VF were varied considerably from VF. VF is white, with a high L^* value (89.88), a low a^* value (0.31), and a low b^* value (2.44). VF-Ag samples displayed a significant change of (L^*, a^*, b^*) values compared to the VF. The values of L^* were significantly decreased while values of a^* and b^* increased dramatically with increasing the Ag ions concentration. The decrease in the values of L^* is the result of the coloration of the VF with silver nanoparticles. The increase in values of a^* represents some of the reddish color for treated viscose fibers. Furthermore, the considerable increase in b^* values is related to the yellow/brownish color obtained. The VF-Ag samples had positive a^∗ and b^∗ values. This is attributed to yellow or brownish colors which are imparted on the surface of VF. The hue angle ranged from 64.06° to 67.84⁰, which confirmed the yellow/brownish color of the VF as shown in Fig. 4A.

The effect of silver nanoparticle incorporation on the surface of VF on the dyeing of VF with CI-reactive blue-19 was investigated by K/S, color space (L^*, a^*, b^*), and hue angle, and the results are presented in Table 2. In the absence of silver nanoparticles, the K/S values increase as the concentration of the dye increases from 2.5 to 5% for the dyed VF. In the presence of silver nanoparticles, the dyed VF-Ag samples showed higher K/S values compared to the dyed VF samples. These results indicate the role of silver nanoparticles, which can act as reactive sites on the surface of VF, and they can be attached to dye molecules, leading to an improvement in color strength (Ahmed et al. 2018). The K/S values increase as the concentration of dye and silver content increases.

The dyeing of VF with CI-reactive blue-19 dye showed negative values of b^* (-37.36, and -42.33) and the hue angle was 277.13⁰ and 273.17⁰ for dyed VF (2.5%) and VF (5%), confirming that the dyed VF samples exhibited a blue color.

The CIE L^*a^*b^* color space model and the hue angle confirm the change of dyed VF-Ag samples compared to dyed VF. These results show that there was a decrease in the lightness values (L^*), indicating that the gradual increase in silver content imparts a darker color of dyed VF-Ag samples than dyed VF samples. The values of a^* and b^* varied significantly, corroborating the great visual color change in the dyed VF-Ag samples compared to the dyed VF samples. At all the VF-Ag samples, the dyed VF-Ag samples showed negative values of a^* and positive values of b^*, indicating the color of the dyed VF-Ag samples changed to green color. The hue angle values range from the green region (111.36⁰ to 144.57⁰). The greenish color is attributed to corresponding to the mixture between the blue color of the CI-reactive blue-19 and the yellow/brownish color of VF-Ag samples.

These results confirmed the role of silver nanoparticles in the improvement of the dyeing process with reactive dye as follows: (i) Because of the yellow/brownish color of VF-Ag, its combination with reactive blue dye resulted in a color change in dyed fibers to the green color that they required, especially in medical applications. (ii) Silver nanoparticles immobilized on the source of viscose fibers can function as a mordant in the dyeing process, increasing dye affinity and providing additional opportunities for dye molecules to bind to the fiber functional groups, resulting in different shades.

The colorfastness properties of the VF-Ag and dyed VF-Ag samples are important for dyed fiber acceptance. Table 3 shows the colorfastness properties of VF-Ag and dyed VF-Ag samples.

Table 3 Colorfastness of VF-Ag, dyed VF, and dyed VF-Ag samples

This table reveals that VF-Ag samples displayed excellent washing and rubbing fastness properties based on a grey scale for color change from 1 to 5. The VF-Ag samples displayed very good light-fastness properties based on a blue scale for color change from 1 to 8. The excellent colorfastness could be attributed to the chemical stability of Ag on the surface of VF as well as long-term durable interactions between Ag, and functional groups of VF such as (OH, and COOH).

The dyed VF with CI-reactive blue-19 showed excellent washing and rubbing fastness properties as well as very good light-fastness properties. In the dyed VF-Ag samples, the silver nanoparticles deposited on the surface of VF did not affect the stability of the dye on fibers and the fastness properties were still at nearly the same rate.

UV protection and antioxidant properties of VF-Ag

The damaging UV radiation of the sun is now reaching the Earth's surface as a result of climate change and ozone layer depletion. UV radiation has a wavelength of 200–400 nm and is classified into three regions: UVA (320–400 nm), UVB (280–320 nm), and UVC (200–275 nm). Ultraviolet radiation in the (UV-A) area is the most damaging to human skin, causing diseases like freckles, sunburn, and skin cancer. These skin diseases are life-threatening to the population, necessitating protection from long-term sun exposure. Therefore, UV protection of any substrate is primarily due to resistance to UVA (320–400 nm) region (Zhou et al. 2017).. As a result, the development of efficient, multifunctional protective fabrics/fibers has become crucial for human safety. The Ultraviolet Protection Factor (UPF) of textiles reveals how much UV light (UVB and UVA) it lets reach your skin (Louris et al. 2018). Anti-ultraviolet textiles must meet two characteristics, according to GB/T 18830–2009 (Textiles-Evaluation for Solar Ultraviolet Radiation Protective Properties). The UPF value must be higher, and the transmission of UVA (T UVA) must be lower (Rajaboopathi and Thambidurai 2018).

The UV protection properties of the untreated and VF and VF-Ag samples were evaluated by the UV transmittance percentage in the UV-A region (320–400 nm) and the results are presented in Fig. 5a. This figure reveals that the UV transmittance % of untreated VF was high, indicating that VF had a low UV protection activity. On the other hand, the VF-Ag samples exhibited a low UV transmittance %. Figure shows that the VF-Ag samples can block over 90% of the incident UV light. Additionally, an increase in the silver ions concentration resulted in a decrease in UV transmission %, which in turn increased the UV protection activity.

Fig. 5

UV transmittance spectra for VF and VF-Ag samples (a), and UPF for VF and VF-Ag samples before and after five washing cycles (b)

The ultraviolet protection factor (UPF) can estimate the UV-blocking activity of VF and VF-Ag samples. Figure 5b shows the UPF values of VF and VF-Ag samples before and after five washing cycles. This figure shows that the VF-Ag samples exhibit higher UPF values than VF. The UPF values increased as the concentration of silver ions increased. The UPF value was 280, 320, and 355 for VF-Ag 1, VF-Ag 3, and VF-Ag 5, respectively, compared to 103 for VF. The UV protection properties of VF-Ag samples may be attributed presence of guava leaf extract and silver nanoparticles. Guava leaf extract includes flavonoids and phenolic acids, which have free-radical scavenging properties, resulting in UV-blocking properties. Silver nanoparticles change the color of VF from white to yellow-brownish causing significant ultraviolet blocking. Also, Silver nanoparticles cause ultraviolet scattering because of their high refractive index (Rehan et al. 2017a).

The UPF values of VF-Ag samples were slightly decreased after washing. After five washing cycles, the UPF value was 265, 301, and 334 for VF-Ag 1, VF-Ag 3, and VF-Ag 5, respectively. The decreased % of the UPF was 5.3, 5.9, and 6% for VF-Ag 1, VF-Ag 3, and VF-Ag 5 respectively. A slight decrease in UPF values was attributed to the release of Ag NPs and guava leaf extract in the washing liquor during the washing process. The high UVF values of VT-Ag samples after washing verified the close interaction and stability between Ag NPs and the surface of VF.

Antioxidant fibers are important for the development of healthy textiles because they can provide good protection against oxidative damage caused by free radicals such as active oxygen radicals. The phenolic and flavonoid compounds present in guava leaf extract are important for healthy textiles field because of their ability to scavenge free radicals. The hydroxyl groups (-OH) present in the phenolic and flavonoid compounds are responsible for promoting free-radical scavenging, which helps protect the skin from various damages by slowing the effect of free radicals, which start oxidation, a process that causes damage from oxygen and can lead to cell dysfunction.. The antioxidant activities were assessed using the DPPH and ABTS assays, and the findings are presented in Fig. 6a. This figure reveals that VF has extremely low antioxidant activity. VF-Ag samples have outstanding antioxidant activity. The ABTS assay of the VF-Ag samples showed higher antioxidant activity than that of the DPPH assay. As the concentration of silver ions increased, the antioxidant activities were decreased. The antioxidant activity % (ABTS assay) was 85, 82, and 79% for VF-Ag 1, VF-Ag 3, and VF-Ag 5, respectively, compared to 9% for VF. The antioxidant activity of VF-Ag is attributed to the presence of hydroxyl groups (-OH) in polyphenolic and flavonoid compounds in the guava leaf extract which has the potential to stabilize free radicals by interaction and electron denotation on the surface of VF (Butola and Kumar 2020; Rehan et al. 2018a, 2019a). The decrease in the antioxidant activity of VF-Ag samples as the Ag⁺ ions concentration increases is due to some hydroxyl groups (-OH) participating and being consumed during the reduction of Ag⁺ to Ag⁰, confirming the role of hydroxyl groups (-OH) in the reduction process. These results indicate the role and potential of guava leaf extract to improve the antioxidant activity of VF-Ag.

Fig. 6

Antioxidant activities of VF and VF-Ag samples before washing (a), and after five washing cycles (b)

Figure 6b shows the antioxidant activities of VF and VF-Ag samples after five washing cycles. This figure shows that antioxidant activities % was slightly decreased after washing. This is mainly attributed to the gradual release of polyphenolic and flavonoid compounds from the VF-Ag surface. After five washing cycles, the antioxidant activities % (ABTS assay) was 75, 73, and 69% for VF-Ag 1, VF-Ag 3, and VF-Ag 5, respectively. The antioxidant activity results confirmed that the guava leaf extract provided VF-Ag samples with good antioxidant activity of more than 70% after washing as well as providing a continuous supply during use, which is important for the production of sustained-release materials in the medical field. As a result, VF-Ag can be used in medical applications.

In-situ Ag NP deposition leads to more Ag NP deposition and an increase in the durability of the modified fibers. This is because in situ synthesis permits Ag NPs to grow within a cellulose fibers matrix, resulting in more nanoparticle entanglement inside the matrix (Abdelhameed et al. 2018; Emam et al. 2018b).

Antimicrobial activities of VF-Ag

The antimicrobial property of fibers is considered to be a critical indicator for functional applications in the medical field. In the current study, the antimicrobial activities of VF and VF-Ag were evaluated qualitatively using the zone of inhibition method, and the antibacterial activities were evaluated quantitatively using the colony-forming unit method.

The zone of inhibition method was performed to evaluate the antimicrobial activities qualitatively by measuring the inhibition zone and evaluating microbial reproduction. Figure 4S and Table 4 shows the inhibition zone results of the antimicrobial activities of VF, and VF-Ag samples against four microorganisms.

Table 4 Inhibition zones of pathogenic microorganisms for VF and VF-Ag

The results demonstrated that VF lacks antimicrobial activities, as evidenced by the absence of an inhibitory zone for microorganisms, indicating that VF is not enough to inhibit the growth of microorganisms.

VF-Ag 1 showed moderately active activity against Staphylococcus aureus and slightly active activity against Escherichia coli, VF-Ag 1 lacks anti-yeast and antifungal efficacy due to the absence of an inhibitory zone around Candida albicans and Aspergillus niger. A possible explanation for such an observation is that the Ag NP incorporated on the VF surface has a small rate of diffusion to nutritional agar. VF-Ag 3 and VF-Ag 5 showed remarkably antibacterial, and anti-yeast activities. VF-Ag 3 showed highly active activity against Staphylococcus aureus and Escherichia coli, and slightly active activity against Candida albicans. VF-Ag 5 showed highly active activity against Staphylococcus aureus and Escherichia coli, and moderately active activity against Candida albicans. All samples showed a lack of antifungal efficacy.

From the Inhibition zone results, it can be summarized that the inhibition zone is affected by silver content. At low concentration content (VF-Ag 1), the inhibition zone tended to decrease and become negligible. At high concentrations content (VF-Ag 3 and VF-Ag 5) the inhibition zone tended to increase and be observable. The VF-Ag 3 and VF-Ag 5 samples showed excellent antibacterial activities against S. Aureus and E. coli. VF-Ag 5 sample showed very good anti-yeast and antifungal activities.

The antibacterial activity of VF and VF-Ag samples was further evaluated by percentage reduction of bacteria. Figure 5S and Table 5 shows the Colony-forming unit (CFU) results of the antibacterial activities of VF and VF-Ag samples against Staphylococcus aureus and Escherichia coli. The antibacterial activities were examined at bacterial concentrations ranging from 10^–4 to 10^–6 for 24 h at 37 °C.

Table 5 The reduction % of pathogenic microorganisms

The results show that VF did not exhibit antibacterial activities against S. Aureus and E. coli. The VF-Ag samples exhibited greater antibacterial activity against S. aureus (Gram-positive) strains than against E. coli (Gram-negative). VF-Ag 1 showed a reduction % from 90 to 100% against S. Aureus and from 80 to 92% against E. coli as the concentration of bacterium decreased from 10^–4 to 10^–6. VF-Ag 3 and VF-Ag 5 eradicated S. Aureus colonies, demonstrating the excellent bacterial activities of these samples against Gram-positive bacteria at all concentrations of bacteria. VF-Ag 3 and VF-Ag 5 eradicated E. coli colonies at 10^–6 concentration of bacterium. In the presence of VF-Ag 5, colonies of S. Aureus and E. coli were eliminated which demonstrated the excellent bacterial activity of this sample.

The durability of antibacterial activities was evaluated after five washing cycles, and the results are presented in Table 2S. The results show that the antibacterial activities of the VF-Ag samples were affected by repeated washings. The antibacterial activities % was decreased after washing. The decrease in antibacterial activities could be attributed to the release of guava leaf extract and silver nanoparticles during the washing. The release of guava leaf extract is attributed to the fact that its compounds are not chemically bound to the surface of viscose fibers, but they adsorb physically on the surface. The regulated release mechanism of Ag NPs' antibacterial activity necessitates controlled leaching of Ag⁺ and Ag NPs from the VF-Ag surface in the presence of H₂O. The increase in silver content on the surface viscose fiber resulted in increased durability of the antibacterial activity after washing. Although the antibacterial activities decreased after washing, VF-Ag 3 and VF-Ag 5 showed very good antibacterial activities. This very good antibacterial activity could be attributed to the synergistic effect between guava leaf extract and silver nanoparticles on the surface of viscose fibers.

The Silver nanoparticles achieve antimicrobial activity in two ways. (i) Ag NPs can release Ag⁺, which can adhere to or penetrate microbial cells, inhibiting microbial growth by causing DNA damage, creating an electrostatic attraction with the negatively charged microorganism's cell membrane, or reacting with the –SH of cell proteins (Salleh et al. 2020; Yin et al. 2020). (ii) Ag NPs can generate reactive oxygen species (ROS) as O₂^·−, HO^·, and H₂O₂. As a result, ROS could assault a microbial cell wall, causing damage to the cell membranes, increased cell permeability, and finally leaking intracellular contents through cell disturbances (Dasgupta and Ramalingam 2016; Xu et al. 2012).

Silver release and cytotoxicity evaluation of VF-Ag

The persistence of antimicrobial activity in VF-Ag samples used in medical applications over time and/or after immersion in an aqueous medium is an essential characteristic. A stable and sustained release of Ag⁺ ions at a sufficient concentration is critical for obtaining an efficient and "permanent" action; a too-slow or too-fast release of Ag⁺ ions would be inappropriate for principal applications (Pinto et al. 2009). Although metallic silver is relatively nonreactive, Ag⁺ ions are released in the aqueous medium, and antimicrobial action is dependent on the intracellular accumulation of low concentrations of Ag⁺ ions. The silver release from VF-Ag samples was evaluated for 72 h, Fig. 7a shows the amount of silver released from the VF-Ag samples as a function of immersion time.

Fig. 7

Silver release from VF and VF-Ag samples (a), and Cell viability (%) of VF and VF-Ag samples against NHEK (b) and NHDF (c)

This figure demonstrated that the Ag⁺ ions are released from VF-Ag samples into the solution through diffusion. Silver release % from VF-Ag was consistent and consistent, with no obvious first burst release. Silver release % observed from 6 to 72 h. The release of silver from VF-Ag samples increased with the release time and silver content. After 42 h, the release is nearly linear. VF-Ag 1 released the lowest amount of Ag + ions as expected in the explanation of the results of antimicrobial activities. The silver release results supported the long-term potential of VF-Ag as an antimicrobial substrate by allowing the surface to release several Ag⁺ ions to diffuse into the media in a controlled way and inhibit microbe growth.

The release of silver as particles or in ionic form from VF-Ag samples could damage human cells, limiting their application (Pal et al. 2017). The VF-Ag samples as a potential substrate in medical applications would be in close contact with the skin, so the possible cytotoxicity of VF-Ag samples must be evaluated to investigate the nature of their possible impact on the skin, Hence, the cytotoxicity of VF-Ag samples against normal human epidermal keratinocytes (NHEK) and normal human dermal fibroblasts (NHDF) was investigated using MTT assay (Cell viability %). Cell viability % was used to examine human cell attachment, and the results shown in Figs. 7b and c show the cell viability % of NHEK and NHDF respectively when attached to the surface of VF and VF-Ag samples. Cell viability % explains the cellular response to a VF-Ag sample. Also, they give information on cell death and survival,

Figures show that the VF does not produce toxicity in the two human cells that were examined. VF-Ag 1 showed no substantial change in the viable cells with two human cells, indicating low cytotoxicity. The cell viability % was decreased when the two human cells were attached to VF-Ag 3 and VF-Ag 5 for 48 and 72 h. The cell viability % differs with the increase in Ag ions concentration. The results of cytotoxicity for the two tested cells showed that the VF-Ag exhibited a marginally cytotoxic effect (slight cytotoxic). The average cell viability % of the two tested cells was over 80%, indicating that the VF-Ag samples are low in toxicity and have good compatibility. Based on the literature, materials are regarded as safe when the vitality of the cells is over 80% (Krkobabić et al. 2022; Krkobabić et al. 2023). This result confirms the nontoxicity of the VF-Ag to human cells, ensuring their potential use in medical applications.

Functional properties of VF-guava leaf extract and dyed fibers

To investigate the role of guava leaf extract in contributing to the multifunctional properties of VF-Ag, the VF surface was modified with 10 mL of guava leaf extract without silver nitrate solution (VF-guava leaf extract). The functional properties, including UV protection, antioxidant activity, and antibacterial activity, of VF-guava leaf extract were evaluated, and the results are shown in Table 6.

Table 6 Functional properties of VF-guava leaf extract and dyed fibers

The VF-guava leaf extract showed high UPF value which indicates the guava leaf extract played the role on the UV protection for VF-Ag samples bedside the silver nanoparticles (Zhou et al. 2017). The reason for the high UPF value of the VF-guava leaf extract is due to the flavonoids and phenolic acid compounds present in guava leaf extract which act as UV absorbers.

The VF-guava leaf extract showed high antioxidant activity. The antioxidant activity of VF-VF-guava leaf extract chiefly owes to the redox property of the flavonoids and phenolic acid compounds present in guava leaf extract which plays an imperative role in captivating and neutralizing free radicals (Brewer 2011). The antioxidant activity of VF-Ag 5 decrease, which is attributed to decreased concentration of free guava leaf extract biomolecules on the surface of fibers due to their consumption in reduction of Ag⁺ (Čuk et al. 2021). This result shows the main role of flavonoids and phenolic acid compounds present in guava leaf extract and their contribution to the radical scavenging activity to impart antioxidant activities for the VF-Ag.

The VF-guava leaf extract showed good antibacterial activity. The antibacterial activity of the VF-guava leaf extract demonstrated higher efficiency against Gram-positive bacterial strains (S. aureus) than Gram-negative bacterial strains (E. coli). The difference could be attributed to the multilayered construction of gram-negative bacterial cell walls against the single-layered gram-positive cell wall. Gram-positive bacteria have a mesh-like peptidoglycan coating that allows extract to permeate more easily (Biswas et al. 2013). Many studies have been conducted on the mechanism of antibacterial activities of plant extracts (Biswas et al. 2013; Elchaghaby et al. 2022; Rehan et al. 2018a, 2019a, 2022). This result shows the main role of guava leaf extract and its contribution to the enhancement of the antibacterial efficacy of the VF-Ag.

All the results above confirmed the role of guava leaf extract in reducing and stabilizing Ag NPs on the surface of viscose fibers, as well as additively contributing to the multifunctional properties of viscose fibers.

The in situ biosynthesis and deposit of Ag NPs on the surface of viscose fibers using guava leaf extract could offer preferable advantages, as follows: (i) It avoids nanoparticle aggregation on the surface of the fibers. (ii) The guava leaf extract could be used as a reducing agent instead of traditional harmful chemical reagents, as well as as a stabilizing agent. (iii) The guava leaf extract deposited on the nanoparticles and viscose fibers could enhance, simultaneously, desirable and durable UV protection, antioxidant activities, and antibacterial activity.

The influence of the dyeing process on the multifunctional properties of VF and VF-Ag 5 was examined, and the results are shown in the Table 6. In this part, two samples were selected including dyed VF 5%, and dyed VF-Ag 5 (5%) and compared with VF, VF-Ag 5. Table displays that, the dyed VF showed a moderate reduction in the different microbial pathogens. The antibacterial activity of dyed VF may be attributed to the dye molecules: The dyeing of VF-Ag 5 samples with reactive dye showed a positive effect on the multi-functional properties of treated fibers. These results confirm that the dyeing process does not affect the multifunctional properties of VF-Ag.

The silver content of dyed VF-Ag 5 (5%) was decreased to 1489 mg/Kg compared to 1543 mg/Kg for VF-Ag 5. This result can be attributed to the release of silver throughout the dying process in the dye bath.

Sensor properties of VF-Ag

Due to their ease of transmission in the food chain, heavy metal ions pose a severe hazard to our society (Chatterjee et al. 2022; Tchounwou et al. 2012). One of the most dangerous and widely used heavy metals is mercury. Mercury can be used in various industries and waste products from these industries can pollute water and soil (Campbell et al. 2003). Mercury exists in the environment in three forms: elemental (Hg°), inorganic compounds (Hg⁺ and Hg²⁺), and organic compounds (mainly CH₃Hg⁺ and C₂H₅Hg⁺) (Faghiri and Ghorbani 2019). Even at extremely low doses, (Hg²⁺) can harm the brain, heart, kidney, stomach, and intestines due to its significant cellular toxicity and carcinogenicity. Hence, it is crucial to sense Hg²⁺ ions from various sources using a method that is both inexpensive and maintains a high level of selectivity and sensitivity. Ag NPs have received a lot of interest in heavy metal ion sensors due to their long-term stability, which results in less material usage. In particular, Ag NPs have received a lot of interest in the creation of mercury sensors, particularly because of their high sensitivity to changes in Hg²⁺ micro-level concentration (Budlayan et al. 2022; Kaewnok et al. 2022; Samuel and Rao 2023; Singaravelu et al. 2023). In the current study, an easy, novel, and low-cost viscose fibers-based silver nanoparticle sensor (VF-Ag) was created for the naked-eye colorimetric detection of Hg²⁺ ions.

The naked-eye colorimetric sensing ability of the VF-Ag 5 for selective and sensitive detection of metal ions was evaluated for common environmentally relevant ions, including (Co²⁺, Pb²⁺, Ni²⁺, Fe²⁺, Hg²⁺, Cd²⁺, Cu²⁺, and Zn²⁺). Figure 8 shows photos before (a) and after the addition of VF-Ag 5 to eight metal ions. The photos were taken after the addition of VF-Ag to a metal ion solution, after 30 s (b) and 5 min (c) of the interaction of heavy metals with VF-Ag.

Fig. 8

Naked-eye colorimetric sensing ability of the VF-Ag 5 to different metal ions, after the addition of VF-Ag to metal ions solution (a), after 30 seconds (b), and after 5 min (c) of the interaction of heavy metals with VF-Ag 5

The results showed that VF-Ag did not exhibit naked-eye colorimetric sensing ability toward other metals after 30 s or 5 min, except Hg²⁺. When VF-Ag interacted with the Hg²⁺⁻containing solution, its color changed immediately from dark brown to white, as shown in Fig. 8b. It is therefore concluded that VF-Ag is highly selective and specific for sensing Hg²⁺. It is therefore concluded that VF-Ag 5 can be utilized as a colorimetric sensor for Hg²⁺ detection with the naked eye.

To find out the detection limit of the sensor's ability of VF-Ag 5 to detect Hg²⁺, the naked-eye colorimetric response times of VF-Ag 5 interacted with various concentrations of Hg²⁺ were noted. The results showed that with concentrations of Hg²⁺ ranging from 100 to 200 ppm, the color of VF-Ag 5 changed in 30 s. Similarly, from 50 to 100 ppm of Hg²⁺ concentration, the change in color of VF-Ag 5 took 1 min. At the lower concentration of 1 to 50 ppm Hg²⁺, the change in color of VF-Ag 5 took 2 min. A concentration below 1 ppm could be detected, but it would take time (from 4 to 8 min). The findings revealed that an increase in the concentration of Hg²⁺ ions caused a rapid change in the color of VF-Ag from dark brown to white.

Two feasible mechanisms for VF-Ag sensing Hg²⁺ ions have been suggested. The electrochemical difference between Hg²⁺ and Ag⁰ allows for the selective detection of Hg 2 + ions. Hg²⁺ ions can oxidize Ag⁰ to Ag⁺ ions and then become reduced to Hg⁰ because they have a larger reduction potential of + 0.85 V than Ag⁰, which has a reduction potential of + 0.8 V (Jeevika and Shankaran 2022). The second mechanism relies on the aggregation approach of Ag NPs. This approach concludes that Hg²⁺ coordinates with VF-Ag, changing the particles' state from monodispersed to aggregate. When Hg²⁺ ions come from the solution to come into contact with the surface of VF-Ag, the monodispersed state of Ag NPs tends to aggregate via the formation of coordinate bonds between Hg²⁺ ions and functional groups present in the viscose fibers, such as OH, NH₂, and COOH, and surface-stabilizing molecules of guava leaf extract on the surface of Ag NPs, which leads to the color change of VF-Ag (Lu 2022).

Conclusion

The primary purpose of this research is to investigate the application potential of guava leaf extract and demonstrate its role in the decoration of viscose fibers (VF) with silver nanoparticles (Ag) to obtain viscose fibers@Ag NPs (VF-Ag) that can be used in versatile applications. VF was decorated with in situ biosynthesis Ag through a green route by using guava leaf extract as a reducing and capping agent. The TEM image revealed that the silver nanoparticles were spherical or quasi-spherical in shape. SEM, EDX, FTIR, and XPS proved the simultaneous biosynthesis and incorporation of silver nanoparticles onto viscose fibers.

The findings indicated that Ag NPs endowed viscose fibers with beautiful yellow to yellowish/brownish colors. A greenish color was obtained after dyeing VF-Ag samples with CI-reactive blue-19, compared to a blue color for VF after dyeing with CI-reactive blue-19. The VF-Ag as well as the dyed VF-Ag showed high color strength compared to VF and dyed VF and excellent all-round fastness properties.

VF-Ag samples demonstrated excellent UV protection activities, excellent antibacterial activities, and very good antifungal activities, as well as extremely good antioxidant activities, indicating their potential use in the creation of healthcare and hygienic textiles. VF-Ag 5 exhibited a high UPF value (355) in comparison to VF (103). VF-Ag 1 exhibited a high antioxidant activity (85%) in comparison to VF (8%). The VF-Ag samples showed a slight decrease in UPF values and antioxidant activities after washing cycles, confirming the durability of the samples.

VF-Ag 1 showed moderate antibacterial activity and lacked anti-yeast and antifungal efficacy. VF-Ag 3 and VF-Ag 5 showed remarkably antibacterial and anti-yeast activities. The VF-Ag samples showed a stable and sustained release of Ag⁺ ions with low cytotoxicity to human cells. These results confirm that VF-Ag samples ensure their potential use in medical applications. VF-Ag 5 provides a low-cost, rapid, portable, and dependable sensor for on-site detection and monitoring of Hg²⁺ levels in the water, indicating its potential for usage in analytical applications. The detection of Hg²⁺ is based on the color change of VF-Ag from yellow/brown to colorless.