Novel Eco-Friendly Chitosan-Loaded CuO-SiO₂ Coating on Cotton Fabric for Durable, Multifunctional, and Mechanical Properties

Abstract

Developing durable multifunctional clothing with enhanced mechanical and comfort properties utilizing eco-friendly, cost-effective hybrid nano finishes is highly challenging. The reason behind the nondurable functionality is the lack of bonding ability of nanoparticles (NPs) with cotton fabric, and this additional coating has a great impact on the mechanical, thermo-physiological, and sensorial comfort properties of cotton fabric. Focusing on these issues, this paper attempts to develop biogenic chitosan-loaded CuO-SiO₂ hybrid nano finishes with three distinct formulations, namely Chi-CuO-SiO_2(5g/L), Chi-CuO-SiO_2(10g/L), and Chi-CuO-SiO_2(20g/L) hybrid nanofluids, to incorporate on cotton fabric by pad-dry-cure method. These hybrid nanofluids from biogenic Chi-CuO and rice husk SiO₂ NPs have been newly introduced for textile application. The NPs CuO and SiO₂ are synthesized from lemon peel zest extract and rice husk, respectively. Characterization of CuO NPs by Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDX), and X-ray diffractometers (XRD) evidences that spherical-shaped, amorphous, and 60–80 nm sized NPs are synthesized. The hydrodynamic performance of hybrid nanofluids measured by Zeta Sizer shows that the chitosan-loaded CuO-SiO_2(5g/L) hybrid nanofluid is the most stable among the three, and the value is +29.4 mV. The presence of CuO NPs, SiO₂ NPs, and chitosan on cotton fabric was confirmed by FTIR, FESEM, and EDX spectra of the hybrid nanofluid-deposited fabric. The cotton fabric coated with chitosan-loaded CuO-SiO₂ hybrid nanofluids exhibits better durable antimicrobial efficacy, UV-protective properties, and thermo-physiological comfort properties than that of the uncoated fabric. More specifically, CuO-SiO_2(20g/L)-coated fabric demonstrates approximately 99.99% bacterial efficacy against both gram-positive and gram-negative bacteria even after 15 washing cycles, and excellent UV-protective properties. In addition, CuO-SiO_2(5g/L)-coated fabric displays around 75% enhancement of overall moisture management properties and 1.22% and 0.53% enhancement of tensile strength in warp and weft directions with excellent elongation compared to the pristine one. Moreover, assessment of the mechanical sensorial comfort properties of this fabric depicts that it is smoother, and has better thermal conductivity than that of the control one. In addition, CuO-SiO_2(5g/L) hybrid nanofluid-treated cotton fabric exhibited cell viability above 95%, which confirms its non-cytotoxicity. The outcomes of this study suggest that chitosan-loaded CuO-SiO_2(5g/L) hybrid nanofluid-treated cotton fabric can be considered as optimum and employed as biomedical textiles with better mechanical and comfort properties.

1. Introduction

Cotton fiber is the most favored material for apparel manufacturing because of its versatile amenities, such as comfort, flexibility, biodegradability, nontoxicity, and hydrophilicity [1,2,3]. The porous and hydrophilic nature of cotton fiber yields to the growth of microorganisms that create unpleasant odor, allergic reactions, and hygiene problems [4,5], which also lead to a reduction of the mechanical strength of the fabric [6]. Therefore, demand for antibacterial finishing is a vital issue among consumers, especially in biomedical applications like masks, surgical gowns, bandages, hospital bed sheets, curtains, drapes, and mattress covers, etc. [7,8]. Extensive research regarding the antibacterial properties of metal nanoparticle-treated fabric is currently being conducted. Among metal NPs, bio-based silver (Ag), gold (Au), and copper/copper oxide (Cu/CuO) are extremely renowned antibacterial agents because of their rapid, cheap, eco-friendly, and sustainable approaches [9,10,11]. The latter attained significant attention because of the low cost of precursors and their distinctive properties like UV-protective properties and electrical conductivity, along with antibacterial properties [1]. Moges et al. (2024) evidenced the UV-protective properties of green-synthesized CuO NP-treated fabric, which is another important requirement among consumers at this time [12]. Green synthesis of copper oxide NPs involves various sources like plants (leaves, roots, flowers, and fruits) and microbes (bacteria, algae, and fungi) [13]. Among them, agro-waste lemon peel, a byproduct of the citrus industry, earned significant attention because of its abundance of bioactive compounds [14]. Very little research regarding bio-based synthesis of CuO NPs utilizing lemon peel extract has been reported. The majority of studies exploited copper (II) nitrate trihydrate, copper (II) chloride dihydrate, copper (II) chloride, and copper sulphate pentahydrate as precursors to be reduced and stabilized by lemon peel extract [14,15,16,17,18]. None of the researchers, however, apply these synthesized CuO NPs to cotton fabric to assess their effect on it due to lack of a binding agent that improves wash durability. Focusing on wash durability, some of the researchers formulated chitosan-loaded copper oxide NPs on cotton fabric and assessed their effect on it. Gouda and Hebeish (2010) prepared chitosan-loaded CuO NPs from chitosan and copper sulphate as precursors in a chemical synthesis method and attained 99% and 96% reductions against S. aureus and E. coli bacteria with better wash durability [19]. Later, Dhineshbabu and Rajendram (2015) chemically synthesized a CuO/chitosan composite solution to coat cotton fabric by the pad-dry method and obtained excellent antibacterial properties with a slight reduction in wash durability [20]. More recently, Saleh et al. (2021) devised Cu/CS nano composites from CS and CuSO₄·5H₂Oprecursors and applied them on cotton by gamma radiation and found better antibacterial activity against gram-positive bacteria [21]. Xiao et al. (2022) assembled cotton–CS–Cu-treated fabric by soaking cotton in chitosan solution and achieved excellent bacterial reduction against both bacteria with excellent wash durability [22]. In all cases, the chemical synthesis method was adopted, and CuSO₄ was used as a precursor, which has the possibility of making the fabric cytotoxic for human cells [23]. Also, the aforementioned research only focuses on durable antibacterial properties in expensive chemical synthesis methods, avoiding UV-protective ability, mechanical, and comfort properties, which are also of great concern among consumers today. Besides, cytotoxicity analysis is an important aspect for the treated fabric when it is utilized for biomedical clothing purposes [21].

Based on the above discussion, it can be pointed out that there is a scope for producing biogenic synthesis of hybrid nanofluids. Subsequently, the present study provides an innovative method for bio-synthesizing CuO NPs and SiO₂ NPs utilizing agro-waste such as lemon peel zest and rice husk, respectively, in a simple, rapid, low-cost, and eco-friendly way. From these, three distinct formulations of hybrid nanofluids, namely Chi-CuO-SiO_2(5g/L), Chi-CuO-SiO_2(10g/L), and Chi-CuO-SiO_2(20g/L), are green-synthesized and applied on cotton fabric by the pad-dry method. Then, investigations were conducted among untreated and treated specimens in terms of durable antibacterial properties, UV protection ability, mechanical properties, thermo-physiological and sensorial wear comfort properties to meet the recent growing demand of consumers.

The first novelty of this study is to prepare CuO NPs in a green route employing agro-waste, lemon peel zest, in a non-expensive and eco-friendly approach, where the utilization of copper acetate also assists in avoiding toxicity on cotton fabric. Another novelty is the preparation of Chi-CuO-SiO₂ hybrid nanofluids from bio-based Chi-CuO and rice husk SiO₂ NPs, which have not yet been synthesized. The core objectives of this study are to incorporate these novel synthesized hybrids on cotton fabric for the purpose of acquiring durable, multifunctional, mechanically strong, thermo-physiological, and sensorial comfort properties for cotton fabric for biomedical and protective clothing.

2. Materials and Methods

2.1. Materials

Silver Composite Mills Ltd., Gazipur, Bangladesh, supplied 100% pretreated cotton woven fabric with 164 g/m² and 142 ends per inch and 74 picks per inch of 30 Ne count. Lemon and rice husk were purchased from the local market of Dhaka, Bangladesh. Acetic acid, sodium hydroxide, and chitosan were purchased from Sigma-Aldrich, Darmstadt, Germany, and copper acetate monohydrate was collected from Giant Chem Solutions, Miami, FL, USA.

2.2. Methods

2.2.1. Bio-Synthesis of CuO NPs

Figure 1 displays the experimental route to biogenic synthesis of CuO NPs. Firstly, the extraction of lemon peel zest was carried out with an M:L ratio of 1:10 utilizing distilled water heated at 80 °C for 1 h. Then, it was filtered with Whatman filter paper No. 1 to obtain a pale, bright yellow-colored extraction. In a 5 mM copper acetate solution, the filtered extract was added dropwise slowly with an M:L ratio of 5:95 with continuous magnetic stirring at room temperature for 2 h. Subsequently, a deep green-colored colloidal solution was obtained from a light blue-colored copper acetate solution. The colloidal solution was centrifuged and washed with distilled water three times, followed by ethanol three times. The final wash was also performed using distilled water, and the sample was dried in an oven dryer at 80 °C until completely dry. After mortaring, powder of CuO NPs was achieved and stored for further testing.

2.2.2. Bio-Synthesis of SiO₂ NPs

SiO₂ NPs were synthesized from rice husk according to our previous article [24]. In short, acid-pretreated rice husk was carbonized and then calcined at 700 °C for 3 h by heating at a rate of 5 °C/min in a muffle furnace. In a 2.5 M NaOH solution of 80 mL, rice husk ash was added and refluxed at 80 °C for 1 h to achieve a clear solution of sodium silicate, which was filtered with Whatman Grade No. 41. This clear solution was titrated with 2 M acetic acid solution to precipitate nano silica. Further washing, filtering, drying, and mortaring of this precipitate would produce powder of nano silica.

2.2.3. Assembling of Chitosan-Loaded CuO-SiO₂ Hybrid Nanofluids

In a prepared CuO nano solution, 0.2% chitosan solution was added dropwise and stirred for 1.5 h. In this solution, different concentrations of SiO₂ NPs (5 g/L, 10 g/L, and 20 g/L) were added with stirring for 2 h to prepare three distinct formulations of chitosan-loaded CuO-SiO₂ hybrid nanofluids. Then, the samples were immersed in these prepared hybrid nanofluids at room temperature and kept for 10 min, followed by passing through a laboratory padding mangle with a two-dip and two-nip process to achieve 75% pick up. The nanofluid-deposited specimens were air dried and cured at 130 °C for 2 min.

2.3. Characterization

Characteristic peaks of bio-reduced CuO NPs were investigated by a UV–visible spectrophotometer (UV-1800, Shimadzu Corporation, Kyoto, Japan) in the range of 400–700 nm. Chemical bonding of CuO NPs and the structure of NPs with the fabric surface were characterized by Fourier Transform Infrared spectroscopy (FTIR-8400, Shimadzu Corporation, Kyoto, Japan) coupled with a variable-angle attenuated total reflection accessory (ATR) at a range of 4000–400 cm⁻¹, respectively. Field Emission Scanning Electron Microscopy (FESEM) by a ZEISS Sigma 300 VP (Carl Zeiss AG, Oberkochen, Germany) with Energy Dispersive X-ray Spectroscopy (EDX), was conducted to explore the surface morphology, particle size, and elemental composition of CuO NPs, respectively. It also examines the surface morphology and distribution of NPs, and the chemical composition of the pristine and hybrid nanofluid-coated fabric specimens. X-ray diffraction (XRD) analysis was carried out using X-ray diffractometers (Malvern Panalytical Empyrean, Almelo, Netherlands). The zeta potential stability of chitosan-loaded CuO-SiO₂ hybrid nanofluids was assessed using a Malvern Zeta Sizer (Malvern Instruments, Malvern, England).

The standard test method ASTM E 2149-01 (2001) [25] was conducted to assess the antibacterial activity of fabric specimens against gram-positive (S. aureus) and gram-negative (E. coli) bacteria under dynamic contact time. Firstly, the bacterial strain was grown in tryptic soy broth (TSA) and then diluted to achieve 1.5–3 × 10³ colony-forming units (CFUs) per mL⁻¹ bacteria. Later, a small piece of sterile cotton specimen was placed inside the flask, which had 50 mL of buffer solution with 1.5–3 × 10³ CFU mL⁻¹ bacteria. These flasks were incubated at 37 °C and shaken continuously for 1 h, followed by 24 h of contact time. After incubation, these solutions were diluted and plated on a petri dish with TSA. All the petri dishes were again incubated at 37 °C for 24 h. Finally, the CFUs of control and coated specimens were calculated to determine the bacterial reduction percentage (%), which is expressed by the following:

$$\mathrm{Reduction} (\%) = {\displaystyle \frac{\mathrm{F}\mathrm{o}-\mathrm{F}\mathrm{t}}{\mathrm{F}\mathrm{o}}}\times 100$$

(1)

where F_o and F_t are the number of bacterial colonies viable from control and coated specimens, respectively, after 1 and 24 h of contact time [26,27]. Standard test method AATCC 61-2013 was carried out to investigate the wash durability of antibacterial specimens after five and 15 washes [28].

The UPF factor was determined by an in vitro method. In this method, transmittance% of control and treated specimens were recorded utilizing UV-1800 (Shimadzu Corporation, Kyoto, Japan) in the range of 290–400 nm. Each specimen was scanned three times, and the mean values were calculated. By putting these values in the following Equation (2), the ultraviolet protection factor was calculated. The UV protection factor (UPF) is calculated by using the following equation:

$$UPF={\displaystyle \frac{{\sum }_{\lambda =290}^{400}{E}_{\lambda }{\times S}_{\lambda }\times \Delta \lambda }{{\sum }_{\lambda =290}^{400}{E}_{\lambda }{\times S}_{\lambda }\times T_{\lambda }\times \Delta \lambda }}$$

(2)

where E_λ, S_λ, T_λ, ∆λ, and λ indicate relative erythermal spectral effectiveness, solar spectral irradiance in W·m⁻²nm⁻¹, spectral transmittance of the sample, wavelength in nm, and wavelength in nm, respectively. By assessing the value of UPF rating, the samples were classified according to Australian/New Zealand standard AS/NZS 4399-2017 [29,30].

The strip test method based on a constant rate of extension was employed to measure tensile strength and elongation at break in both warp and weft directions using the Titan Universal Strength tester from James Heal, England, according to the ISO 13934-1:2013 standard test method [31]. The tear strength of specimens was assessed by the Elma tear of James Heal, England, by adopting the standard ISO13937-1 test method [32].

The thermo-physiological comfort properties of specimens were assessed by a Moisture Management Tester (MMT) from SDL Atlas, South Carolina, USA, by the AATCC-195 standard test method [33]. A specimen (8 cm × 8 cm) was employed to place instrumentally one drop of 9 g/L standard saline solution for 20 s. Then, several indicators such as the wetting time, absorption rate, spreading speed, and one-way transport capability were monitored for a duration of 120 s. At the same time, overall moisture management capability (OMMC) was also determined by using the following formula:

OMMC = 0.25 BAR + 0.5 OWTC + 0.25 SSb

(3)

where BAR points out the moisture absorption rate on the bottom side, OWTC points out the one-way transport capability, and SSb points out the moisture spreading speed at the bottom side. These indicators were measured and graded as per a five-grade system of the AATCC test method 195 [34]. The pristine and hybrid nanofluid-deposited specimens were conditioned in a conditioning chamber under standard atmosphere (at 20 ± 5 °C and 65 ± 2% relative humidity for 12 h) before every test.

Skin sensorial comfort properties were evaluated by a Fabric Touch Tester (FTT) from SDL Atlas, South Carolina, USA. This device simultaneously measured 13 fabric indices, such as bending, heat, surface roughness, and compression, during testing. From these values, primary sensory indices of smoothness, softness, and warmness were calculated utilizing FTT QC Evaluation Software Version 2.0.

Before testing, each specimen was cut L-shaped (30 cm × 30 cm) to the shape of a template. Six measurements were tested for each specimen, with three inner surfaces and three outer surfaces. Before starting the test, the temperature difference between the upper and lower plate was created instrumentally by 10 °C to fabricate a temperature difference between the skin and the textiles. Firstly, the sample was placed on the lower plate, followed by continuous movement of the upper heated plate until it reached the lowest position, and then returned to the initial position. During this movement, 13 fabric indices, namely, bending, compression, thermal, and surface properties (friction and roughness), were measured [35]. These 13 indices are listed in

Table 1. Thirteen FTT fabric indices with units and interpretation [35].

Fabric Indices	Index	Description	Unit Given in FTT Software	Interpretations
Bending	BAR	Bending Average Rigidity	gf mm rad−1	Force needed to bend per radian
	BW	Bending Work	gf mm rad	Work needed to bend
Surface friction	SFC	Surface Friction Coefficient	-	Friction coefficient on the surface with a ribbed plate
Surface roughness	SRA	Surface Roughness Amplitude	µm	Roughness irregular wave amplitude
	SRW	Surface Roughness Wavelength	mm	Roughness irregular wave wavelength
Compression	CW	Compression Work	gf mm	Work is needed to compress the specimen
	CRR	Compression Recovery Rate	-	Percentage of thickness changes after compression
	CAR	Compression Average Rigidity	gf mm−3	Forces needed to compress per mm
	RAR	Recovery Average Rigidity	gf mm−3	Forces reflected when recovery per mm
	T	Thickness	mm	Thickness of the materials
Thermal conductivity	TCC	Thermal Conductivity under Compression	10−3 W m−1 °C−1	Energy per degree per m per second transmitted under specimen compression
	TCR	Thermal Conductivity under Recovery	10−3 W m−1 °C−1	Energy per degree per m per second transmitted under specimen recovery
	Qmax	Thermal Maximum Flux	W mm−2	Maximum energy is transmitted during compression

.

Cytotoxicity of the treated specimen that contains 5 g/L silica NPs was evaluated by assessment of the viability of the Vero cell line by an in vitro assay method. In this method, a kidney epithelial cell line extracted from an African green monkey was maintained in DMEM (Dulbecco’s Modified Eagle’s medium) containing 1% penicillin–streptomycin (1:1), 0.2% gentamycin, and 10% fetal bovine serum (FBS). Cells (1.5 × 10⁴ per 100 µL) were seeded onto a 48-well plate and incubated at 37 °C with 5% CO₂. The next day, a 25 µL sample (autoclaved) was added to each well. Cell viability was assessed under an inverted light microscope after 48 h of incubation by using the following formula:

$$\mathrm{Cell} \mathrm{Survival} (\%) = {\displaystyle \frac{\mathrm{V}\mathrm{i}\mathrm{a}\mathrm{b}\mathrm{l}\mathrm{e} \mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}\mathrm{s} \mathrm{i}\mathrm{n} \mathrm{t}\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{d} \mathrm{w}\mathrm{e}\mathrm{l}\mathrm{l}}{\mathrm{V}\mathrm{i}\mathrm{a}\mathrm{b}\mathrm{l}\mathrm{e} \mathrm{c}\mathrm{e}\mathrm{l}\mathrm{l}\mathrm{s} \mathrm{i}\mathrm{n} \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{l} \mathrm{w}\mathrm{e}\mathrm{l}\mathrm{l}}}\times 100$$

(4)

Vero cell viability above 95% indicates non-cytotoxicity [36].

3. Results and Discussion

3.1. Characterization of CuO NPs

The UV–Visible spectra in Figure 2a show a strong surface plasmon resonance at a wavelength of 335 nm, which suggests the formation of CuO NPs. This outcome strongly agrees with the previous work regarding green synthesis of CuO NPs, where a characteristic peak in the range of 250–395 nm was obtained [37,38,39,40]. The FTIR spectra of CuO NPs are presented in Figure 2b, where peaks in the range of wave number 3200–3700 cm⁻¹ are ensured for O-H stretching of phenolic compounds. Absorption peaks at wave numbers 1632 cm⁻¹ and 1538 cm⁻¹ are associated with the stretching vibration of the carbonyl group (C=O) stretching band [20]. The spectrum around 1120 cm⁻¹ and 2349 cm⁻¹ is attributed to C-O and -C-O-C- stretching, respectively, due to alcohol and esters [17]. It can be noted that the presence of these peaks is due to the existence of biomolecules from green synthesis. In general, the characteristic peaks in the range of 400–650 cm⁻¹ represent the Cu-O stretching. Accordingly, peaks at 579 cm⁻¹ and 546 cm⁻¹ confirm the stretching vibration of the Cu-O bond in CuO NPs. This observation agrees with Keabadile et al. (2020) [41]. Moreover, the FESEM image of CuO NPs in Figure 2c, illustrates a spherical shape with variable sizes and slight aggregations. The majority of the particles lie in a size range between 60 and 80 nm. This observation is aligned with the previous literature [42]. EDX analysis shown in Figure 2d exhibits the elemental composition of bio-synthesized CuO NPs. This spectrum specifies the characteristic peaks of bio-synthesized Cu, along with peaks of C and O. The dominance of (copper) Cu and oxygen (O) confirms the synthesis of CuO NPs with a purity of around 70%.

3.2. XRD of SiO₂ and CuO NPs

In our previous study, characterization of silica NPs was carried out in detail [24], except XRD of silica NPs, which is illustrated in this study. The X-ray diffraction pattern of SiO₂ nano powder derived from rice husk is shown in Figure 3a. This pattern affirms a broadening peak in the range of 2θ = 18° to 35° [43] with characteristic peak intensities at 2θ = 22.29°, confirming the amorphous silica NPs [44,45]. These findings are evidenced by comparing and matching the obtained data with the ICSD card no. 01-081-0069. This XRD pattern of rice husk SiO₂ NPs matches very well with Wang et al. (2011), Azat et al. (2019) and Yuan et al. (2024) [43,44,46].

The XRD pattern of bio-synthesized CuO NPs is presented in Figure 3b. The broad spectrum with the absence of a sharp peak is a hallmark of amorphous CuO NPs. A strong peak at 2θ values, 38.16, shows Miller indices of 111, which confirms the formation of CuO NPs according to the International Centre for Diffraction Data [47]. These findings are validated by comparing and matching the obtained data with the ICSD card no. 00-044-0706. The obtained pattern resembles the pattern obtained by Anchani et al. (2024) and Millavithanachchi et al. (2025) [48,49].

3.3. Characterization of Chitosan-Loaded CuO-SiO₂ Hybrid Nanofluids

The stability of hybrid nanofluids is pivotal, as it significantly affects the further characteristics of the treated fabric. Zeta potential refers to the electrostatic repulsion and electrical potential of NPs in the fluids. A zeta potential value at around ±25 mV and higher is regarded as stable [50]. The graphical depiction of the zeta potential distribution of Chi-CuO-SiO_2(5g/L), Chi-CuO-SiO_2(10g/L), and Chi-CuO-SiO_2(20g/L) hybrid nanofluids is illustrated in Figure 4a–c. Among the prepared bio-based hybrid nanofluids, the highest zeta potential distribution of Chi-CuO-SiO_2(5g/L) is +29.4 mV, as depicted in Figure 4a, indicating good colloidal stability. This outcome aligns with that of Mehta et al. (2021) [51]. They acquired a zeta potential stability of green-synthesized chitosan-loaded CuO NPs of +23.6 mV. In congruence with this literature, it can be conclusively observed that the addition of SiO₂ NPs in Chi-CuO increases the stability of the hybrid nanofluid in this context. Besides, the increment of SiO₂ concentration from 5 to 20 g/L leads to a lowering of the dispersion stability of fluids. In addition, good colloidal stability is attributed to the chitosan polymer that repels the nuclei of NPs in the solution to prevent aggregation. Positive surface is due to the positive charge of the chitosan amino group at a lower p^H level and also from CuO NPs [52]. Although SiO₂ NPs exhibited a negative surface charge [53], the combination of these three finally provides a higher positive surface charge.

3.4. Characterization of Hybrid Nanofluid-Treated Fabric

3.4.1. FTIR Analysis

Figure 5 exposes the FTIR-ATR spectrum of various Chi-CuO-SiO₂-deposited specimens. For pristine fabric, the characteristic peaks of 3327 cm⁻¹ and 2890 cm⁻¹ are assigned to O-H and -C-H stretching, respectively. For all specimens, bending near 1640 cm⁻¹ corresponds to water molecules (H-O-H). The asymmetric stretching vibration glucose ring of cellulose is observed at 1052 cm⁻¹. Bands at 1025 cm⁻¹ and 1160 cm⁻¹ are attributed to the bending vibrations of C-O and C-O-C, respectively [20]. These are manifested by observing the graph; the mentioned peaks are very similar, with a slight shift of the peak and a reduction of peak intensities for all specimens.

The signal from the cotton fabric eclipses the aspect of peaks of the SiO₂ NP band at (1081–995) cm⁻¹ for (Si-OH) and the band at 791 cm⁻¹ for (Si-O-Si) groups [54]. A shift of peak from 2890 cm⁻¹ to 2850 cm⁻¹ also confirms the presence of -NH deformation, which is assigned for chitosan. The shift of peak from 3327 cm⁻¹ to 3332 cm⁻¹, 3334 cm⁻¹, 3334 cm⁻¹ for three treated specimens is associated with the overlapping of the -OH group and -NH group with a broader peak when the cotton is crosslinked with chitosan [22,55]. A minimum shift of other peaks compared with the control one is attributed to the existence of the new element, chitosan, SiO₂ NPs, and CuO NPs, on the fabric.

3.4.2. FESEM Analysis

The FESEM analysis is demonstrated in Figure 6, where Figure 6a,b stands for untreated fabric, Figure 6c,d for Chi-CuO-SiO_2(5g/L)-treated fabric, Figure 6e,f for Chi-CuO-SiO_2(10g/L)-treated fabric and Figure 6g,h for Chi-CuO-SiO_2(20g/L)-treated fabric. Figure 6a illustrates a smooth surface that stipulates no deposition of NPs on it. On the other hand, FESEM micrographs of Chi-CuO-SiO₂-treated fabric from Figure 6c,e,g clearly evidences the deposition of NPs. Among them, uniform and well-dispersed NPs are observed for Chi-CuO-SiO_2(5g/L)-treated fabric. Non-uniform dispersion of NPs appears on Chi-CuO-SiO_2(10g/L)-treated fabric, which is clearly visible from Figure 6e, and agglomeration of NPs is obtained for Chi-CuO-SiO_2(20g/L)-treated fabric due to deposition of a high amount of silica NPs.

Elemental analysis of specimens provides rapid quantitative data on chemical composition. Figure 6b depicts that the untreated fabric contains only carbon (C) and oxygen (O). In contrast, the treated specimens carry silicon (Si), copper (Cu), and nitrogen (N) along with carbon (C) and oxygen. Another vital issue is that upon treatment, the amount of oxygen increases drastically for all treated specimens compared with the pristine one, which also authenticates the presence of SiO₂ NPs, CuO NPs, and chitosan on the treated fabric. Further, the existence of nitrogen (N) confirms the presence of chitosan on all the treated fabrics. A higher amount of SiO₂ NP deposition is observed for the fabric treated with 5 g/L SiO₂ NPs compared with the fabric treated with 10 g/L silica NPs may be related to the zeta potential stability of these fluids. It becomes double for Chi-CuO-SiO_2(20g/L)-treated fabric, which leads to agglomeration of NPs on the fabric.

Treatment with 5 g/L SiO₂ NPs compared with the fabric treated with 10 g/L silica NPs may be related to the zeta potential stability of these fluids. It becomes double for Chi-CuO-SiO_2(20g/L)-treated fabric, which leads to agglomeration of NPs on the fabric.

3.4.3. Elemental Mapping

EDX mapping of untreated and Chi-CuO-SiO_2(5g/L)-treated fabric is conducted to accurately explain the presence of NP distribution on the fabric. Figure 7a exhibits the image of pristine fabric with a size of 50 µm, and the elemental mapping of it is shown in Figure 7b,c, whereas Figure 7d shows the image of Chi-CuO-SiO_2(5g/L)-treated fabric, and the individual elemental distributions of it are shown in Figure 7e–i. These figures show that only C and O are present on the pristine one. In comparison with this, the distribution of Cu, Si, and N, along with C and O, in the treated fabric confirms the presence of SiO₂ NPs and CuO NPs on it, while the presence of N authenticates the existence of chitosan on it.

3.5. Assessment of Functional Properties

3.5.1. Evaluation of Antibacterial Properties

The antibacterial efficacy of non-functionalized and functionalized cotton woven textiles with chitosan-loaded CuO-SiO₂ hybrid nanofluids is displayed in Figure 8 against gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) bacteria. The bacterial reduction percentage is observed before washing, after five and 15 washing cycles. In this figure, the chitosan-loaded CuO-SiO_2(5g/L), CuO-SiO_2(10g/L), and CuO-SiO_2(20g/L) hybrid nanofluid-treated fabric is denoted by CCS-1, CCS-2, and CCS-3, respectively. Figure 9a–h and Figure 10a–h illustrate the disk image of agar plate for bacterial viability of untreated, Chi-CuO-SiO_2(5g/L)-, Chi-CuO-SiO_2(10g/L)-, and Chi-CuO-SiO_2(20g/L)-treated fabrics before washing after 1 h and 24 h contact time, respectively. Investigations of these graphs and figures demonstrate that the reduction percentage against gram-positive and gram-negative bacteria after 1 h and 24 h contact time is found as 99.99% against both bacteria for all functionalized specimens before washing.

Sharma et al. (2022) reported that chemically synthesized CuO NPs demonstrated very good antimicrobial activity up to 97% [56]. Comparing with these outcomes, the outstanding achievement of this context is due to the existence of bio-synthesized CuO NPs, along with chitosan, and SiO₂ NPs in hybrid nanofluids. The mechanism of the antibacterial activity of CuO NPs causes the destruction of the cell wall of bacteria, producing reactive oxygen species, and degrading DNA, and thus inhibiting the DNA replication in the microorganism [27,57]. Chitosan is an effective organic antibacterial agent that has a positive effect on antibacterial activity [58]. Chitosan-loaded CuO NPs enhance antibacterial efficacy remarkably, which has also been reported by Saleh et al. (2021) [21].

However, it is observed graphically from Figure 8 that all the specimens retained their antibacterial activity as unwashed specimens after five washing cycles against both bacteria after 1 h and 24 h of contact time. After 15 washing cycles, the three treated specimens retained excellent bacterial efficacy against S. aureus bacteria for 1 and 24 h of contact time. On the contrary, the three treated fabrics ascribed 86.44%, 89.49% and 92.88% bacterial efficacy at 1 h contact time, whereas they retained 97.97%, 97.97%, and 99.99% bacterial efficacy after 24 h contact time in the case of E. coli bacteria. This excellent wash durability after washing is due to the formation of crosslinking of chitosan between NPs and cotton fabric.

3.5.2. Evaluation of Ultraviolet Protection Factor

The UV transmittance curve and obtained approximate quantitative outcomes of untreated and treated specimens are presented in

Table 2. T% with ultraviolet protection factor of untreated and various Chi-CuO-SiO₂-treated specimens.

Sample	UV-A (320–400) nm	UV-B (290–320) nm	UV-R (290–400) nm	UPF with Respect to the Average T %	UPF	UV Protection Category
Untreated	84.15	64.61	69.43	5.96 ± 1.2	-	Insufficient
Chi-CuO-SiO2(5g/L)-treated	4.63 ± 0.1	2.5 ± 0.18	3.58 ± 0.11	31.29 ± 0.05	30	Very Good
Chi-CuO-SiO2(10g/L)-treated	4.83 ± 0.63	3.16 ± 0.3	3.93 ± 0.25	29.27 ± 0.98	30	Very Good
Chi-CuO-SiO2(20g/L)-treated	2.74 ± 0.6	2.1 ± 0.52	2.47 ± 0.52	41.5 ± 0.43	40	Excellent

and Figure 11, respectively. It is illustrated that the pristine specimen transmits around 70% UVR, which is inadequate for UV protection. Conversely, chitosan-loaded CuO-SiO_2(5g/L), CuO-SiO_2(10g/L), and CuO-SiO_2(20g/L)-deposited specimens block around 96.42%, 96.07% and 97.53% UVR, respectively, with UPF values of 30, 30, and 40. These are categorized as very good, very good, and excellent according to the AS/NZ standard [59]. It is evidenced that the incorporation of hybrid nanofluid on cotton fabric significantly enhanced the UV protection efficacy of the specimen. The highest UV protection provision efficacy is achieved for the chitosan-loaded CuO-SiO_2(20g/L)-treated specimen. It can be pointed out that, from 5 g/L to 20 g/L silica concentration, the UV protection properties have enhanced remarkably. This finding is in line with Attia et al. (2017), who proved that with increased concentrations of rice husk silica NPs, the UV-protective efficacy of fabric is significantly enhanced [60]. Boruah et al. (2024) found that green-synthesized CuO NPs reduced with Syzygium cumini leaf extract acquired very good UV-protective properties with a UPF factor of 36.18 [61]. In relation to these findings, the outstanding outcomes for Chi-CuO-SiO_2(20g/L)-treated fabric are inferred to be superior. Thus, it is notable that these hybrid nanofluids have enormous potential as UV-protective agents.

3.6. Assessment of Mechanical Properties

Table 3. Mechanical properties of untreated and various Chi-CuO-SiO₂ hybrid nanofluid-treated fabric.

Sample	Tensile Strength (N)		Elongation %		Tear Strength (N)
	Warp	Weft	Warp	Weft	Warp	Weft
Untreated	857.45 ± 19.7	520.91 ± 23.6	12.09 ± 0.11	15.38 ± 0.3	9.62 ± 0.42	9.67 ± 0.3
Chi-CuO-SiO2(5g/L)-treated	867.89 ± 18.48	523.69 ± 37.57	22.20 ± 0.37	15.62 ± 0.22	8.7 ± 0.11	7.2 ± 0.32
Chi-CuO-SiO2(10g/L)-treated	828.97 ± 62.91	479.90 ± 49.91	18.57 ± 1.067	16.37 ± 0.61	8.8 ± 0.23	7.3 ± 0.15
Chi-CuO-SiO2(20g/L)-treated	826.22 ± 12.63	469.54 ± 21.89	20.17 ± 0.17	15.98 ± 0.57	8.9 ± 0.19	7 ± 0.14

illustrates the impact of mechanical properties on Chi-CuO-SiO₂ hybrid nanofluids deposited on cotton fabric. Figure 12 represents the effect of tensile strength on extension% of (a) untreated, (b) Chi-CuO-SiO_2(5g/L)-treated, (c) Chi-CuO-SiO_2(10g/L)-treated, and (d) Chi-CuO-SiO_2(20g/L)-treated fabric. It is perceived, as shown in Table 3 and Figure 12, that the tensile strength of Chi-CuO-SiO_2(5g/L)-treated fabric has improved 1.22% and 0.53%, respectively, both in warp and weft directions, compared with that of the control one. On the other hand, the tensile strength of Chi-CuO-SiO_2(10g/L)- and Chi-CuO-SiO_2(20g/L)-treated fabrics has decreased by around 3.32% and 3.64% for warp, and 7.8% and 9.86% for weft directions, respectively, in contrast to the control one. This is due to the utilization of 1% acetic acid and increased silica NP concentration jointly reducing the p^H below the required level during the preparation of hybrid nanofluids, which affects the fiber structure. This phenomenon has been explained by the FTIR spectrum from Figure 5, where the achieved peak of the glucose ring is at wave number 1052 cm⁻¹ and 1053 cm⁻¹ stretching for the untreated and Chi CuO-SiO_2(5g/L)-treated fabric. On the contrary, the diminution of peak position from 1052 cm⁻¹ to 1037 cm⁻¹ and also the reduction of peak intensity for both Chi-CuO-SiO_2(10g/L)- and Chi-CuO-SiO_2(20g/L)-treated fabric indicate the damage to the fiber structure that ultimately affects the strength of the fabric. Xiao et al. (2022) fabricated chitosan and Cu(II) ions on cotton fabric along with succinic acid and attained a depletion of around 18.41% tensile strength [22]. This acquired outcome is very relevant to the present context.

The average GSM of untreated, Chi-CuO-SiO_2(5g/L)-, Chi-CuO-SiO_2(10g/L)-, and Chi-CuO-SiO_2(20g/L) hybrid nanofluid-treated fabric is 164, 177, 174, and 172, respectively, whereas the average ends per inch (EPI) and picks per inch (PPI) of those specimens are 142 and 74, 143 and 76, 141 and 75, and 140 and 74, respectively. In particular, the EPI and PPI of Chi-CuO-SiO_2(5g/L)-treated fabric have been enhanced and reduced for the other two compared with the untreated one. This is another reason for the enhancement of the tensile strength of Chi-CuO-SiO_2(5g/L)-treated fabric compared with the others.

Additionally, elongation percentage follows an increasing trend for both warp and weft directions in all modified specimens, in congruence with the control ones. Elongation at break reaches the highest 22.20% in warp direction for the Chi-CuO-SiO_2(5g/L)-treated specimen and 16.37% for the Chi-CuO-SiO_2(10g/L)-treated specimen for weft direction. More specifically, elongation at break has risen approximately 83.62%, 53.5% and 66.8% in the warp direction, and 1.6%, 6.4%, and 3.9% in the weft direction, compared with the pristine one. The highest 9.56% deterioration of tear strength is attained in the warp direction for the Chi-CuO-SiO_2(5g/L)-treated specimen, and 27.6% in the weft direction for the Chi-CuO-SiO_2(20g/L)-treated specimen. The reduction in tear strength is higher for the weft than the warp direction. The reason behind the decline in tear strength is that the crosslinking of fiber and yarn hinders the slippage and thus lessens tear strength [62].

3.7. Assessment of Comfort Properties

3.7.1. Assessment of Moisture Management Properties

To transfer the liquid or sweat vapor from the body to the atmosphere via clothing is referred to as the moisture management properties of textiles. This helps to improve the thermo-physiological comfort properties of fabric by keeping the thermal balance of the body [7].

The impact of Chi-CuO-SiO₂ hybrid nanofluids on the moisture management properties of cotton fabric is tabulated in

Table 4. MMT test results of control and various chitosan-loaded CuO-SiO₂ hybrid nanofluid-treated fabric.

Parameters		Uncoated	Chi-CuO-SiO2(5g/L)-Coated	Chi-CuO-SiO2(10g/L)-Coated	Chi-CuO-SiO2(20g/L)-Coated
Wetting time (s)	Top	0.749	3.183	6.272	6.365
	Bottom	1.966	2.34	3.276	5.71
Absorption rate (%/s)	Top	9.7243	9.7711	5.196	12.82
	Bottom	16.5463	47.3384	25.08	32.08
Max wetted radius(mm)	Top	25	30	20	20
	Bottom	25	30	25	20
Spreading speed (mm/s)	Top	8.1697	8.0781	3.67	2.46
	Bottom	5.6993	6.0365	4.36	2.30
One-way transport capability (%)		147.6503	414.043	405.46	395.84
Overall moisture management		0.4878	0.8537	0.7919	0.6701

. The grading system of the MMT test for all parameters is graphically displayed in Figure 13a–d. The results for the untreated fabric indicate that the wetting time required for both the top and bottom surfaces is lower for the pristine one than for the others, and it is graded as excellent. The presence of a coating of hybrid nanofluids leads to an increase in the wetting time of both surfaces of all the coated fabrics. Among the treated specimens, Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric exhibits the lowest wetting time and is graded as very good and excellent for top and bottom surfaces, respectively. In the case of the absorption rate, it is found that these values are raised significantly for all treated fabrics in comparison to the pristine ones. In particular, the bottom surface of Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric depicts the highest moisture absorption rate, indicating that the highest amount of moisture is absorbed by it due to the hydrophilic characteristics of silica NPs [63]. The larger difference in absorption rates between the two fabric layers of this fabric points out the slower movement of moisture from the bottom to the top surface [33]. The grading of absorption rates from the graphics illustrates that the rating from the bottom to top surface of untreated fabric is fair to poor, whereas for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric is good to poor. Moreover, the highest wetted radius is exploited for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric and graded as excellent for both surfaces. The larger wetted radius eases faster drying periods, which take the moisture vapor away from the skin quickly. The highest dispersion stability of NPs and the hydrophilic nature of Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric facilitates achieving a higher absorption rate and wetted radius than other treated specimens. The moisture spreading speed for untreated and Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric is graded as excellent, which is better than the other two.

Outcomes of one-way transportability (OWT) from the table and graph demonstrate that better OWT is achieved for all treated specimens than for untreated ones. All treated specimens are graded as excellent, while the untreated specimen is graded as good. The highest value of one-way transportability is attained at 414.043 for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric. Following this, the highest value of overall moisture management properties (OMMC) is gained at 0.8537, for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric, which is 75% better than the untreated one and graded as excellent, whereas CuO-SiO_2(10g/L)- and CuO-SiO_2(20g/L)-treated specimens are graded as very good, and the untreated one is good.

Khandual et al. (2020) incorporated only silica NPs on cotton fabric and acquired OMMC at 0.7782 and graded it as very good [63]. Comparing with this context, a remarkable improvement in OMMC is achieved for chitosan-loaded Chi-CuO-SiO_2(5g/L) hybrid nanofluid-coated fabric. Consequently, it is clearly evidenced that the presence of CuO NPs and chitosan, along with silica NPs, has a great positive impact on the moisture management properties of cotton fabric.

3.7.2. Assessment of Sensorial Mechanical Comfort Indices

Thirteen FTT predicted mechanical comfort indices determined by the FTT software are tabulated in

Table 5. Outcomes of FTT indices of untreated and chitosan-loaded CuO-SiO₂ hybrid nanofluid-treated fabric.

Parameters	Indices	Unit Given in FTT Software	Untreated	Chi-CuO-SiO2(5g/L)-Treated	Chi-CuO-SiO2(10g/L)-Treated	Chi-CuO-SiO2(20g/L)-Treated
Bending	BARa	gf mm rad−1	752.62	71.62	68.58	128.48
	BARe	gf mm rad−1	1013.7	78.48	671.79	1582.52
	BWa	gf mm rad	2590.46	374.03	331.90	355.68
	BWe	gf mm rad	3174.07	463.7	2062.47	3811.89
Compression	T	Mm	0.42	0.42	0.39	0.38
	CW	gf mm	2003.56	668.13	825.16	1036.37
	CRR	-	0.40	0.64	0.58	0.53
	CAR	gf mm−3	149.30	328.85	419.45	434.20
	RAR	gf mm−3	825.37	1139.61	1333.70	1548.76
Flux	TCC	10−3 W m−1 °C−1	43.17	48.15	47.87	40.24
	TCR	10−3 W m−1 °C−1	43.74	49.88	49.66	44.76
	Qmax	W mm−2	1203.57	1348.73	1269.94	1252.65
Friction	SFCa	-	0.28	0.31	0.32	0.33
	SFCe	-	0.28	0.31	0.31	0.31
Roughness	SRAa	µm	16.91	3.88	9.45	8.69
	SRAe	µm	15.41	8.53	5.98	7.16
	SRWa	Mm	1.13	0.53	0.52	0.68
	SRWe	Mm	1.18	0.37	0.47	0.63

. The primary indices (smoothness, softness, and warmness) obtained from these 13 indices are diagrammatically represented in Figure 14 with standard deviation.

Characteristics of the fabric surface, such as surface friction and roughness, are utilized to determine fabric smoothness. The surface friction coefficient quantifies the frictional force relative to the normal force. Fabric with a lower frictional coefficient is perceived as smoother [64]. Data from Table 5 points out that the lowest surface friction coefficient is obtained for the untreated specimen in comparison with other hybrid nanofluid-treated specimens. These attributes indicate the smooth surface of untreated fabric than others.

But the smoothness of fabric is also greatly influenced by surface roughness. The maximum height of a fiber wave measured from the flat surface of the fabric is termed surface roughness amplitude. Fabric with higher roughness amplitude points out pronounced irregularities on the fabric surface. The distance between successive crests on a surface of a fabric is referred to as the surface roughness wavelength. Fabric with a shorter surface roughness wavelength is perceived as smooth [64]. Here, the outcomes from Table 5 suggest that the highest surface amplitude and surface wavelength are observed for untreated fabric, and the lowest values are achieved for Chi-CuO-SiO_2(5g/L) nanofluid-treated fabric. Following the above discussion, finally, the highest value of smoothness from Figure 14 is obtained, 0.62 for both untreated and Chi-CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric, which also confirms the even distribution of NPs on this treated fabric. In situ application of Ag NPs on cotton fabric diminished the smoothness of the fabric achieved by Saha et al. (2025) [65], whereas this context shows the Chi-CuO-SiO_2(5g/L) nanofluid-treated fabric is as smooth as the control one because good dispersion stability properly facilitates the dispersion of the NPs on the fabric surface.

Bending average rigidity (BAR), bending work (BW), and compression modules are very relevant in determining fabric softness. Fabric with a higher value of bending average rigidity and bending work is considered stiff [66]. The lowest values of bending average rigidity and bending work are acquired for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric, and the softness value is 0.56. This value is higher than untreated fabric, for which it is 0.11. With an increase in silica concentration from 10 g/L to 20 g/L, BAR and BW increased gradually, and the softness value reduced from 0.23 to 0.15. So, it is observed that with increased silica concentration in this hybrid nanofluid, the fabric softness is reduced; however, all the hybrid nanofluid-treated specimens are still softer than the untreated fabric.

From the compression module, it is found that the value of thickness remains the same (0.42) for untreated and Chi-CuO-SiO_2(5g/L) nanofluid-treated fabric, and is reduced to 0.39 and 0.38 for Chi-CuO-SiO_2(10g/L)- and Chi-CuO-SiO_2(20g/L) hybrid nanofluid-treated fabric. The highest value, 2003.56 of compression work, is gained for the control fabric, whereas lower values are achieved for all treated specimens, which confirms the stiffness of the control fabric compared with others. Compression recovery rate (CRR) is referred to as the percentage of thickness changes after compression.

Fabric that has a higher CRR is considered soft. Here, the highest CRR value, 0.64, is observed for Chi-CuO-SiO_2(5g/L)-treated fabric, and the lowest CRR value, 0.40, is achieved for the pristine one. So, following the value of bending average rigidity, the compression module also confirms that Chi-CuO-SiO_2(5g/L)-treated fabric is softer than the pristine one.

Thermal conductivity during compression and recovery shows a significant enhancement for the treated specimens compared to the untreated counterpart due to the presence of highly conductive CuO NPs on the fabric. Among the treated specimens, the highest conductivity with Q_max value is achieved for Chi-CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric. Following this, the lowest warmness value 0.47 is obtained for this sample. So, it can be said that the application of Chi-CuO-SiO₂ hybrid nanofluid has a significant positive effect on the thermal conductivity of the fabric. With increased silica concentration, the thermal conductivity of treated fabric has reduced as the presence of silica NPs makes the fabric thermally resistive. Saha et al. (2025) observed that the incorporation of Ag NPs on cotton fabric resulted in an increased Q_max value compared to that of the untreated one. The acquired outcomes of this research are in agreement with this observation [65].

From the above discussions, it can be concluded that chitosan-loaded Chi-CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric provides better mechanical sensorial comfort properties than the untreated one in terms of smoothness, softness, and thermal conductivity.

3.8. Assessment of Cytotoxicity

The microscopic observations of survival Vero cells and the outcomes of data interpretation for the percentage of survival cells are exhibited in Figure 15 and

Table 6. Viable cell percentage with data interpretation for various specimens.

Treatment	Well	Cells Seeded	Viable Cells Counted	Cell Survival (%)	Average Cell Survival (%)
Solvent (−)	1	1.5 × 104	1.5 × 104	100	100
Solvent (−)	2	1.5 × 104	1.5 × 104	100
Solvent (+)	1	1.5 × 104	1.44 × 104	96	96.35
Solvent (+)	2	1.5 × 104	1.45 × 104	96.7
Chi-CuO-SiO2(5g/L)-Treated (1)	1	1.5 × 104	1.43 × 104	95.3	95.8
Chi-CuO-SiO2(5g/L)-Treated (2)	2	1.5 × 104	1.445 × 104	96.3

, respectively. A microscopic image of Vero cells after exposure to negative solvent (control) illustrates 100% survival of cells, whereas Vero cells after exposure to positive solvent and positive solvent with Chi-CuO-SiO_2(5g/L)-treated fabric show some destruction of cells compared with control ones. Arrow marks on the Vero cells after exposure to positive solvent with Chi-CuO-SiO_2(5g/L) indicate the fiber on the Vero cell culture. More specifically, data interpretation from Table 5 illustrates that 100%, 96.35%, and 95.8% survival of cells is achieved for Vero cells subjected to control (-solvent), positive solvent, and positive solvent with Chi-CuO-SiO_2(5g/L)-treated fabric. As cell viability above 95% is regarded as non-cytotoxic, chitosan-loaded CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric can be considered as non-cytotoxic under the conditions of this in vitro assay. Green synthesis of CuO and SiO_2, and non-toxic chitosan, facilitates achieving these remarkable outcomes. Rezaie et al. (2018) examined the cytotoxicity of environmentally friendly lower concentrations of CuO NPs on cotton fabric and found 75.36% cell viability [67]. Compared with that study, excellent results are obtained in this context.

4. Conclusions

This research aimed to bio-synthesize hybrid nanofluids in a cost-effective and eco-friendly approach to develop durable, functionalized textiles with better serviceability as well as thermo-physiological and sensorial comfort properties. Three distinct varieties of bio-synthesized hybrid nanofluids, namely chitosan-loaded CuO-SiO_2(5g/L), CuO-SiO_2(10g/L), and CuO-SiO_2(20g/L), are applied on cotton woven fabric for optimizing so that this can be employed for biomedical applications. Among the hybrids, the Chi-CuO-SiO_2(5g/L) hybrid nanofluid demonstrates the highest zeta potential stability, which leads to uniform deposition of NPs. It is found that the Chi-CuO-SiO_2(5g/L)-deposited fabric achieves the highest 99.99% antibacterial efficacy against S. aureus and E. coli bacteria, even after only 1 h contact time before wash. Surprisingly, the highest antibacterial efficacy, 99.99%, is retained even after 15 washing cycles against S. aureus bacteria after 1 h contact time with 5 g/L silica concentration in hybrid nanofluids, and this value is regarded as optimal, whereas for E. coli, similar outcomes are attained for Chi-CuO-SiO_2(20g/L)-deposited fabric. These outstanding outcomes affirm the significant durability of hybrid nanoparticles on cotton fabric even at low silica concentration. Besides the intrinsic antibacterial properties, the UV-blocking performance of Chi-CuO-SiO_2(5g/L)-, Chi-CuO-SiO_2(10g/L)-, and Chi-CuO-SiO_2(20g/L)-functionalized fabric displays UPF factors of 30, 30, and 40, which can be categorized as very good, very good, and excellent, respectively. It can be highlighted that the UV-protective performance reaches to its highest with increased silica concentration. Assessment of mechanical properties shows the augmentation of tensile strength and elongation of Chi-CuO-SiO_2(5g/L)-functionalized fabric in comparison with the pristine one. Moreover, the quantitative data of thermo-physiological and sensorial comfort properties authenticate a notable enhancement in comfort properties for all treated fabrics. A remarkable enhancement of OMMC value, 0.8537, which is around 75% better than the untreated one, ensures excellent thermo-physiological comfort properties of the hybrid nanofluid-treated fabric that contains 5 g/L silica NPs. Also, the Chi-CuO-SiO_2(5g/L)-deposited specimen provides better sensorial comfort properties in terms of smoothness, softness, and warmness than that of the others. Cell viability for Chi-CuO-SiO_2(5g/L)-treated fabric is 95.8% with no observable cytotoxic effects, which confirms the non-cytotoxicity of this treated fabric.

Considering the aforementioned discussions, a conclusive statement can be made that Chi-CuO-SiO_2(5g/L) hybrid nanofluid-treated fabric can be effectively utilized as durable, multifunctional, mechanically strong, and comfortable clothing for biomedical approaches. Further extensive study can be conducted on more fascinating properties, such as the flame-retardant and self-cleaning properties of the fabricated surface of cotton woven fabric.