Fabrication and characterization of novel, cost-effective graphitic carbon nitride/Fe coated textile nanocomposites for effective degradation of dyes and biohazards

Abstract

Textile-based photocatalysts are the new materials that can be utilized as an effective sustainable solution for biochemical hazards. Hence, we aimed to develop a sustainable, cost-effective, and facile approach for the fabrication of photocatalytic fabric using graphitic carbon nitride (g-C₃N₄) and ferric-based multifunctional nanocomposite. Bulk g-C₃N₄ was prepared from urea by heating it at 500 °C for 2 h. The structure of ball-milled g-C₃N₄ was engineered by doping with various amounts of iron (III) chloride hexahydrate solution (0.006 mol/L) and sintered at 90 °C for 24 h to prepare g-C₃N₄–nanosheets/α-Fe₂O₃ composites. These nanocomposites have potential avenues towards rational designing of g-C₃N₄ for improved photocatalytic, antibacterial, and antiviral behavior. The prepared nanocomposite was characterized for its surface morphology, chemical composition, crystal structure, catalytic, antibacterial, and antiviral behavior. The fabrication of ferric doped g-C₃N₄ nanocomposites was characterized by SEM, EDX, FTIR, and XRD analysis. The coated fabric nanocomposite was characterized for methylene blue dye degradation under visible light, antibacterial and antiviral behavior. The developed textile-based photocatalyst has been found with very good recyclability with photocatalytic degradation of dye up to 99.9 % when compared to conventional g-C₃N₄ powder-based photocatalyst.

Graphical abstract

Highlights

• •A novel g-C₃N₄/α-Fe₂O₃ multifunctional nanocomposite fabrication by facile method.
• •The formation of nanocomposite was confirmed through SEM, EDX, XRD, and FTIR.
• •Application of nanocomposite on textile for photocatalytic and bioactive properties.
• •Excellent durable dye degradation and biocidal activity by treated fabric.

1. Introduction

Biochemical hazards refer to substances or agents that can cause harm to living organisms or the environment [1]. Biochemical hazards include microorganisms such as bacteria, viruses, fungi, and parasites that can cause infectious disease as well as substances that can cause harm to human health or the environment due to their toxic, corrosive, or flammable properties [2]. These hazards arise from exposure to industrial chemicals, pesticides, heavy metals, and other hazardous materials [3,4]. The textile industry is one of the major sources of hazardous substances in the form of solvents, dyes, and other materials and microorganisms in the processing of textiles [5]. The development of functional textiles with antibacterial and antiviral properties, as well as the treatment of wastewater by the textile industries to remove harmful chemicals and pollutants, can help to mitigate these hazardous components and ensure a safer and more sustainable textile industry [6].

Currently, various types of disinfecting agents and catalysts have been studied to address the great challenges concerned with biochemical hazards. Photocatalytic technologies have the potential to trigger a number of significant chemical reactions (CO₂ reduction, photodecomposition of hydrogen, and degradation of pollutants) by sunlight where it generates disinfecting and catalytic agents to perform the cleaning tasks [7,8]. Several groups of researchers have been trying to introduce the new structure of photo-catalysts such as complexes of metal with metal oxides, metal oxides with carbonaceous metal oxides [9], nanocomposites of Ag/TiO₂ [10], SnO₂/ZnO/TiO₂ [11], Ag/SnO_2, etc. [12]. However, some of them are not suitable due to high manufacturing costs, low antibacterial efficiency, and inadequate chemical resistance. Also, they are not suitable for removing contaminants at extremely low concentrations (in the range of parts per billion). Therefore, the development of innovative recyclable multifunctional nanocomposites using sustainable and cost-effective synthesis techniques has gained considerable attention from the research community in both academia and industry [13,14].

Graphitic carbon nitride (g-C₃N₄) has found a strong position among other high-performance photocatalysts because it is developed from urea or melamine which are cheap and abundantly available chemicals in the commercial market [15]. The unique characteristics of g-C₃N₄ such as low toxicity, antibacterial behavior, water splitting, chemical pollutant degradation, good response to visible light, biocompatible in the dark, good resistance against chemical and anti-corrosion make it an ideal candidate for futuristic multifunctional photocatalysts [[16], [17], [18]]. However, low absorption of visible light, high charge recombination rate, and small surface area of the g-C₃N₄ limit its antimicrobial and photocatalytic properties [19]. Furthermore, it is very difficult to recover the g-C₃N₄ catalyst from the solvent even by centrifugation at 14000 rpm, which makes it unsuitable to use after recycling. Various techniques have been adopted such as modification in chemical compositions, varying synthesis temperature, composite structures with semiconductors, and doping with metal particles to enhance the performance properties and characteristics of g-C₃N₄ [20,21].

One promising approach is the development of graphitic carbon nitride (g-C₃N₄)/Fe-coated textiles, which can serve as an effective solution to address the problems of biochemical hazards. Therefore, in this study, we have developed g-C₃N₄/Fe-coated textiles with excellent photocatalytic, antibacterial. To the best of our knowledge, there is no study reported on the doping of g-C₃N₄ with different concentrations of ferric salt and textile-based free-standing recyclable photocatalysts. Moreover, the developed photocatalyst can have excellent reusability thus outperforming the conventional photocatalyst which has the problem of poor recovery. In addition, the developed photocatalyst is highly effective at very low concentration which also makes it superior to conventional photocatalyst. Our developed method is very short, facile, economical, and eco-friendly. At first, the bulk g-C₃N₄ powder was prepared by simple calcination using the ordinary furnace and grinded. Subsequently, the developed Fe-doped g-C₃N₄ nanocomposites were applied to the cotton fabric using the knife-over roller technique. The prepared photocatalysts are firmly coated over the textile structures and do not have problems of leaching, wasting, and recovering from the solvents.

2. Materials and methods

2.1. Materials

Urea (CH₄N₂O) and iron (III) chloride hexahydrate (FeCl₃·6H₂O) were purchased from Daejung Chemicals (Korea). Methylene blue (MB) was purchased from Sigma Aldrich. Water-born polyurethane solution (Lurapret, NDP.S), thickening agent (Lutexil HIT), and wetting agent (Felosan RGN) were purchased from BASF. The 100 % cotton fabric with GSM (gram per square meter) of 130 was obtained from Sapphire Textiles (Pakistan). All the chemicals used in this study were of reagent grade and used without any further purification.

2.2. Preparation of bulk g-C₃N₄, g-C₃N₄–nanosheets and g–C₃N₄–Fe₂O₃ nanocomposites

The bulk g-C₃N₄ was synthesized by placing urea (20 g) in a ceramic crucible covered with a lid. The ceramic crucible was placed in a heated furnace and the temperature of 500 °C was achieved at a rate of 5 °C/min. The adjusted temperature (500 °C) was given for 2 h. The placed urea was converted into yellow compacted sediments of g-C₃N₄. The obtained yellow compacted g-C₃N₄ was cooled down to room temperature. The powder of g-C₃N₄ was placed into a desiccator to preserve it from moisture uptake.

The second step was the conversion of bulk graphitic carbon nitride g-C₃N₄ into the nanosheets. The as-synthesized g-C₃N₄ was grinded with the help of agate/mortar and converted into fine powder. Subsequently, the powder was subjected to the process of dry pulverized ball milling. For 1 h of dry milling, a sintered corundum vessel with a capacity of 80 ml and zirconium balls with a diameter of 10 mm was utilized. The ball-to-material ratio (BMR) was maintained at 8:1 and the material was grinded at 600 RPM. Hence the grinded powder was converted into fine nanosheets of g-C₃N_4.

In order to prepare the g-C₃N₄–nanosheets/α-Fe₂O₃ composites, the different concentrations of iron (III) chloride hexahydrate FeCl₃·6H₂O salt were selected. The FeCl₃·6H₂O aqueous solutions with a concentration of 0.006 mol/L (0, 1 ml, 2 ml, 3 ml, and 4 ml) were mixed with 0.1 g of g–C₃N₄–nanosheets powder. The resulting solutions having different concentrations of FeCl₃ were vigorously stirred with the help of a magnetic stirrer at a constant speed of 500 RPM for 30 min. Afterward, the solution was well dispersed by the process of ultra-sonication for 10 min followed by drying at 90 °C in an oven for 12 h. Subsequently, they were annealed for half an hour in the air at 450 °C for the conversion of Fe precursor to crystalline α-Fe₂O₃. The resulting samples were coded as the g–C₃N₄–Fe composites. Hence, we produced a total of 5 samples of g–C₃N₄–Fe nanocomposites against five (0, 1 ml, 2 ml, 3 ml, 4 ml) concentrations of FeCl₃·6H₂O salt (0.006 mol/L). The listed samples are shown in Table S1 (SI file).

2.3. Preparation of coating paste by using g-C₃N₄/α-Fe₂O₃ nanosheets

A homogeneous mixture of the water-borne polyurethane, thickening agent, wetting agent, and prepared g–C₃N₄–α-Fe₂O₃ nanocomposites was prepared. For this, 0.50 g of g–C₃N₄–nanosheets/α-Fe₂O₃ composite, thickening agent (0.4 %), and wetting agent (4.0%) were dispersed in 50 ml of polyurethane solution. The resultant solution was mechanically stirred for 2 h at 800–900 rpm. The thickening agent is used to maintain rheological properties and uniform application of paste while the wetting agent is utilized to create micro porosity. The prepared homogeneous paste was placed into a vacuum oven for 24 h to eliminate the bubbles.

2.4. Coating of g–C₃N₄–nanosheets/α-Fe₂O₃ on fabric

Prior to coating, the mercerized cotton fabric (3 × 10 inch²) was made alkaline by immersing the fabric in 10% sodium hydroxide (NaOH) solution. Following this, the fabric was squeezed between the padder rollers at a pressure of 1.5 bar and dried in a stenter at 120 °C for 10 min. Afterward, the as-prepared g–C₃N₄–nanosheets/α-Fe₂O₃ paste was applied to the fabric through the knife over-roller method. The coated fabric was passed through a padder to expel the excess amount of coating from the fabric followed by drying in a stenter at 120 °C for 1 min and curing at 150 °C for 3 min. The fabric was coated three-fold to ensure that the g–C₃N₄–nanosheets/α-Fe₂O₃ composite is uniformly applied to the fabric. The average coating thickness achieved was about 0.02 mm. The coated fabric was then subsequently washed with distilled water for 1 h at 40 °C in a low-pressure jigger machine, squeezed, and dried at 100 °C. The design of the experiment for the preparation of all coated fabrics is shown in Table 1.

Table 1.

Design of experiments for the coated fabric samples.

Sr #	Name of fabric sample	Sample name of coating paste	Code of nanocomposites	Number of applied coatings	Rate constant Kapp (min−1)
1	F1	P1	GF0	1	0.03
2	F2			2	0.17
3	F3			3	0.26
4	F4	P2	GF1	1	0.05
5	F5			2	0.21
6	F6			3	0.29
7	F7	P3	GF2	1	0.31
8	F8			2	0.43
9	F9			3	0.78
10	F10	P4	GF3	1	0.30
11	F11			2	0.42
12	F12			3	0.79
13	F13	P5	GF4	1	.0.28
14	F15			2	0.40
15	F16			3	0.75

2.5. Characterization

Fourier transform infrared spectroscopy (FTIR) investigation (Nexus-870) was done to analyze the surface functional groups of as-synthesized composites. The X-ray diffractometer (XRD, Bruker D8 Advance) with Cu Kα radiation (λ = 0.154178 nm) was used to determine the phases of the as-synthesized composites. SEM (TESCAN, Dortmund-Germany) has been used to examine the surface morphology of coated fabrics by supplying an accelerating voltage using the Tescan VEGA III SEM instrument. The element percentages by weight were measured through EDX characterization. A UV-2700 spectrophotometer (Shimadzu) was used to investigate diffuse reflectance spectra (DRS). An F-4600 FL spectrophotometer was used to acquire the photoluminescence (PL) spectrum.

2.6. Photocatalytic activity

Photocatalytic activity of all composites of g-C₃N₄–nanosheets/α-Fe₂O₃ was determined by the following method, developed by Fiaz et al. with a little modification [22]. The photocatalytic activity of the developed nanocomposites was examined by photodegradation of methylene blue (MB) in an aqueous solution at room temperature. Two solar simulators (MASTER TL-D 90 De Luxe 36W/965 SLV/10) were used to provide visible light irradiation for the photocatalytic degradation of MB. Before irradiation, a fabric sample of square shape (1.5 × 1.5 inch²) containing 0.14 mg of the developed photocatalyst and 40 ml of freshly prepared solution of MB (1 × 10⁻³) were stirred continuously at 250 rpm for 30 min in a glass reactor to attain the equilibrium adsorption/desorption between textile substrate-based photocatalyst and MB. For each pre-determined irradiation time, about 2 ml of the reacted solution was withdrawn. A UV–Vis–NIR spectrophotometer (UV-3600, Shimadzu) was used to estimate the residual concentration of MB at 664 m (λ_max of MB).

3. Results and discussion

3.1. Reaction mechanism for the synthesis of graphitic carbon nitride, and attachment to the fabric structure

The reaction scheme for graphitic carbon nitride (g-C₃N₄) formation using urea precursor is given in Fig. 1. The urea precursor undergoes a sequence of pyrolysis-generated condensation reactions related to the release of ammonia gas for melamine formation (Step 1–4) which undergoes a nucleophilic addition reaction to form melam (Step 5). Upon further raising the temperature to 400 °C, melam is converted to melem (Step 6), which then polymerizes into the final g-C₃N₄ product with subsequent elimination of ammonia gas (Step 7). The possible structure of iron-doped graphitic carbon nitride is shown in Fig. S1 (Supplementary Information: SI file).

Fig. 1.

Reaction scheme for graphitic carbon nitride (g-C₃N₄) formation from urea precursor.

The prepared nanocomposites were deposited on the surface of pure cotton fabric. As cotton fibers are composed of cellulosic structures. Due to the enrichment of anionic sites, free hydroxyl and carboxylic acid groups present on the substrate, the fibers were able to make possible ionic attraction and hydrogen bonds. Furthermore, due to the heterogenic nature of cotton cellulose and voids present in fiber and textile structure, further uptake of nanocomposites was supported.

3.2. Photocatalytic reduction of organic pollutant

Photocatalytic behavior of the developed nanocomposites doped with different concentrations of ferric was determined by the photodegradation of MB (1 mM, initial concentration) under visible light (350-W xenon light). The ultraviolet light (400 nm) was filtered out during the photodegradation process. It is important to note that without the addition of developed photocatalysts the characteristic peak of MB at 664 nm (λ_max) does not disappear even after 48 h.

It is obvious from Fig. 2, that under the same conditions of the reaction mixture, the addition of developed nanocomposites results in a decreased intensity of the characteristics peak of MB. The gradual reduction in the peak of MB at 664 nm (λ_max) continues until it disappeared, which indicated that MB has significantly reduced to LMB, with a clear change of color from blue to transparent (Fig. 4f). Depending upon the catalytic efficiency of the various nanocomposites, the photocatalytic reduction process is completed at different intervals of time (Fig. 2).

Fig. 2.

UV–vis absorption spectra (a–d) for the photodegradation of MB in the presence of developed fabricated photocatalysts; Sample F3 (a) Sample F7 (b) Sample F8 (c) Sample F9 (d), Plot of ln(A_t/A_o) versus time for reduction of MB dye to LMB (e), and optical image of MB (right) and reduced LMB (left) (f).

Fig. 4.

Digital photographs of i) virgin ii) g-C₃N₄/Fe coated iii) after degradation reaction iv) after washing v), recycled cotton fabric (sample F9), and vi) MB before degradation (left) and after degradation (right).

The effect of the developed photocatalysts (P1–P5) dose on the reaction kinetics was evaluated by applying the various content of catalysts by coating process (1–3 coating cycle). The results for the reduction of MB using different photocatalysts (P1–P5) are summarized in Table S2 (SI file).

It is obvious from the results that the rate of MB reduction has increased with the increasing amount of developed photocatalysts. Furthermore, doped nanocomposites have significantly higher catalytic rate in comparison to pure g-C₃N₄ samples. Initially, the doping of g-C₃N₄ resulted in an increased catalytic rate until it reached an optimum level (P3, GF2). Further, an increase in ferric doping resulted in decreased reduction rate of MB. For clarity and ease of understanding, the real-time degradation of MB in the presence of our best sample (P3; F7, F8, F9) was monitored using UV–vis spectrograms and compared with samples F3 (Fig. 2a–e). The photocatalytic degradation process of the MB was fitted to pseudo-first-order kinetics and the reaction rate constant k_app can be determined as the corresponding slope of the fitting line and the corresponding results are given in Fig. 2e. Fig. 2f shows that the dye solution is completely clear after degradation.

The degradation rates of Sample P1 containing pure g-C₃N₄ nanocatalyst are lower compared to other samples. It can be attributed to the recombination of photogenerated electron-hole pairs throughout the monomeric carbon nitride which restricts quantum efficiency improvement. It is important to note that in the presence of fabric samples (F3 and F9) and irradiation of visible light, the MB degrades almost completely (99.8 %) with a reaction rate constant (K_app) of 0.16 and 0.78, respectively. We found that the F9 sample has 4.9 times higher catalytic rate compared to the F3 sample, containing pure g-C₃N₄ nanocatalyst. Indicating that the catalytic performance of g-C₃N₄ nanocatalyst can be significantly improved by doping with the suitable metallic dopant.

The catalytic activity of the developed photocatalyst can be attributed to the various reactive species (h+, ∙OH, ∙O₂⁻, and ∙OH⁻) that are generated on visible light irradiation. On exposure to visible light, the electrons jump from the valence band to the conduction band, where they react with the oxygen (O₂) that is absorbed on the photocatalyst surface and produce ∙O₂. The produced ∙O₂ plays a vital role in the photolytic degradation of MB [23]. Ferric oxide, in its pure form, can be excited with visible light due to its large bandgap energy. However, the homogeneous structure of ferric dopped g-C₃N₄ facilitates the electron excitation and their movements in the sub-band and conduction band of ferric oxide. Thus, the holes on the VB of the dopant react with OH−/H₂O to produce ∙OH. Furthermore, these holes may have a direct role in the photocatalytic degradation of MB. Ultimately, reactive oxygen species (∙OH, h+, and O₂) attack MB, causing it to be oxidized. In the meantime, due to the internal electric field, the electrons present in the conduction band of the dopant may migrate and combine with holes in the valence band of graphitic carbon nitride. Thus, these electrons and holes present in the g-C₃N₄ and dopant, respectively, may result in enhanced reduction and oxidation of the developed nanocomposites [24,25]. Therefore, the prepared heterogeneous structure of the ferric doped g-C₃N₄ nanocatalyst greatly improved the photocatalytic activity. The comparative analysis for the catalytic activity of various catalysts is summarized in Table S3.

The photocatalytic stability of the catalyst is an important factor to evaluate its performance. For this, after the completion of the MB degradation, the fabric samples coated with the developed photocatalysts were removed, washed with deionized water, and used again after drying. The catalytic efficiency was evaluated 5 times and it was found that the developed photocatalysts were stable up to 5 consecutive cycles with a conversion efficiency of 99.8 %. Fig. 3 indicates that the developed samples have exceptional catalysis behavior even after 5 successive cycles. This behavior can be attributed to the structural integrity of the nanocomposites that are firmly supported on the textile substrate. This stability can be due to the enhanced aqueous stability of the developed photocatalysts. For the clarity and ease of understanding of the sample F9 digital photographs shown in Fig. 4 (i) virgin ii) g-C₃N₄/Fe coated iii) after degradation reaction iv) after washing v), recycled cotton fabric material, and (vi) MB before degradation (left) and after degradation (right). It is evident from the results that structural integrity of the sample does not change significantly even after 5 successive cycles.

Fig. 3.

Catalytic efficiency of developed nanocomposite (sample F9) after repeated use (error bars indicate the standard deviation of five (5) replicates).

3.3. FTIR

The chemical structure of the developed photocatalyst was revealed by the FTIR analysis and the results are shown in Fig. 5. The sharp bands at around 811 cm⁻¹ and 1425 cm⁻¹ can be attributed to the breathing modes of tri-s-triazine units. The absorption bands in the range of 1000 cm⁻¹ to 1650 cm⁻¹ can be due to typical stretching modes of the heterocyclic C–N and they arise from the extended C₃N₄ arrangement. The absorption band at 1317 cm⁻¹ is attributed to the stretching vibrations of C N. The broad spectrum in the range of 2970 cm⁻¹ to 3450 cm⁻¹ is due to the –NH stretch and hydroxyl (OH) functional groups, present on the surface of the photocatalysts due to the surface bonded H₂O molecules [26,27].

Fig. 5.

FTIR spectra of various photocatalysts, developed in this study.

3.4. XRD of the nanocomposites

The crystal structure of the developed photocatalyst was determined by the XRD pattern using CuKα radiation, operated at 40 kV, 250 mA, and the results are shown in Fig. 6. It can be seen from the XRD pattern that there was a clear and strong peak around 27.1° in pure g-C₃N₄ and ferric doped nanocatalyst. It can be attributed to (002) plane due to the periodic stacking of layers of g-C₃N₄, indicating that the structural integrity of the developed nanocomposites is dominated by the g-C₃N₄ [28]. Another peak, with relatively low intensity at around 12.9°, can be attributed to the (100) plane and it arises due to the in-plane structural packing motif of g-C₃N₄ (hole-to-hole distance of nitride pores). The peaks of sample GF2, exhibited at 16.9°, 19.8°, 24.7°, 27.0°, 32.2°, 36.7°, and 41.5° are corresponding to the (111), (211), (012), (002), (220), (110), and (311) planes of ferric doped g-C₃N₄ nanocomposites [29]. It is evident that the new crystallites appear at the doping of g-C₃N₄ with ferric until the optimum doping level (Sample GF2). The addition of ferric beyond the saturation level results in the amorphous structure of the developed nanocomposites.

Fig. 6.

XRD pattern of the synthesized nanocomposites.

3.4.1. Scanning electron microscopy (SEM)

Scanning electron microscopy was employed to observe the deposition of g-C₃N₄ and g–C₃N₄–nanosheets/α-Fe₂O₃ on the cotton fabric surface. The SEM image in Fig. 7 (a) is showing the surface of cotton fibers without coating, and (b) is showing the dense coating of g-C₃N₄ (like a paste). While the scanning electron microscopy of g–C₃N₄–nanosheets/α-Fe₂O₃ coated samples is shown in Fig. 7 (c, d, e, and f).

Fig. 7.

SEM images for untreated cotton (a), treated fabric GF0 (b), treated fabric GF1 (c), treated fabric GF2 (d), treated fabric GF3 (e), and treated fabric GF4 (f).

The image revealed the nano to micrometer scale of g–C₃N₄–nanosheets/α-Fe₂O₃ particles deposited on the fabric surface. Ferric doping is creating rough irregular clusters with rough surfaces, small agglomeration, and quasi-spherical in shape. The even distribution of the microparticles on the fabric surface was also visualized. Emphasizing the agglomeration is not followed on the larger part of the synthesized materials. Secondly, the deposition behavior was also analyzed with an increase in the concentration of ferric (0–4 ml during doping) and the number of coating cycles (1, 2, and 3). With the increase in the number of coating cycles, the deposition of g–C₃N₄–nanosheets/α-Fe₂O₃ was found more uniform and denser. Furthermore, the elemental composition of the g–C₃N₄–nanosheets/α-Fe₂O₃ coated fabric is also shown with color SEM images (Fig. S2) and an EDX Table S3. The higher contents of ferric were found with an increase in coating cycles (1, 2, and 3) for GF2 samples. The colored images of the elemental analysis, determined by the EDX are also shown in Fig. S2 (SI file). Table S4 (SI file) showed the elemental composition of g–C₃N₄–nanosheets/α-Fe₂O₃ coated fabrics determined by EDX analysis.

3.5. Antibacterial activity

ISO 20743 transfer method was followed to carry out quantitative antibacterial analysis of developed samples. The untreated cotton fabric (control) and treated fabrics (GF0, GF1, GF2, GF3, and GF4) were tested against both gram-positive (S. aureus) and gram-negative (E. coli) bacteria and obtained results have been shown in Table S5 (SI file). The results indicated that the antibacterial activity of treated samples increased with the increase in the concentration of doped material i.e., GF0 (P1, zero, concentration of FeCl₃·6H₂O (ml)) was least effective (75 %) whereas the maximum bactericidal effect (99.99 %) was observed in the case of sample GF4 (P5, concentration of FeCl₃·6H₂O (4 ml)) against S. aureus and E. coli.

It was also observed that for each set of coated fabrics, the antibacterial activity increased with increasing the number of coating layers. In the case of GF0, fabric with a single coating showed 62 % bacterial growth reduction whereas fabric with 3 coating layers was found to have a 75 % reduction in bacterial colonies.

From the results, it has been found that the fabric with a single coating layer of GF3 formulation was best suited for S. Aureus as it killed 99.99 % bacterial colonies (Fig. S3 (SI file)) while 99.99 % E. Coli bacterial reduction was observed for the fabric with 3 coating layers of the same formulation i.e., GF3. The results indicated that complete reduction (99.99) of E. coli occurred at a higher concentration of applied coating materials as compared to S. Aureus. It could be due to the fact that the cell wall of E. coli (gram-negative bacteria) is thicker than the cell wall of S. Aureus (gram-positive bacteria) which causes the attenuation of the penetration process of g-C₃N₄ into the bacterial cell membranes [30,31].

The antibacterial action of the sample GF0 (fabric coated with g-C₃N₄) is due to the graphitic carbon nitride as it has an intrinsic tendency to kill microbes. The g-C₃N₄ exhibits antibacterial action when it is exposed to visible light. Under visible light, excessive free radical species are produced in g-C3N4 which interacts with the bacterial cell membranes and ruptures it leading to apoptosis. The antibacterial activity of fabrics coated with iron-doped g-C₃N₄ was remarkably high as compared to the fabrics coated with pristine g-C₃N₄ and 99.99 % bacterial growth reduction for both gram-negative and gram-positive bacterial strains was achieved with doped g-C₃N_4. Considering the structural changes that occurred in the g-C₃N₄ after doping with FeCl_3, the best possible explanation for the extraordinary antibacterial action of doped g-C₃N₄ could be the presence of Fe⁺² ions in its structure. The Fe⁺² ions interact with essential components of bacterial cell membranes ultimately leading to cell death. The Fe⁺² ions undergo reduction to Fe⁺ in the cytoplasm and generate reactive hydroxyl free radicals. These radicals are capable of reacting non-specifically with nucleic acid, lipids, and proteins and interrupt their structures ultimately causing bacterial cell death [32,33].

3.6. Antiviral activity

The evaluation of the antiviral efficiency of treated fabric (GF3) and untreated fabric (control) was done through a standard quantitative test method. Both control and iron-doped g-C₃N₄ loaded samples were selected. It is obvious from previous studies that metallic NPs exhibit antiviral [34,35]. The iron-doped g-C₃N₄ showed antiviral activity against different viruses types which is attributed to direct iron-doped g-C₃N₄ binding with viral enveloped glycoproteins, thus, inhibiting the penetration of viruses inside host cells, though the action mechanism is not explained well [[36], [37], [38], [39]].

Cotton alone does not show any type of antiviral activity which shows that antiviral behavior associated with composites is due to composite bonded with iron-doped g-C₃N₄. The treated fabric was found to be most effective against Influenza virus and Feline Calicivirus, thus, achieving 99.45 % reduction (2.19 log10) and 99.52 % (2.30 log 10) at 2 exposure hours as compared to the control fabric as given in Table S6 (SI file). The size effect of iron-doped g-C₃N₄ composites on the antiviral activity shows interactive selectivity of Influenza Virus A with smaller particles, as reported previously for other virus types [38].

4. Conclusion

The current research reported the development of textile-based free-standing highly efficient photocatalysts containing g–C₃N₄–α-Fe₂O₃ nanocomposites by simple, versatile, sustainable, and low-cost synthesis techniques. The results revealed that the rate of MB reduction has increased with the increasing amount of developed photocatalysts and maximum degradation i.e., the optimum level was achieved in the case of sample GF2 P3. After that, the increase in the concentration of iron catalyst resulted in decreased degradation. Further, the morphology of coated fabrics was studied using SEM images, and the existence of elements was confirmed through EDX and XRD techniques. The results indicated that the antibacterial activity of treated samples increased with the increase in the concentration of doped material. The antibacterial activity of fabrics coated with iron-doped g-C₃N₄ was remarkably high as compared to the fabrics coated with pristine g-C₃N₄. Moreover, treated fabric (GF3) the iron-doped g-C₃N₄ showed antiviral activity against different viruses. Furthermore, the unique recyclability of the developed product makes it ideal for commercial applications.

Data and code availability

Data will be available on request.

Supplementary information

Added.

Ethical approval

The current study does not include human or animal subjects.

CRediT authorship contribution statement

Munir Ashraf: Conceptualization, Methodology. Fiaz Hussain: Formal analysis, Methodology. Humera Aziz: Conceptualization, Methodology. Umair Riaz: Formal analysis. Muhammad Hamzah Saleem: Formal analysis. Amjed Javid: Conceptualization, Formal analysis. Anum Nosheen: Investigation. Azam Ali: Investigation. Mohammad K. Okla: Resources, Software. Ibrahim A. Saleh: Resources, Software, Writing – original draft. Ibrahim A. Alaraidh: Resources, Software, Writing – review & editing. Mostafa A. Abdel-Maksoud: Resources, Software, Writing – original draft.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

The following is the Supplementary data to this article: