A synergistic self-cleaning and antibacterial studies of photocatalytic carbon nitride/polypyrrole coated cotton fabrics for smart textile application

Smart fabrics are one of the progressing technologies in this era especially in the field of self-cleaning and stain removing applications. Recent years, photocatalyst based self-cleaning technology seek much attention in the fields of therapeutic textiles, athletic clothing, defense uniforms and outdoor material. In this present work, the carbon nitride (CN) blended with conducting polypyrrole polymer (PPY) were coated over cotton fabrics by modified pad-dry cure method. The CNPPY composite coated cotton fabric shows enhanced photocatalytic degradation efficiency of 96.5% compared to individual coatings of CN and PPY. The successful demonstration of photocatalytic stain removal and self-cleaning properties was achieved through the utilization of CNPPY composite-coated cotton fabric. This breakthrough was accomplished with minimal water consumption (1 cm2/ml), employing different colored stains under solar irradiation. Also, the CNPPY composite coated cotton fabric exhibited excellent resistance to bacterial growth. The dual advantages of photocatalytic antibacterial activity and self-cleaning of CNPPY composite coated cotton fabric led to sustainable, innovative textile applications with significant lower water consumption during washing process.


Introduction
Today, the textile industry offers a vast and diverse range of fabrics that cater to a multitude of requirements and preferences.From natural bers like cotton, silk, and wool, to synthetic materials such as polyester, nylon, and spandex, there is a fabric available for every purpose and occasion.These fabrics serve a multitude of applications, including clothing, home textiles, technical textiles, and industrial applications (Yetisen, Qu et al. 2016).Smart textile fabrics have been developed for various applications, including anti-microbial(El-Nahhal, Elmanama et al. 2018),UV protection (Sricharussin, Threepopnatkul et al. 2011), embedded sensor (Sedighi, Montazer et al. 2014),Supercapacitors (Selvam and Yim 2023),Li Ion batteries (Praveen, Sim et al. 2021), hydrophobicity (Jeyasubramanian, Hikku et al. 2016) and dye degradation (Baruah, Downer et al. 2019).In recent times, there has been a growing signi cance attributed to self-cleaning fabrics, which possess the remarkable ability to effectively remove dirt, stains, and other foreign substances from their surface.The development and utilization of self-cleaning textile fabrics offer a promising opportunity to decrease the reliance on surfactants during fabric washing, thereby contributing to the mitigation of water pollution(Ahmadi and Igwegbe 2018).Self-cleaning fabrics play a pivotal role in the textile industry today, as they signi cantly reduce both washing time and water pollution.One effective approach in the production of self-cleaning fabrics involves fabricating photocatalytic materials and coating them onto textile surfaces.The TiO 2 (Doganli, Yuzer et  this process presents certain technical challenges that need to be overcome.Both direct and indirect methods of coating photocatalysts onto fabric have their limitations.One of the primary concerns is the effect of various parameters on the coating process.Factors such as coating temperature, solvent selection, and coating atmosphere can signi cantly in uence the properties of the fabric.The temperature at which the coating is carried out needs to be carefully controlled to prevent any adverse effects on the fabric, such as changes in texture, color, or mechanical properties.Similarly, the choice of solvent plays a vital role in achieving uniform coating and avoiding damage to the fabric's structure.The coating atmosphere, including humidity and oxygen levels, can also impact the adhesion and stability of the photocatalyst coating.Another challenge lies in the limited range of light absorption exhibited by many photocatalysts.Traditionally, most photocatalysts primarily absorb ultraviolet (UV) light, which comprises only a small portion of the solar spectrum.This limited absorption range restricts the photocatalytic activity of the coated fabric to speci c lighting conditions, such as direct exposure to UV light sources.To overcome this limitation, researchers have been exploring innovative approaches to enhance the light absorption capabilities of photocatalysts, particularly by expanding their absorption into the visible light range.Out of many visible light active photocatalyst, a Carbon Nitrite (CN) semiconductor has played an emerging role in many applications such as photocatalyst (Ong, Tan et  without puri cation.The study utilized 100% cotton (CT) fabric with Cambric Yarn count of 60s, warp per inch 120, weft per inch 80, warp to weft ratio 1:1, oat density 9600, fabric weight 109 gms/Sqmts, and Woven made construction, which was purchased from Varsha cotton mills private limited, Erode, Tamilnadu, India.
CN was synthesized from urea using the thermal polymerization method, where the sample was heated up to 550°C at a ramp rate of 15°C min-1 for 2 hrs, followed by retention at the same temperature for another 2 hrs.The resulting yellow-colored akes were collected after cooling.The oxidative chemical polymerization method was employed to prepare the PPY polymer, where 30 ml of 0.15M pyrrole monomer was stirred at 0°-5°C and 77 ml of 0.01M FeCl 3 oxidant was added dropwise for 2 hrs.The dark-colored polymeric precipitate was then obtained and stored at 70°C for 6 hrs.

CNPPY composite
The carbon nitride/polypyrrole (CNPPY) composite was synthesized through the oxidative chemical polymerization method.Firstly, 1g of CN powder and 30 ml of 0.15M pyrrole monomer were stirred for 2 hrs.Then, a 77 ml of 0.01M FeCl 3 oxidant solution was gradually added at 0°-5°C temperature.The initial yellow mixture turned into a dark colored solution.The obtained dark colored polymeric precipitate was washed with distilled water and stored at 70°C for 6 hrs.Various concentrations (25, 50, 100 and 150 mmol) of polypyrrole coated CN were also synthesized following a similar procedure for optimization.
The structure of coated cotton fabrics was analyzed using UV-Visible Spectroscopy and Fourier Transform Infrared Spectroscopy, while SEM coupled with EDAX analyzer was used to study the coated fabrics' surface morphology.

CNPPY nanocomposites coated over cotton fabrics
For the incorporation of CNPPY over cotton fabrics, the modi ed pad dry cure method was employed.The CNPPY coating was mixed with binder and solvent in a ratio of 85:15 to obtain a homogeneous mixture using a mortar for 60 minutes.The mixture was applied to the cotton fabric with constant pressure, rolled over the fabric, and then dried at 70°C.

Characterization technique
The surface morphology of composite materials CT, CNCT, PPYCT, and CNPPYCT was investigated by means of Fourier transform infrared (FT-IR) spectra of the composites were acquired using a powder sample technique with a spectral range of 400 to 4000 cm − 1 employing a PerkinElmer Spectrum Two FT-IR Spectrometer.The SEM-EDX analysis, the samples were coated with a conductive material and imaged using a Carl Zeiss SEM-EDX.The UV − vis diffuse re ectance spectra were obtained by means of a spectrophotometer (Shimadzu UV-2700) using BaSO 4 as the re ectance standard.Thermal stability of CNCT and CNPPYCT sample was calculated under nitrogen atmosphere using a thermogravimetric analyzer (STA7200 HITACHI).The samples were ground to a ne powder before the analysis, and the spectra were collected over a wavelength range of 200 to 800 nm.

Antibacterial studies
The photocatalytic bactericidal effect of CNPPY composites on E. coli ATCC 25922 was quanti ed using the viable count assay method.A prepared bacterial culture was used as inoculum for the assay, where 1×108 bacterial cells were mixed with 30 ml of Luria Bertani broth and inoculated over CT and CNPPY coated fabrics.A control of 1×108 bacterial cells was also maintained.The tubes were incubated in a dark environment using a bacterial incubator for 4 hours, after which the feasible bacterial cells were harvested and added over Luria Bertani agar plates.The cultivated sample plates were incubated at 37ºC for 18 hours and the CFU values of CT and CNPPYCT were visually counted and tabulated.A similar experimental procedure was performed for photo catalytic antibacterial activity under stimulated solar irradiation.

Photocatalytic experiments
The cotton fabrics coated with CNPPYCT of size 5x5 cm were immersed in 1x10-4 M of RhB dye solution and kept in the dark for 1 hour.Following this, the sample was irradiated using a solar simulator at room temperature.During the irradiation, absorbance studies were conducted at 30-minute intervals using 5 mL of RhB solution.The photocatalytic self-cleaning property of CNPPY-coated fabrics was evaluated using various colored dyes as model stains, including RhB, Methyl Violet, Methylene Blue, and Malachite Green dyes.The fabrics were stained with different colored dyes and their discoloration was tested under solar irradiation.Photographs were taken at 10-minute intervals to analyze the photocatalytic self-cleaning performance of the CNPPY-coated fabrics.

Morphological Analysis
The scanning electron microscopic (SEM) images of uncoated and photocatalyst-coated cotton bers are presented in Fig. 1(a-d).The images in Fig. 1(b), (c), and (d) demonstrate that the bers of the cotton fabric are coated with CN, PPY, and CNPPY composite materials.These results validate the e cacy of the modi ed pad dry cure method in successfully coating pre-synthesized photocatalyst materials onto the fabric bres.
The Fig. 2 (a-d

FTIR Analysis
The Fourier transform infrared (FTIR) spectra of uncoated cotton fabric (CT) and CT coated with carbon nitride (CN), polypyrrole (PPY), and CNPPY are presented in Fig. 3(a-d).The pure CT spectrum in Fig. 3(a) exhibits absorption peaks at 3340 cm − 1 , 2902 cm − 1 , and 1371 cm − 1 , which correspond to the stretching and bending vibrations of the OH and CH 2 groups in the cellulose matrix (Himmelsbach, Hellgeth et al. 2006, Yuen, Yip et al. 2012).A weak peak at 1638 cm − 1 corresponds to the asymmetric stretching vibration of C = O, further con rming the presence of cellulose matrix in the cotton fabric (Himmelsbach, Hellgeth et al. 2006).In Fig. 3(b), the bands observed at 1234 cm − 1 , 1316 cm − 1 ,and 1620 cm − 1 represent the -C = N-and C-N moieties present in the carbon nitride structure, while the bands at 801 cm − 1 and 1403 cm − 1 correspond to the presence of the s-triazine ring in the carbon nitride matrix (Shahbaz, Urano et al. 1984).The interactions between CN and the cotton fabrics are con rmed by the broad bands between 2800 cm − 1 and 3500 cm − 1 .In Fig. 3(c), the peaks at 781 cm − 1 , 918 cm − 1 , 1315 cm − 1 , and 1544 cm − 1 correspond to the C-H, C = C, and C-N bonds, con rming the presence of PPY coated over the fabric.
These results are consistent with previous ndings reported in the literature (Varesano, Vineis et al. 2013).In Fig. 3(d), the predominant peaks observed at 781 cm − 1 , 918 cm − 1 , 1544 cm − 1 , and 1315 cm − 1 correspond to the C-H, C = C, C-O-C, and C-N bonds.The bands at 1234 cm − 1 and 1620 cm − 1 con rm the presence of CN-PPY coated over the cotton fabrics.Figure 4 illustrates the bonding interactions between CN, PPY, and cotton fabrics based on the obtained FTIR results.

Optical Analysis
Figure 5 displays the optical absorbance spectra of CT, PPYCT, CNCT, and CNPPYCT.It is evident that CT and PPYCT do not exhibit any light absorption behavior in the UV and visible regions.However, CNCT shows effective light absorption between the 300-550 nm region.Furthermore, the CNPPYCT composite noticeably shifts the light absorbance range a few nanometers towards the visible region.These results con rm that CNCT and CNPPYCT can be utilized for photocatalytic activity under natural sunlight.
The band gaps of CNCT and CNPPYCT were calculated using Tauc's plot, as shown in Fig. 6.The calculated band gap values of CNCT and CNPPYCT are 2.82 eV and 2.81 eV, respectively, which are consistent with previously reported literature (Wang, Maeda et al. 2009).

TGA Analysis
The thermogram presented in Fig. 7. provides visual evidence of the changes occurring in the material under investigation.In this case, the thermogram illustrates a decrease in mass below 100°C, and this phenomenon is attributed to the liberation of water molecules that were previously adsorbed on the cotton fabrics, polypyrrole (PPY), and carbon nitride (CN).Both samples analyzed, CNCT and CNPPYCT, exhibited reductions in mass.The CNCT sample showed an approximate mass reduction of 14%, while the CNPPYCT sample exhibited a slightly lower reduction of around 8%.These mass reductions can be attributed to the removal of hydrogen from the carbon nitride and cotton fabrics, respectively.As the temperature increased within the range of 370°C to 400°C, another notable transformation took place.
The α-cellulose present in the cotton fabrics underwent degradation, which refers to the process of breaking down large polymer chains into smaller units (Shahedifar and Rezadoust 2013).This degradation resulted in the formation of aliphatic char, which subsequently converted into aromatic structures.During this process, water, methane, carbon monoxide, and carbon dioxide were released.As a result, the CNPPYCT sample exhibited a better ame-retardant effect due to the minimal generation of ammable gases and a low decomposition rate.This indicates its improved ability to resist combustion compared to the CNCT sample, making it more suitable for applications requiring ame resistance(Xu, Wang et al. 2017).

Photocatalytic Studies
The degradation of Rhodamine-B (RhB) dye under light irradiation for 120 mins was investigated, and the optical absorbance of RhB dye measured at different time intervals with CT, PPY, CN and CNPPY are presented in Fig. 8 (a, b, c, and d).The optical absorbance spectra of CT indicate a minor decrease in the absorption spectrum corresponding to the RhB dye adsorbed over the surface of CT, but there is no photocatalytic dye degradation.In contrast, PPYCT shows higher dye adsorption tendency than the pure cotton fabrics due to the interactions between dye molecules and PPY, but the degradation e ciency of PPYCT is almost negligible after light irradiation.
Before light irradiation, the CNCT and CNPPYCT show strong RhB dye adsorption, indicating the existence of a larger surface area over the cotton fabric by CN and PPY.After light irradiation, the amount of RhB dye molecules slowly decreases due to the photodegradation of dye molecules.A hypochromic shift is observed at 554 nm after 60 minutes of light irradiation in Fig. 8 (c and d), indicating the residues of photodegraded dye molecules and the formation of its intermediates (Cui, Goldup et al. 2015).The above results demonstrate that CNPPYCT exhibits excellent photocatalytic activity compared to CNCT, PPYCT, and CT.
The C/C 0 vs time plot were estimated, which are shown in Fig. 9.The results indicate that the CNPPY composite coated cotton fabric exhibited the highest photocatalytic dye degradation e ciency of 96.5%, which is signi cantly higher than that of the individual CN (87%) and PPY (58%) coatings over the cotton fabrics.The superior photocatalytic activity of CNPPY composite can be attributed to several factors, including the broadening of the light-harvesting region, which promotes photocharge carrier generation and accelerates the photocatalysis reaction rate; the enhanced dye adsorption rate by PPY through π-π* interactions; and the high charge separation at the CNPPY hetero interfaces, which signi cantly lowers the recombination rate(Ovando-Medina, Dávila-Guzmán et al. 2018).The photodegradation e ciency of CT, PPYCT, CNCT and CNPPYCT coated fabrics was calculated and is shown in Fig. 10.The results clearly show that the degradation level of CNPPYCT reaches 96.5% after 120 min of photocatalytic reaction, while it was 0%, 58%, and 87% for CT, PPYCT, and CNCT respectively.The photocatalytic activities of the coated cotton fabrics follow the order CNPPYCT > CNCT > PPYCT > CT.To validate the stability and reusability of the photocatalyst coating on cotton fabric, a benchmarking CNPPY composite coated fabric was washed, dried, and reused for several experimental cycles.
In Fig. 11, the CNPPYCT reveals that there is no signi cant photodegradation e ciency loss for four cycles.The recyclability test was able to understand that the CNPPY composite was rmly attached to the cotton fabric and are stable for photocatalytic self-cleaning application for longer life cycle.

Antimicrobial Analysis
To evaluate the antimicrobial e cacy of the coated fabric, the bacterial growth inhibition was assessed using the colony count method.Figure 12 illustrates the antimicrobial results of both uncoated and photocatalyst-coated cotton fabrics, indicating that the CNPPYCT composite exhibits highly effective resistance against Gram-negative bacteria Escherichia coli ATCC 25922 compared to CN and PPY.The CFU/ml values of E. coli are listed in Table 1 for further clarity.The superior antibacterial activity of the CNPPY composite can be attributed to the formation of photocatalytic reactive oxidation species, such as  Self-Cleaning Analysis The investigation of the self-cleaning property of CNPPY coated fabrics involved using various colored dyes as model stains, which were kept under simulated solar irradiation for 2 hours and presented in

Conclusion
The CN and PPY composite were synthesized using oxidative chemical polymerization, and a modi ed pad dry cure method was employed to coat the cotton fabrics with PPY, CN, and CNPPY.Elemental analysis and FTIR studies con rmed the presence of PPY and CN on the cotton fabrics.The addition of PPY to the CN-coated fabric resulted in improved photodegradation e ciency, stability, and reusability.Furthermore, the CNPPY composite-coated fabrics exhibited excellent photocatalytic self-cleaning properties and antimicrobial activity.This study provides a promising avenue for the development of smart textiles that utilize photocatalytic self-cleaning, potentially reducing the amount of water and surfactant required and minimizing water pollution.The tauc plot of CNCT and CNPPYCT.

Declarations
Page 22/29 The TGA analysis of CNCT and CNPPYCT.
Page 23/29      Mechanism of photo catalytic stain removal under solar irradiation.
OH − and H 2 O 2 (Abbas, Shao et al. 2016, Ekande and Kumar 2021), which degrade the cytoplasmic membrane and bacterial cell wall, leading to the release of cellular contents such as RNA and proteins, ultimately resulting in complete cell lysis and mineralization of the organism(Abbas, Shao et al. 2016, Ekande and Kumar 2021).These ndings suggest that the CNPPY composite-coated cotton fabric possesses signi cant antimicrobial activity against bacteria.

Figs. 13 and 14 .Figure 14 .
Figs.13 and 14.As shown in Fig.13, the colored dye-stained fabrics changed from their respective colors to colorless under light irradiation, indicating that the CNPPY coated fabrics have self-cleaning activity and the colored dye stains are removed by the photocatalytic process.Based on these experiments, a photocatalytic mechanism for the self-cleaning and stain

Figure 9 C
Figure 9