In-situ synthesis of Cu₂O on cotton fibers with antibacterial properties and reusable photocatalytic degradation of dyes

Graphical abstract

Highlights

• •In-situ synthesis of cuprous oxide (Cu₂O) on cotton and coating with nanocellulose, the Cu₂O crystal structures was ideal octahedron and not easy to ditch.
• •COCO-5 exhibited high photocatalytic degradation of dyes, and the catalytic degradation process was monitored by comprehensive technical tests.
• •COCO-5 exhibited highly effective antibacterial properties against Staphylococcus aureus and Escherichia coli.
• •COCO-5 maintained high stability after multiple photocatalytic degradation of dyes or antibacterial tests, and the mechanical properties of this composite had not decreased.

Abstract

In this study, the cotton fabrics/cuprous oxide-nanocellulose (Cu₂O-NC) flexible and recyclable composite material (COCO) with highly efficient photocatalytic degradation of dyes and antibacterial properties was fabricated. Using flexible cotton fabrics as substrates, Cu₂O were in-situ synthesized to make Cu₂O uniformly grew on cotton fibers and were wrapped with NC. The photocatalytic degradation ability of COCO-5 was verified by use methylene blue (MB), the degradation rate was as high as 98.32%. The mechanism of COCO-5 photocatalysis and the process of dye degradation were analyzed by using electron paramagnetic resonance (EPR) spectrum, transient photocurrent response (TPR) spectrum, Fourier transform infrared (FTIR) spectroscopy and ion chromatography (IC). This study analyzed the complete path from electron excitation to dye degradation to harmless small molecules. Qualitative and quantitative experiments demonstrate that COCO-5 has high antibacterial activity against S. aureus and E. coli, the highest antibacterial rate can reach 93.25%. Finally, the stability of COCO-5 was verified by recycling and mechanical performance tests. The textile-based Cu₂O functionalized material has photocatalytic degradation and antibacterial properties, and the preparation process is simple and convenient for repeated use, so it has great potential in wastewater treatment containing dyes and bacteria.

1. Introduction

The citizens of the bustling metropolis drink clean, non-toxic tap water, but water pollution is still a major threat to human survival in underdeveloped areas [1], [2]. There is always a tendency for industrial areas to migrate to less developed regions because of low labor costs and relatively weak environmental regulations [3], [4]. In particular, the recent COVID-19 outbreak reminds people that the threat of microorganisms and viruses to humans is also huge. It is better to develop an inexpensive material to eliminate the source of disease, that is, water pollution. The dyes in wastewater can kill aquatic plants and plankton, causing ecosystem collapse, which is very difficult to recover. If organism (including humans) drink wastewater containing dyes for a long time, even at lower concentrations, they can cause cancer [5], [6], [7], [8]. Wastewater containing a large amount of bacteria is a hotbed of disease, which not only causes various diseases, but also promotes bacterial growth and contaminates more water and water containers [9], [10], [11]. Therefore, researchers have been investing a lot of energy in the research of wastewater treatment materials.

Nanocellulose (NC) is an ideal environmentally and friendly material, it is green, sustainable and cheap. NC can be derived from plants, bacteria and marine shellfish, which have the advantages of being degradable, flexible, hydrophilic and rich in surface groups [12], [13]. NC has used as an interface “bridge” between inorganic nanomaterials and polymer materials, so NC is an ideal choice in interface chemistry of composite materials [14], [15], [16], [17], [18]. Cu₂O is a semiconductor material because it has a narrow band gap and a suitable conduction band to facilitate absorption of visible light and exhibits photocatalytic properties, which can be used in the field of photocatalytic degradation of dyes [19], [20]. On the other hand, Cu is abundant in nature, inexpensive, and is suitable for a large amount of synthesis. These advantages make Cu₂O industrial applications more preferred than similar photocatalysts such as TiO₂ [21], [22], [23], [24]. Yu et al. [25] used solvothermal method to prepare Zn-doped Cu₂O nanoparticles with various crystal structures, and explored the effect of Zn doping on the structure and properties of Cu₂O. Their samples used for photocatalytic degradation of ciprofloxacin, and the highest degradation rate reached 94.6%. However, the crystal structure of Zn-doped Cu₂O is not clearly resolved, and it is difficult for the nanoparticles to be recycled result in secondary pollution. Nie et al. [26] incorporated Cu₂O nanoparticles and graphene oxide (GO) nanosheets into microcrystalline cellulose (MCC) foam for photocatalytic degradation of MB. The use of GO improves the dispersibility of Cu₂O and promotes itself stratification. Although the degradation rate is improved, the dispersion of physically mixed nanoparticles is still not satisfactory and the cost of GO is too high.

This work in propose to provide a solution that is simple to fabricate, low in cost, and recyclable. In this study, Cu₂O was synthesized in-situ on cotton fabrics, NC as a “bridge” to make the dispersion of Cu₂O very uniform, and not easy to fall off. The use of cotton fabrics as a substrate allows the composite to be easily reused. Among them, COCO-5 was capable of photocatalytic degradation of 98.32% MB and was capable of degrading 85% MB after repeated use for 5 times. On the other hand, COCO-5 can deal with a wide range of dyes and exhibits strong recyclable photocatalytic degradation of complex dye wastewater. The mechanisms of photocatalytic degradation were analyzed using techniques such as EPR, TPR, FTIR and IC. Combine multiple test results to demonstrate a complete dye degradation pathway. Further, COCO-5 showed excellent antibacterial ability, and the antibacterial rates against S. aureus and E. coli reached 93.25 and 89.73%, respectively, and the antibacterial rate after 5 cycles of S. aureus was still 80.99%. Through the mechanical property test, the cotton fabrics as the base material did not exhibit mechanical failure during the recycling process. In summary, this study developed a kind of recyclable cotton fabrics/Cu₂O-NC composite materials with promising capabilities for dye wastewater treatment and antimicrobial applications. In-situ synthesis of nano-functional particles based on textile materials is a promising process route, and the ideal recyclable nanocomposites can be prepared by combining different organic–inorganic materials.

2. Experimental section

2.1. Materials.

Cotton fabrics were fabricated in our textile laboratory. Acrylic acid (AA), acrylamide (AM), Cellulose powder, hydroxylamine hydrochloride (HH, NH₂OH·HCl), copper sulfate (CuSO₄), ammonium persulfate (APS), ethanol, urea, sodium hydroxide (NaOH) and methylene blue (MB) were purchased from Aladdin Chemistry Co. Ltd (Shanghai, China).

2.2. Chemical modification of cotton fabrics and preparation of NC.

Immersed 2 cm × 2 cm cotton fabrics in the mixed solution containing 3 M AA and 3 M AM, stirred the reaction at 45 °C for 1 h, then taken out the cotton fabrics, washed it gently 5 times with deionized water, and put it in a vacuum oven to dry for 4 h. NC was obtained by dissolving cellulose powder in an alkaline urea solution (7 wt% NaOH and 12 wt% urea solution). After the reaction, the NC solutions were filtered and freeze-dried (-70 °C, 72 h) to obtain dry NC.

2.3. In-situ synthesis of octahedral Cu₂O on cotton fibers.

First prepare 5, 10, and 15 mM CuSO₄ solutions, immersed the three chemically modified cotton fabrics in these three solutions, and then used NaOH to adjust the pH of all solutions to about 12, correspondingly added 1, 3 and 5 g NC to the CuSO₄ solution in the above order (the amount of NC added were determined after preliminary experiment optimization). Next, prepared 5, 10, and 15 mL of 0.8 M HH solution, added them to the corresponding precursor solution described above, and stired the reaction at 45° C for 1 h. In this process, CuSO₄ were reduced to Cu₂O in brick-red by HH. After the reaction, the brick-red cotton fabrics were taken out, and the three samples were gently washed three times with ethanol, and then transferred to a vacuum oven for drying for 12 h. Finally, according to the added amount of NC mass, the three samples were named as COCO-1, COCO-3, COCO-5. The reaction mechanism is shown in Fig. 1 .

Fig. 1.

Schematic diagram of in-situ synthesis of Cu₂O on cotton fiber.

2.4. Characterizations.

The microscopic morphology and elemental composition of the synthesis were characterized using an Ultra 55 field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray spectroscopy (EDS). The composite structure of Cu₂O/NC was characterized using a JEOL 2100 transmission electron microscope (TEM). The contents of Cu₂O on textile fabric were quantified through Sollar M6 atomic absorption spectrometry (AAS) with air-acetylene flame. Separate hollow cathode lamps radiating at wavelengths of (Cu) 224.8 were used to determine the amount of Cu. The crystal structure was characterized using a D8 Advance X-ray diffractometer (XRD). The chemical functional group structure was characterized using a Nicolet 5700 Fourier transform infrared spectrometer (FTIR). X-ray photoelectron spectroscopy (XPS, K-Alpha) data was obtained using an electronic spectrometer. The ultraviolet absorption spectrum was characterized using a UV–visible (UV–Vis) spectrometer. The ion chromatography (IC) was carried out with instruments of Metrohm. Free radicals in the system were detected using a Bruker A300 electronic paramagnetic resonance (EPR). The transient photocurrent response (TPR) spectrum was tested using a Zahner Zennium electrochemical station. The mechanical properties were measured on Instron mechanical testing equipment.

2.5. Photocatalytic performance of dyes degradation.

Prepared 200 ppm MB solution, take three 200 mL MB solution into the beaker, put as-prepared COCO-5 (2 × 2 cm) into the beaker respectively and were stored in the dark under magnetic stirring for 120 min to reach absorption–desorption equilibrium. Subsequently, the photocatalytic reaction was performed by exposing the solution to the 350 W xenon lamp coupled with the UV cutoff filter (λ > 400 nm). The photocatalytic reactions were carried out for 120 min under irradiation. Degradation rate (%) of MB, calculated as:

$$D\left(\%\right)=\frac{C_0-C_t}{C_0}\times 100$$ (1)

where C₀ is the initial MB concentration (ppm), and C_t is the MB concentration (ppm) at time t. The photocatalytic degradation process of other dyes (i.e. cationic yellow, cationic red, anionic red, anionic yellow, neutral red) is consistent with this. All experiments of photocatalytic degradation of dyes were carried out three times, and the average value was taken.

2.6. Antibacterial performance

Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 27217) were used as model Gram-negative and Gram-positive bacteria. The plate colony counting method is used to study the antibacterial ability of samples. All materials used in the antimicrobial activity test need to be sterilized in an autoclave, and the experimental operation should be carried out in a clean bench. Approximately 5 × 10⁷ CFU/mL for bacteria and 1 × 10⁷ CFU/mL for yeast at 37 °C for 14 h to count the amount of viable microorganism colonies. Transfer 50 μL of bacterial strains to 50 mL liquid culture medium and add Incubate in a shaking incubator at 37 °C at 100 rpm for 24 h. Then, the activated bacteria were dispensed into 50 μL of liquid culture medium, which respectively contained 0.2 mg samples, and nothing was used as a blank sample for another 24 h culture. Dilute various bacterial solutions to 100 times, and then spread 20 μL of the diluted bacterial solutions evenly on the LB agar plate. The antibacterial activity of these substances can be observed by the number of colonies, and all tests are repeated at least 3 times. Microbial colonies or average colony forming units (CFU), the equation is as follows [27], [28]:

$$AR\left(\%\right)=\frac{N_0-N_1}{N_0}\times 100$$ (2)

where N₀ is the mean number of bacteria on the pure liquid medium with full cells, and N₁ is the mean number of bacteria on the COCO-5.

3. Results and discussions

3.1. Morphological observation

Firstly, the Cu₂O-NC composite sample without cotton fabrics was prepared, and its micro composite structure and crystal structure were analyzed by TEM. As can be seen from Fig. 2 a, Cu₂O were dispersed in the middle of the NC and had quadrilateral or elliptical structures of varying sizes, with Cu₂O having diameter of between about 20–40 nm. The (1 0 0) and (2 0 0) crystal planes of Cu₂O were observed under high resolution TEM, and their interplanar spacings were 0.30 and 0.21 nm, respectively (Fig. 2b) [29], [30]. The above observations prove that the Cu₂O prepared by the research method has good structures and NC assists in the dispersion of Cu₂O.

Fig. 2.

(a-b) TEM images of Cu₂O/NC and the lattice lines exhibited at high magnification.

In order to explore the optimal synthesis conditions, the concentration of CuSO₄ and NC were adjusted to prepare Cu₂O in-situ on the surface of cotton fabrics. Some significant differences in Cu₂O content of three samples was observed by FE-SEM (Fig. 3 ). The COCO-1 cotton fibers were loaded with only a small amount of Cu₂O-NC, and most of the cotton fibers were bare. At high magnification, it can be seen that the Cu₂O of octahedral structure were scattered on the surface of the fibers and is not wrapped by the NC (Fig. 3a-a2). Fig. 3b-b2 showed that the Cu₂O on the cotton fiber of COCO-3 were obviously increased, and the distribution was relatively uniform. The Cu₂O portion of the cotton fibers were wrapped by the NC, which helped prevent Cu₂O from falling off easily, but some of the Cu₂O were exposed. COCO-5 achieved an ideal composite structure, cotton fibers had been densely attached by Cu₂O-NC, while NC coated most of the Cu₂O on the surface of the fiber with some pores (Fig. 3c-c2). NC were clustered together again through the hydrogen bonds network on the cotton fibers, leaving some pores while constructing the NC three-dimensional network, which was conducive to the reaction of the liquid phase with the encapsulated Cu₂O. Furthermore, the AAS was utilized to accurate analyze content of Cu₂O on composite sample for COCO-1, COCO-3 and COCO-5 was 15.78, 21.38, and 30.27 mg/g, corresponding to the FE-SEM analyses. Notably, sample COCO-5 showed the highest Cu₂O content when obtained with the highest concentration of synthetic raw material. On the other hand, combined with some preliminary experiments (including photocatalytic degradation of dyes and antibacterial tests), the COCO-5 was the idea sample for the recyclable photocatalytic and antimicrobial applications.

Fig. 3.

FE-SEM images of (a-a2) COCO-1, (b-b2) COCO-3 and (c-c2) COCO-5.

3.2. Crystal structure and chemical composition analysis

As shown in Fig. 4 , XRD patterns and XPS spectra were used to analyze the crystal structures of Cu₂O and the composite structures of Cu₂O/ cotton fabrics. Fig. 4a clearly shows the XRD patterns of the crystal structures of COCO-5 and pure Cu₂O. The diffraction peaks observed at 2θ = 29.36°, 36.45°, 42.38°, 61.57°, 73.69° and 77.65° correspond to the (1 1 0), (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) crystal planes of Cu₂O (JCPDS no: 77–0199) [31], [32], respectively, as indicated in the Fig. 4a. This is the XRD diffraction patterns of the crystal structures of octahedral Cu₂O [33], [34]. At the same time, the growth of octahedral Cu₂O in the FE-SEM images was verified (Fig. 3c2). The intensities of the diffraction peaks of COCO-5 is higher than that of pure Cu₂O, which because the cotton fiber as a growth substrate promotes the formation of better Cu₂O crystal structures [35]. The TEM images of Fig. 2 also confirmed this phenomenon, in the absence of cotton fabrics as a growth substrate, the crystal structures of Cu₂O were close to an ellipse rather than a regular octahedron. In contrast, there is no Cu₂O crystal diffraction peak on the cotton fabrics because the pure cotton does not carry any Cu₂O [36]. Fig. 4b is XPS analysis of cotton fabrics, Cu₂O and COCO-5. The peaks of C 1 s, N 1 s and O 1 s were detected at 285.4, 399.7 and 532.2 eV in cotton fabrics, and the peaks of O 1 s and Cu 2p were detected at 529.5 and 931.7 eV in Cu₂O, and the above four peaks appeared simultaneously in COCO-5 [37], [38]. In detail, on the XPS spectrum of Cu 2p (Fig. 4c), the peaks located at 932.3 and 952.4 eV are ascribed to the Cu 2p_1/2 and Cu 2p_3/2 [39]. In Fig. 4d, the O 1 s can be fitted into 529.5 and 534.0 eV, which were attributed to lattice oxygen of Cu–O bonds and surface-adsorbed oxygen species [40]. The results of XRD and XPS prove that Cu₂O and cotton fabrics can be well combined with the assistance of NC.

Fig. 4.

(a) XRD patterns and (b) XPS spectra of COCO-5, Cu₂O and cotton fabrics. (c) Cu 2p and (d) O 1 s spectra of COCO-5.

3.3. Photocatalytic degradation of MB and its mechanism analysis

COCO-5 verified its photocatalytic performance by degrading MB under irradiation with a xenon light, and the concentration of MB was monitored by UV–vis, as shown in Fig. 5 . Five reaction times were set to degrade MB using COCO-5, which were 0, 10, 20, 40 and 60 min, respectively (Fig. 5a). The concentration of MB after degradation was then calculated from the corresponding absorption intensity in the standard curve (Fig. 5b-c). From the UV–vis absorption peak (Fig. 5a), the absorption peaks at 664 nm of MB were be weaker and blue-shifted, and the color of the MB solution also changed from blue to colorless. This indicates that the reduction of the chromophore group can determine the occurrence of degradation, and the blue shift of the peak indicated that the energy required for the electronic transition increases to form an intermediate product [41]. After 60 min, almost no MB was left in solution (1.68%), COCO-5 shown excellent photocatalytic degradation property. More importantly, COCO-5 can be easily taken out after photocatalytic degradation of MB, avoiding the problem of secondary pollution, this is a simple and effective solution for photocatalytic degradation of dyes.

Fig. 5.

(a) UV–vis spectra and (b) optical image of MB after different photocatalytic degradation time, (c) UV–vis standard curve with concentrations corresponding to absorbance. The right color ruler is the correspondence between colors and concentrations.

A comprehensive test analysis was carried out on the mechanism and process of photocatalytic degradation of MB by COCO-5. Fig. 6 a shows the presence of free radicals in the COCO-5 catalytic system by EPR spectroscopy. Four characteristic peaks of •OH and four characteristic peaks of •O₂ ^– can be observed by analysis, indicating that •OH and •O₂ ^– radicals will play a major role in the process of degradation [42]. Fig. 6b is a TPR spectrum of COCO-5 and pure Cu₂O turned on and off under visible light. Compared to Cu₂O, COCO-5 had a stronger photocurrent response and was stable. This shows that the photo-electric charge separation rate of COCO-5 was higher than that of pure Cu₂O, and the good dispersion of Cu₂O on cotton fibers accelerated the separation of photogenerated electrons and holes, which made COCO-5 have high photocatalytic activity [43]. Fig. 6c is a FTIR spectra of MB before and after degradation. Compared to MB, products had a –OH characteristic peak at 3300 cm⁻¹, a –NO₂ characteristic peak at 1630 cm⁻¹, 1649 cm⁻¹ was an organic nitrate characteristic peak, the 1100 and 1150 cm⁻¹ characteristic peak were the hydroxyl deformation vibration on secondary and tertiary carbons. A strong absorption peak of N-O at the 870 cm⁻¹ indicated that the degradation product had been degraded into a simple carbon chain. In particular, the presence of –NO₂ also demonstrates the oxidative degradation of MB molecules [44], [45]. The IC (Fig. 6d) further demonstrates this result and will be explained in detail in conjunction with the mechanism explained in the next section.

Fig. 6.

(a) EPR spectra of COCO-5 with visible light irradiation, •O₂^– in methanol dispersions and •OH in aqueous dispersions, (b) transient photocurrent response (TPR) spectra of Cu₂O and COCO-5, (C) FTIR spectra of MB and products of photocatalytic degradation for 30 min, and (d) ion chromatography (IC) of degradation products.

In theory, the conduction band (CB) and valence band (VB) of Cu₂O are calculated according to the following equations: E_VB = κ − E₀ + 0.5E_g and  E_CB = E_VB − E_g, where  E _VB  and  E _CB  are the VB and CB potentials respectively,  E ₀  is the energy of free electrons on the hydrogen scale (ca. 4.5 eV),  E _g  is the band gap energy, and κ  is the electronegativity computed from the geometric mean of the electronegativities for the constituent atoms. Therefore, the CB and VB potentials of Cu₂O are approximately −0.28 and 1.92 eV, respectively. During visible light irradiation of COCO-5, a series of physicochemical reactions occurred in the surface of COCO-5 and solution (Fig. 7 ), including: i, Cu₂O absorbed energy (hv) to generate electrons (e^-) and holes (h⁺), and these e^- and h⁺ react further with oxygen and water to produce superoxide radicals (•O₂ ^–) and hydroxyl radicals (•OH), related free radical reactions are as follows:

Fig. 7.

Schematic illustration of visible light irradiated COCO-5 to generate free radicals and MB degradation process.

Cu₂O + hv → Cu₂O (e^-, h⁺) (3)

O₂ + e^- → •O₂ ^– (4)

H₂O + h⁺ → •OH + H⁺ (5)

•O₂ ^– + H⁺ + e^- → H₂O₂ (6)

H₂O₂ + e^- → •OH + OH^– (7)

ii, firstly, the ·OH radical attacks the -S = bond and the -N = bond of MB to interrupt the MB molecule. Secondly, under the function of •O₂ ^– and •OH, the MB split product is oxidized to phenol, diphenol, etc., because phenol and diphenol have an electron donor –OH present on the benzene ring, which is beneficial to •OH electrical attacks, especially in the presence of –OH on the ortho and para positions. Phenol can be oxidized to hydroquinone, catechol, resorcinol, etc., and diphenol can be quickly oxidized to benzoquinone. In the third step, the intermediate product of the aromatic ring is further oxidized by •OH into a short-chain carboxylic acid such as fumaric acid, oxalic acid, formic acid, etc., and these short-chain carboxylic acids can be rapidly degraded into CO₂ and H₂O [46], [47], [48], [49]. Analysis of the IC verified this degradation process (Fig. 6d). Eventually, under this series of physicochemical reactions, MB is degraded and water is harmless. The gradual degradation process is shown in Fig. 7.

One of the advantages of this study is that it can be easily reused because it is easy to remove the COCO-5 from the liquid. Six photocatalytic degradation cycles were set to test the stability of COCO-5. We performed the cycling tests of sample by simply washing with distilled water for the next cycle of photocatalytic. It can be seen from Fig. 8 a that the photocatalytic activity of COCO-5 can still be maintained above 85% after 6 cycles, which indicates that it has good durability. This performance is significantly better than the Cu₂O photocatalytic material without the cotton fabrics [50], [51], which indicates that the cotton fiber is a good matrix to promote stability, and NC helps Cu₂O to anchor better on the fiber. Fig. 8b shows the photocatalytic degradation properties of COCO-5 for a variety of dyes, including CY (cationic yellow), CR (cationic red), AR (anionic red), AY (anionic yellow) and NR (neutral red). At first step, the concentration of the five dyes decreased by 10–50% when in the dark treatment environment (purple part). In this 120 min, COCO-5 mainly showed the ability to adsorb dyes. In the second step (light blue part), the species dye were rapidly degraded under visible light irradiation, and COCO-5 mainly exhibited photocatalytic degradation properties. This situation indicates that COCO-5 can degrade the chromophore groups (azo group) of a variety of dyes [52], their molecular formula is shown in the Fig. S1 (Supplementary data,) thereby having the potential to handle complex dye wastewater.

Fig. 8.

(a) Cycle photocatalytic degradation of MB by COCO-5, and (b) photocatalytic activity of COCO-5 to a variety of dyes (CY: cationic yellow; CR: cationic red; AR: anionic red; AY: anionic yellow; NR: neutral red).

3.4. Antibacterial performance test

Generally, Cu₂O has strong antibacterial properties, so the samples in this study have also been tested for antibacterial. Similarly, the antibacterial properties of COCO-5 in the aqueous phase can be easily reused. S. Aureus and E. Coli were used to represent Gram-positive and Gram-negative bacteria, respectively. COCO-5 was tested for antimicrobial property using plate colony counting method. Fig. 9 a shows that the CFU on the medium after being treated with COCO-5 for 30 min had dropped to 107 (S. Aureus) and 143 (E. Coli), and the blank (nothing on it) CFU were still 1050 and 984 (Fig. 9c). At the same time, we prepared pure cotton and cotton-NC composite fabrics to test the antibacterial properties. The results showed that the antibacterial properties of pure cotton and cotton-NC composite fabrics were not excellent. Although their tested CFU was lower than that of the blank control group, they were all at a high CFU value, which did not achieve the desired antibacterial effect. The antibacterial rates (AR) of COCO-5 to S. Aureus and E. Coli reached 93.25 and 89.73%, respectively (Fig. 9b). This indicates that the cotton fabrics loaded with Cu₂O had a strong antibacterial activity. Usually, the Cu₂O surface could generate hydrogen peroxide (H₂O₂) with antibacterial effect, and H₂O₂ binds to the bacterial cell membrane to affect its permeability and respiratory function, leading to bacterial apoptosis [53]. Photos of CFU reduction of S. aureus and a significant inhibition zone of E. Coli can be seen in Fig. 9c. The maximum inhibition zone of COCO-5 against E. Coli was 8.6 cm, showing an excellent antibacterial effect. The COCO-5 reuse ability was verified by 5 E. Coli antibacterial cycles (Fig. 9d). After 5 cycles, the antibacterial rate of COCO-5 to E. Coli was still maintained at 80.99%, showing excellent stability.

Fig. 9.

(a) Bacterial reduction of COCO-5, cotton fabrics, cotton fabrics-NC and blank (nothing on it) samples, (b) antibacterial rate of COCO-5 against S. Aureus and E. Coli, (c) Photos of the bacterial CFU reduction of S. Aureus and the zone of inhibition of E. Coli, and (d) antibacterial ratio to E. Coli of COCO-5 after 5 cycles.

3.5. Mechanical stability test

The stability after multiple cycles of COCO-5 was also verified by mechanical performance testing (Fig. 10 ). Divided into two groups tested mechanical properties of cotton fabrics, unused COCO-5 and COCO-5 used five times. In the first group (Fig. 10a), compared to cotton fabrics and unused COCO-5, the stress and strain of COCO-5 after photocatalytic degradation (5 times) decreased slightly, which may be due to the visible light radiation that reduces the mechanical properties of the cotton fibers[54], [55]. In the second group (Fig. 10b), the stress and strain of COCO-5 decreased slightly after antibacterial experiments (5 cycles) compared to the unused COCO-5. This may be because the bacterial medium weakened the strength and toughness of cotton fibers. However, compared with pure cotton fabric, the difference in COCO-5 stress and strain after 5 antibacterial experiments was slight, which verified the durability of COCO-5 in mechanical properties.

Fig. 10.

Stress–strain curves: (a) cotton fabrics, unused COCO-5 and COCO-5 after 5 photocatalytic degradation cycles of dyes, (b) cotton fabrics, unused COCO-5 and COCO-5 after 5 antibacterial cycles.

4. Conclusion

In this study, Cu₂O was synthesized in-situ on cotton fabrics and used NC as “bridge”, which ensured the good dispersion of Cu₂O and allowed it to be recycled. The fabricated cotton fabrics/Cu₂O-NC composite material can efficiently degrade the dye by photocatalysis, and is also an ideal antibacterial material. A variety of technical tests have analyzed the photocatalytic degradation mechanism of cotton fabrics/Cu₂O-NC, and the practicality of this research strategy has been illustrated by recycle using. In-situ synthesis of nano-functional particles based on textile materials is a promising process route, and the ideal recyclable nanocomposites can be prepared by combining different organic–inorganic materials.

5. Credit author statement

Xiuping Su: synthesized the composite materials and wrote the paper. Wei Chen: measured the antibacterial experiments. Yanna Han: designed and supervised the experiments. Duanchao Wang: synthesized the composite materials and wrote the paper. Juming Yao: designed and supervised the experiments.

Declaration of Competing Interest

The authors declared that there is no conflict of competing interest.

Appendix A. Supplementary material

The following are the Supplementary data to this article: