Introduction

Cotton is an abundant renewable natural cellulose material. It has many advantages (Hu et al. 2018) such as hydrophilicity, softness, reproducibility, processability, and biodegradability, which make it widely used as a wearable material. With the development of industrialization and the emphasis on environmental protection, renewable and easily biodegradable cellulosic materials have more uses in industrial textile materials (Chen et al. 2018a), such as wall cloth, awning, tents, table cloth, and curtains. These applications require cotton fabric with some special features such as adjustable color, self-cleaning, UV absorption and near infrared reflection properties.

In the last 10 years, photocatalysts as the new materials, especially for TiO2 and ZnO (Chen et al. 2018a; Hu et al. 2018; Ma et al. 2019), are widely used in fabricating multifunctional cotton fabric due to ultraviolet absorption, photodegrading contaminants, superhydrophobicity, and near infrared reflection property (Ge et al. 2018; Ge et al. 2020; Moridi Mahdieh et al. 2018; Wang et al. 2017). However, due to the wide band gap of TiO2 (3.0–3.2 eV) and ZnO (3.2–3.3 eV), it can only absorb ultraviolet light (λ < 400 nm), which limits its photocatalytic ability to degrade pollutants in sunlight. Recently, the Bi-based semiconductor materials especially for bismuth oxyhalides have obtained more attention as photocatalysts (Chen et al. 2018b; Hao et al. 2019; Shi et al. 2019; Wang et al. 2018a) due to its intrinsic properties including distinct layered structure, harmless, low-priced and simple preparation method (Di et al. 2017; Jia et al. 2017). Among bismuth oxyhalides (BiOX; X = I, Cl, Br, and F), BiOI and BiOBr can absorb visible light of less than 430 nm and 630 nm, respectively, which would impart bright color to textiles (Di et al. 2017). BiOX (X = Br and I) also has a relatively high near-infrared reflectance, which makes it cool pigment (Gao et al. 2018).

In this work, the color adjustable solid solutions nanosheets formed with BiOBr and BiOI can be anchored on cotton fabric for photodegrading organic stain and absorbing ultraviolet light. Raw cotton was first carboxymethylated to adsorb Bi2O22+ to facilitate the growth of crystal nuclei. Subsequently, novel solid solution BiOBrxI1−x nanosheets formed with different molar ratios of BiOBr and BiOI were anchored on carboxymethylated cotton fabric surface via the successive ionic layer adsorption and reaction methods (SILAR) (Zhou et al. 2019a). The structure and morphology of prepared multifunctional cotton fabrics (BiOBrxI1−x-CCF (0 ≤ x ≤ 1)) were characterized. Adjusted color, self-cleaning, UV protection, near-infrared reflectance, and acid and alkali resistance properties of these multifunctional cotton fabrics were also systematically studied.

Experimental section

Materials

Woven cotton (155 g/m2) was purchased from Hua Fang Co., LTD. Bismuth nitrate pentahydrate (Bi(NO3)3·5H2O) anhydrous ethanol, chloroacetic acid, rhodamine B (RhB), potassium bromide (KBr), and potassium iodide (KI) were purchased from Adamas-beta Co., Ltd. The water used in the experiment is ultrapure water. All chemicals are of analytical grade.

Preparation of BiOBrxl1−x-CCF

To facilitate the nucleation of solid solution BiOBrxI1−x nanosheets, cotton fabric was first modified by chloroacetic acid to achieve available carboxylates (Rubin et al. 2018; Wu et al. 2017). Subsequently, carboxymethylated cotton fabric (CCF) was used to electrostatically adsorb bismuth oxygen ions (Bi2O22+) in Bi(NO3)3 solution and then reacted with iodide and bromide ions in mixed solutions of KBr and KI with different molar ratios (Cai et al. 2018; Zhou et al. 2019a) (Scheme 1). The specific experimental details including carboxymethylation of cotton and growth process of solid solution nanosheets were placed in supplementary material. Prepared samples were defined as BiOBrxI1−x-CCF (x = n(KBr)/n(KBr+KI); x = 0, 0.2, 0.4, 0.6, 0.8, and 1).

Scheme 1
scheme 1

Schematic diagram of the preparation process of BiOBrxI1−x-CCF (0 ≤ x ≤ 1)

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Characterization

The morphology and microstructure of the treated cotton were investigated by SEM, TM-1000, Hitachi, Japan and FE-SEM; Hitachi, S-4800, Japan. Infrared spectra of raw cotton fabric and CCF were investigated with a perkinElmer spectrum-two (USA). The X-ray powder diffraction (XRD) patterns were performed on Rigaku D/max-2500PC, Cu Kα (λ = 1.54056 Å) (reflection mode). Raman spectra were collected on Thermo Fisher DXR2xi exciting with a 532.0 nm laser. X-ray photoelectron spectroscopy (XPS) were obtained on Thermo ESCALAB 250. UV-vis diffuse reflection spectrum (UV-vis DRS) and near infrared reflectance (NIR) spectroscopy were achieved on UV 3600PLUS. CIE 1976 L*a*b* colorimetric method was used to represent the color parameters of the samples. Color parameters were obtained from DATACOLOR 650. The UV blocking of the samples were tested by Fabric UV Transmittance Tester (UV-1000F). Contact angle was tested on a Theta contact angle analyzer (Biolin, Sweden).

Results and discussion

Structure and morphology

In order to increase loading efficiency of BiOX (X = Br or I) nanosheets on the cotton surface, the cotton fabric was first functionalized with carboxylate groups. IR spectroscopy and XRD patterns of raw cotton fabric and CCF were investigated to confirm the presence of carboxyl groups.

As displayed in Fig. 1a, the IR absorption peak at 1725 cm−1 of CCF was ascribed to carboxylate group because the sample for testing was in the cellulose –OCH2COOH form, and protonated carboxylic group (–COOH) in CCF yielded a C=O band (Wu et al. 2017). Both raw cotton and CCF were presented in the form of fabrics for XRD test. As displayed in Fig. 1b, XRD peaks at 2θ = 15.14, 16.58, and 22.88° are ascribed to the (1–10), (110) and (200) peaks of the cellulose Iβ pattern. Compared with raw cotton, XRD intensities of CCF at 2θ = 20.5° for the (012) and (102) increase, which means that the modification makes some crystallites on the fiber surface change from preferred orientation to random orientation (French 2014). The carboxyl concentration (CCOO−) on the modified cotton is 1.4 mmol/g and this material was used to prepare multifunctional BiOBrxI1−x-CCF.

Fig. 1
figure 1

a IR spectroscopy, b XRD patterns of raw cotton and CCF

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The contents of BiOX (X = Br or I) loaded on raw cotton and CCF were tested and the results showed the content of the BiOX on CCF is higher than that of raw cotton (Table S1), which is attributed to coulombic force between Bi2O22+ in the solution and carboxyl groups on CCF (Tolba et al. 2017; Zhou et al. 2019b). Structure and morphology of prepared BiOBrxI1−x-CCF (0 ≤ x ≤ 1) were investigated to confirm the existence of solid solution BiOBrxI1−x nanosheets.

As displayed in Fig. 2a, the significant XRD peaks of BiOBrxI1−x-CCF (x = 0) at 2θ = 9.36, 29.44, 31.54, 45.46, and 55.12 were attributed to tetragonal BiOI, which correspond to crystal faces of the (001), (102), (110), (200), and (212) peaks, respectively (Wang et al. 2010; Zhou et al. 2019a), and the significant XRD peaks of BiOBrxI1−x-CCF (x = 1) at 2θ = 10.92, 25.20, 32.24, 46.21, and 57.21° were ascribed to tetragonal BiOBr, which correspond to crystal faces of the (001), (101), (110), (200), and (212) peaks, respectively (Huo et al. 2012; Li et al. 2018). As for BiOBrxI1−x-CCF (0 < x < 1), the XRD pattern of prepared sample is a mixture pattern of BiOI-CCF and BiOBr-CCF, which is because the solid solution BiOBrxI1−x (0 < x < 1) nanosheets consists of BiOI and BiOBr (Cao et al. 2011; Tang et al. 2016; Wang et al. 2018a). As displayed in Fig. 2b, the Raman scattering peaks of BiOBrxI1−x-CCF (x = 0) at 85.4 and 118.4 are ascribed to the A1g (internal Bi-I stretching) and Eg (internal Bi-I stretching mode) of BiOI and the Raman scattering peaks of BiOBrxI1−x-CCF (x = 1) at 119 and 159 cm−1 are ascribed to the A1g (internal Bi–Br stretching) and Eg (internal Bi-Br stretching mode) of BiOBr. Also, as for BiOBrxI1−x-CCF (0 < x < 1), the Raman scattering peaks of prepared sample is a mixture pattern of BiOI-CCF and BiOBr-CCF (Tian et al. 2012; Zhang et al. 2012). Based on the above results, the solid solution formed with different molar ratio of BiOI and BiOBr was anchored on the surface of cotton fabric.

Fig. 2
figure 2

a XRD patterns, b Raman scattering patterns of BiOBrxI1−x-CCF (0 ≤ x ≤ 1)

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From the low-magnification electron micrograph in Fig. 3a–f, it can be found that cotton fabric is completely covered by BiOBrxI1−x (0 ≤ x ≤ 1). As displayed in Fig. 3a´–f´, BiOBrxI1−x (0 ≤ x ≤ 1) formed with different molar ratio of BiOI and BiOBr is in the form of a nanosheet. From the illustration in Fig. 3a´, f´, the average thickness of the nanosheet is 40–50 nm and a size of the nanosheet is 1–2 μm in the other two dimensions (Xia et al. 2011; Zhang et al. 2013). With the increase of bromide ion content, the nanosheets changed from interlaced arrangement to clustered flower-like (Cai et al. 2018; Huang et al. 2017a; Jia et al. 2017).

Fig. 3
figure 3

SEM images of BiOBrxI1−x-CCF (a, a´: x = 0; b, b´: x = 0.2; c, c´: x = 0.4; d, d´: x = 0.6; e, e´: x = 0.8; f, f´: x = 1)

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The elemental composition of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) was tested and displayed in Fig. 4. As displayed in Fig. 4b, iodine is from BiOI and the peaks at 630.4 eV and 618.9 eV are ascribed to I 3d3/2 and I 3d5/2, respectively (Wang et al. 2016). As displayed in Fig. 4c, bromine is from BiOBr and the peaks at 69.3 eV and 68.3 eV are ascribed to Br 3d3/2 and 3d5/2, respectively. As for BiOBrxI1−x-CCF (0 < x < 1), XPS survey spectra exhibited the existence of Bi, O, I, Br, and C-related peaks, which is due to the co-existence of BiOX (X = I, Br) and cellulose. Bi-related peaks in all samples are attributed to the solid solution BiOBrxI1−x nanosheets formed with BiOBr and BiOI. In Fig. 4d, the peaks of Bi 4f at 159.3 and 164.6 eV confirm the valence state of Bi3+ (Yu et al. 2017). In Fig. 4e, the peaks at 532.2 eV and 530.1 eV are mainly attributed to the surface absorbed oxygen and lattice oxygen.

Fig. 4
figure 4

a XPS survey spectra of BiOBrxI1−x-CCF (0 ≤ x ≤ 1); High-resolution XPS spectrums of I 3d (b), Br 3d (c), Bi 4f (d) and O 1s (e)

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Optical performance

For textile materials, bright colors help to enhance the appreciation and added value of products. As displayed in Fig. 5a, by regulating the molar ratio of bromine ions to iodide ions in mixed solution, a series of colored fabrics (BiOBrxI1−x-CCF) were obtained (Lu et al. 2018; Wang et al. 2018a). Color coordinates of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) were listed in Table 1. With the increase of iodine ion content, the lightness (L) of BiOBrxI1−x-CCF decreases, and a* (green(−)/red(+)) value decreases first and then increases, which is opposite to that of b* (blue(−)/yellow(+)) value. With the increase of iodine ion content, the color of the composite fabrics (BiOBrxI1−x-CCF) changes from white to yellow and finally to red. As displayed in Fig. 3b, the chromaticity coordinates of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) were drawn in the CIE two-dimensional chromaticity diagram. As shown in the Fig. 5b, if the molar ratio of bromine to iodine is refined, a chromaticity coordinate curve can be obtained.

Fig. 5
figure 5

a Digital photos of BiOBrxI1−x-CCF (0 ≤ x ≤ 1), b CIE two-dimensional chromaticity diagram of raw cotton and BiOBrxI1−x-CCF (0 ≤ x ≤ 1), c UV–Vis DRS of raw cotton and BiOBrxI1−x-CCF, d UV transmission rate of raw cotton and BiOBrxI1−x-CCF (0 ≤ x ≤ 1)

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Table 1 Color coordinates and band gap of BiOBrxI1−x-CCF (0 ≤ x ≤ 1)
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The color is related to the optical absorption of the composite fabric and the optical absorption of the composite fabric (BiOBrxI1−x-CCF) is mainly decided by the band structure of the solid solution BiOBrxI1−x nanosheets. As displayed in Fig. 5c, with the increase of iodine content, the absorption edge of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) was extended from 430 nm to 630 nm. Band gap of composite fabrics (BiOBrxI1−x-CCF) were calculated (Bai et al. 2019; Wang et al. 2018b) and specific method was placed in supplementary material (Fig. S1). The results were listed in Table 1. With the increase of iodine ion content, band gap of BiOBrxI1−x-CCF gradually decreases from 2.71 to 1.85 eV.

Studies have shown that ultraviolet light can cause a series of skin diseases and it is also an important cause of facial aging (Schuch et al. 2017). As an important textile material for clothes and industry, UV protection of cotton fabric is concerned (Chen et al. 2018a; Ma et al. 2019). As displayed in Fig. 5d, the ultraviolet transmittance (250–450 nm) of raw cotton is much higher than that of BiOBrxI1−x-CCF (0 ≤ x ≤ 1). As the iodine content increases, the UV transmittance of BiOBrxI1−x-CCF gradually decreases, but the magnitude of the change is small. UV protection can be expressed as a numerical value of UV protection factor (UPF). Transmittance percentages (UV-A and UV-B) and UPF of raw cotton and BiOBrxI1−x-CCF can be calculated according to the following formulas (Zhou et al. 2019a).

$$ {\text{T}}\left( {{\text{UV}} - {\text{A}}} \right) = \frac{{\mathop \sum \nolimits_{{315\;{\text{nm}}}}^{{400\;{\text{nm}}}} T_{\lambda } \Delta_{\lambda } }}{{\mathop \sum \nolimits_{{315\;{\text{nm}}}}^{{400\;{\text{nm}}}} \Delta_{\lambda } }} $$
(1)
$$ {\text{T}}\left( {{\text{UV}} - {\text{B}}} \right) = \frac{{\mathop \sum \nolimits_{{280\;{\text{nm}}}}^{{315\;{\text{nm}}}} T_{\lambda } \Delta_{\lambda } }}{{\mathop \sum \nolimits_{{280\;{\text{nm}}}}^{{315\;{\text{nm}}}} \Delta_{\lambda } }} $$
(2)
$$ {\text{UPF}} = \frac{{\mathop \sum \nolimits_{{280\;{\text{nm}}}}^{{400\;{\text{nm}}}} E_{\lambda } S_{\lambda } \Delta_{\lambda } }}{{\mathop \sum \nolimits_{{280\;{\text{nm}}}}^{{400\;{\text{nm}}}} E_{\lambda } S_{\lambda } T_{\lambda } \Delta_{\lambda } }} $$
(3)

where Eλ, Sλ, Tλ, and ∆λ are the relative erythemal spectral effectiveness, solar spectral irradiance, average spectral transmission of the specimen, and measured wavelength interval (nm), respectively.

As listed in Table 2, the UV protection of raw cotton is weak (UPF < 10). Compare with raw cotton, UPF of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) is 50+ and its T(UV-A) is less than 5%, which is ascribed to the strong ultraviolet absorption ability of BiOBrxI1−x nanosheets (Zhou et al. 2019a). According to GB/T18830-2009, BiOBrxI1−x-CCF (0 ≤ x ≤ 1) can be used as “UV protection product”.

Table 2 Transmittance percentages (UV-A and UV-B) and UPF of raw cotton and BiOBrxI1−x-CCF (0 ≤ x ≤ 1)
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Self-cleaning performance

Awning and decorative fabrics generally need to have self-cleaning properties. Self-cleaning of textiles mainly includes two features (Banerjee et al. 2015). First, textiles are not easily stained by stains. To facilitate the observation of the staining effect, a colored aqueous solution was used to test the staining effect of the fabrics (raw cotton and BiOBrxI1−x-CCF (x = 1)). As displayed in Fig. 6a, raw cotton was easily stained by the colored aqueous solution, while BiOBrxI1−x-CCF (x = 1) were not easily stained by the colored aqueous solution. Contact angles between the water and the surface of raw cotton and BiOBrxI1−x-CCF also were tested. As displayed in Fig. 6b, water was easily spread on cotton fabrics and is not easily spread on BiOBrxI1−x-CCF (0 ≤ x ≤ 1). This result can be attributed to two factors: (1) The solid solution is a crystal sheet which is insoluble in water; (2) The cross-arranged BiOBrxI1−x nanosheets on cotton fiber surface have a “lotus-like effect”. The contact angles between BiOBrxI1−x-CCF (0 ≤ x ≤ 1) and water range from 139 to 143 degrees, which make BiOBrxI1−x-CCF (0 ≤ x ≤ 1) not easily stained by the water-based stains in life.

Fig. 6
figure 6

a Wetting properties of raw cotton and BiOBrxI1−x-CCF (x = 1), b Contact angle between the water and the surface of raw cotton and BiOBrxI1−x-CCF (0 ≤ x ≤ 1), c Photodegrading Rh B in aqueous solution with BiOBrxI1−x-CCF (0 ≤ x ≤ 1) under visible light irradiation (500 W xenon lamp, λ > 400 nm), d Photocatalytic decontamination of Rh B on the surface of raw cotton and BiOBrxI1−x-CCF (x = 1) under visible light irradiation (500 W xenon lamp, λ > 400 nm)

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Second, once textiles are stained, the stain can be effectively degraded (Chen et al. 2019; Huang et al. 2017b; Qin et al. 2019). The ability of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) to photodegrade organic stain solution (Rh B) was tested under visible light irradiation (500 W xenon lamp, λ > 400 nm) and experimental details were placed in supplementary material. The results showed that all the samples (BiOBrxI1−x-CCF (0 ≤ x ≤ 1)) can photodegrade Rh B in aqueous solution. As displayed in Fig. 6c, with the increase of bromide ion content, the photodegradation effect of Rh B is gradually increasing and BiOBrxI1−x-CCF (x = 1) can photodegrade > 99% Rh B in 180 min. Photocatalytic decontamination of stains on the surface of raw cotton and BiOBrxI1−x-CCF (x = 1) was further simulated under visible light irradiation (500 W xenon lamp, λ > 400 nm). The BiOBrxI1−x-CCF (x = 1) was first wetted with a mixture of ethanol and water, and then the stain (10 mg/L Rh B solution) was dripped onto the surface of the fabric and illuminated by xenon lamp (~ 500 W; λ > 400 nm) to observe the color change of the stain (Valenzuela et al. 2019). As displayed in Fig. 6d, as the irradiation time was prolonged, the color of the stain on BiOBrxI1−x-CCF (x = 1) gradually faded, while the color of the stain on raw cotton hardly changed. These results indicate that BiOBrxI1−x-CCF has the ability to photodegrade stain. Therefore, BiOBrxI1−x-CCF (0 ≤ x ≤ 1) can be used as self-cleaning textile.

NIR reflectance property

In tropical and subtropical regions, the near infrared reflection performance (700–2500 nm) of outdoor tents and curtains is critical for thermal isolation. Photocatalysts can be used as NIR reflective pigments (Gao et al. 2017; Lu et al. 2017).

As displayed in Fig. 7a, the near infrared reflectance of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) is higher than that of raw cotton without photocatalyst, which is attributed to the near-infrared reflection properties of the solid solution BiOBrxI1−x nanosheets. The near infrared reflectance of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) has no linear relationship with the ratio of bromine to iodine. As displayed in Fig. 7b, the samples (BiOBrxI1−x-CCF) were placed on a plate made of foil paper and polystyrene foam under an infrared lamp (Philips BR 250 W) (Gao et al. 2018). The outer surface temperature and thermography images of raw cotton of BiOBrxI1−x-CCF were obtained by a forward-looking infrared radiometer IR imaging camera (FLK-TIR329HZ, Fluke, USA). As displayed in Fig. 7c–i, the surface temperature of BiOBrxI1−x-CCF (0 ≤ x ≤ 1) is lower than that of raw cotton, which is attributed to near infrared reflectance of solid solution BiOBrxI1−x nanosheets. From the Fig. 7a and c–i, it can be found that the higher the near infrared reflectance of the sample, the lower its surface temperature. Among these Samples, BiOBrxI1−x-CCF (x = 0.4) has the highest near infrared light reflectivity and the lowest surface temperature under an infrared lamp irradiation. Therefore, BiOBrxI1−x-CCF (0 ≤ x ≤ 1) can be used as infrared reflectance textile material.

Fig. 7
figure 7

a NIR reflectance of BiOBrxI1−x-CCF (0 ≤ x ≤ 1), b A simple device used for testing the surface temperature of BiOBrxI1−x-CCF (0 ≤ x ≤ 1); Thermography image of raw cotton (c) and BiOBrxI1−x-CCF (d, x = 0; e, x = 0.2; f, x = 0.4; g, x = 0.6; h, x = 0.8; i, x = 1) (the sample size is 6.5×8 cm) under an infrared lamp (250 W)

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Acid and alkali resistance

The solid solution BiOBrxI1−x nanosheets on cotton fabric were regarded as inorganic pigments. The acid and alkali resistance of inorganic pigments is an important factor affecting its practical application and further functional finishing. In order to facilitate observing the change of the sample in acid/alkali solutions, colored BiOBrxI1−x-CCF (x = 0) was selected as the test sample and was placed in solution with different pH for 3 h.

As displayed in Fig. 8a, when BiOBrxI1−x-CCF (x = 0) was soaked in a solution with pH = 1.1 and 12.1, its color changes significantly, which means the structure of BiOI nanosheets has been destroyed. However, when BiOBrxI1−x-CCF (x = 0) was immersed in the solution with pH 2.3 and 11.2 for 3 h, there was no change in color. Soaked samples in pH 2.3 and 11.2 were characterized by SEM and X-ray powder diffraction. As displayed in Fig. 8b, c, there is no difference between the X-ray powder diffraction peaks and the morphology of BiOBrxI1−x-CCF (x = 0) treated with acid/alkali solutions and the original sample. This result indicates that BiOBrxI1−x-CCF (0 ≤ x ≤ 1) has a certain acid and alkali resistance.

Fig. 8
figure 8

a Digital photos of BiOBrxI1−x-CCF (x = 0) treated with acidic and alkaline solution, b X-ray powder diffraction patterns and c SEM of BiOBrxI1−x-CCF (x = 0) treated with acid/alkali solutions

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Conclusion

Multifunctional cotton fabric was simply fabricated by anchoring the solid solution BiOBrxI1−x nanosheets formed with different molar ratios of BiOBr and BiOI on the carboxymethylated cotton fabric. The color of the composite fabrics (BiOBrxI1−x-CCF) can be adjusted. The solid solution nanosheets formed with different molar ratios of BiOBr and BiOI impart the self-cleaning, excellent UV protection (UPF > 50, T(UV-A) < 5%), and NIR reflective properties to cotton fabrics. These multifunctional cotton fabrics (BiOBrxI1−x-CCF) have great potential usage in self-cleaning and outdoor protection.