Introduction

Semiconductor metal selenide materials have attracted growing attention due to their unique optoelectronic behavior with a big potential in electrical, optical, thermal sensitive, and photoelectric conversion applications (Zhao et al. 2017; Sparks et al. 2020; Burton et al. 2018; Li et al. 2016). Among various semiconductor compounds, copper chalcogenides (Cu2-xE, E = S, Se, Te) have fine-tuned localized surface plasmon resonant effect and high absorption capability in near infrared (NIR) region (Liu et al. 2013a; Zhu et al. 2020). Their good biocompatibility and low production cost bring unique advantages in fabrication of Cu2-XE nanocomposite devices. As one of the most widely studied thermoelectric materials, binary compound p-type copper selenide (Cu2-XSe) has a stoichiometry dependent band gap of 2.2 eV (Dennler et al. 2014; Xie et al. 2019; Kannimuthu et al. 2021). It is expected to be an inexpensive and eco-friendly candidate for potential development in smart semiconductor devices.

Various Cu2-XSe based nanocomposites have been developed to enhance the complex performance. It was reported that heavily-doped Cu2-XSe nanocrystals exhibited robust NIR absorption ability to meet the requirement of vivo biomedical imaging (Liu et al. 2013b; Maddinedi 2017). Zhang et al. fabricated judicious structured Cu2-XSe@MSiO2 with core–shell nanosphere, and it was used in efficient near-Infrared radiation mediated treatment to provide better care to esophageal cancer patients (Zhang et al. 2020a). The composite counter electrode film consisting of graphene and Cu2-XSe nanoparticles was also fabricated, in which the graphene provided an effective channel for the transmission of electron, and the Cu2-XSe nanoparticles effective ensured the catalytic activity of nanocomposites (Chu et al. 2021). In addition, Qi et al. reported the biosynthesized Cu2-XSe nanospheres which exhibited high photo catalytical activity under the irradiation of sunlight, and it was used for the degradation of methylene blue dyes with good recyclability (Qi et al. 2019). A facile one-step hydrothermal approach to prepare both hierarchical starfish-like and nanocrystals Cu2-XSe was further developed, and the thin nanosheet structure facilitated the diffusion of solid-state Mg 2+ enhanced by hierarchical morphology. It can be used for the fabrication of Mg-storage cathodes with high reversiblity, excellent rate capability, and long-term cycling stability (Chen et al. 2020).

Demand for multifunctional textiles has gradually been increasing in recent years (Mao et al. 2018; Zhang et al. 2020b). In comparison with commonly studied functional textiles, multifunctional textiles exhibit the advantage of integrating different functionality simultaneously (Zhang and Shi 2019; Zhao et al. 2020). However, the relatively complex fabrication process has limited the applications and development of multifunctional textiles. For example, excellent photothermal behavior has been considered as the foundation to achieve thermal imaging and photo-induced heating, but it is generally difficult to strongly combine the functional nanoparticles with fibrous surface considering the inherent characteristics of inorganic photothermal agents (Farouk et al. 2014; Boufi et al. 2019; Xu et al. 2019). Generally, the dispersion and fastness of nanoparticles onto fabric surface have significantly determined the functional finishing process of coated fabric. The hot-pressing coating can effectively achieve the deposition of functional layer with the advantages of low production cost, facile operation, and environmental friendliness. Furthermore, waterborne polyurethane film can improve the adhesion of uniformly dispersed nanoparticles on fabric surface. Therefore, it is necessary to develop facile techniques to construct multifunctional layer on commercial fabrics, which will greatly facilitate the promising smart textiles applications.

The aim of the present study is to prepare WPU/Cu2-XSe nanocomposites for the fabrication of multifunctional cotton fabrics by coating and hot-pressing approach. The coated fabrics were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TG). Furthermore, the photothermal conversion behavior of the coated fabrics was investigated under different irradiation light, and their thermal imaging efficiency along with the temperature heating process were evaluated. The promising applications as wearable wrister were also explored for future smart textiles design and manufacture. The photochromic performance of the coated fabrics under different ultraviolet irradiation conditions was also studied, and red, yellow, and blue light spots were observed. The facile hot-pressing method to the fabricate coated cotton fabrics is promising for potential wearable electronic device applications.

Experimental

Materials

cotton fabrics (135 g/m2) were supplied by Wuhan Yudahua Imp&Exp Co., Ltd., China. Sodium hydroxide (NaOH), potassium hydroxide (KOH), selenium powder, cupric chloride (CuCl2) and sodium borohydride (NaBH4) were purchased from China National Medicine Corporation Ltd. Anionic waterborne polyurethane (WPU, solid content 30 wt%) was provided by Wuhan Hongyi Copolymerization New Material Technology Co., Ltd. China. Thermochromic inks were bought from Dongguan Qiansebian New Material Co., Ltd., China. All chemical reagents were in analytic grade and were used without any further purification treatment.

Fabrication

The fabrication of WPU/Cu2-XSe coated cotton fabrics is schematically illustrated in Fig. 1. The Cu2-XSe nanoparticles were synthesized using a modified method based on a reported method (Fu and Lin 2013). Firstly, 6.45 g NaOH and 8.5 g KOH were dissolved into 50 mL deionized water under magnetically stirring conditions at 80 °C. 0.2 g selenium powder and 0.6 g CuCl2 were then added into the mixture under magnetically stirring to complete the dissolving of the multicomponent materials. 3 mL sodium borohydride (NaBH4) as a strong reducing agent was incorporated into the solution under stirring for 30 min to reach an adequate chemical reaction. Then, the above prepared solution was poured into an autoclave at 200 °C for 24 h. The Cu2-XSe powder was successfully prepared through filtration, drying, and grinding treatment of the above solution containing copper element and selenium. The Cu2-XSe was then dispersed into the WPU solution with a dry weight ratio of 2:8 under ultrasonic conditions. The mixture was then coated onto the surface of the cotton fabrics by a glass rod. After hot-pressing treatment, a functional layer was formed on cotton fabric surface. The fabricated sample was denoted as WPU/Cu2-XSe coated cotton fabrics.

Fig. 1
figure 1

Schematics of the fabrication of WPU/Cu2-XSe coated cotton fabrics

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Characterization and measurements

The Fourier transform infrared (FT-IR) spectra of modified fabric were measured by a TENSOR 27 instrument (Bruker Co., Ltd, USA). Both surface morphology and chemical element composition of the coated fabrics were observed through scanning electron microscopy (SEM, JSM-5600LV, JEOL, Japan) equipped with energy dispersive X-ray spectroscopy (EDS, Oxford Instruments, Oxford, UK). X-ray photoelectron spectroscopy (XPS) measurement was performed on a PHI 5000C ESCA system with a Mg Kα source at 14.0 kV and 25 mA (Perkin-Elmer, USA). The crystal structure was detected by X-Ray diffraction (XRD) (D/max 2500, Rigaku, Japan) using Cu K α radiation with the diffraction angle 2θ in the range of 10–80°. Thermogravimetry analysis was carried out on a TG209 F1 thermal analyzer (Netzsch, Germany) with a heating rate of 10 °C/min and the temperature ranging from 30 to 800 °C under nitrogen atmosphere conditions.

The photothermal conversion performance of the coated fabrics was evaluated by irradiation under 2 W laser power at varied distance (10 cm, 20 cm, 30 cm and 40 cm, respectively) while the surface temperature was recorded by a digital thermometer. Different laser power (0.5 W, 1 W, 1.5 W, and 2 W) was used under a constant distance of 10 cm. The cyclic photothermal conversion efficiency was also investigated, in which the temperature was periodically increased to its maximum followed by dropping to room temperature. The photothermal properties of coated fabrics were also characterized by an Infrared thermal camera (FLIR ONE Pro), and thermal images together with the surface temperature were recorded.

Thermochromic inks of different colors were uniformly painted on the back side of WPU/Cu2-XSe coated cotton fabrics. After drying, the front side of the as-prepared fabrics were irradiated by a 808 nm laser (with a power of 2 W/cm2 and at a distance of 10 cm) and the color change of ink was recorded by a mobile phone.

Results and Discussion

Characterization

The FTIR spectra of both control and WPU/Cu2-XSe coated cotton fabrics were characterized to investigate the functional chemical groups of modified fabrics. In Fig. 2a, the absorption peaks of control cotton fabrics at 1030 cm−1, 2902 cm−1, and 3340 cm−1 are due to the C–O–C, CH, and OH stretching vibrations, respectively (Ran et al. 2019a, 2021). In Fig. 2b, the absorption peak located at 3435 cm−1 is related to stretching vibration of N–H, indicating the successful coating of waterborne polyurethane layer through hot-pressing process. The peak at 2360 cm−1 can be attributed to the stretching vibration of NCO. The peaks centered at 1705 cm−1, 1242 cm−1, and 1095 cm−1 are assigned to the stretching vibration of C = O in the amide, the amide II band, C-H deformation of and CH2, and stretching in C–O–C, respectively (Bhuiyan et al. 2019; Muzaffar et al. 2021). In addition, two slight peaks can also be observed at 2964 cm−1 and 2922 cm−1, which are associated with C-H and CH2 deformations, respectively. These absorption peaks have suggested the good deposition and bonding between cotton fabrics and waterborne polyurethane layer.

Fig. 2
figure 2

FTIR of control a and WPU/Cu2-XSe coated cotton fabrics b

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The surface morphology of both control and WPU/Cu2-XSe coated cotton fabrics was characterized by SEM. In Fig. 3a, the surface morphology of control cotton fabric is presented, and the fabric exhibits a white and smooth surface with longitudinal convolutions and grooves. The SEM image of Cu2-XSe as shown in Fig. 3b shows well dispersed nanoparticles with spherical shape. The Zeta potential of Cu2-XSe nanoparticles was also measured (as shown in Fig. 3c) to be − 25.8 mV negative charge. Herein, anionic waterborne polyurethane was used to improve the dispersion of nanoparticles in waterborne polyurethane, thus the WPU/Cu2-XSe composite can be dispersed evenly on the fabric surface. In Fig. 3d, WPU/Cu2-XSe layer was deposited on the cotton fabric surface, leading to the surface of the fabric becomes smooth and the color changes from white to brown. After the coating of WPU/Cu2-XSe under 30 min ultrasonic treatment, there is little change in the surface of the fabric, and it has exhibited good durability after washing, as seen from Fig. 3e. These results suggest that the WPU/Cu2-XSe nanocomposites have uniformly deposited on the cotton fabric surface without obvious aggregations phenomenon. In this work, polyurethane was used to trap WPU/Cu2-XSe nanoparticles, as a result the bonding strength was increased, and the dispersion of nanocomposites was improved. Due to the strong adhesion effects of polyurethane, WPU/Cu2-XSe was well anchored on cotton fiber surface to ensure the reutilization of the coated fabrics. The EDS results have suggested the existence of carbon (C), oxygen (O), nitrogen (N), copper (Cu) and selenium (Se) elements, as shown in Fig. 3f. The obvious copper and selenium signals have evidently confirmed the deposition of WPU/Cu2-XSe onto the surface of the cotton fabrics. In summary, both FTIR and SEM–EDS results have confirmed the successful coating and uniform distribution of WPU/Cu2-XSe nanocomposites on the cotton fabric surface.

Fig. 3
figure 3

SEM images of a control cotton fabric, b Cu2-XSe, and c Zeta potential of Cu2-XSe, d WPU/Cu2-XSe coated fabric without ultrasonic treatment, e 30 min ultrasonic treatment of WPU/Cu2-XSe fabric after washing, and f the EDS of coated cotton fabric

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The surface elements analysis of both control and WPU/Cu2-XSe coated cotton fabrics were conducted using XPS. As seen from Fig. 4a, the XPS scanning spectrum of control cotton fabrics exhibits obvious binding energy point at 286.2 eV and 532.7 eV corresponding to C 1 s and O 1 s, respectively (Cheng et al. 2018, 2020). The spectrum of the coated cotton fabrics in Fig. 4b shows three new signals of Cu 2p, N 1 s, and Se 3d, suggesting that the WPU/Cu2-XSe layer has been successfully deposited on cotton fabric surface. In Fig. 4c, the high-resolution XPS spectrum of Cu 2p consists of two peaks, and the binding energy of Cu 2p1/2 can be observed at 952.7 eV and Cu 2p3/2 at 932.5 eV (Zhang et al. 2020c; Zhang et al. 2021). In addition, the binding energy of Se 3d can be observed at 54.1 eV binding energy (Fig. 4d). These results have confirmed the deposition of WPU/Cu2-XSe nanocomposites layer on cotton fabrics.

Fig. 4
figure 4

The survey spectra of control a and WPU/Cu2-XSe coated cotton fabrics b with high resolution XPS spectra of Cu 2p c and Se 3d d

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The crystal structure of both Cu2-XSe nanoparticles, control cotton fabrics, and WPU/Cu2-XSe coated cotton fabrics was investigated by X-ray diffraction analysis. In Fig. 5a, the major diffraction peaks (111), (200), (220), (311), (400) and (331) match well with the pure cubic phase of Cu2-XSe (JCPDS No.06–680) (Kong et al. 2019; Jin et al. 2021). In Fig. 5b, the diffraction peaks at 2θ = 15.1°, 16.6°, 22.5° and 34.5° are due to (1–10), (110), (200) and (004) planes of cotton fabrics, respectively (Ran et al. 2019b, 2020). The XRD pattern of WPU/Cu2-XSe coated cotton fabrics (Fig. 5c) shows all the above-mentioned diffraction peaks for both cotton fabrics and Cu2-XSe. It can be concluded that well crystallized WPU/Cu2-XSe nanocomposites have been deposited on the surface of cotton fabrics.

Fig. 5
figure 5

XRD patterns of Cu2-XSe nanoparticles a, control cotton fabrics b and WPU/Cu2-XSe coated cotton fabrics c

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The TG curves of control cotton fabrics and WPU/Cu2-XSe coated cotton fabrics are shown in Fig. 6. It can be seen from Fig. 6a that the initial decomposition temperature of control cotton fabrics is 314.5 °C, and the major decomposition ends at 371.5 °C. In Fig. 6b, the total decomposition temperature is 405.5 °C for WPU/Cu2-XSe coated cotton fabrics, indicating a higher decomposition temperature as compared to the control cotton fabrics. The weight residue of control cotton fabrics is 5.81 wt% at 800 °C, whereas the weight residue of the coated cotton fabrics is 10.59 wt%. The difference in weight residue can be attributed to the deposition of Cu2-XSe nanoparticles on the fiber surface, which hinders the carbonization of cellulose molecular chain. After calculation, the mass fraction of Cu2-XSe nanoparticles as-coated on cotton fabrics is 4.78 wt%.

Fig. 6
figure 6

TG curves of control a and WPU/Cu2-XSe coated cotton fabrics b

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Photothermal conversion behavior

The light absorption of WPU/Cu2-XSe nanocomposite materials was mainly in the near-Infrared region. In this work, the photothermal conversion WPU/Cu2-XSe coated cotton fabrics was measured under the laser irradiation of 808 nm wavelength. As seen from Fig. 7a, the surface temperature of WPU/Cu2-XSe coated cotton fabrics gradually increases under the laser irradiation conditions. For different power of 0.5 W, 0.0 W, 1.5 W, and 2.0 W with a distance of 10 cm, the maximum temperature can be quickly achieved within 30 s. However, 0.5 W power is too weak to generate obvious photothermal conversion phenomenon of WPU/Cu2-XSe coated cotton fabrics, and the heating-temperature curve is very flat. It can be seen that the heating rate increases dramatically with the increase of laser power. The obtained temperature can be as high as 58.4 °C when the laser power is 2 W.

Fig. 7
figure 7

The temperature curves of WPU/Cu2-XSe coated cotton fabrics with different laser power (0.5–2.0 W) a, with different irradiation distance (10–40 cm) b, under cyclic heating–cooling process c, and irradiated by different power per unit area conditions d

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In order to further investigate the effect of the irradiation distance on the photothermal conversion process, the distance was varied from 10 to 40 cm when the power was constant as 2 W. In Fig. 7b, it can be observed that the heating temperature gradually increases with the irradiation distance deceasing from 40 to 10 cm. In addition, the decrease in irradiation distance greatly reduces the heating time for the coated fabrics to reach the maximum temperature. The robust heating efficiency is mainly due to the strong absorption capability of Cu2-XSe as photothermal conversion agent in near-infrared region (Wang et al. 2017, 2021).

Moreover, cyclic cooling and heating experiment was carried out to evaluate the durability of WPU/Cu2-XSe coated cotton fabrics in photothermal conversion applications. In details, the suspended fabric sample at the distance of 10 cm was firstly irradiated by laser for 70 s, and then paused for 100 s. This cyclic process was repeated for 4 times under a constant power of 2 W. As shown in Fig. 7c, the temperature of the modified fabrics is 58.2 °C after 40 s irradiation, and it drops to 19.3 °C after the termination of irradiation. The temperature can rise to 58.2 °C again when the laser irradiation process is resumed. It has indicated the excellent heating/cooling thermal stability and reusability of WPU/Cu2-XSe coated cotton fabrics. From Fig. 7d, the WPU/Cu2-XSe coated cotton fabrics demonstrate good photothermal response and photothermal stability under different irradiation power cyclic transformation. The temperature peaks of the fabrics under different powers are in good agreement with the tested results in Fig. 7c. These results show that WPU/Cu2-XSe coated cotton fabrics exhibit good photothermal stability and response under the irradiation of laser source.

Thermal imaging

The high photothermal conversion efficiency of WPU/Cu2-XSe coated cotton fabrics has a big potential for the coated fabrics to be used as thermal imaging device. A self-developed equipment was established to demonstrate the thermal imaging performance of the coated fabrics, as shown schematically in Fig. 8a. The WPU/Cu2-XSe coated cotton fabric was placed on a plate for the laser irradiation treatment, and a mobile phone was used as the thermal imager. The on and off mode can be well operated through the system with the surface temperature of the fabrics monitored, as shown in Fig. 8b. It can be seen that the luminous area was gradually increased, and fabric heater temperature increased to 58.2 °C under the laser irradiation for 50 s (Fig. 8c).

Fig. 8
figure 8

Schematic illustration of thermal imaging of WPU/Cu2-XSe coated cotton fabrics under laser irradiation a. Evolution of heating temperature b and thermal imaging c of the WPU/Cu2-XSe coated cotton fabrics

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Furthermore, photothermal stability of the WPU/Cu2-XSe coated cotton fabrics against folding, bending and twisting was tested. WPU/Cu2-XSe coated cotton fabrics experienced robust folding, bending, and twisting when the thermal imaging was taken, as shown in Fig. 9a. The shape of WPU/Cu2-XSe coated cotton fabrics can be clearly observed from the thermal imager. In Fig. 9b, the wearable applications of WPU/Cu2-XSe coated cotton fabrics was demonstrated. As a textile heater, the surface temperature can be quickly enhanced to 53.6 °C within 20 s irradiation time. These experimental results have indicated that WPU/Cu2-XSe nanocomposite coated cotton fabrics are promising candidates as photothermal imaging devices and as wearable heaters for body warming.

Fig. 9
figure 9

Photothermal stability of the WPU/Cu2-XSe coated cotton fabrics against folding, bending and twisting a. Wearable application of the fabric heater on arm b

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Photochromic performance

Photochromic materials exhibit high color-changing capability under the irradiation of ultraviolet light source (Little and Christie 2010; Wang et al. 2018). In this work, the photochromic performance of WPU/Cu2-XSe coated cotton fabrics was studied. Figure 10a is the schematic illustration of color changing for WPU/Cu2-XSe coated cotton fabrics under laser irradiation. Here, three thermochromic inks have been uniformly sprayed on the back side of WPU/Cu2-XSe coated cotton fabrics. Before laser irradiation, the fabrics show black, red and russet, respectively (Fig. 10b). When a 808 nm laser irradiates the as-prepared fabrics, the local temperature of the fabrics rises rapidly, causing the inks on the back side of the fabrics to change from black, red and russet to red, yellow and blue, respectively (Fig. 10c). The discoloration temperature of three ink pigments is 45 °C. When laser light source was used to irradiate the coated fabric, 48.9 °C was obtained after 10 s. It is higher than the discoloration temperature of the thermochromic inks, thus resulted into the discoloration of the ink. With the removal of the external light source the coated fabrics quickly recovers to the initial colors. These color changes suggest that WPU/Cu2-XSe coated cotton fabrics have good photochromic effects. In a word, the WPU/Cu2-XSe coated cotton fabrics exhibit excellent thermochromic performance with potential applications in information recording materials, dye lasers and anti-counterfeiting.

Fig. 10
figure 10

Schematic illustration of color change of WPU/Cu2-XSe coated cotton fabrics under laser irradiation a. Photochromic performance of WPU/Cu2-XSe coated cotton fabrics before c and after b laser irradiation

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Conclusions

In summary, WPU/Cu2-XSe nanocomposites were fabricated and successfully coated onto the surface of cotton fabrics. The WPU/Cu2-XSe functional layer was strongly bonded with cotton fabrics due to the chemical bonding and strong adhesion of waterborne polyurethane. The structural characterizations results have confirmed the uniform dispersion of Cu2-XSe nanoparticles within the coated layer. The existence of the WPU/Cu2-XSe was further confirmed by FTIR, SEM–EDS, XPS analysis and XRD diffraction. Furthermore, WPU/Cu2-XSe nanocomposites coated cotton fabrics showed excellent photothermal conversion efficiency, and the coated fabrics were demonstrated to be applied in thermal imaging and photochromic sensing textiles. Cyclic experiment has suggested the robust photothermal behavior stability of the coated cotton fabrics. This work provides novel strategy of developing multifunctional cotton fabrics for potential multifunctional applications.