Environmental method for preparation of higher color strength dyeing cotton fabrics with colored nanosilica pigment

Colored wastewater discharge into the water system would pose a severe threat to human health and aquatic life. It is critical to enhance dye utilization and reduce dye discharge in the textile industry. In this work, a novel colored silica nanosphere was designed as pigment to dye cotton fabrics and could be recycled in the dyeing process. The worm-like hydrophilic porous silica (WHMS) nanospheres possess a large specific surface area of 968.61 m2/g, an average size of 300 nm, and strong electronegativity. The WHMS-dye nanosphere was fabricated through the adsorption of rhodamine B (RB) and methylene blue (MB) onto WHMS nanospheres. The adsorption capacities of WHMS nanospheres towards RB and MB were above 500 mg/g. It demonstrated that the prepared WHMS-dye nanospheres possessed good stability and coloration performance on the cotton fabrics, originating from the enrichment of dyes on the WHMS nanospheres. The color strength of colored nanospheres-dyed cotton fabrics is deeper compared with the pure dye. Moreover, the dyed cotton fabrics show satisfactory color fastness and hand feel. The colored silica nanospheres could be reused for the next dyeing process to reduce dyes discharge. This work shows that WHMS-dye nanospheres may be used as an environmentally sound pigment for dyeing cotton fabrics to avoid a large amount of dyes discharge.

Abstract Colored wastewater discharge into the water system would pose a severe threat to human health and aquatic life. It is critical to enhance dye utilization and reduce dye discharge in the textile industry. In this work, a novel colored silica nanosphere was designed as pigment to dye cotton fabrics and could be recycled in the dyeing process. The worm-like hydrophilic porous silica (WHMS) nanospheres possess a large specific surface area of 968.61 m 2 /g, an average size of 300 nm, and strong electronegativity. The WHMS-dye nanosphere was fabricated through the adsorption of rhodamine B (RB) and methylene blue (MB) onto WHMS nanospheres. The adsorption capacities of WHMS nanospheres towards RB and MB were above 500 mg/g. It demonstrated that the prepared WHMS-dye nanospheres possessed good stability and coloration performance on the cotton fabrics, originating from the enrichment of dyes on the WHMS nanospheres. The color strength of colored nanospheres-dyed cotton fabrics is deeper compared with the pure dye. Moreover, the dyed cotton fabrics show satisfactory color fastness and hand feel. The colored silica nanospheres could be reused for the next dyeing process to reduce dyes discharge. This work shows that WHMS-dye nanospheres may be used as an environmentally sound pigment for dyeing cotton fabrics to avoid a large amount of dyes discharge.

Introduction
Cotton fabric, as an essential natural fiber, has been widely used in a variety of textiles due to its exceptional qualities of moisture absorption, comfort, and biodegradability (Li et al. 2020). As dyed fabrics exhibit good properties in bright color, good hand feel and fastness, tons of organic dyes like acid dyes, cationic dyes and reactive dyes are applied in the dyeing process each year. However, the textile colored wastewater is difficult to be removed due to high chemical stability. To enhance dye utilization, some dyeing technologies were developed, including modification technology on the cotton fabrics and pigment dyeing technology. For instance, cotton fabrics were modified using organosilicon-loaded hyperbranched poly(amidoamine) to achieve salt-free dyeing (Zhang et al. 2021). Due to its large particle size and poor dispersibility, there were some shortcomings for the pigment in poor color yield, crocking fastness, and stiff hand feel (Kan and Man 2017;Steiert and Landfester 2010). Nevertheless, the pigment dyeing method for fabrics possesses some superiorities in low water and energy consumption, high efficiency and less wastewater discharge, and has become a dominant trend in the textile industry (Song et al. 2020), which is corresponding to the idea of environmental and clean production. Compared with dyes, pigment exhibits high stability and hiding power property. Furthermore, the pigment has no affinity to fabrics, so that it can be applied in diverse fabrics through the binder to fix the pigment.
The produced colored wastewater is neither readily amenable to treatment and nor easy to be cleaned and biodegraded naturally (Isari et al. 2018). Focusing on reducing colored wastewater discharge, some methods have been investigated to remove organic dyes from colored solution, such as photocatalytic degradation and adsorption (Gao et al. 2019;Essandoh et al. 2021). Adsorption, as one of the most popular methods, is widely used to treat dyes because of its low cost, simplicity, and high efficiency. During the adsorption process, some special adsorbents could not only be utilized as the carrier of dyes or pigment to acquire the good color ability but also produce clean and reusable water and reduce the usage of auxiliaries.
Dyes/nanospheres perform great properties in promoting dye utilization and color depth of fabrics because their nano/microscale size and special structure could absorb more visible light in comparison to conventional dyes (Wilson et al. 2012). Inorganic matrix materials, which could be used as the carrier of dyes, include silica, hematite and titanium dioxide. Among these inorganic materials, silica material is an excellent inorganic matrix owing to its low index of refraction, and high specific surface area (Liang et al. 2017). Besides, it possesses some properties in harmlessness for humans, good biocompatibility, chemical stability and high thermal stability (Nagappan et al. 2019;Reid et al. 2018). Metanil yellow (My) dyes were effectively removed from dyes solution using the as-synthesized MCM-41 (Nagappan et al. 2019). In addition, many researchers took advantage of silica material to improve the stability of pigment. Hematite-silica heteromorphic pigment played a significant role in the protection of the occluded red a-Fe 2 O 3 chromophore crystals and show great chemical and thermal stability (Hosseini-Zori and Taheri-Nassaj 2012). Yin et al. synthesized modified silica coatings (OMSC) by sol-gel manner to apply in knitted cellulose fabric (Yin and Wang 2012). To some extent, the color fastness and stability of knitted fabrics treated with the OMSS were enhanced. Zhang et al. employed thermochromic silica nanocapsules (TLD@SiO 2 ) in the dyeing process. The dyeing polyester fabrics with TLD@SiO 2 exhibited good fastness ). Up to date, On the one hand, the silica material could be used for adsorption capacity towards organic dyes from solution. On the other hand, it was usually used by the copolymerization method or direct mixture with colorant instead of the carrier of dyes. However, the reported silica material presented poor adsorption performance. The research that silica material adsorbed dyes to form colored nanoparticles as pigment to enhance adsorption performance has rarely been reported in the reported literature.
In this work, cotton fabrics were dyed using colored worm-like hydrophilic porous silica (WHMS) pigment by padding, which the pigment was prepared through the adsorption of cationic dyes onto WHMS nanospheres from dye solution, realizing high dye utilization, good coloration performance and low dye discharge. The WHMS nanospheres showed a regular spherical shape, high specific surface area, good stability and distribution. During the adsorption of the dye process, the adsorption performance was investigated through UV-vis spectra. Colored nanospheres were characterized by XRD and TG tests, and possessed great stability and coloration ability. The dyed cotton fabrics with colored nanospheres show good color fastness and higher color depth than those with pure dyes. Besides, pigment can be collected to be recycled due to the good dispersibility.

Preparation of WHMS nanospheres
Cetyltrimethylammonium bromide (2 mmol) was added to water and stirred for 20 min. Triethylamine and anhydrous alcohol were mixed with the transparent solution, and the reaction was performed at 65°C for 1.5 h. Then tetraethyl-orthosilicate was dropped into the above mixed solution under rapid stirring condition. Finally, the precipitates were obtained after centrifugation and calcination at 520°C for 5 h in air.

Fabrication of colored nanospheres (WHMS-dye nanospheres)
Adsorption was conducted by batch adsorption experiments under the conditions of pH value (pH = 5), initial dye concentration (450 mg/L), temperature (20°C), and contact time (100 min). The WHMS nanospheres were put into a glass beaker with 100 mL of dye solution and stirred at 220 rpm until adsorption equilibrium, then the mixture solution was stopped for 5 min waiting the colored nanospheres settled to the bottom. The colored nanospheres were acquired by centrifugation. The dye absorption capacity q e (mg/g) on WHMS nanospheres was calculated using Eq. 1.
where q e (mg/g) is the adsorption capacity at equilibrium for dyes, m(g) refers to the mass of the adsorbent. c 0 and c e signify the concentration of dye at initial and equilibrium conditions, respectively, V (L) represents the solution volume.
Dyeing procedure with colored nanospheres 1 g of colored nanospheres and the pure dyes in accord with the dye contents of colored nanospheres were respectively added into 20 g of deionized water in a beaker. The mixture solution was treated by ultrasound for 10 min to diffuse. Then, the thicker and 2 g of binder were added into the above mixture solution, and 6 cm * 6 cm cotton fabrics were dyed by the padding manner under the wet pick-up of 70% condition using horizontal resin pressing and dyeing machine (rolling mill) (P-B1). Finally, the dyed cotton fabrics were dried at 90°C for 4 min and cured at 120°C for 3 min through heat setting machine (MINITENTER).

Characterization
The surface morphologies of the cotton fabrics and WHMS nanospheres were evaluated by field emission scanning electron microscopy (FESEM, S-4800, Japan) and scanning electron microscopy (SEM, T1000, Japan) at room temperature. The thermal stability of WHMS nanospheres was carried out by thermogravimetric analysis (TG) from 50 to 800°C at the heating rate of 10°C/min. The particle diameter was performed by Malvern nanometer particle size analyzer (Nano ZS, UK). Contact angle (CA) was examined by contact angle meter (DSA30). Brunauer-Emmett-Teller (BET, TriStarII3020M) was used to determine surface area and pore volume by N 2 adsorption-desorption. The powder X-ray diffraction (XRD, D/max-2550VB?/PC, Japan) and Fourier transform infrared (FT-IR, Spectrum Two, USA) were employed to analyze sample crystal structure and chemical groups. The UV-Vis spectra of the WHMSdye nanospheres were tested by a UV-visible Spectrophotometer (U-3310). The morphologies of the fibers before and after dyeing were photographed through the ultra-depth 3D microscope (VHX-6000). The viscosity of the paste was performed by a viscometer (Bookfield viscometer DV2TLV, USA). The soaping test of colored nanospheres was performed to evaluate the stability. 0.1 g of samples were added into 50 g of deionized water in a beaker and washed under 2 g/L soap solution condition by water bath shaker (DLS-1000 A, Daelim Starlet Co., Ltd) for 10 min at 80°C, and then the residue of the solution was measured by UV-visible Spectrophotometer (U-3310). The rubbing fastness of dyed fabrics was evaluated according to GB/T 3920-2008. The samples were carried out to separately rub 10 times for dry condition and wet condition with the moisture of 95% water by fastness tester (Y571B). The washing fastness of dyed fabrics was tested according to GB/T 3920-2008. The samples were washed under 2 g/L soap solution condition by water bath shaker (DLS-1000 A, Daelim Starlet Co., Ltd). The K/S value and L*, a*, b* values were carried out by color gameter (DATACOLOR 650) to estimate the apparent color depth of cotton fabrics, the hand feel of fabrics was tested by PhabrOmeter (PHABROMETER MODEL 3). The color uniformity of dyed fabrics was tested by the K/S values on the different areas of dyed cotton fabrics. The eight K/S values were randomly attained on the surface of dyed fabrics by color gameter (DATACOLOR 650) measurement. Then the average value of the K/S values (K=S) and the deviation value (the relative unevenness, Sr) were concluded.

Characteristics of WHMS nanospheres
The WHMS structure plays an important role in the adsorption capacity towards dyes. It can be clearly observed that WHMS nanospheres with the mean value of about 300 nm were relatively spherical shape and had a rough surface in Fig. 1a, b. TEM image reveals that the WHMS nanospheres with similar WO nanophase (worm-like) and parallel pore channels were formed. As the WHMS nanospheres existed the hydrolysis layer in water solution, the particle size (Fig. 1a, inset) was larger than 300 nm (Kobler et al. 2008). Figure 1c shows the WHMS nanospheres possess a high specific surface area of 968.60 m 2 /g and a big pore volume of 0.84 cm 3 /g. The water contact angle (CA) test was presented in Fig. 1d. CA of WHMS nanospheres is 50°, suggesting that WHMS nanospheres have higher hydrophilicity property, which is caused by hydroxy groups on the surface of WHMS nanospheres (Marjani et al. 2020). In Fig. 1e, the diffraction peak of WHMS nanospheres at approximately 2h = 2.4°was assigned to the existence of the worm-like structure, corresponding to the (100) crystal plane (Zhang et al. 2013). Thus, these indexes proved that prepared porous silica nanospheres displayed a worm-like and porous structure, which was favorable for dye adsorption. The thermal stability of WHMS nanospheres was estimated from 50 to 800°C as presented in Fig. 1f. The result found that WHMS nanospheres only had one degradation stage occurring at about 200°C and approximately weight loss reached 2.8%, which was ascribed to the lack of chemically contained water and a part of hydroxy groups (Polshettiwar et al. 2010), indicating that WHMS nanospheres had high thermal stability.

Characteristics of WHMS-dye nanospheres
The effect of loading conditions on WHMS-dye nanospheres Because dye contents on the nanospheres could affect the coloration ability of colored nanospheres, some important factors of dye adsorption such as pH values, temperature and time were investigated. The preparation route of colored nanospheres pigment is presented in Fig. 2. The WHMS nanospheres were prepared for the hydrolysis of TEOS by a simple sol-gel method, and the as-prepared WHMS nanospheres loaded dyes to form colored nanospheres. Finally, colored nanospheres were collected as pigment by centrifugation. In Fig. 3a, the color of powders transferred from white color to blue and red color after adsorption using WHMS nanospheres, and colored nanospheres powders displayed bright and vivid color, confirming that WHMS nanospheres exhibited good adsorption ability towards dyes. The intra-particle diffusion model for dye adsorption on the WHMS nanospheres was investigated (Fig. 3b). The curves of q t against t 1/2 present three linear segments, which are expressed as the boundary layer diffusion process, the steady adsorption process, and adsorption on the interior surface of nanospheres process, respectively. All the fitting curves of q t versus t 1/2 did fail to pass through the origin, confirming that intra-particle diffusion and surface adsorption might participate concurrently in the dye adsorption process (Kang et al. 2018). The adsorption capacities of WHMS nanospheres for MB and RB dyes show a decreased trend with increasing temperature (Fig. 3c, d). Figure 3e showed that the adsorption capacity of dyes gradually increased until saturation adsorption as time extended. In Fig. 3f, when the pH value increased, the adsorption performance of MB onto the WHMS nanospheres displayed a gradually increased phenomenon, while the adsorption capacity of RB increased with pH value increasing from 3 to 5, and then appeared decreasing tendency as the pH value increased from 5 to 11. For WHMS nanospheres, it is possible to completely remove dyes from solution when the dyes solution of 20 mL was in a state of suitable pH values and dosage of WHMS nanospheres, and ye concentration of 200 mg/L. The adsorption mechanism for WHMS nanospheres was explained in Fig. 3g. The pigment was obtained through the adsorption of dyes onto WHMS nanospheres from dye solution due to their electronegative surface.

Property of WHMS-dye nanospheres
The FTIR spectra of the WHMS nanospheres, MB and RB dyes, and colored nanospheres were analyzed in Fig. 3a, b. The peaks of 1080 cm -1 were caused by the Si-O-Si of stretching vibrations, and the appearing peaks around 3320 cm -1 and 960 cm -1 were Fig. 1 a SEM images of WHMS nanospheres (inset is size distributions of WHMS in water), b TEM images of WHMS nanospheres, c N 2 adsorption-desorption isotherms curves (inset presents BJH pore size distribution), d the water contact angle of WHMS nanospheres, e the low-angle XRD of WHMS nanospheres, f TG analysis of WHMS nanospheres corresponding to the stretching vibrations of Si-OH (Huang et al. 2017). It can be seen that the obvious characteristic peak of 578 cm -1 stands for frame vibration of C-S-C, and peaks of 1400 cm -1 and 1590 cm -1 refer to the aromatic ring (Xiao and Man 2007). Additionally, the characteristic peak of C-H stretching groups for WHMS-RB appeared at 2920 cm -1 (Ghorai et al. 2014). These results manifested that RB and MB dyes were successfully adsorbed on the surface of WHMS nanospheres.
The obtained XPS spectra are shown in Fig. 4c-e. The peaks intensity of WHMS-MB and WHMS-RB become weak in terms of O1s and Si2p compared with WHMS nanospheres, because the introduced dyes molecules on WHMS materials decrease the transmittance. The N1s region was fitted with peaks at 399.4, 399.6, and 402.3 eV in Fig. 4d, e. The peaks at 399.4 and 399.6 eV could be assigned to imino groups (=N-R) of MB and RB (Yan et al. 2018;Zangmeister et al. 2013). Meanwhile, the peak locating at 402.3 eV Fig. 2 The fabrication route of colored nanospheres pigment Fig. 3 a The images of powders before and after dye adsorption using WHMS nanospheres, b fitting curves of intra-particle diffusion model, the effect of adsorption temperature on dye adsorption capacity c MB and d RB, e the effect of contact time on dye adsorption capacity (dye concentration = 200 mg/L, dosage of WHMS nanospheres = 10 mg), f the effect of pH on dye adsorption capacity (dye concentration = 200 mg/L, dosage of WHMS nanospheres = 10 mg), g the adsorption of dye mechanism on WHMS nanospheres could be ascribed to substituted amines (N-R) (Yan et al. 2018). After adsorption, the binding energy of =N-R and N-R increases. The results are likely to exist hydrogen bonding and electrostatic interaction between WHMS nanospheres and N ? and N-R of MB and RB (Feng et al. 2021;Wang et al. 2018). These correlative peaks verify the existence of RB and MB and the connection between dyes and WHMS materials through electronic interaction. The particles sizes of nanospheres increased after dye adsorption from Fig. 4f, which was related to loaded dyes on the WHMS nanospheres.
For colored nanospheres, thermal stability was analyzed to apply in the practical dyeing process. TG and DTG curves of various powders were shown in Fig. 5a-d. Figure 5a, c exhibited that multiple endothermic reactions appeared, and the first stage suggested the weight loss of 2.5% located at 100-200°C, which could be caused by the loss of water. For RB and MB dyes, there are some obvious weight loss peaks located at 230-600°C due to the thermal decomposition of the dye structure. The 25% weight loss occurred at 230-350°C, which was assigned to the degradation of azo groups (N = N) in the RB and MB structure (Kang et al. 1994). About 35.0% weight loss at the stage of 350-600°C occurred, originating from the degradation of aromatic rings (Yavuz et al. 2018). Comparatively, in terms of WHMS-RB and WHMS-MB nanospheres, it is found that the WHMS nanospheres and the colored ones Fig. 4 a The FTIR spectra of WHMS and MB before and after dye adsorption, b the FTIR spectra of WHMS and RB before and after dye adsorption, c XPS full-range spectra of WHMS before and after dye adsorption, d, e N1s spectra of WHMS-MB and WHMS-RB, respectively, f the size distributions of WHMS nanospheres loaded dye in water have similar thermal degradation trends. The residue mass of WHMS-dye nanospheres was higher than that of pure dyes. This can be explained as the existence of strong interaction between dye molecules and nanospheres, which formed a new structure that hindered the decomposition of the dyes during the heating process (Song et al. 2020). The soaping test of WHMS-dye pigment was conducted to better understand the colored nanosphere's stability. Figure 5e and f display the UV-Vis spectra of soaping residue for colored nanospheres. The adsorption peaks of the residue of WHMS-RB and WHMS-MB nanospheres were low after the soaping test, and the residue images presented lighter color. These results further proved that WHMS nanospheres have strong interaction with RB and MB dyes.

Preparation and characteristics of dyeing cotton fabrics
The dyeing process and mechanism for cotton fabrics were revealed in Fig. 6. It was observed that cotton fabrics were dipped into the colored paste and treated to obtain dyed fabrics with deeper color depth. Figure 6b illustrated that the pigment was fixed on the surface of cotton fabrics through the binder. After dyed cotton fabrics were treated, the surface of cotton fabrics formed a layer film to fix the pigment. To analyze the effect of WHMS nanospheres on coloration ability, as shown in Fig. 7a, the UV-Vis spectra of the WHMS nanospheres, WHMS-dye nanospheres, and dyes were investigated. The characteristic peaks of WHMS-MB and WHMS-RB spectra emerged the blue-shift phenomenon in comparison to the MB and RB dyes, originating from the interaction between WHMS nanospheres and dyes (Fu et al. 2016). Besides, MB appeared obvious blue-shift in contrast to RB, which was related to dye structure. To further investigate the effect of WHMS nanospheres on the paste system, the viscosity of paste was conducted. In Fig. 7b, the viscosity of paste gradually decreased with increasing shear rate for both pure paste and WHMS-paste. The viscosity of WHMSpaste had a slight difference from that of pure dye paste, which proved that WHMS nanospheres has rarely an effect on paste viscosity. The morphologies  Fig. 7c, d. In Fig. 7c, SEM shows that the original cotton fabrics have clear gaps between fibers, a flat and stripes surface. The fibers of dyed cotton fabrics (Fig. 7d) were adhered together through the binder, and the colored nanospheres were fixed on the surface of the dyed fabrics, causing a rough surface of dyed fabrics. The colored nanospheres fixed on the cotton fabrics could absorb more visible light due to higher dye contents, contributing to the enhancement of coloration performance.

Coloration property of dyed cotton fabrics with WHMS-dye nanospheres
The color parameters of dyed cotton fabrics, such as the color strength (K/S value) and the CIE1931 chromaticity diagrams, are evaluated in Fig. 8a-e. The K/S values are defined as the ratio of the scattering coefficient to absorption and usually used to illustrate the color depth of dyed fabrics, which the higher the value is, the color strength is greater (Lee and Kim 2004). Besides, the CIE 1931chromaticity diagram can directly give visualized color property according to the color values of X and Y (Chen et al. 2020). In Fig. 8a, b, it can be concluded that the K/S value of dyed fabrics with WHMS-dye nanospheres is higher than that of pure dyes in the dyebath. The color depth of WHMS-MB nanospheres-dyed cotton fabrics increased by 1.1 times. At the same time, the K/S values of dyed cotton fabrics are 0.48 and 0.8 for RB and WHMS-RB nanospheres, respectively. The color of colored nanospheres was dependent on the type of dye, suggesting that the dyed cotton fabrics could obtain different colors using different colored nanospheres. To further elucidate the color change of the dyed cotton fabrics, the relationship with different pigments can be observed from the CIE 1931 chromaticity diagrams (Fig. 8c). The results indicated that color changes of dyed cotton fabrics could be obtained by tuning the variety of WHMS-dye pigments. In addition, the chromatic parameters of L*, a*, and b* values were studied. The chromatic parameter of L* shows the property of color lightness. The parameters of a* and b* refer to red-green color properties, and yellow-blue color properties, respectively (Chen et al. 2019). As shown in Fig. 8d, it reveals that the dyed fabrics with WHMS-MB nanospheres become higher green and blue and possess lower lightness compared with pure MB dye. In Fig. 8e, it also existed a similar trend that the dyed fabrics with WHMS-RB nanospheres become more Fig. 6 Schematic of dyeing illustration: a the dyeing process, and b dyeing mechanism red and blue and have lower lightness compared with pure RB dye. In Fig. 8f, g, the images further explained the dyed fabrics with WHMS-dye nanospheres present deeper color depth.
Dyed cotton fabrics properties in hand feel, rubbing fastness, washing fastness, and uniformity were investigated in Fig. 9; Tables 1 and 2. It could be found that the stretch, wrinkle and drap of dyed fabrics have not obviously decreased in comparison to pristine cotton in Fig. 9a and b, and the hand feel and softness of the colored nanospheres dyed cotton fabrics have nearly the same property as the dye dyed cotton fabrics. The hand feel and softness could meet the requirement of the application. From Fig. 9c, d, dyed cotton fabrics showed uniform and bright color, and the dyed cotton fabrics with colored nanospheres show much deeper color than dyed cotton fabrics with dyes, corresponding to the K/S values for dyed cotton fabrics (Fig. 8). From Table 2, the average K/S values (K=S) are close to K/S values for dyed fabrics, and the deviation values (the relative unevenness, Sr) are relatively small. Therefore, the dyeing uniformity of dyed cotton fabrics is good. These results demonstrate colored nanospheres as pigment would be potentially employed in dyeing fabrics. The colorfastness is relevant to the strong connection between the binder  (Li et al. 2018). The level of rubbing and washing fastness of dyed cotton fabrics is gained in Table 1. The dyed cotton fabrics exhibited satisfactory rubbing and washing fastness with at least 3-4 grades.

Recycled colored properties on the cotton fabrics with WHMS-dye nanospheres
The colored WHMS nanoparticles as a novel pigment were designed to avoid the overuse of water resources and dyes discharge. The benefit of this study is that WHMS nanospheres in the residual solution can be collected through centrifugation to reuse for the next dyeing process, achieving a clean and green dyeing process. The recycled WHMS-dye nanospheres are employed to dye cotton fabrics based on the previous dyeing steps to verify the dyed effect. The coloration ability of colored nanospheres on the dyed fabrics after recycle is shown in Fig. 10. Dyed cotton fabrics with a small variation of K/S values for samples before and after recycling are observed, indicating that the color strength of the gained cotton fabrics has almost no change using the recycled pigment. The color repeatability of the obtained cotton fabrics demonstrated the feasibility of the recycled pigment, providing a method to realize a clean production process in the textile industry.

Conclusions
The colored nanospheres as pigment were successfully prepared and dyed cotton fabrics, exhibiting enhanced color performance, and high dye utilization. The asprepared porous silica nanospheres possessed a nearly spherical shape, a rough surface, and a high specific surface area of 968.60 m 2 /g with an average size of 300 nm. The WHMS nanospheres exhibited great adsorption performance towards RB and MB, which the dye contents on the WHMS nanospheres are calculated of above 500 mg/g. From TG measurement and soaping test, it is shown that the cationic dye molecules formed strong interaction with the WHMS nanospheres. After dyeing on cotton fabrics, the dyed fabrics using colored nanospheres exhibited higher coloration performance, resulting from the enrichment of dyes on the porous silica nanospheres. In comparison with pure dyes, the dyed cotton fabrics with   The dyed fabrics also show satisfactory color fastness and hand feel. Besides, the colored nanospheres could be collected in the residue for the next dyeing process.