Preparation of Y2O3/TiO2-Loaded Polyester Fabric and Its Photocatalytic Properties under Visible Light Irradiation

In this study, Y2O3/TiO2-loaded polyester fabric was prepared to improve the catalytic activity of the TiO2 and to increase its reuse efficiency. The samples were systematically characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FT-IR). Furthermore, the degradation performance of methyl orange in the presence of simulated visible light irradiation was also investigated. The results showed that the TiO2 in the Y2O3/TiO2 composite photocatalyst was suitably anatase. In addition, Y2O3/TiO2-loaded polyester fabric had higher photocatalytic performance than that of pure polyester fabric under visible light and the degradation rate reached 83% after 120 min of light exposure but remained above 50% after repeated exposure (three times). Compared to the pure polyester fabric, Y2O3/TiO2-loaded polyester fabric had self-cleaning effects in methyl blue and soy sauce solutions under visible light.


Introduction
Recently, the development of functional and intelligent textiles has attracted considerable attention worldwide [1] and among these, fabrics with photocatalytic and self-cleaning properties have been widely studied [2,3]. The energy band structure of semiconductors contributes to the theoretical basis of photocatalytic reactions [4], and most semiconductor photocatalysts are of the n-type semiconductor material with a band gap between the valence and conduction bands. An incident photon makes the electrons in the valence band become excited and transition to the conduction band after energy absorption, leaving holes in the valence band. At the same time, many photo-generated holes (h + ) and electrons (e − ) will be produced in the conduction band and valence band, which makes the valence band reduced, and the electrons in the conduction band oxidized, leading to oxidation or reduction of the contaminants. The surface of the fabric is modified by loading a photocatalyst [5], which will generate electrons and holes with redox ability under sunlight to purify pollutants [6].
Commonly used photocatalysts include TiO 2 [7,8], SnO 2 [9,10], ZnO [11,12], and ZrO 2 [13,14]. Among them, TiO 2 , as a photosensitive semiconductor, has attracted widespread attention due to its high stability and non-toxicity [15] and therefore, has been widely used in the field of photocatalysis. However, the wide band gap of TiO 2 (3.2 eV) means that it can only be photo-activated under ultraviolet light, resulting in low collection efficiency of the visible light in sunlight [16]. It has been reported that TiO 2 has various size, nanostructure, and polymorphs (anatase polymorph, rutile polymorph, mixed anatase-rutile polymorphs, etc.) [17]. Moreover, the TiO 2 lattice is distorted by doping with rare earth oxides, which can accept more light to excite holes and generate stronger surface free radicals causing oxidation of the pollutant molecules [18]. In addition, rare earth elements have a special electronic structure of 4fx5dy, which plays an important role in the photo-generated charge transfer between the 4f energy level and the conduction band or valence band of TiO 2 [19]. As a heavy rare earth oxide, Y 2 O 3 has a relatively small atomic radius with the energy gap of 6.3 eV [20], which can improve the photocatalytic activity of TiO 2 [21] and it has been found that an appropriate combination of Y 2 O 3 can effectively improve the photocatalytic activity of TiO 2 in the visible light band [22].
To date, Jiang et al. [23] prepared Ag-loaded TiO 2 /Y 2 O 3 hollow microspheres with a double shell structure of melamine formaldehyde using the sol-gel method and high temperature calcination reduction. The results showed that the degradation efficiency of methyl orange by TiO 2 /Ag/Y 2 O 3 increased seven times under visible light when compared to TiO 2 hollow spheres. Using the combustion and precipitation method, Li et al. [24] synthesized a novel composite photocatalyst TiO 2 /Y 2 O 3 :Yb 3+ , Tm 3+ and the photocatalytic activity of this composite was higher than that of pure TiO 2 under solar light irradiation. Ahmed et al. [25] prepared an Eu-doped Y 2 O 3 :TiO 2 nanocomposite via the sol-gel synthesis process and the optical properties of the synthesized nanocomposite were investigated at different temperatures, and its application as a potential material for thermographic phosphor and in LED fabrication was investigated.
Although photocatalysts from the above research exhibited enhanced photoactivity, photocatalysts mostly exist in the form of nano powders, which are difficult to separate and recover from bodies containing water causing a waste of resources. Therefore, the development of matrix materials loaded with photocatalysts to improve the service efficiency of photocatalysts is urgently needed. Zhu et al. [26] developed a nanoparticle/polymeric capsule via an in situ growth method, of which lead-free bismuth halide peroskite nanocrystals and covalent organic frameworks are used as core and shell, respectively, demonstrating good water processability as well as excellent photocatalytic performance. Polyester fabrics are also widely used because of their low cost, good durability, and high stability [27,28]. However, polyester fabric macromolecules lack polar functional groups on their surfaces as well as a highly crystalline structure. It is reported that nanoparticle/polymer composites designed with combination of initial interpenetrating polymer network structure and organo-inorganic interpenetrating polymer network structure could significantly influence the relaxation behavior of the composites [29]. Moreover, the ordered polymer chains in the crystal lattice are too dense, which makes low bonding strengths when combining them with inorganic nano-photocatalytic materials [30]. Polar functional groups can be introduced onto the surface by chemical modification and plasma treatment to improve the speed of bonding of the inorganic powder and fabric surface [31].
In this study, tetrabutyl titanate and yttrium nitrate hexahydrate were used as raw materials to prepare Y 2 O 3 /TiO 2 with photocatalytic activity in the visible light range using the sol-gel method. Y 2 O 3 /TiO 2 was modified by 3-aminopropyltrimethoxysilane (APTMS) to enhance, the interaction between Y 2 O 3 /TiO 2 and polyester fabrics through Si-O-Ti bonds [27] for the preparation of Y 2 O 3 /TiO 2 loaded polyester fabrics. The samples were systematically characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FT-IR). Furthermore, methyl orange was used as an organic pollutant and the photocatalytic self-cleaning properties of modified polyester fabrics were studied under xenon lamp irradiation.

Preparation of Y 2 O 3 /TiO 2
First, 46 mL of absolute ethanol and 6 mL of glacial acetic acid were mixed followed by the addition of 10 mL of tetrabutyl titanate under vigorous stirring, and then 3 mL of distilled water and an appropriate amount of Y(NO 3 ) 3 ·6H 2 O were sequentially added with vigorous stirring for 60 min. After this, the xerogel was prepared via aging for 90 min and drying at 60 • C for 24 h. Finally, the xerogel was calcined in a resistance furnace at 500 • C for 2 h to obtain a Y 2 O 3 /TiO 2 catalyst. Composite catalysts containing different mole fractions (0.5%, 0.75%, 1%) of Y 2 O 3 were prepared with different molar ratios of Y(NO 3 ) 3 ·6H 2 O. The preparation flow chart of Y 2 O 3 /TiO 2 is shown in Figure 1.

Preparation of Y2O3/TiO2
First, 46 mL of absolute ethanol and 6 mL of glacial acetic acid were mixed followed by the addition of 10 mL of tetrabutyl titanate under vigorous stirring, and then 3 mL of distilled water and an appropriate amount of Y(NO3)36H2O were sequentially added with vigorous stirring for 60 min. After this, the xerogel was prepared via aging for 90 min and drying at 60 °C for 24 h. Finally, the xerogel was calcined in a resistance furnace at 500 °C for 2 h to obtain a Y2O3/TiO2 catalyst. Composite catalysts containing different mole fractions (0.5%, 0.75%, 1%) of Y2O3 were prepared with different molar ratios of Y(NO3)36H2O. The preparation flow chart of Y2O3/TiO2 is shown in Figure 1.

Preparation of Y2O3/TiO2-Loaded Polyester Fabrics
First, 0.5 g of Y2O3/TiO2 was dispersed in 100 mL of diluted ethanol solution (Vethanol:Vdistilled water = 95:5), and then 5 mL of 3-aminopropyltrimethoxysilane (APTMS) was added and sonicated for 30 min. The mixture was then centrifuged and washed with alcohol, followed by drying in a vacuum oven at 70 °C to obtain amino functionalized Y2O3/TiO2, which was abbreviated to NH2-Y2O3/TiO2. The polyester fabrics were immersed in a solution containing 1 mg/L NH2-Y2O3/TiO2, and then oscillated for 1 h to

Preparation of Y 2 O 3 /TiO 2 -Loaded Polyester Fabrics
First, 0.5 g of Y 2 O 3 /TiO 2 was dispersed in 100 mL of diluted ethanol solution (V ethanol :V distilled water = 95:5), and then 5 mL of 3-aminopropyltrimethoxysilane (APTMS) was added and sonicated for 30 min. The mixture was then centrifuged and washed with alcohol, followed by drying in a vacuum oven at 70 • C to obtain amino functionalized Y 2 O 3 /TiO 2 , which was abbreviated to NH 2 -Y 2 O 3 /TiO 2 . The polyester fabrics were immersed in a solution containing 1 mg/L NH 2 -Y 2 O 3 /TiO 2 , and then oscillated for 1 h to ensure that ester groups in polyester fabrics and amino groups in NH 2 -Y 2 O 3 /TiO 2 were fully reacted, followed by drying at 60 • C to obtain Y 2 O 3 /TiO 2 loaded polyester fabrics.
The schematic diagram of APTMS modified Y 2 O 3 /TiO 2 is shown in Figure 2 and the local enlarged view of Y 2 O 3 /TiO 2 -NH 2 nanoparticles bonded on polyester fabrics is shown in Figure 3. ensure that ester groups in polyester fabrics and amino groups in NH2-Y2O3/TiO2 w fully reacted, followed by drying at 60 °C to obtain Y2O3/TiO2 loaded polyester fabrics The schematic diagram of APTMS modified Y2O3/TiO2 is shown in Figure 2 and local enlarged view of Y2O3/TiO2-NH2 nanoparticles bonded on polyester fabrics is sho in Figure 3.

Photocatalytic Degradation of Methyl Orange
Methyl orange solution with a concentration of 20 mg/L was prepared, and then mL of the prepared solution taken to the photocatalytic materials, followed magnetically stirring for 30 min in the dark to reach the adsorption equilibrium. A xen light source (300 W) was used to simulate a visible light source to analyze the visible li catalytic performance of the photocatalyst. The supernatant was extracted at regu intervals and the absorbance at a wavelength of 464 nm was measured by a dual-be UV-Vis spectrophotometer (TU-1900).

Surface Morphology Analysis
The surface characteristics and crystal shape of the catalysts were analyzed by us ZEISS Gemini SEM 300 field emission scanning electron microscope. ensure that ester groups in polyester fabrics and amino groups in NH2-Y2O3/TiO2 w fully reacted, followed by drying at 60 °C to obtain Y2O3/TiO2 loaded polyester fabrics The schematic diagram of APTMS modified Y2O3/TiO2 is shown in Figure 2 and local enlarged view of Y2O3/TiO2-NH2 nanoparticles bonded on polyester fabrics is sho in Figure 3.

Photocatalytic Degradation of Methyl Orange
Methyl orange solution with a concentration of 20 mg/L was prepared, and then mL of the prepared solution taken to the photocatalytic materials, followed magnetically stirring for 30 min in the dark to reach the adsorption equilibrium. A xe light source (300 W) was used to simulate a visible light source to analyze the visible l catalytic performance of the photocatalyst. The supernatant was extracted at reg intervals and the absorbance at a wavelength of 464 nm was measured by a dual-be UV-Vis spectrophotometer (TU-1900).

Surface Morphology Analysis
The surface characteristics and crystal shape of the catalysts were analyzed by us ZEISS Gemini SEM 300 field emission scanning electron microscope.

Photocatalytic Degradation of Methyl Orange
Methyl orange solution with a concentration of 20 mg/L was prepared, and then 100 mL of the prepared solution taken to the photocatalytic materials, followed by magnetically stirring for 30 min in the dark to reach the adsorption equilibrium. A xenon light source (300 W) was used to simulate a visible light source to analyze the visible light catalytic performance of the photocatalyst. The supernatant was extracted at regular intervals and the absorbance at a wavelength of 464 nm was measured by a dual-beam UV-Vis spectrophotometer (TU-1900).

Surface Morphology Analysis
The surface characteristics and crystal shape of the catalysts were analyzed by using ZEISS Gemini SEM 300 field emission scanning electron microscope.

Crystal Structure Analysis
The photoelectric spectrum was analyzed using X-ray photoelectron spectroscopy with the model K-Alpha+ produced by Thermo Scientific (Waltham, MA, USA).

Chemical Composition Analysis
The phase composition of the catalyst was analyzed by using the D/MAX-2500 Xray diffractometer (XRD) produced by Rigaku Corporation (Tokyo, Japan), with a 40 kV working voltage, 100 mA current as well as a 10 • -80 • scanning range (2θ).
The samples were irradiated with infrared light in the scanning range of 8300-350 cm −1 using a model of Spectrum Two equipment produced by Perkin Elmer (Boston, MA, USA). When the vibration of the molecular groups was the same as the frequency of the infrared spectrum, they could be distinguished. This group was compared with the standard infrared spectrum to determine the composition of the sample.

UV-Vis Analysis
A UH4150 UV-Vis spectrophotometer (UV-vis), produced by Hitachi (Tokyo, Japan) was used to measure the UV-visible light absorption spectrum of the samples at a scanning speed of 1200 nm/min at intervals of 1 nm.

Self-Cleaning Property
To investigate the self-cleaning performance of the pure polyester fabric and Y 2 O 3 / TiO 2 -loaded polyester fabric under simulated visible light, 0.1 mL of methyl blue solution and soy sauce were dropped on the polyester fabric and that loaded with Y 2 O 3 /TiO 2 and irradiated under a xenon lamp for 18 h and sample images taken every 6 h. Figure 4 shows scanning electron microscope images of TiO 2 and Y 2 O 3 (the molar content is 0.75%) under 100,000 times magnification. It can be seen from Figure 4a that the prepared TiO 2 nanoparticles were spherical, with a diameter of about 10 nm, and the distribution is relatively uniform. As shown in Figure 4b, Y 2 O 3 /TiO 2 remained spherical without differences in morphology due to the low content of Y 2 O 3 . However, there were slight clusters between the particles because the diameters of the particles were slightly reduced after recombination, and the nanoparticles with small diameters were more likely to agglomerate. This showed that addition of an appropriate amount of Y 2 O 3 inhibited the growth of TiO 2 grains.

Crystal Structure Analysis
The crystalline structure of the three photocatalytic materials, namely TiO 2 , Y 2 O 3 , and Y 2 O 3 /TiO 2 (the molar content of Y 2 O 3 is 0.75%) are shown in Figure 6. As shown in Figure 6a [32]. In addition, contrast diffraction peak positions were in accordance with TiO 2 standard diffraction card (JCP-DS84-1285), indicating that the prepared TiO 2 was anatase type [33]. In Figure 6b [34]. However, the diffraction peak of Y 2 O 3 could not be seen in Figure 6c; this may be due to the low content of Y 2 O 3 which may not have been enough to change the crystal form of TiO 2 [35], where TiO 2 remained the titanite type in the Y 2 O 3 composite photocatalyst [36].
The         [38], while the Ti peak, O peak, and Y peak were from Y 2 O 3 /TiO 2 composite photocatalyst in polyester fabric. In Figure 8b, two Ti2p peaks (Ti2p3/2 and Ti2p1/2) were detected at 456.05 eV and 463 eV, respectively, indicating the presence of Ti 4+ on the polyester fabric [37,39]. Figure 8c is the XPS spectrum of the O1s region of Y 2 O 3 /TiO 2 -loaded polyester fabric, which is mainly divided into three peaks. The O element appearing at 529.03 eV shows the Ti-O-Y bond, while that at 529.9 eV indicates O 2− in the sample [40]. The content of O 2− was relatively high, indicating that O in the Y 2 O 3 /TiO 2 composite photocatalyst mainly existed in the form of the negative divalent [41]. Moreover, the O element at 532 eV was derived from the -OH produced by the adsorption and dissociation on the sample surface [39], indicating that the holes generated by the Y 2 O 3 /TiO 2 composite photocatalyst after light excitation reacted with the adsorbed H 2 O or OH ions on the surface, forming the hydroxyl radicals, which helped to improve the photocatalytic performance of Y 2 O 3 /TiO 2 composite photocatalyst [42].

Chemical Composition Analysis
O, and Y in the Y2O3/TiO2-loaded polyester fabric. It can be seen from Figure 8a that Y2O3/TiO2-loaded polyester fabric mainly contained Ti, Y, O, and C elements, and the C peak and O peak were mainly from polyester [38], while the Ti peak, O peak, and Y peak were from Y2O3/TiO2 composite photocatalyst in polyester fabric. In Figure 8b, two Ti 2p peaks (Ti 2p3/2 and Ti 2p1/2) were detected at 456.05 eV and 463 eV, respectively, indicating the presence of Ti 4+ on the polyester fabric [37,39]. Figure 8c is the XPS spectrum of the O1s region of Y2O3/TiO2-loaded polyester fabric, which is mainly divided into three peaks. The O element appearing at 529.03 eV shows the Ti-O-Y bond, while that at 529.9 eV indicates O 2-in the sample [40]. The content of O 2-was relatively high, indicating that O in the Y2O3/TiO2 composite photocatalyst mainly existed in the form of the negative divalent [41]. Moreover, the O element at 532 eV was derived from the -OH produced by the adsorption and dissociation on the sample surface [39], indicating that the holes generated by the Y2O3/TiO2 composite photocatalyst after light excitation reacted with the adsorbed H2O or OH ions on the surface, forming the hydroxyl radicals, which helped to improve the photocatalytic performance of Y2O3/TiO2 composite photocatalyst [42].  Figure 9 shows the Fourier infrared spectra of two photocatalytic materials, the polyester fabric, and Y2O3/TiO2-loaded polyester fabric (the molar content of Y2O3 is 0.75%). As shown in Figure 9, the polyester fabric had an obvious characteristic peak at  Figure 9 shows the Fourier infrared spectra of two photocatalytic materials, the polyester fabric, and Y 2 O 3 /TiO 2 -loaded polyester fabric (the molar content of Y 2 O 3 is 0.75%). As shown in Figure 9, the polyester fabric had an obvious characteristic peak at 1714.47 cm −1 , which was the peak of polyester C=O stretching vibration. Moreover, peaks at 1339.37 cm −1 and 1240.05 cm −1 were attributed to CH 2 groups and CO stretching vibration, respectively [43]. In addition, the peaks at 1058.77 cm −1 and 1014.41 cm −1 corresponded to Si-O-Si stretching vibration and the trans conformation band of the CH bond on the benzene ring [44], respectively. Furthermore, those at 960.71 cm −1 and 850.48 cm −1 were assigned to Ti-O-Si bonds and CH 2 in-plane rocking vibration, respectively. The peak of Ti-O bond stretching vibration and the absorption peak of CH 2 out-of-plane bending on the benzene ring of the polyester fabric overlapped at 724.17 cm −1 . This indicated that the Y 2 O 3 /TiO 2 was modified by 3-aminopropyltrimethoxysilane (APTMS), in which the effect of organosilicon on the adsorption and interaction of Y 2 O 3 /TiO 2 was attained through the formation of Si-O-Ti bonds. During this, the Y 2 O 3 /TiO 2 was loaded onto the surface of the polyester fabric, where the silanized Y 2 O 3 /TiO 2 was nucleophilically attacked by the introduction of amine groups, causing breakage of the ester bonds and the formation of the amide bonds to form a covalent bond with the surface of the polyester fabric. Eventually, Y 2 O 3 /TiO 2 after amino functionalization treatment was successfully loaded on the polyester fabric.   Figure 10 shows the UV-Vis absorption spectra for the polyester fabric and Y 2 O 3 /TiO 2loaded polyester fabric (the molar content of Y 2 O 3 is 0.75%). When compared to the polyester fabric, the Y 2 O 3 /TiO 2 -loaded polyester fabric not only absorbed in the entire spectrum, but also was enhanced in the entire visible range. In addition, the absorption spectrum of Y 2 O 3 /TiO 2 -loaded polyester fabric appeared red shift at the boundary of the visible range due to changes in the conduction band and valence band of the Y 2 O 3 /TiO 2 photocatalysts [19]. As shown in Figure 10, the absorption edge of the polyester fabrics and the Y 2 O 3 /TiO 2 -loaded polyester fabrics was about 390 nm and 420 nm, respectively. According to the formula Eg = 1240/λ, the corresponding band gaps were calculated as 3.17 eV and 2.95 eV and compared to polyester fabric, the band gap of Y 2 O 3 /TiO 2 -loaded polyester fabric was narrower, indicating a higher light absorption rate to improve the photocatalytic performance of the fabric.  Figure 10 shows the UV-Vis absorption spectra for the polyester fabric and Y2O3/TiO2-loaded polyester fabric (the molar content of Y2O3 is 0.75%). When compared to the polyester fabric, the Y2O3/TiO2-loaded polyester fabric not only absorbed in the entire spectrum, but also was enhanced in the entire visible range. In addition, the absorption spectrum of Y2O3/TiO2-loaded polyester fabric appeared red shift at the boundary of the visible range due to changes in the conduction band and valence band of the Y2O3/TiO2 photocatalysts [19]. As shown in Figure 10, the absorption edge of the polyester fabrics and the Y2O3/TiO2-loaded polyester fabrics was about 390 nm and 420 nm, respectively. According to the formula Eg = 1240/λ, the corresponding band gaps were calculated as 3.17 eV and 2.95 eV and compared to polyester fabric, the band gap of Y2O3/TiO2-loaded polyester fabric was narrower, indicating a higher light absorption rate to improve the photocatalytic performance of the fabric.  Figure 11 shows the degradation curves with methyl orange solutions under irradiation with a 300 W xenon lamp for 120 min for the polyester fabric and Y2O3/TiO2loaded polyester fabric (with a molar content of 0.75% of Y2O3). When samples were left in the dark for 40 min, some of the methyl orange solution could be absorbed by the samples and reach adsorption equilibrium of the catalyst and the solution, then the methyl orange solution was irradiated with different fabrics using the 300 W xenon lamp to simulate sunlight for 120 min. The supernatant was taken every 20 min for absorbance testing, and the control samples were 100 mL and 20 mg/L of methyl orange solution. As shown in Figure 11, the methyl orange solution hardly degraded in the absence of fabrics. However, the methyl orange solution added to the polyester fabric was slightly degraded under irradiation, whereas that added to Y2O3/TiO2-loaded polyester fabric was degraded at a rapid rate. After 120 min of light exposure, the removal efficiency of the polyester fabric, Y2O3/TiO2-loaded polyester fabric and methyl orange were 16.9%, 83%, and 10%, respectively.  Figure 11 shows the degradation curves with methyl orange solutions under irradiation with a 300 W xenon lamp for 120 min for the polyester fabric and Y 2 O 3 /TiO 2 -loaded polyester fabric (with a molar content of 0.75% of Y 2 O 3 ). When samples were left in the dark for 40 min, some of the methyl orange solution could be absorbed by the samples and reach adsorption equilibrium of the catalyst and the solution, then the methyl orange solution was irradiated with different fabrics using the 300 W xenon lamp to simulate sunlight for 120 min. The supernatant was taken every 20 min for absorbance testing, and the control samples were 100 mL and 20 mg/L of methyl orange solution. As shown in Figure 11, the methyl orange solution hardly degraded in the absence of fabrics. However, the methyl orange solution added to the polyester fabric was slightly degraded under irradiation, whereas that added to Y 2 O 3 /TiO 2 -loaded polyester fabric was degraded at a rapid rate. After 120 min of light exposure, the removal efficiency of the polyester fabric, Y 2 O 3 /TiO 2loaded polyester fabric and methyl orange were 16.9%, 83%, and 10%, respectively.

Degradability Analysis
From Figure 12, it can be seen that methyl orange had a maximum absorption at 464 nm [45], and the absorbance was the highest at 0 min whereas it was the smallest after 120 min of irradiation with the xenon lamp. Furthermore, the color of the methyl orange solution changed significantly from bright orange (0 min) to colorless (120 min), indicating the decrease of the chromophore and the destruction of the benzene ring of methyl orange under the irradiation of the xenon lamp [46]. In addition, no new peaks appeared during the whole irradiation process, indicating that the methyl orange was successfully degraded. From Figure 12, it can be seen that methyl orange had a maximum absorption at 464 nm [45], and the absorbance was the highest at 0 min whereas it was the smallest after 120 min of irradiation with the xenon lamp. Furthermore, the color of the methyl orange solution changed significantly from bright orange (0 min) to colorless (120 min), indicating the decrease of the chromophore and the destruction of the benzene ring of methyl orange under the irradiation of the xenon lamp [46]. In addition, no new peaks appeared during the whole irradiation process, indicating that the methyl orange was successfully degraded. The used polyester fabric loaded with Y2O3/TiO2 (the molar content of Y2O3 is 0.75%) was recycled, collected, washed, and dried. Then, the photocatalytic degradation of methyl orange on the dried polyester fabric loaded with Y2O3/TiO2 was carried out three times under visible light irradiation. Figure 13 shows the cycles for the degradation of methyl orange by Y2O3/TiO2-loaded polyester fabric under visible light. The degradation efficiency changes from 80% to 70%. This result indicates that the photocatalytic activity  From Figure 12, it can be seen that methyl orange had a maximum absorption nm [45], and the absorbance was the highest at 0 min whereas it was the smallest af min of irradiation with the xenon lamp. Furthermore, the color of the methyl solution changed significantly from bright orange (0 min) to colorless (120 min), ind the decrease of the chromophore and the destruction of the benzene ring of methyl under the irradiation of the xenon lamp [46]. In addition, no new peaks appeared the whole irradiation process, indicating that the methyl orange was succe degraded. The used polyester fabric loaded with Y2O3/TiO2 (the molar content of Y2O3 is was recycled, collected, washed, and dried. Then, the photocatalytic degrada methyl orange on the dried polyester fabric loaded with Y2O3/TiO2 was carried ou times under visible light irradiation. Figure 13 shows the cycles for the degrada methyl orange by Y2O3/TiO2-loaded polyester fabric under visible light. The degra efficiency changes from 80% to 70%. This result indicates that the photocatalytic a The used polyester fabric loaded with Y 2 O 3 /TiO 2 (the molar content of Y 2 O 3 is 0.75%) was recycled, collected, washed, and dried. Then, the photocatalytic degradation of methyl orange on the dried polyester fabric loaded with Y 2 O 3 /TiO 2 was carried out three times under visible light irradiation. Figure 13 shows the cycles for the degradation of methyl orange by Y 2 O 3 /TiO 2 -loaded polyester fabric under visible light. The degradation efficiency changes from 80% to 70%. This result indicates that the photocatalytic activity does not obviously deteriorate after three recycles for the photodegradation of methyl orange, revealing the good stability of Y 2 O 3 /TiO 2 -loaded polyester fabric. does not obviously deteriorate after three recycles for the photodegradation of methyl orange, revealing the good stability of Y2O3/TiO2-loaded polyester fabric.

Photocatalytic Reaction Kinetics
Several recent reports claim that Langmuir-Hinshelwood kinetic model can describe the photocatalytic degradation of heterogeneous TiO2 well [47,48].
The form of the photocatalytic degradation rate model can be expressed by the following equation [49,50].
where C0 is the organic concentration, Kr is reaction rate constant, Ks is the apparent adsorption constant, and t is the time of reaction. The term KsC0 is often negligible when the concentration is low, and the reaction rate can be expressed as pseudo-first-order model as follows: where Kapp is the apparent first-order reaction rate. Integration of the equation yields the following equation: A plot of -ln(C/C0) against (t) and slope of linear regression analysis is equal to the value of Kapp. The calculated results indicated that photocatalytic degradation at the reaction conditions follows pseudo-first-order kinetics ( Figure 14). The values of Kapp were obtained directly from the regression analysis of the linear curve in the plot.

Photocatalytic Reaction Kinetics
Several recent reports claim that Langmuir-Hinshelwood kinetic model can describe the photocatalytic degradation of heterogeneous TiO 2 well [47,48].
The form of the photocatalytic degradation rate model can be expressed by the following equation [49,50].
where C 0 is the organic concentration, K r is reaction rate constant, K s is the apparent adsorption constant, and t is the time of reaction. The term K s C 0 is often negligible when the concentration is low, and the reaction rate can be expressed as pseudo-first-order model as follows: where K app is the apparent first-order reaction rate. Integration of the equation yields the following equation: A plot of −ln(C/C 0 ) against (t) and slope of linear regression analysis is equal to the value of K app . The calculated results indicated that photocatalytic degradation at the reaction conditions follows pseudo-first-order kinetics ( Figure 14). The values of K app were obtained directly from the regression analysis of the linear curve in the plot.  Table 1 summarizes the pseudo-first-order constants and correlation coefficients, and the results show that the photodegradation process follows a pseudo-first-order reaction. As shown in the Table 1, the reaction rate constant of Y2O3/TiO2-loaded polyester fabric is about four times higher than that of polyester, exhibiting good degradation activities.  Table 1 summarizes the pseudo-first-order constants and correlation coefficients, and the results show that the photodegradation process follows a pseudo-first-order reaction. As shown in the Table 1, the reaction rate constant of Y 2 O 3 /TiO 2 -loaded polyester fabric is about four times higher than that of polyester, exhibiting good degradation activities.

Self-Cleaning Performance Analysis
To test the self-cleaning performance of Y 2 O 3 /TiO 2 -loaded polyester fabric under simulated visible light, 0.1 mL of methyl blue solution and soy sauce were dropped on the polyester fabric and Y 2 O 3 /TiO 2 -loaded polyester fabric and then irradiated under a xenon lamp for 18 h. Sample images were taken every 6 h, and the results are shown in Figure 15. Figure 15a,c,e,g represent the polyester fabric with methyl blue solution. It can be found that the blue mark of the polyester fabric dyed with methyl blue basically remains after 6 h of xenon lamp irradiation. Figure 15b,d,f,h show the Y 2 O 3 /TiO 2 -loaded polyester fabric with methyl blue solution. It can be seen that the methyl blue was degraded significantly after irradiation for 18 h with the xenon lamp. Figure 15i,k,m,o show the polyester fabric with the applied soy sauce. Although the soy sauce was degraded after 12 h of irradiation, there were no obvious changes in color, and there still existed a large stain on the surface of the polyester fabric after 18 h of irradiation, indicating a low degradation rate for soy sauce on the surface of the polyester fabric. As shown in Figure 15j,l,n,p, the soy sauce on the Y 2 O 3 /TiO 2 -loaded polyester fabric began to degrade significantly after 6 h of light exposure and was completely decomposed after 18 h of xenon lamp irradiation. The reason for this is that the Y 2 O 3 /TiO 2 will produce electron-hole pairs when irradiated by photons which have greater energy than its band gap energy [51], and the holes in the valence band can react with H + and ·OH generated from adsorbed water, and the electrons can reduce oxygen to produce O 2− . These active functional groups such as ·OH and O 2− could oxidize the organic compounds in methyl blue and soy sauce until they were completely mineralized [52].

Conclusions
Our Y2O3/TiO2 photocatalyst was prepared and treated with 3aminopropyltrimethoxysilane (APTMS), and then the Y2O3/TiO2-loaded polyester fabric was successfully prepared via covalent bonding between Y2O3/TiO2 and the polyester fabric by the formation of an amide bond.

Conclusions
Our Y 2 O 3 /TiO 2 photocatalyst was prepared and treated with 3-aminopropyltrimethoxysilane (APTMS), and then the Y 2 O 3 /TiO 2 -loaded polyester fabric was successfully prepared via covalent bonding between Y 2 O 3 /TiO 2 and the polyester fabric by the formation of an amide bond.
The TiO 2 in the Y 2 O 3 /TiO 2 composite catalyst (anatase type) was uniformly distributed on the surface of the polyester fabric. The diffraction peaks obtained from the Y 2 O 3 /TiO 2 -loaded polyester fabric were in good agreement with those from Y 2 O 3 /TiO 2 powder.
Furthermore, compared to polyester fabrics, the Y 2 O 3 /TiO 2 -loaded polyester fabrics had better photocatalytic performance under simulated sunlight. After 120 min of light exposure, the degradation rate of methyl orange reached 83% and when compared to the polyester fabric with the same drop of methyl blue solution and soy sauce, the Y 2 O 3 /TiO 2loaded polyester fabric had superior photocatalytic self-cleaning properties.