Abstract:
A method of fabricating a sheet or a fabric with crystalline TiO 2  nano-particles includes providing a polymer material as a support, and then synthesizing the crystalline TiO 2  nano-particles with immobilizing them on a surface of the support, followed by forming the fabric or the sheet. The fabric is a textile or a nonwoven fabric. A type of the support is a fiber or a sheet type. The synthesizing of the crystalline TiO 2  nano-particles is performed by occurring a sol-gel reaction under a microwave irradiation, wherein a TiO 2  precursor, water, an alcohol, and an ionic liquid applied in the sol-gel reaction during the synthesizing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of and claims priority benefit of an U.S. application Ser. No. 12/661,508, filed on Mar. 17, 2010, now pending, which claims the priority benefit of Taiwan application serial no. 98135277, filed on Oct. 19, 2009. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method of fabricating a sheet or a fabric with crystalline titanium dioxide (TiO 2 ) nano-particles. 
     2. Description of Related Art 
     Crystalline titanium dioxide nano-particle is frequent used as a photocatalyst due to its superior oxidation-reduction ability and high chemical stability. Crystalline titanium dioxide nano-particle can be synthesized by various methods and one of methods is sol gel method. The usage of ionic liquid (IL) in sol gel method for synthesizing crystalline titanium dioxide nano-particle under ambient condition was first published in J. AM. CHEM. SOC. 2003, 125, 14960-14961, 2003. Owing to the self-organizing ability of ion liquid, anatase crystalline TiO 2  nano-particle, which has large surface area, can be obtained by this method (“TiO 2  particles” and “crystalline TiO 2  nano-particles” both refer to the anatase crystalline TiO 2  nano-particles thereinafter). Combining with the high microwave (MW) absorbing ability of ionic liquid, IL/MW method is recognized as a green synthetic method for synthesizing inorganic nano-material. The two principal benefits of this method are high reaction rate and short reaction time. 
     In photocatalytic water treatment application, crystalline TiO 2  nano-particles, mainly anatase type, are directly dispersed in an aqueous phase or immobilized on different supports such as ceramic tile, glass, polymer material, stainless steel plate, aluminum sheets, and so on. In conventional immobilization process, because of high calcination temperature requirement of forming crystalline TiO 2  nano-particles, above 400° C., high temperature-resistant materials, such as glass, steel, and the like, are generally used. However this is a costly process and thus the commercial application has met its bottleneck. Hence, the usage of low cost polymer material as the immobilization support is currently an active research topic in recent year. 
     Polymer material is thermal sensitive material. The immobilization of crystalline TiO 2  nano-particles on the polymer material is generally by two step process. For example, TiO 2  sol is firstly synthesized and then coated on the polymer materials by dip coating method. Alternatively, an embedding process can also be applied, where crystalline TiO 2  nano-particles are embedded into melted polymer materials such as polyethylene by hot press at suitable condition. However, the crystalline TiO 2  nano-particles are easily aggregated and difficult to be homogeneously dispersed in these methods and then the immobilization adhesion strength is poor and the crystalline TiO 2  nano-particles peel off easily. 
     SUMMARY OF THE INVENTION 
     The disclosure is directed to a method of fabricating a sheet or a fabric with a plurality of crystalline TiO 2  nano-particles, wherein the fabric comprises a textile or a nonwoven fabric. In the method, a polymer material is provided as a support, wherein a type of the support is a fiber or a sheet type. The crystalline TiO 2  nano-particles are synthesized simultaneously with immobilizing the crystalline TiO 2  nano-particles on a surface of the polymer material by occurring a sol-gel reaction on the surface under a microwave irradiation, wherein a TiO 2  precursor, water, an alcohol, and an ionic liquid applied in the sol-gel reaction during the synthesizing. After the synthesizing, the sheet or the fabric is formed by using the support after the synthesizing. 
     In light of the foregoing, in the disclosure, the ionic liquid is used in the sol-gel process under the microwave irradiation with one step process. Then the crystalline TiO 2  nano-particles are produced in-situ and directly immobilized on the surface of the fabric or the sheet. Moreover, the immobilization adhesion strength of the crystalline TiO 2  nano-particles on the surface of the polymer material by this disclosure is high. 
     In order to make the aforementioned and other features and advantages of the disclosure more comprehensible, embodiments accompanying figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1  is a schematic diagram a method of one step synthesizing and immobilizing crystalline TiO 2  nano-particles simultaneously on the polymer material according to an embodiment of the disclosure. 
         FIG. 2  is a magnified view of a partial area in  FIG. 1 . 
         FIG. 3  is an X-ray diffraction (XRD) diagram of Experiment 1 in the disclosure. 
         FIG. 4A  is a scanning electron microscope (SEM) photograph of a sheet of PMMA material in the presence of IPA under microwave irradiation. 
         FIG. 4B  is a SEM photograph of PMMA in the presence of IL under microwave irradiation. 
         FIG. 5  is a SEM photograph of a cross-section of the PMMA material with the immobilized titanium dioxide (TiO 2 ) obtained from Experiment 3. 
         FIG. 6  illustrates the figure of photocatalytic efficiencies of the crystalline TiO 2  nano-particles synthesized by this disclosure under different ratios of reagents. 
         FIG. 7  is the figure of photocatalytic efficiencies of immobilized TiO 2  using the slab type PMMA. 
         FIG. 8  is the figure of photocatalytic efficiencies of TiO 2  immobilized on different polymer materials. 
         FIG. 9  is the temperature profiles of the reaction in Experiment 3 of the disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following embodiments and the attached figures are merely used to describe the applications of the disclosure in detail. Nevertheless, the disclosure may also be embodied in different forms and should not be limited to the embodiments set forth hereinafter. For clarity, the sizes and relative sizes of each of the elements in the drawings may be illustrated in exaggerated proportions. 
       FIG. 1  is a schematic diagram of one step synthesizing and immobilizing crystalline TiO 2  nano-particles simultaneously on the polymer material according to an embodiment of the disclosure. In the present embodiment, a material of the polymer support  100 , for example, is a thermoplastic polymer material such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyester, polyamide, and the like. In addition, although the polymer support  100  has a shape of a plate, the disclosure is not limited thereto. Any materials made of polymer can utilize as the polymer support  100  in the method of the disclosure to immobilize the crystalline TiO 2  nano-particles on the surface thereof in one step regardless of its shape (i.e., a shape of a slab, a plate, a sheet, or a fiber). 
     In  FIG. 1 , a sol-gel reaction is occurred to form the crystalline TiO 2  nano-particles on the surface of the polymer support  100 . The ingredients used in the sol-gel reaction, include TiO 2  precursor  102 , water  104 , an alcohol  106 , and an ionic liquid  108  under a microwave irradiation  110 . The ionic liquid  108  is, for instance, a conventional ionic liquid (IL) or a deep eutectic mixture solvent type ionic liquid. In this embodiment, the frequency of the microwave irradiation is ranged from 0.3 GHz to 300 GHz, and the reaction site temperature under the microwave irradiation is ranged from 40° C. to 200° C., for example. 
     In one embodiment, the ionic liquid  108  is the conventional ionic liquid, for example. Moreover, a cation thereof includes, for example, 1-alkyl-3-methylimidazolium, [C n MIM] + , where n represents a number of linear alkyl carbons, N-alkylpyridinium, [C n PY] + , where n represents a number of linear alkyl carbons, tetraalkylammonium, or tetraalkylphosphonium. Additionally, an anion thereof includes, for example, hexafluorophosphate (PF 6   − ), tetrafluoroborate (BF 4   − ), trifluoromethylsulfonate (CF 3 SO 3   − ), (bis[(trifluoromethyl)sulfonyl]amide, [(CF 3 SO 2 ) 2 N] − , trifluoroethanoate (CF 3 CO 2   − ), ethanoate (CH 3 CO 2   − ), or a halide such as Br − , Cl − , or I − . The anion combines with different organic or inorganic cations to form an ionic liquid with a large molecular weight. 
     In another embodiment, the ionic liquid  108  is the deep eutectic mixture solvent type ionic liquid such as an eutectic mixture having a low melting point and formed by quaternary ammonium salt and hydrogen donors. For example, the eutectic mixture having the low melting point is formed by mixing an oxalic acid and a choline cholide. 
     The TiO 2  precursor  102  used in the sol-gel process is, for instance, titanium alkoxide, or a titanium compound capable of undergoing hydrolysis and condensation reaction with water. For example, the titanium alkoxide is titanium ethoxide (Ti(OC 2 H 5 ) 4 ) or titanium isopropoxide (Ti(OCH(CH 3 ) 2 ) 4 ). The alcohol  106  used in the sol-gel process includes an alcohol having a carbon number of 1-10; a primary alcohol (1°), a secondary alcohol (2°), or a tertiary alcohol (3°), such as ethanol, isopropyl alcohol, or tert-butyl alcohol; or diols or triols, such as ethylene glycol or glycerol. A molar ratio of the compounds used in the sol-gel process is, for example: TiO 2  precursor:water:alcohol:ionic liquid=0.5-20:0.5-200:0.5-100:0.5-200. 
       FIG. 2  is a magnified view of a partial area of  FIG. 1 . As shown in  FIG. 2 , when components, such as the compounds applied in the sol-gel reaction under microwave irradiation, contact the polymer support  100 , a surface  100   a  thereof becomes rough, and then crystalline TiO 2  nano-particles  112  are immobilized directly on a plurality of cavities  100   b . At this time, a superior surface adhesion is found between the crystalline TiO 2  nano-particles  112  and the polymer support  100 . The superior adhesion strength still retains after 30 minutes of ultra-sonic treatment. 
     In the method of the aforementioned embodiment, the microwave irradiation is adopted. Since conventional polymer materials do not absorb microwave, the entire system is only microwave heated at reaction sites containing polar materials such as water, ionic liquid or alcohol. Therefore, the surrounding temperature of the reaction system can be controlled under 150° C., accordingly, the crystalline anatase TiO 2  nano-particles are synthesized and immobilized on the surface of the support made of polymer material by one step without affecting the physical and mechanical properties of the polymer material. Hence, the method in the embodiment mentioned above is suitable to be applied in immobilization of crystalline anatase TiO 2  nano-particle (i.e. photocatalyst products) using the polymer materials as the support. The foregoing polymer materials are the materials of the polymer support  100  in the embodiment aforementioned. As long as the material itself is made of a polymer, the crystalline anatase TiO 2  nano-particles can be synthesized on the surface of the polymer material using the methods aforementioned regardless of the shape being a slab, a plate, a sheet, or a fiber. For instance, when the polymer material is a fiber type, the crystalline anatase TiO 2  nano-particles can be directly synthesized and immobilized thereon with the method of the disclosure by one step. Obviously, this method can be applied to non-woven fabrics and the like. 
     The following exemplifies a plurality of experiments to demonstrate efficacy of the disclosure. 
     Experiment 1 
     In this experiment, the ingredients include the following: titanium tetraisopropoxide, (TTIP, manufactured by E. Merck) as the TiO 2  precursor, isopropyl alcohol (IPA, manufactured by E. Merck) as the alcohol, deionized water, and 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim] + [BF 4 ] − , (manufactured by E. Merck), as the ionic liquid (IL). With a molar ratio of the ingredients being TTIP:IPA:H 2 O=1:3:5, the amount of the IL added is changed, where the molar ratio of IL/TTIP is 0, 0.5, and 2 respectively. The deionized water is then added to the reaction mixture. Afterwards, the mixture is further stirred for 10 minutes at room temperature and then microwave irradiated for 20 minutes, where the microwave power is 800 W and the frequency thereof is 2.45 GHz. The dried product of TiO 2  after filtration is examined with X-ray diffraction (XRD) and  FIG. 3  is obtained therefrom. As shown in  FIG. 3 , the crystalline anatase TiO 2  nano-particles are formed and the anatase crystallinity increased with the increasing of IL. 
     Experiment 2 
       FIG. 4A  is a scanning electron microscope (SEM) photograph of a PMMA sheet treated with IPA for 3 minutes under microwave irradiation. An SEM photograph of  FIG. 4B  is the PMMA sheet treated with IL (IL is [Bmim] + [BF 4 ] − ) for 30 minutes under microwave irradiation. As illustrated in  FIG. 4A  and  FIG. 4B , IPA and IL both roughens the surface of PMMA. 
     Experiment 3 
     In this experiment, the PMMA sheet (i.e. with a size of, for example, 20 mm×10 mm×2 mm) or the sheet-shaped PMMA (i.e. a cylinder with a diameter of 4 mm and a height of 3 mm) is first placed within a reaction vessel. The IL is [Bmim] + [BF 4 ] − , where the molar ratio of TIPP:IPA:IL:H 2 O=1:3:1:100. The deionized water is added to the reaction mixture of TTIP, IPA, and IL at a rate of 20 mL/min and then the mixture is microwave irradiated directly for 30 minutes. 
     The final PMMA sheet is shown in  FIG. 5 , which illustrates a SEM photograph of a cross-section of crystalline TiO 2  immobilized on the surface of the PMMA support obtained from Experiment 3. 
     Experiment 4 
     In this experiment, the PMMA sheet (i.e. 20 mm×10 mm×2 mm) is first placed within a reaction vessel. Further, the ingredients in Experiment 1 are used to perform under microwave irradiation by adjusting different ratios of ingredient. The photocatalytic efficiency of the immobilized TiO 2  is examined. 
     In the photocatalytic efficiency test, 300 ml of aqueous solution with 5 ppm methylene blue (MB) is first prepared. Several immobilized TiO 2  samples are added. Thereafter, the UV light is applied, the wavelength of UV is 365 nm and light intensity is 13 W. The irradiation time is 6 hours. A sample for analysis is aliquot every 2 hours and the results are shown in  FIG. 6 . From the results of  FIG. 6 , it can be seen that the immobilized TiO 2  sample prepared with the method of the disclosure does have significant photocatalytic performance. 
     Experiment 5 
     In this experiment, the slab type chip PMMA (a cylinder with a diameter of 4 mm and a height of 3 mm), the same method as that performed in Experiment 4 is carried out. 
     The photocatalytic efficiency experiment includes the following. Here, 300 ml of aqueous solution with 5 ppm methylene blue (MB) is first prepared. Several PMMA samples have been placed therein, raw water. The light source is the same as that of Experiment 4. The irradiation time is 6 hours. A sample for analysis is aliquot every 2 hours and the results are shown in  FIG. 7 . 
     From the results of  FIG. 7 , it can be seen that immobilized TiO 2  sample prepares in this experiment does have significant photocatalytic performance. 
     Experiment 6 
     In this experiment, the sheet-shaped PE-PVAc, and PVAE are respectively placed in the reaction vessel. The reagents with a molar ratio of TIPP:IPA:IL:H 2 O=1:3:1:100. IPA:IL:H 2 O=1:3:1:100. With the same photocatalytic performance test method in Experiment 3, the photocatalyst efficiency of crystalline TiO 2  immobilized on different polymer support is examined, and the results are shown in  FIG. 8 . 
     As the results are illustrated in  FIG. 8 , it can be seen that crystalline TiO 2  nanoparticle synthesized with the method of the disclosure can be immobilized on the surface of PMMA, PE-PVAc, or PVAE. The immobilized TiO 2  retains the photocatalytic effect. 
     Experiment 7 
     All the steps performed in Experiment 7 are identical to those implemented in Experiment 3 besides the addition of IL. The temperature profiles reveal that the temperature of the reaction system is under 100° C., as shown in  FIG. 9 . However, the reaction temperature slightly increases when IL is added. 
     In summarizing the illustrations and experiments above-mentioned, in the disclosure, the ionic liquid and microwave irradiation are used simultaneously in this one step method. Therefore, the crystalline anatase TiO 2  nano-particles are in-situ synthesized and immobilized on the surface of the polymer support. The disclosure achieves the synthesis and immobilization simultaneously by one step process, thus is much more time saving and energy saving than the conventional two steps immobilization method. In addition, the IL can be recycled, so the disclosure is a green technology. 
     Although the disclosure has been described with reference to the above embodiments, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the disclosure. Accordingly, the scope of the disclosure will be defined by the attached claims not by the above detailed descriptions.