Fabrication of Inorganic Oxide Fiber Using a Cigarette Filter as a Template.

Inorganic oxides with unique physical and chemical properties have attracted much attention because they can be applied in a wide range of fields. Herein, recycled cigarette filters are deacetylated to cellulose filters (CFs), which are then applied as templates to prepare fiber-like inorganic oxides (titanium dioxide, TiO2, and silicon dioxide, SiO2). Inorganic oxides are prepared using CF as a template by a typical sol-gel reaction of metal alkoxides. Owing to the fibrous structure of the CF template, the prepared inorganic oxides (TiO2 and SiO2) show similar fibrous structures, which was confirmed by scanning electron microscopy and nitrogen adsorption-desorption analysis. Moreover, the prepared inorganic oxides (TiO2 and SiO2) show high surface areas and pore volumes. Furthermore, the TiO2 fiber-like materials are evaluated for their photocatalytic properties by analyzing the methylene blue (MB) and methyl orange (MO) degradation. In this study, we provide a clean method, which can convert cellulose acetate-based waste into useful templates to prepare inorganic oxides with relatively simple steps, and the prepared inorganic oxides can be applied in water treatment.

Introduction

Inorganic oxides with unique physical and chemical properties have attracted much attention because they can be applied in a wide range of fields, including electrochromic devices,[1] photocatalysis,[2] sensors,[3] batteries,[4] and solar cells.[5] Inorganic oxides can be tailored to exhibit desired physical and chemical properties under different operating conditions (e.g., temperature, frequency, or pressure). Two materials, titanium dioxide (TiO2) and silicon dioxide (SiO2), were chosen to demonstrate a simple templating technique as they are widely used in the abovementioned areas: TiO2 is well known for its utilization in solar energy operations[5] and photocatalysis,[6] and SiO2 is becoming increasingly important in the fields of drug delivery[7] and ion or molecule adsorption.[8] Among plenty of preparation routes to inorganic oxides, a sol–gel method using metal alkoxides as a raw material has been shown to be a particularly useful method due to low cost, ambient operating conditions, and simple one-pot processing route.[9] In the sol–gel process, the hydrolysis and condensation reactions of metal alkoxides are preferably combined into a template through chemical bonds. Accordingly, giving appropriate reaction conditions can simultaneously form a cocontinuous structure, resulting in a network structure of an inorganic material skeleton.[10] The most commonly used synthetic technique for the fabrication of inorganic oxides is “nanocasting” (hard template), in which a polymer is used as a template to prepare polymer-inorganic composite, and then the composite material is carbonized and the template is removed.[11−13]

Cellulose and cellulose acetate derivatives are stable in aqueous or alcoholic media and undergo pyrolysis upon heating. Utilizing the hydrophilic but water-insoluble properties of cellulose or its acetate derivative, it is possible to incorporate metal alkoxides into a template skeleton during the sol–gel process. While cellulose-based materials are used in numerous industrial products, many of them, such as cellulose acetate-based cigarette filters, are disposed of after usage, posing a waste disposal and environmental pollution hazard.[14] The number of cigarette filters disposed off annually on a global basis is estimated to be up to 5.6 trillion,[15] and the number is increasing annually. Moreover, cigarette filters do not biodegrade easily.[16] Fortunately, unlike many materials that end up mixed with other types of waste, it is possible to collect and reutilize cigarette filters because they are mainly disposed off in designated smoking areas.[17]

Inspired by the concept of sustainable chemistry and engineering, some research studies have attempted to convert cigarette filters into valuable products. For example, waste cigarette filters were used to prepare a flow catalytic reactor, which shows great potential for water treatment.[18] The used cigarette filters were utilized to produce ester-rich bio-oil via a cleaner production process.[19] Ubaidullah et al. used a waste cigarette filter as a nitrogenous carbon source to produce a low-cost novel material via a hydrothermal approach.[20] Huang et al. purified cellulose acetate from a waste cigarette filter and prepared a cellulose/poly(vinylidene fluoride-cohexafluoropropylene) nanofiber membrane.[14] Meshes coated with waste cigarette filters were prepared by a facile electrospinning method, and the meshes showed remarkable underwater superoleophobicity or underoil superhydrophobicity, which can be used for the on-demand separation of various immiscible oil/water mixtures and emulsions.[21] All of the previously mentioned treatments of waste cigarette filters provide useful ways to reuse waste cigarette filters. Most of the reuse of waste cigarette filters usually focused on one aspect (morphology or chemical properties), and few studies have utilized the combination of cigarette filters’ morphology and chemical properties. Therefore, it is expected that more reasonable and effective methods can be used to develop high-value-added materials that simultaneously utilize the morphology and chemical properties of cigarette filters. Cigarette filters, which are mainly composed of cellulose acetate, can be deacetylated into cellulose filters (CFs). On the other hand, the fibrous CFs can be easily converted into the fibrous structure of inorganic oxide by subjecting an appropriate amount of metal alkoxide to a sol–gel reaction and then removing the template. Therefore, recycling cellulose acetate cigarette filters and using them as templates to prepare inorganic oxides not only reduces environmental pressure but also produces value-added products.

In this study, recycled cellulose acetate filters (CAFs) were deacetylated to cellulose filters (CFs) and then applied as templates to prepare fiber-like inorganic oxides (TiO2 and SiO2). CF-inorganic oxide composites were prepared in the presence of CFs by a typical sol–gel reaction of metal alkoxides. Hydrolysis and condensation reactions of metal alkoxides occur during the sol–gel process. Finally, CF-inorganic oxide composites were burned in air to remove the template and obtain fiber-like inorganic oxides (TiO2 and SiO2); the prepared inorganic oxides (TiO2 and SiO2) exhibited similar fibrous structures. Moreover, the obtained inorganic oxides (TiO2 and SiO2) exhibited high surface areas and pore volumes. The TiO2 fiber-like materials were evaluated for their photocatalytic properties by analyzing the methylene blue (MB) and methyl orange (MO) degradation.

Results and Discussion

The used cigarette butts generally consisted of wrapping paper, remaining tobacco ash, and cellulose acetate fibers mixed together (Figure a). After detaching the paper and ash, CAFs were repeatedly washed using ethanol;[18] the obtained clean CAFs were white filters. Then, the CAF was fixed into a heat-shrinkable tube and NaOH/methanol solution was circulated through the CAF using a peristaltic pump; the CAF was gradually deacetylated to CF during this process. It should be noted that the deacetylation treatment did not destroy the structure of CAFs because this process was conducted in methanol under relatively mild conditions. Fourier transform infrared spectroscopy (FT-IR) was performed to confirm the success of this reaction (Figure b). Characteristic peaks of CAF are seen at 1018 and 1736 cm–1, which can be assigned to C–O–C and C=O bonds, respectively. The strong characteristic peak at 1736 cm–1 due to the stretching vibration of C=O of the acetyl group completely disappeared in the spectrum after the hydrolysis. Additionally, the broad absorbance peak at ∼3400 cm–1 due to the stretching vibration of O–H became much larger after the hydrolysis. Meanwhile, the CF features bands at 1018 cm–1, which can be assigned to the C–O–C bond.[18] The results confirm that the CAFs were hydrolyzed to CFs. The morphology of CAF and CF was examined via scanning electron microscopy (SEM), and Figure c,d shows that CAFs and CF have similar anisotropic structures.

Figure 1

(a) Preparation process of CFs from cigarette butts. (b) FT-IR spectra of CAF and CF. SEM images of (c) CAF and (d) CF.

Figure a illustrates the process for preparation of TiO2 fiber-like materials using CF as a template. First, CF-TiO2 was prepared by a sol–gel method by a reaction of titanium isopropoxide (TTIP) with CF. After the sol–gel reaction, CF-TiO2 retained a columnar shape. CF-TiO2 was then burned at 500 °C to remove the CF template and obtain a TiO2 fiber-like material with a good columnar shape, despite some shrinkage compared to CF-TiO2. The prepared TiO2 fiber-like material was brittle because it did not exhibit a network structure. Similar to the preparation of TiO2, a SiO2 fiber-like material prepared using CF as a template and the sol–gel method also produced a good columnar shape that was brittle (Figure S2a). Thermogravimetric analysis (TGA) was performed to study the thermal decomposition behavior of the samples from 40 to 800 °C. The weight loss of CF, CF-TiO2, and CF-SiO2 commenced at 300 °C and stopped above 450 °C; TiO2 and SiO2 did not show any weight loss (Figure S1). Therefore, a burning temperature higher than 500 °C was sufficient to remove the CF template.

Figure 2

(a) Preparation process of TiO2 using CF as a template. (b) Reaction between metal alkoxides and CF. (c) FT-IR spectra and (d) X-ray diffraction (XRD) of CF, CF-TiO2-20, and TiO2-20.

During the sol–gel reaction, a condensation reaction occurs with the hydroxyl groups of CF and metal alkoxides (Figure b). In the sol–gel process, a solid substrate with hydroxyl groups on its surface is allowed to react with the metal alkoxides in solution to form covalent bonds.[22] Owing to the hydroxyl groups on the surface, CF can participate in the surface sol–gel process. This means that it is possible to produce a fiber-like structure of inorganic oxide in which the CF structure can be transferred by subjecting an appropriate quantity of metal alkoxides to a sol–gel reaction and then removing the template. Moreover, inorganic oxide oligomers and nanoparticles diffuse into the CF skeleton, which causes the formation of a CF-inorganic oxide network.

Chemical structures of the samples were studied by FT-IR analysis. The FT-IR spectrum of the CF features bands at 1018 and ∼3400 cm–1, which can be assigned to C–O–C and −OH, respectively (Figure c).[23] The peaks of the cellulose OH groups are weakened after the sol–gel process, indicating that the cellulose OH groups are bonded with TTIP. CF-TiO2 exhibits bands at 500–800 cm–1, which can be assigned to a combination of the vibrations of Ti–O–Ti and Ti–O–C bonds.[24] XRD patterns of CF, CF-TiO2, and TiO2 are shown in Figure d. The CF shows a peak consistent with the amorphous phase at 2θ = 19.7°.[25] CF-TiO2 has peaks at 2θ = 25.2, 37.8, 48.0, 55.1, and 62.7°, which can be indexed to the (101), (004), (200), (211), and (204) crystal faces of anatase TiO2. TiO2 also shows peaks consistent with the anatase phase at 2θ = 25.2, 37.8, 48.0, 54.3, 55.1, 62.7, 69.0, 70.4, and 75.3°, which can be indexed to the (101), (004), (200), (105), (211), (204), (116), (220), and (215) crystal faces of anatase TiO2 (PDF # 001-004-0477),[26] while the peaks located at 2θ = 27.4 and 36.0° can be indexed to the (110) and (101) diffraction peaks of rutile TiO2 (PDF # 00-001-1292). The FT-IR spectrum of CF-SiO2 shows a band at 1063 cm–1, which can be assigned to the Si–O–C bond, while SiO2 shows a band at 1072 cm–1, which can be assigned to the Si–O–Si bond (Figure S2b).[27] These results indicate that the prepared SiO2 can be fixed to the CF template because of a condensation reaction between the hydroxyl group of CF and tetraethyl orthosilicate (TEOS). The XRD patterns of CF-SiO2 and SiO2 show a broad peak located at 2θ = ∼22.5°, which suggests amorphous SiO2 (JCPDS card no. 01-086-1561) (Figure S2c).[28]

The morphology of CF, CF-TiO2, TiO2, CF-SiO2, and SiO2 was examined via SEM (Figures d and 3). Similar to the fiber-like structure of the CF, the obtained CF-TiO2, TiO2, CF-SiO2, and SiO2 showed fiber-like structures. The fiber diameter at each reaction stage was investigated, and the results are shown in Figure a,d. The fiber diameter of CF-TiO2-20 is 18.4 ± 2.6 μm, which is larger than that of a CF template (16.4 ± 1.6 μm). Furthermore, the fiber diameter was significantly decreased after removing the CF template, which gave a fiber diameter of 14.2 ± 1.6 μm (TiO2-20). The fiber diameter of CF-SiO2-20 is 18.4 ± 2.5 μm, which is larger than that of CF (16.4 ± 1.6 μm). Furthermore, there is a significant decrease after removing the CF template to a fiber diameter of 16.0 ± 2.1 μm (SiO2-20).

Figure 3

(a) Diameters of CF, CF-TiO2, and TiO2 fibers prepared with different TTIP contents. SEM images of (b) CF-TiO2-20, and (c) TiO2-20. (d) Diameters of CF, CF-SiO2, and SiO2 prepared with different TEOS contents. SEM images of (e) CF-SiO2-20, and (f) SiO2-20.

As the metal alkoxide content is considered to affect the amount of synthesized inorganic oxides, the fiber diameters of CF-TiO2, TiO2, CF-SiO2, and SiO2 were investigated by varying the metal alkoxide content. As shown in Figures a–c and S3, increasing the TTIP content tends to increase the fiber diameter of CF-TiO2 and TiO2. As shown in Figures d–f and S4, increasing the TEOS content tends to increase the fiber diameter of CF-SiO2 and SiO2. These results indicate that with an increase in the metal alkoxide content, the fiber diameter of the prepared CF-inorganic oxides and inorganic oxides increases because of the increased amount of inorganic oxide covering the skeleton surface.

Nitrogen adsorption–desorption analysis was carried out to evaluate the porous features of TiO2 and SiO2. The isotherms and pore-size distribution plots are shown in Figure . All curves can be classified as type IV with adsorption hysteresis loops in terms of IUPAC classification, indicating the presence of mesopores (Figure a,c).[29] The Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore width are summarized in Table . For the TiO2 fiber-like materials, TiO2-20 shows the highest surface area and pore volume (135 m2 g–1, 0.26 cm3 g–1). With the increase in the TTIP content, the BET surface area and pore volume of TiO2 decreased from 135 m2 g–1 and 0.26 cm3 g–1 (TiO2-20) to 42 m2 g–1 and 0.08 cm3 g–1 (TiO2-50), respectively, indicating that some pores become filled at a higher TTIP content. The mesopore diameters of TiO2 were ∼5 nm (Figure b and Table ). Anyway, all of the prepared fiber-like TiO2 materials show higher BET surface areas and pore volumes than the P25 powder (Table ). In addition, SiO2-20 shows the highest surface area and pore volume (727 m2 g–1, 1.10 cm3 g–1). With an increase in the TEOS content, the BET surface area and pore volume of SiO2 decreased from 727 m2 g–1 and 1.10 cm3 g–1 (SiO2-20) to 250 m2 g–1 and 0.54 cm3 g–1 (SiO2-50), respectively, indicating that some pores are filled at a higher metal alkoxide content. Meanwhile, the pore-size distribution of SiO2 remains mainly in the range of 2–6 nm (Figure d and Table ).

Figure 4

(a) Nitrogen adsorption–desorption isotherms and (b) corresponding pore-size distribution curves of TiO2 prepared with different TTIP contents. (c) Nitrogen adsorption–desorption isotherms and (d) corresponding pore-size distribution curves of SiO2 prepared with different TEOS contents.

Table 1

BET Surface Areas, Mesopore Diameters, and Pore Volumes of TiO2 and SiO2

	surface area (m2 g–1)	mesopore diameter (nm)	pore volume (cm3 g–1)
P25	7	1.9	0.02
TiO2-20	135	6.5	0.26
TiO2-30	108	7.7	0.23
TiO2-40	63	7.9	0.33
TiO2-50	42	6.5	0.08
SiO2-20	727	2.4	1.10
SiO2-30	404	2.4	0.64
SiO2-40	339	1.5	0.60
SiO2-50	250	1.4	0.54

The photocatalytic activity results are shown in Figure . For the tests, 20 mg of the catalyst was mixed into an MB solution (50 mL, 10 mg L–1) with stirring and exposed to UV illumination (Figure a, inset). Control experiments were performed in the absence of the catalyst or in the presence of P25. Before photodegradation, the catalysts in the MB solution were stirred for 30 min in the dark to reach adsorption–desorption equilibrium. After 30 min, TiO2-20 can adsorb 3.0% of the MB solution and only 3.3% of the initial MB solution can be adsorbed after 120 min; the result shows that TiO2-20 reached adsorption saturation after 30 min. The blank run of the samples showed ∼6.6% MB degradation after 120 min. Under UV illumination, 94.2% of the MB solution was decomposed after 30 min, and after 120 min, 99.8% of the MB solution was decomposed for P25 powders. All of the results showed high MB degradation under UV irradiation. TiO2-20 and TiO2-30 degraded 98.4 and 97.5% of the MB solution after 30 min, respectively. They also showed better degradation efficiency than P25. TiO2-40 and TiO2-50 degraded 71.6 and 47.3% of the MB solution after 30 min, respectively, which showed lower degradation efficiency than P25. Nevertheless, after 120 min, all of the samples could degrade 99% of the initial dye, except for TiO2-50. With an increase in the TTIP content, the degradation efficiency of TiO2 decreased, which can be attributed to the decreased surface area of TiO2 prepared at a higher TTIP content. Owing to its high MB degradation efficiency, the stability of TiO2-20 was evaluated through recycling photocatalytic degradation experiments. As shown in Figure b, after five successive uses, 99.8% of the MB dye was decomposed after 120 min. Figure c shows the photocatalytic degradation efficiency of TiO2-20 under varying MB concentrations from 10 to 25 mg L–1. With increasing MB concentration, the degradation efficiency of TiO2 shows a little decrease from 99.9% (10 mg L–1) to 97.9% (25 mg L–1) after 120 min. The photocatalytic activity of TiO2-20 for MO degradation is shown in Figure d; under UV illumination, 63.7% of the MO solution was decomposed after 120 min, and 99.6% of the dye solution was decomposed after 300 min for TiO2-20. These results indicate that TiO2-20 fibers exhibited excellent photocatalytic efficiency and reusability for dye removal.

Figure 5

(a) Photocatalytic activity of TiO2 and P25 for MB degradation (10 mg L–1) (inset shows the schematic representation of the experimental setup used for the photocatalytic test). (b) Reusability efficiency of the TiO2-20 after several photocatalytic cycles. (c) Photocatalytic degradation efficiency of TiO2-20 under varying MB concentrations from 10 to 25 mg L–1. (d) Photocatalytic activity of TiO2-20 for MO degradation (10 mg L–1).

Conclusions

Recycled cellulose acetate cigarette filters were deacetylated to cellulose filters and then applied as templates to prepare fiber-like inorganic oxides (TiO2 and SiO2). The fiber-like inorganic oxides were fabricated using CF as a template and metal alkoxides as raw materials. The structure was varied by changing the metal alkoxide content. The porous features of the fiber-like inorganic oxides (TiO2 and SiO2) were evaluated by SEM and nitrogen adsorption–desorption analysis. TiO2-20 and SiO2-20 showed the highest surface areas and pore volumes. With an increase in the metal alkoxide content, the BET surface area and the pore volume of the inorganic oxides decreased, indicating that some pores were filled at a higher metal alkoxide content. TiO2-20 exhibited excellent photocatalytic efficiency; the degradation efficiency of MB reached 98.4% after 30 min and 99.9% after 120 min. Even on increasing the MB concentration to 25 mg L–1, TiO2-20 can still degrade 97.9% of the MB solution after 120 min. After five cycles, TiO2-20 also showed a degradation efficiency of more than 99.8% after 120 min. Moreover, the degradation efficiency of MO reached 63.7% after 120 min and 99.6% after 300 min. Therefore, the TiO2 fiber-like materials are stable and reusable for water treatment. More importantly, this strategy could also be used to prepare other inorganic oxide fiber-like materials. The present study provides a clean method, which can convert cellulose acetate-based waste into useful templates for the fabrication of fiber-like inorganic oxides with relatively simple steps, and the prepared inorganic oxides can be applied in water treatment. We believe that the prepared inorganic oxides (TiO2 and SiO2) are promising for other applications and further modifications.

Experimental Section

Materials

Cellulose acetate filters (CAFs) from PEACE-Super Light cigarettes (Japan Tobacco Inc., Japan) were collected from cigarette butts consumed by our laboratory mates. Cetyltrimethylammonium bromide (CTAB) was purchased from Nacalai Tesque, Inc. (Kyoto, Japan). Titanium isopropoxide (TTIP), tetraethyl orthosilicate (TEOS), and 2-propanol were commercially obtained from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Titanium (IV) oxide (P25) was purchased from Fujifilm Wako Pure Chemical Corporation (Osaka, Japan). All other chemicals used were chemically purified and purchased commercially.

Preparation of CFs

To remove impurities of CAFs, after detaching the paper and ash, the CFs were washed using 100 mL of ethanol in a shaker and the solution was exchanged with fresh ethanol every hour until the solution became clear. After drying under a vacuum, the obtained CAFs with a length of ∼25 mm were fixed into a heat-shrinkable tube. A 0.5 M NaOH/methanol solution (40 mL) was circulated through the sample using a peristaltic pump (EYELA, MP-1000) at a flow rate of 3 mL min–1 to react with the CAFs for 1 h, and then fresh methanol (40 mL) was flowed through the sample to remove the residual NaOH solution. As a result, the CAFs were deacetylated to form CFs.[18]

Preparation of TiO2 Fiber-Like Material

CF-TiO2 was prepared via a sol–gel reaction in the presence of CF. TTIP was added to 2-propanol under stirring; the CF was immersed in a TTIP/2-propanol solution. Subsequently, deionized water was added to the mixture under vigorous stirring. The volume ratio of 2-propanol:water was 1:10, the total volume of the solution was 15 mL, and the TTIP content was defined as the ratio of the TTIP volume to the total volume of the solution. The solution was subsequently heated to 80 °C under stirring for 5 h and cooled to room temperature to obtain CF-TiO2-x, where x refers to the content of TTIP (%); the sample was washed with deionized water and dried at 80 °C. To remove the CF, CF-TiO2 was burned in air from room temperature to 500 °C at a rate of 1 °C min–1, maintained at 500 °C for 2 h, and then cooled to room temperature to prepare the TiO2-x fiber-like material.

Preparation of SiO2 Fiber-Like Material

CF-SiO2 was prepared via a sol–gel reaction in the presence of CF. First, CTAB and an aqueous ammonia solution (28 wt %) were dissolved into deionized water under stirring to form a CTAB/ammonia solution with a CTAB/water/ammonia ratio of 0.05:8:0.15 (g:mL:mL). Next, the CTAB/ammonia solution was added to the CF, which was immersed in a continuously stirred solution of n-hexane and TEOS at 35 °C. The total volume of the solution was 15 mL, the volume ratio of the CTAB/ammonia solution to n-hexane was 8:1, and the TEOS content was defined as the volume ratio of TEOS to the total solution. The solution was stirred for 16 h, the samples were washed with deionized water and ethanol, and then dried by vacuum drying for 3 h to obtain CF-SiO2-x, where x refers to the content of TEOS (%). To remove the CF, CF-SiO2 was burned in air from room temperature to 600 °C at a rate of 5 °C min–1, maintained at 600 °C for 2 h, and then cooled to room temperature to prepare the SiO2-x fiber-like material.

Characterization

Fourier transform infrared (FT-IR) measurement was performed using a Thermo Scientific Nicolet iS5 spectrometer equipped with an iD5 ATR attachment. Scanning electron microscopy (SEM) images were taken using a field-emission scanning electron microscope (Hitachi S-3000N, Japan). The powder X-ray diffraction (XRD) patterns were carried out with SmartLab (In-plane, Rigaku Corporation, Japan) with a Cu K-β X-ray source at a scanning speed of 5° min–1 over a 2θ range of 5–80°. The Brunauer–Emmett–Teller (BET) surface area was studied by nitrogen adsorption–desorption analysis (Quantachrome Instruments). The pore diameter distribution and pore volume were calculated using Barrett–Joyner–Halenda (BJH) analysis. Thermogravimetric analysis (TGA) was conducted using a thermogravimetric analyzer (Hitachi, STA7200RV) in the temperature range of 40–800 °C at a heating rate of 10 °C min–1 under nitrogen.

Photocatalytic Tests

The photocatalytic activity of TiO2 and P25 was tested by studying their effect on the decomposition of MB and MO under UV light in a batch system at room temperature. The adsorption of TiO2 was tested under the same method without UV light. The catalyst (20 mg) was mixed with an MB solution (50 mL, 10, 15, 20, and 25 mg L–1) or an MO solution (50 mL, 10 mg L–1) under stirring and exposed to a UV LED lamp (λ = 365 nm, 100 mW cm–2, PiPhotonics, Inc. HLKK60). Prior to the decomposition experiment, the dye solution with the catalyst was allowed to stir without UV light for 30 min to ensure adsorption–desorption equilibrium. The concentration of the dye solution was measured at different times after centrifugation (14 × 1000 rpm, 90 s, Centrifuge MiniSpin plus, Eppendorf, Japan) using a UV–visible spectrophotometer (HITACHI, U-2810, Japan). The decrease in the intensity of the most prominent absorption (MB: 664 nm, MO: 465 nm) was analyzed to follow the degradation of the dye solution. The reusability of the TiO2 fibers was tested by studying their effect on the decomposition of MB using the same method. This experiment was repeated under identical conditions. TiO2 was washed with water to remove the remaining reactants from the catalyst and then dried at 80 °C overnight before testing its recycling performance.