Titanium dioxide decorated natural cellulosic Juncus effusus fiber for highly efficient photodegradation towards dyes

Journal Pre-proof Titanium dioxide decorated natural cellulosic Juncus effusus fiber for highly efficient photodegradation towards dyes Sijie Zhou, Liangjun Xia, Kai Zhang, Fu Zhuan, Yunli Wang, Qian Zhang, Lisha Zhai, Yunshan Mao, Weilin Xu

PII:

S0144-8617(20)30004-7

DOI:

https://doi.org/10.1016/j.carbpol.2020.115830

Reference:

CARP 115830

To appear in:

Carbohydrate Polymers

Received Date:

11 October 2019

Revised Date:

16 December 2019

Accepted Date:

2 January 2020

Please cite this article as: Zhou S, Xia L, Zhang K, Zhuan F, Wang Y, Zhang Q, Zhai L, Mao Y, Xu W, Titanium dioxide decorated natural cellulosic Juncus effusus fiber for highly efficient photodegradation towards dyes, Carbohydrate Polymers (2020), doi: https://doi.org/10.1016/j.carbpol.2020.115830

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Titanium dioxide decorated natural cellulosic Juncus effusus fiber for highly efficient photodegradation towards dyes Sijie Zhoua,1, Liangjun Xiab,a,1, Kai Zhangc,d, Fu Zhuana, Yunli Wanga, Qian Zhanga, Lisha Zhaia, Yunshan Maoa, Weilin Xua,* a

State Key Laboratory of New Textile Materials and Advanced Processing Technologies, Wuhan Textile University, Wuhan 430200, China. b

College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China. d

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c

Institute for Frontier Materials, Deakin University, Geelong, Victoria 3216, Australia.

Luthai Textile Co., Ltd., Luthai Group, Shandong 255100, China. These authors contributed equally to this work.

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*Corresponding

author: State Key Laboratory of New Textile Materials and Advanced Processing Technologies, Wuhan Textile University, Wuhan, China. E-mail addresses: [email protected] (W.X.).

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Graphical Abstract

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Highlights

A natural cellulosic Juncus effusus fiber was used for photodegradation towards dyes.

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Three-dimensional network structure and interconnected channels were observed.

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99.9 % of degradation efficiency was obtained towards different types of dyes.

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An orientate fabric was fabricated using the prepared TiO2-JE fibers.

Abstract: The removal of dyes via photocatalytic degradation has been identified as an eco-friendly

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method for producing clean and purified water. Natural cellulosic fibers are significant renewable resource and important in a wide range of applications. Herein, we report a natural cellulosic Juncus effusus (JE) fiber with 3D network structure as a framework to provide controllable space for the growth of TiO2 particles. The TiO2-JE showed remarkable activity in the removal of C.I. Reactive Red 120 (RR120), C.I. Direct Yellow 12 (DY12), and methylene blue (MB) with a photodegradation 2

efficiency of 99.9% under simulated sunlight irradiation. Additionally, an orientate fabric was fabricated using the prepared TiO2-JE fibers for the photocatalytic degradation of dye-contaminated water in the sun, further confirming its practical application. The TiO2 decorated natural cellulosic JE fiber can be a promising material for photocatalysis and sustainable chemistry.

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Keywords: Juncus effusus, cellulosic fiber, 3D network, TiO2, photocatalytic degradation

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1. Introduction Water is one of the most vital requirements of living organisms on earth (Vorosmarty et al., 2010). A common observation is that water is abundant on earth but only a small amount is easily accessible, and in the fresh water cases, this is especially true for human (Oki, 2006). However, industrial processes produce toxic wastewater containing aromatic compounds from dyes, which have harmful effects on human immune system and ecosystems. (Dhanya & Aparna, 2016; Meseck, Kontic, Patzke, &

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Seeger, 2012; Zhang, Li, Li, Li, & Yang, 2018). Conventional adsorption technologies, such as biological degradation (Oh et al., 2014), chemical oxidation (Li, Zhang, Liang, & Yediler, 2013; Sohrabi, Ross, Martin, & Barker, 2013), activated carbon absorption

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and carbon nanotube nanocomposite absorption (Gao, Zhao, Cheng, Wang, & Zheng, 2013; Hashemian, Salari, Salehifar, & Atashi Yazdi, 2013), ultrafiltration by chemical

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agents or physical filtration, reverse osmosis, coagulation, and ion exchange. (Galindo

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C, 2001; Karimifard & Alavi Moghaddam, 2018; Konstantinou & Albanis, 2004; Natarajan, Thomas, Natarajan, Bajaj, & Tayade, 2011; Tang W Z, 1995)，because of

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quantity production and harsh experimental conditions, generation of by-products, and regeneration and reasonable disposal of adsorbents restrict their broader, acceptable

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application.

As one of the most widely used photodegradable materials, TiO2 has attracted

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much attention for the treatment of organic and contaminated components (Hoşgün & Aydın, 2019), due to its biological activity and chemical stability, high oxidizing power toward organic materials, low price, and non-toxicity (Fernández-Ibáñez et al., 2015; D. Wang et al., 2017; Yang et al., 2017). However, as a single constituent, TiO2 has some disadvantages, most of which are associated with its limited photocatalytic efficiency in the visible light range on account of its wide band gap and rapid 4

recombination of hole–electron pairs (Da Vià, Recchi, Gonzalez-Yañez, Davies, & Lopez-Sanchez, 2017), low absorption capacity, and low surface area (Cheng, Wang, Zhao, & Han, 2014), thereby reducing its photocatalytic activity. Moreover, in the practical applications, residual TiO2 nanoparticles in the photocatalytic reaction solution need to be recycled. To address these problems, a large number of synthetic materials, such as polymer films and porous inorganic membranes (Leong et al., 2014; Xiuyun Liu, Chen, Lv, Feng, & Meng, 2015), porous composites (Lefatshe, Muiva, &

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Kebaabetswe, 2017), composite sponges (Hickman, Walker, & Chowdhury, 2018), clays and clay minerals, zeolites, silica gels, and metal-organic frameworks, as well as

complicated methods synthesis have been used to immobilize nano-TiO2 particles

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(Butburee et al., 2018; Gu et al., 2016; Kangwansupamonkon, Klaikaew, & Kiatkamjornwong, 2018; Meseck et al., 2012). However, most methods have their

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limitations owing to complicated process of synthesis, inconvenient, harsh, and not

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environment friendly conditions, as well as expensive raw materials. Therefore, for the applications of industrial dye wastewater adsorption, the cost of the dye wastewater adsorbent has to be further reduced.

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Juncus effusus (JE) fiber is natural cellulosic fiber with excellent biocompatibility, non-hazard, low cost, substantial biodegradability, and recyclability, which has

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extensively planted in provinces in China such as Jiangxi, Sichuan, and Guizhou (X

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Wang, Ke C, Tang C, Yuan D, & Ye Y, 2009). More importantly, compared with other cellulose materials used for dispersing nanoparticles to the photocatalytic degradation experiment,

such

as

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ZnO-blended

cellulose

acetate-polyurethane

membrane(Rajeswari, Vismaiya, & Pius, 2017), β-FeOOH@tunicate cellulose hydrogels (Wang et al., 2019), TiO2-MFC (Microfibrillated cellulose) thin films (Ng & Leo, 2019), Ag3PO4/ nanocellulose composite (Lebogang, Bosigo, Lefatshe, & Muiva, 5

2019), and N-doping of cellulose photocatalytic materials (Chhetri et al., 2017), JE fiber exhibits the natural three-dimensional network structure and interconnected channels, which can be a promising candidate for the in-situ growth of TiO2 particles by providing a limited space and controlling the size. It is considered that the 3D network structure of an adsorbent is beneficial for adsorption of dyes and the control growth of TiO2 is vital to photodegradation performance towards dye in water (Froschl et al., 2012). Therefore, the TiO2-JE material can be a promising material for alleviating the

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environmental pollution via adsorption and photodegradation towards dyes from wastewater.

Herein, we developed a novel route to immobilize the functional photocatalyst of

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TiO2 particles utilizing 3D-porous cellulosic JE fibers. The TiO2-JE fibers were prepared using a sol-gel approach, followed by stewing and baking crystal treatment.

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The aim of designing TiO2-JE fiber material was to bring out the excellent properties

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of respective components and through the combination of inorganic and organic enhance their respective performance, to make up for their respective shortcomings. JE fiber is one of the potential candidates for supporting TiO2 particles due to its 3D net-

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working structure and the composite was prepared by incorporating the photocatalyst with a 3D interpenetrated network structure based on TiO2 particles with JE fibers for

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the absorption and degradation of dyes from water.

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2. Experimental 2.1. Materials

The chemicals used for synthesis include tetrabutyl orthotitanate (TBOT) (97 %, Aldrich, USA), acetic acid (99.9 %, Aldrich, USA), and absolute ethanol (99.9 %, Merck, USA). JE fibers were obtained from Jiangxi Juncus effusus Co. Ltd., Jiangxi, 6

China. C.I. Reactive Red 120 (RR120), C.I. Direct Yellow 12 (DY12), and methylene blue (MB) were supplied by Luthai Textile Co. Ltd., Shandong, China. Deionized water was used in all the experiments.

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2.2. Preparation of TiO2-JE composites

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Fig. 1. Schematic illustration of preparation of TiO2-JE Fibers.

A

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Tab. 1. TiO2-JE fibers with different concentrations of Tetrabutyl orthotitanate sol.

B

Absolute ethanol(mL)

TBOT (mL)

Deionized water(mL)

Acetic acid(mL)

T-10% T-20% T-30% T-40%

90.0 80.0 70.0 60.0

10.0 20.0 30.0 40.0

2.0 4.0 5.0 6.0

2.0 4.0 7.0 10.0

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NO.

JE fibers (g)

WGR (%)

1.0 1.0 1.0 1.0

122.6 235.5 338.6 504.2

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In recent years, the method of sol-gel has been extensively investigated for possible

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applications. The conventional method of sol-gel was carried out to prepare the titanium dioxide (R. Asahi, 2001). Firstly, a desired liquid (A) was prepared by dissolving the TBOT in absolute ethanol with continuous stirring to obtain a clear solution at 30°C. At room temperature, a mixed solution (B) of acetic acid and deionized water was then prepared with continue stirring. Next, solution B was tardily dropped into solution A,

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followed by stirring at 30°C. After 30 min, a sol was slowly formed with stirring. Secondly, the JE fibers were immersed into the above sol for 60 min at room temperature (25 °C). Finally, the resultant sol with JE fibers gelled was dried at 100 °C to eliminate water and ethanol, and the TiO2-JE fiber of different weight gain rates (WGRs) were obtained. The preparation procedures are shown in Fig.1 and Tab.1, indicating the TiO2-JE fibers with different concentrations of TBOT solution.

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2.3. Photocatalytic experiment

The photocatalytic dye degradation experiments were carried out under ultraviolet (UV) radiation. The photocatalytic activities of TiO2-JE fibers was measured by the

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photodegradation of RR120, DY12, and MB under simulated solar irradiation (Xe lamp,

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125 W) as model reaction (Sun et al., 2019), which placed 14.5 cm away from the solution. The intensity of the UV-light was measured by the Light Intensity Instrument

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(CEL-NP2000) at the same position, showing intensity and density of 150 mW and 200

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mW/cm2, respectively (Rezaei, Irannejad, & Ensafi, 2018). All the photocatalytic dye degradation experiments in this manuscript were carried out under the same UV

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irradiation. Firstly, to determine the photocatalytic properties of these TiO2-JE fibers with different WGRs, a 20 mL RR192 solution was prepared with the concentration of

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100 mg/L. 0.2 g of the TiO2-JE fibers was then added to this solution. The sample was stayed in the dark for ten minutes, to achieve the equilibrium on the surfaces of the TiO2-JE fibers. Finally, the sample was exposed to UV light, and the photocatalysis took place. The dye solution was analyzed using a UV-visible spectrophotometer throughout. This method was used to determine the various concentration. Owing to 8

the influence of the concentration of TBOT on the JE fibers for degradation, the optimal TiO2-JE fiber composite was selected. The degradation experiments of the three kinds of dyes at various initial dye concentrations were then carried out. Each experiment was conducted in quintuplicate. The curve presented in the manuscript for each experiment is a representative, which is closest to the average value obtained from the repeated trials.

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2.4. Characterization The scanning electron micrographs (SEMs) (JSM-IT300 scanning electron microscope

at a voltage of 10 kV) provided additional morphological details and further verified

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the phase structures of the materials, and the results of energy dispersive X-ray

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spectroscopy (EDS) were employed to detect the constituents of the samples. The Xray diffraction (XRD) measurements were conducted using a wide-angle XRD analysis

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instrument (X’Pert PRO, PANalytical B.V., Almelo, The Netherlands) with Cu Kα radiation at 40 kV and 40 mA. The X-ray photoelectron spectroscopy (XPS) spectra

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were obtained using a dual anode XSAM800 spectrometer from KRATOS with non-

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monochromatic Al Kα X-radiation (hʋ= 1486.6 eV). Fourier transform infrared (FTIR) spectroscopy analysis was formed on a Bruker Vertex 70 instrument in German.

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Thermogravimetric analysis (TGA) was performed on a Netzsch TG 209 F1 thermal analyzer under nitrogen flow in the temperature range of 30-600 °C at a heating rate of 10°C/min. The UV-visible absorption spectroscopic images of dye degradation were recorded using a UV-2550 visible light spectrophotometer (Shimadzu, Japan) at room

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temperature, in the spectral range 185-900 nm. The optical densities were measured using a UV quartz cuvette (path length of 1 cm).

3. Results and discussion 3.1. Characterization of TiO2-JE composites Fig.2 and Fig.S1 show the surface morphologies, cross sections and longitudinal sections of the JE and TiO2-JE fibers. From the SEM images of the cross-sectional and

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longitudinal sectional views, a natural 3D porous structure and the rough surface of the JE fiber were clearly observed. Fine porous structure and excellent surface properties

improve the composite materials surface activity. Some TiO2 particles were formed

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after aggregation, as shown in Fig.2(b1)-(b3) and Fig.S1(a1)-(c3). As the concentration

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of TBOT increased Fig.2(b1)-(b3) 40mL/100 mL, Fig.S1(a1)-(a3) 10 mL/100 mL, Fig.S1(b1)-(b3) 20 mL/100 mL, Fig.S1(c1)-(c3) 30 mL/100 mL, a smoother surface

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decorated by TiO2 particles was formed along the longitudinal morphologies of the

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TiO2-JE fiber when compared with that of the JE fiber. However, when the concentration of TBOT was 40 %, the longitudinal morphologies of the TiO2-JE fiber

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appeared to be more amorphous, and there was a successful adherence of the TiO2 particles to the JE fiber (Hickman et al., 2018). The images of the TiO2-JE fiber samples

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(Fig.2 (b2)), revealed their clear network structure, indicating that the TiO2-decorated mesoporous fiber materials retained the morphology of the JE fibers. The TiO2 was deposited on the net-work structure, indicating that the JE fibers showed outstanding physical properties as excellent carriers. Owing to the special structure of the JE fibers, as shown in Fig.2 (b3), the longitudinal section of the TiO2-JE fibers showed a perfect 10

3D network structure with TiO2 nanoparticles, contributing to the increased adsorption capability toward dyes in water and a likely increase in the reaction area, which promoted photodegradation. Their morphology was rather close to that of rough grain derived from nanoparticles, which increased the surface area available for the occurrence of photocatalysis. The JE fiber could provide skeleton to develop mesoporous TiO2 particles, for which the average pore size of the as-prepared TiO2

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matched well with the size of the JE fibers (Xue et al., 2017). As a photodegradtion composite material, it illustrates high surface area as well as high porosity, which are of great vital to the photocatalytic performance.

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Fig.2c presents the composition of the composite TiO2-JE fiber materials as determined

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by X-ray analysis. It presents the amount of elements distributed on the TiO2-JE fibers in terms of atomic and weight percentages. The carbon peak was likely indicative of

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the contribution of the JE fiber. It was difficult to differentiate the intense O peak from

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those of JE fiber and TiO2. However, the Ti and O peaks confirmed the presence of a composite on the TiO2-JE fibers (Meseck et al., 2012). This result pointed to the

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successful preparation of the TiO2-decorated mesoporous fiber composite materials.

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Fig. 2. SEM images of (a1) (e1) morphologies of longitudinal surface, (a2) (b2) cross section and (a3) (b3) longitudinal section for JE fiber and T-40 % TiO2-JE fibers, respectively; (c) representative EDX spectrum for the sample T-40%.

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The regions shown in Fig.3(a1)-(a4) are for the T-40 % fibers analyzed by XPS. These

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XPS regions clearly show the peaks of O, Ti, and C. The peak of element C should be attributed to the organic substrate of the TiO2-JE fibers. Fig.3(a2) shows the Ti 2p peaks;

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the binding energies of Ti 2p1/2 and Ti 2p3/2 are about 464.42eV and 458.42 eV (Gonell, Puga, Julián-López, García, & Corma, 2016; Yan, Zhao, Li, & Hun, 2015), respectively,

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manifesting a normal Ti4+ match with TiO2 (Conceição et al., 2017; Xu, Da, Wu, Zhao, & Zheng, 2012). The XPS spectra of O 1s (Fig.3(a3)) contain two obvious peaks, one of the peaks centered at 529.39 eV should be assigned to the Ti-O bonds, i.e., pattern the TiO2 particles present in the composite TiO2-JE fibers (Haque, Nandanwar, & Singh, 2017; Vargas Hernández, Coste, García Murillo, Carrillo Romo, & Kassiba, 2017). 12

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Fig. 3. (a1)-(a4)XPS region of T-40%;(b) XRD pattern of TiO2 powders and samples of T-10%, T20%, T-30% and T-40%; (c) FTIR spectra of for the samples (from bottom to top): T-40%, T-30%, T-20%, and T-10% and JE fiber; (d) TGA, (e) DTG curves of T-10%, T-20%, T-30% and T-40% and JE fiber.

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The XRD of the TiO2 nano-powders developed via the sol-gel method is shown in Fig.3b. The TiO2 nano-powders were examined to gain insight into their crystal

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structure. As reported, the crystallization of anatase formed by high-temperature

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calcination exhibits the peaks at 25.3°, 37.9°, and 40.8° corresponding to the 101, 004, and 200 phases respectiveely (Andrade-Guel et al., 2018; Hoşgün & Aydın, 2019; Kangwansupamonkon et al., 2018; Kutuzau et al., 2019; Uddin et al., 2007). The XRD pattern does not show any clear peaks characteristic of TiO2 crystalline phase, which indicates that the TiO2 nano-powders are amorphous (Akhavan Sadr & Montazer, 2014). The sharp crystalline peak of TiO2 can hardly be seen owing to the low amount of TiO2. 13

Most TiO2 peaks of the TiO2- JE fibers were covered by the amorphous peak of the JE fibers (Metanawin, Panutumron, Thongsale, & Metanawin, 2018). The FTIR spectra of the different samples are depicted in Fig.3c. It is noted that the FTIR spectra of all the samples present the typical band of TiO2, which is a wide band in the range 500-900 cm-1 owing to the Ti-O vibration (L P Liu et al., 2017; Sasani Ghamsari & Bahramian, 2008; Valencia, Vargas, Rios, Restrepo, & Marín, 2013). The titanium dioxide crystal

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lattice vibration Ti-O-Ti was assigned with the distinctive peak below 1000 cm-1 (Farshchi, Pirsa, Roufegarinejad, Alizadeh, & Rezazad, 2019; Mohamed et al., 2015).

The TiO2-JE fiber samples have diverse properties as evident from the TGA and DTG.

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The thermal stability of the TiO2- JE fibers was characterized using TGA in the

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temperature range 30-600 °C. The degradation of the various samples took place in three phases (Blas-Sevillano, 2018; Giesz, 2016). As shown in Fig.3d, the weight loss

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in stageⅠwas observed in the temperature range 30-100 °C, owing to the evaporation

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of moisture from the JE fibers (Balaji & Nagarajan, 2017). The following two decomposition processes conform to the decomposition process of cellulose fiber. The

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thermal stabilities of the JE and TiO2- JE fibers gradually decreased, at the temperature region 100-250 °C, owing to the molecule of the cellulose start to thermal

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depolymerization, such as hemicellulose, lignin, and the glycosidic linkages. (Senthamaraikannan & Kathiresan, 2018). Stage Ⅲ of the mass loss took place in the temperature range 250-370 °C, with a primary mass loss of about 40%, 30%, and 50% in the TiO2-JE fibers of different concentration of TBOT and JE fibers owing to the decomposition of cellulose (Sathishkumar, Navaneethakrishnan, Shankar, & Rajasekar, 14

2013). From the DTG (Fig.3d), it was clearly seen that the degradation temperature of the TiO2-JE fibers increase about 10-30 °C higher than that of JE fibers. This result clearly indicated that the TiO2-JE fibers could be preferentially used as photocatalysts due to their excellent thermal stability. At 600°C, the residuals of the T-10 %, T-20 %, T-30 %, T-40 %, and JE fibers were about 40.2 %, 49.68 %, 46.75 %, 47.04 % and

significantly higher than that of the JE fibers. 3.2. Photodegradation of dyes by TiO2-JE fibers

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19.74 %, respectively, establishing that the loss in mass of the TiO2-JE composites was

A schematic illustration of photodegradation under UV-light is shown in Fig.4a. A total

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of 0.2 g of T-40 % fibers were added into 20 mL each of RR120, DY12, MB liquor with

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the desired dye concentrations based on their different chemical properties, toxicities and industrial applications. These samples were then placed under UV -light for the

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required duration. The contact angles of water on the surfaces of the JE and TiO2-JE

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fibers, as shown in Fig.4a, obviously established that the surface of the JE fiber was highly hydrophobic. This may be ascribed to the microstructure of the JE fiber shown

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in Fig.2(a1). In contrast, the longitudinal surface of the TiO2-JE fiber exhibited good hydrophilicity, which was mainly owing to its rough surface structure and micro grids

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having been completely embedded in the TiO2 particles, which contributed to its dye absorption ability. In addition, it can be seen from Video S1 that the TiO2-JE fibers showed excellent hydrophilicity. These results suggest that the TiO2-JE fibers can combine with the dye molecules in the solution, thereby accelerating photodegradation on the fiber carrier. 15

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Fig. 4. (a) Schematic illustration of photodegradation under the UV-light and the contact angle of water on the surface of JE and TiO2-JE fiber; (c) the UV spectrum and (d) degradation of RR120 with TiO2-JE fibers of different concentration of TBOT and (e) effect of pH on the degradation of TiO2-JE Fibers with RR120, DY12 and MB (Experimental conditions: m=0.2 g, V=20 mL, C0=50 mg/L).

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Fig.4c presents the UV spectra of RR120 before and after photocatalytic degradation,

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and the photocatalytical degradation effects of the photocatalysts were recorded and analyzed. In order to maximize the degradation efficiency, it is important to use the

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optimal mass of catalyst. To determine the effect of the amount of TiO2 (represented by the concentration of TBOT) on photocatalytic reaction was studied. The tests were

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carried out at concentrations ranging from 10mL/100mL to 40mL/100mL. At higher TBOT concentrations the catalytic performance of the TiO2-JE fibers in terms of dye decomposition was much better for the same photocatalytic time. Among all the samples tested, the T-40 % specimen showed the best photocatalytic process to disintegration RR120, and achieved a degradation of 99.99 % in 60 min. Hence, the T16

40 % was verified as a handy and efficient photocatalyst to greatly improve the decomposition of the dye RR120. The TiO2-JE fibers with T-40 % was selected for all photodegradation experiments. The pH of reaction environment significantly affects the surface properties of the photocatalyst and its photoactivity (Yuan et al., 2019). To evaluate the suitability of the TiO2-JE fibers, three kinds of dyes named as RR120, DY12, and MB, were selected as

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representative dyes. The pH of these dye solution was examined in the pH value range

5.0-10.0. As shown in Fig.4d, the photocatalytic performance of TiO2-JE fibers is strongly dependent on the pH of the dye solution. Under acid and alkaline conditions,

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the photodegradation of efficiency RR120 and DY12 were higher than the ones under

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the neutral conditions. The photodegradation efficiency of RR120 and DY12 were first reduced and then enhanced with the increase of pH value, whereas the photodegradation

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efficiency of MB was increased when pH value enhanced. The higher pH value could

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provide higher concentration of the hydroxyl ions to react with holes and form hydroxyl radicals (Adam, Pozina, Willander, & Nur, 2018), which subsequently may cause an

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increased photodegradation efficiency. Therefore, the investigated dyes exhibited the maximum photodegradation efficiency at the pH value of 10.0. All the subsequent

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photodegradation experiments were performed under the pH value of 10.0. The enhanced photocatalytic activity could be attributed to the adsorption of the 3D porous structure, which has significant positive effects on the diffusion of dyes into the 3D porous structure, resulting in the enhancement of photodegradation efficiency (Pan et al., 2013; Sun et al., 2019). Aiming at verifying the adsorption performance of the 17

JE and TiO2-JE fibers towards the dyes, the absorbance curves of the dye solutions after the adsorption process in absolute darkness were examined According to the weight gain ratio of the 40%-TiO2-JE fiber compared to the JE fiber, the same mass of the JE fibers were weighed. Then the desired JE fibers and TiO2-JE fibers were added into the RR120, DY12, and MB dye solution for 100 min, respectively, with the initial dye concentration of 50 mg/L at the pH value of 10.0. The results shown in Fig.S2 indicated

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that the JE and TiO2-JE fibers exhibited the adsorption capacity towards dyes, and the

adsorption capacity of TiO2-JE fibers is higher than that of the JE fibers under the same conditions, which can effectively promote the photodegradation.

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To investigate the cooperative effect between TiO2 particles and JE fiber, according to

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the weight gain ratio of the 40%-TiO2-JE fiber compared to the JE fiber, the same weight of TiO2 particles were prepared on the basis of the method provided in the

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section 2.2. The as-prepared mass TiO2 particles were immersed into the RR120 dye

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solution with the initial dye concentration of 50 mg/L at the pH value of 10.0. The results in Fig.S2 indicates that the TiO2-JE fibers for RR120 dye solution achieved a

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photodegradation of 99.74 % at the same reaction conditions under the UV-light with the 81.21% of TiO2 particles (Fig. S3). The combination of JE fibers with TiO2 particles

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can effectively promote the photodegradation. In order to studied the photocatalytic reaction at the molecular level, the UV spectra of these dyes before and after degradation were analyzed to demonstrate the changes. As shown in Fig.5(a)-(c), the UV spectrums in the range of 200 - 800 nm of the samples photocatalyzed with T-40 % at 0-50 min, 0-60 min, 0-100 min, respectively, and these 18

curves reveal the changes in absorbance after photocatalysis. The characteristic peak intensity decreased significantly during photodegradation, indicating that the

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photocatalysts destroyed the chromophores of the dyes (Miao, Zhang, & Zhang, 2018).

Fig. 5. UV scans in the range of 200 to 800 nm: (a) RR120, (b) DY12 and (c) MB at 0 min to 100 min; (d) the TiO2-JE Fibers of different photodegradation time for RR120, DY12 and MB; (e) the photodegradation efficiency of three kind of dyes, (Experimental conditions: m=0.2 g, V=20 mL, C0= 50 mg/L); (f) the photograph of dye photodegradation with different dye concentration (g)-(j) effect of dye concentrations on the photodegradation of TiO2-JE Fibers with RR120 (Experimental conditions: m=0.2 g, V=20 mL, C0=50 mg/L, 100 mg/L, 200 mg/L, 300 mg/L); (k) Ct/C0 of different dye concentrations; (l) Redegradation efficiency of TiO2-JE fibers for RR120, DY12 and MB, respectively.

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As seen from Fig.5d, these fibers became darker in color and then lighter during the photocatalytic process. The reactions associated with both absorption and photodegradation occurred, by means of dye adsorption onto the surfaces and mesopores of the JE fibers and via degradation of the dye in close contact with the mesopores of the fibers, respectively. The absorption of the various samples occurred in three phases. The first stage was that of the faster external surface adsorption. The

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second stage was associated with intra-particle diffusion toward the pores in the inner surfaces of the JE fibers, and this diffusion started to slow down because of the extremely low concentration of dye in the reaction solution, thereby leading to the final

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equilibrium stage (Bouabidi, El-Naas, Cortes, & McKay, 2018). The photodegradation

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rates of the three dyes could reach 100 % (Fig.5e).

As shown in Fig.5 (f)-(k), the images of the dyes at different concentrations, the UV

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spectra of the samples differing in initial dye concentration illustrate the degradation

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percentages as functions of reaction time under UV light, and the rates of photocatalytic degradation. It was observed that the time to complete the degradation of a dye in an

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aqueous solution depended dominantly on its initial concentration. In the case of RR120, the degradation efficiency reduced with increase in dye concentration from 50 mg/L to

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300 mg/L. When the degradation was 100%, with the lower the dye concentration or the higher the amount of catalyst, the faster the degradation rate would be obtained. By increasing the initial concentration of the dye, not only the surfaces of the TiO2-JE fibers saturated earlier but also the luminous energy of the UV -light was intercepted before it could react with the photocatalyst. When the photocatalyst surface was saturated, the 20

photodegradation efficiency could reduce, owing to the fewer active sites. (Shafeeyan, Wan Daud, & Shamiri, 2014). Interception of photons decelerated the degradation, thereby increasing the time required for dye degradation. In Fig.5k, the ratio of Ct/C0 has been employed to explain the rate of photodegradation; the lower the dye concentration, the faster was the degradation rate, and a photodegradation efficiency of 99.9% could be achieved under different concentrations. It was found that extension in

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the photodegradation time increased the photocatalytic efficiency significantly (Fig.S4). The photodegradation of dyes mainly occurred in two stages. First, the TiO2-JE fibers

absorbed the dye with a small number of superoxide radical anions and active hydroxyl

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radicals conducting the photodegradation. In the second stage, photocatalytic

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degradation increased gradually alongside the completion of adsorption. A lot of superoxide radical anions and active hydroxyl radicals were produced, and the

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photocatalytic degradation rate accelerated.

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As shown in Fig.S5(a), the TiO2-JE fibers retained their original color and morphological characteristics. The reactions associated with both absorption and

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photodegradation occurred. Subsequently, photodegradation of the dyes was accomplished on the TiO2-JE fibers. The TiO2-JE fibers that were repeatedly used

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exhibited properties identical to those of the initial TiO2-JE fibers, with no obvious drop in photocatalytic efficacy even after five cycles, achieving photodegradation efficiency of 98 % (Fig.5l). The SEM images of the cross-sectional and longitudinal sectional views of these fibers demonstrate their surface features and morphological characteristics. Comparing the images obtained before (Fig.3(a1)-(a3)) with those 21

obtained after (Fig.S5(b)-(d)) the use of the TiO2-JE fibers in the degradation of various dyes, the porous structures in the net-work and the 3D porous structures were clearly observed in the cross-sections and longitudinal sections of the fibers. After the photocatalytic reaction, the fiber retained its original porous structure, which indicated that the 3D porous fiber materials could be good carriers of TiO2 during photodegradation. Additionally, the TiO2-JE fiber catalyst could be easily retrieved

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through ordinary filtration.

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3.3. Photodegradation under visible light by TiO2-JE fiber braided fabric

Fig. 6. (a)Photocatalytic of dye liquor under Visible Light; (b) UV scans in the range of 250 to 800 nm and (c) degradation of dye liquor under Visible Light.

Fig.6a shows a typical braided fabric of the TiO2-JE fiber. A large piece of the TiO2-JE fiber braided fabric photocatalytic generator was added to dye liquor under visible light. 22

The sample tested for the device demonstrated had dimensions of 115 mm × 100 mm × 2.5 mm, and the image of the process of photodegradation under sunshine is presented in Fig.S6. TiO2 was activated directly by UV irradiation of the visible light to generate electron (e−)/hole (h+) pairs(Bai et al., 2019), And then the O2 reduced to produce superoxide radical anions •O2− and the hydroxyl groups form the very active hydroxyl radicals •OH. The oxidative substances generated, including •OH/•O2−, oxidized and decomposed the dye macromolecules to small molecules (Bai et al., 2019; Guo et al.,

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2018; Song et al., 2018; Zhang, Li, Li, Li, & Yang, 2018). A reusable photocatalysis system is highly desirable for the realization of dye degradation in water, and its

scalability with stable performance and high photodegradation efficiency renders our

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demonstration of the photocatalytic degradation of materials extremely attractive for practical applications. The UV scans of dye liquor in the range 250 - 800 nm under

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visible light at 4h are presented in Fig.6(b). The experimental conditions were as

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follows: mass, 0.2 g; volume, 500 mL; C0, 50 mg/L; pH, 10; temperature, 19-25°C; time, 9:30(am)-13:30(pm)). Under these conditions, the photodegradation rate of the three dyes could reach 100% Figure 6c.

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To investigated the regeneration of the TiO2-JE fabrics, reuse of the fabrics was carried out in the sun. As shown in Fig.S7, the TiO2-JE braided fabrics could be repeatedly

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used exhibited properties identical to those of the initial, which have no obvious drop

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in photocatalytic efficacy even after five cycles, achieving photodegradation efficiency of 98 %.

The braided fabric for the TiO2-JE fibers showed excellent photodegradation and absorption performance of the TiO2-JE fiber braided fabric, conferring it with enormous potential in practical wastewater treatment.

4. Conclusions 23

In summary, the TiO2 decorated mesoporous JE fibers were successfully prepared via a simple sol-gel processes using precursors. The natural cellulosic JE fiber has concluded to be a promising material for the controllable growth of TiO2 due to its 3D network structure. The TiO2-JE fiber showed stable properties and high degree of absorption and excellent photodegradation for dyes under UV and visible light; nearly 99.9 % each of RR120, DY12 and MB were degraded within 50 min, 60 min and 100 min, respectively, at dyes solution pH value of 10. This is ascribed to the significant enhancement in light

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absorption due to the 3D network structure of the TiO2-JE fiber, thereby achieving accelerated photodegradation and enhancement of photodegradation efficiency. Moreover, the TiO2-JE fibers prepared can both adsorb and degrade organic pollutants

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repeatedly for more than five times. Finally, the TiO2-JE fiber braided fabric demonstrated a reusable system of photocatalysis, which exhibited attractive

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performance for practical applications. This work indicates that the TiO2-JE could

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improve the photo-response and inhibit charge carrier recombination, which may be beneficial to further studies in sustainable chemistry and engineering.

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Acknowledgments

We are very grateful for the financial support from the National Natural Science

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Foundation of China (51773158) and the China Chemical Fibers Association, Lv Yu

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Foundation (CCFALY2018-2-4).

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