Scholarly article on topic 'Photocatalytic of N-doped TiO2 Nanofibers Prepared by Electrospinning'

Photocatalytic of N-doped TiO2 Nanofibers Prepared by Electrospinning Academic research paper on "Materials engineering"

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{"TiO2 " / nanofibers / electrospinning / nitrogen}

Abstract of research paper on Materials engineering, author of scientific article — Sineenart Suphankij, Wanichaya Mekprasart, Wisanu Pecharapa

Abstract Nitrogen-doped TiO2 nanofibers were prepared by electrospinning process using ammonium acetate (CH3COONH4) as nitrogen sources and titanium (IV) isopropoxide (TiP) in 2-methoxyethanol as starting precursor. The different amount of nitrogen in TiO2 was introduced into the fibers. The structural properties of nitrogen-doped TiO2 nanofibers were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and X-ray photoelectron spectroscopy (XPS). XRD results indicated that the crystallinity of as-prepared fibers and after calcined corresponds to phase of TiO2 independent on nitrogen content. XPS indicates that nitrogen was doped effectively into the fibers. Nitrogen-doped TiO2 nanofiber materials were utilized as the photocatalyst in dye photodegradation under visible light. The significant absorption enhancement in visible region was obtained by nitrogen-doped TiO2 nanofibers relating to the improvement of photocatalytic efficiency comparing to undoped-TiO2.

Academic research paper on topic "Photocatalytic of N-doped TiO2 Nanofibers Prepared by Electrospinning"

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Energy Procedia 34 (2013) 751 - 756

10th Eco-Energy and Materials Science and Engineering (EMSES2012)

Photocatalytic of N-doped TiO2 Nanofibers Prepared by Electrospinning

Sineenart Suphankija, Wanichaya Mekprasartab, Wisanu Pecharapaab*

aCollege ofNano technology, King Mongkut's Institute of Technology Ladkrabang, Ladkrabang Bangkok 10520, Thailand _bThEP Center, CHE,328 Siayuthtaya Rd.,Bangkok 10400,Thailand_

Abstract

Nitrogen-doped TiO2 nanofibers were prepared by electrospinning process using ammonium acetate (CH3COONH4) as nitrogen sources and titanium (IV) isopropoxide (TiP) in 2-methoxyethanol as starting precursor. The different amount of nitrogen in TiO2 was introduced into the fibers. The structural properties of nitrogen-doped TiO2 nanofibers were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and X-ray photoelectron spectroscopy (XPS). XRD results indicated that the crystallinity of as-prepared fibers and after calcined corresponds to phase of TiO2 independent on nitrogen content. XPS indicates that nitrogen was doped effectively into the fibers. Nitrogen-doped TiO2 nanofiber materials were utilized as the photocatalyst in dye photodegradation under visible light. The significant absorption enhancement in visible region was obtained by nitrogen-doped TiO2 nanofibers relating to the improvement of photocatalytic efficiency comparing to undoped-TiO2.

© 2013 The Authors. Published by Elsevier B.V.

Selection and peer-review under responsibility of COE of Sustainalble Energy System, Rajamangala University of Technology Thanyaburi (RMUTT)

Keywords—TiO2, nanofibers, electrospinning, nitrogen

* Corresponding author. Tel.: +66-2329-8000; fax: +66-23298265. E-mail address: kpewisan@gmail.com.

1876-6102 © 2013 The Authors. Published by Elsevier B.V.

Selection and peer-review under responsibility of COE of Sustainalble Energy System, Rajamangala University of Technology

Thanyaburi (RMUTT)

doi: 10.1016/j.egypro.2013.06.810

1. Introduction

Titanium dioxide (TiO2) is one of metal oxide semiconductor applied to environment applications because of non-toxic, strong ultraviolet (UV) absorption, widely energy bandgap of 3.2 eV and good stability in photocatalyst reaction. TiO2 photocatalyst is used in various applications such as photodegradation of organic and inorganic pollutant in waste water, hydrogen generation, air purification, bacteria elimination and dye decolorization [1-3]. Phenomenon of photocatalyst that occurs under UV irradiation resulting to the movement of electron from valence band to conduction band called photoelectron-hole pair. However, UV in the natural light approximately is 3-5% relating to the inactivation of TiO2 in this region [4] therefore low absorption in visible light is one of drawback in TiO2.

Nitrogen (N) doping in TiO2 is one of methods for enhancing its performance such as the decrease of electron - hole recombination and the extension of photoresponse from UV to the visible light region. Therefore TiO2 efficiency is increased by these phenomena resulting to the improvement in the photocatalytic activity. N-doped TiO2 structures can be fabricated by various methods such as nanoparticle, nanorod, nanosheet, nanotube and nanofiber. In this study, the preparation in form of nanofiber by electrospin process was chosen because of long-continuous fiber, controlled its diameter size, porous structure after calcination and uncomplicated process.

The main objective of this work is to synthesize N-doped TiO2 nanofibers that used as photocatalyst in the photocatalytic degradation of Rhodamine B (RhB) under visible light.

2. Experimental

N-doped TiO2 nanofibers (NF) were prepared by electrospinning process. First, the polymer solution was prepared by dissolving 4 g of poly (viny pyrrolidone) (PVP; Mw 40,000, Sigma-Aldrich) in 8 mL of Ethanol followed by stirred for 2 h. Next, the solution of nitrogen doped TiO2 was prepared by mixing CH3COONH4 (ACl Labscan) as nitrogen source at 1, 3 and 5 wt.% in 3 ml 2 methoxyethanol. After that 1.4 g titanium (IV) isopropoxide (TiP) (Sigma-Aldrich) and 2 ml acetic acid (Merck) were added in the solution and stirred for 15 min. Finally, the precursor mixture was stirred until optimized viscosity in the solution was attained. For electrospinning process, 10 ml precursor solution was loaded into a syringe. Distance between a needle tip and collector was fixed at 15 cm with feeding rate 0.5 ml/h and applied voltage at 16 kV. As-prepared electrospun of undoped TiO2 and N-doped TiO2 nanofibers were dried at 80 oC for 12 h. Finally, the electrospuns were obtained after calcined at 500 oC for 2 h.

The Photocatalytic activities of as-prepared NFs were evaluted by degradation Rhodamine B(RhB) under visible light using solar simulator. 16 mg of electrospun TiO2 nanofibers were dispersed in 5.9 x 10-6 mol/. of RhB and stirred 30 min, in the dark. After, the solution was stirred under illumination for various time. The concentration of degraded RhB was measured by mean of its corresponding absorption intensity.

3. Results and Discussion

XRD patterns of as-spun and after-calcined fibers are shown in Fig. 1. No characteristic peak of crystalline phase of TiO2 is observed in as-spun sample. After calcinations at 500 oC, N-doped TiO2 NF shows prominent diffraction peaks positioned at 20 = 25.5o, 38.0o, 48.2o, 54.5o, 55.3o, 63.06°, 69.2o, 70.4o and 75.2o that are assigned to (101), (104), (200), (105), (211), (204), (116), (220) and (215) planes of anatase phase, respectively [5]. Another peaks positioned at 20 = 27.58o, 36.2o, 41.2o and 44.0o are assigned to (110), (101), (111) and (210) planes of rutile phase, respectively.

This XRD results indicate the formation of TiO2 with crystalline phase of anatase and rutile without noticeable alternation in phase after nitrogen doping.

FE-SEM images in Fig.2 show the morphologies of as-synthesized and after calcined of undoped and N-doped TiO2 NF. Morphologies of as-synthesized of undoped and N-doped TiO2 exhibit nonuniform nanofibers with beads as observed in Fig. 2(a) and 2(c). Meanwhile, Fig. 2(b) and 2(d) show uniform nanofibers of undoped and N-doped TiO2, continuity and smooth surface caused by burn-out of PVP from the nanofibers after calcinations. After-calcined TiO2 NFs have average diameter of 140-180 nm.

As-synthesized Calcined at 500 °C

---1---1-1-1-1-1-1-1---

20 30 40 50 60 70 80

29 (degree)

Fig. 1 XRD pattern of as-synthesized and calcined N-doped TiO2

XPS survey spectrum of N-doped TiO2 is illustrated in Fig.3. The electron binding energy and oxidation number of the elements on the surface material were analyzed. The result shows the existence of nitrogen accompanying the appearance of N 1s region (396-404 eV) corresponding to binding energy peak of N 1s at 399.32 eV. The Ti 2p reigion was observed at 461.52 eV and O 1s at 530.41 eV [8-11].

The photocatalytic performnance of as-prepared N-doped TiO2 NF were investigated by RhB photodegradation under visible light. The absorbance at normalized maximum wavelength of RhB versus irradiation time is shown in Fig.4. The complete decolrization of RhB by undoped TiO2 was achieved after 120 min of reaction. Whereas, N-doped TiO2 NF photocatalyst performs shorter degradation time comparing to undoped TiO2. The improvement of catalytic efficiency was obtained by increasing nitrogen doping in TiO2. N-doped TiO2 photocatalyst at 3 wt.% exhibited much better activity than the other due to the optimized doping amount of nitrogen that can induce the defect level in optical band gap of TiO2, leading to the improvement in optical absorptivity of TiO2 in visible region. Furthermore, with high aspect ratio nature of nanofibers can also considerably provide greater surface areas which play a key role on catalytic performance.

TISTR SEI 5.0kV xl,000 10pm HD 8mm I TISTR SEI 5.0kV xl5,000 1pm HD 8mm

Fig.2 FE-SEM images of N-doped TiO2 nanofibers (a) As-synthesized undoped, (b) After calcined undoped, (c) As-synthesized N-doped TiO2 and (d) After calcined N-doped TiO2

Binding Energy (eV)

Fig.3 XPS spectrum of 5 wt. % N-doped TiO2 nanofiber.

0 min 20 min 40 min 60 min 80 min 100 min 120 min Time (min)

Fig.4 Absorbance of RhB versus reaction time under visible light source using 0, 1, 3 and 5 wt.% N-doped TiO2 nanofibers

4. Conclusions

Electrospun undoped and N-doped TiO2 were successfully prepared using CH3COONH4 as nitrogen source. XRD patterns of N-doped TiO2 nanofibers exhibits the characteristic peaks of anatase and rutile phase after calcinations. FE-SEM images disclose the excellent nanofiber formation of as-spun samples. N-doped TiO2 with 5% doping content perform superior degradation of RhB under visible light that may be originated from the proper nitrogen doping which can create the defect level in the band gap of TiO2. In addition, the observable photodegradation of undoped samples under solar simulator may be due to the remained impurity-induced defect active site generated during electrospinning process and photon-activated degradation by UV spectrum existing in solar spectrum of the solar simulator.

Acknowledgements

This work has been financially supported by the National Nanotechnology Center (NANOTEC), NSTDA, Ministry of Science and Technology Thailand, through its program of Center of Excellence Network. This work has been also partially supported by Nation Research Council of Thailand (NRCT).

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[2] Jong-Sik Lee, Young-In Lee, Hanbok Song, Dae-Hwan Jong, and Yong-Ho Choa. Synthesis and characterization of TiO2 nanowires with controlled porosity and microstructure using eletrospinning method. Current applied physics 2011;11: S210-S214.

[3] Qiming Li, Daoxing Sun, and Hern Kim. Fabrication of porous TiO2 nanofiber and its photocatalytic activity. Materials research bulletin 2011;46: 2094-2099.

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