尼龙论文4

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CERAMICS

INTERNATIONAL

Ceramics International 39(2013)7143–7148

www.elsevier.com/locate/ceramint

Fabrication and photocatalytic activity of electrospun nylon-6nanofiberscontaining tourmaline and titanium dioxide nanoparticles

Seung-Ji Kang a , 1, Leonard D. Tijing a , b , n , 1, Bo-sang Hwang a , Zhe Jiang c , Hak Yong Kim d , e ,

Cheol Sang Kim a , c , n

b

Division of Mechanical Design Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea

Department of Mechanical Engineering, College of Engineering and Design, Silliman University, Dumaguete City, Negros Oriental 6200, Philippines

c

Department of Bionanosystem Engineering, Graduate School, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea d

Department of Organic Materials and Fiber Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea e

Center for Healthcare Technology Development, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea

Received 18January 2013; received in revised form 18February 2013; accepted 18February 2013

Available online 14March 2013

a

Abstract

In this paper, we report the effect of the incorporation of titanium dioxide (TiO2) nanoparticles (NPs)on the photocatalytic properties of a tourmaline NP/nylon-6composite mat prepared by one-step electrospinning process. Several characterization techniques were utilized to check the successful incorporation of NPs in/onthe nanofibers.Both TiO 2and tourmaline NPs were confirmedto be incorporated on the surface of the nylon-6nanofibersor fully embedded in the fibersthrough SEM and TEM observations. The fiberdiameter showed increasing size trend in the order of nylon-6o tourmaline/nylon-6o TiO 2-tourmaline/nylon-6.The incorporation of both TiO 2and tourmaline NPS on/innylon-6nanofibershas resulted to increased photocatalytic degradation of organic pollutant. The successful immobilization on nylon-6nanofibersthrough simple electrospinning of tourmaline possessing unique properties, and photocatalytic TiO 2showed synergistic effect in the degradation of organic pollutants, which could have potential application in water treatment applications.

&2013Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Keywords:D. TiO 2; Electrospinning; Photocatalytic; Tourmaline; Nylon-6

1. Introduction

Among the current technologies, electrospinning of nanofiberspresents itself as a simple and effective method in fabricating nanofibrousmaterials decorated with or containing nanoparticles [1–4].Electrospun nanofibershave very large surface areas providing more reactive sites and small pore sizes, which can then be utilized in different applications such as in water and air filtration,textiles, and in biomedical engineering [5, 6].There are many fillermaterials available to functionalize nanofibrousmats,

Corresponding authors at:Division of Mechanical Design Engineer-ing, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea. Tel.:þ[1**********]; fax:þ[1**********].

E-mail addresses:[email protected],[email protected](L.D.Tijing), [email protected](C.S.Kim). 1

These authors contributed equally to this work.

n

and most of the reports include the use of nanoparticles (NPs)such as Ag, TiO 2, zinc oxide, carbon nanotubes, grapheme, alumina, silica, etc. Only few studies have incorporated tourmaline nanoparticles to impart function-alities on a nanofibrousmat. In our previous study, we reported an increase in mechanical properties and wett-ability of polyurethane (PU)nanofiberswhen tourmaline nanoparticles were incorporated [7]. Synergistic effects in killing bacteria was also realized when tourmaline nano-particles were exposed in high frequency electric fields[8]. Tourmaline (TM)is a type of complex borosilicate mate-rial belonging to a trigonal space group [9]. Its general formula can be expressed as XY 3Z 6[T6O 18][BO3]3V 3W, where X ¼Na, K, Ca, (vacancy);Y ¼Li, Mg, Fe 2þ, Mn 2þ, Al, Cr 3þ, V 3þ, Fe 3þ, Ti; Z ¼Al, Fe 3þ, Cr 3þ, V 3þ, Mg; T ¼Si, Al; V ¼OH, O; W ¼OH, F, O [10, 11].Tourmaline possesses spontaneous surface electric fields,

0272-8842/$-see front matter &2013Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.02.057

7144S.-J. Kang et al. /Ceramics International 39(2013)7143–7148

and it has been utilized in different applications such as heavy metal absorption [9, 12],bacterial inactivation [13], and decomposition of waste water contaminants [14]. We also paired tourmaline NPs with Ag NPs on PU mat by electrospinning and UV photoreduction, and found better bacterial inactivation compared to tourmaline/PUcompo-site mat and PU mat only.

In this study, we impart photocatalytic properties on a tourmaline/nylon-6composite mat by incorporating TiO 2nanoparticles. Titanium dioxide (TiO2) is one of the most widely used photocatalysts because it is cheap and easily available, non-toxic, and has relatively high chemical stability [15, 16].TiO 2is useful for UV solar absorption and has some important photonic applications too [17]. However, TiO 2possesses wide band gap (3.2eV), which can only absorb a UV fraction of solar light (3–5%),making it not very efficientin solar-assisted photocatalysis [18]. Noble metal deposition, non-metal doping and semiconductor coupling are some of the methods used to enhance the photocatalytic performance of TiO 2[19]. The unique properties of tourmaline make it desirable for the enhancement of TiO 2performance in photocatalysis. Yeredla and Xu [20]reported that the surface electric fieldsof tourmaline can enhance the e À–hþpairs separa-tion of TiO 2and improve the photosplitting of water. They conducted their experiments using TiO 2-tourmaline com-posite in powder form. Nylon-6is one of the most used engineering polymers because of its excellent mechanical and thermal properties, easy to process, and good compat-ibility with other materials.

Here, we immobilized both TiO 2and tourmaline NPs on/innylon-6nanofibersvia a simple electrospinning process. Our objective in this study was to determine the synergistic effect of the incorporation of TiO 2and tourma-line NPs on the physical, and photocatalytic properties of the electrospun composite nanofibers.2. Experimental

Neat nylon-6(KN20grade, Mw ¼35,000, Kolon, Korea) solution was prepared by dissolving 20wt%nylon-6pellets in 4:1solvent mixture of formic acid/aceticacid. To prepare tourmaline (TM)/nylon-6or titanium dioxide-tourmaline/nylon-6(TiO2-tourmaline/nylon-6)solution, 3wt%TM (ball-milled,UBS) or a mixture of 3wt%TM and 3wt%TiO 2(TiO2, anatase, d ¼500nm) NPs in a given amount of formic acid/aceticacid solution was firstsonicated in a homogenizer at 10,000rpm for at least 30min and then added to the neat nylon-6solution and stirred by magnetic stirring overnight. Note that the wt%of TM and TiO 2were based on the weight of nylon-6. The prepared solutions were then directly electrospun onto a flatmetallic substrate at an applied voltage of 20kV, a tip-to-collector distance of 15cm, and a solution feed rate of 0.3ml/h.The spinneret with an inner diameter of 0.51mm makes a translational oscillatory motion perpen-dicular to the flatsubstrate driven by a step motor with an

oscillation distance of about 20cm. After electrospinning, the collected nanofibrousmat was dried in an oven at 601C for at least 48h. The prepared electrospun mat samples are named as S0, S1, and S2corresponding to neat nylon-6, TM/nylon-6and TiO 2-TM/nylon-6,respectively. Morphological characterizations were carried out by fieldemission scanning electron microscopy (FESEM,Hitachi S-4800, Japan) and transmission electron micro-scopy (TEM,H-7650, Hitachi, Japan). The samples for FESEM were coated with platinum using a Pt coater (K575x,Emitech) and examined at an accelerating voltage of 15kV. The TEM samples for nanofiberswere prepared by electrospinning directly on a copper grid mesh coated with carbon and formar for 15s. The distribution of fibersizes was determined using an image processing software (ImageJ,NIH, USA), checking the diameters of at least 100fibersand the average was calculated. Water contact angle measurements were carried out using GBX, Digidrop (France)water contact angle meter. Deionized water with a drop diameter of 6m m was automatically dropped onto the mat. The FTIR spectra of the samples were measured using a Paragon 1000Spectrometer (PerkinElmer, USA) in the range of 400–4000cm À1with a signal resolution of 1cm À1and a minimum of 16scans. X-ray powder diffraction (XRD)analysis was carried out X-ray diffractometer (CuK a , l ¼1.54059A)

by a Rigaku

over Bragg angles ranging from 201to 801.

The photocatalytic activity of the composite mats was assessed by the degradation of methylene blue (MB).Here, photocatalytic reactions were carried out in Petri dishes (d ¼55mm, h ¼15mm). A 10-ppm dye concentration (dyevolume ¼10ml) was reacted with the nanofibrousmat samples (size¼30mm Â30mm) in the Petri dish under UV light irradiation (320–500nm, Omnicure). At specifictime intervals, samples of the reacted dye solution were taken out and were subjected to UV–visspectroscopy measuring their absorbance at 663nm. 3. Results and discussion

Fig. 1shows the SEM images and the corresponding EDS spectra and contact angles of the prepared samples. The neat nylon-6sample showed uniform, smooth and beadless fiberswith an average diameter of 120724nm (Fig. 1a). The addition of 3wt%TM NPs (Fig. 1b) to nylon-6solution resulted to thicker nanofibers(d ¼130725nm) and further addition of TiO 2NPs (Fig. 1c) increased the fiberdiameter to 153741nm. The increase in fiberdiameter could be attributed to the increase in the viscosity of the electrospinning solution when nanopartiles were incorporated as also observed in other studies. Tourmaline and TiO 2NPs can be clearly observed to be deposited on/inthe nanofibers.Some beads were observed to form on the fibersurfaces of S3(TiO2–TM/nylon-6),which could be due to the increased viscosity of S3solution. Increased soluton viscosity requires more energy to overcome the surface tension for electrospinning,

S.-J. Kang et al. /Ceramics International 39(2013)7143–71487145

Fig. 1. SEM images of electrospun mats from (a)neat nylon-6, (b)tourmaline/nylon-6,and (c)TiO 2-tourmaline/nylon-6.The insets show the respective contact angle measurements.

Fig. 2. TEM images of electrospun nanofibrousmats from (a)tourmaline/nylon-6,and (b)TiO 2

-tourmaline/nylon-6.

thus resulting to some bead formation and thicker fibers[21]. The EDS spectra (notshown) also confirmedthe presence of both tourmaline and TiO 2NPs on the nanofibers.Contact angle is a quantitative measure of the wettability of a surface [22, 23].The wettability of the samples was observed to be more hydrophilic when nanoparticles where incorporated from a contact angle of 1221for the neat nylon-6mat (Fig. 1a inset), to 1101and 1041(Fig. 1c inset) for the TM/nylon-6and TiO 2-TM/nylon-6mats, respectively. The increase in hydrophilicity was expected since TM and TiO 2NPs are hydrophilic in nature. The better hydrophilic behavior of the nanofibrouscomposites increases their antifouling property, since it was reported that hydrophilic surface has less tendency to fouling compared to hydrophobic surface especially for water filtrationapplication [24]. Fig. 2shows the TEM images of the composite mats. Tourmaline (Fig. 2a) and TM–TiO2(Fig. 2b) nanoparticles are observed to be embedded in and on the surface of the nanofibersand were distributed uniformly. The TEM line-EDS in Fig. 3confirmsthe presence of both tourmaline and TiO 2NPs along the fiber.Elements of tourmaline such as potassium, sodium, silicon and chlorine were clearly obtained as well as titanium, signifying the presence of both NPs.

The XRD spectra of the samples are shown in Fig. 4. The peak at 2y ¼21.31in Fig. 4a signifiesthe g -phase crystalline peak (200)of nylon-6[25]. The pattern of Tm/nylon-6composite showed an additional peak at 2y ¼26.31, a characteristic peak of the present tourmaline.

The TiO 2–TM/nylon-6composite mat also had same crystalline characteristic peaks analogous with the char-acteristic peaks of nylon-6and tourmaline, and additional anatase TiO 2peaks at 2y ¼25.21and 37.61[26]. The XRD results further proves the successful incorporation and uniform distribution of nanoparticles in/onthe nylon-6mat by simple electrospinning. To observe whether there was interaction between nylon-6and nanoparticles, we further evaluated the mats through FT-IR. Fig. 5shows the infrared spectra of the present samples. All samples showed the characteristic peaks of nylon-6as reported in literature [25]. The bands at 3300cm À1, 3098cm À1, 2931cm À1, 2865cm À1, 2208cm À1, 1647cm À1, 1560cm À1, and 719cm À1can be assigned to hydrogen-bonded N–Hstretching, NH Fermi resonance, CH 2asymmetric stretching, CH 2symmetric stretching, C R N stretching, amide I, amide II, and amide V(g ), respectively [25]. However, for the TM/nylon-6and TiO 2-TM/nylon-6composite mats, a slight shift to the right was observed at 2208cm À1indicating a possible interaction between nylon-6and the nanoparticles.

The photocatalytic activity of the present samples were evaluated by degrading organic pollutant methylene blue (MB)under UV-light irradiation. As shown in Fig. 6, insignificantdegradation of MB occured when only neat nylon-6was irradiated with UV. In the presence of tourmaline NPs on/innylon-6nanofibers,a much better photocatalytic degradation compared to nylon-6was observed. Faster degradation rate was obtained when both TiO 2and tourmaline nanoparticles were

incorporated

7146S.-J. Kang et al. /Ceramics International 39(2013)7143–7148

Fig. 3. TEM line-EDX of TiO 2-tourmaline/nylon-6

nanofibers.

Fig. 4. XRD spectra of electrospun mats from (a)neat nylon-6, (b)tourmaline/nylon-6,and (c)TiO 2

-tourmaline/nylon-6.

on/inthe nylon-6electrospun mat. After 180min of UV irradiation, the MB degradation performance was in the order S34S24S1. For S3, tourmaline NP serves as an electron acceptor of the photogenerated electrons from anatase TiO 2, which effectively suppress the recombination of e À–hþpairs, and leaves more photogenerated holes to form reactive species that can facilitate the degradation of MB pollutant [27]. Yeredla and Xu [20]reported an improved photosplitting of water when tourmaline was integrated with Degussa P25titania. The inherent surface electric fieldsof tourmaline could have possibly caused the reduction of barrier potential for the migration of charge carriers to the surface of TiO 2by reducing the band bending in the space charge layer and increasing the chemical potential of the electrons in TiO 2. This leads to spatially

Fig. 5. FT-IR spectra of electrospun mats from (a)neat nylon-6, (b)tourmaline/nylon-6,and (c)TiO 2-tourmaline/nylon-6.

separated oxidation and reduction reactions, with a reduced oxidation potential for the photogenerated holes [20]. 4. Conclusions

In this report, we have successfully immobilized both TiO 2and tourmaline nanoparticles in/onnylon-6nanofibersby simple electrospinning process. Various techniques were utilized to characterize the fabricated composite nanofibers.The incorporation of nanoparticles has resulted to bigger fiberdiameters with TiO 2-tourmaline/nylon-6nanofibersshowing the largest average fiberdiameter. This is attributed to the increase in viscosity of the composite solution.

SEM

S.-J. Kang et al. /Ceramics International 39(2013)7143–71487147

Fig. 6. Photocatalytic degradation of methylene blue utilizing different electrospun mat samples of (a)neat nylon-6, (b)tourmaline/nylon-6,and (c)TiO 2-tourmaline/nylon-6.

and TEM images clearly showed embedded nanoparticles on the surface or at the internal layer of the nylon-6nanofibers.TEM-EDS and XRD have confirmedthe presence of TiO 2and tourmaline NPs in the composite nanofibers.TiO 2-tourmaline/nylon-6mat under UV light showed the highest photocatalytic performance among the present samples. The incorporation of both TiO 2and tourmaline NPs in/onnylon-6nanofibersshowed synergistic effects on improving the photocatalytic degradation of methylene blue, and could findpotential application in water treatment. Acknowledgments

This research was supported by a grant from the Basic Science Research Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (MEST)(Projectnos. 2012-0001611and 2012-013341), and also by a grant from MEST and NRF through the Human Resource Training Project for Regional Innovation (Projectno. 2012H1B8A2025931). We also would like to thank KBSI-Jeonju (Korea)for taking high-quality TEM images. References

[1]S. Nataraj, K. Yang, T. Aminabhavi, Polyacrylonitrile-based nano-fibers-Astate-of-the-art review, Progress in Polymer Science 37(2012)487–513.

[2]N.A.M. Barakat, M.A. Kanjwal, F.A. Sheikh, H.Y. Kim, Spider-net

within the N6, PVA and PU electrospun nanofibermats using salt addition:Novel strategy in the electrospinning process, Polymer 50(2009)4389–4396.

[3]J.S. Xie, Q.S. Wu, D.F. Zhao, Electrospinning synthesis of ZnFe 2O 4/

Fe 3O 4/Agnanoparticle-loaded mesoporous carbon fiberswith mag-netic and photocatalytic properties, Carbon 50(2012)800–807.

[4]P.T. Zhao, J.T. Fan, Electrospun nylon 6fibrousmembrane coated

with rice-like TiO 2nanoparticles by an ultrasonic-assistance method, Journal of Membrane Science 355(2010)91–97.

[5]S. Lee, Multifunctionality of layered fabric systems based on

electrospun polyurethane/zincoxide nanocomposite fibers,Journal of Applied Polymer Science 114(2009)3652–3658.

[6]M. Botes, T.E. Cloete, The potential of nanofibersand nanobiocides

in water purification,Critical Reviews in Microbiology 36(2010)68–81.

[7]L.D. Tijing, M.T.G. Ruelo, A. Amarjargal, H.R. Pant, C.H. Park,

D.W. Kim, C.S. Kim, Antibacterial and superhydrophilic electro-spun polyurethane nanocomposite fiberscontaining tourmaline nanoparticles, Chemical Engineering Journal 197(2012)41–48.

[8]A. Amarjargal, L.D. Tijing, M.T.G. Ruelo, C.-H. Park, H.R. Pant,

F.P. Vista IV, D.H. Lee, C.S. Kim, Inactivation of bacteria in batch suspension by fluidizedceramic tourmaline nanoparticles under oscillating radio frequency electric fields,Ceramics International 39(2012)2141–2145.

[9]Y.A. Zheng, A.Q. Wang, Removal of heavy metals using polyvinyl

alcohol semi-IPN poly(acrylicacid)/tourmalinecomposite optimized with response surface methodology, Chemical Engineering Journal 162(2010)186–193.

[10]L.P. Ogorodova, L.V. Melchakova, I.A. Kiseleva, I.S. Peretyazhko,

Thermodynamics of natural tourmaline-elbaite, Thermochimica Acta 419(2004)211–214.

[11]F. Yavuz, A.H. Gultekin, M.C. Karakaya, CLASTOUR:a computer

program for classificationof the minerals of the tourmaline group, Computers and Geosciences (UK)28(2002)1017–1036.

[12]K. Jiang, T.H. Sun, L.N. Sun, H.B. Li, Adsorption characteristics of

copper, lead, zinc and cadmium ions by tourmaline, Journal of Environmental Sciences (China)18(2006)1221–1225.

[13]S. Qiu, F. Ma, Y. Wo, S.W. Xu, Study on the biological effect of

tourmaline on the cell membrane of E. coli , Surface and Interface Analysis 43(2011)1069–1073.

[14]S.H. Song, M. Kang, Decomposition of 2-chlorophenol using a

tourmaline-photocatalytic system, Journal of Industrial and Engi-neering Chemistry 14(2008)785–791.

[15]Q.J. Xiang, J.G. Yu, M. Jaroniec, Synergetic effect of MoS 2and

graphene as cocatalysts for enhanced photocatalytic H-2production activity of TiO 2nanoparticles, Journal of the American Chemical Society 134(2012)6575–6578.

[16]A.L. Linsebigler, G.Q. Lu, J.T. Yates, Photocatalysis on TiO 2

surfaces —principles, mechanisms, and selected results, Chemical Reviews 95(1995)735–758.

[17]R. Pandiyan, V. Micheli, D. Ristic, R. Bartali, G. Pepponi,

M. Barozzi, G. Gottardi, M. Ferrari, N. Laidani, Structural and near-infra red luminescence properties of Nd-doped TiO 2filmsdeposited by RF sputtering, Journal of Materials Chemistry 22(2012)22424–22432.

[18]Y.S. Li, F.L. Jiang, Q. Xiao, R. Li, K. Li, M.F. Zhang, A.Q. Zhang,

S.F. Sun, Y. Liu, Enhanced photocatalytic activities of TiO 2nanocomposites doped with water-soluble mercapto-capped CdTe quantum dots, Applied Catalysis B:Environmental 101(2010)118–129.

[19]H.I. Kim, J. Kim, W. Kim, W. Choi, Enhanced photocatalytic and

photoelectrochemical activity in the ternary hybrid of CdS/TiO2/WO 3through the cascadal electron transfer, Journal of Physical Chemistry C 115(2011)9797–9805.

[20]R.R. Yeredla, H.F. Xu, Incorporating strong polarity minerals of

tourmaline with semiconductor titania to improve the photosplitting of water, Journal of Physical Chemistry C 112(2008)532–539.

[21]L.D. Tijing, A. Amarjargal, Z Jiang, M.T.G. Ruelo, C.H. Park,

H.R. Pant, D.W. Kim, D.H. Lee, C.S. Kim, Antibacterial tourmaline nanoparticles/polyurethanehybrid mat decorated with

silver

7148S.-J. Kang et al. /Ceramics International 39(2013)7143–7148

membranes by plasma polymerization for low organic fouling, Journal of Membrane Science 369(2011)420–428.

[25]K.H. Lee, K.W. Kim, A. Pesapane, H.Y. Kim, J.F. Rabolt,

Polarized FT-IR study of macroscopically oriented electrospun nylon-6nanofibers,Macromolecules 41(2008)1494–1498.

[26]C. Wen, Y.J. Zhu, T. Kanbara, H.Z. Zhu, C.F. Xiao, Effects of I and

F codoped TiO 2on the photocatalytic degradation of methylene blue, Desalination 249(2009)621–625.

[27]K.X. Li, T. Chen, L.S. Yan, Y.H. Dai, Z.M. Huang, H.Q. Guo,

L.X. Jiang, X.H. Gao, J.J. Xiong, D.Y. Song, Synthesis of mesopor-ous graphene and tourmaline co-doped titania composites and their photocatalytic activity towards organic pollutant degradation and eutrophic water treatment, Catalysis Communications 28(2012)nanoparticles prepared by electrospinning and UV photoreduction, Current Applied Physics 13(2013)205–210.

[22]P. Roach, N.J. Shirtcliffe, M.I. Newton, Progess in superhydropho-bic surface development, Soft Matter 4(2008)224–240.

[23]S.A. Wang, Y.P. Li, X.L. Fei, M.D. Sun, C.Q. Zhang, Y.X. Li,

Q.B. Yang, X. Hong, Preparation of a durable superhydrophobic membrane by electrospinning poly (vinylidenefluoride)(PVDF)mixed with epoxy-siloxane modifiedSiO 2nanoparticles:A possible route to superhydrophobic surfaces with low water sliding angle and high water contact angle, Journal of Colloid and Interface Science 359(2011)380–388.

[24]L. Zou, I. Vidalis, D. Steele, A. Michelmore, S.P. Low,

J.Q.J.C. Verberk, Surface hydrophilic modificationof RO

196–201.