Cataloged from PDF version of article.Electrospun polymeric nanofibers were either surface-decorated with zinc oxide (ZnO) nanoparticles or coated with a continuous ZnO thin film with a precise thickness (similar to 27 nm) via atomic layer deposition (ALD) for the fabrication of flexible photocatalytic nanofibrous membranes

Biyikli, N.

Kayaci, F.

Ozgit Akgun, C.

Uyar, T.

Electrospun polymeric nanofibers were either surface-decorated with zinc oxide (ZnO) nanoparticles or coated with a continuous ZnO thin film with a precise thickness (∼27 nm) via atomic layer deposition (ALD) for the fabrication of flexible photocatalytic nanofibrous membranes. © 2013 The Royal Society of Chemistry

Kayaci F.

Ozgit-Akgun, C.

Bilkent University Institutional Repository

   Electronic Supplementary Information  Surface-Decorated ZnO Nanoparticles and ZnO Nanocoating on Electrospun Polymeric Nanofibers by Atomic Layer Deposition for Flexible Photocatalytic Nanofibrous Membranes  Fatma Kayacia, Cagla Ozgit-Akguna, Necmi Biyiklia* and Tamer Uyara* aUNAM-Institute of Materials Science & Nanotechnology, Bilkent University, Ankara, 06800, Turkey *Corresponding authors (email): NB (biyikli@unam.bilkent.edu.tr) and TU (tamer@unam.bilkent.edu.tr)       Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 20131. Experimental 1.1. Materials  Nylon 6,6  pellets (relative viscosity: 230.000-280.000), formic acid (98-100 %) and rhodamine-B (Rh-B, dye content ~95 %) were purchased from Sigma-Aldrich and used without any purification. For ZnO deposition by ALD, diethylzinc ((C2H5)2Zn or DEZn, Sigma-Aldrich) and HPLC-grade water (H2O) were used as the zinc and oxygen precursors, respectively. 1.2. Electrospinning of Polymeric Nanofibers  8 wt % nylon 6,6 was dissolved in formic acid by stirring for 3 h at room temperature, for each sample. The resulting homogeneous clear solutions were located in 10 ml syringes fitted with metallic needles having inner diameter of 0.8 mm. The syringes were fixed horizontally on the syringe pump (Model: SP 101IZ, WPI). The polymer solutions were pumped with feed rate of 1 ml/h during electrospinning and the tip-to-collector distance was set to 10 cm.  Voltage of 15 kV was applied to the metal needle tip by using high voltage power supply (Matsusada, AU Series) for the electrospinning of the prepared solutions. The solvent evaporated on the way to the grounded stationary cylindrical metal collector (height: 15 cm, diameter: 9 cm) covered with a piece of aluminum foil, on which the electrospun nylon 6,6 nanofibers were deposited. The electrospinning setup was enclosed in Plexiglas box and the electrospinning was carried out at 23 oC and 36 % relative humidity.  1.3. Preparation of ZnO Structures by ALD  ZnO depositions were carried out at 200 °C in a Savannah S100 ALD reactor (Cambridge Nanotech Inc.) using diethylzinc (DEZn, or (C2H5)2Zn) as the zinc precursor and HPLC-grade water (H2O) as the oxidant. N2 was used as both carrier and purge gas with flow Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013rates of 20 and 10 sccm under dynamic and static vacuum conditions, respectively. 144 cycles were deposited using different deposition parameters. For the first set of samples, one ALD cycle consisted of H2O pulse (0.015 s) / N2 purge (10 s) / DEZn pulse (0.015 s) / N2 purge (10 s). Increased doses of DEZn and H2O (i.e. 0.09 s) were used for the second set, again with a 10 s N2 purge between the precursor pulses. Another set was prepared by using the exposure mode (a trademark of Cambridge Nanotech Inc.). In this mode, dynamic vacuum was switched to static vacuum before each precursor pulse by closing the valve between the reaction chamber and the pump. After a certain period of time (i.e. exposure time) it was switched back to dynamic vacuum for purging excess precursor molecules and gaseous by-products. For this process, one ALD cycle was as follows: valve OFF / H2O pulse (0.015 s) / exposure (10 s) / valve ON / N2 purge (10 s) / valve OFF / DEZn pulse (0.015 s) / exposure (10 s) / valve ON / N2 purge (10 s). 1.4. Characterization Techniques The morphology of the pristine nylon nanofibers and nylon/ZnO nanofibers were investigated by using scanning electron microscope (SEM, FEI–Quanta 200 FEG). The nanofibers were coated with 5 nm Au/Pd for SEM imaging. Around 100 fiber diameters were measured from the SEM image of pristine nylon nanofibers in order to calculate the average fiber diameter. Detailed morphological investigation of the nylon/ZnO nanofibers was performed by using transmission electron microscope (TEM, FEI–Tecnai G2F30, Hillsboro, OR). Small pieces of nylon/ZnO nanofibrous membranes sonicated in ethanol for 5 minutes to obtain individual nanofibers dispersed through the solvent, followed by dropping the suspensions onto the copper TEM grids (HC200), and allowed them to dry under IR lamp for a few minutes prior to TEM imaging. Crystal structure of ZnO on nanofibers was investigated from selected area electron diffraction (SAED) patterns of nylon/ZnO nanofibers obtained by TEM. PANalytical X’Pert Multi Purpose X-ray Diffractometer with Cu Kα radiation was Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013used to collect X-ray diffraction (XRD) data of the pristine nylon  and nylon/ZnO nanofibers in a range of 2θ = 10o-100o. X-ray photoelectron spectroscopy (XPS, Thermo Scientific) was used to detect the surface elemental composition of pristine nylon and nylon/ZnO nanofibers. XPS data were taken from 400 µm diameter circular spot on the sample surface by means of a flood gun charge neutralizer system equipped with a monochromated Al Kα X-ray source (hν = 1486.6 eV). Wide energy survey scans were obtained over a 0-1360 eV binding energy (BE) range, at pass energy of 150 eV, and with an energy step of 1 eV. Zn 2p high resolution XPS scan was also taken at pass energy of 30 eV, and with energy steps of 0.1 eV in order to analyze the bonding states. Thermal analysis of the nanofibers was performed by using thermogravimetric analyzer (TGA, TA Instruments–Q500) from room temperature to 600 oC at a heating rate of 20 oC/min under nitrogen atmosphere.  1.5. Photocatalytic Activity of the Nylon/ZnO Nanofibrous Membranes  Photodegradation of rhodamine-B (Rh-B) (1.04×10−5 M) in aqueous medium with nylon/ZnO nanofibers were investigated to determine the efficiency of photocatalytic activity of the samples. 10 mg nylon/ZnO nanofibrous membranes with three different ZnO morphologies (about 3.0 cm×2.5 cm) were put into quartz cuvettes (width: 1 cm, length: 1 cm, and height: 5 cm, Hellma) filled with Rh-B solution, separately. Then these cuvettes were kept under the irradiation of UV-light with a wavelength of 365 nm by placing them at a distance of 10 cm from the UV source (8 W, UVLMS-38 EL). UV-Vis-NIR spectrophotometer (Varian Cary 5000) was used to measure dye concentrations in the cuvettes at certain time intervals. The nanofibrous membranes which stayed at the bottom of the dye solution during UV-Vis measurement did not interfere with the UV-light; hence they did not contribute to the measurement results.  Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013Table: Table S1. Atomic concentrations generated from XPS wide energy survey scans.  samples C (%) O (%) Zn (%) N (%) pristine nylon 77.06 11.61 - 11.33 nylon/ZnO NP 68.13 15.95 5.53 10.38 nylon/ZnO NP (highly dense) 31.23 36.19 29.76 2.81 nylon/ZnO nanocoating 30.74 38.53 30.73 -                 Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013Figures: (a)nanofiberspolymer solutionhigh voltage power supplysyringe pump15 kVcollector1st precursor excess precursor moleculesbyproduct(s)(b)ALDcycle2nd precursorexcess precursor moleculesbyproduct(s) Fig. S1. Schematic representations of the processing steps for the production of polymer/inorganic nanofibers: (a) electrospinning, (b) atomic layer deposition (ALD).  Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 20135 μma bc d5 μm5 μm5 μm Fig. S2. Representative SEM images of nanofibers; (a) pristine nylon (b) nylon/ZnO NP, (c) nylon/ZnO NP (highly dense), and (d) nylon/ZnO nanocoating.       Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013200 nm 100 nm 200 nmb ca Fig. S3. Representative TEM images of nanofibers; (a) nylon/ZnO NP, (b) nylon/ZnO NP (highly dense), and (c) nylon/ZnO nanocoating.                Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 20132 1/nm2 1/nm 2 1/nma b c Fig. S4. SAED patterns of nanofibers; (a) nylon/ZnO NP, (b) nylon/ZnO NP (highly dense), and (c) nylon/ZnO nanocoating.          Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 201310 20 30 40 50 60 70 80 90 100intensity (a.u)2 theta100 002112 201004202203211114103110102101 pristine nylon nylon/ZnO NP nylon/ZnO NP (highly dense) nylon/ZnO nanocoating Fig. S5. XRD patterns of pristine nylon and nylon/ZnO nanofibers.     Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 20131020 1030 1040 1050 Intensity (arb. units)Binding energy (eV) Fig. S6. Zn 2p high resolution XPS scan of nanofibers of nylon/ZnO nanocoating.     Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 201350 100 150 200 250 300 350 400 450 500 550020406080100Weight (%)Temperature (°C) pristine nylon  nylon/ZnO NP nylon/ZnO NP (highly dense) nylon/ZnO nanocoating Fig. S7. TGA thermograms of nylon and nylon/ZnO nanofibers.           Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013a b c Fig. S8. Representative photographs of flexible nanofibrous membranes; (a) nylon/ZnO NP, (b) nylon/ZnO NP (highly dense), and (c) nylon/ZnO nanocoating.                   Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013450 500 550 6000.00.20.40.60.81.0AbsorbanceWavelength 0 hour 1 hour 2 hour 3 hour 4 hour 5 hour 6  hour 8 hour 10 hour 12 hour 14 hour 16 hour 20 hour 24 hour450 500 550 6000.00.20.40.60.81.0AbsorbanceWavelength 0 hour 1 hour 2 hour 3 hour 4 hour 5 hour 6  hour 8 hour 10 hour 12 hour 14 hour 16 hour 20 hour 24 hour450 500 550 6000.00.20.40.60.81.0AbsorbanceWavelength 0 hour 1 hour 2 hour 3 hour 4 hour 5 hour 6  hour 8 hour 10 hour 12 hour 14 hour 16 hour 20 hour 24 hour450 500 550 6000.00.20.40.60.81.0RhB nylon/ZnO NP nylon/ZnO NP (highly dense) nylon/ZnO nanocoatingAbsorbanceWavelength 0 hour 1 hour 2 hour 3 hour 4 hour 5 hour 6  hour 8 hour 10 hour 12 hour 14 hour 16 hour 20 hour 24 hour0 hour 24 hour 0 hour 24 hour 0 hour 24 hour 0 hour 24 hour  Fig. S9. UV–Vis spectra and color of the Rh-B solution with and without nylon/ZnO nanofibers as a function of the UV irradiation time.       Electronic Supplementary Material (ESI) for RSC AdvancesThis journal is © The Royal Society of Chemistry 2013

Surface-decorated ZnO nanoparticles and ZnO nanocoating on electrospun polymeric nanofibers by atomic layer deposition for flexible photocatalytic nanofibrous membranes

Cite this: RSC Advances, 2013, 3, 6817Received 23rd January 2013,Accepted 19th March 2013Surface-decorated ZnO nanoparticles and ZnOnanocoating on electrospun polymeric nanofibers byatomic layer deposition for flexible photocatalyticnanofibrous membranes3DOI: 10.1039/c3ra40359awww.rsc.org/advancesFatma Kayaci, Cagla Ozgit-Akgun, Necmi Biyikli* and Tamer Uyar*Electrospun polymeric nanofibers were either surface-decoratedwith zinc oxide (ZnO) nanoparticles or coated with a continuousZnO thin film with a precise thickness (y27 nm) via atomic layerdeposition (ALD) for the fabrication of flexible photocatalyticnanofibrous membranes.Water pollution is a growing environmental issue which severelythreatens human health. Consequently, development of novelmaterials for water purification and waste treatment is animportant research topic.1,2 Functional nanomaterials3 exhibitingphotocatalytic properties, along with a very high surface area, havebeen widely investigated, since these nanostructures are quiteeffective in the degradation of organic contaminants under UVlight and sunlight. For instance, metal oxides such as ZnO4 andTiO25 are very well known for their photocatalytic activity andtherefore, these materials in the form of nanoparticles,4b,5ananorods4c,d,5c and nanofibers4b,5d have been studied intenselyfor water purification purposes. However, the brittle nature ofthese metal oxides often causes problems when they are used as amembrane. Therefore, designing photocatalytic membranes withflexible character is highly desired. For instance, flexible mem-branes composed of electrospun polymeric nanofibers functiona-lized with ZnO nanorods,4c,d formed by using a hydrothermalmethod have been shown to be effective for the photocatalyticdegradation of organic molecules, so they have the potential forwater purification and organic waste treatment. However, novelmaterials are always needed for the development of advancedfiltering systems for water treatment.In this work, polymeric nanofibers surface-decorated with ZnOnanoparticles (NPs) and a ZnO nanocoating were fabricated usinga two-step approach: electrospinning and atomic layer deposition(ALD) (Fig. 1 and Fig. S1, ESI3). Initially, polymeric (nylon 6,6)nanofibers with an average fiber diameter of y80 nm wereproduced via electrospinning technique. In the next step, ZnO wasgrown onto smooth surfaces of polymeric nanofibers via ALD6 byaltering the deposition parameters. Altering the ALD parametersresulted in various ZnO morphologies on the polymeric nanofi-bers; surface-decorated ZnO NPs and highly dense ZnO NPs, and acontinuous ZnO nanocoating with a uniform thickness (y27 nm).The resulting ZnO nanostructures onto nanofibers are illustratedschematically in Fig. 1. The scanning electron microscopy (SEM)images clearly elucidated that the ALD process did not destroy thefibrous structure of the polymer. In addition, when compared tothe pristine polymeric nanofiber, nylon–ZnO nanofibers hadrougher surfaces due to the deposition of ZnO NPs and thenanocoating (Fig. 2 and Fig. S2, ESI3). Overall, the sampledecorated with highly dense ZnO NPs exhibited the highestsurface roughness due to the presence of a greater number ofindividual ZnO NPs (Fig. 2c and 3b).The transmission electron microscopy (TEM) images clearlyrevealed the morphologies of ZnO deposited on polymericnanofibers (Fig. 3 and Fig. S3, ESI3). For the sample shown inUNAM-Institute of Materials Science & Nanotechnology, Bilkent University, Ankara,06800, Turkey. E-mail: tamer@unam.bilkent.edu.tr; biyikli@unam.bilkent.edu.tr;Fax: +90(312)266 4365; Tel: +90(312)290 35713 Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra40359aFig. 1 Schematic representation of the formation of polymer–ZnO nanofibers:electrospinning of the polymeric nanofiber and ZnO deposition with differentmorphologies on the electrospun nanofiber by using various ALD parameters.RSC AdvancesCOMMUNICATIONThis journal is  The Royal Society of Chemistry 2013 RSC Adv., 2013, 3, 6817–6820 | 6817Published on 20 March 2013. Downloaded by Bilkent University on 15/05/2014 08:31:04. View Article OnlineView Journal  | View IssueFig. 3a, ALD was performed under dynamic vacuum conditionswith 0.015 s pulses and 10 s purges. The resulting morphology wasin the form of randomly distributed individual ZnO NPs with anaverage size of 20¡ 15 nm. When run for 800 cycles, this reciperesulted in a y90 nm thick uniform ZnO coating on theelectrospun nylon nanofibers.7 The deposition of highly denseZnO NPs was obtained when the pulse times of diethylzinc (DEZn)and H2O were both increased to 0.09 s (Fig. 3b). The TEM imageshown in Fig. 3c belongs to a sample which was prepared by usingthe exposure mode (a trademark of Cambridge Nanotech Inc.),with 0.015 s pulses, 10 s exposures, and 10 s purges. The exposuremode keeps the precursor molecules inside the reaction chamberfor a certain period of time by switching the dynamic vacuum to astatic vacuum just before the precursor pulses. After the exposure,the static vacuum is switched back to a dynamic vacuum forpurging. The resulting morphology was a y27 nm thick ZnOcoating around the polymeric nanofibers. This process, therefore,yielded a ZnO nanocoating with a uniform thickness over therelatively large surface area of electrospun nanofibers.All three samples were decorated with ZnO NPs or coated witha uniform ZnO thin film. The formation of NPs instead of acontinuous film for the samples prepared under the dynamicvacuum conditions is not due to the limitation of diffusion, sincewe observed that the precursor molecules can reach every part ofthe nanofibrous membranes and produce either randomlydistributed NPs or a continuous thin film. As the number ofprecursor molecules increases, the probability for these moleculesto coincide with one of the reactive sites on the substrate alsoincreases. Therefore, the increased number of ZnO NPs with theincreased DEZn and H2O doses was an expected outcome. Ourresults indicate that the nucleation and growth of ZnO onpolymeric nanofibers proceeds through the formation of islandsand subsequent coalescence of these islands to form a continuousfilm, i.e. Volmer–Weber (3D) growth. The ALD technique has beenused to produce conformal and very thin inorganic coatings ontopolymeric fibrous materials.7,8 In contrast, ZnO NPs have beengrown on single-walled carbon nanotubes by ALD.9 In anotherstudy, Libera et al.10 reported that the ALD of ZnO on amorphoussilica forms NPs in the early stages of growth, instead of a uniformthin coating. In our study, by taking advantage of the slownucleation and/or growth kinetics of ZnO, ZnO NPs weredecorated onto polymeric nanofibers under the dynamic vacuumconditions. Although it has been shown that the number ofparticles can be increased by increasing the precursor doses, theparameters controlling the size of these NPs are currentlyunknown. Research is underway to investigate the very initialstages of growth, as well as to fully control the morphology of theresulting NPs.The polycrystalline nature of the deposited ZnO was revealedfrom the selected area electron diffraction (SAED) patterns of thenylon–ZnO nanofibers (Fig. S4, ESI3), which correlate well with theX-ray diffraction (XRD) results (Fig. S5, ESI3). Moreover, brightspots on the polycrystalline diffraction rings were observed for allof the three samples, which showed the existence of large crystalgrains. The intensities of the SAED patterns were different for thedifferent morphologies due to the relative amounts of ZnO presenton the nanofibers. The semi-crystalline nature of the pristinenylon nanofibers was confirmed by XRD, with two distinctdiffraction peaks at 20.4u (100) and 23.0u (010, 110).11 Thesepeaks, although suppressed due to the deposition of ZnO, werealso observed in the XRD patterns of the nylon–ZnO samples,suggesting that the crystalline structure of the polymer was notaffected during the ALD process. The crystal structure of ZnOdeposited onto the nanofibers by ALD was determined ashexagonal wurtzite structure from the XRD patterns of thesamples, in which the diffraction peaks were indexed accordingto The International Centre for Diffraction Data (ICDD) (ReferenceCode: 01-074-0040). Similar to the SAED patterns, the intensities ofthe ZnO diffraction peaks in the XRD patterns were amplified asthe relative amount of ZnO on the sample increased.The surface chemical composition of the nylon–ZnO nanofi-bers was investigated by using X-ray photoelectron spectroscopy(XPS) (Table S1, ESI3). As expected, the C 1s, O 1s, and N 1s peaksfrom the polymer (nylon 6,6) were observed in the XPS scans ofboth of the nylon–ZnO NP samples. In the case of the nylon–ZnOnanocoating, the N 1s peak could not be detected due to thecontinuous layer of ZnO, as also proven by TEM analysis (Fig. 3c).In addition, contamination could increase the amount of Cobserved in the scans for all of the samples. The presence of a Zn2p3 peaks and the increased intensity of the O 1s peaks in the XPSFig. 3 Representative TEM images of nanofibers: (a) nylon–ZnO NPs, (b) nylon–ZnONPs (highly dense), and (c) nylon–ZnO nanocoating.Fig. 2 SEM images of nanofibers: (a) pristine nylon, (b) nylon–ZnO NPs, (c) nylon–ZnO NPs (highly dense), and (d) nylon–ZnO nanocoating.6818 | RSC Adv., 2013, 3, 6817–6820 This journal is  The Royal Society of Chemistry 2013Communication RSC AdvancesPublished on 20 March 2013. Downloaded by Bilkent University on 15/05/2014 08:31:04. View Article Onlinescans were assigned to the ZnO structures on the nanofibers(Table S1, ESI3). A high resolution XPS scan was also taken toconfirm the formation of ZnO on the surface of the nylonnanofibers. A Zn 2p doublet, consisting of Zn 2p3/2 and Zn 2p1/2subpeaks located at 1022.88 and 1045.86 eV respectively, wasobserved confirming the Zn–O bonding state (Fig. S6, ESI3).12The compositional wt% of the samples was calculated from thethermogravimetric analysis (TGA) thermograms (Fig. S7, ESI3).Compositions of 17, 54, and 82 wt% ZnO were determined in thenylon–ZnO NPs, nylon–ZnO NPs (highly dense), and nylon–ZnOnanocoating samples, respectively. It was also observed that themain decomposition temperature of nylon for the nylon–ZnOsamples was lower (y280 uC) compared to that of the pristinenylon nanofibers, which is y350 uC. The lower degradationtemperature observed for the nylon–ZnO nanofibers was possiblydue to the catalytic activity of ZnO, resulting in earlier polymerdecomposition.7,13The resulting nylon–ZnO nanofibrous membranes were easilyhandled and folded as a free standing material due to the flexiblepolymeric component (Fig. 4 and Fig. S8, ESI3). In order toinvestigate the effect of the ZnO morphology on the efficiency ofthe photocatalytic activity, nylon–ZnO nanofibers with threedifferent ZnO morphologies were tested. The photocatalyticactivities of these flexible nylon–ZnO nanofibrous membraneswere tested by following the photocatalytic decomposition of amodel azo-reactive dye, rhodamine-B (Rh-B), under the irradiationof UV light. The changes in the absorption peaks of Rh-B at 554nm as a function of the UV irradiation time are shown in Fig. S9,ESI.3 The degradation rates of Rh-B were calculated by using theabsorption peak points and defined as C/C0 where C0 and Crepresent the initial concentration of Rh-B before UV irradiationand after a specific time of UV irradiation, respectively (Fig. 4). Nosignificant direct photolysis was observed for the blank Rh-Bsolution, and therefore the pink color of the dye solution did notchange after UV irradiation over a period of 24 h (Fig. S9, ESI3). Incontrast, the effective photocatalytic degradation of Rh-B wasclearly observed for all of the Rh-B solutions containing nylon–ZnO nanofiber samples. The absorbencies of these solutions werereduced distinctly with respect to UV irradiation owing to thephotocatalytic activity of the ZnO nanostructures on the nanofi-bers (Fig. 4 and Fig. S9, ESI3). The Rh-B solutions containingnylon–ZnO nanofiber membranes were decolorized during the UVirradiation, and the pink color of the solution almost disappearedafter 24 h, revealing the successful photocatalytic decompositionof Rh-B by the nylon–ZnO nanofibers (Fig. 4 and Fig. S9, ESI3). Forthe nylon–ZnO NPs, 53% of the Rh-B decomposed in 4 h, and 93%decomposed in 24 h. A similar result was obtained for the nylon–ZnO nanocoating; 49% of Rh-B decomposed in 4 h and 94%decomposed in 24 h. In the case of the nylon–ZnO NP (highlydense) sample, the decomposition of Rh-B was 63% and 99% in 4and 24 h, respectively. Therefore, the highest photocatalyticdegradation rate of Rh-B was observed for the nylon–ZnO NP(highly dense) sample, which is possibly because of the presenceof a large number of individual ZnO NPs, resulting in a highersurface area. This result clearly indicates that there is no need for acontinuous ZnO nanocoating on the polymeric nanofibers, sincesurface-decorated ZnO NPs, depending on their concentration,exhibited similar or improved efficiency for the photocatalyticdecomposition of model organic dye compared with the ZnOnanocoating.In summary, we have fabricated flexible photocatalyticnanofibrous membranes by combining the electrospinning andALD techniques. By altering the ALD parameters, various ZnOmorphologies on polymeric nanofibers such as ZnO NPs or acontinuous ZnO nanocoating were obtained. The nanofibrousmembrane surface-decorated with highly dense ZnO NPs exhib-ited the highest efficiency for the photocatalytic decomposition ofRh-B dye due to its large surface area. These functionalnanofibrous membranes may find applications as filteringmaterials for water purification and organic waste treatment. Weshowed that ALD can provide not only uniform and conformalcoatings with precise thickness control, but can also be used tosurface-decorate polymeric nanofiber templates with inorganicNPs, and the distribution density of the NPs can easily be adjustedby altering the deposition parameters. This approach can be usedto produce functional flexible nanofibrous membranes forfiltration, catalysis, sensors, photonics, electronics, energy andbiotechnology, depending on the selection of the polymer andinorganic components.AcknowledgementsDPT is acknowledged for the support of UNAM. T. Uyar and N.Biyikli acknowledge Marie Curie IRG for funding theNANOWEB and NEMSmart projects, respectively. F. Kayaciand C. Ozgit-Akgun acknowledge TUBITAK for the PhDScholarship. M. Guler is acknowledged for the TEM imaging.References1 Q. Li, S. Mahendra, D. Y. Lyon, L. Brunet, M. V. Liga, D. Li andP. J. J. 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Surface-decorated ZnO nanoparticles and ZnO nanocoating on electrospun polymeric nanofibers by atomic layer deposition for flexible photocatalytic nanofibrous membranes

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