Synthesis and optical properties of TiO2-based magnetic nanocomposites

Synthesis and optical properties of TiO2-based magnetic nanocomposites

Accepted Manuscript Title: Synthesis and optical properties of TiO2 -based magnetic nanocomposites Author: M. Scarisoreanu I. Morjan C.-T. Fleaca I.P...

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Accepted Manuscript Title: Synthesis and optical properties of TiO2 -based magnetic nanocomposites Author: M. Scarisoreanu I. Morjan C.-T. Fleaca I.P. Morjan A.-M. Niculescu E. Dutu A. Badoi R. Birjega C. Luculescu E. Vasile V. Danciu G. Filoti PII: DOI: Reference:

S0169-4332(14)02851-7 http://dx.doi.org/doi:10.1016/j.apsusc.2014.12.125 APSUSC 29360

To appear in:

APSUSC

Received date: Revised date: Accepted date:

16-7-2014 15-12-2014 18-12-2014

Please cite this article as: M. Scarisoreanu, I. Morjan, C.-T. Fleaca, I.P. Morjan, A.M. Niculescu, E. Dutu, A. Badoi, R. Birjega, C. Luculescu, E. Vasile, V. Danciu, G. Filoti, Synthesis and optical properties of TiO2 -based magnetic nanocomposites, Applied Surface Science (2014), http://dx.doi.org/10.1016/j.apsusc.2014.12.125 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

Synthesis and optical properties of TiO2-based magnetic nanocomposites

M. Scarisoreanu1, I. Morjan1, C.-T. Fleaca1,2,*, I.P. Morjan1, A.-M. Niculescu1, E. Dutu1,

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A. Badoi1, R. Birjega1, C. Luculescu1, E. Vasile3, V. Danciu4, G. Filoti5 National Institute for Lasers, Plasma and Radiation Physics (NILPRP) , Atomistilor 409, POB MG-36,

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Magurele, Bucharest 077125, Romania;

"Politehnica" University of Bucharest, Physics Department, Independentei 313, Bucharest, Romania;

3

"Politehnica" University of Bucharest,Faculty of Applied Chemistry and Materials Science, Department

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2

of Oxide Materials and Nanomaterials, Gh. Polizu 1-7, Bucharest, Romania; 4

National Institute for Materials Physics (NIMP), Atomistilor 105bis, P.O. Box MG7, R-077125 Magurele,

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Bucharest, Romania;

"Babes-Boyai" University, Faculty of Chemistry and Chemical Engineering, Electrochemical Research

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Laboratory, 11 Arany Janos Str, Cluj- Napoca, 400028, Romania;

Abstract

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Keywords: Laser pyrolysis; Nanoparticles; Band-gap; Magnetic properties

Magnetic titania nanoparticles covered/embedded in SiO2 shell/matrix were simultaneously manufactured

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by the single-step laser pyrolysis. The present study is a continuation of our previous investigations on the TiO2/Fe and TiO2/HMDSO (hexamethyldisiloxane) derived-systems. The aim of this work is to study the

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synthesis by IR (Infrared) laser pyrolysis of magnetic TiO2 based nanocomposites which implies many concurrent processes induced in the gas phase by the laser radiation. The dependence between characteristic properties and the synthesis parameters was determined by many analytical and complementary methods: XRD (X-ray diffraction) structural analysis, UV-Vis (Ultraviolet-visible) and EDAX (Energy-dispersive X-ray) spectroscopy, TEM and HRTEM (Transmission Electron Microscopy at low and high resolution)

analysis and magnetic measurements. The results of analysis indicate the

presence of disordered silica, Fe, α-Fe2O3 and mixtures of anatase and rutile phases with mean crystallite dimensions (in the 14-34 nm range) with typical character of diluted magnetic oxide systems and a lower bandgap energy (Eg= 1.85eV) as compared with TiO2 P25 Degussa sample.

PACS: 81.16.Mk, 75.50.Tt, 78.67.Bf *

Corresponding author Tel.: +4021-4574489; fax: +4021-4574243 E-mail address: [email protected]

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1. Introduction Titania (TiO2) is intensively studied due to its exceptional properties: high stability, high refractive index, having also a low-cost and being not toxic [1-5], offering a wide range of applications. In the context of increasing global pollution, several

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research studies aimed to synthesize and study environmentally friendly materials which have applications in cleaning wastewater by decomposition organic compounds. In the

process of photocatalysis, TiO2 is considered an almost ideal semiconductor and is used

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in photodegradation processes of organic compounds due to their higher specific surface area, efficient absorption of light, and good aqueous media dispersibility Following the

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photodegradation process, the separation/recovery of the TiO2 nanoparticles from the treated water represents a bottleneck which needs to be overcame in order to be used on

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an industrial scale. By the introduction of iron into the structure of TiO2 the new magnetic composite obtained can be separated/collected from the water by applying an external magnetic field. In this regard, nanoparticles of core-shell type in which the core is

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magnetite and the shell is TiO2 are reported in the most studies because are considered to be inexpensive and non-toxic materials [9-15]. Also, recent studies have shown that the

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photocatalytic efficiency of TiO2 has decreased by introducing magnetic core, and was thus necessary the introduction of an additional inert shell between the magnetic core and TiO2 to prevent the photodissolution of magnetic core and the transfer of electrons and

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holes from TiO2 to core particle. This shell can be a passive SiO2 layer which can contribute to improved stability and dispersibility of the magnetic core in corrosive

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solutions. All nanocomposites obtained in the above studies have been synthesized following the multi-stage synthesis [16-19]. In this paper, the magnetic TiO2 nanocomposites coated/embedded in SiO2

shell/matrix was obtained in a single step synthesis, the laser pyrolysis method featuring this major advantage. This work is a continuation of our previous studies in which TiO2 nanoparticles have been intensively studied for photocatalytic applications both pure and doped with C, S, N, Fe [20-22]. The new obtained TiO2 based nanocomposites have been studied in detail using structural, optical and magnetic characterization.

2. Experimental

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Magnetic titania nanoparticles covered/embedded in SiO2 shell/matrix were obtained using laser pyrolysis as synthesis method. This is a bottom-up method in a single step process which allows to obtain nanopowders starting from precursors that can be both gases and liquids with a significant vapor pressure at room temperature.

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Consequently, we chose the volatile titanium tetrachloride, hexamethyldisiloxane and iron pentacarbonyl as precursor for titania, silica and iron-based phases, respectively. These substances were entrained as vapors from liquid-containing bubblers using an inert

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gas (Ar) as a carrier (with the exception of Fe(CO)5 from the TFS-2 experiment). To obtain oxidic nanopowders we added air as oxidant in the reactive mixture. In order to

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start and maintain a laser pyrolysis process, at least one of the components from the reactive mixture needs to interact with the infrared laser photons. In our case, neither the

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TiCl4, nor the HMDSO molecules infrared spectra do not overlap with the CO2 laser emission zone (10.6 µm) and thus a supplementary IR absorber species is required for the developing of the pyrolysis process. We used ethylene as sensitizer because one of their

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molecular/vibrational bands matches the CO2 laser energy and absorbs the laser radiation [23]. Thus, after the photons absorption, the C2H4 molecules became vibrationally excited

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and transfer the excess energy to the other species from the reactive mixture via intermolecular collisions. The ethylene molecules return to lower energy levels restart the photon absorption process. The combination of these processes in a very short period of

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time lead to a sudden increases of the reactive mixture temperature. The oxidative exothermic processes which simultaneously occurs also contribute to this increase.

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Consequently, fast cascade reactions of decomposition/oxidation homogeneously result in gas phase with the formation of reactive atoms, molecules and free radicals and then, with the formation of first metallic/oxidic clusters, the heterogeneous reactions on the surface of these small nanoparticles became important, accompanied by coalescenceinduced collisions between these hot solid particles. Due to the rapid cooling that occurs after leaving the flame, the nanoparticles growth process stops, maintaining their nanosize dimension when are collected on the porous filter. The triple concentric configuration of the injector (presented in the Fig.1) allows to keep a lower oxidant concentration in the center of the flame, where the Fe(CO)5 vapors are introduced through the central fine nozzle in a similar manner to that recently reported by us in [24].

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Simultaneously, a more oxidative environment towards the flame periphery was induced due to the complex mixture which contains TiCl4 and HMDSO vapors together with the oxygen/nitrogen (air) and ethylene delivered through the second annular nozzle. The third concentric tube allows the introduction of an argon annular flow to confine the inner

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reactive flows. Two supplementary argon flows were used to protect the infraredtransparent reaction chamber windows from unwanted deposition of particles (see also Fig.1). The working pressure was kept constant using a throttle valve which allows the

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equilibration of the incoming and vacuum-pump extracted gas flows. The main experimental parameters for our titania-based nanoparticles are presented in the Table 1.

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The difference between TFS-1 and TFS-2 experiments where the titania/silica containing iron phases type nanoparticules were synthesized is due to the iron precursor carrier gas

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(Ar for TFS-1 and C2H4 for TFS-2) and is translated into a less or more reductive environment in the center of the pyrolysis flame. Also, the TS-1 experiment was made as reference (towards TFS-1) without the silica precursor, whereas in the other basic

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reference experiment, TSO, only the titania precursor (and of course the sensitizer and

Characterization

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oxidant) were introduced.

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The structure characterization of the nanopowders was analyzed using PANalytical X’Pert PRO MPD X-ray diffractometer with Cu Ka radiation (wavelength of 1.5418 Å)

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and Scanning Electron Microscope (SEM), FEI Co., model Quanta Inspect S, 0-30 kV accelerating voltage, with an EDAX Co. SiLi detector and using standardless method for the atomic percentages estimation provided by EDAX Genesis software was used to evaluate the composition of the nanopowders. TEM and HRTEM investigations of the samples were performed using a TECNAI F30 G2 S-TWIN microscope operated at 300 kV with Energy Dispersive X Ray (EDX) Spectrometer with Si(Li) detector. The UV–vis diffuse reflectance spectra were plotted as the Kubelka–Munk function or remission, F(R). The Mossbauer spectra were collected using a constant acceleration spectrometer with a symmetrical waveform, having a

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Co source incorporated in Rh matrix. The

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resulted isomer shifts are referred to bcc Fe. A liquid helium-cooled cryostat was used for low temperature measurements.

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3. Results and discussion EDX measurements

In the Table 1 are presented the experimental parameters and the the results of EDX semi

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quantitative elemental analysis for all the samples. The results of the analyzes indicate a good correlation between the gas flows and Si content, and because the introduction of

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Fe(CO)5 is made using ethylene in the sample TFS-2 (as compared with TFS-1), its growth is also correlated with increasing carbon and iron content. The iron amount in

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TiO2 samples increases (from 1.7 to 1.9 atomic %) because in the laser pyrolysis process the ethylene played the sensitizer role and by their supplementary introduction in the intimate mixture with iron precursor enhances the iron pentacarbonyl molecules

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decomposition by collisions. Also, the freshly formed iron atoms and clusters increases in turn the C2H4 molecules decomposition (in the low oxygen conditions) by catalytic

XRD analysis

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effect, translated in an enhanced productivity for the TFS-2 powder.

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The XRD diffraction patterns (Fig.2) of all as-synthesized samples show a mixture of TiO2- anatase phase (JCPDS file 21-1272) and the TiO2- rutile phase (JCPDS file 21-

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1276). The manifest trend of the effect of Fe doping is the preponderance of the rutile phase. The evolution of proportion of the anatase and rutile phases evaluated according to empiric formula of Spurr and Myers [25] shows an almost linear increase with the Fe/Ti atomic ratio estimated via EDAX (inset in Fig XRD). In the sample with the highest amount of Fe (TFS-2) peaks of metallic Fe (JCPDS file 06-0696) are observed. The result is consistent with the Mossbauer analysis. Weak peaks are also observable, in particular in the TFS-1 XRD pattern. A common peak is presented in all the Fe containing, samples which is clearly visible in TFS-1. It can tentatively be assigned to an α-Fe2O3 phase (JCPDS file 39-0238). The existence of amorphous it is also to be considered, in particular in the HMDSO derived syntheses. The mean crystallite sizes estimated by the

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Scherrer formula, using the instrumentally corrected width at half-height of the most intense maxima of the two TiO2 phases are included in table 2. The effect of Fe doping is the decrease of crystallite dimensions and also to significantly increase the titania rutile phase amount (in parallel with the decreasing of the anatase phase). The increasing of the

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rutile percentage in the titania was reported by us in [26], [27], [28] for the TiO2-based nanoparticles fabricated from TiCl4 precursor by laser pyrolysis when various amount of Fe(CO)5 vapors were introduced in the reactive mixture. Morover, the same tendency was

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observed when titania-based nanoparticles synthesized from diethanolamine - titanium

tetrabutoxide aduct using an induction-thermal-plasma-assisted aerosol reactor were

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doped with different amount of iron provided by the ferocene vapors [29]. This preference of TiO2 phase formation from rutile over anatase by the introduction of iron

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species into TiO2 was attributed to higher rutile over anatase towards defects such as oxygen vacancies and interstitial cations (Fe3+, Ti3+, Ti4+) formed when substitutional Fe3+ doped the titania [29]. Moreover, the sample TFS-2 which contains the higher

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atomic carbon (from ethylene decomposition in the oxygen depleted environment of the center of the pyrolysis flame) concentrations have also the highes rutile percent, which

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can be explained by the role of carbon in enhancing the transformation of anatase to rutile

TEM analysis

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through the formation of oxygen vacancies [30].

Higher magnification TEM micrographs for samples exhibit both round shaped and

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elongated or facetted particles, with irregular shapes and sizes, (Fig. 3a-c, for samples T, TF and TFS-1). For the sample TFS-1 the morphology consisting of core–shell particles, with various thicknesses of the shells of amorphous SiO2 matrix are reveals. The associated SAED patterns in which the formation of different phase in the synthesized nanocomposites was also analyzed and presented as insets in Fig. 3a,b. The major anatase phase signature (corresponding to (101), (200), (105) and (204) crystalline planes) can be detected in the sample T (pure TiO2) while rutile phase is evidenced in samples containing iron by reduced FFT of TFS-1sample (inset Fig.3c). The simultaneously anatase and rutile phases presence in the SAED image from the titania containing iron TF powder (see the inset from Fig. 3b) is consistent with the corresponding X-ray pattern

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(Fig.2). Thus, the following anatase planes: (101) at 3.52 Ǻ, (004) at 2.38 Ǻ and (200) at 1.89 Ǻ as well as the rutile planes: (110) at 3.25 Ǻ, (101) at 2.49 Ǻ and (111) at 2.19 Å can be unambiguously identified both in SAED (as rings of bright spots) and in XRD (as diffraction peaks) images of this sample. Fig. 4 displays the HRTEM images for sample:

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TF (a, c) and TFS-1(b). A mixture of anatase and rutile (d = 3.52 Å and 3.24 Å interplanar distances, respectively) with α-Fe2O3 (d = 3.7 Å) surrounded/embedded by disordered layer seems to be present in sample. By corroborating the atomic ratio

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between the elemental titanium, silicon and oxygen content in TF, TFS-1 and TFS-2

samples and their XRD data (which provide clear signature of crystalline TiO2 phases),

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because the Ti to O ratio in titania is 1:2, the remaining oxygen should be under the silica form and (in smaller proportion) as oxygenated groups on the carbonaceous

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materials provided by ethylene decomposition in presence of limited amount of oxygen. Thus, the composition of the observed amorphous layer can be attributed to silica and carbon, and/or to presence of some carbosiloxane reticulated polymers, similar with those

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also synthesized by laser pyrolysis from Fe(CO)5, C2H4 and HMDSO precursors [31].

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Characterization by UV-Vis spectroscopy

The optical properties of titania based nonocomposites were investigated by measuring their band-gap energy (Eg). This value reported in the literature is 3.2 eV for anatase

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phase of TiO2. The UV-Vis absorption edge and band gap energies of the samples have been determined from the reflectance [F(R)] spectra using the K-M (Kubelka–Munk)

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formalism [23,24] and the Tauc plot for the synthesized TiO2 based samples. By the extrapolation lines shown in Fig. 5 have been used to determine the band gaps for three different kind of samples: pure-TiO2 (sample T), magnetic-TiO2 (sample TF) and magnetic TiO2 nanoparticles covered/embedded in SiO2 shell/matrix (sample TFS-1). The results are presented in Table 3, reveal that: all the samples have lower band gap energy than the TiO2 Degussa commercial sample (3.2 eV) and the greatest reduction in the band gap (Eg= 1.85 eV) is observed for magnetic-TiO2 sample (TF). A decrease in the bandgap energy of a titania-silica material (as film) after doping with iron ions (and thiourea) from 3.08 to 2.88 eV was reported and this coating was successfully tested for formaldehyde photodegradation under both indoor (fluorescent lamps) and outdoor

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(diffuse sunlight) conditions [34]. Also, we have recently reported that similar titaniabased magnetic nanocomposites having different amount of iron phases (without the silica component) synthesized by the same laser pyrolysis method and using similar configuration show photocatalytic effect under ultraviolet light in the case of

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acetylsalicylic acid decomposition in aqueous media [24]. Magnetic analysis and Mossbauer Spectroscopy of

doublets

(from

(super)paramagnetic

phases)

and

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Very low temperature Mossbauer spectra (at 5 K) of TF and TFS-1 show a superposition sextets

(from

magnetic

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blocked/ordered phases) that can be ascribable to iron oxide clusters highly dispersed in/impurified with TiO2 for TF or TiO2 and SiO2 for TFS-1, the TFS-1cluster mean size

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(containing 95% Fe3+ and 5% Fe2+) being smaller as compared with those from TF (with Mossbauer blocking temperature ~ 20 K); also, in the TFS-1sample, the amount of Fe3+ completely dispersed ions is greater than those

from TF powder. A completely

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paramagnetic behavior can be seen at 60 K for TF sample. The hyperfine field values associated with the three sextets from TF sample vary between 46 to 40 T, ascribable to

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very small and defective clusters (~2-3 nm) of Fe oxides highly impurified with Ti ions. The reference sample without Fe content (or any other magnetic traditional elements) - T - shows a very low saturation magnetization ( ~ 3.4 x 10-2 emu/g at 5 K with B > 0.5 T)

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which can be associated to defects of TiO2 matrix, presenting thus a diluted magnetic oxide (DMO) behavior. This behavior was found also in oxygen-deficient anatase films

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deposed by laser ablation [35] or nanoparticles obtained by sol-gel method and annealed under different reducing atmosphere [36] free from magnetic ions. The oxygen-deficient medium in the laser flame during the synthesis of our reference titania-based sample (T) is reflected by the presence of carbon (provided by partial decomposition of the sensitizer) in this anatase-based nanopowder (see Table 1 - EDAX analyzes). The signal is weaker at room temperature (RT, 300 K) due to oxide diamagnetism. After substraction of the diamagnetic component, the long-range ordered component appears that has a coercive field of ~ 100 Oe at 5K and 30 Oe at RT, confirmed also by temperature-magnetization curve. At least two magnetic components can be extracted from RT hysteresis curve of the TF (Fe-containing) sample. Corroborated with

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Mossbauer spectra, the ferromagnetic component in this sample can be associated again with TiO2 matrix and the paramagnetic component with Fe3+ ions.

The lacking of

saturation of magnetization at 5 K for this sample is related with the very defective cluster structure and the predominance of magnetic signal from Fe. Again, from RT

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hysteresis curve, after the substraction of the superparamagnetic component, the resulted ordered magnetic component saturation magnetization is ~ 3.5 x 10-2 emu/g (very near to

corresponding Ms value T sample at 5 K). TFS-1sample shows a very similar behavior

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with those of TF sample. The sample TFS-2 shows a consistent RT magnetization (~ 3

emu/g, with approximately an order of magnitude higher than previous samples). At low

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temperatures, a superposition of paramagnetic contributions and a magnetically ordered (saturation magnetization and coercive field) magnetic component having a saturation

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magnetization of the same order 3 emu/g is observed. Coercive field is about 350 Oe at 5 K and 115 Oe at RT, therefore higher values than those observed in previous samples. Because the magnetization related to the presence of a DMS (Diluted Magnetic

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Semiconductor) phase can only take very small values (of the order 0.1- 0.2 emu/g) and for a magnetically ordered phase the magnetization value at RT is very close to the

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magnetically ordered phase at low temperature, this seems to indicate the presence of distinct magnetic phases, separated by their DMS character. The answer to the problem is given by Mossbauer spectroscopy which reveals, besides the iron oxide phases (clusters

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with average size 2-3 nm, but with their size dispersion much larger than in the previous sample) the presence of a phase having a hyperfine field of approximative 30 T with a

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negligible isomer shift, which can be associated only to metallic strongly impurified Fe phases. The contribution of this phase decreases from 27% to 5 K, from 15% to 30 K, and then remains approximately constant (hyperfine field environment remains stationary at about 29 T), suggesting the formation of iron nanoparticles with high blocking temperature (probably above RT) and explaining thus the consistent magnetization of this sample.

The saturation magnetization of the titania-based magnetic nanocomposites do not need to be high, due to the fact that strong NdFeB magnets (and also electromagnets) are available and powerful enough to separate these particles from their liquid dispersions. For example, titania deposed on soft ferrite activated carbon (TFAC) particles prepared

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by sol-gel and dip-coating technique with magnetization saturation Ms around 8 emu/g (close to the 3 emu/g value of our TFS-2 sample) were attracted from the homogeneous suspension to the cylindrical glass container wall in less than 5 minutes using a rectangular magnet [37]. Another example of magnetically separable photocatalyst with

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Ms ~ 10 emu/g was obtained by modification of TiO2 Degussa P25 with nanomaghemite using polyelectrolytes which resisted to four successive cycles of dispersion/magnetic recovery showing in the same time an unchanged photoactivity under UV light against

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herbicide propachlor [38].

4. Conclusions

[email protected] nanoparticles were successfully synthesized by the laser pyrolysis

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method; this technique offers the advantage of using a single-step gas-phase doping/covering method. Samples were characterized using several analytical methods which delivered concordant results, indicating the presence of mixtures of anatase and

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rutile phases, with mean crystallite dimensions (in the 14-34 nm range) and good crystallinity. Magnetic analysis reveals that the Fe-doped TiO2-based samples present a

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typical character of diluted magnetic oxide systems (for TFS-1 sample)/weak ferromagnetic character (for TFS-2 sample). Iron-doped [email protected] samples have a lower bandgap energy than the TiO2 P25 Degussa sample (Eg= 1.85 eV for the sample

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near future.

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ITP-1). The photocatalytic efficiency of samples on different polutants is our aim for the

Acknowledgements

The financial support is gratefully acknowledged to Romanian Ministry of

Education and Research under the Project PNCD2 IDEI nr. 80/2011 and to Romanian Ministry of European Funds and Sectoral Operational Program for Human Resources Development 2007-2013 through the Financial Agreement POSDRU/159/1.5/S/132395 (INNOResearch).

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[25] R.A. Spurr, H. Myers, Quantitative analysis of anatase rutile mixtures with an X-ray diffractometer, Anal. Chem. 29 (1957) 760-762. [26] R. Alexandrescu, I. Morjan, M. Scarisoreanu, R. Birjega, E. Popovici, I. Soare, L.

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Gavrila-Florescu, I. Voicu, I. Sandu, F. Dumitrache, G. Prodan, E. Vasile, E. Figgermeyer, Structural investigations of TiO2 and Fe-TiO2 doped nanoparticles

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synthesized by laser pyrolysis, Thin Solid Films 515 (2007) 8438-8445.

[27] R. Alexandrescu, I. Morjan, M. Scarisoreanu, R. Birjega, C. Fleaca, I. Soare, L.

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Gavrila, V. Ciupina, W. Kylberg, E. Figgemeier, Development of the IR laser pyrolysis. Infrared Phys. Technol. 53 (2010) 94-102.

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for the synthesis of iron doped TiO2 nanoparticles: structural properties and photoactivity,

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nanocomposites by single-step laser pyrolysis, Appl. Surf. Sci. 278 (2013) 305-312. [29] X.H. Wang, J.-G. Li, K. Kamiyama, T. Ishigaki, Fe-doped nanopowders by oxidative pyrolysis of organometallic precursors in induction thermal plasma: synthesis

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[32] S. Valencia, J. M. Marín, G. Restrepo, Study of the bandgap of synthesized titanium dioxide nanoparticules using the sol-gel method and a hydrothermal treatment, The Open Mater. Sci. J. 4 (2010) 9-14.

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Figure captions Fig.1. Experimental setup for the synthesis of titania based nanocomposites by laser pyrolysis

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Fig. 2. XRD diffraction patterns for the samples T, TF, TFS-1and TFS-2 with anatase (A) rutile (R), iron (αFe) and hematite (αFe2O3) peaks identification.

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Fig. 3. TEM micrographs of the TiO2 based nanocomposites and the corresponding SAED patterns (as inset in figures): a - for the TiO2 sample (T); b-for the Fe- TiO2

sample (TF) and c - for sample Fe-TiO2 covered/embedded in SiO2 shell/matrix . Note

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the different scale bars in the three images.

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Fig. 4. HRTEM images showing interplanar spacings which may correspond to: a -

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anatase (101), (004), (200); b – rutile (101), (200) and c – hematite (012) Fig. 5. Absorbance spectra for the indirect electronic transition F(R)1/2 vs. E (eV) for the

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sample T ( TiO2 iron-free), TF (TiO2 with iron) and TFS-1 (TiO2 with iron and silica)

and TFS-2 (c)

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Fig. 6. Magnetization and Hysteresis magnetization curves for the samples: T (a), TF (b)

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nanocomposites

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Fig.7. Mossbauer spectra at low temperatures for (a) TF, (b) TFS-1 and (c)TFS-2

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Highlights

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 Magnetic titania @silica nanoparticles were synthesized by the single step laser pyrolysis

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 Fe(CO)5, TiCl4, HMDSO and O2 from air were the precursors and C2H4 was the sensitizer

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 samples present a typical character of diluted magnetic oxide systems  samples have a lower bandgap energy (down to Eg= 1.85 eV) than the P25

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Table

Sample

Arconf Air

Ar→ C2H4 TiCl4 [sccm] [sccm] [sccm] [sccm]

Ar→ HMDSO

[sccm]

Inner nozzle

Yield

 Ar→  C2H4→ Fe(CO)5 Fe(CO)5 [sccm] [sccm]

[g/h]

Fe

EDAX (atomic%)

Ti

Si

C

64.8 56.9 61.1 57.1

0 0 12.4 13.7

6.1 9.9 8.3 13.6

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600 1400 200 30 0 0 0 1.05 0 29.1 600 1400 200 30 0 0 1.03 1.7 31.5 10 600 1400 200 30 10 0 1.92 1.7 16.5 20 600 1400 200 30 20 0 2.25 1.9 13.7 10 a The following parameters were maintained constant: the flows of Ar for windows flushing (ΦAr window = 1750 sccm), the working pressure (p = 450 mbar) and the laser power (PL = 400 W).

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T TF TFS-1 TFS-2

Middle (intermediate) nozzle

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Outer nozzle

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Table 1. Experimental parameters and EDS measurements for the TiO2 based samples a

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T TF TFS-1 TFS-2

TiO2 phases R/A proportion DA (nm) 0.14 22 0.27 18 3.00 10 5.67 14

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Table 2. Crystallographic parameters estimated from XRD measurements for the TiO2 based nanocomposites.

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Table 3. The energy values of the indirect bandgap transitions for the synthesized TiO2 based nanocomposites

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1.85

TFS-1

2.22

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Bandgap energy (eV) for Indirect transition type

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Sample

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