Fe-based polymeric nanocomposites by single-step laser pyrolysis

Fe-based polymeric nanocomposites by single-step laser pyrolysis

Accepted Manuscript Title: Development of TiO2 and TiO2 /Fe-based polymeric nanocomposites by single-step laser pyrolysis Authors: R. Alexandrescu, I...

1MB Sizes 0 Downloads 9 Views

Accepted Manuscript Title: Development of TiO2 and TiO2 /Fe-based polymeric nanocomposites by single-step laser pyrolysis Authors: R. Alexandrescu, I. Morjan, F. Dumitrache, M. Scarisoreanu, C.T. Fleaca, I.P. Morjan, A.D. Barbut, R. Birjega, G. Prodan PII: DOI: Reference:

S0169-4332(12)02245-3 doi:10.1016/j.apsusc.2012.12.094 APSUSC 24853

To appear in:

APSUSC

Received date: Revised date: Accepted date:

19-6-2012 15-12-2012 17-12-2012

Please cite this article as: R. Alexandrescu, I. Morjan, F. Dumitrache, M. Scarisoreanu, C.T. Fleaca, I.P. Morjan, A.D. Barbut, R. Birjega, G. Prodan, Development of TiO2 and TiO2 /Fe-based polymeric nanocomposites by single-step laser pyrolysis, Applied Surface Science (2010), doi:10.1016/j.apsusc.2012.12.094 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.

*Highlights (for review)

Highlights



Core-shell structural characteristics were primarily found in the TiO2/Fe/HMDSO-based systems

Ac ce p

te

d

M

an

us

cr

 

Polymer based nanocomposites provided with TiO2 inorganic cores were synthesized by the single step laser pyrolysis TiCl4 and alternatively methyl methacrylate (MMA) and hexamethyl disiloxane (HMDSO) were used as precursors Major anatase TiO2 phase was identified by XRD

ip t



Page 1 of 28

*Manuscript

Development of TiO2 and TiO2/Fe-based polymeric nanocomposites by single-step laser pyrolysis R. Alexandrescu1*, I. Morjan1, F. Dumitrache1, M. Scarisoreanu1, C. T. Fleaca1, I. P. Morjan1, A. D. Barbut1, R. Birjega1,G. Prodan2 1

National Institute for Lasers, Plasma and Radiation Physics, POB MG-36, Bucharest 077125, Romania

Ovidius University of Constanta, Bd. Mamaia 124, Constanta, Romania

ip t

2

cr

Abstract

us

Polymer- based nanocomposites provided with inorganic cores were simultaneously manufactured by the single-step laser pyrolysis. A comparative study was performed on

an

two types of nanocomposites, starting from two different systems: TiO2 / methyl methacrylate (MMA) and TiO2/Fe / hexamethyl disiloxane (HMDSO) polymer. The

M

reactive mixture contained TiCl4 as Ti precursor and alternatively, Fe(CO)5 (in case of TiO2/Fe mixture). The analytical techniques used for the characterization indicate

ed

distinct morphologies for the obtained nanostructures. Polyhedral and almost spherical

ce pt

nanoparticles in a coalescent matrix and very rare individual core-shell particles are noticed for the TiO2/MMA nanocomposites. Instead, nanoparticles presenting core-shell structures were often present in the TiO2/Fe / HMDSO polymeric nanocomposites. Keywords: nanoparticles, TiO2-based polymeric nanocomposites; laser pyrolysis;

Ac

methyl methacrylate; hexamethyl disiloxane.

Page 2 of 28

1. Introduction The possibility to prepare monodisperse inorganic nanoparticles of pure materials in the nanometer size domain, associated with the capping of these particles by polymeric molecules, represents now an exciting field of research. Inorganic nanoparticles are

ip t

finding a multiplicity of uses, ranging from traditional ones, such as coloring agents and catalysts to more novel ones, such as magnetic drug delivery, cancer therapy, solar

cr

photovoltaics, and emission control in diesel vehicles (see for instance Ref. [1]). Much

us

more, the polymer matrix could prevent further aggregation and acts as a stabilizer and a protective shell which formation takes place simultaneously with the inorganic core

an

(mostly, semiconductor-metal hybrid composites) [2]. These shells provided good protection to the core from oxidation, in particular magnetic coated particles retained

M

their magnetism for longer periods of time and show superior magnetic properties. The shell-surface modification of these particles could increase the solubility in water and

biomedical research.

ed

different buffer solutions which demonstrate the suitability of these nanoparticles for

ce pt

Nano-scale composite materials containing highly crystallized titanium oxide nanoparticles are interesting because of their potential applications in the field of

[5].

Ac

photocatalytic degradation of pollutants [3], solar cells [4], and optoelectronic devices

We have reported recently on the formation of Fe/Fe2O3 nano cores enveloped

with different polymeric shells [6,7] by using the laser pyrolysis [8]. The laser pyrolysis is a versatile approach which supposes the infrared (IR) laser irradiation of two mixed volatile compounds, one serving as a precursor of the metal and the other as a precursor of the polymer.. In this work we have performed a comparative study on the synthesis and characterization of TiO2 -based polymer nanocomposites, by alternatively using

Page 3 of 28

representative specimens of monomers belonging to two classes of polymers: an organic polymer (methyl methacrylate MMA) and a siloxane polymer (hexamethyl disiloxane HDMSO). From the point of view of the temperatures evolved during the laser pyrolysis

ip t

process, the two polymers mainly differ by their thermal properties. These are crucial for the final morphologies of the polymer matrix which may contain cross-linked

cr

polymers or partially carbonized fragments.

us

In a first step, we have produced novel TiO2/polymer nanocomposites with TiO2 nanoparticles inserted in a partially carbonized MMA polymer matrix, by the photo-

an

sensitized pyrolysis of titanium tetrachloride (TiCl4) and MMA-based mixtures, with the advantages of: (i) single step process for production of the nanocomposites, (ii)

M

rather high degree of dispersibility, due to a reduction of the interparticle interactions by the wrapping of nanoparticles in the polymer matrix.

ed

In a second step, we have used the laser synthesis method for the formation of TiO2-Fe nanoparticles surrounded by thin polyoxocarbosilane polymer shells. Primarily,

ce pt

Fe-doping of TiO2 nanocomposites was chosen because inclusion of transition metals (V, Cr, Mn, Fe) dopants leads to a reduction of the TiO2 band gap (capturing most part of the solar light when working as a catalyst). Much more, data concerning the Fe

Ac

doping of Ti are of great interest also because of the occurrence of titano-maghemite in nature. On the other hand, here we report results where the flow of polymer precursor was maintained at low values in order to produce thin wrapping sheets for maximizing transparency towards the metal oxide core. 2. Experimental TiO2 – based materials under nanoparticulate form are here obtained continuously, in a single step, using the laser pyrolysis [9]. The laser synthesis technique is based on the

Page 4 of 28

resonance between the emission of a CW CO2 laser line and the infrared absorption band of a gas precursor. The chemical reaction is triggered by the subsequent heating of precursors by collisional energy transfer. 2.1. TiO2/MMA-based pyrolysis systems

ip t

The synthesis by laser pyrolysis was applied to a gas mixture of TiCl4 (vapors), synthetic air and MMA (C5H8O2). These additives acted as titanium, oxygen and

cr

polymer precursors, respectively. C2H4 (which plays also the role of a sensitizer) or Ar

us

is bubbled through liquid TiCl4 and MMA, both held at ambient temperature. We should mention that due to the rather high temperature induced in the reaction zone by

an

the CO2 laser radiation, MMA may be also considered as carbon donor since partial carbonization is likely to occur.

M

A special irradiation geometry employing a triple central nozzle system was used [10]. For avoiding spontaneous reactions, air and MMA flows were allowed to

ed

flow through the inner nozzle while TiCl4 (carried by ethylene) was admitted through the middle nozzle. Complementary Ar flows are employed for the confinement of

ce pt

reactant gases towards the flow axis and for flushing the windows, respectively. Four representative samples (labeled TM) and their synthesis parameters are listed in Table I. They are ordered in the sense of increasing MMA concentration in the

Ac

reactive gas mixture. The first sample, TM14 is the reference, pure nanoTiO2 sample. The representative samples TM17, TM15 and TM16 are obtained for increased MMA concentration in the reactive gas mixture (successively carried out by 5, 10 and 15 standard cubic centimeters per minute (sccm) of Ar, respectively). The flows of the oxidizer (air), the total pressure and the laser power were maintained constant (at 225 sccm, 650 mbar and 400 watt, respectively) 2.2. TiO2/HMDSO-based pyrolysis systems

Page 5 of 28

In a second step, we have used the laser synthesis method for the concurrent formation of TiO2-Fe nanoparticles surrounded by polyoxocarbosilane polymer shell. Mixtures containing iron pentacarbonyl, hexamethyldisiloxane and titanium tetrachloride were used as gas-phase precursors. The chemical structure of the freshly-obtained

ip t

nanocomposites was studied as a function of the Ti loading (the variation of the TiCl4 flow in the precursor mixture) and the laser intensity. The experimental parameters for

cr

two representative runs (TS1 and TS2) are presented in Table 1I. The samples were

us

obtained by maintaining constant the HMDSO flow (at 10 sccm) and by varying the laser power (from 100 to 200 W, respectively). For the increase of the TICl4 flow, a

an

complementary Ar carrier flow was introduced (sample TS1 in Table II). 2.3 Sample characterization

M

After synthesis, the morphology and composition of the nanocomposites were characterized by different analytical techniques: energy dispersive X-ray analysis

ed

(EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and Infrared Spectroscopy (IR). The XRD patterns

ce pt

were collected on a PANalytical X’Pert MPD theta-theta system in continuous scan mode. In the diffracted beam, a Ni filter, a curved graphite monochromator and a programmable divergence slit, enabling constant sampling area irradiation, were placed

Ac

(λ = 0.15418 nm). The samples were recorded under the very same conditions (45 KV and 40 mA).

3. Results and discussions 3. 1. TiO2/MMA-based systems The laser decomposition of both MMA and tetramethyl tin is chiefly based on the excitation of ethylene (IR photosensitizer) and a collisional energy transfer between the excited ethylene and these compounds. We should mention that a detailed description of

Page 6 of 28

MMA polymerization and consequent degradation routes is beyond the scope of this work. However, the analysis of our results allows for some phenomenological comments. It was shown [11] that in the laser homogeneous decomposition of methyl methacrylate, dominant acyl-oxygen and C-Me cleavage reactions occur and generate

ip t

very active radical-chain mechanism. It is well known that the polymerization of the double bond can be initiated by the attack of a free radical, with the formation of a new

cr

radical which grows by attacking a new double bond and so on. Thus, the free radicals

us

attack also the double bonds of the MMA molecule, initiating their radical polymerization. Moreover, the polymerization can occur both homogeneous in the gas

an

phase and heterogeneous on the TiO2 surface, as modeled in [12] for the case of pure formaldehyde.

M

The overall picture of this complex laser pyrolysis process is complementarily complicated by the presence of the oxygen (diluted with nitrogen) in the reactive

ed

annular flow. The oxygen molecules can react with both ethylene and MMA (and also with the other double-bond containing molecules) and via radical mechanisms can form

ce pt

various intermediate oxygenated species products. There are reports of MMA polymerization in the presence of molecular oxigen where, at low temperatures, the peroxyl radical is involved [13,14].

Ac

EDS measurements (in at% and wt%, respectively) for the TiO2/MMA -based

nanocomposites are presented in the right side columns of Table I. These are averaged values, obtained by performing measurements in three different points. For a better comparison of the compositional evolution of samples with the varying experimental conditions, the data expressing the atomic percentage as well as the weight percentage of each element (in at % and wt%, respectively) are listed.. From the EDS analysis one observes the rather high carbon content of all samples, entering probably in the

Page 7 of 28

composite matrix under different forms (turbostratic carbon, polymer nanoparticles (see below the HRTEM analysis) and/or polymer fragments). The source of carbon could be both MMA and ethylene (unwanted) dissociation. The XRD diffraction patterns of all as-synthesized samples show a mixture of

ip t

two crystalline phases: the major anatase phase (JCPDS file 21-1272) and the rutile phase (JCPDS file 1276). No other impurity phases were identified. The superposed

cr

XRD patterns of samples obtained at three different MMA concentrations in the reactive

us

mixture (the curves are labeled according to the MMA flows during laser pyrolysis: 0, 5, 10 and 15 sccm, respectively) are presented in Figure 1. The mean crystallite

an

dimension was estimated by the Scherrer formula, using the instrumentally corrected width at half-height of the most intense maxima of the two TiO2 phases. The four

M

diffractograms have many common features. Slight differences appear when a parameter like the one discussed here (MMA relative concentration) is varied and the

ed

spectra are ordered accordingly.

The main crystallographic characteristics of the analyzed samples are presented

ce pt

in Table III. It presents estimations on the relative content of anatase versus rutile phases as well as on the crystallite dimensions. The percent anatase and rutile phases were evaluated according to the empiric formula of Spurr and Myers [15]. Major TiO2-

Ac

anatase phase was found by XRD analysis. At the increasing MMA concentration, a slight increase of the rutile phase proportion may be noticed. The IR spectrum of a representative sample in the wavenumber region 3000–

1000 cm−1 is presented in Fig. 2. The intermediate decomposition molecules, as well as the MMA monomer and ethylene sensitizer interact in a complex oxidative radical copolymerization process. Thus, in the polymeric shell various fragments possibly exist and the IR signature of different groups (such as -C(=O)OCH3, CH-C(CH3), CH2-CH2,

Page 8 of 28

CH=O, O-CH2-O) may be found. The IR peak at 1367 cm-1 may be attributed to CH2 wagging vibration, found also in the amorphous polyethylene polymer IR spectrum [16] If we suppose that a partial polymeric shell of the PMMA-type is formed, then we may compare the spectrum in Fig 2 with the standard IR spectrum of pure PMMA in which 2951 cm-1 (–CH3

ip t

the main characteristic IR bands were assigned in Ref. [17]:

asymmetric stretching), 1736 cm-1 (C=O stretching), 1483 cm-1 (CH2 scissoring) and

cr

1449 cm-1 (CH3 asymmetric stretching mode). On the other hand, for polyoxymethylene

us

groups (–CH2OCH2O-), the literature [18] reports the following bands (for pure crystalline polymers): 1238 cm-1 (CH2 rocking and –C-O-C symmetric stretching) and

an

1196/1091 cm-1 (C-O-C asymmetric stretching modes)

Due to the complex copolymerizaton/reticulation reactions occurring rapidly in

M

the laser pyrolysis flame, the IR bands of the TiO2-PMMA FTIR spectrum often appear only as traces and do not overlap exactly with the corresponding peaks of the pure

ed

reference polymers (such as PMMA or polyoxymethylene). Further structural characterization of the TiO2 –based samples was carried out

ce pt

using TEM image analysis. Figs. 3 a and b show the TEM images o samples TM14 (a) and TEM 16 (b). The sample obtained in the absence of MMA (Fig. 3a) seems to exhibit a lower size and a higher degree of crystallinity. Irregular, mostly polyhedral

Ac

shape particles are present. In contrast with the enhanced crystalline features for TM14, the sample TM16 (increased MMA concentration, Fig. 3b) exhibit two kinds of particles: polyhedral-shaped and almost round-shaped ones (about 10 nm diameter). These last ones seem to present a fluffy consistency and most probably are polymeric (poly) MMA nanoparticles [19,20] produced in the laser pyrolysis. Individual core-shell particles are rarely visible.

Page 9 of 28

The particle size distributions (maximum value of the Log Normal fitting function) are presented as insets, at the right side of Figs. 3a and 3b.

As the

contribution of MMA in the reaction increases, a decrease growth tendency is observed (from about 25 nm to about 21 nm). This effect could be due to a decrease of the

ip t

residence time in the reaction zone, due to an increased velocity of the MMA (and Ar carrier) flows [21].

cr

The particle distributions are narrow, presenting often a short ”tail” towards

us

higher values.

In Figs. 4 a, b, c, d, e a variety of high resolution TEM images, dedicated to

an

samples discussed here is displayed. The HRTEM image in Fig. 4a shows TiO2-based MMA nanoparticles (sample TM15) which demonstrate different sizes and

M

morphologies. The identified interplanar distances of d=3.52 Ả and d=2.38 Ả correspond to the anatase titanium oxide (101) and (004) planes, respectively. In the

ed

upper part of Fig. 4a, an irregular anatase nanoparticle (with identified diameter of 12 nm and interplane distance of 3.52 Ả), encased in a quasi-amorphous thick coverage

ce pt

appears. On the lower, right-hand side of the figure, layers with quite different structures appear (e.g. a partial thick cover with disordered layers but also thin, crystallographic ordered shear planes of different composition). According to Ref. [22],

Ac

these could be surface defects due to traces of nonstoichimetric TiO2. In Fig. 4b, a group of nanoparticles is analyzed by HRTEM. Some of particles,

presenting also coalescent-like features in their background matrix, belong to anatase titanium oxide (sea the identification of the characteristic interplanar distances in the right-down side of the image). This part is presented at a higher magnification in the inset of Fig. 4b which reveals with clarity the crystalline anatase network.

Page 10 of 28

The electron diffraction (SAED) pattern taken over a group of TiO2 composite nanoparticles (sample TM15) is presented as inset of Fig. 4c. It shows spotty ring patterns of the nano-TiO2 powders in anatase and rutile phases (with a major anatase representation), without any addition of diffraction spots and rings of any second

ip t

phases. The rather well crystallized state of the nanomaterial is revealed. The indexed diffraction rings are in agreement with XRD results (for both anatase and rutile titania,

cr

respectively).

us

In Fig. 4d an almost spherical, crystalline dark core, with identified interplanar distances 2.18 Ả (111) and 3.24 Ả (101) (for the rutile titania phase) is exposed. It is

an

buried in a lighter but rather thick shell (of about 8-9 nm). The core-shell shaped particle seems to be coalescent with the rest of quite similar agglomerated nanoparticles,

M

suggesting a portion of a polymeric matrix. This matrix seems to present major amorphous, non-organized features, suggesting amorphous carbon. In the upper part of

ed

the Fig. 4d, the interplanar distance C (002), namely 3.4 Ả is found. The measurement was performed on very short lamellae distances and was difficult to observe/identify,

ce pt

maybe due to the irregular thickness of the supposed capping polymer. 3. 2. TiO2/HMDSO-based systems

In the laser pyrolysis system, the reaction is initiated and sustained by the heat

Ac

generated from the resonant absorption of the laser energy by a sensitizer gas such as ethylene which has strong rotational-vibrational bands that match the emission lines of the CO2 laser. The thermal decomposition of all reactants (TiCl4/ Fe(CO)5 metal precursors and HMDSO) is based on the collisional energy transfer between the excited ethylene and these compounds. The CO2 laser decomposition of hexamethyldisiloxane occurs via (i) primary cleavage of the Si-C and C-H bonds and (ii) subsequent splits of the Si-O bonds in intermediate products. The formation of the solid polyoxocarbosilane,

Page 11 of 28

was accounted for in terms of polymerization of transiently produced silicon-centred radicals and silanones [23]. This mechanism was confirmed in Ref. [24], where the degradation of polydimethylsiloxane ( a commonly used polymer) was observed. It was found that at

ip t

high temperatures, this mechanism follows the thermodynamically favored pathway resulting from the cleavage of the Si-C bond, which is less stable than the Si-O and C-H

cr

bonds.

us

Fe-doped TiO2/HMDSO samples (TS1, TS2, see Table II) are discussed in this work according to their increasing input Fe/Ti atomic ratio. The Fe/Ti ratios were

an

adjusted by controlling the Fe (CO)5 and TiCl4 flows, respectively. In the last column of the Table II, the average values of the Fe/Ti (in at %) ratios in powders, as estimated by

M

EDS semi- quantitative elemental analysis are displayed.

Considering the experimental errors of the measurement device, the as measured

ed

values of the Fe/Ti atomic ratios in samples can only constitute a qualitative estimation. For sample TS1, with increasing TiCl4 precursor flow, an increase of Ti incorporation

ce pt

relatively to sample TS2 (from 20 to25 at%, respectively) may be noticed. The XRD patterns of the Ti/Fe-polyoxo-carbosilane composites are presented in Fig. 5. The evolution of the diffraction patterns for the doped TiO2 specimens with the

Ac

Fe/Tiatomic ratios 5% and 25 %, respectively show the sharp and highly intense anatase peak (101). As expected, no trace of siloxane polymer fragments or derived carbon-or silicon-containing materials could be detected. A major effect of iron doping seems to be a decrease of the anatase -TiO2 crystalline phase with the increase of the iron concentration (from TS1 to TS2) and consequently an increase of the amorphous phase.

Page 12 of 28

According to XRD calculations (see Table IV), the decrease of the crystalline phase with the increase of the Fe loading is accompanied by the diminishing of the amount of the anatase phase that leads to an increase of the rutile proportion. We should mention that the decrease of the strongest diffraction from anatase (101) with the

ip t

increase of Fe/Ti ratio was also reported in previous studies (see for instance Wang et al. [25])

cr

A decrease of particle sizes takes place at increasing the Fe doping (probably as

us

following the interstitial accommodation of Fe atoms in the nanocomposite network). This effect was also noticed by TEM analysis (see below) and is more visible in case of

an

the rutile phase. By XRD, the only identified Fe compounds are the weak features of the crystalline α-Fe-phase (JCPDS file 06-0696) (see Fig. 5). The main Fe peak ( (110) at

M

44.7°) is very weak and ill-defined. Due to the overlapped peaks the presence of traces of the orthorhombic cohenite Fe3C phase (JCPDS file 34-0001) may be not excluded.

ed

We could suggest that the iron dopant is partly isomorphously substituted into the TiO2 crystalline phases possibly forming a so called “amorphous to XRD” phase, i.e. a phase

ce pt

in which a great number of very fine and defective crystallites are probably present. The core-shell morphology of the Ti-Fe /polyoxocarbosilane nanocomposite (supported by the TEM images presented below) could be also favoured by the gas

Ac

flows geometry in the reaction zone. These nanocomposites could become partially oxidised in outer layers upon contact with the air (the partial change of the Fe dopant into Fe2O3). Such behaviour is indicative of the incomplete coverage by the polymeric matrix or of a porous polymer structure. For the improvement of the polymeric coverage, the laser power was increased (from 100 to 200 W), thus addressing a transformation towards more or less interconnected nanoparticle because of the removal of organic species by heating.

Page 13 of 28

Studies of PMMA decomposition in presence of TiO2 cores show that the decomposition temperatures of the PMMA beads increase when they have implanted nano-cores. It was reported that in situ activation of the surface-initiated atom transfer radical polymerization gave rise to PMMA polymer shell layers tethered to TiO2

ip t

nanoparticle cores [26]. Overview TEM images of the as-synthesized samples, displaying groups of

cr

nanoparticles are presented in Figure 6. In this case and in contrast with the TiO2/MMA

us

nanocomposites, the polymer matrix was rarely visible; instead, the great majority of the rather well dispersed produced nanoparticles presented the core shell structure.

an

Indeed, one may observe that many particles exhibit dark cores and a lighter shell with irregular thickness of the coverage, possibly attributed to the polyoxocarbosilane. Most

M

importantly, the core–shell structure provides oxidative resistance but also broadens their potential applications (such as optical–electronic devices or in the biomedical

ed

area) since the shell can be functionalized with organic or biomolecular materials. The sharp particle distributions, pointing to different mean diameter values are

ce pt

presented as insets of the images of Fig. 6 (right-hand side of Figures). From the estimated particle size distributions and in agreement with the XRD analysis, a tendency to a decreased mean particle diameter at increased Fe loading may be noticed (from

Ac

about 29.4 nm to about 22.8 nm, at Fe/Ti 5% and 25%, respectively). Images with a higher magnification of the nanoparticles are presented in Fig. 7 a

and b. The well defined core-shell structure (with a rather thick polymer coverage) seems to characterize the nanoparticle presented in Fig. 7 a. In Fig. 7 b, coalescent and irregular features of the polymer matrix appear, surrounding particles with different thicknesses . 4. Conclusions

Page 14 of 28

We have used the single-step laser pyrolysis technique in order to perform a comparative study on the synthesis and characterization of two types of TiO2/polymer and TiO2/Fe /polymer -based nanocomposites. The chosen polymer precursors were methyl methacrylate and hexamethyl disiloxane, respectively. The reactive mixture

ip t

contained TiCl4 as Ti precursor and, Fe(CO)5 (in the second case), for the TiO2/Fe /polymer -based nanocomposites. All the as-synthesized samples show a mixture of the

cr

two anatase and rutile crystalline phases. For most samples, the anatase TiO2 is the

us

major crystallographic phase. TiO2/MMA-based nanocomposites exhibit two kinds of particles: polyhedral-shaped (as a major component in the absence of MMA) and

an

almost round-shaped nanoparticles (possibly polymeric in nature). As the contribution of MMA in the reaction increases, a tendency for the decreased growth of the

M

nanoparticle mean sizes of the nanocomposites is appears. Almost spherical nanoparticles in a coalescent matrix and very rare individual core-shell structures are

ed

noticed. Instead, in case of the TiO2/Fe / HMDSO system, nanoparticles presenting core-shell structures demonstrate a major presence (mean nanocomposites particle

ce pt

diameters between about 22 nm to about 29 nm). Acknowledgements

The authors acknowledge the support of the Romanian Ministry of Education and

Ac

Research under the Project PNCD2 IDEI No 80/2011.

References

[1] H.M. Xiong, X.Y. Guan, L.H. Jin, W.W. Shen, H.J. Lu, Y.Y. Xia, Surfactant-free synthesis of [email protected] and [email protected] core-shell nanobeads designed for peptide/protein enrichment and MALDI-TOF MS analysis, Angew. Chem. Int. Ed. Engl. 47 (2008) 4204-4207.

Page 15 of 28

[2] W. Qi, Linbao Luo, H.-S. Qian, G. Ouyang, K. K. Nanda, S. O. Obare, Core-shell nanostructures: modeling, fabrication, properties and applications, Journal of Nanomaterials Volume 2012 (2012), Article ID 526923, 2 pages,doi:10.1155/2012/ 526923.

ip t

[3] T.X. Liu, F.B. Li, X. Z Li, TiO2 hydrosols with high activity for photocatalytic degradation of formaldehyde in a gaseous phase, J. Hazard. Mater. 152 (2008) 347-355.

us

sensitised colloidal TiO2 films, Nature 353(1991) 737-740.

cr

[4] B. O’Regan, M. Gräzel, A low-cost, high-efficiency solar cell based on dye-

[5] K.Balachandaran, R.Venckatesh, R. Sivaraj, Synthesis and characterization of nano

an

TiO2–PEG composite, International Journal of Engineering Science and Technology, 3

M

(2011) 4200-4204

[6] A. Galykova, Z. Bastl, R. Alexandrescu, I. Morjan, J.Pola, Thermal behavior of polyoxocarbosilane shells in Fe-based (core)-polyoxocarbosilane (shell)

ed

nanocomposites, Thermochimica Acta 439 (2005) 80–85.

ce pt

[7] R. Alexandrescu, I. Morjan, A. Tomescu, C. E. Simion, M. Scarisoreanu, R. Birjega, C. Fleaca, L.Gavrila, I. Soare, F. Dumitrache, G. Prodan, Preparation of iron/iron oxide -based nanocomposites by the laser pyrolysis of Fe (CO)5/ MMA mixtures: structural and sensing properties, Journal of Nanomaterials, Volume 2010, Article ID 324532, 12

Ac

pages.

[8] W.R. Cannon, S.C. Danforth, J.H. Flint, J.S. Haggerty, R.A. Marra, Synthesis of ceramic powders by laser-driven reactions, J. Am. Ceram. Soc. 65 (1982) 324–330.

[9] R. Alexandrescu, I. Morjan, I. Voicu, D. Dumitrache, L. Albu, I. Soare, G. Prodan,, Combining resonant/non-resonant processes: nano-meter-scale iron-based material preparation via the CO2 laser pyrolysis, Appl. Surf. Sci. 248 (2005) 138-146.

Page 16 of 28

[10] I.Morjan, R. Alexandrescu, M. Scarisoreanu, R. Birjega, F. Dumitrache, L. Gavrila, C. Fleaca, I. Soare, V. Ciupina , C. E. Simion, A. Tomescu, Development of Ti-doped iron-polyoxocarbosilane nanocomposite with sensing properties by single-step laser pyrolysis, International Journal of Nanomanufacturing 6 (2010) 334 – 349.

[11] J. Pola, Laser powered homogeneous decomposition of methyl acrylate and

ip t

methacrylate, Tetrahedron 45 (1989) 5065–5072.

cr

[12] P.R. McGill, T. Söhnel, A study of gas phase and surface formaldehyde

us

polymerisation from first principles, Phys. Chem. Chem. Phys. 14 (2012) 858-68

[13] C. H. Bamford, P. R. Morris, The oxidative polymerization of methyl methacrylate,

an

Die Makromolekulare Chemie 87 (1965) 73-89

[14] A.K. Nanda, A. Kishore, Novel phenomenon of autoacceleration in the free radical

M

oxidative polymerization of vinyl monomers: a thermochemical approach, Eur. Polym.

ed

J. 37 (2001) 671-676

[15] R.A Spurr , H. Myers , Anal. Chem. 29 (1957) 760.

1964

ce pt

[16] R. Zbinden, Infrared spectroscopy of high polymers, Academic Press New York,

[17] K. Kanniphan, S. Latha , Certain investigations in the formulation and

Ac

characterization of Polystyrene /Poly(methylmethacrylate) blens, Int. J. Chem Tech, Res. 3 (2011) 708-717 [18] H. Tadokoro, M. Kobayashi, Y. Kawaguchi, A. Kobayashi, S. Murahashi, Normal vibrations of the polymer molecules of helical configuration. III. Polyoxymethylene and Polyoxymethylene‐d2, J. Chem. Phys. 38, (1963) 703

[19] W. Chen, X. Liu, Y. Liu, Y. Bang, H.-I. Kim, Synthesis of PMMA and PMMA/PS nanoparticles by microemulsion polymerization with a new vapor monomer feeding

Page 17 of 28

system, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 364 (2010) 145–150.

[20] W. Liao, A. Gu , G. Liang , L. Yuan, New high performance transparent UVcurable poly(methyl methacrylate) grafted ZnO/silicone-acrylate resin composites with

Physicochemical and Engineering Aspects, 396 (2012) 74–82.

ip t

simultaneously improved integrated performance, Colloids and Surfaces A:

cr

[21] P. E. Di Nunzio, S. Martelli, Coagulation and aggregation model of silicon

us

nanoparticles from laser pyrolysis, Aerosol Science and Technology 40 (2006) 724-734.

[22] X. H. Wang, J.-G. Li, H. Kamiyama, M. Katada, N. Ohashi, Y. Moriyoshi, T. Ishigaki, Pyrogenic iron(III)-doped TiO2 nanopowders synthesized in RF thermal

an

plasma: phase formation, defect structure, band gap, and magnetic properties,

M

Journal American Chemical Society 127 (2005) 10982-10990.

[23] J. Pola, M. Maryjsko, V. Vorljcek, Z. Bastl, A. Galýkova, K. Vacek, R. Alexandrescu, F. Dumitrache, I. Morjan, L. Albu, G. Prodan, Infrared laser synthesis

ed

and properties of magnetic nano-iron-polyoxocarbosilane composites, Applied

ce pt

Organometallic Chemistry 19 (2005) 1015–1021.

[ 24] K. Chenoweth, S. Cheung, A. C. T. van Duin, W. A. Goddard III, E. M. Kober, Simulations on the Thermal Decomposition of a Poly(dimethylsiloxane) Polymer Using the ReaxFF Reactive Force Field, J. Am. Chem. Soc. 2005, 127, 7192-7202

Ac

[25] X. H.Wang, J. G. Li, H. Kamiyama, T. Ishigaki, Fe-doped TiO2 nanopowders by oxidative pyrolysis of organometallic precursors in induction thermal plasma: synthesis and structural characterization, Thin Solid Films 506-507 (2006) 278–282.

[26] X. Fan, L. Lin, P. B. Messersmith, Surface-initiated polymerization from TiO2 nanoparticle surfaces through a biomimetic initiator: A new route toward polymer– matrix nanocomposites, Composites Science and Technology 66 (2006) 1195–1201.

Page 18 of 28

Figure captions

Fig. 1. XRD patterns of TiO2 / MMA–based samples obtained at three different MMA concentrations in the reactive mixture (the curves are labeled according to the MMA flows during laser pyrolysis ( 0, 5, 10 and 15 sccm, respectively)

ip t

Fig. 2. The IR spectrum of a representative sample (TiO2 / MMA–based

cr

nanocomposites) in the wave number region 3000–1000 cm−1

Fig.3. TEM micrographs forTiO2 / MMA–based nanoparticles: sample TM14 (a) and

us

sample TM16 (b)

Fig.4. High resolution TEM images of TiO2/ MMA- based nanoparticles. demonstrating

an

different sizes and morphologies (sample TM15): identified interplanar distances corresponding to the anatase titanium oxide planes and an anatase nanoparticle (about

M

12 nm diameter) encased in a quasi-amorphous thick coverage (upper part of Fig.)- (a); group of nanoparticles with coalescent -like features belonging to anatase titanium oxide - (b); the identification of the interplanar characteristic distances is presented as

ed

inset in Fig (b); a group of TiO2 composite nanoparticles with the inset presenting the SAED pattern– (c); a crystalline dark core identified as the rutile titania phasea0 buried

ce pt

in a lighter, thick shell–(d)

Fig. 5. XRD patterns of the Ti/Fe-polyoxo-carbosilane composites with different Fe/Ti atomic ratios

Ac

Fig 6. Overview TEM images of the as-synthesized TiO2/Fe / HMDSO–based samples, displaying groups of rather well dispersed nanoparticles, mostly with core shell structures: samples TS1-(a) and TS2-(b). Right-hand side of Figures: particle diameter distributions

Fig. 7a and b. Higher magnification images of nanoparticles belonging to the TiO2/Fe / HMDSO–based samples, whith well- defined core-shell structures

Page 19 of 28

Ac

ce pt

ed

M

an

us

cr

ip t

Figures Revised Alexandrescu.doc

Figure 1

Page 20 of 28

ip t cr us an M ed ce pt Ac

Figure 2

Page 21 of 28

ip t cr us an M ed ce pt Ac Figure 3

Page 22 of 28

ip t cr us an M ed ce pt Ac Figure 4

Page 23 of 28

ip t cr us an M ed ce pt

Ac

Figure 5

Page 24 of 28

us

cr

ip t

a

Ac

Figure 6

ce pt

ed

M

an

b

Page 25 of 28

ip t cr us

Ac

ce pt

ed

M

an

a

b

Figure 7

Page 26 of 28

Revised Tables Alexandrescu.doc

Table I. Synthesis parameters and EDAX EDS measurements (in at% and wt%, respectively) for the TiO2/MMA -based nanocomposites* Ar→ EDAX EDS MMA Wt% O C sccm Ti

EDAX EDS At% Ti O C

0 5 10 15

27.27 25.05 22.48 23.72

53.92 51.19 46.25 49.44

40.18 41.75 45.61 42.95

5.90 7.06 8.14 7.61

ip t

 Ar → TiCl4 sccm 160 160 160 160

cr

TM14 TM17 TM15 TM16

C2H4 → TiCl4 sccm 100 100 100 100

60.84 61.17 63.43 61.71

us

Samples

11.90 13.78 14.08 14.57

ce pt

ed

M

an

*The following parameters were maintained constant: the flows of Ar confinement and windows flushing (Ar conf =1700 sccm; Ar window =1750 scc), the flow of the oxidizer (air) (Air = 225 sccm), the total pressure (Pmbar= 650 )and the laser power Pwatt = 400)

Table II. Synthesis parameters , EDAX EDS measurements and average Fe/Ti (in at%) ratio for the TiO2-Fe/HMDSO nanocomposites*

Ac

Samples C2H4→ C2H4 HMDSO → sccm Fe(CO)5 sccm TS1 10 3 TS2 10 10

C2H4 → TiCl4 sccm 100 100

Arcompl → TiCl4 sccm 60 0

PL watt Fe 100 200

Ti 25 1.25 20 5.00

EDAX At% Si C O 2.05 1.8

34 37.7 34.7 38.5

Fe/ Ti 0.05 0.25

* The following parameters were maintained constant: the pressure in the reaction chamber and the Ar confinement flow (at 450 mbar and 500 sccm, respectively).

Page 27 of 28

A (%) 90.2 89.4 88.1 85.9

R (%) 9.8 10.6 11.9 14.1

DA(nm) 22.0 21.8 22.7 21.9

DR(nm) 21.3 22.7 21.7 21.4

cr

Φ MMA 0 5 10 15

ce pt

ed

M

an

us

Sample TM14 TM17 TM15 TM16

ip t

Table III. Main crystallografic characteristics, as estimated from XRD analysis, for the TiO2 /MMA- based samples

Table IV. Main crystallografic characteristics, as estimated from XRD analysis, for the TiO2/Fe /HMDSO -based samples

Ac

Sample TS1 TS2

A (%) 87.4 81.7

R (%) 12.6 18.3

DA(nm) 16.8 15.1

DR(nm) 20.6 11.2

Page 28 of 28