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Materials Chemistry and Physics 144 (2014) 498e504

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Materials Chemistry and Physics

journal homepage: www.elsevier .com/locate/matchemphys

Facile two-step preparation of polystyrene/anatase TiO2 core/shellcolloidal particles and their potential use as an oxidation photocatalyst

R. Bengü Karabacak a, Murat Erdema, Sedat Yurdakal b, Yasemin Çimen a, Hayrettin Türk a,*

aAnadolu University, Department of Chemistry, 26470 Eskisehir, TurkeybAfyon Kocatepe University, Department of Chemistry, 03200 Afyonkarahisar, Turkey

h i g h l i g h t s

* Corresponding author. Tel.: þ90 222 335 0580x47E-mail addresses: rbkarabacak@anadolu.edu.tr

anadolu.edu.tr (M. Erdem), sedatyurdakal@gyasemincimen@anadolu.edu.tr (Y. Çimen), hturk@ana

0254-0584/$ e see front matter � 2014 Elsevier B.V.http://dx.doi.org/10.1016/j.matchemphys.2014.01.026

g r a p h i c a l a b s t r a c t

� Facile two-step preparation of PS/TiO2 core/shell colloidal particles.

� Anatase TiO2 shell forms in an acidicaqueous solution.

� Calcination is not needed to obtainanatase TiO2.

� The core/shell particles show higherp-anisaldehyde selectivities in MBAoxidation.

a r t i c l e i n f o

Article history:Received 11 August 2013Received in revised form14 December 2013Accepted 12 January 2014

Keywords:PolymersChemical synthesisSolegel growthCrystal structure

a b s t r a c t

Titania and materials containing titania have received considerable attention due to their technologicalimportance in many areas. In this study, anatase crystalline titania (TiO2) coated polystyrene (PS)colloidal particles were successfully prepared in two easy steps. First, a one pot synthesis of the colloidalparticles was produced via an emulsifier-free emulsion copolymerization of styrene (S) and 2-(dime-thylamino)ethyl methacrylate (DMA) at pH 4.0. In the second step, the synthesized particles were coatedby titania using a solegel process in-situ hydrolysis and a condensation reaction of titanium(IV) iso-propoxide in an acidic aqueous solution. In this way, anatase crystalline titania, rather than the usualamorphous form, was obtained as a shell on the PS colloidal particles. Both the PS colloidal particles andthe polystyrene/anatase titania (PS/TiO2) core/shell colloidal particles had monodisperse morphologyand were characterized using SEM, Zetasizer, FTIR, XRD and TGA techniques or measurements. Inaddition, the photocatalytic activity of the PS/TiO2 core/shell particles was tested for the first time in anoxidation reaction, in the oxidation of 4-methoxybenzyl alcohol (MBA) with O2 in water. Much higherselectivities of the target product, p-anisaldehyde (AA), were obtained with the PS/TiO2 core/shell par-ticles than with a commercial anatase crystalline TiO2.

� 2014 Elsevier B.V. All rights reserved.

87; fax: þ90 222 320 4910.(R.B. Karabacak), merdem@mail.com (S. Yurdakal),dolu.edu.tr (H. Türk).

All rights reserved.

1. Introduction

In recent years, inorganic-coated polymer particles haveattracted increasing attention due to their unique material char-acteristics, such as thermal stability, mechanical strength, and theirelectrical, catalytic, magnetic and optical properties [1,2]. They aregenerally called core/shell particles and combine the advantages ofcore organic polymer and shell inorganic material. Titania [3],

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504 499

magnetite [4], cadmium sulfide [5], zinc sulfide [6], silica [7], silver[8], alumina [9], aluminum hydroxide [10], and zirconia [11] havebeen commonly employed as materials for inorganic shells. Alongwith polymeric beads, polystyrene based polymeric colloids(nanoparticles) containing functional groups have been mostlyemployed as cores [3,12]. Uniform and controllable sizes, largesurface areas, adsorption capacities and easy preparations ofpolymeric colloids make them attractive core and/or templatematerials in the preparations of colloidal organic/inorganic core/shell particles. Furthermore, colloidal polymer templated core/shellparticles can also be used in the production of inorganic hollowparticles through removal (burning or dissolution) of the template.

Titania (TiO2) has received considerable attention as a materialdue to its scientific and technological importance over the last fewdecades [13e15]. Titania and titania-containing materials havebeen used as photocatalysts [8,16e20], catalyst supports [13e15,21e23], materials for medical use [24,25], and as white pig-ments for paints [26].

In the preparation of titania-coated particles and their hollows,the coating is usually achieved by deposition or layer-by-layer self-assembly. Imhof [3] used cationically-charged polystyrene (PS)nanospheres in the preparation of titania-coated particles andhollow titania shells. Titania was deposited on the cationic surfacesof the polystyrene spheres, created by using the cationic initiator2,20-azobis(2-methylpropionamidine) dihydrochloride (AIBA), byhydrolysis of titanium tetraisopropoxide in ethanol. Later, Imhofet al. [27] were able to coat titania onto cationic PS particles in thepresence a nonionic surfactant in ethanol and were successful incontrolling the thickness of the titania shells. Yang et al. [28,29]utilized sulfonated-polystyrene core/shell gel particles in ethanol/water (1:1 vol/vol) as a template for the preparation of titaniacoated and hollow titania spheres of tunable cavity size. The use ofsuch gel particles allowed an inward diffusion and growth of thetitania precursor inside the gel particles. Kim et al. [12] report asimple preparation of monodisperse polymer core-titania shellnanospheres and hollow titania. Cationically-charged polymercores were prepared using styrene, butyl acrylate, 2-(meth-acryloxy)ethyltrimethylammonium chloride monomers and acationic initiator AIBA. The cationic surface charge of the polymericparticles facilitated rapid adsorption and hydrolysis of a negatively-charged titania precursor on the surfaces of colloidal particles inethanol. Fang et al. [30] also prepared polystyrene/titanium dioxide(PS/TiO2) core/shell particles via an in-situ solegel method inethanol by depositing TiO2 on the cationic PS particles. Here 2-(methacryloyloxy)ethyltrimethylammonium chloride was alsoused as a cationic monomer to obtain a positively charged surfaceon the polystyrene particles. Wang et al. [31] were able to coatanionic PS particles with titania in ethanol/acetonitrile mixed sol-vents by ammonia catalysis and prepared hollow titania spheres.Here ammonium ions, the conjugate acid of ammonia, acted ascounter ions of eSO4

� groups on the surface of PS particles andfacilitated the condensation process of the titanium precursor. Theresults show that smooth and homogeneous coatings with tunablethicknesses were achieved. Apart from Fang et al. [30], which didnot provide information about the phase of titania in their PS/TiO2core/shell particles, all of these studies reported the formation ofamorphous titania-polymer core particles. In order to have crys-talline titania, these particles had to be calcined. It is well knownthat amorphous titania has only limited use in photocatalysis andcertain other applications. It is a fact that the calcination processcarried out to obtain crystalline titania decomposes the particlecore, demolishes particle integrity and changes the surface char-acteristics of titania from a hydrophilic nature to a hydrophobicone. In this study, we succeeded in forming polystyrene-anatasecrystalline titania core/shell particles. Another approach used to

prepare titania-coated PS particles is via a layer-by-layer self-as-sembly technique. Caruso et al. [32e34] extensively used thistechnique to prepare such particles. By using this technique, theywere able to deposit pre-prepared anatase TiO2 nanoparticles ontopolyelectrolyte coated PS particles [33]. Although this techniquewas time consuming and laborious, it enabled the researchers toobtain anatase TiO2 shells and have some control over the coatingthickness and the coated particle morphology.

Titania-coated core/shell particles have been used as a photo-catalyst for the removal of organic pollutants [16e18]. Furthermore,in recent years, bare titania has been utilized as a photocatalyst inthe oxidation of organic compounds in water to producecommercially important products by the Palmisano group[19,20,35e37]. Although photocatalytic oxidation processes per-formed in water satisfy one of the main conditions of green pro-cesses, they are highly unselective due to the fact that their reactionmechanisms involve radical species.

In this study, we report an easy route to prepare anatasenanocrystalline titania-coated polymer colloidal particles in waterusing tertiary amine functionalized polystyrene colloidal particles.First, we prepared polystyrene (PS) colloids via emulsifier-freeemulsion copolymerization of styrene (S) with 2-(dimethylamino)ethyl methacrylate (DMA) at pH 4.0. The nanocrystalline titaniumdioxide was synthesized by a solegel process in situ hydrolysis anda condensation reaction using titanium(IV) isopropoxide in acidicaqueous solution, deposited simultaneously onto the cationic sur-faces of the polymer colloidal particles in this medium. The pho-tocatalytic activity of the core/shell particles was tested in anoxidation of 4-methoxybenzyl alcohol (MBA) with O2 in water.

2. Material and methods

2.1. Materials

Styrene (S, from Aldrich) and 2-(dimethylamino)ethyl methac-rylate (DMA, from Merck) were purchased and purified by beingpassed through basic alumina columns before use. Potassium per-sulfate (from Merck) was of analytical grade. Titanium(IV) iso-propoxide was purchased from Aldrich. 4-Methoxybenzyl alcohol(MBA) was obtained from SigmaeAldrich. Commercial titaniumdioxide (Merck TiO2) was purchased from Merck. Deionized waterwas used in all experiments.

2.2. Instrumentation

The colloidal particle sizes and their distributions weremeasured by dynamic light scattering using a Malvern Zeta-sizerNano ZS utilizing a Red-He/Ne laser operating at 633 nm. Thesame instrument with an MPT-2 autotitrator was used to measurezeta potentials of the colloidal particles at different pH values. Themorphologies of the colloidal and core/shell particles were exam-ined by scanning electron microscope (SEM, Carl Zeiss ULTRA Plus).The crystallinity of the coated titania on the polymer surface wasdetermined by a Bruker D8 Advance X-ray powder diffraction(XRD) system using a detector scan mode and operating at 40 kVand 40 mA in the region of 2q ¼ 20�e80�. FTIR spectra wererecorded with a PerkineElmer Spectrum 100 FTIR spectrometerusing KBr pellets. A Sartorius SM 16309 ultrafiltration system wasused to filtrate titania-coated particles. Thermogravimetric ana-lyses (TGA) of the particles were achieved using a Seteram (Labsys)Thermogravimetric/Differential Thermal Analyzer under nitrogenatmosphere heating the samples from 30 �C to 800 �C at a rate of10 �C min�1. In the oxidation studies, identification and quantita-tive analysis studies were performed by means of a ShimadzuProminence LC-20A HPLC equipped with a SPD-M20A detector.

10203040506070

al (m

V)

a

b

c

d

e

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504500

2.3. Preparation of emulsifier-free PS colloidal polymer

Preparation of the polystyrene colloidal polymerwas carried outthe sameway as previously reported [38] using a typical emulsifier-free emulsion polymerization procedure [39,40]. Styrene (3.0 g)was used as a main monomer with 2-(dimethylamino)ethylmethacrylate (1.0 g) as a comonomer. The polymerization wascarried out at pH 4.0.

-70-60-50-40-30-20-100

1 2 3 4 5 6 7 8 9 10 11 12

Ze

ta

p

ote

nti

pH

Fig. 1. Zeta potential vs. pH curves obtained for colloidal PS particles before and aftertitania coating. (a) PS, (b) TiO2, (c) PS/TiO2-4h, (d) PS/TiO2-8h, (e) PS/TiO2-20h.

2.4. Titanium dioxide coating studies onto PS colloids

A titania coating process on the PS particles was carried outaccording to Tung and Daoud [41]. The total reaction volume was15 mL. Titanium(IV) isopropoxide (0.75 mL) was mixed with aceticacid (100%, 0.75mL) and a hydrochloric acid solution (37%, 0.21mL)in a 25 mL flask. To this medium, 13.3 mL of the PS colloid(7.53 mg polymer mL�1) was added immediately and the mixturewas heated under vigorous stirring at 60 �C for 20 h. The samereaction was carried out for 4 h and 8 h. The resulting core/shellparticles of 4, 8 and 20 h experiments were coded as PS/TiO2-4h,PS/TiO2-8h, and PS/TiO2-20h, respectively. The titania deposited PSparticles were filtered via an ultrafiltration system using pore sized0.1 mm cellulose nitrate filter papers and washed three times withacidic water (0.1 M HCl, 5 mL). Finally, the cleaned particles wereredispersed in 10 mL of pH 5.0 solution.

To pyrolyze the PS/TiO2-8h and PS/TiO2-20h particles, they wererecovered first after drying from aqueous dispersions and thenheated to 450 �C for 3 h.

2.5. Photoreactivity set up and oxidation of MBA

The photo-reactor was a 250mL beaker containing a suspensionvolume of 150 mL. It was irradiated at the top by means of 4 fluo-rescent black lamps (Philips, 8 W) which emit a monochromaticradiation at 365 nm. The distance of the lamps to the upper surfaceof the suspensionwas 6.8 cm. The initial concentration of MBAwas1mM and the TiO2 content in a typical reactionwas 0.40 g L�1. All ofthe reactions were carried out at an ambient temperature. The ra-diation energy impinging on the upper area of the suspensions forthe reactor had an average value of 2.1 mW cm�2 measured using aradiometer (Delta Ohm, DO 9721, of wavelength range: 315e400 nm). The experimental procedure and the detail of the productanalysis were carried out in the same manner as that reported inthe literature [37].

3. Results and discussion

This study reports a facile two-step preparation of polystyrene/anatase titania (PS/TiO2) core/shell colloidal particles with mono-dispersemorphology (Scheme 1) and its preliminary photocatalyticuse in the oxidation of MBA with O2 in water.

Scheme 1. Schematic representation of a two-step pr

3.1. Preparation and characterization of the emulsifier-free PScolloid

Polystyrene (PS) colloidal particles containing tertiary aminefunctionality were obtained after a one-pot polymerization process.Styrene and 2-(dimethlamino)ethyl methacrylate (DMA) in 3:1(wt/wt) were copolymerized using an emulsifier-free emulsionpolymerization method at pH 4.0. The amine functionality of theDMA moiety was utilized to bring about a cationic surface chargeon the PS colloidal particles in an acidic medium which stabilizedthe particles. The cationic surface charge on the particles in theacidic medium is a result of protonation of the tertiary amine groupof the DMA moiety yielding its conjugate acid, the quaternaryammonium ion. It is also well known that a cationic surface chargefacilitates adsorption of negatively-charged titania precursors [12].In this way, the PS colloid preparation was simple, used two com-mon, easily available monomers and yielded almost uniform PScolloidal particles. The stability of the colloid was excellent. In theliterature, in order to obtain stable PS colloids, usually either theionic fragments from the initiator were utilized or a monomerbearing a cationic or anionic functionality (usually requiring priorsynthesis) was introduced into the polymerization feed. Here,simply adjusting pH, stability of PS particles was attained.

The prepared PS colloidal particles had positive zeta potentialvalues almost up to pH 8.0 [38,42,43] and their isoelectronic point(IEP) was pH 8.27 (Fig. 1a). When the particles were dispersed inpure water, the zeta potential was þ52.3 mV and the average par-ticle size was 193 nm with a polydispersity index (PDI) value of0.02. Both values are calculated by the software of the Zeta-sizerinstrument. The SEM micrograph of the colloidal polymer in-dicates that the particles were of spherical shape with a smooth

eparation of core/shell PS/TiO2 colloidal particles.

Fig. 2. SEM images of the nanocrystalline titania-coated polymer particles: (a, b) PS; (c) PS/TiO2-4h; (d) PS/TiO2-8h; (e) PS/TiO2-20h.

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504 501

surface (Fig. 2a and b). The FTIR spectrum clearly showed a peak at1729 cm�1 due to the carbonyl functionality of the DMA moietyincorporated into the polymer chains (Fig. 3).

3.2. Preparation and characterization of core/shell PS/TiO2 particles

Titania-coated particles were formed by a solegel process in-situ hydrolysis and a condensation reaction on the surface of thecationically charged colloidal PS particles using titanium(IV) iso-propoxide in acidic aqueous solution. The process was one step andthe colloidal particles or their surface were not treated or modified

in any way before deposition. This procedure enabled us to preparethe PS/TiO2 core/shell colloidal particles easily with good stabilityin aqueous solution without any stabilizer being added. The effectof the reaction time on the morphology and properties of thecoated particles was examined in detail by SEM, XRD, FTIR, Zeta-sizer and Zeta potential techniques or measurements. Fig. 2ceeshows the SEM images of the titania-coated PS particles obtainedafter 4, 8, and 20 h coating times. As the coating time increased, anincrease in the overall diameter of the particles was observed,indicating the formation of thicker shells with time (Table 1).Furthermore, a roughening of the particle surfaces, as a result of

Fig. 3. FTIR spectra of the titania-coated PS colloids.

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504502

titania deposition, was evidenced. Considering the average di-ameters of the colloidal PS particles (193 nm) and of the coatedparticles (227 nm after a 20 h coating time), the thickness of thetitania shell can be estimated as 17 nm. It appears that the coatedparticles have monodisperse and uniformmorphology which is thesame as the original polymer particles. From the FTIR spectra of thecoated particles it appears that a 20 h coating time is needed inorder to have effectively coated PS particles. In the FTIR spectrum ofPS/TiO2-20h (Fig. 3) the characteristic peaks of the PS particlesalmost diminished. However, the FTIR spectrum of the PS/TiO2-4hwas quite similar, with peaks almost as sharp as that of the PSparticles. These results indicate that the hydrolysis of titanium(IV)isopropoxide was slow in acidic aqueous solution and it appearsthat a stable shell structure was not constituted on the surface ofthe PS particles in 4 h (Fig. 3). However, in the literature, it is statedthat water causes rapid hydrolysis of titanium alkoxides [29,32,34].As a result, ethanol was usually the preferred solvent during titaniacoating [3,12]. In addition to the FTIR spectra of the titania-coatedparticles, their TGA curves supported the idea that a long titaniadeposition time was needed to have a significant amount of coatedtitania on the PS particles. Fig. 4 illustrates the TGA curves of the PSparticles and the PS/TiO2-8h and PS/TiO2-20h core/shell particles.The thermographs indicate a significant loss of mass occurringbetween 300 �C and 450 �C, as a result of thermal decomposition ofthe PS core in all curves. The remaining masses from PS/TiO2-8hand PS/TiO2-20h (that was titania) were approximately 9% and 50%,respectively.

The crystallinity of the titania shells was examined by XRD.Fig. 5 shows the XRD patterns of PS/TiO2-8h and PS/TiO2-20h,respectively. Both patterns indicate highly crystalline titaniacoating on the PS particles with typical anatase peaks at 25.4�, 38.0�

and 48.0� [41]. This finding was quite surprising since the crystal-line titania, rather than the amorphous one, formed on the polymersurface. In the literature, many studies report the formation of onlyamorphous titania on the titania-coated core/shell particles in asolegel technique along with certain other preparation methodswith the crystalline titania being obtained after calcination at hightemperature [3,12,27,28,31]. Using the Scherrer formula and thediffraction peak at 2q ¼ 25.4�, the crystallite sizes of both PS/TiO2-8h and PS/TiO2-20h were calculated as ca. 4.7 nm.

Fig. 1 gives the zeta potentials of titania-coated PS particles (PS/TiO2-4h, PS/TiO2-8h, PS/TiO2-20h) and bare titania particles alongwith that of the PS colloidal particles. The isoelectronic point (IEP)of bare titania particles was pH 5.20 (Fig. 1b) and close IEP values tothis value for titania particles have already been reported in theliterature [3,44]. The zeta potential curve for the PS/TiO2-4h core/shell particles almost superimposed to that of the PS particles(Fig. 1c). Depending on the treatment time of the PS particles withthe titania precursor, the thickness of the titania shells increasedand eventually the zeta potential curves and IEP values of thetitania-coated particles shifted toward that of bare titania (Fig. 1dand e).

To obtain hollow titania particles, the titania-coated polymerparticles, PS/TiO2-8h and PS/TiO2-20h were calcined at 450 �C. TheFTIR spectra and the SEM micrographs of the hollow TiO2 particlesare given in Figs. 3 and 6, respectively. The FTIR peaks relating topolystyrene were completely absent after the calcination processindicating that the polymer was completely removed (Fig. 3). Asexpected, the XRD patterns of the hollow (calcined) titania particlesshow that the sizes of the crystallites increased to ca.11.0 nm for thecalcined PS/TiO2-8h and to ca. 8.0 nm for the calcined PS/TiO2-20hdue to their sintering and agglomeration at high temperature.

3.3. Photocatalytic reactivity

Preliminary studies were carried out to test the photocatalyticactivities of the PS/TiO2-20h core/shell colloidal particles and theircalcined product in the oxidation of 4-methoxybenzyl alcohol(MBA). No oxidation of MBA was observed in the lack or absenceof either irradiation, catalyst or oxygen. For all the reactions car-ried out, the main product was p-anisaldehyde (AA). The data ofconversion, selectivity and yield obtained from the photocatalyticoxidation of MBA is given in Table 2. The PS/TiO2-20h colloidalparticles and their calcined product show high photocatalytic se-lectivities (ca. 64e70%) considering that the experiments werecarried out in water, whereas the lowest selectivity (24%) wasshown by the commercial TiO2, which is an anatase crystallinematerial. The high selectivities exhibited by the PS/TiO2-20hcatalyst can be attributed to its hydrophilic surface. Hydrophilicnature of the surface of low temperature prepared and thermallyuntreated TiO2 particles has already been shown by the extensivestudies of the Palmisano group [19,20,37,45]. Furthermore, anadverse relationship between selectivity to AA and titania crys-tallinity was reported by the same group [45]. Thus the thermaltreatment of titania enhances its crystallinity but, simultaneously,this process converts its surface from a hydrophilic to a hydro-phobic one [19,20,37,45]. This creates a situation whereby AA, theMBA oxidation product, cannot desorb from the catalyst surface,so it undergoes over-oxidation to CO2 and water. On the otherhand, the PS/TiO2-20h-450 also shows high activity and selectivityeven though it was a calcined product of the PS/TiO2-20h. Thismay be due to the presence of an initial polymer core in thetitania-coated particles which may have prevented the titaniabecoming hydrophobic during calcination. Indeed the peak at1640 cm�1 in the FT-IR spectrum (Fig. 3) indicates that PS/TiO2-20h-450 is hydrophilic, may be as not much as PS/TiO2-20h [45].The 1640 cm�1 peak is due to the bending vibration mode ofadsorbed water in the sample. In addition, the calcination of thePS/TiO2-20h which resulted in a greater active-surface titania area,due to the inner portion of the shell becoming available, couldfunction as a photocatalyst (Fig. 6). This could be the reason whyits photoreactivity increased compared to that of the PS/TiO2-20h.This unexpected result is interesting because the work reported inthe literature shows that calcination of titania decreases the

Table 1Certain properties of the titania-coated PS colloidal particles.

Particle Reaction time (h) Diameter (nm) Polydispersity index

PS/TiO2-4h 4 219 0.03PS/TiO2-8h 8 222 0.07PS/TiO2-20h 20 227 0.01

-100-90-80-70-60-50-40-30-20-1001020

0 200 400 600 800

wei

ght (

%)

temperature (°C)

PS/TiO2-20h

PS/TiO2-8hPS

Fig. 4. TGA curves of the uncoated and titania-coated colloidal polymers.

Fig. 6. SEM image of hollow titania particles after removal of polymer by calcination at450 �C.

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504 503

selectivity of aromatic alcohol photooxidations performed in water[20].

Fig. 7a gives the plot of the experimental data of MBA and AAconcentrations versus the irradiation time for runs carried out us-ing 0.40 g L�1 of PS/TiO2-20h. During the photocatalytic reaction, asexpected, MBA concentrations continuously decreased and AAconcentrations increased. However, AA selectivity remained almostconstant during the reaction (Fig. 7b). As previously reported, the

Fig. 5. XRD patterns of titania-coated polymer particles and titania shells after calci-nation at 450 �C.

TiO2 surface possesses two types of sites, specific for mineralizationto CO2 and water and selective for oxidation [19]. At the mineral-izing sites, the alcohol molecules adsorb and produce CO2, althoughthe mineralization proceeds through a series of intermediates thatdo not desorb into the bulk of the solution. At the selectiveoxidizing sites, the molecules adsorb and produce correspondingoxidation product (in the presence case AA) that can desorb.Therefore by considering previous reported results, the selectiveoxidation sites reside in hydrophilic areas of the TiO2 surface,whereas the mineralization sites are located in the hydrophobicareas. In the present case, the sites on the PS/TiO2-20h and itscalcined product appear to be specific for the selective oxidation ofMBA to AA.

Crystalline anatase phase TiO2 catalysts are generally generatedat high temperatures, ca. 400 �C. Therefore, it is not possible toobtain crystalline TiO2 coated polymer particles after calcinationbecause of degradation of the polymer at the calcination tem-peratures. For this reason, the PS/anatase TiO2 core/shell particlesreported here are new titania photocatalysts containing a poly-meric core and may be used in self-cleaning applications.Furthermore, because no heat treatment is needed to obtaincrystalline titania, the coated titania keeps its hydrophilic nature,which may lead to different photocatalytic activity and surfaceproperties.

Table 2Photocatalytic performance of PS/TiO2-20h and its calcined product for oxidation ofMBA.a

Expt. Catalyst Absorbedirradiance(%)b

TiO2

(g L�1)Conversion(%)

AA yield(%)

AAselectivity (%)c

1. PS/TiO2-20h 98 0.40(0.80)d

15 10 67

2. PS/TiO2-20h 95 0.20(0.40)d

14 9 64

3. PS/TiO2-20h-450e 96 0.40 20 14 704. Commercial TiO2 99 0.40 25 6 24

a [MBA] ¼ 1.0 mM; irradiation time: 3 h.b Calculated considering only the irradiances transmitted by the suspension.c The ratio of the produced moles of AA per reacted moles of MBA.d The values in parenthesis are the concentration of the colloidal PS/TiO2.e Calcined at 450 �C.

Fig. 7. Experimental results of representative runs of photocatalytic oxidation of MBAusing PS/TiO2-20h (0.40 g L�1 TiO2). (a) Concentration changes of MBA (A) and AA (>)with time; (b) Percentages of selectivity (-) and conversion (,) with time.

R.B. Karabacak et al. / Materials Chemistry and Physics 144 (2014) 498e504504

4. Conclusions

A one pot easy preparation of tertiary amine functionalitybearing polystyrene colloidal particles from two common mono-mers, styrene and 2-(dimethylamino)ethyl methacrylate was ach-ieved at pH 4.0. Colloidal stability was maintained simply bykeeping the pH of the colloidal medium slightly acidic. Moreover,providing stability to the colloidal particles, the cationic charge onthe particles was utilized to coat titania on the particles in one step.The coated titania was anatase rather than the usual amorphousphase. In the photocatalytic oxidation of a substrate, core/shell PS/TiO2 particles were used for the first time ever. In the photocatalyticoxidation of 4-methoxybenzyl alcohol with O2 in the presence ofthe core/shell PS/TiO2, particles yielded much higher p-anisalde-hyde selectivities than did the highly crystalline commercial TiO2.

Acknowledgment

We thank Dr. Özer Gök for the XRD measurements and Prof. Dr.Servet Turan for suggestions and instrumentation about the SEMimages.

References

[1] F. Caruso, Adv. Mater. 13 (2001) 11e22.[2] W. Schӓrtl, Adv. Mater. 12 (2000) 1899e1908.[3] A. Imhof, Langmuir 17 (2001) 3579e3585.[4] H.-Y. Wen, G. Gao, Z.-R. Han, F.-Q. Liu, Polym. Int. 57 (2008) 584e591.[5] X. Cheng, Q. Zhao, Y. Yang, S.C. Tjong, R.K.Y. Li, J. Colloid Interface Sci. 326

(2008) 121e128.[6] X. Cheng, Q. Zhao, Y. Yang, S.C. Tjong, R.K.Y. Li, J. Mater. Sci. 45 (2010) 777e

782.[7] H. Zou, S. Wu, J. Shen, Chem. Rev. 108 (2008) 3893e3957.[8] N.Y. Hebalkar, S. Acharya, T.N. Rao, J. Colloid Interface Sci. 364 (2011) 24e30.[9] S.J. Park, E. Ruckenstein, Polymer 31 (1990) 175e179.

[10] H.T. Oyama, R. Sprycha, Y. Xie, R.E. Partch, E. Matijevic, J. Colloid Interface Sci.160 (1993) 298e303.

[11] R.C. Stephenson, R.E. Partch, Mater. Res. Soc. Symp. Proc. 458 (1997) 435e441.[12] T.H. Kim, K.H. Lee, Y.K. Kwon, J. Colloid Interface Sci. 304 (2006) 370e377.[13] A. Hanprasopwattana, S. Srinivasan, A.G. Sault, A.K. Datye, Langmuir 12 (1996)

3173e3179.[14] X.C. Guo, P. Dong, Langmuir 15 (1999) 5535e5540.[15] I. Pastoriza-Santos, D.S. Koktysh, A.A. Mamedov, M. Giersig, N.A. Kotov,

L.M. Liz-Marzan, Langmuir 16 (2000) 2731e2735.[16] F. Shi, Y. Li, H. Wang, Q. Zhang, Appl. Catal. B 123e124 (2012) 127e133.[17] M.E. Fabiyi, R.L. Skelton, J. Photochem. Photobiol. A 132 (2000) 21e128.[18] Y. Li, H. Zhang, X. Hu, X. Zhao, M. Han, J. Phys. Chem. C 112 (2008) 14973e

14979.[19] L. Palmisano, V. Augugliaro, M. Bellardita, A. Di Paola, E. García López,

V. Loddo, G. Marcì, G. Palmisano, S. Yurdakal, ChemSusChem 4 (2011) 1431e1438.

[20] S. Yurdakal, G. Palmisano, V. Loddo, V. Augugliaro, L. Palmisano, J. Am. Chem.Soc. 130 (2008) 1568e1569.

[21] S. Srinivasan, A.K. Datye, M. Hampden-Smith, I.E. Wachs, G. Deo, J.M. Jehng,A.M. Turek, C.H.F. Peden, J. Catal. 131 (1991) 260e275.

[22] R. Castillo, B. Koch, P. Ruiz, B. Delmon, J. Mater. Chem. 4 (1994) 903e906.[23] M.-L. Wang, C.-H. Wang, W. Wang, J. Mater. Chem. 17 (2007) 2133e2138.[24] M. Zaharescu, M. Crisan, L. Simionescu, D. Crisan, M. Gartner, J. Sol-gel. Sci.

Technol. 8 (1997) 249e253.[25] K. Fujita, J. Konishi, K. Nakanishi, K. Hirao, Sci. Technol. Adv. Mater. 7 (2006)

511e518.[26] S. Farrokhpay, Adv. Colloid Interface Sci. 151 (2009) 24e32.[27] A.F. Demirörs, A. Blaaderen, A. Imhof, Langmuir 26 (2010) 9297e9303.[28] Z. Yang, Z. Niu, Y. Lu, Z. Hu, C.C. Han, Angew. Chem. Int. Ed. 42 (2003) 1943e

1945.[29] J. Rong, J. Ma, Z. Yang, Macromol. Rapid Commun. 25 (2004) 1786e1791.[30] X. Fang, H. Yang, G. Wu, W. Li, H. Chen, M. Wang, Curr. Appl. Phys. 9 (2009)

755e759.[31] P. Wang, D. Chen, F.-Q. Tang, Langmuir 22 (2006) 4832e4835.[32] F. Caruso, X. Shi, R.A. Caruso, A. Susha, Adv. Mater. 13 (2001) 740e744.[33] R.A. Caruso, A. Susha, F. Caruso, Chem. Mater. 13 (2001) 400e409.[34] X. Shi, T. Cassagneau, F. Caruso, Langmuir 18 (2002) 904e910.[35] V. Augugliaro, M. Bellardita, V. Loddo, G. Palmisano, L. Palmisano, S. Yurdakal,

J. Photochem. Photobiol. C 13 (2012) 224e245.[36] S. Yurdakal, V. Augugliaro, V. Loddo, G. Palmisano, L. Palmisano, New. J. Chem.

36 (2012) 1762e1768.[37] S. Yurdakal, B.S. Tek, O. Alagöz, V. Augugliaro, V. Loddo, G. Palmisano,

L. Palmisano, ACS Sustain. Chem. Eng. 1 (2013) 456e461.[38] R.B. Karabacak, H. Türk, J. Macromol. Sci. A 49 (2012) 680e688.[39] P.H. Wang, C.Y. Pan, J. Appl. Polym. Sci. 75 (2000) 1693e1698.[40] P.H. Wang, C.Y. Pan, Colloid Polym. Sci. 280 (2002) 152e159.[41] W.S. Tung, W.A. Daoud, J. Colloid Interface Sci. 326 (2008) 283e288.[42] Z. Xiong, B. Peng, X. Han, C. Peng, H. Liu, Y. Hu, J. Colloid Interface Sci. 356

(2011) 557e565.[43] M. Zhai, Y. Chen, M. Yi, H. Ha, Polym. Int. 53 (2004) 33e36.[44] D.H. Ryu, S.C. Kim, S.M. Koo, D.P. Kim, J. Sol-gel. Sci. Technol. 26 (2003) 489e

493.[45] V. Augugliaro, H. Kisch, V. Loddo, M.J. López-Muñoz, C. Márquez-Álvarez,

G. Palmisano, L. Palmisano, F. Parrino, S. Yurdakal, Appl. Catal. A 349 (2008)189e197.