Facile one-step fabrication of polymer microspheres with high magnetism and armored inorganic particles by Pickering emulsion polymerization

https://doi.org/10.1016/j.colsurfa.2012.08.038Get rights and content

Abstract

Facile one-step Pickering emulsion polymerization was employed to prepare magnetic polymer microspheres with high magnetism and armored inorganic particles. Partially hydrophilic CTAB-modified Fe3O4 particles were employed as stabilizer of Pickering emulsion and were armored on the as-prepared microspheres, while totally hydrophobic oleic acid-modified Fe3O4 particles were encapsulated in the obtained microspheres. The microspheres were characterized by scanning electron microscopy (SEM), energy dispersive X-ray microanalyses (EDX) and magnetic measurements. Total Fe3O4, encapsulated Fe3O4 and armored Fe3O4 were detected and catalytic activity of microspheres for Fenton reaction was evaluated. The results showed that steady barrier formed by CTAB-modified Fe3O4 on droplet surface can prevent oleic acid-modified Fe3O4 from escaping away the polymerization vessel, which lead to an efficient encapsulation to oleic acid-modified Fe3O4. The encapsulated Fe3O4 enables the microspheres to be separated by external magnetic field and the armored Fe3O4 endows the composites with special catalytic property.

Highlights

Microspheres with encapsulated and armored Fe3O4 were prepared by Pickering emulsion. ► Particles-formed film on Pickering droplet ensures high encapsulation to particles. ► Encapsulated Fe3O4 enables microspheres to be separated conveniently. ► Armored Fe3O4 endow microsphere with catalytic activity to Fenton reaction.

Introduction

Magnetic microspheres, since their introduction in the 1970s, have benefited from a variety of applications in pollutant removal [1], drug targeting [2], biosensor [3] and biomedicine [4]. The prominent merit of magnetic microspheres lies in the fast and cost-efficient separation by applying an external magnetic field. Traditionally, magnetic microspheres were fabricated conveniently by monomer polymerization in the presence of magnetic particles [5], [6], [7] and magnetic fillers are randomly dispersed in the polymer matrix.

Recently, interest was arisen on polymer microspheres with armored inorganic particles, because the armored nanoparticles can endow the composites with some special properties [8], [9], [10], [11], [12]. For example, microspheres with armored TiO2 present excellent photovoltage properties [9] and photocatalytic performance [10], [11]. Armored ZnS endows polymer microspheres with special optical property [12]. For particles-armored microspheres, post-surface reaction [10], [13] and layer-by-layer self-assembly [8], [14] have been considered as most feasible ways, although both of them include complicated process.

Recently, self-assembly of solid particles at the liquid–liquid interface to stabilize so-called Pickering emulsion has been well documented [15], [16], [17], [18]. In Pickering emulsion, solid particles are absorbed irreversibly on the monomer–water interface and act as effective stabilizers during polymerization. After polymerization, the particles are captured on the surface of polymer microspheres. This technique offers a straightforward pathway for the fabrication of particles-armored microspheres [19], [20], [21], [22], [23], [24] and possesses many advantages over other polymerization methods. The nanoparticles with a suitable wettability presents excellent stabilizing effect to emulsion, eliminating the need of any conventional surfactants. The nanoparticles act as both a stabilizer during polymerization and become a component of prepared microspheres. There are also no by-products produced in the process, and no unwanted contaminants are left in the polymer [21]. A variety of particles-armored microspheres, such as PS/SiO2 microspheres [22], polyaniline microspheres [23] and PS/Fe3O4 microspheres [24], have been documented.

Herein, we present a facile one-step Pickering emulsion polymerization to fabricate polymer microspheres with encapsulated Fe3O4 and armored inorganic particles. Inorganic particles acted as the solely stabilizer of Pickering emulsion during polymerization and armored on the surface of prepared microspheres after polymerization. Large amount of Fe3O4 was encapsulated within the microspheres. The encapsulated Fe3O4 can endow the microspheres with high magnetism and the armored nanoparticles can endow the composites with special property, as verified by our preliminary catalytic experiment.

Section snippets

Materials

FeCl3·6H2O, FeSO4·7H2O, NaOH, H2O2 were received from Xi’an Chemical Factory (China). Styrene (St) and divinylbenzne (DVB) were supplied by Shanghai Shanpu Co., Ltd. (China) and treated with 1 M NaOH solutions to remove the inhibitor. Cetyltrimethylammonium bromide (CTAB), oleic acid and azobisisobutyronitrile (AIBN) were obtained from Beijing Chemical Reagent Co., Ltd. (China). 1,10-Phenanthroline, rhodamine B and ascorbic acid were received from Sinopharm Chemical Reagent Co., Ltd. (China).

Preparation and modification of Fe3O4 nanoparticles

Results and discussions

The preparation, as illustrated as Fig. 1, was a combination of Pickering emulsion polymerization and suspension polymerization. CTAB-Fe3O4 was employed as Pickering stabilizer and oleic-Fe3O4 was encapsulated in the Pickering droplet (Fig. 1b). After polymerization, microspheres with both encapsulated and armored Fe3O4 was formed (Fig. 1c).

Conclusions

In summary, magnetic PS microspheres with encapsulated Fe3O4 and armored Fe3O4 were fabricated by a facile Pickering emulsion polymerization. The method combines the advantages of suspension polymerization and Pickering emulsion polymerization. (1) The method is process-simplified, as only one step included in the fabrication. (2) Solid particles were employed as the solely stabilizer, which avoid the detrimental effects of surfactant or dispersant to the products. (3) High encapsulation

Acknowledgements

The supports by NWPU Foundation for Fundamental Research (NWPU-JC20120250), National Nature Science Foundation of China (51173147 and 51173146) and graduate stating seed fund of NWPU (Z201216) are highly appreciated.

References (38)

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