Rational design of a polypyrrole-based competent bifunctional magnetic nanocatalyst

Abstract

The combination of conducting polymers with semiconductors for the fabrication of organic/inorganic hybrid nanocatalysts is one of the most promising research areas for many applications. In this work, the synthesized nanocomposite combines several advantages such as the photoresponse shift from the UV region toward visible light by narrowing the band gap of the semiconductor, magnetic separation ability and dual applications including the catalytic reduction of p-nitrophenol (PNP) and the photocatalytic degradation of methylene blue (MB) dye. In addition to the core magnetite nanoparticles (NPs), the synthesized nanocomposite contains polypyrrole (PPY) and TiO₂ shells that are decorated with silver metal NPs to prevent electron-hole recombination and to enhance the catalytic performance. Indeed, the catalytic PNP reduction experiments reveal that the synthesized nanocomposite exhibits significantly high catalytic activity with a rate constant of 0.1169 min^-1. Moreover, the photocatalytic experiments show that the synthesized nanophotocatalyst has a boosting effect toward MB dye degradation under normal daytime visible light irradiation with a rate constant of 6.38 × 10^-2 min^-1. The synergetic effect between silver NPs, PPY and TiO₂ is thought to play a fundamental role in enhancing the photocatalytic activity.

Scheme 1. The formation mechanism of MTPS nanocomposite.

Fig. 1. XRD patterns of the prepared Fe₃O₄ NPs (A), Fe₃O₄@TiO₂ nanospheres (B), and MTPS nanocomposite (C).

Fig. 2. FTIR spectra of the Fe₃O₄ NPs (A), and Fe₃O₄@TiO₂ nanospheres (B), Fe₃O₄@TiO₂/PPY nanocomposite (C), and MTPS nanocomposite (D).

Fig. 3. TEM images of (A) Fe₃O₄ NPs, (B) Fe₃O₄@TiO₂ nanospheres, (C) Fe₃O₄@TiO₂/PPY nanocomposite, and (D) MTPS nanocomposite.

Fig. 4. (A) SEM and (B) EDX of MTPS nanocomposite.

Fig. 5. Magnetic hysteresis loop (M − H) of Fe₃O₄@TiO₂ and MTPS nanocomposite.

Fig. 6. UV-vis spectra for the reduction of PNP using 1 mg MTPS nanocatalyst.

Fig. 7. Reusability of 1 mg of MTPS nanocatalyst for the PNP reduction.

Fig. 8. The separation technique of the heterogeneous MTPS nanocatalyst.

Fig. 9. Absorbance change during PNP reduction using different precursor materials as nanocatalysts.

Fig. 10. Time-resolved photocatalytic spectra of MB dye (4 mg L⁻¹) upon the treatment with 0.04 g of MTPS nanophotocatalyst under the normal day light.

Scheme 2. Mechanism of MTPS nanocomposite to enhance the photocatalytic activity under visible light.

Scheme 3. A proposed mechanism for MB dye degradation using MTPS nanocomposite as a nanophotocatalyst under the normal day visible light.