In situ oxidative polymerization of aniline in the presence of manganese dioxide and preparation of polyaniline/MnO2 nanocomposite

SEM measurements

Figure  ¹ shows the scanning electron microscopy (SEM) image of pure polyaniline. As can be seen from this picture, the pores of PANI are formed and the smooth surface is determined. It shows that the blank PANI is constructed with rodlike aggregates. PANI chains are prepared in acidic media and exist in the form of polycations. The strong interactions between charged PANI chains [ ¹⁹ ] facilitate the formation of nanorods.

Figure 1

Findings showed that PANI/MnO ₂ nanocomposite comprises platelike particles, which are about 50 nm in thickness (Figure  ² ). The morphology of the product after polyaniline being intercalated between manganese oxide layers is maintained. In addition, the incorporation of MnO ₂ nanoparticles would effectively avoid the entanglement of PANI chains due to repulsion between charged MnO ₂ nanoparticles in an acidic media. The SEM image of PANI/MnO ₂ nanocomposite reveals that the nanocomposite is composed of many nanoparticles which are connected to each other resulting in a porous structure.

Figure 2

FT-IR characterization

Structural information of the synthesized PANI/MnO ₂ nanocomposite was identified by Fourier transform infrared (FT-IR) spectroscopy. Figure  ³ shows the FT-IR spectra of PANI. It can be seen in the spectra the range of 1,600 to 1,000 cm ⁻¹ which comes from the vibrational and rotational bands of the functional groups in PANI. The bands at 1,568 and 1,495 cm ⁻¹ can be assigned to C=C stretching of quinoid and benzenoid rings; the C-N stretchings for the benzenoid unit appear at 1,297 and 1,239 cm ⁻¹ , respectively; the peak at 1,144 cm ⁻¹ can be attributed to the in-plane bending vibration of aromatic C-H. The weak band at 3,320 cm ⁻¹ is attributed to N-H stretching.

Figure 3

The FT-IR spectra obtained from PANI/MnO ₂ nanocomposite showed characteristic peaks of PANI (Figure  ⁴ ). For example, vibrational peaks centered at 1,565 and 1,468 cm ⁻¹ are attributed to the stretching peaks of quinoid and benzenoid deformations of PANI. We also observed C-N stretching peaks at 1,238 and 1,300 cm ⁻¹ and C-H bending of protonated PANI at 1,124 cm ⁻¹ . The band in the regions over 400 cm ⁻¹ can be assigned to Mn-O stretching vibrations [ ²⁰ ]. FT-IR spectra of the PANI/MnO ₂ nanocomposite are similar to those of PANI, but the bands' characteristic of polymer backbone at 1,500 and 1,600 cm ⁻¹ are shifted to higher values after annealing, indicating deprotonation. The peak at 1,195 cm ⁻¹ is suppressed after annealing to a greater extent for PANI compared to that for the nanocomposites, indicating a higher extent of deprotonation in pure PANI compared to nanocomposites. The results of FT-IR spectra confirm the presence of both components in the nanocomposite.

Figure 4

Instrumentation

The morphology of the samples was studied using a scanning electron microscope XI-300 model Philips (Amsterdam, The Netherlands). Also, FT-IR spectra were recorded by PerkinElmer Spectrum 100 (Branford, CT, USA). KBr pellets were used to prepare samples, with a sweeping range of 400 to 4,000 cm ⁻¹ at a 4-cm ⁻¹ resolution.

Synthesis of PANI/MnO2 nanocomposite

First, 30 ml of 1 M HCl solution was prepared, and 0.5 g MnO ₂ and 0.46-ml monomer of aniline were added to the solution simultaneously. As soon as they were added, it obtained a dark color. After 30 min of sonication in an ice bath, the temperature of the solution decreased to 0°C until polymerization was stopped. After filtering, the precipitates were washed with deionized water and ethanol (96%). The product was then dried at 60°C in an oven for 1 h.