Polyaniline/MnTiO₃ Nanocomposites: Fabrication, Characterization and Optical band gap

Introduction

PANI as a typical conducting polymer has recently received a great deal of attention. PANI is one of the most promising electrically conducting polymers due to its unique electrical and electrochemical properties, easy polymerization, high environmental stability and low cost of monomer^1-3,and its wide applications in microelectronic devices, diodes, light weight batteries, sensors, super capacitors, microwave absorption, corrosion inhibition^4-8, etc.The properties of PANI can be tailored by changing its oxidation states, dopants or through blending it with other organic, polymeric or inorganic nanosized semi conducting particles.To obtain materialswith synergetic advantage between PANI and inorganic NPs, various composites of PANI with inorganic NPs such as CeO₂, TiO₂, ZrO₂, Fe₂O₃, and Fe₃O₄ are reported.The titanium-based oxides, such as barium titanate ⁹, cadmium titanate ¹⁰, bismuthtitanate ¹¹, cobalt titanate ¹² and lead titanate ¹³, can be referred to as a‘smart’familyowing to their excellent dielectric, piezoelectric, pyroelectric and photostrictiveproperties.Manganese ion in oxides is a well-known activator used mainly for producing tunablesolid-state laser media, holographic recording and optical data storage as well as thermoluminescentdetectors ^14–16.Recently, manganese titanate (MnTiO₃) has attracted muchattention for its strong absorption in the visible region which may be propitious to theutilisation of solar energy ¹⁷ and photocatalysis ¹⁸.Manganese titanate, pyrophanite MnTiO₃, is a humidity sensing material with excellent sensitivity, good selectivity, low temperature coefficient near zero and goodstability.The pyrophanite MnTiO₃ has also been studied for magnetic and photoelectrochemical properties ^19–21.Physical properties (mechanical, thermal, etc.) of polymers can be improved by adding inorganic materials to polymer matrixes. In this study, PANI/MnTiO₃NCs with two (10, 20wt%) contents loading of MnTiO₃ were prepared,and the whole procedure and structural characterization of PANI/MnTiO₃NCs phases have been investigated by SEM, EDX, DRS, and Zeta Potential.

Materials and Methods

Manganeseacetylacetonate, tetra-n-butyltitanate, stearic acid,potassiumiodateandsulfuric acid used in experimentswere all of analytical grade reagents.The composition of the sample was estimated using a model Oxford of Energy dispersive analysis of X-rays (EDX).The UV-vis diffused reflectance spectra (DRS) were obtained from UV-vis Scincom 4100 spectrometer. The SEM pictures were recorded with KYKY Model EM 3200 instrument at the accelerating voltage of 25 kV. Streaming zeta potential measurements were carried outon a ZetaCAD instrument (France).

Synthesis of MnTiO₃ Nanoparticles

PANI/MnTiO₃composites were prepared along a synthetic procedure. MnTiO₃NPs were prepared through a modified wet-chemistry synthesismethod which is described in the literature ²². In this procedure, a fixed amount of manganeseacetylacetonate was added to the melted stearic acid and dissolved. Then, stoichiometric tetra-n-butyltitanate was added to the solution, stirred to form sol, naturally cooled down to room temperature, and was dried to obtain dried gel. Finally, the gel was calcined at 900°C in air to obtain MnTiO₃NPs.

Synthesis of PANI/MnTiO₃ Nanocomposite

In order to prepare ofPANI/MnTiO₃NCs,the essential substances for preparation of PANI were initiallyadded. To prepare PANI, 1g potassium iodate was added to 100 ml of sulfuric acid (1 M) and then uniform solution was resulted by using magnetic mixer. After 30 min, the sufficient amount of ultrasonicated MnTiO₃ NPs was added to solution to prepare 10 and 20 persent of PANI/ MnTiO₃NCs and after 20 min, 1 ml fresh distilled aniline monomer was added to stirred aqueous solution. The reaction was carried out for 5h at room temperature. Then the obtained product was dried at temperature about 60°C in oven for 24h²³.Finally after heat-treatment from 60°C to 300°C for 2h, the PANI/MnTiO₃NCs were obtained.The whole procedure and structural characterization of PANI/MnTiO₃NCs phases have been investigated by SEM, EDX, PSD, DRS, and Zeta Potential.

Results and Discussion

Drsstudy

The absorption coefficient and optical band gap of a material are two important parameters by which the optical characteristics and its practical applications in various fields are judged.Fig.1. shows the DRS patterns of pure MnTiO₃ and the PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading. In fig.1a. a sharp absorption peak is observed around 325 nm, which indicates the optical band gap attributed to the O^2-→Ti⁴⁺ ‏charge-transferinteraction¹⁷. Also in the PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading a sharp absorption peak are observed around 345 and 350 nm. For direct b and gap determination, plot of versus  is presented in Fig . 2. Band gap value was obtained by extrapolating the straight portion of the graph on h axis at =0, as indicated by the solid line in Fig.2.The value of direct band gap for MnTiO₃and the PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading using the Taucmodelcame out to be 1.15 Ev, 1.35 and 1.25. Band gap analysis indicates semiconducting behavior of the NCs.

Figure1: DRS patterns of (a) MnTiO3  nanopowders (b) PANI/ MnTiO3 nanocomposite with MnTiO3 content of (10 wt%) and (c) (20 wt%)  Click here to View figure

 

Figure2: Band gap patterns of (a) MnTiO3  nanopowders (b) PANI/ MnTiO3 nanocomposite with MnTiO3 content of (10 wt%) and (c) (20 wt%)  Click here to View figure

 

Morphology of samples

Fig.3. shows the scanning electron micrograph of pure MnTiO₃ (Fig.3a.)) and the PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading, respectively (Fig.3(b–c).). The particles have agglomerated graining structure.In the scanning electron micrograph of the NCs, with the increase of MnTiO₃ content, the agglomeration become more appreciable and display some connections in some regions. SEM images reveal a homogeneous dispersion of  MnTiO₃NPs in the PANI matrix.EDX patterns of pure MnTiO₃ (Fig.4(a).) and the PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading, respectively are shown in Fig. 4b. EDX patterns of pure MnTiO₃ (Fig .4(a).)shows separate peaks of Manganese(Mn), Titanium (Ti), and Oxygen, which compositional analysis by EDX confirms that the MnTiO₃nanopowders were obtained. EDX  pattern  of  PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading,are  displayed  in  Fig.4b.  which shows  separate  peaks  of  Manganese(Mn), Titanium (Ti), Oxygen, Carbon and Nitrogen (N),  confirm  that  the  sample  is  of  desired  composition  having both the PANI and MnTiO₃ nanoparticles. The results show that as the MnTiO₃ content increases in 10 and 20 weight fractions, the intensity of MnTiO₃ crystalline peaks gradually increases.

Figure3: SEM images of (a) MnTiO3  nanopowders (b) PANI/ MnTiO3 nanocomposite with MnTiO3 content of (10 wt%) and (c) (20 wt%)  Click here to View figure

 

Figure4: EDX patterns of (a) MnTiO3  nanopowders (b) PANI/ MnTiO3 nanocomposite with MnTiO3 content of (10 wt%) and (c) (20 wt%)  Click here to View figure

 

Particle Size Distribution (PSD)

Particle size distribution analysis (PSD) is a measurement designed to determine information about the size and range of a set of particles in a representative material. Particle size was determined using dynamic light scattering measurements. Fig.5. shows the size distribution histogram of pure MnTiO₃. The Zeta sizer software uses algorithms to extract the decay rates for a number of size classes to produce a size distribution. The X-axis shows a distribution of size classes, whereas the Y-axis shows the relative intensity of the scattered light. The particle size distribution of the pure MnTiO₃ had a wide distribution (three peaks); therefore, its distribution is very heterogeneous. The particle size distribution of MnTiO₃ for 88.2% of the particles were 85 nm, 6.4% were 250 nm, and 5.4% were 1088 nm.

Figure5: PSD curves of MnTiO3  Click here to View figure

 

Zeta Potential Measurements

Fig.6. shows the zeta potential measurements obtained for pure MnTiO₃ (Fig.6(a).) and the PANI/ MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading. Initially, MnTiO₃ had an average ζ of -9.75mV and the PANI/ MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs loading had an average ζ of -20 and -50.81 mV. With respect to Fig. 6.Zeta potential indicated that the fabricated PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs were increased with 34 and 67% efficiency respectively.

Figure6: Zeta potential patterns of (a) MnTiO3  nanopowders (b) PANI/ MnTiO3 nanocomposite with MnTiO3 content of (10 wt%) and (c) (20 wt%)  Click here to View figure

 

Conclusion

We have successfully synthesized PANI/MnTiO₃NCs with two (10, 20wt%) contents loading of MnTiO₃using wet chemical method. The whole procedure and structural characterization of PANI/MnTiO₃NCs phases have been investigated by SEM, EDX, DRS, and Zeta Potential.The particle size distribution of MnTiO₃ for 88.2% of the particles were 85 nm, 6.4% were 250nm, and 5.4% were 1088 nm. Zeta potential indicated that the fabricated PANI/MnTiO₃NCs with 10 and 20wt% of MnTiO₃NPs were increased with 34 and 67% efficiency respectively.

Acknowledgement

The authors express gratitude and thanks to Islamic Azad University and the Iranian Nanotechnology Initiative for supporting this study.

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