MnO 2 /Cr 2 O 3 /PANI nanocomposites prepared by in situ oxidation polymerization method: Optical and electrical behaviors Mohammad Reza Mohammad Shafiee, 1 Ahmad Sattari, 2 Mahboubeh Kargar , 3 Majid Ghashang 1 1 Department of Chemistry, Najafabad Branch, Islamic Azad University, P.O. Box 517, Najafabad, Iran 2 Department of Chemistry, University of Zanjan, P.O. Box 45195-313, Zanjan, Iran 3 Department of Physics, Najafabad Branch, Islamic Azad University, P.O. Box 517, Najafabad, Iran Correspondence to: M. Kargar (mahboubehkargar@yahoo.com) ABSTRACT: Metal oxide–polyaniline (PANI) nanocomposite with spherical morphologies were prepared in a one-pot oxidation– reduction method via various salts as reactive oxidants. Aniline monomers polymerize as a shell on the surface of one-pot prepared metal oxides, when the aqueous solutions of aniline, a free-radical oxidant, and/or a metallic salt were exposed together. The particle size and morphology of as-prepared narrowly dispersed PANI nanocomposites were revealed by field emission scanning electron microscope images. Fourier transform infrared spectra of nanocomposites indicate that the PANI exists in the emeraldine form. The ultraviolet– visible analysis not only shows PANI is in the emeraldine form, but also indicates modified optical properties of PANI in the composite form. The hypsochromic shift of the n–π* and polaron transitions of PANI reveals the incorporation of PANI by metal oxides. The direct current (dc) electrical conductivity (σ) of as-prepared nanocomposites was measured by a four-probe method in the room tem- perature. Compared to PANI nanoparticles, the electrical conductivity of the composites increased with the presence of metal oxides in the nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 136, 47219. KEYWORDS: dc electrical conductivity; in situ polymerization; metal oxide–PANI nanocomposite; optical properties Received 1 February 2018; accepted 14 September 2018 DOI: 10.1002/app.47219 INTRODUCTION In recent years, because of growing demand for low cost, high- performance, eco-friendliness, and lifetime materials used in many applications such as catalysts, transistors, sensors, and actuators, innovative metal oxide embedded polymeric materials and structures have attracted great interest. 1–3 The challenge is to balance conductivity, kinetics, diffusion, capacity, durability, and possibility within a manufactured apparatus. The combined elec- tric conductive polymers and metal oxide structures have attracted great interest because they excel in terms of some of the aforementioned challenges. 4,5 Then, as-mentioned unique proper- ties of these materials arise from a combination of one or more inorganic nanoparticles with a polymer up to almost molecular level, so that some properties of the latter can be modified by the former and provide the oncoming unique qualities. 6,7 Electric conductive polymers [e.g., polyacetylene, polythiophene, polypyrrole, and polyaniline (PANI)] have been considered as the most promising candidate for fabrication of these composite materials for many years. 8 Among them, PANI became the point of convergence for fabrication of new materials used in industrial devices because of high conductivity, high doping/dedoping rate during charge/discharge process, environmental stability, good thermal stability, rather simple synthesis, and especially in doped state, high resistance against common solvents. 9,10 Although PANI has an intrinsic capability to conduct electric currents without the addition of any conductive (inorganic) substances, its electronic and electrocatalytic activity is strongly affected by the pH value of solution, and is strictly limited at higher pH. 11 Thus, electrocatalytic activity in neutral or basic aqueous solution improved when PANI mixed, doped, or encapsulated by metals or metal oxides. 12,13 PANI-metal/metal oxide nanoparticle com- posites reportedly show enhanced sensing and catalytic capabili- ties, as compared to those of pure PANI. 14 Among the various materials studied so far, such as TiO 2 , ZnO, Fe 2 O 3 , CeO 2 , and rhenium oxides, manganese, and chromium oxides have been considered to be the most promising candidate in view of its low cost, environmentally friendly nature and especially its high theo- retical capacity. 15,16 More importantly, manganese oxides have long been known as materials of technological importance for catalytic, sensing, and electrochemical applications. However, these metal oxides exhibit a much lower electrochemical capaci- tance compared to another oxidation state. Thus, the challenge © 2018 Wiley Periodicals, Inc. 47219 (1 of 7) J. APPL. POLYM. SCI. 2018, DOI: 10.1002/APP.47219