**1. Introduction**

The development of nanomaterials has been a useful and important task during the last fifteen years. These nanomaterials have original multifunctionalities, which make them very helpful products in a variety of industries. The nanocomposites are classified into structural and functional materials. Structural nanocomposites focus on the improvement of mechanical properties due to the addition of nanoparticles, while for the functional ones,

**Citation:** Ahmad, M.N.; Nadeem, S.; Soltane, R.; Javed, M.; Iqbal, S.; Kanwal, Z.; Farid, M.F.; Rabea, S.; Elkaeed, E.B.; Aljazzar, S.O.; et al. Synthesis, Characterization, and Antibacterial Potential of Poly(*o*-anisidine)/BaSO4 Nanocomposites with Enhanced Electrical Conductivity. *Processes* **2022**, *10*, 1878. https://doi.org/ 10.3390/pr10091878

Academic Editors: Iliyan Ivanov and Stanimir Manolov

Received: 29 July 2022 Accepted: 14 September 2022 Published: 16 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the presence of nanoparticles adds extra functionalities to the polymer, such as electrical conductivity, special optical properties, antimicrobial features, and many more. The hybrid nanomaterials consist of organic–inorganic components, e.g., organic polymer matrix and inorganic filler, and have potential applications as antimicrobial agents, biocompatible materials, sensors, and electrical devices. Moreover, they are utilized as high-value coatings in gas separation, ultra- and nanofiltration, and corrosion prevention, as well as in artificial membranes [1–3]. In addition, they can be used as catalysts, toxic-compound adsorbents, biomaterials, and information display materials with specialized optical, magnetic, and electrical capabilities [4–6].

These nanomaterials offer unique properties due to the fact that their components have a different nature to prepare some tailor-made novel nanomaterials [7–10]. In particular, the composites made by adding multi-walled carbon nanotubes to thin layers of poly(3,4-ethylenedioxythophene) and poly(4-styrenesulfonate) exhibited intriguing characteristics regarding the interdependence of electrical properties towards the large temperature range [11]. Thus, the inorganic and organic species interact at a molecular level at the nanoscopic range. Similarly, Mt-PS-BZO-PANI hybrid composites showed valuable luminescence properties [12]. Moreover, polyurethane (PU) and poly(hydroxyethyl methacrylate) composited with poly(titanium oxide) showed excellent viscoelastic and thermophysical properties [13]. The ability of these organic–inorganic hybrid materials to blend the heterogeneous properties of inorganic–organic components in a single material is its key benefit. In recent years, nanomaterials have offered one of the most interesting developments in the subject of materials chemistry [14–16].

The conducting polymer is one of a new class of polymers that are being used for a variety of applications. The merging of different unique properties, such as the chemical, electrical, and electrochemical properties of these polymers, may cause them to be used in several scientific applications [17–20]. Polyaniline has the unique property to coordinate with metallic ions, which provides the multi-metallic system and also prepares the nanocomposite materials with some other species. Polyaniline and its derivatives have achieved considerable attention over the last few years due to their conducting properties. The electro-active characteristics of polyaniline films, in particular, have been determined useful for the development of batteries, electrochromic displays, and microelectronics devices. Poly(*o*-anisidine) exhibits some interesting and unique properties [21–24]. Poly(o-anisidine) was found to have greater solubility compared with polyaniline in some organic solvents as it has a low boiling point while maintaining its crystalline property. This is very important because this polyaniline derivative can be used in technological applications [25–29].

Polymeric nanocomposites are modern and superior composites that are obtained from nanoparticles and the polymeric matrix, in which NPs are covered by polymers; through this, a core-shell arrangement can be developed [30]. Due to the particular shape, chemical nature, and exceptional structure of polymers, nanoparticles can be spread in a polymer matrix in the best and unique shapes. As a result of covering nanoparticles and their functionalization, the Van der Waals forces among NPs become reduced and the distribution of NPs in the matrix is improved and amplified [31,32]. The importance of polymer nanocomposites lies in the fact that polymers are always preferred for the covering of nanoparticles. On the other hand, appropriate functional groups in polymer structures can be used as reaction sites to organize the one-pot synthesis of nanocomposites [33,34].

Polymeric materials can be extensively employed in industries because of their lightweight and their simplicity of preparation, in addition to their elastic properties. Nevertheless, these materials have several drawbacks, such as their small modulus as well as potency compared to ceramics and metals [35]. Thus, to improve the mechanical properties, a very useful and valuable approach can be the addition of fibers, platelets, particles, or whiskers into such polymeric materials as reinforcements. The polymeric materials are composited with other filler materials to tune the properties of the materials, such as the temperature resistance, impact opposition, mechanical strength, fire or flame resistance, gas permeability, conductivity, and microbial resistance [36].

Due to the addition of reinforcements or filler materials to a wide range of polymer resins, their unique properties have greatly been improved. This is a great example of polymer-matrix nanocomposites acting as eco-friendly systems. Furthermore, the latest information on nano-industries' nanomaterials showed complete and effective applications in the form of polymer nanocomposites and has been successfully reported [31,37]. Moreover, the barium sulfate has versatile applications and can be utilized as an antibacterial agent, a paint, a film, a fiber, and a luminescence material, and for photocatalysis [38–41]. Consequently, the versatile properties of barium-sulfate-nanocomposite materials proved their widespread applications in every field. Thus, there exists a big and wonderful demand for such hybrid materials. Generally, these hybrid materials, based on organic polymers, have many advantages, such as good processability, long-term stability, and wonderful optical, electronic, and catalytic as well as magnetic properties [42,43]. Thus, the resulting nanocomposites could offer numerous applications in different fields, for example, antibacterial, optoelectronics, electrical devices, sensors, etc. [44]. Moreover, barium-sulfate nanoparticles show antibacterial properties due to its small size, greater surface area, and high penetration power to inhibit the growth of bacteria [43]. The barium-sulfate nanoparticles not only exhibit the antimicrobial properties towards the nanocomposite but also control the electrical conductivity of the materials. Therefore, the antibacterial properties of BaSO4 nanoparticles as filler and conducting properties of the poly(*o*-anisidine) matrix were combined to obtain novel composite materials with bactericidal and conducting properties, and for biomedical and sensor applications.

## **2. Material and Methods**

For the present research work, all the chemicals, such as ammonium persulfate [(NH4)2S2O8], *o*-anisidine monomer as an oxidant, diaminodiphenylamine (DDPA), HCl/H2SO4, DI water, barium chloride, and ammonium sulfate, were procured from the Sigma Aldrich company (St. Louis, MI, USA). They were chemicals of the analytical and research grade, and they were utilized directly.
