During the past few decades, metal oxide nanoparticles (MNPs) have been considered as a very important class of nanostructured materials not only because of their attractive, unique and excellent physical and chemical properties, but also because of their wide application in catalysis, especially when combined with other metal nanoparticles or polymer [1]. The utilization of MNPs has a number of advantages, despite this, due to their high surface energy and thermodynamic instability, MNPs tend to aggregate and lose their intrinsic properties [2]. Therefore, for improving the properties and maintaining their stability, it is necessary to add these nanoparticles into polymeric support (solid), carbon compounds and biological components [1, 3]. It is known that heterogeneous catalysis based on metal oxide has attracted considerable research because it is important not only in the chemical, refining and pharmaceutical industries, but also in other important and strategic applications such as the removal of hazardous gases and volatile organic substances, which are mostly considered hot topics in environmental pollution control [4, 5].
Among the various support materials, all conducting polymers were found to be appropriate because of inter-molecular forces, in which they act like electro-active links between metal nanoparticles [6]. The polymers have proven to be effective hosts, preventing the formation of nanoparticles by modulating nucleation and thus serving as surface coatings or stabilizers. The PANI has drawn the most interest among these conducting polymers because of its facile synthesize and affordable price [7], substantial electrical permeability [8], biological compatibility, ecological sustainability and distinctive π-conjugated structure resulting in remarkable electrochemical performance [9].
CuO/GO nanocomposites were synthesized by hydrothermal self-assembly process to increase the catalytic activity in reduction of nitro-aromatics reported by Zhang et. al. [10]. Liu et. al., reported that Fe3O4/PEG2000/Cu nanocomposites showed best anti-oxidant activeness against 2,2-diphenyl-1-picrylhydrazyl (DPPH) [11]. Agobi et. al., reported that fabrication of PVP/Cu/GO were synthesized by electrochemical deposition on fluorine dopped TiO2 substrate. This has been demonstrated that GO loading affects nanocomposites' optical band gaps to decrease from 3.51–2.02 eV [12]. Among the above mentioned composite materials, the nanocomposite of conductive polymers and metal oxides are essential due to its diverse surface structure, cost-effective and high sensitivity and selectivity [13].
PANI, a conducting polymer, has been employed in different applications such as sensors [14], supportive catalysts [15], water purifications [16], protection against corrosion in organic coverings [17], electrical appliances [18] and power devices because of its good electrical conductivity, high ecological oxygen moisture absorption and ease of manufacturing [19, 20]. In a recent research, PANI is doped with reduced graphene oxide (RGO). The conversion efficiency of PANI/RGO at optimal concentration was stated to be just 1.27% lower than the typical Pt counter electrode-based DSSC [21]. CuO nanoparticles have a significantly larger surface area compared to bulk CuO materials due to their small size, and it can be beneficial for various applications, such as catalysis and sensing. CuO incorporated into PANI to enhance its magnetic traits, catalytic and directed adsorption sites because of empty d-orbital in CuO [22]. The recent study shows that hybridization of PANI and CuO nanoparticles is thought to provide more effective nanofluid behavior than a mono nanofluid system [23].
The catalytic activity of CuO/polyaniline nanocomposite in the reduction of organic dyes and nitro compound in the presence of (NaBH4)/H2O2 aqueous solution was also investigated [24]. Aquatic organisms are negatively impacted by the presence of poisonous dye molecules in water and its reduction of sunlight penetration [25]. Therefore, it is crucial to properly treat wastewater containing dye before discharging it into neighboring bodies of water. The chemical structure of dye molecules gives it considerable molecular weight stability and makes it difficult to degrade into a non-toxic component [26]. A significant issue nowadays is industrial effluent that contains hazardous colors, heavy metal ions, and nitroarenes.
The p-nitrophenol (C6H5NO3) is a well-known phenolic raw material has been listed as a main organic contaminant with possible carcinogenicity in petrochemical synthesis such as drugs (painkillers), insecticides, plasticizing agents, fungicides and genuine leather. For p-nitrophenol, the approximate absorption range in chemical/organic waste from industry is 190 mg/L [27]. The non-biodegradable and harmful azo dyes found in water, including RB-5, MB, RB, CV, EY, MR, EBT and MO have been recognized as a serious issue that poses a risk to both the health of people and surroundings. The cationic dye MB (C16H18N3ClS) is frequently present in textile effluent, it makes a rigid solution with H2O and extremely soluble in it (43.6 g/L) soluble at 25°C [28].
The focus of research has been shifted to the development of energy-efficient methods for the degradation of this type of wastewater. Methyl orange, also known as sodium 4-[(4-dimethylamino) phenyldiazenyl] benzenesulfonate, is a popular azo dye that functions in aqueous solutions as both a dye and an acid-base indicator [29]. Azo dye adsorption process on niobium electrodeposited nanostructured polyaniline films investigated by electrochemical impedance spectroscopy [29, 30]. Some of the dangerous chemicals that leads to various health issues in people are organic dyes like CR, MG, MB, Rh B, and CV. Rhodamine Blue (Rh B) is a water-soluble dye that may be risky to individuals if it gets into the body since it is very poisonous, can cause cancer, and can itch the skin and eyes [31]. Various techniques such as degradation of photocatalyst, splitting membrane, combustion, absorption, exchange of ions and electrochemical techniques have been used to remove harmful organic dyes [32–34]. Gnanasekaran and co-workers febricated a composites of polyaniline and TiO2 from an saturated solution of MO and MB [35].
The present focus is to synthesize nanocomposites by incorporating copper oxide nanoparticles into polyaniline. The size of nanoparticles is controlled by using oxalic acid as capping agent. The catalytic activity of the composites is evaluated through degradation of organic dye under UV irradiation is performed. Structural and morphological details of the synthesized products are gained by using several characterization techniques such as XRD, SEM, EDX and FTIR.
Based on the literature, the interface of CuO and PANI in hybrid form and the catalytic activity of resulting nanoparticles and nanocomposites in the degradation and reduction of dyes and nitro-compounds have not been studied. In this work, CuO and CuO/PANI were synthesized by sol-gel method and in-situ polymerization method. The catalytic reduction/ degradation of CuO and CuO/PANI were performed by using MR, MB, MO, CV, EY, EBT, Rh B, RB-5, 4-NP, 2-NP, 2,4-DNP and PA in the presence of NaBH4 and H2O2. Pseudo-first-order reaction, with kapp, reduction time, % reduction, reduced concentration and with half-life also not studied with CuO and CuO/PANI. Impressively, in this work the synthesized CuO showed highly enhanced catalytic activity by degradation of dyes due to large band gap while CuO/PANI showed highly enhanced catalytic activity by nitro-compounds due to large surface area and more active sites.