Many dyes are produced due to the waste and residuals of textile, dyeing, printing, rubber, paper, plastic, and related industries. Most dyes have aromatic rings in their structure making them highly toxic, non-biodegradable, carcinogenic, and mutagenic to the human body and aquatic animals (Yaman & Gündüz 2015). Meanwhile, in terms of dye production, the most important industries are usually the textile and dyeing industries (Somayajula et al. 2012).The textile industry is an important part of the industries of developing countries (Aksakal & Ucun 2010). About one-fifth of the total dye production in the textile industry is transferred to the environment through wastewater (Chládková et al. 2015). Dyes are classified into three main categories: anionic (direct, acidic and reactive), cationic (all primary colors), and non-ionic (dispersed colors) (Mahmoud et al. 2016). Azoic dyes are the largest group of dyes used for textile dyeing and other industrial applications (Mate & Pathade 2012). Dyes are chemical compounds that are important for a variety of reasons, including reduced light permeability and disrupted photosynthesis in water sources. Aesthetically, these compounds also negatively affect water quality and cause allergies, dermatitis, skin irritation, cancer, and genetic mutations in humans (Mahmoud et al. 2013). Reactive red 195 contains an active group consisting of an aromatic heterocyclic ring containing fluoride or chloride ions (Tahir et al. 2016). This dye is commonly used for dyeing cellulose fabrics and printing on fabric textures (Birmole et al. 2019).
Many aromatic color rings can affect the residues of various substances that are mutagenic, non-biodegradable, carcinogenic, and toxic to humans. Traditional methods cannot easily eliminate colors (Clavijo & Osma 2019). Thus, the removal of dye from industrial wastewater for environmental safety is challenging (Rani et al. 2017). Azo RR 195 dye is one of the dyes that includes the reaction group and is used in industries (Raval, Shah, Ladha, et al. 2016). There are various methods introduced as water treatment, such as Fenton, flocculation and adsorption processes, biological treatment, electrochemical techniques, ion exchange, advanced oxidation processes, and photocatalytic degradation under ultraviolet light (Rahimi et al. 2011). Advanced oxidation process or AOPs can be used in the decomposition of most organic and inorganic compounds without producing waste and problems with temperature and atmospheric pressure (Raval, Shah, & Shah 2016).
An important mediator produced in this process is reactive hydroxyl radicals (OH−) which can support primary oxidants such as TiO2, H2O2, UV, etc. In recent years, the use of magnetic nanoparticles as adsorbents to remove various contaminants has increased for RR 195 due to their important properties such as easy separation by an external magnetic field, easy synthesis, high surface area, and easy surface modification (Badruddoza et al. 2011). On the other hand, magnetic nanoparticles have challenges that prevent applications such as rapid aggregation, oxidation, etc. (Solisio & Aliakbarian 2017).
One way to mitigate such challenges is to use a composite shell structure to preserve the core and magnetic properties of FeNi3 as well as other iron alloys. When an insulating shell is used, nanocomposites in RR red 195uce the performance, stability and aggregation of nanoparticles and RR red 195 their toxicity (Zhu et al. 2018). On the other hand, the special properties of TiO2 as a cost-effective, non-toxic, and stable nanoparticle for a long time can be used as a catalyst to purify water and eliminate air pollution (Farooghi et al. 2018). Studies have shown that doping non-metals such as nitrogen (N), carbon (C), sulfur (S), and fluorine (F) with Tio2 would lower the recombination property and improve the photocatalytic activity of this particle under visible light with a wavelength greater than 400 nm (Ho et al. 2006). Among these non-metals, nitrogen is important due to its low ionization energy, similar size to oxygen, and high stability (Asahi et al. 2001). In the created structure, nitrogen ions replace oxygen ions in the Tio2 lattice and create a new energy level in the Tio2 bond gap, reducing the electron-hole recombination property (Huang et al. 2007). The process of TiO2 oxidation begins with the exchange of adsorption and diffusion (Lu et al. 2011). The photocatalytic limitations of TiO2 are due to the small surface area and low adsorption properties. Formation of different composites and hybrids can cover these limitations thus enhancing their efficiency and reverse degradation (Liu et al. 2005). In general, TiO2 interacts with metal ions in oxidation radicals to reduce oxidation and improve the light absorption spectrum. In addition, metal ions help reduce electron hole recombination by trapping electrons (Nasseh, Taghavi, et al. 2019). In addition, as shown in our previous studies (Khodadadi et al. 2019), the significant degradation efficiencies of organic pollutants using Fe-Ni3/TiO2 indicate the good potential of this technique as a real wastewater treatment system of an oil refinery. The results revealed that the combination of iron with Ni3 can turn it into a photocatalyst (Nasseh et al. 2018). In the present paper, FeNi3 magnetic nanoparticles have been fabricated using nickel and iron salts (Eslami et al. 2016; Nasseri & Sadeghzadeh 2013) and N-dopped in the Fe-Ni3/TiO2 synthesized structure. Its photocatalytic activity to remove RR 195 from aqueous solution in the presence of visible light has been examined (Kamranifar et al. 2018; Nasseh, Barikbin, et al. 2019).