# Removal of Cochineal Dye Color through Atmospheric Pressure Plasma Discharge Jet
## 1 Introduction  
The application of synthetic dyes in textile and painting industries is increasing [1, 2]. However, these chemical compounds produce highly polluting effluents in water bodies [3, 4, 5], which poses a significant environmental concern. The scientific community is exploring new methods for degrading and bleaching effluents. An alternative approach involves the use of organic dyes; however, it is important to note that the dyeing process with natural dyes also generates pollutants and textile effluents that come from the chemical compounds used in their processing and the coloring itself [6, 7, 8, 9, 10]. The removal of textile effluent dyes using conventional methods is challenging and adversely impacts the flora and fauna of aquatic environments [4, 5]. Cochineal dyes, derived from the adult female cochineal insect (Dactyllopius [PERSON]), are widely utilized in various industries, including textiles, food, and cosmetics [10]. The primary component of cochineal dye is carminic acid, an anthraquinone-7-glucopyranosyl-3,5,6,8-tetrahydrooxy-1-methyl-2-carboxylic acid, which is classified as an anthraquinone. The chemical formula of cochineal dye is C\({}_{22}\)H\({}_{20}\)O\({}_{13}\)[9, 11, 12, 13]. In Peru, cochineal dye is readily available and cost-effective, making it highly valued in the artisanaltextile industry for coloring natural fibers in the production of crafts such as blankets and ponchos. Its vibrant color intensity and resistance to wear are among the reasons why it is the preferred choice for fabric production [11]. Among the various techniques for removing environmental contaminants, those that generate reactive species through advanced oxidation processes (POA) are particularly noteworthy [14; 15]. One such technique that has received attention is the use of atmospheric-pressure plasma jets (APPJ) to generate reactive species [15; 16]. This method is cost-effective, versatile, and scalable. Plasmas can be classified into two categories based on the temperature reached during generation: high- and low-temperature plasma [17]. The APPJ technique falls under the latter category, where ionized gas is maintained at room temperature [18; 19; 20; 21; 22]. The APPJ technique produces a variety of reactive species, including positive and negative ions, meta-stable atoms, free radicals, electrons, electric field, and photons [17; 18]. The reactive species generated by APPJ discharge can be characterized by analyzing the spectral lines of the emitted light using optical emission spectroscopy [23; 24; 25]. The transport and interaction of these reactive species with different media, such as air, liquid, and solid, result in the formation of three types of species: primary, secondary, and tertiary [18]. In the research conducted, the APPJ discharge technique was employed with air as the working gas to generate reactive oxygen (ROS) and nitrogen (RNS) species [18; 26; 27]. The primary reactive species are generated when the working gas ionizes, and accelerated electrons collide with neutral particles, producing electrons (e\({}^{-}\)), ionized gases (M\({}^{+}\)), excited gases (M\({}^{*}\)), such as atomic N, O, and H [18; 26]. When the primary reactive species interact with the air, they give rise to secondary reactive species like NO, NO\({}_{2}\), and 0\({}_{3}\)[18; 26]. The interaction of these secondary reactive species with the dye solution results in the generation of tertiary reactive species, such as long-lived O\({}_{3}\), H\({}_{2}\)O\({}_{2}\), NO\({}_{3}\)\({}^{-}\), and NO\({}_{2}\)\({}^{-}\)[18]. Some of these reactive species like NO\({}_{2}\), and NO\({}_{3}\) are soluble in water, immediately transforming into NO\({}_{3}\)\({}^{-}\) and NO\({}_{2}\)\({}^{-}\), potentially lowering the pH of the liquid through dissolution. These radicals play a crucial role in the degradation process of organic compounds [18; 19; 20; 27].