# Novel ZIF-67@Bentonite (ZIF-67@BNT) Nanocomposite for Aqueous Methyl Orange Removal
## 1 Introduction  
Human activities with an ever-increasing introduction of pollutants continue to diminish the availability of clean water [1, 2]. Such aquatic pollution results from a range of inorganic and organic contaminants including heavy metals and dyes [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]. For example, the treatment of wastewater with dyes has been looked into to reduce the respective environmental concerns [2]. One such dye is methyl orange (MO). Its chemical structure is provided in Figure 1 and its IUPAC name is sodium-4-(4-dimethylamino phenyl di-azenyl) benzenesulfonate [6]. MO dye is also noted in several industrial discharges, thus prompting the need for an effective treatment for its removal from wastewater streams.  
Considering this, several techniques have been used for MO removal from wastewater, including photocatalysis and adsorption processes [8; 13; 14; 15; 16].  
Further, the adsorption capacity of a given adsorbent is contingent upon its inherent characteristics such as the specific surface area and surface functional groups [10]. Recently, there has been a surge of interest in novel materials known as metal organic frameworks (MOFs). MOFs have various types including zeolite imidazole framework-67 (ZIF-67). It comprises cobalt ions coordinated with imidazole ligands. This porous material is employed as an adsorbent for various treatments including wastewater treatment, and it is also used as catalyst [11; 12]. Researchers have shown that different ZIFs can adsorb dyes, including methylene blue (MB), methyl orange (MO), and rhodamine B (RB) [13; 14]. In one study, ZIF-67 with layered double hydroxide (ZIF-67@LDH) showed higher MO and MB removal compared to LDH-only systems [15]. Furthermore, several natural clay minerals have also been used for removing contaminants from the water phase [16] and the use of clay surface modification techniques to improve pollutant removal has also been reported [17; 18; 19]. Additionally, the response surface methodology (RSM) and artificial intelligence (AI)-based techniques have also been used for process optimization and environmental modeling [5; 20]. Further, various ZIF-67-based materials have been explored for the removal of different pollutants and adsorption studies [21; 22; 23; 24; 25; 26; 27; 28; 29; 30] and the aforementioned clay [17; 18; 19; 20] materials' application for water decontamination show promising results that can be further explored for the application of nanocomposites of ZIFs with clay material. With this impetus, this study looked into the application of novel ZIF-67@BNT for aqueous methyl orange adsorption, which offers a viable solution for the treatment of aqueous waste streams. In summary, the aforementioned applications of ZIFs and clay-based materials for water decontamination applications support that both materials can be used as adsorbents for water decontamination. Furthermore, the literature review also indicates that the nanocomposite ZIF-67@BNT has not been used for the removal of MO from aqueous streams. Considering this, the present work investigated the use of ZIF-67@BNT-based adsorption for the removal of aqueous phase MO under a varying set of process conditions. Additionally, RSM and AI-based modeling were also employed for process optimization purposes, and the respective details are provided in the sections below.