# Aminated Covalent Organic Polymers for Anionic Dye Adsorption in Aqueous Systems
## 1 Introduction  
Wastewaters containing dyes that are discharged from textile, paper, food, pharmaceutical, and other chemical manufacturing processes are among the major causes of environmental pollution [1, 2]. Annually, approximately 7 \(\times\) 10\({}^{5}\) tons of dyes are used in various applications, and about 5% of these dyes are discharged without proper treatment [3, 4]. Most dye molecules are visualized at deficient concentrations, and they can interfere with the availability of sunlight underwater, which may affect living organisms in aqueous environments. Furthermore, dye molecules can increase biochemical oxygen demand (BOD), and the molecules themselves may be toxic and carcinogenic [5, 6]. To remove these dyes from wastewater, various techniques such as biological treatment, chemical oxidation, ion exchange, and adsorption are utilized [7, 8, 9, 10, 11, 12]. Among the mentioned techniques, adsorption is widely used for wastewater treatment to remove dye molecules owing to its advantages including low cost, flexibility, design simplicity, profitability, efficiency, and the lack of formation of secondary pollutants [13, 14]. Based on these benefits of the adsorption technique, various organic/inorganic adsorbents such as activated carbon,clays, zeolite, polymer-based materials, metal-organic frameworks (MOFs), and covalent organic polymers (COPs) have been studied for removing dyes from water [3; 15; 16; 17; 18; 19; 20; 21]. Covalent organic polymers (COPs), or covalent organic frameworks, have recently attracted attention due to their stability, functional tunability, and straightforward synthesis [22; 23]. In particular, diverse combinations of COPs created by utilizing deliberately selected building blocks have been investigated for use in energy, biomedical, and environmental applications [24; 25; 26; 27; 28]. COP as an adsorbent for water treatment has also been reported. [PERSON] et al. reported the charge-specific size-dependent separation of organic molecules using fluorinated COP [29]. The selective adsorption of cationic dye molecules on disulfide-linked COPs prepared through the polymerization of aliphatic thiols was reported in our recent studies [19; 30]. However, because the surfaces of these COPs are negatively charged, the adsorption of anionic dye molecules on them is limited [31]. To overcome this limitation, [PERSON] et al. prepared a catalyst-free melamine-based aminated covalent polymer (ACOP) through Schiff base chemistry [32]. Schiff base chemistry is a well-known organic synthesis tool for realizing complex molecular architectures through the condensation of carbonyl compounds with primary amines [33]. The powder form of the prepared melamine-based ACOP was expected to be insoluble in aqueous, acidic, and alkaline solutions, and it exhibited high thermal stability. Owing to these advantages, ACOPs have been studied as catalysts [34; 35], CO\({}_{2}\) capture materials [36], and adsorbents [31; 37]. Moreover, ACOPs are known to have positive surface charges owing to the protonation of the amine group under acidic conditions [38]. Because of this feature of ACOPs, they are candidate materials for the selective adsorption of anionic pollutants, and it might be possible to reuse ACOPs by controlling the solution pH [39]. Despite these advantages of ACOPs, they have been used only as support materials for metal catalysts, CO\({}_{2}\) capture materials, and heavy metal adsorbents [34; 36; 40; 41]. In this study, an ACOP is prepared through one-pot synthesis by utilizing terephthaladehyde and melamine as monomers without a catalyst. The prepared ACOP is characterized intensively using several characterization techniques, including Fourier transform infrared (FT-IR) spectrometry, scanning electron microscopy (SEM), N\({}_{2}\) adsorption-desorption analysis, zeta potentiometry, and X-ray photoelectron spectroscopy (XPS).