Impact of Crosslinking Agent on Sorption Properties of Molecularly Imprinted Polymers in Relation to Silver  
[PERSON]  
1 Faculty of Chemistry and Chemical Technology, Al-Farabi Kazakh National University, Al-Farabi Ave. 71, 050040 Almaty, Kazakhstan, [EMAIL_ADDRESS] (L.A.); [EMAIL_ADDRESS] (D.K.) [PERSON]  
2 Biochemical Engineering Department, International Engineering and Technological University, Al-Farabi Ave. 93a, 050060 Almaty, Kazakhstan, [EMAIL_ADDRESS]  
2 [PERSON]  
physical adsorption or chemical binding of Ag\({}^{+}\) ions with the functional groups of the sorbent. Nowadays, the following sorbents for silver extraction can be named: activated coal; ion-exchange resins; inorganic sorbents; and biosorbents [23; 24; 25; 26; 27; 28; 29]. As an alternative to the above-mentioned sorbents, the application of molecularly imprinted polymers (MIPs) can be assumed. MIPs are synthetic, tailor-made materials designed to selectively recognize and bind target molecules (templates), mimicking natural molecular recognition [30; 31]. They offer high selectivity, stability, and reusability, making them superior to conventional sorbents in many applications [32; 33]. Key applications of MIPs can be named as follows: metal recovery [34]; environmental remediation [35]; medicine and diagnostics [36]; sensors [37; 38]; and food safety and analysis [39; 40]. The advantages of MIPs over traditional sorbents are presented in Table 1[41; 42; 43; 44; 45]. Molecularly imprinted polymers are created by forming a polymer around a target molecule using functional monomers and cross-linkers; once the template is removed, the resulting cavities enable selective rebinding of the target from complex mixtures [46]. There are several studies on developing MIPs based on various monomers and crosslinkers for the extraction of silver [47; 48]. For example, a biopolymer chitosan was used as a raw material and glutaraldehyde as a crosslinker for obtaining MIP for selective removal and preconcentration of Ag(I) ions from aqueous solutions [49; 50]. As for organic monomers, various acrylic and pyridine compounds were used. The most often used functional monomers among pyridine ones are 2-vinylpyridine (2-VP) and 4-vinylpyridine (4-VP). For example, in [51], ion-imprinted polymer (UA-DSPE-IIP) nanoparticles based on 2-VP were developed for the selective extraction of silver ions using ultrasonic-assisted dispersive solid-phase extraction. The binding properties of silver ion-imprinted polymers based on 4-VP were characterized by equilibrium and kinetic models [52]. 4-VP was used for obtaining magnetic ion imprinted polymers using functionalized magnetite (Fe\({}_{3}\)O\({}_{4}\)) nanoparticles [53] and by coating on the surface of magnetic graphene oxide [54] as a magnetic core. Another example of magnetic MIP using Fe\({}_{3}\)O\({}_{4}\)-SiO\({}_{2}\)-TiO\({}_{2}\) nanoparticles as a magnetic support of adsorbent and Ag(I)-2,4-diamino-6-phenyl-1,3,5-triazine (DPT) complex as the template molecule was obtained based on the most often used acrylic monomer--methacrylic acid (MAA) [55]. The latter was also used for obtaining an Ag(I)-ion imprinted polymer with silver (Ag) dithizone complex as a template [56] and by the formation of 2-(4-hydroxypent-3-en-2-ylideneamine) phenol complex with silver ions [57]. The peculiarity of all these studies is the use of a single monomer for obtaining MIP. Therefore, our study was devoted to the preparation of MIPs based on two monomers--MAA and 4-VP. Another peculiarity of these studies is the use of ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The crosslinker is an important component in MIP synthesis, determining the structural stability, binding capacity, and selectivity of the polymer [58]. The common crosslinkers used in molecular imprinting are ethylene glycol