## 2 Fundamentals of Ion-Imprinted Polymers
### Components of the IIP
#### 2.3.3 Porogenic Solvent  
The porogenic solvent choice plays a crucial role in the synthesis of IIP. The porogenic solvent must solubilize all the reagents used in the synthesis to form a homogeneous solution without interfering with the interaction between the metal ion and the functional monomer. It also has a higher influence on the morphological characteristics of the polymer, specifically, in the porosity [65]. In addition, the porogenic solvent might influence the selectivity of the polymer. [PERSON] and [PERSON] assessed the effect of the porogenic solvents 2-methoxyethanol, methanol (MeOH), tetrahydrofuran (THF), acetic acid (HAc), dichloroethane (DCE), \(N\),\(N\)-dimethylformamide (DMF), and toluene on the adsorption capacity from IIP to UO\({}_{2}\)\({}^{2+}\)[66]. From the results, the imprinted polymer synthesized in 2-methoxyethanol showed a higher adsorption capacity (34.10 mg g\({}^{-1}\)) when compared to MeOH (11.28 mg g\({}^{-1}\)), THF (7.03 mg g\({}^{-1}\)), HAc (27.28 mg g\({}^{-1}\)), DCE (6.80 mg g\({}^{-1}\)), DMF (15.62 mg g\({}^{-1}\)), toluene (6.62 mg g\({}^{-1}\)), and in the respective control polymers (NIP). In general, solvents with a higher boiling point, as observed by 2-methoxyethanol are more indicated to provide IIP with micropores and with higher surface area. [PERSON] and coworkers synthesized several IIP for the Ni\({}^{2+}\) ions in the porogenic DMSO (Dimethylsulfoxide) and using mixtures of acetonitrile (ACN)-(ACN:DMSO, 1:1%, \(v/v\)) and 2-methoxyethanol:DMSO (1:1%, \(v/v\)), named as IIP-D, IIP-A/D, and IIP-M/D, respectively [67]. The authors compared the structure and adsorption properties of the polymers and observed that although polymers IIP-A/D (134 m\({}^{2}\) g\({}^{-1}\)) and IIP-M/D (177 m\({}^{2}\) g\({}^{-1}\)) had lower porosity than IIP-D (275 m\({}^{2}\) g\({}^{-1}\)) and the respective non-imprinted polymers (NIP-D: 380 m\({}^{2}\) g\({}^{-1}\), NIP-A/D: 181 m\({}^{2}\) g\({}^{-1}\) and NIP-M/D: 457 m\({}^{2}\) g\({}^{-1}\)), these have a higher adsorption capacity (23.9 and 22.4 mg g\({}^{-1}\), respectively) and imprinting factor (2.77 and 2.52, respectively), even in the presence of Zn\({}^{2+}\), Co\({}^{2+}\), and Pb\({}^{2+}\) ions. These results show clearly that the greater the boiling point of the solvent the higher presence of micropores and the higher the surface area. However, as noticed, the higher surface area of IIP obtained by using DMSO as a solvent, did not guarantee higher adsorption capacity. In this case, most likely DMSO strongly interacted with a metal ion (template) hindering the interaction with functional monomer and, thereby, decreasing the chemical imprinting formation. Table 1 shows the porogenic solvents most used in the synthesis of IIP, which are organized by increasing polarity. These solvents are classified as apolar, polar aprotic, and polar protic. It is important to point out that in the synthesis of IIP it is also common to use a porogenic mixture of solvents, such as ACN:DMSO [44], MeOH:DMF [45; 58], EtOH:ACN [48], MeOH:EtOH [49], and EtOH: 2-methoxyethanol [52]. [PERSON] and coworkers [68] evaluated the effect of the amount of solvents MeOH or ACN, as well as their mixture, on the adsorption and morphological properties of IIP for Hg\({}^{2+}\) ions. Thus, the authors observed that the mixture of MeOH:ACN, as a porogenic solvent, provided the IIP with a greater adsorption capacity for Hg\({}^{2+}\) ions compared to polymers synthesized merely in MeOH or ACN, which was attributed to the increase in the material's porosity. Likewise, the authors observed that higher adsorption capacity for Hg\({}^{2+}\) ions was obtained with polymers that were synthesized in larger amounts of the porogenic solvent. However, when comparing the results obtained by [PERSON] and [PERSON] [66] with the results from [PERSON] and coworkers [68], it can be inferred once again that the adsorption capacity of an IIP cannot always be attributed to its porosity.