## 4 Critical Comparison
Cr(III) ions contributed, as synergetic ions, to increasing the imprinting of arsenate on the ion-imprinted polymer. Molecularly imprinted polymer resins have been reported for the removal of As(V) from a water medium, e.g., drinking water, lakes, streams, irrigation runoff, industrial effluent, mine waste, etc. and in water treatment (both industrial and residential wastewater treatment). Particularly in the work of the authors of [63], suspension polymerization (stirring at 320 rpm, 80 \({}^{\circ}\)C for 5 h) has previously been applied, using styrene as a functional monomer, DVB as a cross-linking monomer, AIBN as an initiator, and aqueous phase as a porogen. The prepared material seems to be in the form of resin beads with a permanent porous structure, even in their dry state. The particle size of the resin beads was between 250 and 841 nm for 97% of them, a bit larger than in previous research. Therefore, it seems that UV polymerization with the specific conditions and proportions of these specific compounds leads to more efficient molecularly imprinted resins. Furthermore, MIP-cryogels have been reported regarding the removal of As(V) from water solutions [32], in which AAm and MBAAm were used as a monomer solution. By constructing a composite adsorbent combining cryogels with particles (at both nano- and micro-scales), an increase in mechanical stability was observed. The MIP-cryogels have a macroporous structure (20-100 \(\upmu\)m), and the adsorption capacity was found to be 7.91 \(\pm\) 0.7 mg/g. Furthermore, it was found that co-ions (nitrate, sulfate, and phosphate) affected arsenic removal less for MIP-cryogels than other cryogel materials. However, the development of MIP-cryogels is needed, considering their low adsorption capacity. In addition, MIP-monoliths have been reported [32; 78] for the separation, recovery, and removal of As(V) from environmental water samples and water solutions, by two studies. Bulk polymerization (60 \({}^{\circ}\)C for 48 h) has been applied, using 4-OHBPH and 2-VP as the functional monomers, EDMA as the cross-linking monomer, AIBN as the initiator, and methanol as the porogen. The monolith was heterogeneously distributed, and its particle size was <38 \(\upmu\)m. It produced a satisfactory surface area equal to 80.23 m\({}^{2}\)/g and the adsorption capacity was found to be 6.94 \(\pm\) 0.4 mg/g. Moreover, bulk polymerization (60 \({}^{\circ}\)C overnight) has been applied using 1-VIm, 4-VP, and styrene as the functional monomers, EDMA as the cross-linking monomer, AIBN as the initiator, and acetic acid-methanol as the porogen [78]. The monolith was a white rigid solid, and the particles had a non-spherical appearance. The formation of As-imprinted cavities at MIPs and the rough surface of NIPs was observed, with a lack of comparable porous structure. In terms of selectivity, as well as imprinting effects, compared with the non-imprinted polymer (NIP), MIPs with 1-VIm exhibited superior analyte recognition for the As ion among 23 competing elements, and it appeared to offer a 25-fold enhancement in adsorption capacity, equal to 0.00362 mg/g. Therefore, it seems that bulk polymerization with the specific conditions and proportions of these specific compounds leads to more efficient molecularly imprinted monoliths. Previous research has reported that magnetic arsenate molecularly imprinted polymer (mMIIP) can be used for the selective adsorption of As(V) [79]. For this reason, the surface imprinting technique was applied (stirred and refluxed for 16 h at 70 \({}^{\circ}\)C), using two different amine-containing functional monomers (allylamine hydrochloride and APTES), with MBA as the cross-linking monomer, K\({}_{2}\)S\({}_{2}\)O\({}_{8}\) as the initiator, ethanol-aqueous solution as the porogen, and tetraethyl orthosilicate-modified magnetic Fe\({}_{3}\)O\({}_{4}\) nanoparticles as a support. It was found that coupling allylamine hydrochloride as a co-functional monomer and MBA as a cross-linker can increase the surface roughness of the material.