# Green Strategies for Molecularly Imprinted Polymer Development
## Green Strategies in MIP Development
### Supercritical Fluid Technology
#### 2.1.1 3D-Imprinted Porous Structures in scCO\({}_{2}\)  
3D-imprinted materials have been a steadily growing field allowing to build other polymer geometries. In 2007, [PERSON] group [48] reported the use of poly(styrene-_co_-maleic acid) (PSMA) for molecularly imprinted membranes prepared by phase inversion in scCO\({}_{2}\) for uracil (URA). URA-imprinted membrane was prepared using 15 wt % of PSMA and 2 wt % of URA in DMF, DMSO, and NMP solvents. Membranes were prepared at two different temperatures, 35 and 50 \({}^{\circ}\)C, and the system was slowly depressurized. URA was extracted from membrane with 1 vol % acetic acid solution, and after that, a large quantity of water for 1 week at 30 \({}^{\circ}\)C was passed through, and in the end, vacuum dried. The solvent used was shown to have a strong impact on membrane development, which could be confirmed by SEM. Membranes prepared at 50 \({}^{\circ}\)C presented higher affinity than membranes prepared at 35 \({}^{\circ}\)C, which corresponded to 12.6 and 9.2 umol g-1, respectively. Selectivity studies were performed using binary substrate solutions containing each of URA/DMURA, URA/thymine, and URA/cytosine at 2 um. The results suggested that the URA imprinted membrane was effectively prepared.  
Four years later, [PERSON] et al. [49] described oleanolic acid (OA)-imprinted membranes for OA extraction purposes. Oleanolic acid is a typical ingredient of medicinal plants, having anti-inflammatory properties [50]. PA6/PSMA-OA molecularly imprinted composite membranes were produced by phase inversion method in supercritical CO\({}_{2}\) using polyamide-6 (PA6) as base membrane and poly(styrene-_co_-maleic acid) (PSMA) obtained by the conventional method. The mass ratio between PSMA and OA ranged from 3:1 to 8:1, and temperature and pressure from 35 to 50 \({}^{\circ}\)C and 12 to 17 MPa, respectively. As a result, the specific conditions mass ratio of PSMA and OA 6:1, 40 \({}^{\circ}\)C, and 15 MPa, had the best performance, where the imprinted membrane could adsorb 50.4% and 96.1% of OA, respectively. Therefore, OA-imprinted membranes produced using scCO\({}_{2}\) provided a feasible method to selectively separate OA from other compounds.  
Molecularly imprinted composite membranes were reported by [PERSON] et al. [18; 19] for poly(MAA-_co_-EGDMA) and poly(BPADM-_co_-EGDMA)-MIPs for BPA that had been obtained by non-covalent and semi-covalent imprinting, used in membrane preparation by scCO\({}_{2}\) assisted-phase inversion. The strategy was to confer affinity to the membrane by incorporating the MIP particles within the membrane. For membrane preparation, 30 wt % of polymer blend consisting of 70:30 PMMA/poly(MAA-_co_-EGDMA) and PMMA/poly(BPADM-_co_-EGDMA) were dissolved in DMF. The inversion process occurred for 3 h at 45 \({}^{\circ}\)C, and at the end, the system was slowly depressurized over 20 min. The non-covalent imprinted and semi-covalent imprinted membranes were obtained as thin and homogeneous layers, and could adsorb 1.3 and 2.1 times more BPA, respectively, than the corresponding control membranes.