## 3 Results and Discussion  
### Physicochemical Characterization of MIL-88A Carriers  
The XRD patterns of the synthesized materials are shown in Figure 1. They confirmed obtaining crystalline phases specific to MIL-88A metal-organic frameworks. Depending on the synthesis temperature and solvent used, the characteristic reflections registered for all materials have slightly different positions, widths, and intensities in comparison to simulated patterns. This is consistent with previous literature reports [26; 43]. Additionally, changes could be attributed to the presence of free fumaric acid or water molecules in the material pores [26]. In the case of MIL-88A-1 and MIL-88A-2 samples, prepared in distilled water, the most intensive reflections located at 20-10.8\({}^{\circ}\), 11.8\({}^{\circ}\) and 10.1\({}^{\circ}\), 10.8\({}^{\circ}\), respectively, can be assigned to the (100) and (101) planes. When DMF was used as a solvent during synthesis, there was a transition in the crystal orientation of MIL-88A from (101) to (100). The XRD patterns of MIL-88A-3 and MIL-88A-4 contain distinct reflections at 20-10.1\({}^{\circ}\), 10.8\({}^{\circ}\) and 10.8\({}^{\circ}\), 11.8\({}^{\circ}\), respectively. Slight shifts of diffraction peaks indicate the flexibility of the MIL-88A structure [44]. Physisorption of nitrogen was conducted for all the iron-based MOF carriers, and the resulting isotherms are illustrated in Figure 2. The nitrogen adsorption/desorption isotherm of MIL-88A-1, prepared in distilled water at 70 \({}^{\circ}\)C, has a shape comparable to type IV in line with the IUPAC (International Union of Pure and Applied Chemistry) classification, specific to mesoporous materials [26]. In turn, the MIL-88A-2 sample synthesized at a higher temperature (120 \({}^{\circ}\)C) exhibits a type I nitrogen adsorption/desorption curve, indicating the presence of micropores in its structure. For this isotherm, a stage of rapid growth is observed at low relative pressure values, followed by saturation [45]. The nitrogen adsorption/desorption curves of the MIL-88A-3 and MIL-88A-4 materials obtained in N,N-Dimethylformamide correspond to the combination of I and II types [26]. They have a microporous structure with a small amount of macropores. The textural parameters of MIL-88A materials are summarized in Table 2. MIL-88A-1 was characterized by the lowest specific surface area and total pore volume--10 m\({}^{2}\)/g and 0.05 cm\({}^{3}\)/g, respectively. These values correspond to the results reported in the literature for MIL-88A synthesized under similar conditions [43; 46; 47]. Synthesis of MIL-88A-2 material at a higher temperature leads to the generation of higher porosity. It shows a higher specific surface area of 292 m\({}^{2}\)/g, a pore volume of 0.21 cm\({}^{3}\)/g, and an average pore diameter of 2.83 nm. MIL-88A-2 micropore surface area represents 89% of the total surface area, confirming mainly the microporous character of this material. The best-developed specific surface areas were obtained for MIL-88A-3 and MIL-88A-4 materials synthesized in N,N-Dimethylformamide, 326 and 307 m\({}^{2}\)/g, respectively, with the micropore surface areas of 279 and 122 m\({}^{2}\)/g. The difference between the specific surface area and pore volume of MIL-88A-1 and other samples could be ascribed to the framework opening and closing [48]. This phenomenon is characterized by a reversible cell volume doubling during the conversion of topology from closed to open [49]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **BET Surface Area** & **Total Pore Volume** & \multicolumn{2}{c}{**Average Pore**} & \multirow{2}{*}{**Micropore Area**} \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **Diameter** & & **(m\({}^{2}\)/g)** \\ \hline MIL-88A-1 & 10 & 0.05 & 20.30 & - \\ MIL-88A-2 & 292 & 0.21 & 2.83 & 261 \\ MIL-88A-3 & 326 & 0.47 & 5.74 & 279 \\ MIL-88A-4 & 307 & 0.33 & 4.27 & 122 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Textural parameters of MIL-88A carriers.