# Removal of Metal Ions in Spin-on Hardmask Using Functionalized Porous Silica Adsorbents
## 3 Result and Discussion  
### Synthesis and Characterization of Mesoporous Adsorbents  
Figure 1 shows a schematic illustration of the synthesis of functionalized mesoporous silica adsorbents (MCM-41 and SBA-15) and the metal ion removal process from SOH solution. MCM-41 and SBA-15 were synthesized using CTAB and P123, respectively, as structure-directing surfactants. The surfactants were removed under acidic conditions through an extraction process, followed by surface functionalization to introduce specific functional groups onto the mesoporous silica framework. The resulting functionalized adsorbents were subsequently applied in metal ion removal experiments under SOH solution environments. TEM and small-angle XRD analyses were employed to confirm the structures of MCM-41 and SBA-15, and the results are presented in Figure 2. MCM-41 (Figure 2a-c) exhibited spherical particles with sizes ranging from 400 to 500 nm. SBA-15 (Figure 2d-f) appeared as chain-like rod-shaped particles with sizes of approximately 700-800 nm. Both samples displayed well-ordered mesoporous structures with uniform pore arrangements. Small-angle XRD analysis revealed that MCM-41 exhibited peaks corresponding to the (100), (110), (200), and (210) at 20 values of 2.15\({}^{\circ}\), 3.72\({}^{\circ}\), 4.3\({}^{\circ}\), and 5.69\({}^{\circ}\), respectively, confirming the hexagonal lattice structure of the synthesized MCM-41. These peaks correspond to the characteristic diffraction planes, indicating the well-ordered mesoporous structure [14]. Incontrast, SBA-15 showed a strong peak corresponding to the (100) plane at 20 = 1.035\({}^{\circ}\), along with smaller peaks at 1.675\({}^{\circ}\) and 1.915\({}^{\circ}\) that correspond to the diffraction of (110) and (200), suggesting a well-ordered structure with a hexagonal lattice symmetry of ppmm [19; 20]. To confirm the pore characteristics of functionalized MCM-41 and SBA-15, nitrogen adsorption-desorption analysis based on the Brunauer-Emmett-Teller (BET) method was conducted, and the pore size distribution was illustrated in Figure 3. Additionally, the pore characteristics of the surface-functionalized MCM-41 and SBA-15 materials were summarized in Table 1. All of the functionalized MCM-41 exhibited a Type-IV adsorption-desorption isotherm with an H1 hysteresis loop attributed to capillary condensation of mesopores at a relative pressure (p/p\({}_{0}\)) range of 0.3-0.4. Functionalized  
Figure 1: Schematic diagram depicting the synthesis of functionalized adsorbents and their application in metal ion removal from SOH solutions. Figure 2: Transmission electron microscopy (TEM) images of (**a–c**) MCM-41 and (**d–f**) SBA-15, and small-angle X-ray diffraction (XRD) patterns of (**g**) MCM-41 and (**h**) SBA-15. SBA-15 samples also displayed a similar Type-IV isotherm with an H1 hysteresis loop at a p/p\({}_{0}\) range of 0.65-0.8. This indicates that both synthesized MCM-41 and SBA-15 possess well-developed cylindrical mesoporous structures [19; 21]. The specific surface area, average pore size, and total pore volume of MCM-41 were 1120 m\({}^{2}\) g\({}^{-1}\), 3.6 nm, and 1.0 cm\({}^{3}\) g\({}^{-1}\), respectively. In contrast, SBA-15 exhibited values of 593.8 m\({}^{2}\) g\({}^{-1}\), 7.7 nm, and 1.1 cm\({}^{3}\) g\({}^{-1}\) for specific surface area, average pore size, and total pore volume, respectively. Compared to SBA-15, MCM-41 exhibited a smaller pore diameter and more than twice the surface area. In the case of surface-modified materials, it was observed that the specific surface area, pore size, and pore volume all decreased compared to the pristine materials. This observation indicates the formation of functional groups not only on the adsorbent's surface but also within the pores. Among the functionalized