# Removal of Metal Ions in Spin-on Hardmask Using Functionalized Porous Silica Adsorbents
Therefore, the removal of these metal ions is essential to improve product yield. A common method for metal ion removal involves the use of porous membrane filters with ion-exchange capability. However, such filters are often costly to purchase and maintain. Moreover, since ion exchange membranes typically employ strongly acidic functional groups, they may cause unintended chemical reactions particularly when used with materials that are sensitive to acidic environments. Therefore, there is a need for an alternative approach that can effectively and economically remove metal ions without adversely affecting the SOH solution. Various methods have been proposed for removal of the metal ions including chemical precipitation, reverse osmosis, and electrocoagulation. However, these techniques present drawbacks such as high operational costs, the generation of hazardous sludge, incomplete removal efficiency, and excessive consumption of energy and materials. Adsorption, in contrast, is a well-established method for metal ion removal, widely recognized for its simplicity, cost-effectiveness, and adaptability to various treatment environments. This technique typically utilizes porous materials with high surface area as adsorbents, such as activated carbon and clay minerals. However, the irregular pore structure of activated carbon and the high cost associated with its activation process limit its applicability. In addition, the weak adsorption capacity of untreated clay minerals for metal ions results in insufficient ion-exchange performance for large-scale applications [6; 7; 8; 9]. Mesoporous silica materials have attracted considerable interest as efficient adsorbents for metal ion removal. Characterized by pore sizes in the range of 2 to 50 nm, they offer a high surface area, uniform and tunable pore structures, and favorable adsorption characteristics. Furthermore, they exhibit excellent thermal and mechanical stability, low toxicity, and ease of surface functionalization, enabling the adsorption of specific metal ions. These properties make mesoporous silica particularly suitable for removing trace metal contaminants from chemically sensitive systems such as SOH solutions [10; 11]. Previous studies have demonstrated the potential of amine-functionalized mesoporous silica for the selective removal of hexavalent chromium (Cr(VI)) from aqueous environments. In particular, [PERSON] et al. reported that mesoporous silica functionalized with (3-aminopropyl) trimethoxysilane (APTMS) exhibited strong electrostatic interactions between protonated amine groups (-NH\({}_{3}\)+) and anionic Cr(VI) species, leading to efficient adsorption even under acidic conditions. Their work highlighted that while excessive APTMS loading reduced the surface area due to pore narrowing, the increase in functional group density significantly improved adsorption performance [12]. This suggests that the chemical nature and protonation state of surface functionalities play a more critical role than the pore structure itself. In this study, two types of mesoporous silica, MCM-41 and SBA-15, were investigated as adsorbents for the removal of metal ions from SOH solutions. These materials were selected due to their well-defined pore structures, pore uniformity, large surface areas, and suitability for surface functionalization, which make them ideal platforms for adsorption-based applications. In particular, MCM-41 and SBA-15 represent widely used mesoporous silica frameworks with similar structural order but different pore sizes, allowing for a comparative evaluation of pore size effects on adsorption performance [10]. To tailor their surface properties, each material was functionalized with different groups, including hydroxyl (-OH), amine (-NH\({}_{2}\)), thiol (-SH), and methyl (-CH\({}_{3}\)).