Engineering sulfonated polymers for the removal of ultra-trace complexed Cr(Ⅲ) in tris(2-carboxyethyl) isocyanurate photoresist resin monomers

The semiconductor manufacturing industry imposes stringent requirements on the metal ion content of photoresist resin monomers. Tris(2-carboxyethyl) isocyanurate (H₃tci), a critical raw material for photoresist resin monomers, inevitably incorporates metal ions during production. However, its inherent carboxyethyl groups form stable coordination complexes with Cr(Ⅲ), hindering the semiconductor-grade resin monomer production. To achieve the ultra-deep removal of Cr(Ⅲ) at ultra-trace concentrations, inspired by the hard–soft-acid–base theory, we systematically modulated the electron-rich sulfonic acid group on polymers via controlled sulfonation conditions to achieve a novel series of adsorption materials (St) with ultra-high Cr(Ⅲ) adsorption affinity. The adsorption–recrystallization process using 6 g of St-V-15 could reduce the Cr(Ⅲ) concentration in a solution containing 1 g of H₃tci from 840 ppb to 27.5 ppb. Furthermore, St-V-15 exhibited a maximum adsorption capacity of 145 mg g⁻¹ calculated using the Langmuir model and a rapid initial adsorption rate of 82.92 mg g⁻¹ min⁻¹ at 333 K. Additionally, St-V-15 demonstrated exceptional selectivity for Cr(Ⅲ) over competing ions (e.g., K(Ⅰ), Mg(Ⅱ), Na(Ⅰ) and Zn(Ⅱ)) and maintained stable performance over at least 10 adsorption–desorption cycles. The superior performance originated from the chelation between Cr(Ⅲ) and the sites of O atoms (S–O and S=O) combined with the electrostatic interaction between deprotonated sulfonic acid groups and Cr(Ⅲ). These results position St-V-15 as a promising adsorption material for ultra-trace Cr(Ⅲ) removal in H₃tci, offering a cost-effective solution for semiconductor-grade resin monomer production for the very first time.