Formaldehyde-Free Melamine-Glutaraldehyde Resin Microspheres for Metal Ion Removal from PGME/PGMEA Photoresist Thinners

Melamine-formaldehyde (MF) resin microspheres show great promise as high-performance adsorbents for the purification of wet electronic chemicals. However, their reliance on formaldehyde introduces severe toxicity risks and leads to free aldehyde leaching that contaminates the purification process. In this work, glutaraldehyde was employed to completely replace formaldehyde for the preparation of melamine resin microspheres via a facile suspension polymerization process. The preparation parameters (such as feed molar ratio, polymerization temperature, and the oil–water ratio) were systematically optimized to regulate the morphology, particle size, and specific surface area. The physicochemical properties of the as-prepared microspheres were comprehensively characterized via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nitrogen adsorption–desorption isotherms, thermogravimetric analysis (TGA), and swelling resistance tests. The results indicate that the optimized glutaraldehyde-cross-linked melamine resin microspheres exhibit a regular spherical morphology, a narrow particle size distribution, adequate thermal stability for engineering applications, and a low swelling ratio in wet electronic chemical media without leaching of free glutaraldehyde. The adsorption of Cu, Fe, and Ti ions in a propylene glycol methyl ether/propylene glycol methyl ether acetate (PGME/PGMEA) photoresist thinner was investigated via isotherm, kinetic, and cyclic reusability studies. The adsorption data are well fitted by the Langmuir–Freundlich isotherm and pseudo-second-order kinetic models, revealing a mixed monolayer-multilayer chemisorption mechanism. The maximum adsorption capacity for various ions ranged from 4405.21 to 5298.43 μg/g, and the microspheres maintained a decrease in adsorption efficiency of no more than 15.8% after five regeneration cycles. This work offers a green, scalable synthesis strategy and sheds light on the advanced purification of high-purity wet electronic chemicals.