(658f) Photochemically Patterning Multifunctional Membranes to Enhance the Heavy Metal Ion Capture and Detection

Heavy metal pollution represents a significant threat to human health and natural ecosystems. Consequently, the selective capture and detection of heavy metal ion in water has emerged as a pivotal challenge to ensuring a sustainable supply of clean water in the modern world. Among various detection methods, colorimetric sensing has attracted significant attention due to its high efficiency and operational simplicity. Although previous researchers have developed several ligands that demonstrate distinct color responses in the presence of a diverse array of heavy metal ions, the incorporation of multiple ligands within a unified platform has not been investigated in detail. In this study, an adsorptive membrane derived from reactive poly(phenolphthalein)-based (PPH-based) polymers was fabricated and the pore wall chemistry tailored to facilitate post-synthetic modification via click chemistry. Subsequent application of thiol-yne reactions produced membranes patterned with two distinct ligands, namely carboxylic acid and terpyridine moieties. Using a photomask, the ligands were introduced only at designated areas to form alternating stripe patterns as small as 200 µm in width. Compared to the single-ligand membranes, patterned membranes had advantages in both the detection range for single ion concentrations and indication of multiple ions within a mixed ion solution. Moreover, the incorporation of the adjacent ligands expedited the color saturation period, as evidenced by a complete colorimetric response for both stripes within 10 minutes, which is noticeably shorter than that of a pure terpyridine membrane (~2 hours). Furthermore, treatment with hydrochloric acid allowed for the regeneration and reuse of the multifunctional adsorptive membranes. While exhibiting an excellent colorimetric response, the patterned membrane maintained an overall higher binding affinity (K = 1768 M^-1) and saturation capacity (0.57 mmol g^-1) for cupric ions compared to the binding affinity (K = 110 M^-1) and saturation capacity (0.36 mmol g^-1) of a PSf/PS-PAA membrane developed previously. The precise manipulation of surface patterns on membranes, coupled with a high density of binding sites along the pore walls, demonstrates a considerable potential for the membrane platform to achieve more complicated pattern (e.g., QR codes) with multiple ligands, while maintaining a high adsorption capacity and affinity.