Room-temperature covalent organic polymers with hydroxyl engineering for ultra-high polychlorinated biphenyls uptake

Polychlorinated biphenyls (PCBs) posed serious threats to human being even at trace levels, and developing functional materials enabling high PCBs uptake was urgent for critical monitoring. Covalent organic polymers (COPs) exhibited high adsorption performance have emerged intensively. However, challenges still exist in term of common 2D COPs, because the non-planar angle between benzene rings in PCBs could weaken the planar π-π conjugation, and the polar nature of halogen atoms in PCBs weakens typical hydrophobic interaction. Thus, efficient synthesis of 3D COPs with surface modification of polar groups for spatial matching and multiple interactions towards non-planar PCBs was needed and interesting.

A unique hydroxyl engineering 3D COPs with multiple interactions through a simple room-temperature synthesis were proposed, and applied for ultrahigh PCBs uptake via solid-phase microextraction (SPME). A series of [HO]x-3D COPs with various ratios of OH groups (x = 0-100 %) were tailored. Mixed-mode interactions towards PCBs including hydrogen bonds, hydrophobic effect, and aromatic π-π interaction were adopted synergistically. Altering the ratio of hydroxyl groups in COPs adjusted their specific surface area and multiple interactions against PCBs. The optimal [HO]_83 %-COPs exhibited ultrahigh PCBs uptake with enrichment factors up to 5402-9157, which was 1.1-2.3 and 11-225 folds better than that of traditional PDMS and PDMS/CAR respectively, and equivalent or superior to most COFs. Meanwhile, an excellent stability of [HO]_83 %-COPs remained after application in 165 cycles. Applied to soil samples, recovery yields were achieved with 82.9 % ± 6.6 %∼97.6 % ± 3.6 % (n = 3), 84.3 % ± 4.9 %∼103.3 % ± 3.9 % (n = 3), respectively.

This study pioneered a simple yet powerful room-temperature synthesis strategy that achieved high-performance [HO]x-3D COPs with high specific surface area and hydroxyl adjustment for ultrahigh PCBs uptake. It expands an attractive COPs material alternative to traditional COFs or organic polymers for SPME, enabling cost-effective and high-performance PCBs uptake for environmental assays.