Dual-functional metal-organic framework for chemisorption and colorimetric monitoring of cyanogen chloride

Given the growing concern over the deployment of toxic chemicals in warfare, the rapid and accurate removal and detection of cyanogen chloride (CK) as a blood agent has become increasingly critical. However, conventional physisorbents and chemisorbents used in military respirators are insufficient for the effective removal of CK. In this study, we demonstrate the chemisorption and sensing abilities of Co₂(m-DOBDC) (m-DOBDC⁴⁻ = 4,6-dioxo-1,3-benzenedicarboxylate) for CK via electrophilic aromatic substitution (EAS) in humid environments. Unlike the chemisorption in triethylenediamine (TEDA) impregnated carbon materials, which generates by-products through hydrolysis, the electron-rich C5 sites in m-DOBDC⁴⁻ ligands give rise to cyano substitution with CK. This leads to the formation of stable C–C bonds and chloride ions (Cl⁻) coordinating with open Co²⁺ sites. Such a mechanism prevents the generation of toxic by-products like cyanic acid and hydrochloric acid. Breakthrough experiments conducted in a packed-bed system conclusively demonstrated the superior CK removal capacity of Co₂(m-DOBDC) (1662 min/g), compared to TEDA-impregnated activated carbon (323 min/g) under humid conditions. Considering that MOF-74 series, isostructural with Co₂(m-DOBDC), barely adsorb CK under similar conditions, this finding marks a significant advancement in developing novel sorbents for CK removal. Moreover, this chemisorption not only exhibited rapid and highly efficient CK removal but also enabled colorimetric monitoring via the distinctive color change induced by the coordination of Cl⁻ acting as σ donors. These findings facilitate the development of adsorption and sensing equipment to protect military personnel from toxic chemical threats.