Amidoxime-functionalized covalent organic framework as simultaneous luminescent sensor and adsorbent for organic arsenic from water

Organoarsenic compounds are widely used as feed additives in the poultry industry. However, the release of organoarsenic-containing wastewater can cause serious poisoning to the ecosystem. For this reason, detection and adsorption of organic arsenic from wastewater is crucial but also very challenging. Here, the use of covalent organic frameworks (COFs) as fluorescence sensors and adsorbents for the detection and adsorption of organic arsenic from water has been investigated for the first time. Two isoreticular crystalline and highly porous sp2 carbon-conjugated COFs were synthesized, and amidoxime-functionalized via post-synthetic modification (PSM). The long-range order and π-conjugated system ensure that both COFs act as fluorescent sensors for detecting the representative organic arsenic, roxarsone (ROX). The fluorescence quenching efficiencies of ROX on both COFs are over 98%. The limits of detection (LOD) for ROX by both COFs are estimated to be 6.5 and 12.3 nM. Additionally, the regular pores and the abundantly decorated amidoxime moiety exhibit extraordinary accessibility, which facilitates the adsorption of ROX. High adsorption capacities were obtained for both materials which amounts are up to 732 and 787 mg g−1. After five times of recycling, a negligible decrease in the adsorption capacity was noted, which reveals the excellent regeneration ability of those two amidoxime-functionalized COFs. These results indicate that the state-of-the-art sp2 carbon-conjugated amidoxime-functionalized COFs exhibit a high potential for the practical detection and adsorption of organoarsenic compounds from wastewater.