A 2D pillared-layer Co-based MOF as a “two-in-one” chemosensor for S2- with meticulous chemodosimetric screening of HSO4- in absolute aqueous medium and photo-induced thiol-ene for CO2 conversion

Herein, we have designed a new Co(II)-based MOF, {[Co(1,4-NDC)(4,4′-BPY)(H2O)2].H2O}∞ (Co-NDC-BPY) by using mixed ligands 1,4-napthalenedicarboxylic acid (1,4-NDC) and 4,4′-bipyridine (4,4′-BPY). Interestingly, the MOF can selectively and discriminatively detect S2- and HSO4- from purely aqueous medium via mutually independent mechanism with prompt response (∼6 s) at very low detection thresholds of 29.9 μM and 9.4 μM for S2- and HSO4-, respectively. In the presence of S2-, “turn-off” fluorescence response is perceived via static quenching due to facilitation of photoinduced electron transfer (PET) process via ground state complexation. On the other hand, protic anion, HSO4- systematically enhanced the fluorescence at 435 nm via releasing the co-ligand. Moreover, detection from several field-water samples with good recovery, demonstrates the real-world applicability of this Co-NDC-BPY MOF. To the best of our knowledge, this is the first MOF based chemosensor, which could discriminatively detect HSO4- and S2- from fully aqueous solutions. Additionally, this MOF exhibits excellent catalytic activity in the CO2 fixation on epoxides. The potential energy calculation suggests the possible mechanistic pathway for this cycloaddition reaction. As it possesses a moderately low band gap with n-type conductivity, this Co-NDC-BPY MOF is also explored as photocatalyst in thiol-ene chemistry for the synthesis of thiol-ether bridged bis-carbonate from allyl-glycidyl carbonate monomer, which is a platform chemical for the synthesis of valuable polymers.