Blue-red emission color change from a heavily-doped Eu@MOF composite: Synthesis, characterization and application for 2,4,6-trinitrophenol sensing

2,4,6-trinitrophenol (TPA) natural degradation is nearly impossible and its accumulation threatens ecosystem. Optical sensing is an attractive detection method for TPA with low demand of equipment and data processing, but still needs to be improved. This work was dedicated to increasing probe-loading content so as to improve sensing sensitivity. Three probes derived from Eu(III)-benzimidazole were designed, with their active H atoms replaced by alkyl groups to eliminate the hydrogen bond with supporting host and thus to improve probe-loading content. Their molecular structure, absorption, emission, and excitation spectra were discussed to confirm their sensing potential to TPA. Then these three probes were loaded into host (bio-MOF-1) via ionic exchange method, which was confirmed by XRD, N2 adsorption/desorption, ICP, and SEM. The loading content and sensing performance of these three probes in bio-MOF-1 were compared. It was found that the elimination of active H atoms indeed increased probe loading content from 44% to 78%, with sensing coefficient increased from 0.010 μM-1 to 0.029 μM-1. A ratiometric sensing towards TPA was observed, with blue emission from bio-MOF-1 host increased and red emission from Eu(III) probe decreased, which was detectable by naked eyes. Linear working equations were fitted with high selectivity.