Highly effective detection of picric acid by a Ca(II)-Framework with adjustable crystal morphology and size

It is of great significance to synthesize photo-functional metal-organic frameworks (MOFs) for specific identification of pollutants and to control the morphology of MOFs for practical applications. In this article, a Ca(II)-organic framework [HBU-170, H3L ​= ​4, 4′, 4'' - (1H-imidazole-2, 4, 5-triyl) tribenzoic acid] with controllable morphology and size, was successfully synthesized under solvothermal conditions by regulating pH and characterized. With the decrease of pH value, the size of crystals is getting larger and the appearance changes from spherical to the flowers “blossomed” gradually. For the best crystallinity and better thermal stability, HBU-170–25 was selected as the volunteer for fluorescent detections. To investigate the concentration effect of detection, two groups of nitro aromatic compounds are used as additive agent. The most striking properties of HBU-170–25 are the distinct red shift and fluorescence changes observed in the presence of picric acid. The limit of detection (LOD) is calculated to be 19.06 ​μM (based on the linear regression in the range of 65.420–310.345 ​μM). The fluorescence quenching rates of picric acid is 6.7 × 103 in the linear range of 65.420–310.345 ​μM. According to the quenching efficiency, HBU-170–25 represents the better detection ability in the lower concentration. Moreover, the results of actual sample analysis indicate that HBU-170–25 owns the potential of application in the tests of actual samples.