Cu-MOF-74 as Fluorescent Probe: Selective Optical Sensor for H2S Gas

In order to address the air quality issues and industrial gas leakages effectively, gas sensors must be highly sensitive, selective, stable, cost-effective, and with high life time. We present here a facile solvothermal method to synthesize a Cu based metal-organic framework (Cu-MOF-74) and demonstrated its potential as a selective fluorescent probe for environmental H₂S gas detection. Cu-MOF-74 based fluorescence sensor shows strong affinity towards H₂S with the limit of detection as low as 7 ppm., Though Cu-MOF-74 based sensor exhibited high sensitivity and selectivity for H₂S gas over H₂, SO₂ and NH₃, Co-MOF-74 is inactive towards H₂S sensing. The increased fluorescence intensity in presence of H₂S gas as well as the decreased fluorescence intensity in presence of NO₂ gas was investigated by experimental observation and theoretical calculation. In presence of H₂S gas, interaction between Cu and sulphur atoms occur, the bond between Cu and ligand. This reduces the extent of ligand to metal charge transfer, resulting in increase in fluorescence intensity. The present attempt led to the progress of highly selective and sensitive fluorescence-based environmental gas sensing probe using metal organic framework with a wide operating temperature ranging of 25 °C to 90 °C.