Fluorometric and naked eye detection of cadmium ion by reduced Schiff base zinc-based probe in potable water: Theoretical and experimental approach

Alarmingly increasing population and industrial growth has immensely affected water bodies and potable water sources by elution of many heavy toxic metal ions, including cadmium (II). The rising threat has demanded easy and cost-effective detection of this heavy metal ion so as to spread widely across the masses and eliminate the poisoning of water. With this aim, we have synthesized a zinc-based fluorescent probe (rBDZn) having reduced Schiff base backbone with N- and O- donor atoms derived from 5-bromosalicaldehyde and 2,2-dimethylpropane-1,3-diamine, characterized with the aid of single crystal X-ray analysis, revealing a trimeric structure linearly bridged by azide ion. The complex has been found to exhibit a cyan blue fluorescence getting 'turned-off' in the presence of cadmium ion selectively along with many other cations in the aqueous solution together with a naked-eye visible color change from pale yellow to colorless. Steady-state and time-resolved fluorescence titration, and absorption titration experiments were performed. During the investigation of the sensing pathway it is observed that the detection of Cd2+ is being associated with the formation of the cadmium complex rBDCd from the probe rBDZn and this has been explained though a probable mechanism. In support of the fact a single crystal of Cd-substituted complex have been isolated and verified with single crystal XRD and computational calculations. Proper justification of the selectivity of the probe towards cadmium ion with a very low detection limit of 1.72 nM enables its genuine impact in the pollution management.