Sustainable synthesis of tunable emissive sulphur-doped CDs: a synergistic approach for metal ion sensing and antimicrobial applications

Abstract

Over the last two decades, materials from the carbon family attracting increasing attention, carbon dots (CDs) have been synthesized via naturally or synthetically derived precursors, which are mostly limited to single fluorescence emission. Tunable emissive CDs have great importance in multiple applications. Therefore, in the present study, multi-emissive sulphur doped carbon dots (S-CDs) were synthesized using the leaves of Nyctanthes arbor tristis, commonly known as night-flowering jasmine (NFJ), as a precursor, by a simple acid carbonization method. Interestingly, different synthesis parameters were employed for tuning the optical properties of the S-CDs, of which the synthesis time played a vital role for tuning the fluorescence emission of the S-CDs. Bright blue (BB-CDs), yellow (Y-CDs), and cyan blue (CB-CDs) fluorescence emissions with reaction times of 1, 6, and 8 h were observed. These three CDs have emission ranges of 391, 661 and 408 nm with corresponding quantum yields of 38.96, 6.59, and 25.06%, respectively. The structural and functional morphology of all three S-CDs were analyzed using various characterization techniques. S-CDs showed both excitation dependent (BB-CDs, CB-CDs) and independent (Y-CDs) emission behavior with good photo and pH stability. Furthermore, all the S-CDs were utilized as fluorescent probes for the detection of metal ions, and BB-CDs selectively detect Fe³⁺, Y-CDs detect Cr⁶⁺and Mn⁷⁺, and CB-CDs detect Cr⁶⁺ and Fe³⁺ions with corresponding LODs of 0.1, 1.66, 0.96, 2.18 and 1.56 μg mL⁻¹, respectively. The static quenching mechanism was observed for BB-CDs and CB-CDs, while in the case of YB-CDs, Cr⁶⁺ shows the dynamic quenching mechanism. In addition, the antibacterial behavior of all three S-CDs was analyzed against S. aureus and K. pneumoniae (Gram positive and Gram negative) bacteria. These S-CDs show good potential in metal ion sensing in environmental water samples and biological activity.