Inherent photocatalytic activity of luminescent multi-doped carbon dots manufactured from expired medicine and its application for efficient water remediation and nanosensing

[Display omitted] •Expired vitamin B1 and phosphate were used as feedstock for carbon dots synthesis.•A fast green microwave-assisted synthesis of multidoped-carbon dots.•The multidoped-carbon dots have dual functions as nanosensor and photocatalyst.•The multidoped-carbon dots have been applied as a nanosensor for thiocolchicoside.•The multidoped-carbon dots were used as a photocatalyst for degradation of EBT dye. A fast and green synthesis of multi-doped carbon dots (multi-doped CDs) has been accomplished within 6 min of microwave treatment of a mixture of expired medicine, Vitamin B1, and phosphate salt as a feedstock. Characterization of the prepared quantum dots revealed multi-doping with nitrogen, sulfur, phosphorus, sodium, and chlorine. The prepared multi-doped CDs were applied for dual functions as an efficient photocatalyst and a sensitive fluorescence nanosensor that are not restricted by toxicity, cost, or stability. The efficient light absorption, electron transfer, and separation of photogenerated charge carriers within the multi-doped CDs enabled their use as an effective photocatalyst for remediation of organic dye-polluted water. Efficacious degradation of eriochrome black T dye (≈88 %) was accomplished within 80 min under visible light irradiation. Radical scavenging experiments demonstrated that the active species are hole, superoxide, and hydroxyl radicals. Furthermore, the multi-doped CDs were applied as a nanosensor for sensitive determination of the muscle relaxant drug thiocolchicoside (TCC) via fluorescence switch-off mechanism mediated by inner filter effect and dynamic quenching. The nanosensor was applied for the determination of TCC in its tablets with mean recovery % of 99.95 ± 1.55 and excellent selectivity. The present approach is a further step for circular economy applications hence it converts valueless chemical waste into valued products with useful applications.