Eco-friendly biosynthesis of ZrS₂ quantum dots using diverse bacterial strains and their optical properties

In this study, for the first time, a novel biosynthesis method for producing zirconium disulfide quantum dots (ZrS₂ QDs) using both Gram-negative ( Acinetobacter baumannii, Enterobacter aerogenes and Pseudomonas aeruginosa ) and Gram-positive ( Bacillus subtilis, Enterococcus faecalis and Staphylococcus aureus ) bacterial strains is presented. All 6 synthesized ZrS 2 QDs were studied by fluorescence, UV–Vis and FTIR spectroscopy. The synthesized ZrS 2 QDs A. baumannii, E. faecalis and S. aureus were characterized by using XRD, DLS, Raman, SEM and EDX techniques. The Tauc plot method was applied for the calculation of bandgap energies (E g ) of the biosynthesized ZrS 2 QDs; the E g for those QDs were found within the range of 4.66 to 4.86 eV. Also, by applying the Brus equation, the size (D) of biosynthesized ZrS 2 QDs was found to be less than 1 nm. Quantum yield (Φ) of all ZrS₂ QDs were studied and among those, the biosynthesized ZrS₂ QDs with S. aureus exhibited highly quantum yield (86 %). The D of the biosynthesized QDs were also studied with the XRD and DLS techniques and results showed that the D were between 2.80 and 3.45 nm. The elemental compositions of the ZrS 2 QDs were studied with the EDX technique and confirming the presence of Zr and S elements in the structure of the ZrS 2 QDs. This work introduces the biosynthesis of ZrS 2 QDs via different bacterial strains with very high fluorescence intensity and quantum yield. • First-time biosynthesis of ZrS₂ QDs using six diverse bacterial strains (both Gram-positive and Gram-negative). • Eco-friendly synthesis using bacterial pathways, avoiding toxic chemicals/harsh conditions. • High quantum yield (86 %) achieved for S. aureus -derived ZrS₂ QDs, surpassing previous reports. • Ultra-small size (<1 nm) confirmed by Brus equation, showing strong quantum confinement effects. • Multi-technique size characterization: Brus equation (<1 nm quantum confinement), XRD (2.8–3.4 nm crystallite size), and DLS (1.3–6.6 nm hydrodynamic diameter) provide comprehensive size validation. • Excellent optical fluorescence properties of the biosynthesized ZrS₂ QDs were achieved.