Biomass valorization of liquid whey into carbon quantum dots via hydrothermal process for food pathogenic bactericidal activity and photocatalytic degradation of brilliant red dye

Whey is the primary waste material of the dairy industries; therefore, the present study focuses on the valorization of milk processing industry-originated liquid whey into valuable products, specifically liquid whey carbon quantum dots (LW-CQDs) for pathogenic bactericidal and photocatalytic dye reduction efficacy. Facile synthesis of fluorescent LW-CQDs was carried out by employing a green hydrothermal approach at 200 °C for 12 h. Several analytical techniques were used to confirm the thermally stable spherical particles, measuring 9.04 ± 0.76 nm size in diameter, primarily composed of carbon and oxygen LW-CQDs. The presence of diverse functional groups (hydroxyl, carboxyl, carbonyl, and methyl groups) of LW-CQDs contributed to overall optical properties, which manifested a blue emission peak at 418 nm with 240 nm excitation wavelength in fluorescence spectroscopy. UV–Visible spectra featured two peaks (π → π ∗ transition of C = C bonds and n → π ∗ transition of C = O bonds) at around 249 and 293 nm, respectively. Moreover, the synthesized LW-CQDs exhibited a significantly higher zone of inhibition (25.98 ± 0.17 mm) and significantly lower minimum inhibitory concentration (4.47 ± 0.01 μl/ml) against the Staphylococcus aureus. In addition, LW-CQDs revealed a higher killing rate of reaction for S. aureus as compared to K. pneumoniae, P. aeruginosa, and S. typhi and remarkably degraded 92.95 % of brilliant red dye under visible light (2000 lux). Hence, these facile LW-CQDs hold potential for applications in the effectiveness of antimicrobial and photocatalytic dye reduction activity, which show valuable contributions to both waste valorization and sustainable material development.