Dr. Valdes-Morales, Hector

Light-induced photocatalytic degradation of ceftiofur sodium (CFS) has been assessed in the presence of plasmonic zinc oxide nanostructures (ZnONSTs), like, ZnO nanoparticles, ZnO nanorods (ZnONRs) and ZnO nanoflowers (ZnONFs). Silver nanoparticles (Ag NPs) loaded ZnO nanostructures (Ag-ZnONSTs) are obtained through seed-assisted chemical reaction followed by chemical reduction of silver. The surface modification of ZnO nanostructures by Ag NPs effectually altered their optical properties. Further, the surface plasmonic effect of Ag NPs facilitates visible light absorption by ZnONSTs and improved the photogenerated electron and hole separation, which makes the ZnONSTs a more active photocatalyst than TiO2 (P25) nanoparticles. Especially, Ag-ZnONRs showed higher CFS oxidation rate constant (k' = 4.6 × 10−4 s−1) when compared to Ag-ZnONFs (k' = 2.8 × 10−4 s−1) and Ag-ZnONPs (k' = 2.5 × 10−4 s−1), owing to their high aspect ratio (60:1). The unidirectional transport of photogenerated charge carriers on the Ag-ZnONRs may be accountable for the observed high photocatalytic oxidation of CFS. The photocatalytic oxidation of CFS mainly proceeds through •OH radicals generated on the Ag-ZnONRs surface under light illumination. In addition, heterogeneous activation of peroxymonosulfate by Ag-ZnONRs accelerates the rate of photocatalytic mineralization of CFS. The quantification of oxidative radicals supports the proposed CFS oxidation mechanism. Stability studies of plasmonic Ag-ZnONSTs strongly suggests that it could be useful to clean large volume of pharmaceutical wastewater under direct solar light irradiation.

Monodispersed silver quantum dots (Ag QDs) of sub 5 nm range are prepared through a facile and size-controllable green synthesis route using sweet lime (Citrus limetta) peel (SLP) extract. Powder X-ray diffraction studies confirm the formation of face-centered-cubic structured Ag QDs which is corroborated by selected area electron diffraction. The Ag QDs show an absorption maximum at ~415 nm due to characteristic surface plasmon resonance. The Ag QDs prepared at 80 °C exhibit high photoluminescence quenching, indicating low recombination rate and high lifetime of photoexcited electrons. The examination of SLP extract by Fourier-transform infrared spectroscopy, LC-MS and NMR spectroscopy reveals the presence of citrate and carbohydrate biomolecules that could be responsible for the formation of small and stable Ag QDs. The cytotoxic studies indicate that the synthesized Ag QDs are able to effect 71% cancer cells death at 100 µg/mL concentration. Moreover, Ag QDs exhibit minimum inhibitory concentration (MIC) value of 50 μg/mL against all the selected pathogenic bacteria. Present findings suggest that Ag QDs obtained by SLP extract mediated green synthesis can be employed as a low-cost and eco-friendly biocidal agent.