Dr. Valdes-Morales, Hector

2020, Dr. Valdes-Morales, Hector, Pugazhenthiran, Nalandhiran, Mangalaraja, R., Vijaya, S., Suresh, S., Kandasamy, M., Sathishkumar, P., Gracia-Pinilla, M., Murugesan, S., Anandan, S.

A facile, fluorine-free and non-toxic one-pot solvothermal technique was adopted to synthesis TiO2 nanoflowers with anatase phase having 98% highly exposed {001} facets (TiO2 {001} NFs). The morphology, grain size and crystallinity of pure TiO2 {001} NFs and reduced graphene oxide (RGO) sheets modified TiO2 {001} NFs (RGOTiO2 {001} NFs) were inspected by diffuse reflectance spectroscopy (DRS), X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM images showed the development of anatase TiO2 {001} NFs with high crystallinity and uniform shape. The influence of RGO on the performance of the TiO2 {001} NFs as a photoanode material in dye-sensitized solar cell (DSSC) was examined. High energy conversion efficiency (ɳ) was observed for the DSSC based on a photoanode made of RGO-TiO2 {001} NFs when compared to DSSCs based on photoanodes fabricated using pure TiO2 {001} NFs and commercial Degussa P25 TiO2, which exhibited η of 6.78, 4.59 and 2.71%, respectively. The improved performance of the DSSC based on a photoanode composed of RGOTiO2 {001} NFs was due to its good crystallinity, high dye intake and enhanced light-harvesting properties. Moreover, the presence of RGO greatly hindered the recombination of photogenerated electrons and increased their lifespan. This work discloses a novel efficient photoanode design for improving performance of the DSSCs.

2021, Pugazhenthiran, N., Murugesan, S., Muneeswaran, T., Suresh, S., Kandasamy, M., Valdes-Morales, Hector, Selvaraj, M., Savariraj, A. Dennyson, Mangalaraja, R. V.

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.

2022, Dr. Valdes-Morales, Hector, Nalandhiran, Pugazhenthiran, Murugesan, S., Selvaraj, M., Sathishkumar, P., Smirniotis, P., Anandan, S., Mangalaraja, R.

In this study, 250 nm sized porous anatase TiO2 nanospheres (TiO2 NSPs) composed of 10 nm sized anatase TiO2 nanoparticles are obtained through a green synthetic route and their surfaces have been decorated with 3–4 nm sized plasmonic silver nanoparticles (AgNPs). Photoluminescence studies confirm that the AgNPs presence on TiO2 NSPs surface effectively inhibits the radiative charge recombination and thus facilitates charge separation process at the Ag-TiO2 NSPs interface, causing an enhanced photocatalytic activity. About 92% of the ceftiofur sodium (CFS) antibiotic taken initially is oxidized by Ag-TiO2 NSPs upon 90 min white light irradiation, while Ag loaded Degussa P25 TiO2 nanoparticles effects only 71% CFS oxidation. The synergistic effect given by plasmonic AgNPs and the continuous framework of anatase TiO2 NPs contributes to inhibit the electron-hole recombination in the Ag-TiO2 NSPs. Oxidation products of CFS in different water sources and their eco-toxicity effects identified through LC-MS and microtoxbioassays, respectively, indicate that the obtained oxidation products are non-toxic compared to pure CFS. Therefore, porous Ag-TiO2 NSPs could be successfully applied in photocatalytic oxidation technologies, exploiting sunlight for the effective removal of pharmaceutical pollutants from wastewater.