To photo-catalytically degrade RhB dye using solar irradiation, CeO₂ doped TiO₂ nanocomposites were synthesized hydrothermally at 700 °C for 9 hrs. All emission spectra showed a prominent band centered at 442 nm that was attributed to oxygen related defects in the CeO₂-TiO₂ nanocrystals. Two sharp absorption bands at 1418 cm⁻¹ and 3323 cm⁻¹ were attributed to the deformation and stretching vibration, and bending vibration of the OH group of water physisorbed to TiO₂, respectively. The photocatalytic activities of Ce-TiO₂ nanocrystals were investigated through the degradation of RhB under UV and UV+ visible light over a period of 8 hrs. After 8 hrs, the most intense absorption peak at 579 nm disappeared under the highest photocatalytic activity and 99.89% of RhB degraded under solar irradiation. Visible light-activated TiO₂ could be prepared from metal-ion incorporation, reduction of TiO₂, non-metal doping or sensitizing of TiO₂ using dyes. Studying the antibacterial activity of Ce-TiO₂ nanocrystals against E. coli revealed significant activity when 10 μg was used, suggesting that it can be used as an antibacterial agent. Its effectiveness is likely related to its strong oxidation activity and superhydrophilicity. This study also discusses the mechanism of heterogeneous photocatalysis in the presence of TiO₂.

In recent decades focus of research has been toward an alternative antibacterial agent because of growing bacterial resistance and side effects of antibacterial agents. In the current study, the antibacterial activity of gold nanoparticles has been evaluated on selected human pathogens. In this study, we used panchagavya (PG) to synthesize gold nanoparticles, and the resulting nanoparticles (PG-AuNPs) were characterized by several spectroscopic techniques. In addition, antibacterial activity of PG-AuNPs against Escherichia coli, Bacillus subtilis, and Klebsiella pneumoniae were studied by well diffusion method. The synthesis of AuNPs was affirmed by a colour change, which was further validated by UV-vis spectra with a maximum absorption peak at 527 nm. Bandgap energy was calculated as 2.13 eV by Tauc method from the UV result. The presence of amino acids and proteins in PG was responsible for the conversion of gold ions to AuNPs, according to FTIR analysis. (111), (200), (220), and (311) crystallographic planes were observed by XRD; further crystalline nature was validated by SAED analysis. The size and zeta value were found to be 53.29 nm and -9.8 mV respectively. Spherical shaped nanoparticles and elemental structure of PG-AuNPs were confirmed by HRTEM and EDS analysis. The antibacterial activity of PG-AuNPs showed the maximum and minimum zone of inhibition against K. pneumoniae (17.12 ± 0.14 mm) and B. subtilis (11.42 ± 0.58 mm). Antibacterial activity of PG-AuNPs was found to be strong against gram negative bacteria and moderate against gram positive bacteria. Based on the result, it was concluded that PG-AuNPs could be used to combat antibiotic drug resistance. Besides, in vitro and in vivo toxicity studies of PG-AuNPs should be conducted.