Biosynthesis, characterization and optimization of TiO nanoparticles by novel marine halophilic Halomonas sp. RAM2: application of natural dye-sensitized solar cells.

Background: Metal oxide nanoparticles (NPs) are becoming valuable due to their novel applications. The green synthesis of TiO NPs is more popular as a flexible and eco-friendly method compared to traditional chemical synthesis methods. TiO NPs are the most commonly used semiconductor in dye-sensitized solar cells (DSSCs).

Results: The biogenic TiO NPs were produced extracellularly by the marine halophilic bacterium Halomonas sp. RAM2. Response surface methodology (RSM) was used to optimize the biosynthesis process, resulting in a starting TiO concentration of 0.031 M and a pH of 5 for 92 min (⁓15 nm). TiO NPs were well-characterized after the calcination process at different temperatures of 500, 600, 700 and 800 °C. Anatase TiO NPs (calcined at 500 °C) with a smaller surface area and a wider bandgap were nominated for use in natural dye-sensitized solar cells (NDSSCs). The natural dye used as a photosensitizer is a mixture of three carotenoids extracted from the marine bacterium Kocuria sp. RAM1. NDSSCs were evaluated under standard illumination. After optimization of the counter electrode, NDSSC (10 layers) demonstrated the highest photoelectric conversion efficiency (η) of 0.44%, which was almost as good as NDSSC (0.55%).

Conclusion: The obtained results confirmed the successful green synthesis of TiO NPs and suggested a novel use in combination with bacterial carotenoids in DSSC fabrication, which represents an initial step for further efficiency enhancement studies.