Effect of nanosized TiO₂ on photofermentation by Rhodobacter sphaeroides NMBL-02

Hydrogen, being a clean energy source is considered as a promising future fuel. In the present investigation, we have studied the H₂ production by photosynthetic bacterial lab isolate Rhodobacter sphaeroides NMBL-02 in presence of TiO₂ nanoparticles. The mixed phase (Anatase and Rutile) distributed TiO₂ nanoparticles enhanced hydrogen production by R. sphaeroides NMBL-02 in the visible light and made the batch system operative for longer duration. The average size of the annealed TiO₂ nanoparticles was between 8–20 nm with spherical shapes. There was no detectable amount of hydrogen produced by TiO₂ nanoparticles alone in the same medium containing malate as carbon source. Whereas, significant amounts of hydrogen and CO₂ were detected with pyruvate as carbon source in the same media which confirmed that the nanoparticles utilized pyruvate as preferred electron donor and facilitated conversion of the intermediate (pyruvate) into CO₂ and H₂. Rate of H₂ production was enhanced by 1.54 folds and duration 1.88 folds in the presence of 60 μg/mL concentration of annealed TiO₂ nanoparticles in comparison to the control. Maximum hydrogen produced was 1900 mL/L with 63.27% malate conversion in a batch process with annealed TiO₂ nanoparticles during photofermentation by R. sphaeroides in modified Sistrom's media using malate (22.38 mM) and glutamate (1.7 mM) as carbon and nitrogen sources respectively. - Highlights: • Effect of nanosized TiO₂ has been reported on photohydrogen production by R. sphaeroides-NMBL-02. • Maximum hydrogen produced was 1900 mL/L with 63.27% malate conversion with annealed TiO₂ nanoparticles during photofermentation. • Rate of H₂ production was enhanced by 1.54 folds and duration 1.88 folds in the presence of 60 μg/mL concentration of annealed TiO₂ nanoparticles