Development of a new biophotocatalytic system for biofuel production

Currently, global energy requirements rely heavily on fossil fuels, the primary contributors to global warming and severe climate changes. It is imperative to decarbonize the energy supply sector, by utilizing an alternative, clean and sustainable energy source, like hydrogen, that can be generated from renewable resources, such as solar energy. The aim of this dissertation was the construction of a new biophotocatalytic system using non-photosynthetic anaerobic bacteria coupled with semiconductor metal sulfide nanoparticles, for light-driven H2 production. In this system, nanoparticles act as light-harvesting material, enabling the microorganism to capture and absorb sunlight energy, using it for H2 generation. In the present work, four bacteria Citrobacter freundii , Clos tridium acetobutylicum , Desulfovibrio vulgaris and Desulfovibrio desulfuricans were used as biocatalysts with self-produced cadmium sulfide (CdS) nanoparticles to produce hydrogen. The performance of these biohybrids was further compared with the control system Escherichia coli -CdS. Moreover, new semiconductor combinations were tested, by loading cocatalysts metals tungsten (W), nickel (Ni) and molybdenum (Mo) into CdS. The D. desulfuricans -CdS biohybrid was demonstrated to be the best photocatalytic system for light-driven H2 production from the four biohybrids proposed and E. coli -CdS control system. D. desulfuricans -CdS system presented a remarkable H2 production both in the presence and absence of the electron mediator methyl viologen (MV), with 46.0±4.8 and 31.7±8.1 µmol of H2, respectively, after 45 and 142 h of light irradiation. The D. desulfuricans -CdS performance was improved by adding cocatalysts, especially Mo, that allowed the increase of H2 production rate from 34.0±0.8 to 130.8±9.3 µmol gdcw-1h-1, without MV. Finally, D. desulfuricans -CdS-MoS2 was successfully immobilized in calcium alginate beads and a batch photoreactor for H2 production was constructed. These results show the high potential of D. desulfuricans -CdS-MoS2 biohybrid photosystem for an efficient and clean hydrogen production.