Escherichia coli Bacteria-Templated Synthesis of Nanoporous Cadmium Sulfide Hollow Microrods for Efficient Photocatalytic Hydrogen Production

A simple sonochemical method has been utilized to synthesize nanoporous hollow structures of semiconducting cadmium sulfide (CdS) using Escherichia coli bacteria as template. To enable adsorption and reaction throughout the E. coli cell envelope, the cell permeability is enhanced by suitable ethanol treatment while preserving the morphology. With cadmium acetate and thioacetamide as reactants, CdS nanostructures in the form of monodisperse quantum dots, nearly monodisperse nanocrystals, and nanoporous hollow microrods are controllably formed on ethanol-treated E. coli with increasing reaction time. Additionally, nanorod antennas have been fabricated by utilizing the pili formed during the growth phase of the bacteria. The CdS crystal structure can be tuned from being pure cubic to a mixture of cubic and hexagonal or pure hexagonal by simply adjusting the sulfur/cadmium molar ratio of the reactants. Photoanodes fabricated using the hexagonal structured CdS nanoporous hollow microrods exhibit excellent performance for photocatalytic hydrogen production, with a maximum photoelectrochemical cell efficiency of 4.3% under global AM 1.5 illumination. This is significantly better than the 1.2% efficiency obtained using CdS nanoparticles synthesized utilizing the same procedure in the absence of E. coli. The bacterial template route has been extended to the synthesis and assembly of other chalcogenide nanostructures, including PbS, HgS, and ZnS. Use of chalcogenide hollow nanostructures with mixed stoichiometry can potentially lead to further improvements in the photoconversion efficiency.