Increasing demand of noble-metal nanoparticles (MNPs) in catalysis research urges the development of a nontoxic, clean, and environmentally friendly methodology for the production of MNPs on solid surface. Herein we have developed a facile approach for biosynthesis of MNPs (Pd, Pt, and Ag) on the surface of Rhizopous oryzae mycelia through in situ reduction process without using any toxic chemicals. The size and shape of the biosynthesized MNPs varied among the MNPs, and "flower"-like branched nanoparticles were obtained in case of Pd and Pt, while Ag produced spheroidal nanoparticles. The cell-surface proteins of the mycelia acted as protecting, reducing, and shape-directing agent to control the size and shape of the synthesized MNPs. Proteins of 78, 62, and 55 kDa were bound on the MNPs surfaces and played a significant role in determining the morphology of the MNPs. The catalytic efficiency varied among the MNPs, and Pd nanoflower exhibited superior catalytic activities in both hydrogenation and Suzuki coupling reactions. Surface composition, concentration, and intracellular localization of MNPs determine the catalytic activity of the biosynthesized MNPs. The nanocatalyst could be easily separated and reused multiple times without significant loss in activity (95% average conversion). Overall, the understanding of this complex biomineralization mechanism and catalytic behavior at the nano−bio interface has provided an alternative for the synthesis of supported metal nanocatalyst to improve the environmental sustainability.

No abstract

The interfacial interaction and charge transfer dynamics between a F 16 CuPc molecular thin film and rutile TiO 2 (110) (1×1) surface have been studied by photoelectron spectroscopy (PES), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and resonant photoemission spectroscopy (RPES). The evolution of PES spectra as a function of F 16 CuPc film thickness shows strong coupling between the molecules and the TiO 2 surface. Adsorbed molecules experience substrate mediated charge transfer. Electrons being pulled away from nitrogen atoms toward to carbon ring results in an opposite direction binding energy shift for C 1s and N 1s. Moreover, the molecule gets deformed due to their strong interaction with the TiO 2 surface. Ultrafast charge transfer from F 16 CuPc molecules to the TiO 2 substrate takes place on the time scale of 10 fs due to their strong electronic coupling. The results pave the way for the design and realization of F 16 CuPc based electronic devices.

The structures of Pd islands at three different Pd coverages (0.028, 0.064, and 0.150 monolayer (ML)) on Ag(111) were studied at room temperature with scanning tunneling microscopy (STM). While previous studies have shown that the structure and composition of Pd islands on Ag(111) change at elevated temperatures, we found that Ag atoms migrate to cover the Pd islands even at room temperature. These Ag atoms occupy sites in the middle of the islands, and second layer growth begins at these sites. The migration of Ag atoms leads to the formation of vacancy islands in the Ag(111) terraces. Upon annealing to 340 K, the majority of the Pd islands are encapsulated by Ag atoms to form an Ag/Pd/Ag(111) structure. However, upon further annealing the composition of some islands at a Pd coverage of 0.150 ML changed to Ag/Ag/Pd/Ag(111).

No abstract