We report on the synthesis and characterization of catalytic palladium nanoparticles (Pd NPs) and their immobilization in microfluidic reactors fabricated from polydimethylsiloxane (PDMS). The Pd NPs were stabilized with D-biotin or 3-aminopropyltrimethoxysilane (APTMS) to promote immobilization inside the microfluidic reactors. The NPs were homogeneous with narrow size distributions between 2 and 4 nm, and were characterized by transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and x-ray diffraction (XRD). Biotinylated Pd NPs were immobilized on APTMS-modified PDMS and glass surfaces through the formation of covalent amide bonds between activated biotin and surface amino groups. By contrast, APTMS-stabilized Pd NPs were immobilized directly onto PDMS and glass surfaces rich in hydroxyl groups. Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy (XPS) results showed successful attachment of both types of Pd NPs on glass and PDMS surfaces. Both types of Pd NPs were then immobilized in situ in sealed PDMS microfluidic reactors after similar surface modification. The effectiveness of immobilization in the microfluidic reactors was evaluated by hydrogenation of 6-bromo-1-hexene at room temperature and one atmosphere of hydrogen pressure. An average first-run conversion of 85% and selectivity of 100% were achieved in approximately 18 min of reaction time. Control experiments showed that no hydrogenation occurred in the absence of the nanocatalysts. This system has the potential to provide a reliable tool for efficient and high throughput evaluation of catalytic NPs, along with assessment of intrinsic kinetics.
We report the electrochemical properties and charge storage ability of thioether stabilized Pd nanoparticles. A new synthetic strategy was used to prepare monodisperse Pd nanoparticles less than 2 nm in diameter. Pd nanoparticles brought in contact with a charged semiconductor were found to accept and store the charge. By employing an iron (III) porphyrin complex as a redox couple (Fe III/II ), we observed transfer of electrons from the Pd nanoparticles. The data supports the notion that Pd nanoparticles in the 1-2 nm size range are capable of behaving as small capacitors and are thus able to store charge and transfer them as needed.
Palladium's role in the catalysis of various chemical reactions has resulted in a strong interest towards the development of straightforward synthetic methods for its preparation on the nanoscale. In this chapter we review some of the most significant advances that have been made in the synthesis of palladium particles with nanoscale dimensions. Approaches to control the morphology are described, with an emphasis on reactions that have produced uniform particles with well‐defined sizes and shapes in high yields. In addition, several characterization techniques that have been employed to elucidate the morphology of the particles are illustrated. Finally, we briefly outline the applications of palladium nanoparticles as they relate to the life sciences.
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