Zhang Wei,Wang Qiao,Qin Fan,Zhou Huamin,Lu Zhong,Chen Rong
Palladium nanoparticles (NPs) were successfully synthesized via a rapid and facile microwave route in HEPES (2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid) buffer solution. The shape- and size-controlled Pd nanoparticles could be obtained by one-step method without dependence
of seed-mediated growth. The capping agent plays a key role in the formation of Pd NPs with different shape and size, which could be tuned by varying capping agents such as polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), sodium citrate (Na3(cit)) and potassium
bromide (KBr). The size-dependent catalytic activities of the obtained Pd NPs for Suzuki coupling reaction were also investigated. It demonstrated that the catalytic activity of Pd NPs was enhanced regularly with the decrease of particle size. Pd NPs less than 10 nm exhibited better catalytic
activities for Suzuki reaction than the commercial Pd/C catalyst. Pd/MWCNTs and Pd/SBA-15 nanocomposites were also prepared by a facile method and afforded good catalytic activity and reusability. This "green" synthetic protocol could be used as a general method for the rapid synthesis of
transition metal nanoparticles.
Size- and morphology-controlled zinc oxide (ZnO) micro-/nanostructures have been successfully synthesized via a facile and rapid microwave and ultrasonic wave combined method in HEPES solution (HEPES = 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid). The as-prepared ZnO products are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–vis diffuse reflection spectroscopy (DRS). Various morphologies of ZnO products, including grenade-like, column-like, spindle-like, rod-like, shuttle-like and flower-like micro-/nanostructures are obtained, which are strongly dependent on Zn/HEPES moral ratio, pH value and Zn precursor. It is found that HEPES plays a crucial role in the formation of ZnO micro-/nanostructures with controllable size and morphology. The photocatalytic activities of the prepared ZnO micro-/nanostructures are evaluated by degradation of methylene blue (MB) under UV light irradiation, among which spindle-like ZnO microstructures exhibit superior photocatalytic activity compared with other ZnO products.
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