The synthesis of nanocrystals is in the limelight in modern nanotechnology. Biosynthesis of nanoparticles by plant extracts is currently under exploitation. Not only could silver nanoparticles ranging from 55 to 80 nm in size be fabricated, but also triangular or spherical shaped gold nanoparticles could be easily modulated by reacting the novel sundried biomass of Cinnamomum camphora leaf with aqueous silver or gold precursors at ambient temperature. The marked difference of shape control between gold and silver nanoparticles was attributed to the comparative advantage of protective biomolecules and reductive biomolecules. The polyol components and the water-soluble heterocyclic components were mainly responsible for the reduction of silver ions or chloroaurate ions and the stabilization of the nanoparticles, respectively. The sundried leaf in this work was very suitable for simple synthesis of nanoparticles.

The development of dependable, environmentally benign processes for the synthesis of nanoscale materials is an important aspect of nanotechnology. In the present study, we report one-pot biogenic fabrication of palladium nanoparticles by a simple procedure using broth of Cinnamomum camphora leaf without extra surfactant, capping agent, and/or template. The mean size of palladium nanoparticles, ranging from 3.2 to 6.0 nm, could be facilely controlled by merely varying the initial concentration of the palladium ions. The polyols components and the heterocyclic components were believed to be responsible for the reduction of palladium ions and the stabilization of palladium nanoparticles, respectively.National Natural Science Foundation of China [20776120, 20576109]; National High Technology Research and Development Program of China [2007AA03Z347]; Natural Science Foundation of Fujian Province of China [2008J0169

Biological production of silver nanoparticles by lixivium of sundried Cinnamomum camphora leaf in continuous-flow tubular microreactors was investigated. Properties of silver nanoparticles were examined by transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD), and energy dispersive X-ray (EDX). The concentration of residual silver ions after reaction was measured by atomic absorption spectophotometry (AAS) spectroscopy. Fourier transform infrared (FTIR) spectra of C. camphora leaf lixivium were analyzed and temperature profiles along the tubes were calculated to explore formation mechanism of silver nanoparticles. Comparison of FTIR spectra of C. camphora leaf lixivium before and after reaction demonstrated the polyols in the lixivium may be mainly responsible for reduction of silver ions. According to the temperature profiles, at the inlet of the microreactors at 90 °C, the soar of the fluid temperature induced the burst of silver nuclei by homogeneous nucleation. Subsequently, the nuclei grew gradually along the reactors into silver nanoparticles from 5 to 40 nm. Polydisperse particles were formed by combination of heterogeneous nucleation and Ostwald ripening along the tubes at 60 °C.

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