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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Biosynthesis of nanoparticles has arisen as a promising alternative to conventional synthetic methodologies owing to its eco-friendly advantages, and the involved bioprotocol still needs further clarification. This research, for the first time from the standpoint of statistics, confirmed an electrostatic force or ionic bond-based interaction between the chloroauric ions and the involved bioconstituents and manifested that reducing sugars and flavonoids were both important reductants responsible for conversion of Au(III) to Au(0). The result also demonstrated that the proteins were not the reducing agents, yet they might be protection agents in biosynthesis of gold nanoparticles (GNPs). Besides, a significant linear relationship was found between the anti-oxidant ability of the foliar broths and their capability to reduce Au(III) into Au(0). Furthermore, the preliminary investigation based on the boxplot on the size/shape distribution of the biosynthesized GNPs revealed that gold nanospheres with higher degree of homogeneity in size tended to be promoted by foliar broths containing higher content of reducing sugars/flavonoids and proteins. Otherwise, i.e., for those broths with lower content of the above biocompounds, sphere GNPs of wider size distribution or even gold nanotriangles tended to be fabricated.(See supplementary material 1)

Tea time! Gold nanoparticles (GNPs) could be readily prepared by a general strategy involving the reduction of aqueous HAuCl(4) in the presence of traditional Chinese medicines (TCMs). Spheroidal and triangular gold nanoparticles were observed depending on the TCM used. The strategy exemplified the universal application of plant bioresources for the synthesis of GNPs and catalytic purposes.