Carbon nanotubes and Cu–Zn nanoparticles synthesis using hyperaccumulator plants

This article reports a novel way to synthesize carbon nanotubes and Cu/ZnO nanoparticles using metal hyperaccumulator plants. Metal hyperaccumulator plants are traditionally used for phytoremediation to clean soil polluted by toxic metals. However, the transfer of toxic metals in plant shoots and leaves is an environmental issue because animals and other living organisms feeding on plants will transfer the metals to the ecosystem. Therefore, we suggest that hyperaccumulator plants could be used to synthesize nanoparticles. Here, Brassica juncea L., a Cu-hyperaccumulator plant, was collected around a copper mine and used as a raw chemical to produce carbon nanotubes and Cu/ZnO nanoparticles. The chlorophyll in shoots of B. juncea plants was ethanol extracted to yield chlorophyllin. Cu and Zn were extracted by HNO₃ to form Cu/Zn(NO₃)₂. The chlorophyllin reacted with Cu/Zn(NO₃)₂ to form Cu/Zn chlorophyllin. Cu/ZnO nanoparticles were synthesized by direct precipitation of Cu/Zn chlorophyllin with NaOH and ethanol. The vascular bundles in B. juncea plants, which have been purified and carbonized by HNO₃, were rapidly heated to about 400°C and then they were cooled to room temperature to obtain carbon nanotubes. Results indicate that the outer diameter of carbon nanotubes was around 80 nm. Cu/ZnO nanoparticles have a Cu_0.05Zn_0.95O composition, and had a diameter of about 97 nm. Our study not only inspires the search for a new strategy on the synthesis of nanostructure from renewable natural products, but also breaks through the traditional and limited ideas about the reuse of metals by hyperaccumulator plants.