Green and energy-efficient methods for the production of metallic nanoparticles

In the last decade, researchers paid great attention to the concept of “Green Chemistry”, which aims at development of efficient methods for the synthesis of nanoparticles (NPs) in terms of the least possible impact on human life and environment. Generally, several reagents including precursors, reducing agents, stabilizing agents and solvents are used for the production of NPs and in some cases, energy is needed to reach the optimum temperature for reduction. Therefore, to develop a green approach, researchers had the opportunity to investigate eco-friendly reagents and new energy transfer techniques. In order to substitute the harmful reagents with green ones, researchers worked on different types of saccharides, polyols, carboxylic acids, polyoxometalates and extracts of various plants that can play the role of reducers, stabilizers or solvents. Also, there are some reports on using ultraviolet (UV), gamma and microwave irradiation that are capable of reducing and provide uniform heating. According to the literature, it is possible to use green reagents and novel energy transfer techniques for production of NPs. However, these new synthesis routes should be optimized in terms of performance, cost, product quality (shape and size distribution) and scale-up capability. This paper presents a review on most of the employed green reagents and new energy transfer techniques for the production of metallic NPs

Nanoparticle size and concentration dependence of the electroactive phase content, electrical and optical properties of Ag/poly(vinylidene fluoride) composites

This paper describes the processing of silver nanoparticle doped poly(vinylidene fluoride). The effect of filler concentration and size on the electroactive phase of the polymer, as well as on the optical and electrical properties is discussed. Spherical silver nanoparticles incorporated into the poly(vinylidene fluoride) polymeric matrix induced the nucleation of the electroactive phase. The electroactive phase content strongly depends on nanoparticle content and size. In particular, there is a critical nanoparticle size, below which the filler losses the nucleation efficiency, due to the small size relative to the polymer macromolecules. Furthermore, the presence of surface plasmon resonance absorption in the composites is observed, once again showing a strong dependence on particle concentration and size. The absorption is larger for larger concentrations and for a given concentration increases with particle size. This behavior is correlated to the electrical response and is related to the extra bands and electrons provided by the nanoparticles in the polymer large energy band gap.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETE" and by national funds by FCT- Fundação para a Ciência e a Tecnologia, project references NANO/NMed-SD/0156/2007, PTDC/CTM/69316/2006 and PTDC/CTM-NAN/112574/2009. FCT is acknowledged for the grant SFRH/BD/62507/2009 (for ACL) and CIENCIA 2007 program (for SACC). The authors also thank support from the COST Action MP1003, the ‘European Scientific Network for Artificial Muscles’ (ESNAM)