Synthesis and Characterization of Metallic Nanoparticles Stabilized with Polyvinylpirrolidone

Abstract

The study of ultra-fine particles has been extensive in the last years for its unique properties and potential technological applications in different areas [1][2][3]. Magnetic ultra-fine metallic particles have been broadly investigated by its great coercive force and residual magnetization [2]. Many methods have been developed for the synthesis of nanoparticles, however there are several important problems to be solved: to prepare nanoparticles with a uniform size, to control the chemical and structural nature of these and to keep the particles well dispersed. In the objective of the present work is the synthesis and characterization of metallic nanoparticles of Fe, Co and Ni and its bimetallic compounds (FeCo, CoNi and FeNi) by the method of salt reduction stabilized with polyvinylpyrrolidone (PVP) and to study its magnetic properties by EPR.The nanoparticles of Fe, Co and Ni and the FeCo were obtained by the reduction of the metal acetylacetonate: Ni(acac) 2 , Co(acac) 3 and Fe(acac) 3 with sodium boron hydride (NaBH 4 ) in ethanol and they were stabilized with polyvinylpyrrolidone (PVP = 40.000) to 25 ºC. The synthesis was carried out in inert atmosphere placing in a ball the precursor, the stabilizer, the reducing agent and the solvent under continuous agitation for 24 hours until the solution turns brown or black. The characterization of the obtained systems was carried out by: Transmission Electron Microscopy (TEM), Electron Paramagnetic Resonance (EPR) and Fourier Transform Infrared Spectroscopic (FT-IR). The samples for transmission electron microscopy were prepared by placing a drop of the solution on a holey carbon grid and immediately before observation in order to avoid possible oxidation effects. However, samples observed a period after prepared did not show any changes. The IR spectra shows the disappearance of the bands (C = O and C =C) present in the precursors, this implies that in the reactions it is possible to displace the acac totally -to stabilize the particles in the polymeric matrix. The figure 1 show the dark field images for each metallic system. The system Fe/PVP presented a wide distribution of size particle in the range of 4-12 nm. In the Ni/PVP material the size and distribution was in the range of 7-15 nm. In the case of Co/PVP a narrow distribution (2-6 nm) was observed. For all bimetallic systems the distribution was narrow with particle size in the range of 2-5nm. Electron diffraction patterns of these samples identified the formation of the metallic compounds and the bimetallic compounds respectively. The formation of oxide was detected for the Fe nanoparticles, but not for the case of Ni, Co or the intermetallic compounds. For these the formation of the intermetallic compound was identified by electron diffraction. Figure 2 shows the unnormalized EPR spectra for Fe, Co and FeCo supported onto a PVP matrix. The spectrum for Fe shows clearly two Lorentzian signals, a high field signal very intense around g = 2.017 and a ∆Hpp = 18.6 mT and a less intense one at g = 3.857 with ...

Features of Structure and Properties of pHEMA-gr-PVP Block Copolymers, Obtained in the Presence of Fe2+

“…PVP is also a very good choice for making hydrogels [ 40 , 41 , 42 ]. The use of PVP opens up additional opportunities for the synthesis and stabilization of metal nanopowders [ 43 , 44 ], modification of various substances and materials [ 45 , 46 , 47 , 48 , 49 , 50 ], the improvement of modern technologies [ 51 , 52 , 53 ], the obtainment of new functional materials [ 54 , 55 , 56 , 57 ] and, accordingly, the expansion their application field.…”

Novel Ni/pHEMA-gr-PVP Composites Obtained by Polymerization with Simultaneous Metal Deposition: Structure and Properties

“…Polyvinylpyrrolidone (PVP) has attracted much attention due to its impressive properties, such as its biocompatibility, nontoxicity, solubility in water and many organic solvents, pH stability, affinity to complex both hydrophobic and hydrophilic substances, and status as chemically inert in physiological reactions [34]. The use of PVP opens additional opportunities for the synthesis [35] and stabilization of metal nanopowders [36,37], modification of various substances [38,39] and materials [40,41], improvement of modern technologies [42,43], production of new functional materials [44,45], and the respective expansion of their fields of use [10,46].…”

Investigation of nickel chemical precipitation kinetics

“…На даний час в літературі існує достатньо експе-риментальних даних щодо досліджень відновлення металів у присутності водорозчинних полімерів, зо-крема ПВП [16,17]. Переважно, полівінілпіролідон ви-користовують у невеликих кількостях, як стабілізатор металевих частинок.…”