SYNTHESIS, CHARACTERIZATION AND APPLICATION OF NICKEL NANOPARTICLES

Abstract

A new facile and effortless method has been introduced for the fabrication of l-cysteine capped nickel nanoparticles (Ni NPs) in an organic solvent (ethylene glycol) under microwave irradiation with the aim to employ such nanoparticles as catalysts in remediation/reduction of pollutants for environmental or analytical purposes. Appropriate amounts of NaOH, Na 2 CO 3 and l-cysteine were significant for the formation of Ni NPs. The surface interaction of l-cysteine with Ni NPs was monitored by UV-Vis spectrometry and Fourier transform infrared (FTIR) spectroscopy while size and shape of as-synthesized Ni NPs were judged by transmission electron microscopy (TEM). These studies confirmed the interaction of biomolecules with the surface of Ni NPs via the -S- linkage to form spherical Ni NPs. The Ni NPs were recovered and reused four times for the reduction of fresh 4-nitrophenol (4-NPh) with 100-98% efficiency that exhibit negligible catalytic poisoning with excellent economic output. Further these Ni NPs were also used to investigate their catalytic efficiency to reduce hexavalent chromium i.e. Cr(VI) to trivalent chromium i.e. Cr(III) in aqueous system. We observed complete reduction of Cr(VI) in only five minutes by the use of 0.5 mg quantity of l-cysteine derived Ni NPs as catalysts. Synthesis of nickel nanowires (Ni NWs) by a simple chemical approach and their use as highly active and recyclable catalysts for conversion of isopropyl alcohol (IPA) to acetone by the transfer hydrogenation reaction was carried out in an aqueous medium. The Ni NWs were obtained by reducing Ni 2+ ions with hydrazine xiiimonohydrate as the reducing agent and capped by l-methionine (amino acid) molecules. The basic pH, high concentration of reducing agent and higher molar ratio of Ni/l-methionine were necessary for synthesis of Ni NWs. UV-Vis spectroscopy, FTIR spectroscopy and scanning electron microscopy (SEM) were used for characterization of Ni NWs. The catalytic test was performed in the presence of the rich hydrogen source NaBH 4 , which helps in the conversion of IPA to acetone. The effects of concentration of IPA, concentration of NaBH 4 , reaction time and amount of Ni NWs were monitored to investigate the efficiency of catalysts. The study also describes synthesis of highly active and ordered structures of nickel nanocatalysts by a green and economically viable approach. The study reveals efficient catalytic activity for the degradation of a number of toxic and lethal organic dyes such as Eosin-B (EB), Rose bengal (RB), Ereochrome black-T (ECBT) and Methylene blue (MB). The stable colloidal dispersions of ordered nickel nanostructures (Ni NSs) arrays were prepared via a modified hydrazine reduction route with unique and controllable morphologies in a lyotropic liquid crystalline medium using a nonionic surfactant (Triton X-100). Characterization studies and optimization of various parameters for preparation of these nanoscale nickel structures, surface binding interactions, size and morphologies of the fabricated Ni NSs were carried out using UV-Vis spectroscopy, FTIR spectroscopy, X-ray diffraction (XRD) and SEM analysis. We introduced a simple and primitive seed-mediated growth approach for fabrication of well dispersed l-threonine derived nickel nanoparticles (Ni NPs) using xivnickel chloride as the precursor in an aqueous medium via a modified borohydride reduction method. L-threonine molecules served to tune the nanoscale composites. Appropriate amounts of NaOH/HCl were added to adjust the pH range of the solution to the range 2.6-11.3, however basic pH 8.5 was found to favor the formation of spherical shapes and achieve well dispersed Ni NPs as shown in TEM micrographs. Freshly prepared Ni NPs covered mean nanoscale dimensions of 5.06 nm for bigger nanospheres and 1.68 nm of smaller NPs, determined from atomic force microscopy (AFM) and TEM data. Microscopy studies reveal that bigger Ni NPs consist of small individual nano-composites with fine crystal structures. The nanoparticles thus prepared were exploited to check their catalytic activity. Congo red (CR) dye was used as a model reagent to monitor catalytic degradation. Experiments highlighted no or very little reduction of dye in the absence of Ni NPs. Conversely the addition of only 0.2 mg of nano-catalysts (Ni NPs) produced 100% conversion/degradation efficiency within a fraction of a minute; the present study also showed recovery and reuse of the same catalysts which performed with no loss of activity even after several cycles of reuse.