Synthesis and Characterization of Carbon Nanotube-Nickel/Nickel Oxide Core/shell Nanoparticle Heterostructures Incorpora
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Synthesis and Characterization of Carbon Nanotube-Nickel/Nickel Oxide Core/shell Nanoparticle Heterostructures Incorporated in Polyvinyl Alcohol Hydrogel Wenwu Shi,1 Kristy Crews,2 Nitin Chopra1* 1 Metallurgical and Materials Engineering, Center for Materials for Information Technology (MINT), the University of Alabama, Tuscaloosa, Al, 35487 2 NSF-REU Fellow (2009), Chemistry, The University of West Alabama, Livingston, AL, 35470 * Corresponding author: E-mail: [email protected] , Tel: 205-348-4153, Fax: 205-348-2164 ABSTRACT Carbon nanotube (CNT)-nickel/nickel oxide (Ni/NiO) core/shell nanoparticles (CNC) heterostructures were prepared in a unique single-step synthetic route by direct chemical precipitation of nanoparticles on CNT surface. Chemical vapor deposition (CVD)-grown CNTs (average diameter ~42.7±12.3 nm) allowed for direct nucleation and uniform coating of Ni/NiO core/shell nanoparticles (average diameter ~11.8±1.7 nm). The crystal structure, morphology, and phases in CNC heterostructures were studied using high resolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Subsequently, the as-produced CNC heterostructures were incorporated into polyvinyl alcohol (PVA) hydrogel resulting in CNC heterostructure-PVA hydrogel with ~ 75% water absorbing capability. These novel hydrogels were also characterized by SEM and showed actuation under 0.2 T magnet. They are promising for smart analytical devices and platform. INTRODUCTION Unique properties of single-component nanostructures (e.g., carbon nanotubes (CNTs), nanowires, and nanoparticles) [1,2,3] are motivating researchers to develop multi-component and hybrid nanostructures [4-6]. Among these, CNT-nanoparticle heterostructures are promising for applications ranging from energy technologies to chemical and biological sensors [3,5,6]. Such heterostructures combine the effects of the individual components such as novel surface chemistry, stability in harsh environments, bioactivity, excellent mechanical strength, and optimum thermal, optical, magnetic, and electrical properties [3]. Interestingly, large curvature of CNTs also allows for the uniform packing of nanoparticles [5]. The approaches to synthesize CNT-nanoparticle heterostructures mostly rely on chemical functionalization methods [6-9]. However, the attachment of nanoparticles on CNTs without the use of covalent chemistry will be critical in obtaining non-contaminated heterostructures and would be desirable for biological applications. Towards this end, enhancing biocompatibility of these heterostructures is also important. Thus, incorporating such heterostructures in a biocompatible hydrogel will result in a hybrid, high strength, and multi-functional system. Hydrogels are porous and viscoelastic materials composed of cross-linked polymer that swell and shrink in presence and absence of an aqueous media [10-14]. For example, polyvinyl alcohol (PVA) hydrogel absorbs water and is biocompatible and non-toxic [14]. Wi
